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Calibri 83ffff̙̙3f3fff3f3f33333f33333.TU Delft Repositoryg 4uuidrepository linktitleauthorcontributorpublication yearabstract
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departmentresearch group programmeprojectcoordinates)uuid:13b3085023c44224ac37895dbf22440dDhttp://resolver.tudelft.nl/uuid:13b3085023c44224ac37895dbf22440d^Pressure Output Feedback Control of Tollmien Schlichting Waves in Falkner Skan Boundary LayersTol, H.J. (TU Delft Control & Simulation); Kotsonis, M. (TU Delft Aerodynamics); de Visser, C.C. (TU Delft Control & Simulation)This paper investigates the use of point wall pressure measurements for output feedback control of Tollmien Schlichtingwaves in Falkner Skan boundary layers.Anewapproach is presented for input outputmodeling of the linear dynamics of the fluid system and the integration withH2"Linear Quadratic Gaussian reducedorder control design. The pressure output at the wall is related with the global perturbation velocity field through the linearized pressure Poisson equation. A Kalman filter is subsequently used to obtain timeresolved estimates of the velocity field using pressure information at discrete points at the wall. The estimated field is in turn used to calculate an optimal state feedback control to suppress the instabilities. The controller is designed in a feedforward, a feedback, and a combined feedforward/feedback actuator/sensor configuration. It is shown that combined feedforward/feedback control gives the best tradeoff between robust performance and robust stability in the presence of uncertainties in the Reynolds number and the pressure gradient. Robust performance in offdesign conditions is enhanced compared to feedforward control, whereas robust stability is enhanced compared to feedback control.enjournal article)uuid:f98cb7b2bec84f75b34abefec1fc93abDhttp://resolver.tudelft.nl/uuid:f98cb7b2bec84f75b34abefec1fc93abwCrossflow Transition of a SweptWing Boundary Layer and its Sensitivity to FreeStream Conditions and Surface RoughnesskRizzo, Paolo (Student TU Delft); Serpieri, J. (TU Delft Aerodynamics); Kotsonis, M. (TU Delft Aerodynamics)The present work is an experimental investigation of stationary crossflow (CF) instabilityinduced transition of the boundary layer over a 45swept wing, under varying freestream turbulence, surface roughness, angle of attack and Reynolds number. Key topological features of the transition front, such as the mean transition location and the jaggedness of the front, are retrieved via IR thermography. Linear Stability Theory (LST) is used to extract the Nfactor of the most amplified stationary crossflow mode at the transition location, identified experimentally. Results show clear causality between freestream turbulence, surface roughness, Reynolds number, angle of attack and transition. Large losses of laminarity and a consistent decrease in the transition Nfactor are observed with rising turbulence and roughness. Remarkably, Nfactor sensitivity to freestream turbulence is found to vary significantly and nonlinearly with angle of attack for the modest levels of turbulence explored in this campaign, whereas the Nfactors scale linearly with the log of the surface roughness level, which is consistent with a receptivity mechanism, which is independent of the angle of attack.conference paper9781624105784)uuid:6c92dbf6aa3b479794ae8be5896b1feaDhttp://resolver.tudelft.nl/uuid:6c92dbf6aa3b479794ae8be5896b1fea6Plasma synthetic jet actuators for active flow controlZong, H. (TU Delft Novel Aerospace Materials; TU Delft Aerodynamics); Chiatto, Matteo (University of Napoli Federico II); Kotsonis, M. (TU Delft Novel Aerospace Materials; TU Delft Aerodynamics); de Luca, Luigi (University of Napoli Federico II)The plasma synthetic jet actuator (PSJA), also named as sparkjet actuator, is a special type of zeronet mass flux actuator, driven thermodynamically by pulsed arc/spark discharge. Compared to widely investigated mechanical synthetic jet actuators driven< by vibrating diaphragms or oscillating pistons, PSJAs exhibit the unique capability of producing highvelocity (>300 m/s) pulsed jets at high frequency (>5 kHz), thus tailored for highReynoldsnumber highspeed flow control in aerospace engineering. This paper reviews the development of PSJA in the last 15 years, covering the major achievements in the actuator working physics (i.e., characterization in quiescent air) as well as flow control applications (i.e., interaction with external crossflow). Based on the extensive nondimensional laws obtained in characterization studies, it becomes feasible to design an actuator under several performance constraints, based on firstprinciples. The peak jet velocity produced by this type of actuator scales approximately with the cubic root of the nondimensional energy deposition, and the scaling factor is determined by the electromechanical efficiency of the actuator (O(0.1% 1%)). To boost the electromechanical efficiency, the energy losses in the gas heating phase and thermodynamic cycle process should be minimized by careful design of the discharge circuitry as well as the actuator geometry. Moreover, the limit working frequency of the actuator is set by the Helmholtz natural resonance frequency of the actuator cavity, which can be tuned by the cavity volume, exit orifice area and exit nozzle length. In contrast to the fruitful characterization studies, the application studies of PSJAs have progressed relatively slower, not only due to the inherent difficulties of performing advanced numerical simulations/measurements in highReynoldsnumber highspeed flow, but also related to the complexity of designing a reliable discharge circuit that can feed multiple actuators at high repetition rate. Notwithstanding these limitations, results from existing investigations are already sufficient to demonstrate the authority of plasma synthetic jets in shock wave boundary layer interaction control, jet noise mitigation and airfoil trailingedge flow separation..Actuators; Flow control; Plasma; Synthetic jetreview)uuid:d4011960ebb94457831862bb159280d0Dhttp://resolver.tudelft.nl/uuid:d4011960ebb94457831862bb159280d0VAirfoil flow separation control with plasma synthetic jets at moderate Reynolds numberFZong, H. (TU Delft Aerodynamics); Kotsonis, M. (TU Delft Aerodynamics)Abstract: An array of 26 plasma synthetic jet actuators (PSJA) is flushmounted on a NACA0015 airfoil model to control the leadingedge flow separation at moderate Reynolds number (Re<sub>c</sub>= 1.7 10 <sup>5</sup>). The stall angle of this airfoil is postponed from 15. 