R. Schmehl
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Leading-edge inflatable (LEI) kites exhibit pronounced anhedral and pressure-side recirculation associated with their double-curved geometry and tubular frame. This study reports wind tunnel stereoscopic particle image velocimetry (PIV) measurements around a rigid 1:6.5 scale model of the TU Delft V3 kite. Measurements are acquired in chordwise planes located between the mid-span and tip at two angles of attack and are compared against slices extracted from Reynolds-averaged Navier–Stokes (RANS) simulations at corresponding spanwise positions. Reflection-prone surface geometry required tailored masking and an additional out-of-plane velocity filter, leaving near-wall data in the pressure-side recirculation region unresolved. Sectional lift and drag were estimated using the Kutta–Joukowski relation, RANS surface pressure integration, and Noca's method. Within the Noca framework, reliable lift and physically consistent drag are obtained only from specific inviscid contributions, indicating that selective use of individual terms is more robust than applying the full formulation in the present configuration. Local discrepancies near strut junctions are consistent with three-dimensional (3D) strut-induced flow effects observed in computational fluid dynamics (CFDs), which are captured by surface pressure integration but not by contour-based planar methods. Comparison confirms agreement between PIV and CFD to within 5 % of the freestream velocity across the majority of the flow field, and circulation distributions obtained from contour integration show consistent spanwise trends between the vortex step method, RANS, and PIV, jointly supporting the use of the dataset as a valuable, albeit not definitive, validation resource for aerodynamic models of LEI kites.
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Leading-edge inflatable (LEI) kites exhibit pronounced anhedral and pressure-side recirculation associated with their double-curved geometry and tubular frame. This study reports wind tunnel stereoscopic particle image velocimetry (PIV) measurements around a rigid 1:6.5 scale model of the TU Delft V3 kite. Measurements are acquired in chordwise planes located between the mid-span and tip at two angles of attack and are compared against slices extracted from Reynolds-averaged Navier–Stokes (RANS) simulations at corresponding spanwise positions. Reflection-prone surface geometry required tailored masking and an additional out-of-plane velocity filter, leaving near-wall data in the pressure-side recirculation region unresolved. Sectional lift and drag were estimated using the Kutta–Joukowski relation, RANS surface pressure integration, and Noca's method. Within the Noca framework, reliable lift and physically consistent drag are obtained only from specific inviscid contributions, indicating that selective use of individual terms is more robust than applying the full formulation in the present configuration. Local discrepancies near strut junctions are consistent with three-dimensional (3D) strut-induced flow effects observed in computational fluid dynamics (CFDs), which are captured by surface pressure integration but not by contour-based planar methods. Comparison confirms agreement between PIV and CFD to within 5 % of the freestream velocity across the majority of the flow field, and circulation distributions obtained from contour integration show consistent spanwise trends between the vortex step method, RANS, and PIV, jointly supporting the use of the dataset as a valuable, albeit not definitive, validation resource for aerodynamic models of LEI kites.
Journal article
(2026)
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Jelle Agatho Wilhelm Poland, Johannes Marinus van Spronsen, Mac Gaunaa, Roland Schmehl
Leading-edge inflatable (LEI) kites are morphing aerodynamic surfaces that are actuated by the bridle line system. Their design as tensile membrane structures has several implications for aerodynamic performance. Because of the pronounced C shape of the wings, a considerable part of the aerodynamic forces is redirected sideways and used for steering. The inflated tubular frame introduces flow recirculation zones on the pressure side of the wing. In this paper, we present wind tunnel measurements of a 1:6.5 rigid-scale model of the 25 m2 TU Delft V3 LEI kite developed specifically for airborne wind energy (AWE) harvesting. Aerodynamic forces and moments were recorded in an open-jet wind tunnel over wide ranges of flow conditions, including angles of attack from -11.6 to 24.5°, sideslip angles from -20 to 20°, and freestream velocities from 5 to 25 ms-1. The wind tunnel measurements were performed with and without zigzag tape along the model's leading edge to investigate the possible boundary layer tripping effect of the stitching seam connecting the canopy to the inflated tube. At a Reynolds number of 5×105, the addition of zigzag tape was found to reduce lift and increase drag, indicating a negative impact on aerodynamic performance. The rigid-scale model was manufactured to match the undeformed geometry employed in Reynolds-averaged Navier–Stokes (RANS) simulations from the literature, rather than the unknown in-flight deformed geometry. A representative subset of the measurements was used to benchmark both these RANS and new vortex-step method simulations. Both computational methods successfully reproduced the measured trends under nominal operating conditions. While the post-stall discrepancy persists, excellent agreement was observed for lift, drag, and side force coefficients, with lift deviations remaining within the 10% range.
