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D. Ragni
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1
Turbulence-interaction noise arises from unsteady surface pressure fluctuations caused by the interaction of incoming turbulence with an aerofoil or rotor. This type of flow induced noise is relevant across a range of diverse applications. Consequently, multiple physical mechanisms must be examined and analytically modelled for use in low-fidelity prediction methods. Such models are particularly valuable during the design and optimisation phases due to their low computational cost. However, their accuracy is critically dependent on the fidelity of the underlying physical assumptions. One of the most widely used and robust approaches, Amiet’s model, has been shown to produce inaccurate results for thick blades, as it was originally developed for flat plates. This limitation is likely due to the distortion of the incoming turbulent structures and the alteration of the noise radiation caused by aerodynamic surfaces of non-negligible thickness. Comparable limitations affect its application to rotors, where an accurate representation of the inflow conditions is essential to ensure the reliability of the prediction. The present study seeks to address the following three research questions:
1. How does turbulence distortion affect noise generation and prediction?
2. How can turbulence-distortion effects be included in Amiet’s model?
3. How does this apply to rotors?
...
1. How does turbulence distortion affect noise generation and prediction?
2. How can turbulence-distortion effects be included in Amiet’s model?
3. How does this apply to rotors?
...
Turbulence-interaction noise arises from unsteady surface pressure fluctuations caused by the interaction of incoming turbulence with an aerofoil or rotor. This type of flow induced noise is relevant across a range of diverse applications. Consequently, multiple physical mechanisms must be examined and analytically modelled for use in low-fidelity prediction methods. Such models are particularly valuable during the design and optimisation phases due to their low computational cost. However, their accuracy is critically dependent on the fidelity of the underlying physical assumptions. One of the most widely used and robust approaches, Amiet’s model, has been shown to produce inaccurate results for thick blades, as it was originally developed for flat plates. This limitation is likely due to the distortion of the incoming turbulent structures and the alteration of the noise radiation caused by aerodynamic surfaces of non-negligible thickness. Comparable limitations affect its application to rotors, where an accurate representation of the inflow conditions is essential to ensure the reliability of the prediction. The present study seeks to address the following three research questions:
1. How does turbulence distortion affect noise generation and prediction?
2. How can turbulence-distortion effects be included in Amiet’s model?
3. How does this apply to rotors?
1. How does turbulence distortion affect noise generation and prediction?
2. How can turbulence-distortion effects be included in Amiet’s model?
3. How does this apply to rotors?
Aeroacoustic Investigation of Propellers Operating at Low-Reynolds Numbers
Study of conventional and unconventional configurations
Unmanned Aerial Vehicles (UAVs) and Urban Air Mobility (UAM) vehicles mark a major advancement in aviation technology, with the potential to reshape the future of aviation, particularly in the field of transportation and logistics in urban and rural environments.
Undoubtedly, the noise generated by their unique propeller-driven propulsion systems poses a significant public health concern. Operating at low altitudes throughout their missions and producing an acoustic signature characterized by strong tonal noise and prominent high-frequency components, these vehicles are expected to have a greater impact on communities than traditional aircraft.... ...
Undoubtedly, the noise generated by their unique propeller-driven propulsion systems poses a significant public health concern. Operating at low altitudes throughout their missions and producing an acoustic signature characterized by strong tonal noise and prominent high-frequency components, these vehicles are expected to have a greater impact on communities than traditional aircraft.... ...
Unmanned Aerial Vehicles (UAVs) and Urban Air Mobility (UAM) vehicles mark a major advancement in aviation technology, with the potential to reshape the future of aviation, particularly in the field of transportation and logistics in urban and rural environments.
Undoubtedly, the noise generated by their unique propeller-driven propulsion systems poses a significant public health concern. Operating at low altitudes throughout their missions and producing an acoustic signature characterized by strong tonal noise and prominent high-frequency components, these vehicles are expected to have a greater impact on communities than traditional aircraft....
Undoubtedly, the noise generated by their unique propeller-driven propulsion systems poses a significant public health concern. Operating at low altitudes throughout their missions and producing an acoustic signature characterized by strong tonal noise and prominent high-frequency components, these vehicles are expected to have a greater impact on communities than traditional aircraft....
Quantifying Unsteady Surface Pressure Fluctuations Induced by a Propeller Slipstream Using a Flexible PCB Measurement Device
Quantification of Propeller Wake-Wing Interactions
With the resurgence of interest in propeller-powered aircraft for short-haul and regional missions, understanding the aerodynamic interaction between propellers and nearby surfaces has become increasingly crucial. While propellers offer superior propulsive efficiency and sustainability benefits, their integration introduces complex unsteady flow phenomena that remain insufficiently explored. Additionally, concepts related to regenerative braking and the negative thrust regime aim to harness the full potential of propellers in the pursuit of sustainable aviation. However, the interactions are more complex in the negative thrust regime and need to be accounted for.
This study investigates the unsteady aerodynamic effects of a pusher-propeller operating upstream of a downstream airfoil, with a focus on both positive and negative thrust regimes. A flexible PCB embedded with microphones and pressure sensors was used to capture unsteady surface pressure fluctuations across different operating conditions. The motivation stems from the limited understanding of unsteady surface pressure fluctuations in negative thrust conditions.
The experimental campaign was conducted in two wind tunnel labs: the M-Tunnel and the Small Low-Turbulence Tunnel in the Low-Speed Wind Tunnel Laboratory of Delft University of Technology, Netherlands. The research was carried out in two experimental phases. In the first phase, the device was validated to verify the response of the microphones and the pressure sensors. A known tonal excitation case, along with a case involving an upstream cylinder, was conducted to assess whether the results aligned with theory and expected trends from the literature. These validation experiments confirmed the device’s capability to capture unsteady flow behaviour. However, certain limitations, such as overshoots in measured pressure data and restricted chordwise and spanwise resolution, were encountered. The second phase was conducted in the Small Low-Turbulence Tunnel featuring a fixed airfoil section downstream of a rotating propeller. The device, comprising the microphones and BMP390 pressure sensors, was wrapped around the leading edge of the airfoil to measure pressure fluctuations across the airfoil surface. Initial validation confirmed the reliability of the device in measuring the flow in the propeller slipstream, with good agreement with results from the literature. Comparative analysis was performed across multiple cases, including nacelle-only baselines and propeller-on conditions at two different advance ratios. In the positive thrust regime, the propeller generated a strong tip vortex trace, which significantly influenced the laminar separation bubble and led to elevated pressure fluctuations and peaks at the tonal harmonic of the blade passage frequency. In contrast, the negative thrust regime featured a weaker tip vortex trace and a broadband-dominated spectrum, with reduced suction observed on the upper surface due to lower dynamic pressure in the slipstream.
The study also highlights that the influence of the propeller slipstream extends well beyond its boundary across the span of the airfoil model. Key limitations included discrepancies in the data measured by two rows of microphones due to surface mounting issues.
Overall, the device proved to be a valuable measurement tool for investigating the unsteady surface pressure fluctuations associated with propeller–wing interaction. The insights gained contribute to a better understanding of surface pressure fluctuations on a body immersed in a propeller slipstream, particularly in energy-harvesting operating regimes. Recommendations for future work include improving sensor mounting fidelity, increasing chordwise resolution, and incorporating time-resolved flow visualisation techniques to complement the surface pressure measurements and provide additional insight into the spatial and temporal evolution of the flow field. ...
With the resurgence of interest in propeller-powered aircraft for short-haul and regional missions, understanding the aerodynamic interaction between propellers and nearby surfaces has become increasingly crucial. While propellers offer superior propulsive efficiency and sustainability benefits, their integration introduces complex unsteady flow phenomena that remain insufficiently explored. Additionally, concepts related to regenerative braking and the negative thrust regime aim to harness the full potential of propellers in the pursuit of sustainable aviation. However, the interactions are more complex in the negative thrust regime and need to be accounted for.
This study investigates the unsteady aerodynamic effects of a pusher-propeller operating upstream of a downstream airfoil, with a focus on both positive and negative thrust regimes. A flexible PCB embedded with microphones and pressure sensors was used to capture unsteady surface pressure fluctuations across different operating conditions. The motivation stems from the limited understanding of unsteady surface pressure fluctuations in negative thrust conditions.
The experimental campaign was conducted in two wind tunnel labs: the M-Tunnel and the Small Low-Turbulence Tunnel in the Low-Speed Wind Tunnel Laboratory of Delft University of Technology, Netherlands. The research was carried out in two experimental phases. In the first phase, the device was validated to verify the response of the microphones and the pressure sensors. A known tonal excitation case, along with a case involving an upstream cylinder, was conducted to assess whether the results aligned with theory and expected trends from the literature. These validation experiments confirmed the device’s capability to capture unsteady flow behaviour. However, certain limitations, such as overshoots in measured pressure data and restricted chordwise and spanwise resolution, were encountered. The second phase was conducted in the Small Low-Turbulence Tunnel featuring a fixed airfoil section downstream of a rotating propeller. The device, comprising the microphones and BMP390 pressure sensors, was wrapped around the leading edge of the airfoil to measure pressure fluctuations across the airfoil surface. Initial validation confirmed the reliability of the device in measuring the flow in the propeller slipstream, with good agreement with results from the literature. Comparative analysis was performed across multiple cases, including nacelle-only baselines and propeller-on conditions at two different advance ratios. In the positive thrust regime, the propeller generated a strong tip vortex trace, which significantly influenced the laminar separation bubble and led to elevated pressure fluctuations and peaks at the tonal harmonic of the blade passage frequency. In contrast, the negative thrust regime featured a weaker tip vortex trace and a broadband-dominated spectrum, with reduced suction observed on the upper surface due to lower dynamic pressure in the slipstream.
The study also highlights that the influence of the propeller slipstream extends well beyond its boundary across the span of the airfoil model. Key limitations included discrepancies in the data measured by two rows of microphones due to surface mounting issues.
Overall, the device proved to be a valuable measurement tool for investigating the unsteady surface pressure fluctuations associated with propeller–wing interaction. The insights gained contribute to a better understanding of surface pressure fluctuations on a body immersed in a propeller slipstream, particularly in energy-harvesting operating regimes. Recommendations for future work include improving sensor mounting fidelity, increasing chordwise resolution, and incorporating time-resolved flow visualisation techniques to complement the surface pressure measurements and provide additional insight into the spatial and temporal evolution of the flow field.
Bachelor thesis
(2025)
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A. Garaiman, E. Iacob, S. Ion, H. Madrid, A. Osman, I.A. Teixeira, R.I. Pop, G. Reurekas, V. Stoica, L.C. Tanasiciuc, D. Ragni, B.A. Püroja
Flame Aegis is a fire-fighting drone designed to combat high-rise building fires in urban areas. This product has been requested by the Gezamenlijke Brandweer, and certain stakeholder requirements have been imposed. There are further regulatory constraints at both national and European levels. A 150 kg drone with a capacity of 40 L of water was designed in the end. The water can be delivered by spraying at a rate of 150 L/min through a nozzle or by dropping the contents of the tank within 2 seconds. The drone is able to perform a 15-minute mission with a 5-minute turnaround time.
...
Flame Aegis is a fire-fighting drone designed to combat high-rise building fires in urban areas. This product has been requested by the Gezamenlijke Brandweer, and certain stakeholder requirements have been imposed. There are further regulatory constraints at both national and European levels. A 150 kg drone with a capacity of 40 L of water was designed in the end. The water can be delivered by spraying at a rate of 150 L/min through a nozzle or by dropping the contents of the tank within 2 seconds. The drone is able to perform a 15-minute mission with a 5-minute turnaround time.