5 <sup>"</sup> to approximately 22 <sup>"</sup>, and the peak lift coefficient is increased by 21%. PSJAs exhibit distinctive separation control mechanisms depending on the relative location between actuation and separation and reduced frequency of actuation (F<sup>"</sup>). At an angle of attack of = 15. 5 <sup>"</sup>, the nonactuated flow separates approximately 4 % chord length downstream of the jet orifices. Plasma synthetic jets (PSJs) applied at F<sup>"</sup>e" 0.5 can displace the separation point downstream to midchord position, as a result of the energizing of the incoming boundary layer through mixing enhancement. As a comparison, with actuation frequency of F<sup>"</sup>d" 0.25 , the separation point at = 15. 5 <sup>"</sup> remains near the leading edge and the zerovelocity line is periodically swept towards the suction surface by the convecting spanwise vortices generated from PSJ actuation, leading to a reduction of timeaveraged backflow area. For the case of separation control at = 22 <sup>"</sup>, the separation point resides always upstream of the actuation position, regardless of actuation frequency. The peak lift coefficient is attained at F<sup>"</sup>= 1 , and the decreasing lift at high actuation frequency (F<sup>"</sup>= 2) is ascribed to the severe interaction between adjacent spanwise vortices at short spacing. Graphical abstract: [Figure not available: see fulltext.].8Electrical Engineering, Mathematics and Computer S< cienceAerodynamics)uuid:58b22f7631c7429f8120a3b585d32b01Dhttp://resolver.tudelft.nl/uuid:58b22f7631c7429f8120a3b585d32b01OTransition in a separation bubble under tonal and broadband acoustic excitationKurelek, J.W. (TU Delft Aerodynamics; University of Waterloo); Kotsonis, M. (TU Delft Aerodynamics); Yarusevych, S. (University of Waterloo)Q Transition and flow development in a separation bubble formed on an airfoil are studied experimentally. The effects of tonal and broadband acoustic excitation are considered since such acoustic emissions commonly result from airfoil selfnoise and can influence flow development via a feedback loop. This interdependence is decoupled, and the problem is studied in a controlled manner through the use of an external acoustic source. The flow field is assessed using timeresolved, twocomponent particle image velocimetry, the results of which show that, for equivalent energy input levels, tonal and broadband excitation can produce equivalent changes in the mean separation bubble topology. These changes in topology result from the influence of excitation on transition and the subsequent development of coherent structures in the bubble. Both tonal and broadband excitation lead to earlier shear layer rollup and thus reduce the bubble size and advance mean reattachment upstream, while the shed vortices tend to persist farther downstream of mean reattachment in the case of tonal excitation. Through a crossexamination of linear stability theory (LST) predictions and measured disturbance characteristics, nonlinear disturbance interactions are shown to play a crucial role in the transition process, leading to significantly different disturbance development for the tonal and broadband excited flows. Specifically, tonal excitation results in transition being dominated by the excited mode, which grows in strong accordance with linear theory and damps the growth of all other disturbances. On the other hand, disturbance amplitudes are more moderate for the natural and broadband excited flows, and so all unstable disturbances initially grow in accordance with LST. For all cases, a rapid redistribution of perturbation energy to a broad range of frequencies follows, with the phenomenon occurring earliest for the broadband excitation case. By taking nonlinear effects into consideration, important ramifications are made clear in regards to comparing LST predictions and experimental or numerical results, thus explaining the trends reported in recent investigations. These findings offer new insights into the influence of tonal and broadband noise emissions, resulting from airfoil selfnoise or otherwise, on transition and flow development within a separation bubble.Baeroacoustics; boundary layer separation; transition to turbulence)uuid:887424924e7c4de393a2d1b08e0b7db8Dhttp://resolver.tudelft.nl/uuid:887424924e7c4de393a2d1b08e0b7db8NSecondary crossflow instability through global analysis of measured base flowsGroot, K.J. (TU Delft Aerodynamics; TU Delft Education AE); Serpieri, J. (TU Delft Aerodynamics); Pinna, Fabio (Von Karman Institute for Fluid Dynamics); Kotsonis, M. (TU Delft Aerodynamics)A combined experimental and numerical approach to the analysis of the secondary stability of realistic sweptwing boundary layers is presented. Global linear stability theory is applied to experimentally measured base flows. These base flows are threedimensional laminar boundary layers subject to spanwise distortion due to the presence of primary stationary crossflow vortices. A full threedimensional description of these flows is accessed through the use of tomographic particle image velocimetry (PIV). The stability analysis solves for the secondary highfrequency modes of type I and type II, ultimately responsible for turbulent breakdown. Several pertinent parameters arising from the application of the