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Leading-edge inflatable (LEI) kites are morphing aerodynamic surfaces that are actuated by the bridle line system. Their design as tensile membrane structures has several implications for aerodynamic performance. Because of the pronounced C shape of the wings, a considerable part of the aerodynamic forces is redirected sideways and used for steering. The inflated tubular frame introduces flow recirculation zones on the pressure side of the wing. In this paper, we present wind tunnel measurements of a 1:6.5 rigid-scale model of the 25 m2 TU Delft V3 LEI kite developed specifically for airborne wind energy (AWE) harvesting. Aerodynamic forces and moments were recorded in an open-jet wind tunnel over wide ranges of flow conditions, including angles of attack from -11.6 to 24.5°, sideslip angles from -20 to 20°, and freestream velocities from 5 to 25 ms-1. The wind tunnel measurements were performed with and without zigzag tape along the model's leading edge to investigate the possible boundary layer tripping effect of the stitching seam connecting the canopy to the inflated tube. At a Reynolds number of 5×105, the addition of zigzag tape was found to reduce lift and increase drag, indicating a negative impact on aerodynamic performance. The rigid-scale model was manufactured to match the undeformed geometry employed in Reynolds-averaged Navier–Stokes (RANS) simulations from the literature, rather than the unknown in-flight deformed geometry. A representative subset of the measurements was used to benchmark both these RANS and new vortex-step method simulations. Both computational methods successfully reproduced the measured trends under nominal operating conditions. While the post-stall discrepancy persists, excellent agreement was observed for lift, drag, and side force coefficients, with lift deviations remaining within the 10% range.
The design and control of airborne wind energy systems requires fast, validated reduced-order models. Because the aerodynamic identification of soft, bridled kites is challenging, models that minimise the number of parameters to be identified can be particularly valuable. This paper presents a reduced-order model for the translational dynamics of bridled kites, consisting of a wing supported by multiple bridle lines. The kite is modelled as a point mass in a spherical reference frame aligned with the instantaneous tangential flight direction, referred to as the course reference frame. The angle of attack follows geometrically from a constant angle between the wing chord and the bridle line system, under the assumption that the wing instantaneously aligns with the pull direction, i.e. the rotational dynamics are neglected. The formulation retains gravitational and inertial terms introduced by the curvilinear reference frame and applies a quasi-steady condition of zero-path-aligned acceleration, modelling the motion as a sequence of quasi-steady (trimmed) states that relate the trim speed and angle of attack. Model validation is based on public flight datasets from two different soft-wing kites and on dynamic simulations that cover higher wing loadings. Results show that for low wing loadings typical of soft kites, the quasi-steady approximation reproduces the dynamic trajectories with less than 1 % deviation in mean reel-out power. For higher loadings and hard-wing kites, inertia introduces substantial phase lag and amplitude damping, causing power deviations of up to 14 %. Overall, the proposed model provides a computationally efficient framework for analysing the translational dynamics of bridled kites. The formulation is well suited to trajectory optimisation, parametric studies, and control design in airborne wind energy systems.
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The design and control of airborne wind energy systems requires fast, validated reduced-order models. Because the aerodynamic identification of soft, bridled kites is challenging, models that minimise the number of parameters to be identified can be particularly valuable. This paper presents a reduced-order model for the translational dynamics of bridled kites, consisting of a wing supported by multiple bridle lines. The kite is modelled as a point mass in a spherical reference frame aligned with the instantaneous tangential flight direction, referred to as the course reference frame. The angle of attack follows geometrically from a constant angle between the wing chord and the bridle line system, under the assumption that the wing instantaneously aligns with the pull direction, i.e. the rotational dynamics are neglected. The formulation retains gravitational and inertial terms introduced by the curvilinear reference frame and applies a quasi-steady condition of zero-path-aligned acceleration, modelling the motion as a sequence of quasi-steady (trimmed) states that relate the trim speed and angle of attack. Model validation is based on public flight datasets from two different soft-wing kites and on dynamic simulations that cover higher wing loadings. Results show that for low wing loadings typical of soft kites, the quasi-steady approximation reproduces the dynamic trajectories with less than 1 % deviation in mean reel-out power. For higher loadings and hard-wing kites, inertia introduces substantial phase lag and amplitude damping, causing power deviations of up to 14 %. Overall, the proposed model provides a computationally efficient framework for analysing the translational dynamics of bridled kites. The formulation is well suited to trajectory optimisation, parametric studies, and control design in airborne wind energy systems.