Bachelor thesis
(2025)
-
M.F. van der Zwart, F.O. Olsson, R. Roy Chowdhury, S. Kuckreja, S. SINGH, R. Khan, M. Pandya, V. Somlai, F. Kirillov, B. Koelman, D. Ragni, B.A. Püroja, C.M. de Zeeuw, P. Ghanoni Bostanabad
This thesis presents the development, implementation, and validation of a low-fidelity Aeroacoustic Prediction Framework designed for airborne wind energy systems (AWES), with the Kitepower system as a case study. As AWES technology moves toward commercial viability, understanding and predicting its acoustic emissions becomes critical for regulatory compliance, public acceptance, and design optimization.
The framework integrates established analytical and semi-empirical aeroacoustic models with aerodynamic data based on derived geometry and detailed flight information. It models all major noise sources from the airborne components, such as the Leading Edge Inflatable (LEI) kite, bridle lines, tether, and onboard ram-air turbine. The most significant contributions to the overall noise signature were found to be turbulent boundary layer trailing edge (TBL-TE) noise from airfoils, modeled using the Brooks–Pope–Marcolini (BPM) approach, vortex-shedding noise from cylindrical structures such as the tether and bridle lines, and tonal harmonics produced by the rotating turbine blades, captured through Hanson’s helicoidal surface theory.
To generate aerodynamic input, spanwise airfoil profiles were automatically extracted from 3D CAD models and analyzed through XFOIL. Real-time flight data was provided by an onboard sensor suite and processed through an Extended Kalman Filter (EKF), allowing dynamic simulation of flight conditions. Audio recordings were collected during test flights using GoPro cameras, enabling experimental validation of the acoustic predictions despite the absence of calibrated SPL measurements.
Validation showed strong agreement between predicted and measured spectra up to 5 kHz, particularly for turbine harmonics and general spectral shape. Deviations in the lower tonal harmonics were primarily attributed to acoustic shielding caused by the turbine’s duct structure. Additionally, the use of GoPro cameras introduced limitations due to their lack of calibration data and the presence of internal low-pass filtering above 5 kHz. Despite these constraints, the model successfully predicted tonal peaks, including the blade passing frequency and higher-order harmonics, aligning well with the experimental observations.
Additionally, the framework investigates the influence of the propagation effects, such as atmospheric absorption and geometric spreading, and integrates them to produce realistic observer-based predictions. Despite using non-professional audio hardware, the predictions captured key features including harmonic roll-off and broadband trends, affirming the framework's validity for early-stage design and evaluation.
This work demonstrates that low-order, physics-based models paired with aerodynamic inputs and synchronized flight data can yield meaningful acoustic predictions for AWES. The framework offers modularity, computational efficiency, and adaptability for future upgrades, such as the use of calibrated microphones or high-fidelity CFD data. It serves as a foundation for future extensions in auralization, psychoacoustic testing, and component-level noise reduction strategies.
Ultimately, the thesis bridges theoretical modeling with field-based validation, supporting the responsible integration of AWES technologies into noise-sensitive environments. ...
The framework integrates established analytical and semi-empirical aeroacoustic models with aerodynamic data based on derived geometry and detailed flight information. It models all major noise sources from the airborne components, such as the Leading Edge Inflatable (LEI) kite, bridle lines, tether, and onboard ram-air turbine. The most significant contributions to the overall noise signature were found to be turbulent boundary layer trailing edge (TBL-TE) noise from airfoils, modeled using the Brooks–Pope–Marcolini (BPM) approach, vortex-shedding noise from cylindrical structures such as the tether and bridle lines, and tonal harmonics produced by the rotating turbine blades, captured through Hanson’s helicoidal surface theory.
To generate aerodynamic input, spanwise airfoil profiles were automatically extracted from 3D CAD models and analyzed through XFOIL. Real-time flight data was provided by an onboard sensor suite and processed through an Extended Kalman Filter (EKF), allowing dynamic simulation of flight conditions. Audio recordings were collected during test flights using GoPro cameras, enabling experimental validation of the acoustic predictions despite the absence of calibrated SPL measurements.
Validation showed strong agreement between predicted and measured spectra up to 5 kHz, particularly for turbine harmonics and general spectral shape. Deviations in the lower tonal harmonics were primarily attributed to acoustic shielding caused by the turbine’s duct structure. Additionally, the use of GoPro cameras introduced limitations due to their lack of calibration data and the presence of internal low-pass filtering above 5 kHz. Despite these constraints, the model successfully predicted tonal peaks, including the blade passing frequency and higher-order harmonics, aligning well with the experimental observations.
Additionally, the framework investigates the influence of the propagation effects, such as atmospheric absorption and geometric spreading, and integrates them to produce realistic observer-based predictions. Despite using non-professional audio hardware, the predictions captured key features including harmonic roll-off and broadband trends, affirming the framework's validity for early-stage design and evaluation.
This work demonstrates that low-order, physics-based models paired with aerodynamic inputs and synchronized flight data can yield meaningful acoustic predictions for AWES. The framework offers modularity, computational efficiency, and adaptability for future upgrades, such as the use of calibrated microphones or high-fidelity CFD data. It serves as a foundation for future extensions in auralization, psychoacoustic testing, and component-level noise reduction strategies.
Ultimately, the thesis bridges theoretical modeling with field-based validation, supporting the responsible integration of AWES technologies into noise-sensitive environments. ...
This thesis presents the development, implementation, and validation of a low-fidelity Aeroacoustic Prediction Framework designed for airborne wind energy systems (AWES), with the Kitepower system as a case study. As AWES technology moves toward commercial viability, understanding and predicting its acoustic emissions becomes critical for regulatory compliance, public acceptance, and design optimization.
The framework integrates established analytical and semi-empirical aeroacoustic models with aerodynamic data based on derived geometry and detailed flight information. It models all major noise sources from the airborne components, such as the Leading Edge Inflatable (LEI) kite, bridle lines, tether, and onboard ram-air turbine. The most significant contributions to the overall noise signature were found to be turbulent boundary layer trailing edge (TBL-TE) noise from airfoils, modeled using the Brooks–Pope–Marcolini (BPM) approach, vortex-shedding noise from cylindrical structures such as the tether and bridle lines, and tonal harmonics produced by the rotating turbine blades, captured through Hanson’s helicoidal surface theory.
To generate aerodynamic input, spanwise airfoil profiles were automatically extracted from 3D CAD models and analyzed through XFOIL. Real-time flight data was provided by an onboard sensor suite and processed through an Extended Kalman Filter (EKF), allowing dynamic simulation of flight conditions. Audio recordings were collected during test flights using GoPro cameras, enabling experimental validation of the acoustic predictions despite the absence of calibrated SPL measurements.
Validation showed strong agreement between predicted and measured spectra up to 5 kHz, particularly for turbine harmonics and general spectral shape. Deviations in the lower tonal harmonics were primarily attributed to acoustic shielding caused by the turbine’s duct structure. Additionally, the use of GoPro cameras introduced limitations due to their lack of calibration data and the presence of internal low-pass filtering above 5 kHz. Despite these constraints, the model successfully predicted tonal peaks, including the blade passing frequency and higher-order harmonics, aligning well with the experimental observations.
Additionally, the framework investigates the influence of the propagation effects, such as atmospheric absorption and geometric spreading, and integrates them to produce realistic observer-based predictions. Despite using non-professional audio hardware, the predictions captured key features including harmonic roll-off and broadband trends, affirming the framework's validity for early-stage design and evaluation.
This work demonstrates that low-order, physics-based models paired with aerodynamic inputs and synchronized flight data can yield meaningful acoustic predictions for AWES. The framework offers modularity, computational efficiency, and adaptability for future upgrades, such as the use of calibrated microphones or high-fidelity CFD data. It serves as a foundation for future extensions in auralization, psychoacoustic testing, and component-level noise reduction strategies.
Ultimately, the thesis bridges theoretical modeling with field-based validation, supporting the responsible integration of AWES technologies into noise-sensitive environments.
The framework integrates established analytical and semi-empirical aeroacoustic models with aerodynamic data based on derived geometry and detailed flight information. It models all major noise sources from the airborne components, such as the Leading Edge Inflatable (LEI) kite, bridle lines, tether, and onboard ram-air turbine. The most significant contributions to the overall noise signature were found to be turbulent boundary layer trailing edge (TBL-TE) noise from airfoils, modeled using the Brooks–Pope–Marcolini (BPM) approach, vortex-shedding noise from cylindrical structures such as the tether and bridle lines, and tonal harmonics produced by the rotating turbine blades, captured through Hanson’s helicoidal surface theory.
To generate aerodynamic input, spanwise airfoil profiles were automatically extracted from 3D CAD models and analyzed through XFOIL. Real-time flight data was provided by an onboard sensor suite and processed through an Extended Kalman Filter (EKF), allowing dynamic simulation of flight conditions. Audio recordings were collected during test flights using GoPro cameras, enabling experimental validation of the acoustic predictions despite the absence of calibrated SPL measurements.
Validation showed strong agreement between predicted and measured spectra up to 5 kHz, particularly for turbine harmonics and general spectral shape. Deviations in the lower tonal harmonics were primarily attributed to acoustic shielding caused by the turbine’s duct structure. Additionally, the use of GoPro cameras introduced limitations due to their lack of calibration data and the presence of internal low-pass filtering above 5 kHz. Despite these constraints, the model successfully predicted tonal peaks, including the blade passing frequency and higher-order harmonics, aligning well with the experimental observations.
Additionally, the framework investigates the influence of the propagation effects, such as atmospheric absorption and geometric spreading, and integrates them to produce realistic observer-based predictions. Despite using non-professional audio hardware, the predictions captured key features including harmonic roll-off and broadband trends, affirming the framework's validity for early-stage design and evaluation.
This work demonstrates that low-order, physics-based models paired with aerodynamic inputs and synchronized flight data can yield meaningful acoustic predictions for AWES. The framework offers modularity, computational efficiency, and adaptability for future upgrades, such as the use of calibrated microphones or high-fidelity CFD data. It serves as a foundation for future extensions in auralization, psychoacoustic testing, and component-level noise reduction strategies.
Ultimately, the thesis bridges theoretical modeling with field-based validation, supporting the responsible integration of AWES technologies into noise-sensitive environments.
Aeroacoustic testing in acoustically disturbed environments
Improvements to closed test section wind tunnel experiments
The research in this thesis aims at improving aeroacoustic testing in acoustically disturbed environments, with particular focus on closed test section wind tunnels. Ideally, it should become possible to perform fully reliable aeroacoustic experimental campaigns without the need of anechoic open—jet facilities.
The investigation of wall cavities for microphone placement was done with Computational Fluid Dynamics simulations, which in turn were validated experimentally. Cavities covered with a mesh cover were investigated, since previous literature shows that these reduce hydrodynamic noise while allowing for the transmission of waves to the microphones. The numerical simulations show that covering microphone cavities with a mesh cover results in a stagnant flow inside the cavities. As consequence, the only source of pressure fluctuations at the cavity bottoms are acoustic waves. The hydrodynamic pressure fluctuations from the wall’s boundary layer still propagate acoustically to the cavity bottoms. The findings show that increasing cavity size, by increasing the cavity opening diameter with respect to the length of the eddies in the turbulent boundary layer, leads to a lower propagation of spurious pressure fluctuations to the cavity bottoms. This in turn leads to an increased signal to noise ratio of acoustic measurements recorded at closed test section wind tunnels.
Wind tunnel wall liners have been characterized based on their viscous resistivity, inertial resistivity and roughness. Several porous liners have been tested experimentally. The aim was to analyze their impact on the aerodynamic properties of the wind tunnel boundary layer, on the generation of spurious noise, and on the absorption of acoustic reflections. The results show that the ideal choice of liner consists of a liner: with high viscous resistivity, which leads to high acoustic absorption; with low roughness, to reduce the impact on the wind tunnel wall’s boundary layer; and with low inertial resistivity, to reduce the generation of spurious noise. The best lining material tested was melamine foam.