proposed methodology are investigated, including the mean flow ensemble size and the measurement domain extent. Extensive use is made of the decomposition of the eigensolutions into the terms of the Reyno< ldsOrr equation, allowing insight into the production and/or destruction of perturbations from various base flow features. Stability results demonstrate satisfactory convergence with respect to the mean flow ensemble size and are independent of the handling of the exterior of the measurement domain. The ReynoldsOrr analysis reveals a close relationship between the type I and type II instability modes with spanwise and wallnormal gradients of the base flow, respectively. The structural role of the inplane velocity components in the perturbation growth, topology and sensitivity is identified. Using the developed framework, further insight is gained into the linear growth mechanisms and later stages of transition via the primary and secondary crossflow instabilities. Furthermore, the proposed methodology enables the extension and enhancement of the experimental measurement data to the pertinent instability eigenmodes. The present work is the first demonstration of the use of a measured base flow for stability analysis applied to the sweptwing boundary layer, directly avoiding the modelling of the primary vortices receptivity processes.0Boundary layer stability; Parametric instability)uuid:a7bc86e437b74976b28addbe4948c3caDhttp://resolver.tudelft.nl/uuid:a7bc86e437b74976b28addbe4948c3caiConditioning of unsteady crossflow instability modes using dielectric barrier discharge plasma actuatorsJSerpieri, J. (TU Delft Aerodynamics); Kotsonis, M. (TU Delft Aerodynamics)CIn this study, experiments are performed towards the identification and measurement of unsteady modes occurring in a transitional swept wing boundary layer. These modes are generated by the interaction between the primary stationary and travelling crossflow instabilities or by secondary instability mechanisms of the stationary crossflow vortices and have a crucial role in the laminartoturbulent breakdown process. Detailed hotwire measurements were performed at the location of stationary instability amplitudesaturation. In order to deterministically capture the spatiotemporal evolution of the unsteady modes, measurements were phase and frequencyconditioned using concurrent forcing by means of a dielectric barrier discharge plasma actuator mounted upstream of the measurement domain. The actuator effect, when positioned sufficiently upstream the secondary modes onset, was tuned such to successfully condition the highfrequency typeI and the lowfrequency typeIII modes without modifying the transition evolution. Two primary stationary crossflow vortices of different amplitude were measured, revealing the effect of baseflow variations on the growth of travelling instabilities. The response of these two stationary waves to the naturally occurring and forced fluctuations was captured at different chordwise positions. Additionally, the deterministic conditioning of the instability phase to the phase of the actuation allowed phaseaveraged reconstruction of the spatiotemporal evolution of the unsteady structures providing valuable insight on their topology. Finally, the effect of locating the actuator at a more downstream position, closer to the typeI mode branchI, resulted in laminarto turbulent breakdown for the highfrequency actuation while the lowfrequency forcing showed milder effects on the transition evolution.TCrossflow instability; Laminartoturbulent transition; Plasma actuator; Swept wing
20200203)uuid:6758b9fed20e4bfda057f7a86df7f9ffDhttp://resolver.tudelft.nl/uuid:6758b9fed20e4bfda057f7a86df7f9ffKOn the origin of spanwise vortex deformations in laminar separation bubbleszMichelis, Theodorus (TU Delft Aerodynamics); Yarusevych, S. (University of Waterloo); Kotsonis, M. (TU Delft Aerodynamics) This work investigates the threedimensional, spatioTemporal flow development in the aft portion of a laminar separation bubble. The bubble is forming on a flat plate geometry, subjected to an adverse pressure gradient, featuring maximum reverse flow of approximately 2 % of the local freestream velocity. Timeresolved velocity measuremen< ts are performed by means of planar and tomographic particle image velocimetry, in the vicinity of the reattachment region. The measurements are complemented with a numerical solution of the boundary layer equations in the upstream field. The combined numerical and measured boundary layer is used as a baseline flow for linear stability theory analysis. The results provide insight into the dynamics of dominant coherent structures that form in the separated shear layer and deform along the span. Stability analysis shows that the flow becomes unstable upstream of separation, where both normal and oblique modes undergo amplification. While the shear layer roll up is linked to the amplification of the fundamental normal mode, the oblique modes at angles lower than approximately are also amplified substantially at the fundamental frequency. A model based on the stability analysis and experimental measurements is employed to demonstrate that the spanwise deformations of rollers are produced due to a superposition of normal and oblique instability modes initiating upstream of separation. The degree of the initial spanwise deformations is shown to depend on the relative amplitude of the dominant normal and oblique waves. This is confirmed by forcing the normal mode through a controlled impulsive perturbation introduced by a spanwise invariant dielectricbarrierdischarge plasma actuator, resulting in the formation of spanwise coherent vortices. The findings elucidate the link between important features in the bubble shedding dynamics and stability characteristics and provide further clarification on the differences in the development of coherent structures seen in recent experiments. Moreover, the results present a