This computational study compares the performance of circular and figure-of-eight flight patterns for fixed-wing ground-generation airborne wind energy (AWE) systems using a PID-based basic controller that effectively controls the kite during each pattern's pumping cycle in a MATLAB® Simulink® environment. A simple, adjustable control framework enables a steady analysis within consistent operational parameters, allowing for fair comparisons of power output, power quality, ground surface area requirements, and structural load impacts. Unlike for small lightweight kites, the simulation results reveal that when using the 150 m2 MegAWES reference kite, the power is not similar over different patterns. The circular flight pattern achieves the highest cycle-averaged power output in a smaller operational area, making it advantageous for maximising energy within limited spatial constraints. Conversely, the figure-of-eight down-loop pattern demonstrates superior power quality with lower power peaks and lower expected structural fatigue due to a reduced cyclic aerodynamic load frequency and amplitude, supporting greater operational stability and system longevity. The figure-of-eight up-loop does not stand out on any of the metrics considered in this work. This study offers insights into the trade-offs between energy output, efficiency, and structural demands associated with each flight path, providing a foundation for future AWE flight path selection and control strategy optimisations.
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This computational study compares the performance of circular and figure-of-eight flight patterns for fixed-wing ground-generation airborne wind energy (AWE) systems using a PID-based basic controller that effectively controls the kite during each pattern's pumping cycle in a MATLAB® Simulink® environment. A simple, adjustable control framework enables a steady analysis within consistent operational parameters, allowing for fair comparisons of power output, power quality, ground surface area requirements, and structural load impacts. Unlike for small lightweight kites, the simulation results reveal that when using the 150 m2 MegAWES reference kite, the power is not similar over different patterns. The circular flight pattern achieves the highest cycle-averaged power output in a smaller operational area, making it advantageous for maximising energy within limited spatial constraints. Conversely, the figure-of-eight down-loop pattern demonstrates superior power quality with lower power peaks and lower expected structural fatigue due to a reduced cyclic aerodynamic load frequency and amplitude, supporting greater operational stability and system longevity. The figure-of-eight up-loop does not stand out on any of the metrics considered in this work. This study offers insights into the trade-offs between energy output, efficiency, and structural demands associated with each flight path, providing a foundation for future AWE flight path selection and control strategy optimisations.
Predicting the community acceptance of airborne wind energy with the integrated acceptance model
Insights from two test sites
Journal article
(2026)
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Helena Schmidt, Florian J.Y. Müller, Valentin Leschinger, Gerdien de Vries, Roland Schmehl, Reint Jan Renes, Gundula Hübner
Airborne wind energy (AWE) harnesses higher-altitude winds using kites to generate renewable electricity. As AWE technologies move closer to potential commercialization, understanding how local communities interact with and are affected by these technologies is crucial for socially responsible deployment. Identifying key predictors of community acceptance can help develop targeted measures to address potential impacts while the technology is still adaptable. This study tested the Integrated Acceptance Model (IAM) on survey data from two European AWE test sites. A linear regression analysis revealed that two of the five explanatory variables significantly predicted acceptance: perceived site impacts (e.g., sound emissions, landscape changes, and aviation lights), as well as developer transparency and fairness in site operations. In contrast, attitudes toward the energy transition, perceived economic impacts, and social norms did not predict acceptance. These findings suggest that while AWE developers prioritize technical challenges, attention must also be given to social factors, such as minimizing impacts and ensuring transparent and fair implementation. The results also have important policy implications, highlighting the need for AWE-specific regulations and socially responsible planning practices. Further research is required to investigate additional acceptance predictors, especially if AWE technologies continue to develop toward commercial applications.
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Airborne wind energy (AWE) harnesses higher-altitude winds using kites to generate renewable electricity. As AWE technologies move closer to potential commercialization, understanding how local communities interact with and are affected by these technologies is crucial for socially responsible deployment. Identifying key predictors of community acceptance can help develop targeted measures to address potential impacts while the technology is still adaptable. This study tested the Integrated Acceptance Model (IAM) on survey data from two European AWE test sites. A linear regression analysis revealed that two of the five explanatory variables significantly predicted acceptance: perceived site impacts (e.g., sound emissions, landscape changes, and aviation lights), as well as developer transparency and fairness in site operations. In contrast, attitudes toward the energy transition, perceived economic impacts, and social norms did not predict acceptance. These findings suggest that while AWE developers prioritize technical challenges, attention must also be given to social factors, such as minimizing impacts and ensuring transparent and fair implementation. The results also have important policy implications, highlighting the need for AWE-specific regulations and socially responsible planning practices. Further research is required to investigate additional acceptance predictors, especially if AWE technologies continue to develop toward commercial applications.