The acoustic propagation and acoustic interference in a closed wind tunnel test section were predicted with a FEM acoustic solver. The propagation was modelled on a baseline test section, with fully reflective walls, and on test sections with lined walls. The numerical results were found to give a very accurate prediction of the acoustic experimental tests. It was possible to use the numerical results to improve the post—processing of experimental data. The Green’s function used to process experimental microphone data with beamforming was corrected, using the numerical results. Beamforming with the Green’s function corrected for the acoustically disturbed environment led to a higher beamforming spatial resolution. In addition, the estimated noise levels are more accurate when the correction is used. This improved approach was shown to work for post—processing experimental measurements of a monopole sound source placed at the center of the test section, with and without free—stream flow.
...
The investigation of wall cavities for microphone placement was done with Computational Fluid Dynamics simulations, which in turn were validated experimentally. Cavities covered with a mesh cover were investigated, since previous literature shows that these reduce hydrodynamic noise while allowing for the transmission of waves to the microphones. The numerical simulations show that covering microphone cavities with a mesh cover results in a stagnant flow inside the cavities. As consequence, the only source of pressure fluctuations at the cavity bottoms are acoustic waves. The hydrodynamic pressure fluctuations from the wall’s boundary layer still propagate acoustically to the cavity bottoms. The findings show that increasing cavity size, by increasing the cavity opening diameter with respect to the length of the eddies in the turbulent boundary layer, leads to a lower propagation of spurious pressure fluctuations to the cavity bottoms. This in turn leads to an increased signal to noise ratio of acoustic measurements recorded at closed test section wind tunnels.
Wind tunnel wall liners have been characterized based on their viscous resistivity, inertial resistivity and roughness. Several porous liners have been tested experimentally. The aim was to analyze their impact on the aerodynamic properties of the wind tunnel boundary layer, on the generation of spurious noise, and on the absorption of acoustic reflections. The results show that the ideal choice of liner consists of a liner: with high viscous resistivity, which leads to high acoustic absorption; with low roughness, to reduce the impact on the wind tunnel wall’s boundary layer; and with low inertial resistivity, to reduce the generation of spurious noise. The best lining material tested was melamine foam.
The acoustic propagation and acoustic interference in a closed wind tunnel test section were predicted with a FEM acoustic solver. The propagation was modelled on a baseline test section, with fully reflective walls, and on test sections with lined walls. The numerical results were found to give a very accurate prediction of the acoustic experimental tests. It was possible to use the numerical results to improve the post—processing of experimental data. The Green’s function used to process experimental microphone data with beamforming was corrected, using the numerical results. Beamforming with the Green’s function corrected for the acoustically disturbed environment led to a higher beamforming spatial resolution. In addition, the estimated noise levels are more accurate when the correction is used. This improved approach was shown to work for post—processing experimental measurements of a monopole sound source placed at the center of the test section, with and without free—stream flow.
...
The research in this thesis aims at improving aeroacoustic testing in acoustically disturbed environments, with particular focus on closed test section wind tunnels. Ideally, it should become possible to perform fully reliable aeroacoustic experimental campaigns without the need of anechoic open—jet facilities.
The investigation of wall cavities for microphone placement was done with Computational Fluid Dynamics simulations, which in turn were validated experimentally. Cavities covered with a mesh cover were investigated, since previous literature shows that these reduce hydrodynamic noise while allowing for the transmission of waves to the microphones. The numerical simulations show that covering microphone cavities with a mesh cover results in a stagnant flow inside the cavities. As consequence, the only source of pressure fluctuations at the cavity bottoms are acoustic waves. The hydrodynamic pressure fluctuations from the wall’s boundary layer still propagate acoustically to the cavity bottoms. The findings show that increasing cavity size, by increasing the cavity opening diameter with respect to the length of the eddies in the turbulent boundary layer, leads to a lower propagation of spurious pressure fluctuations to the cavity bottoms. This in turn leads to an increased signal to noise ratio of acoustic measurements recorded at closed test section wind tunnels.
Wind tunnel wall liners have been characterized based on their viscous resistivity, inertial resistivity and roughness. Several porous liners have been tested experimentally. The aim was to analyze their impact on the aerodynamic properties of the wind tunnel boundary layer, on the generation of spurious noise, and on the absorption of acoustic reflections. The results show that the ideal choice of liner consists of a liner: with high viscous resistivity, which leads to high acoustic absorption; with low roughness, to reduce the impact on the wind tunnel wall’s boundary layer; and with low inertial resistivity, to reduce the generation of spurious noise. The best lining material tested was melamine foam.
The acoustic propagation and acoustic interference in a closed wind tunnel test section were predicted with a FEM acoustic solver. The propagation was modelled on a baseline test section, with fully reflective walls, and on test sections with lined walls. The numerical results were found to give a very accurate prediction of the acoustic experimental tests. It was possible to use the numerical results to improve the post—processing of experimental data. The Green’s function used to process experimental microphone data with beamforming was corrected, using the numerical results. Beamforming with the Green’s function corrected for the acoustically disturbed environment led to a higher beamforming spatial resolution. In addition, the estimated noise levels are more accurate when the correction is used. This improved approach was shown to work for post—processing experimental measurements of a monopole sound source placed at the center of the test section, with and without free—stream flow.
The investigation of wall cavities for microphone placement was done with Computational Fluid Dynamics simulations, which in turn were validated experimentally. Cavities covered with a mesh cover were investigated, since previous literature shows that these reduce hydrodynamic noise while allowing for the transmission of waves to the microphones. The numerical simulations show that covering microphone cavities with a mesh cover results in a stagnant flow inside the cavities. As consequence, the only source of pressure fluctuations at the cavity bottoms are acoustic waves. The hydrodynamic pressure fluctuations from the wall’s boundary layer still propagate acoustically to the cavity bottoms. The findings show that increasing cavity size, by increasing the cavity opening diameter with respect to the length of the eddies in the turbulent boundary layer, leads to a lower propagation of spurious pressure fluctuations to the cavity bottoms. This in turn leads to an increased signal to noise ratio of acoustic measurements recorded at closed test section wind tunnels.
Wind tunnel wall liners have been characterized based on their viscous resistivity, inertial resistivity and roughness. Several porous liners have been tested experimentally. The aim was to analyze their impact on the aerodynamic properties of the wind tunnel boundary layer, on the generation of spurious noise, and on the absorption of acoustic reflections. The results show that the ideal choice of liner consists of a liner: with high viscous resistivity, which leads to high acoustic absorption; with low roughness, to reduce the impact on the wind tunnel wall’s boundary layer; and with low inertial resistivity, to reduce the generation of spurious noise. The best lining material tested was melamine foam.
The acoustic propagation and acoustic interference in a closed wind tunnel test section were predicted with a FEM acoustic solver. The propagation was modelled on a baseline test section, with fully reflective walls, and on test sections with lined walls. The numerical results were found to give a very accurate prediction of the acoustic experimental tests. It was possible to use the numerical results to improve the post—processing of experimental data. The Green’s function used to process experimental microphone data with beamforming was corrected, using the numerical results. Beamforming with the Green’s function corrected for the acoustically disturbed environment led to a higher beamforming spatial resolution. In addition, the estimated noise levels are more accurate when the correction is used. This improved approach was shown to work for post—processing experimental measurements of a monopole sound source placed at the center of the test section, with and without free—stream flow.
Aerodynamics and Aeroacoustics of Propeller Operation at Negative Thrust
A Computational Study
Future regional and short to medium-range aircraft are expected to use propellers for sustainable aviation, possibly with (hybrid-)electric propulsion systems. This will enable innovative integration of aero-propulsive systems, potentially increasing the overall aerodynamic efficiency of the airframe and propellers, resulting in a lighter airframe and increased passenger comfort. The presence of electric motors and propellers in such configurations, in addition, offers a unique opportunity to leverage propellers as airbrakes by operating them at negative thrust. This approach offers multiple potential advantages, including shorter landing runs, enhanced landing maneuverability, energy harvesting during braking operations, faster aircraft turnaround times, and reduced community noise exposure.
Despite these potential advantages, the aerodynamic and aeroacoustic characteristics of propellers operating in negative thrust mode remain largely unexplored. This dissertation addresses this knowledge gap through computational analysis, comparing the performance of isolated propeller configurations in negative thrust mode with the well-understood positive thrust mode. The results reveal that the distinct aeroacoustic characteristics of propellers operating in negative thrust conditions, compared to conventional positive thrust conditions, offer a promising avenue for reducing community noise, not only through the possibility of steeper descents but also through changes in the noise emissions from the propeller itself.
...
Despite these potential advantages, the aerodynamic and aeroacoustic characteristics of propellers operating in negative thrust mode remain largely unexplored. This dissertation addresses this knowledge gap through computational analysis, comparing the performance of isolated propeller configurations in negative thrust mode with the well-understood positive thrust mode. The results reveal that the distinct aeroacoustic characteristics of propellers operating in negative thrust conditions, compared to conventional positive thrust conditions, offer a promising avenue for reducing community noise, not only through the possibility of steeper descents but also through changes in the noise emissions from the propeller itself.
...
Future regional and short to medium-range aircraft are expected to use propellers for sustainable aviation, possibly with (hybrid-)electric propulsion systems. This will enable innovative integration of aero-propulsive systems, potentially increasing the overall aerodynamic efficiency of the airframe and propellers, resulting in a lighter airframe and increased passenger comfort. The presence of electric motors and propellers in such configurations, in addition, offers a unique opportunity to leverage propellers as airbrakes by operating them at negative thrust. This approach offers multiple potential advantages, including shorter landing runs, enhanced landing maneuverability, energy harvesting during braking operations, faster aircraft turnaround times, and reduced community noise exposure.
Despite these potential advantages, the aerodynamic and aeroacoustic characteristics of propellers operating in negative thrust mode remain largely unexplored. This dissertation addresses this knowledge gap through computational analysis, comparing the performance of isolated propeller configurations in negative thrust mode with the well-understood positive thrust mode. The results reveal that the distinct aeroacoustic characteristics of propellers operating in negative thrust conditions, compared to conventional positive thrust conditions, offer a promising avenue for reducing community noise, not only through the possibility of steeper descents but also through changes in the noise emissions from the propeller itself.
Despite these potential advantages, the aerodynamic and aeroacoustic characteristics of propellers operating in negative thrust mode remain largely unexplored. This dissertation addresses this knowledge gap through computational analysis, comparing the performance of isolated propeller configurations in negative thrust mode with the well-understood positive thrust mode. The results reveal that the distinct aeroacoustic characteristics of propellers operating in negative thrust conditions, compared to conventional positive thrust conditions, offer a promising avenue for reducing community noise, not only through the possibility of steeper descents but also through changes in the noise emissions from the propeller itself.
Interactions of Multi-Rotors with Surfaces
Aerodynamic Characterization and Performance Modelling
Recent advancements in electric propulsion technology have paved the way for alternative transportation systems aimed at revolutionizing travel times in congested metropolitan areas. The proposed electric Vertical and Take-Off and Landing (eVTOL) aircraft configurations exist in great diversity, but can be classified depending on their overall propulsion and wing layout. An example is the tilt-wing eVTOL, which combines the maneuverability of a helicopter with the cruise efficiency of an aircraft and therefore provides a promising vehicle architecture for this market. Nonetheless, future eVTOL vehicles face challenges regarding public acceptance and safe operation in urban environments, and successful implementation therefore relies on performance enhancement strategies.
The high power-to-weight ratio and efficiency of electric motors provide an excellent platform to explore disruptive propulsion system configurations. An observable design trend here is the tight integration of distributed, fixed-pitched rotors with aerodynamic surfaces, aimed at generating beneficial aerodynamic coupling effects to increase the aircraft’s efficiency and reduce acoustic emissions.