handle on the development of effective control strategies that can be used to either promote or suppress shedding in separation bubbles, which is of interest for system performance improvement and control of aeroacoustic emissions in relevant applications.Dboundary layer separation; boundary layer stability; boundary layers)uuid:813e16e49a174ffeb5b958c9837604ecDhttp://resolver.tudelft.nl/uuid:813e16e49a174ffeb5b958c9837604ec`Experimental control of sweptwing transition through baseflow modification by plasma actuatorsdYadala Venkata, Srikar (TU Delft Aerodynamics; Universit de Poitiers); Hehner, M.T. (TU Delft Aerodynamics; University of Stuttgart); Serpieri, J. (TU Delft Aerodynamics); Benard, Nicolas (CNRSUniversit de PoitiersISAEENSMA); Drr, Philipp C. (University of Stuttgart); Kloker, Markus J. (University of Stuttgart); Kotsonis, M. (TU Delft Aerodynamics)Control of laminartoturbulent transition on a sweptwing is achieved by baseflow modification in an experimental framework, up to a chord Reynolds number of 2.5 million. This technique is based on the control strategy used in the numerical simulation by Drr & Kloker (J. Phys. D: Appl. Phys., vol. 48, 2015b, 285205). A spanwise uniform body force is introduced using dielectric barrier discharge plasma actuators, to either force against or along the local crossflow component of the boundary layer. The effect of forcing on the stability of the boundary layer is analysed using a simplified model proposed by Serpieri et al. (J. Fluid Mech., vol. 833, 2017, pp. 164 205). A minimal thickness plasma actuator is fabricated using sprayon techniques and positioned near the leading edge of the sweptwing, while infrared thermography is used to detect and quantify transition location. Results from both the simplified model and experiment indicate that forcing along the local crossflow component promotes transition while forcing against successfully delays transition. This is the first experimental demonstration of sweptwing transition delay via baseflow modification using plasma actuators.Eboundary layer control; boundary layer stability; instability control
20181001)uuid:83615fb6c3d64b689f26cfabbffd1ab7Dhttp://resolver.tudelft.nl/uuid:83615fb6c3d64b689f26cfabbffd1ab78Sweptwing transition control using DBD plasma actuatorsYadala Venkata, Srik< ar (TU Delft Aerodynamics; CNRSUniversit de PoitiersISAEENSMA); Hehner, M.T. (TU Delft Aerodynamics; University of Stuttgart); Serpieri, J. (TU Delft Aerodynamics); Benard, Nicolas (CNRSUniversit de PoitiersISAEENSMA); Kotsonis, M. (TU Delft Aerodynamics)In the present work, laminar flow control, following the discrete roughness elements (DRE) strategy, also called upstream flow deformation (UFD) was applied on a 45<sup>%</sup> sweptwing at a chord Reynold s number of Re<sub>c</sub> = 2.1 10<sup>6</sup> undergoing crossflow instability (CFI) induced transition. Dielectric barrier discharge (DBD) plasma actuation was employed at a high frequency (f<sub>ac</sub> = 10kHz) for this purpose. Specialized, patterned actuators that generate spanwinsemodulated plasma jets were fabricated using sprayon techniques and positioned near the leading edge. An array of DREs was installed upstream of the plasma forcing to lock the origin and evolution of critical stationary CFI vortices in the boundary layer. Two forcing configurations were investigatedin the first configuration the plasma jets were directly aligned against the incoming CF vortices while in the second the CF vortices passed between adjacent plasma jets. Infrared thermography was used to inspect transition location, while quantitative measurements of the boundary layer were obtained using particle image velocimetry. The obtained results show that the plasma forcing reduces the amplitude of stationary CF modes, thus delaying laminartoturbulent transition. In contrast to previous efforts [1], the plasma forcing did not introduce unsteady fluctuations into the boundary layer. The mechanism responsible for the observed transition delay appears to leverage more on localised baseflow modification rather than the DRE/UFD control strategy.AIAA
20190201)uuid:05ea54583ce643e791b44d9f0d4fc947Dhttp://resolver.tudelft.nl/uuid:05ea54583ce643e791b44d9f0d4fc947_Effect of twodimensional surface irregularities on swept wing transition: Forward facing stepsRius Vidales, A.F. (TU Delft Aerodynamics); Kotsonis, M. (TU Delft Aerodynamics); Antunes, Alexandre (Embraer S.A); Cosin, Renato (Embraer S.A)An experimental investigation was carried out to examine the effect of twodimensional Forward Facing Steps surface irregularities, on the laminartoturbulent boundarylayer transition on a 45 sweptwing. For the clean reference case, the numerical boundarylayer flow is calculated from pressure measurements, and a thorough linear stability analysis is performed for all variations of Reynolds number and angle of attack. Infrared thermography is employed to determine the transitionfront location which is associated to an NFactor, calculated from the linear stability analysis. The change in the amplification factor "N, caused by the addition of the surface irregularity, is analyzed. The reduction in the critical Nfactor is observed to correlate with the estimated crossflow instability vortex core height to step height ratio and the relative step height. The work presented in this paper is part of an ongoing research project to characterize the effect that surface irregularities have on boundary layer transition. The Nmethod offers an overview of the phenomena related to FFS, capable of guiding future investigations into the underlying flow mechanisms.WCorrection Notice " In section V. Conclusions, the third sentence of the third paragraph should read: A critical regime in which there was a noticeable change in the transition front pattern, and the transition location rapidly shifted upstream towards the step location, departing in this way from the trend indicated by the clean baseline.