Journal article
(2025)
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H.S. Schmidt, R.M. Yupa Villanueva, D. Ragni, R. Merino Martinez, Piet J. R. van Gool, R. Schmehl
This study investigates the relationship between sound quality metrics (SQMs) and noise annoyance caused by airborne wind energy systems (AWESs). In a controlled listening experiment, 75 participants rated their annoyance on the International Commission on Biological Effects of Noise (ICBEN) scale in response to recordings from in-field measurements of two fixed-wing and one soft-wing ground-generation AWES. All recordings were normalized to an equivalent A-weighted sound pressure level of 45 dBA. The results revealed that sharpness was the only SQM predicting participants' annoyance. Fixed-wing kites, characterized by sharper and more tonal and narrowband sound profiles, were rated as more annoying than the soft-wing kite, characterized by higher loudness values. In addition, the effect of some SQMs on annoyance depended on participant characteristics, with loudness having a weaker impact on annoyance for participants familiar with AWESs and tonality having a weaker effect on annoyance for older participants. These findings emphasize the importance of considering psychoacoustic factors in the design and operation of AWESs to reduce noise annoyance.
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This study investigates the relationship between sound quality metrics (SQMs) and noise annoyance caused by airborne wind energy systems (AWESs). In a controlled listening experiment, 75 participants rated their annoyance on the International Commission on Biological Effects of Noise (ICBEN) scale in response to recordings from in-field measurements of two fixed-wing and one soft-wing ground-generation AWES. All recordings were normalized to an equivalent A-weighted sound pressure level of 45 dBA. The results revealed that sharpness was the only SQM predicting participants' annoyance. Fixed-wing kites, characterized by sharper and more tonal and narrowband sound profiles, were rated as more annoying than the soft-wing kite, characterized by higher loudness values. In addition, the effect of some SQMs on annoyance depended on participant characteristics, with loudness having a weaker impact on annoyance for participants familiar with AWESs and tonality having a weaker effect on annoyance for older participants. These findings emphasize the importance of considering psychoacoustic factors in the design and operation of AWESs to reduce noise annoyance.
The European Union has set a goal to become carbon neutral by 2050 through the European Green Deal. Torealize this goal, all sectors of the economy, including shipping, have to become carbon neutral. One way to makeshipping carbon neutral is by directly using wind energy for ship propulsion. Different methods for this are sails,Flettner rotors, and kites. Traditional sails rely on heavy masts and capture low-velocity winds near the oceansurface. Kites operate at higher altitudes where wind speeds are substantially higher and more consistent, usinglightweight materials that induce low vessel bending moments while producing 5 to 25 times more power thanconventional sails [1]. One key advantage of kites is that they can fly cross-wind, achieving much higher apparentwind speed and, thus, thrust. The main disadvantage of kite systems is that they are unstable without active control.To stabilize the system, a controller is needed, and designing such a controller requires an accurate kite model.This work presents a dynamic model of a ground-controlled ram-air kite system for ship propulsion that com-bines a rigid body representation of the kite concerning its dynamic behavior with an aerodynamic model of themain wing and two tether-actuated trailing edges. The key innovation of this work is the accurate modeling of trail-ing edge deformation and twist in a dynamic model capable of real-time. The open-source system model achieves10 times real-time performance on an Intel Core i9-9980HK while maintaining good accuracy in flight simulations.This was achieved using the symbolic modeling framework ModelingToolkit.jl [2] and the Julia programming lan-guage. This modeling framework enables high simulation speed and fast linearization of the model, which willallow the use of modern control design methods, such as model predictive control [3] or machine learning.
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The European Union has set a goal to become carbon neutral by 2050 through the European Green Deal. Torealize this goal, all sectors of the economy, including shipping, have to become carbon neutral. One way to makeshipping carbon neutral is by directly using wind energy for ship propulsion. Different methods for this are sails,Flettner rotors, and kites. Traditional sails rely on heavy masts and capture low-velocity winds near the oceansurface. Kites operate at higher altitudes where wind speeds are substantially higher and more consistent, usinglightweight materials that induce low vessel bending moments while producing 5 to 25 times more power thanconventional sails [1]. One key advantage of kites is that they can fly cross-wind, achieving much higher apparentwind speed and, thus, thrust. The main disadvantage of kite systems is that they are unstable without active control.To stabilize the system, a controller is needed, and designing such a controller requires an accurate kite model.This work presents a dynamic model of a ground-controlled ram-air kite system for ship propulsion that com-bines a rigid body representation of the kite concerning its dynamic behavior with an aerodynamic model of themain wing and two tether-actuated trailing edges. The key innovation of this work is the accurate modeling of trail-ing edge deformation and twist in a dynamic model capable of real-time. The open-source system model achieves10 times real-time performance on an Intel Core i9-9980HK while maintaining good accuracy in flight simulations.This was achieved using the symbolic modeling framework ModelingToolkit.jl [2] and the Julia programming lan-guage. This modeling framework enables high simulation speed and fast linearization of the model, which willallow the use of modern control design methods, such as model predictive control [3] or machine learning.