An auspicious integrated tilt-wing propulsion system layout is known as Over-The-Wing propulsion, which promises favorable aerodynamic effects by the rotor-induced flow and reduced noise signature during fly-over by shielding. However, during the operation of Over-The-Wing propulsion in eVTOL flight conditions, several multi-rotor-surface interactions are encountered, resulting in unexplored aerodynamic and aeroacoustic effects. As a consequence, design guidelines to maximize aerodynamic performance and minimize noise signature for Over-The-Wing propulsion for eVTOL flight conditions are missing in the public domain. This thesis focuses on enabling Over-The-Wing propulsion for vertical flight through experimentation and low-order modeling of the fundamental aerodynamic interactions between distributed rotors and surfaces. ...
The high power-to-weight ratio and efficiency of electric motors provide an excellent platform to explore disruptive propulsion system configurations. An observable design trend here is the tight integration of distributed, fixed-pitched rotors with aerodynamic surfaces, aimed at generating beneficial aerodynamic coupling effects to increase the aircraft’s efficiency and reduce acoustic emissions.
An auspicious integrated tilt-wing propulsion system layout is known as Over-The-Wing propulsion, which promises favorable aerodynamic effects by the rotor-induced flow and reduced noise signature during fly-over by shielding. However, during the operation of Over-The-Wing propulsion in eVTOL flight conditions, several multi-rotor-surface interactions are encountered, resulting in unexplored aerodynamic and aeroacoustic effects. As a consequence, design guidelines to maximize aerodynamic performance and minimize noise signature for Over-The-Wing propulsion for eVTOL flight conditions are missing in the public domain. This thesis focuses on enabling Over-The-Wing propulsion for vertical flight through experimentation and low-order modeling of the fundamental aerodynamic interactions between distributed rotors and surfaces. ...
Recent advancements in electric propulsion technology have paved the way for alternative transportation systems aimed at revolutionizing travel times in congested metropolitan areas. The proposed electric Vertical and Take-Off and Landing (eVTOL) aircraft configurations exist in great diversity, but can be classified depending on their overall propulsion and wing layout. An example is the tilt-wing eVTOL, which combines the maneuverability of a helicopter with the cruise efficiency of an aircraft and therefore provides a promising vehicle architecture for this market. Nonetheless, future eVTOL vehicles face challenges regarding public acceptance and safe operation in urban environments, and successful implementation therefore relies on performance enhancement strategies.
The high power-to-weight ratio and efficiency of electric motors provide an excellent platform to explore disruptive propulsion system configurations. An observable design trend here is the tight integration of distributed, fixed-pitched rotors with aerodynamic surfaces, aimed at generating beneficial aerodynamic coupling effects to increase the aircraft’s efficiency and reduce acoustic emissions.
An auspicious integrated tilt-wing propulsion system layout is known as Over-The-Wing propulsion, which promises favorable aerodynamic effects by the rotor-induced flow and reduced noise signature during fly-over by shielding. However, during the operation of Over-The-Wing propulsion in eVTOL flight conditions, several multi-rotor-surface interactions are encountered, resulting in unexplored aerodynamic and aeroacoustic effects. As a consequence, design guidelines to maximize aerodynamic performance and minimize noise signature for Over-The-Wing propulsion for eVTOL flight conditions are missing in the public domain. This thesis focuses on enabling Over-The-Wing propulsion for vertical flight through experimentation and low-order modeling of the fundamental aerodynamic interactions between distributed rotors and surfaces.
The high power-to-weight ratio and efficiency of electric motors provide an excellent platform to explore disruptive propulsion system configurations. An observable design trend here is the tight integration of distributed, fixed-pitched rotors with aerodynamic surfaces, aimed at generating beneficial aerodynamic coupling effects to increase the aircraft’s efficiency and reduce acoustic emissions.
An auspicious integrated tilt-wing propulsion system layout is known as Over-The-Wing propulsion, which promises favorable aerodynamic effects by the rotor-induced flow and reduced noise signature during fly-over by shielding. However, during the operation of Over-The-Wing propulsion in eVTOL flight conditions, several multi-rotor-surface interactions are encountered, resulting in unexplored aerodynamic and aeroacoustic effects. As a consequence, design guidelines to maximize aerodynamic performance and minimize noise signature for Over-The-Wing propulsion for eVTOL flight conditions are missing in the public domain. This thesis focuses on enabling Over-The-Wing propulsion for vertical flight through experimentation and low-order modeling of the fundamental aerodynamic interactions between distributed rotors and surfaces.
Design of Synthetic Jet Actuators for Jet Noise Control
Towards Aircraft Noise Reduction
This thesis investigates the turbulent jet aeroacoustic phenomena and explores the potential of active flow control using synthetic jet actuators to mitigate noise emissions. The study initially focuses on the development and validation of a comprehensive noise-source prediction model that combines already existing theoretical jet aeroacoustics formulas into an iterative solver that utilises existing jet farfield noise data. The thesis then continues with the goal of designing a synthetic jet actuator to be used as active flow control in the jet that aims to contribute to the emitted noise mitigation. The research begins by analysing the literature revolving around aeroacoustics of jets in general and the efforts to locate and characterise the noise sources in the wake of the jet in specific. The aeroacoustic analogies created for jet noise emissions are reviewed and later on form the basis of the predictive model. The core of this first part of the work involves the integration of the aforementioned analogies in the form of analytical formulas for farfield noise calculation into the modelling framework that incorporates the already existing farfield noise data for the various jets. These noise data are used as the target within a loss function that aims for the convergence of the predicted farfield noise to the experimental one. The characterisation of the noise sources within the jet are then a product of this iterative solving and take the form of energy/frequency requirements. This framework is applied to various jet configurations resulting in a global guide of velocity/frequency requirements for effective actuation of subsonic jets. The major output of the model is regarding a Mach 0.5 jet for which the requirement for effective actuation was to introduce disturbances with an amplitude of 15m/s at the frequency range from 600 to 800Hz. Focus is then given on potential active flow control methods that take the outputs of the noise-source prediction model and are able to provide the specific energy requirement at the required frequency range. Given the Mach 0.5 jet, synthetic jet actuators are chosen as the type of actuation and the research henceforth continuous with the modelling of actuators as a coupled resonator system. Once more, the outcomes of this modelling point at a specific actuator geometry which sparks the design, manufacturing and testing of said actuator. The designed piezoelectric-driven synthetic jet actuator was found to provide the 15m/s requirement at the frequency range of 700 to 900Hz which is deemed sufficient. The report finally discusses the practical implications of these findings in an effort to construct and evaluate an active flow control demonstration using the aforementioned actuators on an actual jet while also putting everything into context for future aeroacoustic modelling and aerospace applications. This work contributes to the ongoing efforts in reducing noise pollution in aerospace environments and provides a foundation for future research in active flow control technologies. The methodologies developed and the results obtained are expected to have broader applications in the design and optimization of quieter, more efficient aircraft.
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This thesis investigates the turbulent jet aeroacoustic phenomena and explores the potential of active flow control using synthetic jet actuators to mitigate noise emissions. The study initially focuses on the development and validation of a comprehensive noise-source prediction model that combines already existing theoretical jet aeroacoustics formulas into an iterative solver that utilises existing jet farfield noise data. The thesis then continues with the goal of designing a synthetic jet actuator to be used as active flow control in the jet that aims to contribute to the emitted noise mitigation. The research begins by analysing the literature revolving around aeroacoustics of jets in general and the efforts to locate and characterise the noise sources in the wake of the jet in specific. The aeroacoustic analogies created for jet noise emissions are reviewed and later on form the basis of the predictive model. The core of this first part of the work involves the integration of the aforementioned analogies in the form of analytical formulas for farfield noise calculation into the modelling framework that incorporates the already existing farfield noise data for the various jets. These noise data are used as the target within a loss function that aims for the convergence of the predicted farfield noise to the experimental one. The characterisation of the noise sources within the jet are then a product of this iterative solving and take the form of energy/frequency requirements. This framework is applied to various jet configurations resulting in a global guide of velocity/frequency requirements for effective actuation of subsonic jets. The major output of the model is regarding a Mach 0.5 jet for which the requirement for effective actuation was to introduce disturbances with an amplitude of 15m/s at the frequency range from 600 to 800Hz. Focus is then given on potential active flow control methods that take the outputs of the noise-source prediction model and are able to provide the specific energy requirement at the required frequency range. Given the Mach 0.5 jet, synthetic jet actuators are chosen as the type of actuation and the research henceforth continuous with the modelling of actuators as a coupled resonator system. Once more, the outcomes of this modelling point at a specific actuator geometry which sparks the design, manufacturing and testing of said actuator. The designed piezoelectric-driven synthetic jet actuator was found to provide the 15m/s requirement at the frequency range of 700 to 900Hz which is deemed sufficient. The report finally discusses the practical implications of these findings in an effort to construct and evaluate an active flow control demonstration using the aforementioned actuators on an actual jet while also putting everything into context for future aeroacoustic modelling and aerospace applications. This work contributes to the ongoing efforts in reducing noise pollution in aerospace environments and provides a foundation for future research in active flow control technologies. The methodologies developed and the results obtained are expected to have broader applications in the design and optimization of quieter, more efficient aircraft.
This UAV system focuses on delivering a 25kg payload to offshore wind turbines. It has a flexible mission profile that can be extended to offshore logistical operations between platforms and ships, as well as on-shore operations. This project aims to provide an innovative, competitive, sustainable, and accessible design capable of fulfilling this mission, all while serving as an educational environment in which a group of 10 students can develop academically.
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This UAV system focuses on delivering a 25kg payload to offshore wind turbines. It has a flexible mission profile that can be extended to offshore logistical operations between platforms and ships, as well as on-shore operations. This project aims to provide an innovative, competitive, sustainable, and accessible design capable of fulfilling this mission, all while serving as an educational environment in which a group of 10 students can develop academically.
A decades-long steady rise in air movements has disproportionally impacted airport-neighbouring communities. These communities bear the brunt of the aviation industry's air, and noise pollution, detrimental to their livelihood. Airports near densely populated areas face increasing societal and governmental scrutiny to reduce their noise pollution and improve the quality of life for airport-neighbouring communities. Airframe noise has become a prominent noise source during approach due to the increased usage of quieter high-bypass ratio turbofan engines. Flyover measurements suggest that the leading edge junction between the fuselage, wing, and slat is a high-intensity localised noise source. This airframe region has been sparsely researched. Therefore, this study aims to describe the relation between the aero-structural design of the fuselage-wing-slat junction and its aeroacoustic footprint for an aircraft in approach configuration.
The research set-up was designed for open-jet numerical simulations using the commercial Lattice Boltzmann Method (LBM) based CFD solver PowerFLOW, with future compatibility for experimental open-jet wind tunnel validation studies at the TU Delft's Anechoic wind tunnel. Three variations of a two-sideplate research set-up were created based on a slat-and-main-wing modified 30P30N airfoil cross-section. A `No Gap' (NG) geometry that connects the slat to both sideplates; a `No Horn & Step Stump' (NH) geometry that has a simplified slat side-edge and slat stump, a feature that blends the main wing with the fuselage; and a `Horn & Smooth Stump' (H) geometry, which incorporates a slat horn on the slat side-edge and a slat stump modelled after the Airbus A320. For all three variations, the relative positions of the slat track, slat side-edge and other junction surfaces were modelled after the Airbus A320 as well. All model variants were analysed based on their far-field noise radiation and the near-field behaviour of aerodynamic turbulent structures.
The results of the simulated scaled models were compared to literature. The noise radiation of the `H' model was scaled in power and frequency (Strouhal-based), and compared to beamforming integration flyover data of a junction of an Airbus A320. The model shows good spectral resemblance for higher frequencies, with larger discrepancies at lower frequencies. The low-frequency discrepancies were attributed to beamforming limitations stemming from Rayleigh's criterion, as well as a likely over-prediction of lower frequency noise by the scaled `H' set-up. Comparison to full-scale Reynolds number tests on a model Airbus A320 revealed the slope of the scaled noise spectrum resembled the slope of the slat noise of the Airbus A320 at full Reynolds number both at low and high frequencies.