20190901)uuid:6c890da8be9b40c88f0f074a7022385bDhttp://resolver.tudelft.nl/uuid:6c890da8be9b40c88f0f074a7022385b`Conditioning of crossflow instability modes using dielectric barrier discharge plasma actuatorsSerpieri, J. (TU Delft Aerodynamics); Yadala Venkata, Srikar (TU Delft Aerodynamics; CNRSUniversit de PoitiersISAEENSMA); Kotsonis, M. (TU Delft Aerodynamics)*In the< current study, selective forcing of crossflow instability modes evolving on a swept wing at is achieved by means of spanwisemodulated plasma actuators, positioned near the leading edge. In the perspective of laminar flow control, the followed methodology holds on the discrete roughness elements/upstream flow deformation (DRE/UFD) approach, thoroughly investigated by e.g. Saric et al. (AIAA Paper 1998781, 1998), Malik et al. (J. Fluid Mech., vol. 399, 1999, pp. 85115) and Wassermann & Kloker (J. Fluid Mech., vol. 456, 2002, pp. 4984). The possibility of using active devices for UFD provides several advantages over passive means, allowing for a wider range of operating numbers and pressure distributions. In the present work, customised alternating current dielectric barrier discharge plasma actuators have been designed, manufactured and characterised. The authority of the actuators in forcing monochromatic stationary crossflow modes at different spanwise wavelengths is assessed by means of infrared thermography. Moreover, quantitative spatiotemporal measurements of the boundary layer velocity field are performed using timeresolved particle image velocimetry. The results reveal distinct steady and unsteady forcing contributions of the plasma actuator on the boundary layer. It is shown that the actuators introduce unsteady fluctuations in the boundary layer, amplifying at frequencies significantly lower than the actuation frequency. In line with the DRE/UFD strategy, forcing a subcritical stationary mode, with a shorter wavelength compared to the naturally selected mode, results in less amplified primary vortices and related fluctuations, compared to the critical forcing case. The effect of the forcing on the flow stability is further inspected by combining the measured actuators body force with the numerical solution of the laminar boundary layer and linear stability theory. The simplified methodology yields fast and computationally cheap estimates on the effect of steady forcing (magnitude and direction) on the boundary layer stability.
20180801)uuid:b4cd758070f74137830489341e16421aDhttp://resolver.tudelft.nl/uuid:b4cd758070f74137830489341e16421aPExperimental Investigation on Frequency Characteristics of Plasma Synthetic Jetsstyle="margin: 0cm 0cm 10pt;">The performance of a two electrode plasma synthetic jet actuator (PSJA) is investigated for a wide range of dimensionless actuation frequencies (f*) using highspeed phaselocked Particle Imaging Velocimetry (PIV) measurements. The jetinduced velocity fields in the axisymmetric plane are measured during both transient and steady working stages of the PSJA. When f* increases, the jet duration time (Tjet) is reduced while the peak suction velocity (Us) increases consistently. Three integral parameters, including the total expelled gas mass,impulse and issued mechanical energy also decline considerably with increasing frequency, which is shown to relate to both the reduced cavity density and the decreasing jet duration. Theoretical analysis reveals that the mean cavity density decreases monotonically with the square root of discharge frequency.The decreasing rate is inversely proportional to a thermal cutoff frequency (fc, 210Hz for the current study), which scales with the convective heattransfer coefficient between the actuator cavity walls and the cavity gas, aswell as the area of the cavity internal surface. In the timeaveraged velocity fields, the jet centreline velocity ( c U ) exhibits a local maximum in the axial coordinate. The nondimensional maximum centreline velocity reduces with increasing frequency of operation. The jet spreading rate of the plasmasynthetic jets (PSJ) decreases from 0.14 to 0.09 with increasing frequency.During the transient working stage of PSJ, the exit velocity trace elapses 20 successive actuation cycles to stabilize. In contrast to the exitvelocity, approximately 130cycles are needed for the mean cavity density/temperature to reach steady values.Bplasma; synthetic jet; actuator; frequency effect; Characteristics
20181201< )uuid:e45fa2a95a124d5e99c3ab25dbd83e7eDhttp://resolver.tudelft.nl/uuid:e45fa2a95a124d5e99c3ab25dbd83e7eKRealisation of plasma synthetic jet array with a novel sequential discharge
20191004)uuid:0bea8476570d4ee988ac9be020008f03Dhttp://resolver.tudelft.nl/uuid:0bea8476570d4ee988ac9be020008f03dLocalised estimation and control of linear instabilities in twodimensional wallbounded shear flowsTol, H.J. (TU Delft Control & Simulation); Kotsonis, M. (TU Delft Aerodynamics); de Visser, C.C. (TU Delft Control & Simulation); Bamieh, B. (University of California)A new framework is presented for estimation and control of instabilities in wallbounded shear flows described by the linearised NavierStokes equations. The control design considers the use of localised actuators/sensors to account for convective instabilities in an optimal control framework. External sources of disturbances are assumed to enter the control domain through the inflow. A new inflow disturbance model is proposed for external excitation of the perturbation modes that contribute to transition. This model allows efficient estimation of the flow perturbations within the localised control region of a conceptually unbounded domain. The statespace discretisation of the infinitedimensional system is explicitly obtained, which allows application of linear control theoretic tools. A reducedorder model is subsequently derived using exact balanced truncation that captures the input/output behaviour and the dominant perturbation dynamics. This model is used to design an optimal controller to suppress the instability growth. The twodimensional nonperiodic channel flow is considered as an application case. Disturbances are generated upstream of the control domain and the resulting flow perturbations are estimated/controlled using point wall shear measurements and localised unsteady blowing and suction at the wall. The controller is able to cancel the perturbations and is robust to both unmodelled disturbances and sensor inaccuracies. For singlefrequency and multiplefrequency disturbances with low sensor noise a nearly full cancellation is achieved. For stochastic forced disturbances and high sensor noise an energy reduction in perturbation wall shear stress of 96 % is shown.1control theory; flow control; instability control