Airborne wind energy systems (AWESs) leverage the generally less variable and higher wind speeds at increased altitudes by utilizing kites, with significantly reduced material costs compared to conventional wind turbines. Energy is commonly harnessed by flying crosswind trajectories, which allow the kite to achieve speeds significantly higher than the ambient wind speed. However, the airborne nature of these systems demands active control and makes them highly sensitive to changes in wind conditions, making accurate wind measurements essential for steering the kite along its optimal trajectory. This paper presents an advanced sensor fusion technique based on an iterated extended Kalman filter (EKF) for state and wind estimation for AWESs. By integrating position, velocity, tether force, and reeling speed, this method provides accurate estimations of system dynamics, including kite orientation and tether shape. The estimates of the wind speed and direction are compared to lidar measurements, showing good agreement across various atmospheric conditions, with 10 min averaged root mean square error (RMSE) values below 1 m s−1 and 5°, respectively. The results demonstrate that this approach can effectively capture the transient dynamics of atmospheric wind using sensors typically already present in AWESs, making it suitable for supervisory control strategies and ultimately enhancing energy efficiency and system reliability across diverse atmospheric conditions.
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Airborne wind energy systems (AWESs) leverage the generally less variable and higher wind speeds at increased altitudes by utilizing kites, with significantly reduced material costs compared to conventional wind turbines. Energy is commonly harnessed by flying crosswind trajectories, which allow the kite to achieve speeds significantly higher than the ambient wind speed. However, the airborne nature of these systems demands active control and makes them highly sensitive to changes in wind conditions, making accurate wind measurements essential for steering the kite along its optimal trajectory. This paper presents an advanced sensor fusion technique based on an iterated extended Kalman filter (EKF) for state and wind estimation for AWESs. By integrating position, velocity, tether force, and reeling speed, this method provides accurate estimations of system dynamics, including kite orientation and tether shape. The estimates of the wind speed and direction are compared to lidar measurements, showing good agreement across various atmospheric conditions, with 10 min averaged root mean square error (RMSE) values below 1 m s−1 and 5°, respectively. The results demonstrate that this approach can effectively capture the transient dynamics of atmospheric wind using sensors typically already present in AWESs, making it suitable for supervisory control strategies and ultimately enhancing energy efficiency and system reliability across diverse atmospheric conditions.
Airborne wind energy (AWE) is an innovative technology that differs from the operating principles of horizontal axis wind turbines (HAWTs). It uses tethered flying devices, denoted as kites, to harvest higher-altitude wind resources. Kites eliminate the need for a tower but introduce a penalty in power generation since the kite has to spend part of its aerodynamic force to counter its weight. The differences between the two technologies lead to different scaling behaviours, and understanding these as well as the design drivers of AWE systems is essential for developing this technology further. To this end, we developed a multidisciplinary design, analysis, and optimisation (MDAO) framework which employs models evaluating the wind resource, power curve, energy production, overall component and operation costs, and various economic metrics. This framework was used to design fixed-wing ground-generation (GG) AWE systems based on the objective of minimising the levelised cost of energy (LCoE). The variables used to define the system were the wing area, aspect ratio, tether diameter, and rated power of the generator. The framework was employed to find optimal system designs for rated power ranging from 100 to 2000 kW. The results show that kite mass, energy storage, and tether replacements are the key LCoE driving factors. Moreover, in contradistinction to HAWTs, the total lifetime operational costs are equal to or higher than the initial investment costs. This distribution of costs over the project's lifetime, rather than as a large upfront investment, could make it easier to secure project financing. The scaling results show that the LCoE-driven optimum lies within the 100 to 1000 kW system size. The reason for this is that the kite mass penalty increases the cut-in and rated wind speeds, reducing the capacity factor of the larger systems. Sensitivity analyses with respect to extreme scenarios considering technological advancements, financial uncertainties, and environmental conditions show that this optimum is robust within our modelling assumptions.
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Airborne wind energy (AWE) is an innovative technology that differs from the operating principles of horizontal axis wind turbines (HAWTs). It uses tethered flying devices, denoted as kites, to harvest higher-altitude wind resources. Kites eliminate the need for a tower but introduce a penalty in power generation since the kite has to spend part of its aerodynamic force to counter its weight. The differences between the two technologies lead to different scaling behaviours, and understanding these as well as the design drivers of AWE systems is essential for developing this technology further. To this end, we developed a multidisciplinary design, analysis, and optimisation (MDAO) framework which employs models evaluating the wind resource, power curve, energy production, overall component and operation costs, and various economic metrics. This framework was used to design fixed-wing ground-generation (GG) AWE systems based on the objective of minimising the levelised cost of energy (LCoE). The variables used to define the system were the wing area, aspect ratio, tether diameter, and rated power of the generator. The framework was employed to find optimal system designs for rated power ranging from 100 to 2000 kW. The results show that kite mass, energy storage, and tether replacements are the key LCoE driving factors. Moreover, in contradistinction to HAWTs, the total lifetime operational costs are equal to or higher than the initial investment costs. This distribution of costs over the project's lifetime, rather than as a large upfront investment, could make it easier to secure project financing. The scaling results show that the LCoE-driven optimum lies within the 100 to 1000 kW system size. The reason for this is that the kite mass penalty increases the cut-in and rated wind speeds, reducing the capacity factor of the larger systems. Sensitivity analyses with respect to extreme scenarios considering technological advancements, financial uncertainties, and environmental conditions show that this optimum is robust within our modelling assumptions.