Contrary to earlier research, the set-up without a sideplate-slat gap, `NG', produced excess noise compared to the `Gap'-models, `NH' and `H'. The excess noise is attributed to a larger spanwise extent of the slat narrow-band peak noise mechanism. The narrow-band peaks stem from a slat-cusp-to-slat-trailing-edge flow-acoustic resonance. The introduction of a side-edge (for the `NH' and `H' models) increases the spanwise velocity in the slat cove and creates a slat cove wake that gets accelerated over the slat track. This study showed that the altered slat cove wake shape prevents the canonical slat-cusp-to-slat-trailing-edge flow impingement from occurring on part of the slat, thus limiting the extent of the resonance mechanism. This phenomenon was portrayed by visualising the slat cove wake through total pressure isosurfaces and visualising the narrow-band peak noise source regions through a Ffowcs-Williams and Hawkings (FWH)-based source visualisation technique. A lack of loading on the slat (which is a property of the non-modified 30P30N cross-section as well) is hypothesised as the reason why the introduction of a slat side-edge does not increase the noise radiation for the models with a slat side-edge (`NH', and `H'). ...
The research set-up was designed for open-jet numerical simulations using the commercial Lattice Boltzmann Method (LBM) based CFD solver PowerFLOW, with future compatibility for experimental open-jet wind tunnel validation studies at the TU Delft's Anechoic wind tunnel. Three variations of a two-sideplate research set-up were created based on a slat-and-main-wing modified 30P30N airfoil cross-section. A `No Gap' (NG) geometry that connects the slat to both sideplates; a `No Horn & Step Stump' (NH) geometry that has a simplified slat side-edge and slat stump, a feature that blends the main wing with the fuselage; and a `Horn & Smooth Stump' (H) geometry, which incorporates a slat horn on the slat side-edge and a slat stump modelled after the Airbus A320. For all three variations, the relative positions of the slat track, slat side-edge and other junction surfaces were modelled after the Airbus A320 as well. All model variants were analysed based on their far-field noise radiation and the near-field behaviour of aerodynamic turbulent structures.
The results of the simulated scaled models were compared to literature. The noise radiation of the `H' model was scaled in power and frequency (Strouhal-based), and compared to beamforming integration flyover data of a junction of an Airbus A320. The model shows good spectral resemblance for higher frequencies, with larger discrepancies at lower frequencies. The low-frequency discrepancies were attributed to beamforming limitations stemming from Rayleigh's criterion, as well as a likely over-prediction of lower frequency noise by the scaled `H' set-up. Comparison to full-scale Reynolds number tests on a model Airbus A320 revealed the slope of the scaled noise spectrum resembled the slope of the slat noise of the Airbus A320 at full Reynolds number both at low and high frequencies.
Contrary to earlier research, the set-up without a sideplate-slat gap, `NG', produced excess noise compared to the `Gap'-models, `NH' and `H'. The excess noise is attributed to a larger spanwise extent of the slat narrow-band peak noise mechanism. The narrow-band peaks stem from a slat-cusp-to-slat-trailing-edge flow-acoustic resonance. The introduction of a side-edge (for the `NH' and `H' models) increases the spanwise velocity in the slat cove and creates a slat cove wake that gets accelerated over the slat track. This study showed that the altered slat cove wake shape prevents the canonical slat-cusp-to-slat-trailing-edge flow impingement from occurring on part of the slat, thus limiting the extent of the resonance mechanism. This phenomenon was portrayed by visualising the slat cove wake through total pressure isosurfaces and visualising the narrow-band peak noise source regions through a Ffowcs-Williams and Hawkings (FWH)-based source visualisation technique. A lack of loading on the slat (which is a property of the non-modified 30P30N cross-section as well) is hypothesised as the reason why the introduction of a slat side-edge does not increase the noise radiation for the models with a slat side-edge (`NH', and `H'). ...
A decades-long steady rise in air movements has disproportionally impacted airport-neighbouring communities. These communities bear the brunt of the aviation industry's air, and noise pollution, detrimental to their livelihood. Airports near densely populated areas face increasing societal and governmental scrutiny to reduce their noise pollution and improve the quality of life for airport-neighbouring communities. Airframe noise has become a prominent noise source during approach due to the increased usage of quieter high-bypass ratio turbofan engines. Flyover measurements suggest that the leading edge junction between the fuselage, wing, and slat is a high-intensity localised noise source. This airframe region has been sparsely researched. Therefore, this study aims to describe the relation between the aero-structural design of the fuselage-wing-slat junction and its aeroacoustic footprint for an aircraft in approach configuration.
The research set-up was designed for open-jet numerical simulations using the commercial Lattice Boltzmann Method (LBM) based CFD solver PowerFLOW, with future compatibility for experimental open-jet wind tunnel validation studies at the TU Delft's Anechoic wind tunnel. Three variations of a two-sideplate research set-up were created based on a slat-and-main-wing modified 30P30N airfoil cross-section. A `No Gap' (NG) geometry that connects the slat to both sideplates; a `No Horn & Step Stump' (NH) geometry that has a simplified slat side-edge and slat stump, a feature that blends the main wing with the fuselage; and a `Horn & Smooth Stump' (H) geometry, which incorporates a slat horn on the slat side-edge and a slat stump modelled after the Airbus A320. For all three variations, the relative positions of the slat track, slat side-edge and other junction surfaces were modelled after the Airbus A320 as well. All model variants were analysed based on their far-field noise radiation and the near-field behaviour of aerodynamic turbulent structures.
The results of the simulated scaled models were compared to literature. The noise radiation of the `H' model was scaled in power and frequency (Strouhal-based), and compared to beamforming integration flyover data of a junction of an Airbus A320. The model shows good spectral resemblance for higher frequencies, with larger discrepancies at lower frequencies. The low-frequency discrepancies were attributed to beamforming limitations stemming from Rayleigh's criterion, as well as a likely over-prediction of lower frequency noise by the scaled `H' set-up. Comparison to full-scale Reynolds number tests on a model Airbus A320 revealed the slope of the scaled noise spectrum resembled the slope of the slat noise of the Airbus A320 at full Reynolds number both at low and high frequencies.
Contrary to earlier research, the set-up without a sideplate-slat gap, `NG', produced excess noise compared to the `Gap'-models, `NH' and `H'. The excess noise is attributed to a larger spanwise extent of the slat narrow-band peak noise mechanism. The narrow-band peaks stem from a slat-cusp-to-slat-trailing-edge flow-acoustic resonance. The introduction of a side-edge (for the `NH' and `H' models) increases the spanwise velocity in the slat cove and creates a slat cove wake that gets accelerated over the slat track. This study showed that the altered slat cove wake shape prevents the canonical slat-cusp-to-slat-trailing-edge flow impingement from occurring on part of the slat, thus limiting the extent of the resonance mechanism. This phenomenon was portrayed by visualising the slat cove wake through total pressure isosurfaces and visualising the narrow-band peak noise source regions through a Ffowcs-Williams and Hawkings (FWH)-based source visualisation technique. A lack of loading on the slat (which is a property of the non-modified 30P30N cross-section as well) is hypothesised as the reason why the introduction of a slat side-edge does not increase the noise radiation for the models with a slat side-edge (`NH', and `H').
The research set-up was designed for open-jet numerical simulations using the commercial Lattice Boltzmann Method (LBM) based CFD solver PowerFLOW, with future compatibility for experimental open-jet wind tunnel validation studies at the TU Delft's Anechoic wind tunnel. Three variations of a two-sideplate research set-up were created based on a slat-and-main-wing modified 30P30N airfoil cross-section. A `No Gap' (NG) geometry that connects the slat to both sideplates; a `No Horn & Step Stump' (NH) geometry that has a simplified slat side-edge and slat stump, a feature that blends the main wing with the fuselage; and a `Horn & Smooth Stump' (H) geometry, which incorporates a slat horn on the slat side-edge and a slat stump modelled after the Airbus A320. For all three variations, the relative positions of the slat track, slat side-edge and other junction surfaces were modelled after the Airbus A320 as well. All model variants were analysed based on their far-field noise radiation and the near-field behaviour of aerodynamic turbulent structures.
The results of the simulated scaled models were compared to literature. The noise radiation of the `H' model was scaled in power and frequency (Strouhal-based), and compared to beamforming integration flyover data of a junction of an Airbus A320. The model shows good spectral resemblance for higher frequencies, with larger discrepancies at lower frequencies. The low-frequency discrepancies were attributed to beamforming limitations stemming from Rayleigh's criterion, as well as a likely over-prediction of lower frequency noise by the scaled `H' set-up. Comparison to full-scale Reynolds number tests on a model Airbus A320 revealed the slope of the scaled noise spectrum resembled the slope of the slat noise of the Airbus A320 at full Reynolds number both at low and high frequencies.
Contrary to earlier research, the set-up without a sideplate-slat gap, `NG', produced excess noise compared to the `Gap'-models, `NH' and `H'. The excess noise is attributed to a larger spanwise extent of the slat narrow-band peak noise mechanism. The narrow-band peaks stem from a slat-cusp-to-slat-trailing-edge flow-acoustic resonance. The introduction of a side-edge (for the `NH' and `H' models) increases the spanwise velocity in the slat cove and creates a slat cove wake that gets accelerated over the slat track. This study showed that the altered slat cove wake shape prevents the canonical slat-cusp-to-slat-trailing-edge flow impingement from occurring on part of the slat, thus limiting the extent of the resonance mechanism. This phenomenon was portrayed by visualising the slat cove wake through total pressure isosurfaces and visualising the narrow-band peak noise source regions through a Ffowcs-Williams and Hawkings (FWH)-based source visualisation technique. A lack of loading on the slat (which is a property of the non-modified 30P30N cross-section as well) is hypothesised as the reason why the introduction of a slat side-edge does not increase the noise radiation for the models with a slat side-edge (`NH', and `H').
With the ever-increasing issues caused by global warming, the emission of carbon dioxide has to be minimized. With the transport section being responsible for 24% of global emissions, the demand for electric alternatives is on the rise.
The electrification of passenger vehicles comes with benefits like a smoother driving experience, requiring less maintenance, and has led to an overall noise decrease. However, annoying noises that were previously masked by loud engines are now audible. Automotive cooling fan noise is such an example. The tonal character of the fan is annoying to pedestrians and residents, especially during car charging. The batteries reach high temperatures while charging, increasing the cooling demand from the fan module compared to conventional cars. In this situation, no inflow is generated from driving and the fan is operating at high rotational velocities and pressure requirements.
When the (axial) inflow to the fan is non-uniform, (the velocity changes over the circumference), a varying force is generated on the fan blade, when it rotates. When this non-uniformity is stationary (constant in time), these force fluctuations are periodic, and this is the main cause of the tonal noise. The non-uniformities in fan modules arise from inflow distortions, like for example heat exchanger, duct bends, or the shape of the shroud.
In current fan modules, unequal blade spacing is used to reduce the annoyance of these tones. This reduces the noise at the Blade Pass Frequency, but introduces tones at other harmonics of the rotational frequency, overall mainly leading to a reduction in noise annoyance.
Flow obstructions have been shown an effective means of reducing noise in equally spaced axial fans with low Mach number, while minimizing aerodynamic losses. They introduce a secondary non-uniformity in the inflow, which creates a secondary aeroacoustic source on the fan blade. When placed at the correct circumferential angle, cancellation between the primary and secondary source is possible. This research investigates if such flow obstructions can still yield adequate noise reduction on unequally spaced fans, and if (multiple) upstream heat exchangers prohibit the working mechanism of flow obstructions.