20180101Control & Simulation)uuid:13cb5cc7be32442eac257f91f7358514Dhttp://resolver.tudelft.nl/uuid:13cb5cc7be32442eac257f91f7358514<Response of a laminar separation bubble to impulsive forcingyMichelis, Theodorus (TU Delft Wind Energy); Yarusevych, S. (University of Waterloo); Kotsonis, M. (TU Delft Aerodynamics)6The spatial and temporal response characteristics of a laminar separation bubble to impulsive forcing are investigated by means of timeresolved particle image velocimetry and linear stability theory. A twodimensional impulsive disturbance is introduced with an alternating current dielectric barrier discharge plasma actuator, exciting pertinent instability modes and ensuring flow development under environmental disturbances. Phaseaveraged velocity measurements are employed to analyse the effect of imposed disturbances at different amplitudes on the laminar separation bubble. The impulsive disturbance develops into a wave packet that causes rapid shrinkage of the bubble in both upstream and downstream directions. This is followed by bubble bursting, during which the bubble elongates significantly, while vortex shedding in the aft part ceases. Duration of recovery of the bubble to its unforced state is independent of the forcing amplitude. Quasisteady linear stability analysis is performed at each individual phase, demonstrating reduction of growth rate and frequency of the most unstable modes with increasing forcing amplitude. Throughout the recovery, amplification rates are directly proportional to the shape factor. This indicates that bursting and flapping mechanisms are driven by altered stability characteristics due to variations in incoming disturbances. The emerging wave packet is characterised in terms o< f frequency, convective speed and growth rate, with remarkable agreement between linear stability theory predictions and measurements. The wave packet assumes a frequency close to the natural shedding frequency, while its convective speed remains invariant for all forcing amplitudes. The stability of the flow changes only when disturbances interact with the shear layer breakdown and reattachment processes, supporting the notion of a closed feedback loop. The results of this study shed light on the response of laminar separation bubbles to impulsive forcing, providing insight into the attendant changes of flow dynamics and the underlying stability mechanisms.
20180115Wind Energy)uuid:d8d729e783bc49d996f52084543e7406Dhttp://resolver.tudelft.nl/uuid:d8d729e783bc49d996f52084543e7406NInteraction between plasma synthetic jet and subsonic turbulent boundary layer
This paper experimentally investigates the interaction between a plasma synthetic jet (PSJ) and a subsonic turbulent boundary layer (TBL) using a hotwire anemometer and phaselocked particle imaging velocimetry. The PSJ is interacting with a fully developed turbulent boundary layer developing on the flat wall of a square wind tunnel section of 1.7 m length. The Reynolds number based on the freestream velocity (U" = 20 m/s) and the boundary layer thickness (99 = 34.5 mm) at the location of interaction is 44 400.Alargevolume (1696mm<sup>3</sup>) threeelectrode plasma synthetic jet actuator (PSJA) with a round exit orifice (D = 2 mm) is adopted to produce highspeed (92 m/s) and shortduration (Tjet = 1 ms) pulsed jets. The exit velocity variation of the adopted PSJA in a crossflow is shown to remain almost identical to that in quiescent conditions. However, the flow structures emanating from the interaction between the PSJ and the TBL are significantly different from what were observed in quiescent conditions. In the midspan xy plane (z = 0 mm), the erupted jet body initially follows a wallnormal trajectory accompanied by the formation of a distinctive front vortex ring. After three convective time scales the jet bends to the crossflow, thus limiting the peak penetration depth to approximately 0.58<sub>99</sub>. Comparison of the normalized jet trajectories indicates that the penetration ability of the PSJ is less than steady jets with the same momentum flow velocity. Prior to the jet diminishing, a recirculation region is observed in the leeward side of the jet body, experiencing first an expansion and then a contraction in the area. In the crossstream yz plane, the signature structure of jets in a crossflow, the counterrotating vortex pair (CVP), transports highmomentum flow from the outer layer to the nearwall region, leading to a fuller velocity profile and a drop in the boundary layer shape factor (1.3 to 1.2). In contrast to steady jets, the CVP produced by the PSJ exhibits a prominent spatiotemporal behaviour. The residence time of the CVP is estimated as the jet duration time, while the maximum extent of the affected flowin the three coordinate directions (x, y, and z) is approximately 32D, 8.5D, and 10D, respectively. An extremely high level of turbulent kinetic energy production is shown in the jet shearlayer, front vortex ring, and CVP, of which the contribution of the streamwise Reynolds normal stress is dominant. Finally, a conceptual model of the interaction between the PSJ and the TBL is proposed.