Although technologically challenging, airborne wind energy systems have several advantages over conventional wind turbines that make them an interesting option for deployment on Mars. However, the environmental conditions on the red planet are quite different from those on Earth. The atmosphere’s density is about 100 times lower, and gravity is about one-third, which affects the tethered flight operation and harvesting performance of an airborne wind energy system. In this chapter, we investigate in how far the physics of tethered flight differs on the two planets, specifically from the perspective of airborne wind energy harvesting. The derived scaling laws provide a means to systematically adapt a specific system concept to operation on Mars using computation. Sensitivity analyses are conducted for two different sites on Mars, drawing general conclusions about the technical feasibility of using kites for harvesting wind power on the red planet.
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Although technologically challenging, airborne wind energy systems have several advantages over conventional wind turbines that make them an interesting option for deployment on Mars. However, the environmental conditions on the red planet are quite different from those on Earth. The atmosphere’s density is about 100 times lower, and gravity is about one-third, which affects the tethered flight operation and harvesting performance of an airborne wind energy system. In this chapter, we investigate in how far the physics of tethered flight differs on the two planets, specifically from the perspective of airborne wind energy harvesting. The derived scaling laws provide a means to systematically adapt a specific system concept to operation on Mars using computation. Sensitivity analyses are conducted for two different sites on Mars, drawing general conclusions about the technical feasibility of using kites for harvesting wind power on the red planet.
In order for off-Earth top surface structures built from regolith to protect astronauts from radiation, they need to be several metres thick. In a feasibility study, funded by the European Space Agency, Technical University Delft (TUD aka TU Delft) explored the possibility of building in empty lava tubes to create rhizomatic subsurface habitats. With this approach natural protection from radiation is achieved as well as thermal insulation because the temperature is more stable underground. It involves a swarm of autonomous mobile robots that survey the areas and mine for materials such as regolith in order to create cement-based concrete reproducible on Mars through in-situ resource utilisation (ISRU). The concrete is 3D printed by means of additive Design-to-Robotic-Production (D2RP) methods developed at TUD for on-Earth applications with the 3D printing system of industrial partner, Vertico. The printed components are assembled using a Human--Robot Interaction (HRI) supported approach. The 3D printed and HRI-supported assembled structures are structurally optimised porous material systems with increased insulation properties. In order to regulate the indoor pressurised environment a Life Support System (LSS) is integrated, which in this study is only conceptually developed. The habitat and the D2RP production system are powered by an automated kite power system and solar panels developed at TUD. The long-term goal is to develop an autarkic, automated and HRI-supported D2RP system for building autarkic habitats from locally obtained materials.
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In order for off-Earth top surface structures built from regolith to protect astronauts from radiation, they need to be several metres thick. In a feasibility study, funded by the European Space Agency, Technical University Delft (TUD aka TU Delft) explored the possibility of building in empty lava tubes to create rhizomatic subsurface habitats. With this approach natural protection from radiation is achieved as well as thermal insulation because the temperature is more stable underground. It involves a swarm of autonomous mobile robots that survey the areas and mine for materials such as regolith in order to create cement-based concrete reproducible on Mars through in-situ resource utilisation (ISRU). The concrete is 3D printed by means of additive Design-to-Robotic-Production (D2RP) methods developed at TUD for on-Earth applications with the 3D printing system of industrial partner, Vertico. The printed components are assembled using a Human--Robot Interaction (HRI) supported approach. The 3D printed and HRI-supported assembled structures are structurally optimised porous material systems with increased insulation properties. In order to regulate the indoor pressurised environment a Life Support System (LSS) is integrated, which in this study is only conceptually developed. The habitat and the D2RP production system are powered by an automated kite power system and solar panels developed at TUD. The long-term goal is to develop an autarkic, automated and HRI-supported D2RP system for building autarkic habitats from locally obtained materials.