It was found that flow obstructions can indeed significantly reduce tonal noise at the fan BPF, by up to 13 dB on the fan axis, and 6dB at an angle 45\degree from the axis. The upstream radiator and condenser did not compromise this reduction, and the obstruction still reduces noise when the fan operates at a lower rotational velocity. Using a superposition of obstructions (creating a multi-modal obstruction) could also control multiple tones. However, with the large number of tones to be controlled in an unequally spaced fan, the overall sound pressure attenuation and annoyance reduction are insignificant.
Furthermore, the low-fidelity analytical tool developed in the thesis was an effective means of rapid obstruction design and optimization. Although information on the fan's primary noise is needed, as well as some parameters to define the obstruction wake (which can be obtained with cheaper, RANS simulations), the model correlated well with simulation data obtained in PowerFLOW. ...
The electrification of passenger vehicles comes with benefits like a smoother driving experience, requiring less maintenance, and has led to an overall noise decrease. However, annoying noises that were previously masked by loud engines are now audible. Automotive cooling fan noise is such an example. The tonal character of the fan is annoying to pedestrians and residents, especially during car charging. The batteries reach high temperatures while charging, increasing the cooling demand from the fan module compared to conventional cars. In this situation, no inflow is generated from driving and the fan is operating at high rotational velocities and pressure requirements.
When the (axial) inflow to the fan is non-uniform, (the velocity changes over the circumference), a varying force is generated on the fan blade, when it rotates. When this non-uniformity is stationary (constant in time), these force fluctuations are periodic, and this is the main cause of the tonal noise. The non-uniformities in fan modules arise from inflow distortions, like for example heat exchanger, duct bends, or the shape of the shroud.
In current fan modules, unequal blade spacing is used to reduce the annoyance of these tones. This reduces the noise at the Blade Pass Frequency, but introduces tones at other harmonics of the rotational frequency, overall mainly leading to a reduction in noise annoyance.
Flow obstructions have been shown an effective means of reducing noise in equally spaced axial fans with low Mach number, while minimizing aerodynamic losses. They introduce a secondary non-uniformity in the inflow, which creates a secondary aeroacoustic source on the fan blade. When placed at the correct circumferential angle, cancellation between the primary and secondary source is possible. This research investigates if such flow obstructions can still yield adequate noise reduction on unequally spaced fans, and if (multiple) upstream heat exchangers prohibit the working mechanism of flow obstructions.
It was found that flow obstructions can indeed significantly reduce tonal noise at the fan BPF, by up to 13 dB on the fan axis, and 6dB at an angle 45\degree from the axis. The upstream radiator and condenser did not compromise this reduction, and the obstruction still reduces noise when the fan operates at a lower rotational velocity. Using a superposition of obstructions (creating a multi-modal obstruction) could also control multiple tones. However, with the large number of tones to be controlled in an unequally spaced fan, the overall sound pressure attenuation and annoyance reduction are insignificant.
Furthermore, the low-fidelity analytical tool developed in the thesis was an effective means of rapid obstruction design and optimization. Although information on the fan's primary noise is needed, as well as some parameters to define the obstruction wake (which can be obtained with cheaper, RANS simulations), the model correlated well with simulation data obtained in PowerFLOW. ...
With the ever-increasing issues caused by global warming, the emission of carbon dioxide has to be minimized. With the transport section being responsible for 24% of global emissions, the demand for electric alternatives is on the rise.
The electrification of passenger vehicles comes with benefits like a smoother driving experience, requiring less maintenance, and has led to an overall noise decrease. However, annoying noises that were previously masked by loud engines are now audible. Automotive cooling fan noise is such an example. The tonal character of the fan is annoying to pedestrians and residents, especially during car charging. The batteries reach high temperatures while charging, increasing the cooling demand from the fan module compared to conventional cars. In this situation, no inflow is generated from driving and the fan is operating at high rotational velocities and pressure requirements.
When the (axial) inflow to the fan is non-uniform, (the velocity changes over the circumference), a varying force is generated on the fan blade, when it rotates. When this non-uniformity is stationary (constant in time), these force fluctuations are periodic, and this is the main cause of the tonal noise. The non-uniformities in fan modules arise from inflow distortions, like for example heat exchanger, duct bends, or the shape of the shroud.
In current fan modules, unequal blade spacing is used to reduce the annoyance of these tones. This reduces the noise at the Blade Pass Frequency, but introduces tones at other harmonics of the rotational frequency, overall mainly leading to a reduction in noise annoyance.
Flow obstructions have been shown an effective means of reducing noise in equally spaced axial fans with low Mach number, while minimizing aerodynamic losses. They introduce a secondary non-uniformity in the inflow, which creates a secondary aeroacoustic source on the fan blade. When placed at the correct circumferential angle, cancellation between the primary and secondary source is possible. This research investigates if such flow obstructions can still yield adequate noise reduction on unequally spaced fans, and if (multiple) upstream heat exchangers prohibit the working mechanism of flow obstructions.
It was found that flow obstructions can indeed significantly reduce tonal noise at the fan BPF, by up to 13 dB on the fan axis, and 6dB at an angle 45\degree from the axis. The upstream radiator and condenser did not compromise this reduction, and the obstruction still reduces noise when the fan operates at a lower rotational velocity. Using a superposition of obstructions (creating a multi-modal obstruction) could also control multiple tones. However, with the large number of tones to be controlled in an unequally spaced fan, the overall sound pressure attenuation and annoyance reduction are insignificant.
Furthermore, the low-fidelity analytical tool developed in the thesis was an effective means of rapid obstruction design and optimization. Although information on the fan's primary noise is needed, as well as some parameters to define the obstruction wake (which can be obtained with cheaper, RANS simulations), the model correlated well with simulation data obtained in PowerFLOW.
The electrification of passenger vehicles comes with benefits like a smoother driving experience, requiring less maintenance, and has led to an overall noise decrease. However, annoying noises that were previously masked by loud engines are now audible. Automotive cooling fan noise is such an example. The tonal character of the fan is annoying to pedestrians and residents, especially during car charging. The batteries reach high temperatures while charging, increasing the cooling demand from the fan module compared to conventional cars. In this situation, no inflow is generated from driving and the fan is operating at high rotational velocities and pressure requirements.
When the (axial) inflow to the fan is non-uniform, (the velocity changes over the circumference), a varying force is generated on the fan blade, when it rotates. When this non-uniformity is stationary (constant in time), these force fluctuations are periodic, and this is the main cause of the tonal noise. The non-uniformities in fan modules arise from inflow distortions, like for example heat exchanger, duct bends, or the shape of the shroud.
In current fan modules, unequal blade spacing is used to reduce the annoyance of these tones. This reduces the noise at the Blade Pass Frequency, but introduces tones at other harmonics of the rotational frequency, overall mainly leading to a reduction in noise annoyance.
Flow obstructions have been shown an effective means of reducing noise in equally spaced axial fans with low Mach number, while minimizing aerodynamic losses. They introduce a secondary non-uniformity in the inflow, which creates a secondary aeroacoustic source on the fan blade. When placed at the correct circumferential angle, cancellation between the primary and secondary source is possible. This research investigates if such flow obstructions can still yield adequate noise reduction on unequally spaced fans, and if (multiple) upstream heat exchangers prohibit the working mechanism of flow obstructions.
It was found that flow obstructions can indeed significantly reduce tonal noise at the fan BPF, by up to 13 dB on the fan axis, and 6dB at an angle 45\degree from the axis. The upstream radiator and condenser did not compromise this reduction, and the obstruction still reduces noise when the fan operates at a lower rotational velocity. Using a superposition of obstructions (creating a multi-modal obstruction) could also control multiple tones. However, with the large number of tones to be controlled in an unequally spaced fan, the overall sound pressure attenuation and annoyance reduction are insignificant.
Furthermore, the low-fidelity analytical tool developed in the thesis was an effective means of rapid obstruction design and optimization. Although information on the fan's primary noise is needed, as well as some parameters to define the obstruction wake (which can be obtained with cheaper, RANS simulations), the model correlated well with simulation data obtained in PowerFLOW.
Turbulent boundary layer trailing edge noise reduction by using a perforated add-on
A Lattice bolzmann approach
Turbulent boundary layer trailing edge noise is becoming an increasingly important problem in wind turbine applications. The wind turbine rotor diameter is expected to keep growing bigger in the future and trailing edge noise is known to scale with the relative rotor tip velocity to the power 5-6. One effective and yet relatively novel method to reduce this type of noise is the addition of perforated add-on devices to the rear end of the rotor blades. The perforated add-ons have been extensively tested experimentally in recent years. The experimental studies have been instrumental in developing design rules but currently, the precise mechanisms behind this noise reduction are not yet fully understood. The project objective is to obtain insights into the aero-acoustic flow physics responsible for the far-field noise reduction for perforated add-on trailing edge noise problems. To accomplish this, the first high-fidelity numerical LBM study in which the geometry of the per- forations is fully resolved is performed. The simulation is performed with the commercial Lattice Boltzmann method-based solver, PowerFLOW. A scaled 2.5D airfoil simulation is performed with an inflow of 20 [m/s] in lifting conditions. Three different airfoil add-on configurations are simulated. One baseline, one with a homogenous perforation spacing, and one geometry where this spacing is decreasing in the downstream direction. The simulation results are validated against experiments and a noise reduction of about 3 − 4 [dB] is found for in the lower frequency range Stc < 10. A distribution of sound sources was found over the add-on for all frequencies. The frequencies up to Stc = 10 show signs of destructive acoustic interference contributing to the observed noise reduction. Besides this phenomenon, two additional mechanisms were identified as contributing to the observed noise reduction. The second is the milder ∆p jump at the trailing edge caused by communicating boundary layers on both sides of the add-on. A good indication of this milder pressure jump is the correlation coefficient Rpp between two points on opposite sides of the add-on close to the edge. No development or growth of the zone of the correlation coefficient was found over the add-on except for the vicinity close to the trailing edge. A mean vertical upward flow is observed, flowing out of and extending above the perforations. This is believed to be relevant for the achieved noise reduction. The effect possibly has simultaneous positive and negative conflicting contributions to noise reduction. Lastly, it was concluded that the spectra of the homogeneous and linear perforated geometries showed too much similarity, therefore it was difficult to couple discrepancies in the near-field between the two cases to observations of the far-field spectra. ...
Turbulent boundary layer trailing edge noise is becoming an increasingly important problem in wind turbine applications. The wind turbine rotor diameter is expected to keep growing bigger in the future and trailing edge noise is known to scale with the relative rotor tip velocity to the power 5-6. One effective and yet relatively novel method to reduce this type of noise is the addition of perforated add-on devices to the rear end of the rotor blades. The perforated add-ons have been extensively tested experimentally in recent years. The experimental studies have been instrumental in developing design rules but currently, the precise mechanisms behind this noise reduction are not yet fully understood. The project objective is to obtain insights into the aero-acoustic flow physics responsible for the far-field noise reduction for perforated add-on trailing edge noise problems. To accomplish this, the first high-fidelity numerical LBM study in which the geometry of the per- forations is fully resolved is performed. The simulation is performed with the commercial Lattice Boltzmann method-based solver, PowerFLOW. A scaled 2.5D airfoil simulation is performed with an inflow of 20 [m/s] in lifting conditions. Three different airfoil add-on configurations are simulated. One baseline, one with a homogenous perforation spacing, and one geometry where this spacing is decreasing in the downstream direction. The simulation results are validated against experiments and a noise reduction of about 3 − 4 [dB] is found for in the lower frequency range Stc < 10. A distribution of sound sources was found over the add-on for all frequencies. The frequencies up to Stc = 10 show signs of destructive acoustic interference contributing to the observed noise reduction. Besides this phenomenon, two additional mechanisms were identified as contributing to the observed noise reduction. The second is the milder ∆p jump at the trailing edge caused by communicating boundary layers on both sides of the add-on. A good indication of this milder pressure jump is the correlation coefficient Rpp between two points on opposite sides of the add-on close to the edge. No development or growth of the zone of the correlation coefficient was found over the add-on except for the vicinity close to the trailing edge. A mean vertical upward flow is observed, flowing out of and extending above the perforations. This is believed to be relevant for the achieved noise reduction. The effect possibly has simultaneous positive and negative conflicting contributions to noise reduction. Lastly, it was concluded that the spectra of the homogeneous and linear perforated geometries showed too much similarity, therefore it was difficult to couple discrepancies in the near-field between the two cases to observations of the far-field spectra.