20180501)uuid:edfac82f712145908c332df392705c6dDhttp://resolver.tudelft.nl/uuid:edfac82f712145908c332df392705c6dNEffect of slotted exit orifice on performance of plasma synthetic jet actuatorbThis study experimentally investigates the influence of exit orifice shape on the performance characteristics of a threeelectrode plasma synthetic jet actuator. Highspeed Schlieren imaging system and phaselocked twocomponent PIV measurements are used for flowfield characterisation in quiescent conditions. Two actuator configurations with the same exit area but different exit orifice shape (round orifice and slot orifice) are studied. Results indicate < a close correspondence between the shapes of the starting vortex ring with the shapes of the respective exit orifices. For the slot orifice, the elongated starting vortex ring gradually expands during propagation, while its ends become warped. A distinct K H instability structure is observed, inducing continuous oscillation of the highspeed jet. Compared with the jet from the round orifice, the slot jet has a higher entrainment rate of surrounding air, thus resulting in a lower propagation velocity of the jet front. The exit velocity of PSJA within one period initially shows a rapid increase, then persists at a relatively high level (100 130m/s), and finally drops with some smallscale oscillations. The oscillation amplitude is less than 10m/s, and the oscillation period is approximately 600s. Under conditions of same exit area, orifice shape has little influence on the variation of the exit velocity.)uuid:27da0fadf61e41b08ade1b24399de3d4Dhttp://resolver.tudelft.nl/uuid:27da0fadf61e41b08ade1b24399de3d4ZSecondary Stability Analysis of Crossflow Vortices using BiGlobal Theory on PIV Base FlowsGroot, K.J. (TU Delft Education AE; TU Delft Aerodynamics); Serpieri, J. (TU Delft Aerodynamics); Kotsonis, M. (TU Delft Aerodynamics); Pinna, Fabio (Von K?arm?an Institute for Fluid Dynamics)9781624104473
20180106Education AE)uuid:df4724af60c74b5a96bd38842fd9a98dDhttp://resolver.tudelft.nl/uuid:df4724af60c74b5a96bd38842fd9a98dSTimeresolved PIV investigation of the secondary instability of crossflow vortices!Timeresolved PIV measurements of the secondary instability modes of crossflow vortices are presented. Measurements are performed on a large scale 45o swept wing at chord Reynolds number of 2.17 million in a low turbulence windtunnel facility. Using acquisition frequencies of 20 kHz, the present study is the first experimental demonstration of spatiotemporally resolved measurements of these structures. Statistical and spectral analysis reveals a fluctuating velocity field, strongly conditioned in space by the primary stationary crossflow vortex. The flow structures related to the typeI highfrequency instability and typeIII are captured by Proper Orthogonal Decomposition of the instantaneous flowfields. Their temporal evolution is analysed showing good agreement with previous studies thus confirming that POD is correctly representing the flow structures of the relevant instability modes. The low frequency meandering oscillation of the stationary vortices, first reported by Serpieri &Kotsonis (2016b), is observed and characterised.TSFP)uuid:94aaf935aaf945279ec1d7cd22d94d98Dhttp://resolver.tudelft.nl/uuid:94aaf935aaf945279ec1d7cd22d94d98ISpanwise flow structures within a laminar separation bubble on an airfoilMichelis, Theodorus (TU Delft Aerodynamics); Kotsonis, M. (TU Delft Aerodynamics); Yarusevych, S. (TU Delft Aerodynamics; University of Waterloo)The present study considers the development of a Laminar Separation Bubble on the suction side of a NACA0018 airfoil under natural and forced conditions. Deterministic forcing is applied by means of a twodimensional plasma actuator installed on the airfoil surface. The spatiotemporal characteristics of the bubble are measured using timeresolved, twocomponent Particle Image Velocimetry in streamwise and spanwise planes. Analysis of the results shows that while the timeaverage bubble is strongly twodimensional, the dominant coherent structures assume three dimensional organisation in the vicinity of laminarturbulent breakdown in both natural and forced conditions.)uuid:8b5f268d2eee416ba296b08838e81c43Dhttp://resolver.tudelft.nl/uuid:8b5f268d2eee416ba296b08838e81c43QEffect of Local DBD Plasma Actuation on Transition in a Laminar Separation BubbledYarusevych, S. (TU Delft Aerodynamics; University of Waterloo); Kotsonis, M. (TU Delft Aerodynamics)This work examines the effect of local active flow control on stability and transition in a laminar separation bubble. Experiments are performed in a wind tunnel facility on a NACA 001< 2 airfoil at a chord Reynolds number of 130 000 and an angle of attack of 2 degrees. Controlled disturbances are introduced upstream of a laminar separation bubble forming on the suction side of the airfoil using a surfacemounted Dielectric Barrier Discharge plasma actuator. Timeresolved twocomponent Particle Image Velocimetry is used to characterise the flow field. The effect of frequency and amplitude of plasma excitation on flow development is examined. The introduction of artificial harmonic disturbances leads to significant changes in separation bubble topology and the characteristics of coherent structures formed in the aft portion of the bubble. The development of the bubble demonstrates strong dependence on the actuation frequency and amplitude, revealing the dominant role of incoming disturbances in the transition scenario. Statistical, topological and linear stability theory analysis demonstrate that significant mean flow deformation produced by controlled disturbances leads to notable changes in stability characteristics compared to those in the unforced baseline case. The findings provide a new outlook on the role of controlled disturbances in separated shear layer transition and instruct the development of effective flow control strategies.Airfoil; Boundary layer separation; DBD plasma actuator; Flow control; Laminar separation bubble; Laminartoturbulent transition; Separated shear layer)uuid:f21f1c508f244ce19630533c2358ddb5Dhttp://resolver.tudelft.nl/uuid:f21f1c508f244ce19630533c2358ddb5MThreedimensional organisation of primary and secondary crossflow instability!