The economic viability of future large-scale airborne wind energy systems critically hinges on the achievable power output in a given wind environment and the system costs. This work presents a fast model for estimating the net power output of fixed-wing ground-generation airborne wind energy systems in the conceptual design phase. In this quasi-steady approach, the kite is represented as a point mass and operated in circular flight manoeuvres while reeling out the tether. This phase is subdivided into several segments. Each segment is assigned a single flight state resulting from an equilibrium of the forces acting on the kite. The model accounts for the effects of flight pattern elevation, gravity, vertical wind shear, hardware limitations, and drivetrain losses. The simulated system is defined by the kite, tether, and drivetrain properties, such as the kite wing area, aspect ratio, aerodynamic properties, tether dimensions and material properties, generator rating, maximum allowable drum speed, etc. For defined system and environmental conditions, the cycle power is maximised by optimising the operational parameters for each phase segment. The operational parameters include cycle properties such as the stroke length (reeling distance over the cycle), the flight pattern average elevation angle, and the pattern cone angle, as well as segment properties such as the turning radius of the circular manoeuvre, the wing lift coefficient, and the reeling speed. To analyse the scaling behaviour, we present a kite mass estimation model based on the wing area, aspect ratio, and maximum tether force. The computed results are compared with 6-degree-of-freedom simulation results of a system with a rated power of 150 kW. The results show the interdependencies between key environmental, system design, and operational parameters. Gravity penalises performance more at low wind speeds than at high wind speeds, and excluding gravity does not yield optimistic performance since it assists in the reel-in phase by reducing the required power. Thin tethers perform better at lower wind speeds but limit power extraction at higher wind speeds and vice versa for thick tethers. Upscaling results in a diminishing gain in performance with an increase in kite wing area. The proposed model is suitable for integration with cost models and is aimed at sensitivity and scaling studies to support design and innovation trade-offs in the conceptual design of systems.
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The economic viability of future large-scale airborne wind energy systems critically hinges on the achievable power output in a given wind environment and the system costs. This work presents a fast model for estimating the net power output of fixed-wing ground-generation airborne wind energy systems in the conceptual design phase. In this quasi-steady approach, the kite is represented as a point mass and operated in circular flight manoeuvres while reeling out the tether. This phase is subdivided into several segments. Each segment is assigned a single flight state resulting from an equilibrium of the forces acting on the kite. The model accounts for the effects of flight pattern elevation, gravity, vertical wind shear, hardware limitations, and drivetrain losses. The simulated system is defined by the kite, tether, and drivetrain properties, such as the kite wing area, aspect ratio, aerodynamic properties, tether dimensions and material properties, generator rating, maximum allowable drum speed, etc. For defined system and environmental conditions, the cycle power is maximised by optimising the operational parameters for each phase segment. The operational parameters include cycle properties such as the stroke length (reeling distance over the cycle), the flight pattern average elevation angle, and the pattern cone angle, as well as segment properties such as the turning radius of the circular manoeuvre, the wing lift coefficient, and the reeling speed. To analyse the scaling behaviour, we present a kite mass estimation model based on the wing area, aspect ratio, and maximum tether force. The computed results are compared with 6-degree-of-freedom simulation results of a system with a rated power of 150 kW. The results show the interdependencies between key environmental, system design, and operational parameters. Gravity penalises performance more at low wind speeds than at high wind speeds, and excluding gravity does not yield optimistic performance since it assists in the reel-in phase by reducing the required power. Thin tethers perform better at lower wind speeds but limit power extraction at higher wind speeds and vice versa for thick tethers. Upscaling results in a diminishing gain in performance with an increase in kite wing area. The proposed model is suitable for integration with cost models and is aimed at sensitivity and scaling studies to support design and innovation trade-offs in the conceptual design of systems.
Three unsteady aerodynamic tools at different levels of fidelity and computational cost were used to investigate the unsteady aerodynamic behavior of a delta kite applied to airborne wind energy. The first tool is an in-house unsteady panel method that is fast but delivers low to mid fidelity predictions. The second tool uses the open-source CFD code SU2 to solve the unsteady Reynolds-averaged Navier–Stokes equations with the (Formula presented.) SST turbulence model. At an intermediate level of fidelity, a semiempirical dynamic stall model that combines the panel method with a phenomenological dynamic stall module is proposed. The latter has free parameters that are fine-tuned with CFD results from the second tool. The research on the dynamic stall model has been inspired by two flight test campaigns suggesting dynamic stall phenomena possibly driven by the periodic variation of the angle of attack (aerodynamic pitching motion) during crosswind maneuvers. The recorded inflow along the flight path was prescribed in the three aerodynamic tools. As expected, the price to pay for the low computational cost of the panel method is its inability to capture the dynamic stall phenomenon. The results from unsteady CFD qualitatively matched the experimental data identifying a leading-edge vortex that forms and detaches cyclically during the pitching motion. Using RANS data, the semiempirical tool was fined-tuned to reproduce the dynamic stall behavior, becoming an accurate and fast aerodynamic tool for coupling with any kite flight simulator. Further discussions on the effects of kite aerostructural deflections are included.