Master thesis
(2023)
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B. Sanchez Diaz, D. Ragni, M. Kotsonis, D.A.M. De Tavernier, Valentina Motta, Marianne Hartung
Forward flow dynamic stall is a heavily researched field with multiple well-established models that appropriately capture this type of flow at moderate angles of attack. However, horizontal axis wind turbines operate at a wide range of angles of attack and rapidly changing wind directions, conditions for which limited literature studying the performance of these models has been found. An especially under-researched field is reverse flow dynamic stall, both in terms of experimental investigation and modelling. Therefore, the purpose of this research is to identify the relevant flow phenomena occurring in reverse flow and to analyze which dynamic stall models can accurately represent these flow conditions.
The performance of established dynamic stall models such as the one developed by Pierce and the current General Electric dynamic stall model (GE2021) was assessed in reverse flow conditions. In addition, improvements to the GE2021 model were proposed to enhance its performance, including a delay in the effective angle of attack as a function of the reduced frequency and the addition of vortex effects in the load calculation. Three options for the inclusion of vortex effects were explored. The first used the formulation of vortex effects developed by Pierce, which, being very similar to those proposed in the original Beddoes-Leishman model, allows assessment of the performance of the latter for reverse flow dynamic stall. The second focused on the interpretation proposed by Sheng, Galbraith, and Coton of the vortex effects calculation formulated by Beddoes. The last consisted of a simplification of the sinusoidal vortex effects computation of the second approach. In addition, study and tuning of the variables and coefficients involved in this calculation were developed in order to provide a versatile model with the ability to provide reliable results in both forward and reverse flow conditions.
This project aims to be a first step in the study of reverse flow modelling and to improve our understanding of its modelling requirements. ...
The performance of established dynamic stall models such as the one developed by Pierce and the current General Electric dynamic stall model (GE2021) was assessed in reverse flow conditions. In addition, improvements to the GE2021 model were proposed to enhance its performance, including a delay in the effective angle of attack as a function of the reduced frequency and the addition of vortex effects in the load calculation. Three options for the inclusion of vortex effects were explored. The first used the formulation of vortex effects developed by Pierce, which, being very similar to those proposed in the original Beddoes-Leishman model, allows assessment of the performance of the latter for reverse flow dynamic stall. The second focused on the interpretation proposed by Sheng, Galbraith, and Coton of the vortex effects calculation formulated by Beddoes. The last consisted of a simplification of the sinusoidal vortex effects computation of the second approach. In addition, study and tuning of the variables and coefficients involved in this calculation were developed in order to provide a versatile model with the ability to provide reliable results in both forward and reverse flow conditions.
This project aims to be a first step in the study of reverse flow modelling and to improve our understanding of its modelling requirements. ...
Forward flow dynamic stall is a heavily researched field with multiple well-established models that appropriately capture this type of flow at moderate angles of attack. However, horizontal axis wind turbines operate at a wide range of angles of attack and rapidly changing wind directions, conditions for which limited literature studying the performance of these models has been found. An especially under-researched field is reverse flow dynamic stall, both in terms of experimental investigation and modelling. Therefore, the purpose of this research is to identify the relevant flow phenomena occurring in reverse flow and to analyze which dynamic stall models can accurately represent these flow conditions.
The performance of established dynamic stall models such as the one developed by Pierce and the current General Electric dynamic stall model (GE2021) was assessed in reverse flow conditions. In addition, improvements to the GE2021 model were proposed to enhance its performance, including a delay in the effective angle of attack as a function of the reduced frequency and the addition of vortex effects in the load calculation. Three options for the inclusion of vortex effects were explored. The first used the formulation of vortex effects developed by Pierce, which, being very similar to those proposed in the original Beddoes-Leishman model, allows assessment of the performance of the latter for reverse flow dynamic stall. The second focused on the interpretation proposed by Sheng, Galbraith, and Coton of the vortex effects calculation formulated by Beddoes. The last consisted of a simplification of the sinusoidal vortex effects computation of the second approach. In addition, study and tuning of the variables and coefficients involved in this calculation were developed in order to provide a versatile model with the ability to provide reliable results in both forward and reverse flow conditions.
This project aims to be a first step in the study of reverse flow modelling and to improve our understanding of its modelling requirements.
The performance of established dynamic stall models such as the one developed by Pierce and the current General Electric dynamic stall model (GE2021) was assessed in reverse flow conditions. In addition, improvements to the GE2021 model were proposed to enhance its performance, including a delay in the effective angle of attack as a function of the reduced frequency and the addition of vortex effects in the load calculation. Three options for the inclusion of vortex effects were explored. The first used the formulation of vortex effects developed by Pierce, which, being very similar to those proposed in the original Beddoes-Leishman model, allows assessment of the performance of the latter for reverse flow dynamic stall. The second focused on the interpretation proposed by Sheng, Galbraith, and Coton of the vortex effects calculation formulated by Beddoes. The last consisted of a simplification of the sinusoidal vortex effects computation of the second approach. In addition, study and tuning of the variables and coefficients involved in this calculation were developed in order to provide a versatile model with the ability to provide reliable results in both forward and reverse flow conditions.
This project aims to be a first step in the study of reverse flow modelling and to improve our understanding of its modelling requirements.
Bachelor thesis
(2023)
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W. Amezguiou, S.D. Bhawan, N.A. van Bohemen, M.L. Capelle, T.M.K. Coutuer, M.I. Piperigou Grammatika, L.L. Hoitingh, Y.Q.F. Karelsz, A.E. Pattiwael, Muneeb SYED MUNEEB UR RAHMAN, D. Ragni, B. Mohammadikalakoo, F. Surma
Airborne wind energy systems offer a promising approach for renewable energy generation. However, the noise emissions associated with these systems should be understood and minimized as well to promote their integration and (social) acceptance. This research aims to identify the noise sources of airborne wind energy systems, systems with leading-edge inflatable (LEI) kites and fixed-wing kites in particular, and establish a foundation for future research in this field. Analytical simulations using the Brooks, Pope, and Marcolini model and the Amiet model were combined with experimental measurements for this research.
The analysis of the fixed-wing kite revealed prominent peaks around 1500 Hz and 2000 Hz in the noise spectra, with the higher frequency peak observed at higher kite velocities. Analytical predictions indicated laminar boundary layer vortex shedding and tether vortex shedding as the main noise sources. The study also investigated the directivity of the turbulent boundary layer trailing edge noise, which revealed dipoles that exhibited slight deformations at higher frequencies.
For the LEI kite, noise analysis identified peaks in the sound pressure level around 300-400 Hz and 1000-2000 Hz. Analytical predictions highlighted turbulent boundary layer trailing edge noise and vortex shedding from the tether and bridle lines as the dominant noise sources.
By considering the implications of these findings, the noise impact of airborne wind energy systems can be minimized, fostering their sustainable deployment and acceptance. ...
The analysis of the fixed-wing kite revealed prominent peaks around 1500 Hz and 2000 Hz in the noise spectra, with the higher frequency peak observed at higher kite velocities. Analytical predictions indicated laminar boundary layer vortex shedding and tether vortex shedding as the main noise sources. The study also investigated the directivity of the turbulent boundary layer trailing edge noise, which revealed dipoles that exhibited slight deformations at higher frequencies.
For the LEI kite, noise analysis identified peaks in the sound pressure level around 300-400 Hz and 1000-2000 Hz. Analytical predictions highlighted turbulent boundary layer trailing edge noise and vortex shedding from the tether and bridle lines as the dominant noise sources.
By considering the implications of these findings, the noise impact of airborne wind energy systems can be minimized, fostering their sustainable deployment and acceptance. ...
Airborne wind energy systems offer a promising approach for renewable energy generation. However, the noise emissions associated with these systems should be understood and minimized as well to promote their integration and (social) acceptance. This research aims to identify the noise sources of airborne wind energy systems, systems with leading-edge inflatable (LEI) kites and fixed-wing kites in particular, and establish a foundation for future research in this field. Analytical simulations using the Brooks, Pope, and Marcolini model and the Amiet model were combined with experimental measurements for this research.
The analysis of the fixed-wing kite revealed prominent peaks around 1500 Hz and 2000 Hz in the noise spectra, with the higher frequency peak observed at higher kite velocities. Analytical predictions indicated laminar boundary layer vortex shedding and tether vortex shedding as the main noise sources. The study also investigated the directivity of the turbulent boundary layer trailing edge noise, which revealed dipoles that exhibited slight deformations at higher frequencies.
For the LEI kite, noise analysis identified peaks in the sound pressure level around 300-400 Hz and 1000-2000 Hz. Analytical predictions highlighted turbulent boundary layer trailing edge noise and vortex shedding from the tether and bridle lines as the dominant noise sources.
By considering the implications of these findings, the noise impact of airborne wind energy systems can be minimized, fostering their sustainable deployment and acceptance.
The analysis of the fixed-wing kite revealed prominent peaks around 1500 Hz and 2000 Hz in the noise spectra, with the higher frequency peak observed at higher kite velocities. Analytical predictions indicated laminar boundary layer vortex shedding and tether vortex shedding as the main noise sources. The study also investigated the directivity of the turbulent boundary layer trailing edge noise, which revealed dipoles that exhibited slight deformations at higher frequencies.
For the LEI kite, noise analysis identified peaks in the sound pressure level around 300-400 Hz and 1000-2000 Hz. Analytical predictions highlighted turbulent boundary layer trailing edge noise and vortex shedding from the tether and bridle lines as the dominant noise sources.
By considering the implications of these findings, the noise impact of airborne wind energy systems can be minimized, fostering their sustainable deployment and acceptance.
Study of high aspect-ratio dual intersecting jets and the installation effect on control authority
An experimental and numerical investigation
With an unprecedented surge in the number of individuals utilizing electric vehicles for commuting across the globe, it is becoming critical to immediately deliver an adequate and range-friendly degree of thermal comfort in car cabins to help drivers remain focused and attentive. The research presented in this thesis is part of the development work carried out by the Aerothermal team at Tesla. The team aims to better understand high aspect ratio subsonic jets, particularly intersecting twin jets, to ventilate the vehicle's passenger compartment.
The intersecting twin jet has recently captured significant attention from the Aerothermal team for several reasons. Firstly, it provides the ability to actively control the flow angle from the HVAC unit into the vehicle cabin without requiring direct interaction with the vent. Additionally, it facilitates the flushing of the vent outlets with the A-class surfaces in the vehicle interior, helps achieve a simple and minimalist design for the instrument panel and other interior surfaces that align with Tesla's design language
The objective pursued in this thesis is to investigate the physics represented by the bulk flow characteristics of intersecting twin jets, and to scrutinize the installation effect on the merging jet, focusing on the influence of the installation surface offset height. This objective is achieved by characterizing the evolution of large-scale flow structures in High AR intersecting twin jets at moderate Reynolds numbers experimentally using planar Particle Image Velocimetry (PIV) in both installed and uninstalled conditions. Once accomplished, the experimental results are then used to help select, validate, and calibrate the appropriate RANS turbulence model.
The experimental results show that the intersecting jets converge before merging and forming a single jet. This jet behaves like a single jet emanating from a more recessed origin. The variation of the flow ratio between the two nozzle outlets results in varying the jet angle. The study reveals that the placement of the surface impacts the jet angle and velocity and introduces a circulation zone that affects the jet's behavior and direction. The surface's impact depends on the offset distance, length, and profile of the surface. The results also suggest that accurate computational prediction of the jet characteristics requires high mesh resolution and an appropriate selection of turbulence intensity. Among the four turbulence models assessed, the k-omega SST model is found to be adequate for the application, although it exhibits some numerical hysteresis. Overall, the findings provide insights into the dynamics of jet-surface interactions and can guide the design of systems involving such flows.
...
The intersecting twin jet has recently captured significant attention from the Aerothermal team for several reasons. Firstly, it provides the ability to actively control the flow angle from the HVAC unit into the vehicle cabin without requiring direct interaction with the vent. Additionally, it facilitates the flushing of the vent outlets with the A-class surfaces in the vehicle interior, helps achieve a simple and minimalist design for the instrument panel and other interior surfaces that align with Tesla's design language
The objective pursued in this thesis is to investigate the physics represented by the bulk flow characteristics of intersecting twin jets, and to scrutinize the installation effect on the merging jet, focusing on the influence of the installation surface offset height. This objective is achieved by characterizing the evolution of large-scale flow structures in High AR intersecting twin jets at moderate Reynolds numbers experimentally using planar Particle Image Velocimetry (PIV) in both installed and uninstalled conditions. Once accomplished, the experimental results are then used to help select, validate, and calibrate the appropriate RANS turbulence model.
The experimental results show that the intersecting jets converge before merging and forming a single jet. This jet behaves like a single jet emanating from a more recessed origin. The variation of the flow ratio between the two nozzle outlets results in varying the jet angle. The study reveals that the placement of the surface impacts the jet angle and velocity and introduces a circulation zone that affects the jet's behavior and direction. The surface's impact depends on the offset distance, length, and profile of the surface. The results also suggest that accurate computational prediction of the jet characteristics requires high mesh resolution and an appropriate selection of turbulence intensity. Among the four turbulence models assessed, the k-omega SST model is found to be adequate for the application, although it exhibits some numerical hysteresis. Overall, the findings provide insights into the dynamics of jet-surface interactions and can guide the design of systems involving such flows.
...
With an unprecedented surge in the number of individuals utilizing electric vehicles for commuting across the globe, it is becoming critical to immediately deliver an adequate and range-friendly degree of thermal comfort in car cabins to help drivers remain focused and attentive. The research presented in this thesis is part of the development work carried out by the Aerothermal team at Tesla. The team aims to better understand high aspect ratio subsonic jets, particularly intersecting twin jets, to ventilate the vehicle's passenger compartment.
The intersecting twin jet has recently captured significant attention from the Aerothermal team for several reasons. Firstly, it provides the ability to actively control the flow angle from the HVAC unit into the vehicle cabin without requiring direct interaction with the vent. Additionally, it facilitates the flushing of the vent outlets with the A-class surfaces in the vehicle interior, helps achieve a simple and minimalist design for the instrument panel and other interior surfaces that align with Tesla's design language
The objective pursued in this thesis is to investigate the physics represented by the bulk flow characteristics of intersecting twin jets, and to scrutinize the installation effect on the merging jet, focusing on the influence of the installation surface offset height. This objective is achieved by characterizing the evolution of large-scale flow structures in High AR intersecting twin jets at moderate Reynolds numbers experimentally using planar Particle Image Velocimetry (PIV) in both installed and uninstalled conditions. Once accomplished, the experimental results are then used to help select, validate, and calibrate the appropriate RANS turbulence model.
The experimental results show that the intersecting jets converge before merging and forming a single jet. This jet behaves like a single jet emanating from a more recessed origin. The variation of the flow ratio between the two nozzle outlets results in varying the jet angle. The study reveals that the placement of the surface impacts the jet angle and velocity and introduces a circulation zone that affects the jet's behavior and direction. The surface's impact depends on the offset distance, length, and profile of the surface. The results also suggest that accurate computational prediction of the jet characteristics requires high mesh resolution and an appropriate selection of turbulence intensity. Among the four turbulence models assessed, the k-omega SST model is found to be adequate for the application, although it exhibits some numerical hysteresis. Overall, the findings provide insights into the dynamics of jet-surface interactions and can guide the design of systems involving such flows.
The intersecting twin jet has recently captured significant attention from the Aerothermal team for several reasons. Firstly, it provides the ability to actively control the flow angle from the HVAC unit into the vehicle cabin without requiring direct interaction with the vent. Additionally, it facilitates the flushing of the vent outlets with the A-class surfaces in the vehicle interior, helps achieve a simple and minimalist design for the instrument panel and other interior surfaces that align with Tesla's design language
The objective pursued in this thesis is to investigate the physics represented by the bulk flow characteristics of intersecting twin jets, and to scrutinize the installation effect on the merging jet, focusing on the influence of the installation surface offset height. This objective is achieved by characterizing the evolution of large-scale flow structures in High AR intersecting twin jets at moderate Reynolds numbers experimentally using planar Particle Image Velocimetry (PIV) in both installed and uninstalled conditions. Once accomplished, the experimental results are then used to help select, validate, and calibrate the appropriate RANS turbulence model.
The experimental results show that the intersecting jets converge before merging and forming a single jet. This jet behaves like a single jet emanating from a more recessed origin. The variation of the flow ratio between the two nozzle outlets results in varying the jet angle. The study reveals that the placement of the surface impacts the jet angle and velocity and introduces a circulation zone that affects the jet's behavior and direction. The surface's impact depends on the offset distance, length, and profile of the surface. The results also suggest that accurate computational prediction of the jet characteristics requires high mesh resolution and an appropriate selection of turbulence intensity. Among the four turbulence models assessed, the k-omega SST model is found to be adequate for the application, although it exhibits some numerical hysteresis. Overall, the findings provide insights into the dynamics of jet-surface interactions and can guide the design of systems involving such flows.
Airline collaboration and Environmental impact
Airline Collaborative Network Planning to mitigate Environmental Impact
Master thesis
(2023)
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E. Verzotti, B.F. Santos, I.C. Dedoussi, A. Bombelli, D. Ragni, Sebastian Birolini, Dirk Gemke
In recent years, the aviation industry has faced escalating environmental scrutiny, prompted by the global shift towards heightened environmental awareness. This study explores a collaboration framework set up by airlines which envision to partially or totally shoulder the environmental impact costs generated by their airborne emissions. The methodology developed includes the production of detailed emissions data to be employed during the airline’s planning strategy. The model conceived introduces a taxation approach exploited by airlines to include and incentive more environmentally sustainable solutions and, a collaboration mechanism based on the possibility to share passenger demand between collaborating airlines. The environmental incentive and collaboration are implemented in a Linear Programming Network and Frequency Planning model with the goal of maximising airlines profitability. A case study is analysed focusing on two airlines, KLM and TAP, collaborating to achieve improved environmental and economic performance. The airlines engage in a scenario where the environmental impact externalities generated by airborne operations are shouldered by the airlines themselves. Employing the model developed, the airlines explore solutions that either reduce the environmental impact or that solely maximise profit of the two airlines. The results underscore the potential benefits of including collaboration in the airline’s planning strategy, with a total 1.33% reduction in environmental impact when prioritising environmental cost abatement. Collaboration also demonstrated to be a consistent tool to achieve a profit recovery, showing up to a total anticipated profit increase of 2.21% when prioritising profitability or 0.71% when the priority is given to environmental impact reduction. In conclusion, this study highlights the potential efficacy of collaboration in addressing aviation’s environmental and economic challenges.
...
In recent years, the aviation industry has faced escalating environmental scrutiny, prompted by the global shift towards heightened environmental awareness. This study explores a collaboration framework set up by airlines which envision to partially or totally shoulder the environmental impact costs generated by their airborne emissions. The methodology developed includes the production of detailed emissions data to be employed during the airline’s planning strategy. The model conceived introduces a taxation approach exploited by airlines to include and incentive more environmentally sustainable solutions and, a collaboration mechanism based on the possibility to share passenger demand between collaborating airlines. The environmental incentive and collaboration are implemented in a Linear Programming Network and Frequency Planning model with the goal of maximising airlines profitability. A case study is analysed focusing on two airlines, KLM and TAP, collaborating to achieve improved environmental and economic performance. The airlines engage in a scenario where the environmental impact externalities generated by airborne operations are shouldered by the airlines themselves. Employing the model developed, the airlines explore solutions that either reduce the environmental impact or that solely maximise profit of the two airlines. The results underscore the potential benefits of including collaboration in the airline’s planning strategy, with a total 1.33% reduction in environmental impact when prioritising environmental cost abatement. Collaboration also demonstrated to be a consistent tool to achieve a profit recovery, showing up to a total anticipated profit increase of 2.21% when prioritising profitability or 0.71% when the priority is given to environmental impact reduction. In conclusion, this study highlights the potential efficacy of collaboration in addressing aviation’s environmental and economic challenges.
Wind-turbine noise can restrict the growing implementation of renewable energy sources and their application close to urban environments. The largest contributor to the noise of modern turbines is the scattering of the turbulent fluctuations at the blade trailing edge. This source of noise is directly correlated with the turbine’s extracted power. Therefore, operating in noise-restricted environments and at night times entails lower energy production. An extensively applied solution for reducing the noise of wind turbines is the use of trailing-edge serrations, i.e. imposing periodic variations in the geometry of the blade trailing edge. Serrations reduce the effectiveness of the scattering at the trailing edge as the turbulent fluctuations reach the trailing edge at different times along the blade span, consequently reducing the wind-turbine noise. Although extensive literature and knowledge exist on serrations, their measured performance does not compare with the predicted one. Even more problematic, the trends predicted for the geometric alterations of the serrations are not observed in reality. Notably, two things are worth mentioning: first, geometries shown as optimal by theory perform worse than other concepts, and second, the noise from serrations is affected by the angle between the insert and the flow. As a result, the design of trailing-edge serrations still requires dedicated experiments and numerical simulations, hampering the assessment of several geometries necessary for complete optimization of the serration design. This work seeks a physical interpretation of the noise generation mechanisms of trailing edges with serrated add-ons. This interpretation is focused on understanding the underlying physical principles of the flow surrounding a serrated trailing edge. This is carried out in this work with three studies, respectively on the observation, modelling, and control of the flow and acoustic properties of serrated trailing edges...
...
Wind-turbine noise can restrict the growing implementation of renewable energy sources and their application close to urban environments. The largest contributor to the noise of modern turbines is the scattering of the turbulent fluctuations at the blade trailing edge. This source of noise is directly correlated with the turbine’s extracted power. Therefore, operating in noise-restricted environments and at night times entails lower energy production. An extensively applied solution for reducing the noise of wind turbines is the use of trailing-edge serrations, i.e. imposing periodic variations in the geometry of the blade trailing edge. Serrations reduce the effectiveness of the scattering at the trailing edge as the turbulent fluctuations reach the trailing edge at different times along the blade span, consequently reducing the wind-turbine noise. Although extensive literature and knowledge exist on serrations, their measured performance does not compare with the predicted one. Even more problematic, the trends predicted for the geometric alterations of the serrations are not observed in reality. Notably, two things are worth mentioning: first, geometries shown as optimal by theory perform worse than other concepts, and second, the noise from serrations is affected by the angle between the insert and the flow. As a result, the design of trailing-edge serrations still requires dedicated experiments and numerical simulations, hampering the assessment of several geometries necessary for complete optimization of the serration design. This work seeks a physical interpretation of the noise generation mechanisms of trailing edges with serrated add-ons. This interpretation is focused on understanding the underlying physical principles of the flow surrounding a serrated trailing edge. This is carried out in this work with three studies, respectively on the observation, modelling, and control of the flow and acoustic properties of serrated trailing edges...