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Three unsteady aerodynamic tools at different levels of fidelity and computational cost were used to investigate the unsteady aerodynamic behavior of a delta kite applied to airborne wind energy. The first tool is an in-house unsteady panel method that is fast but delivers low to mid fidelity predictions. The second tool uses the open-source CFD code SU2 to solve the unsteady Reynolds-averaged Navier–Stokes equations with the (Formula presented.) SST turbulence model. At an intermediate level of fidelity, a semiempirical dynamic stall model that combines the panel method with a phenomenological dynamic stall module is proposed. The latter has free parameters that are fine-tuned with CFD results from the second tool. The research on the dynamic stall model has been inspired by two flight test campaigns suggesting dynamic stall phenomena possibly driven by the periodic variation of the angle of attack (aerodynamic pitching motion) during crosswind maneuvers. The recorded inflow along the flight path was prescribed in the three aerodynamic tools. As expected, the price to pay for the low computational cost of the panel method is its inability to capture the dynamic stall phenomenon. The results from unsteady CFD qualitatively matched the experimental data identifying a leading-edge vortex that forms and detaches cyclically during the pitching motion. Using RANS data, the semiempirical tool was fined-tuned to reproduce the dynamic stall behavior, becoming an accurate and fast aerodynamic tool for coupling with any kite flight simulator. Further discussions on the effects of kite aerostructural deflections are included.
Flexible membrane wings for kite sports, paragliding and airborne wind energy are highly manoeu vrable aerodynamic devices. The manoeuvrability can be quantified by the achievable turning rate of the wing and the dead time between the steering input and the actual flight dynamic response. In this paper, we present an onboard sensor system for measuring the position and orientation of a tethered membrane wing and complement this with an attached low-cost multi-hole probe for measuring the relative flow velocity vector at the wing. To ensure well-defined flow conditions and high quality of the measurement data, the wings selected for testing were towed by a vehicle with a constant speed along a straight track during periods of low ambient wind speeds. A flight control algorithm was adapted from the literature to execute automated, repeatable figure-eight flight manoeuvres and measure the steering gain and the dead time as functions of the steering input. The experimental study confirms the turning behaviour known from kite sports and airborne wind energy applications and provides reproducible quantitative data to develop and validate simulation models for flexible, tethered membrane wings
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Flexible membrane wings for kite sports, paragliding and airborne wind energy are highly manoeu vrable aerodynamic devices. The manoeuvrability can be quantified by the achievable turning rate of the wing and the dead time between the steering input and the actual flight dynamic response. In this paper, we present an onboard sensor system for measuring the position and orientation of a tethered membrane wing and complement this with an attached low-cost multi-hole probe for measuring the relative flow velocity vector at the wing. To ensure well-defined flow conditions and high quality of the measurement data, the wings selected for testing were towed by a vehicle with a constant speed along a straight track during periods of low ambient wind speeds. A flight control algorithm was adapted from the literature to execute automated, repeatable figure-eight flight manoeuvres and measure the steering gain and the dead time as functions of the steering input. The experimental study confirms the turning behaviour known from kite sports and airborne wind energy applications and provides reproducible quantitative data to develop and validate simulation models for flexible, tethered membrane wings
Airborne wind energy is an emerging technology that uses tethered flying devices to capture stronger and more steady winds at higher altitudes. Compared to smaller systems, megawatt-scale systems are substantially affected by gravity during flight operation, resulting in power fluctuations. MegAWES, a 3 MW reference model, experiences power fluctuations between -5.8 MW and +20.5 MW every 12.5 seconds during the traction phase when using its baseline controller at a wind speed of 22 m/s. The baseline controller does not have a power limit, leading to high peak power, and aims to keep the tether force constant, causing it to consume power when the kite is flying upwards. In this paper, we implement an optimal torque controller in the MegAWES framework and show that this eliminates the power consumption during the traction phase. Furthermore, we propose a kite tether force controller that allows setting a power limit when combined with the 2-phase reeling strategy, which decreases the peak power. Our new architecture reduces the power output range by 75% to between +3.7 MW and +9.4 MW in strong wind conditions.
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Airborne wind energy is an emerging technology that uses tethered flying devices to capture stronger and more steady winds at higher altitudes. Compared to smaller systems, megawatt-scale systems are substantially affected by gravity during flight operation, resulting in power fluctuations. MegAWES, a 3 MW reference model, experiences power fluctuations between -5.8 MW and +20.5 MW every 12.5 seconds during the traction phase when using its baseline controller at a wind speed of 22 m/s. The baseline controller does not have a power limit, leading to high peak power, and aims to keep the tether force constant, causing it to consume power when the kite is flying upwards. In this paper, we implement an optimal torque controller in the MegAWES framework and show that this eliminates the power consumption during the traction phase. Furthermore, we propose a kite tether force controller that allows setting a power limit when combined with the 2-phase reeling strategy, which decreases the peak power. Our new architecture reduces the power output range by 75% to between +3.7 MW and +9.4 MW in strong wind conditions.