An experimental investigation of primary and secondary crossflow instability developing in the boundary layer of a 45 swept wing at a chord Reynolds number of 2.17 10<sup>6</sup> is presented. Linear stability theory is applied for preliminary estimation of the flow stability while surface flow visualisation using fluorescent oil is employed to inspect the topological features of the transition region. Hotwire anemometry is extensively used for the investigation of the developing boundary layer and identification of the statistical and spectral characteristics of the instability modes. Primary stationary, as well as unsteady typeI (zmode), typeII (ymode) and typeIII modes are detected and quantified. Finally, threecomponent, threedimensional measurements of the transitional boundary layer are performed using tomographic particle image velocimetry. This research presents the first application of an optical experimental technique for this type of flow. Among the optical techniques, tomographic velocimetry represents, to date, the most advanced approach allowing the investigation of spatially correlated flow structures in threedimensional fields. Proper orthogonal decomposition (POD) analysis of the captured flow fields is applied to this goal. The first POD mode features a newly reported structure related to lowfrequency oscillatory motion of the stationary vortices along the spanwise direction. The cause of this phenomenon is only conjectured. Its effect on transition is considered negligible but, given the related high energy level, it needs to be accounted for in experimental investigations. Secondary instability mechanisms are captured as well. The typeIII mode corresponds to lowfrequency primary travelling crossflow waves interacting with the stationary ones. It appears in the inner upwelling region of the stationary crossflow vortices and is characterised by elongated structures approximately aligned with the axis of the stationary waves. The typeI secondary instability consists instead of significantly inclined structures located at the outer upwelling region of the stationary vortices. The much narrower wavelength and higher advection velocity of these structures correlate with the higherfrequency content of this mode. The results of the investigation of both primary and secondary instability from the exploited techniques agree with and complement each other and are in line with existing literature. Finally, they present th< e first experimental observation of the secondary instability structures under natural flow conditions.2Boundary layer stability; boundary layer structure
20180201)uuid:d07c7adc04e94937a0633c3f69c6383dDhttp://resolver.tudelft.nl/uuid:d07c7adc04e94937a0633c3f69c6383d]Electromechanical efficiency of plasma synthetic jet actuator driven by capacitive dischargelA simplified model is established to estimate the jet exit density variation of a plasma synthetic jet actuator (PSJA) driven by a capacitive arc discharge. This model, in conjunction with phaselocked planar particle imaging velocimetry (PIV) measurements, enables the calculation of jet mechanical energy for different operating conditions. Discharge energy is directly calculated based on waveforms of applied voltage and discharge current. The ratio of jet mechanical energy to discharge energy provides the absolute electromechanical efficiency. Results indicate that PSJA is characterized by a rather low electromechanical efficiency in the order of 0.1%, while the maximum observed value under tested conditions is 0.22%. Electromechanical efficiency improves significantly with nondimensional energy deposition, and appears largely independent of jet exit diameter.+plasma; synthetic jet; actuator; efficiency
20171201)uuid:6e70f66dea2c48d984dee2b75df18c04Dhttp://resolver.tudelft.nl/uuid:6e70f66dea2c48d984dee2b75df18c04DCharacterisation of plasma synthetic jet actuators in quiescent flowAn experimental characterisation study of a largevolume threeelectrode plasma synthetic jet actuator (PSJA) is presented. A sequential discharge power supply system is used to activate the PSJA. Phaselocked planar particle image velocimetry (PIV) and timeresolved Schlieren imaging are used to characterise the evolution of the induced flow field in quiescent flow conditions. The effect of orifice diameter is investigated. Results indicate three distinct features of the actuatorinduced flow field. These are the initial shock waves, the high speed jet and vortex rings. Two types of shock waves with varied intensities, namely a strong shock wave and a weak shock wave, are issued from the orifice shortly after the ignition of the discharge. Subsequently, the emission of a high speed jet is observed, reaching velocities up to 130 m s"1. Pronounced oscillation of the exit velocity is caused by the periodical behaviour of capacitive discharge, which also led to the formation of vortex ring trains. Orifice diameter has no influence on the jet acceleration stage and the peak exit velocity. However, a large orifice diameter results in a rapid decline of the exit velocity and thus a short jet duration time. Vortex ring propagation velocities are measured at peak values ranging from 55 m s"1 70 m s"1. In the case of 3 mm orifice diameter, trajectory of the vortex ring severely deviates from the actuator axis of symmetry. The development of this asymmetry in the flow field is attributed to asymmetry in the electrode configuration.Kplasma; synthetic jet; actuator; flow control; flow field; characterisetion)uuid:29608e3338b5433cac8684dc843108cfDhttp://resolver.tudelft.nl/uuid:29608e3338b5433cac8684dc843108cf<Model Reduction of Parabolic PDEs using Multivariate SplinesTol, H.J. (TU Delft Control & Simulation); de Visser, C.C. (TU Delft Control & Simulation); Kotsonis, M. (TU Delft Aerodynamics)A new methodology is presented for model reduction of linear parabolic partial differential equations (PDEs) on general geometries using multivariate splines on triangulations. Statespace descriptions are derived that can be used for control design. This method uses Galerkin projection with Bsplines to derive a finite set of ordinary differential equations (ODEs). Any desired smoothness conditions between elements as well as the boundary conditions are flexibly imposed as a system of side constraints on the set of ODEs. Projection of the set of ODEs on the null space of the system of side constraints naturally produces a reducedorder model that satisfies these constraints. This meth< od can be applied for both indomain control and boundary control of parabolic PDEs with spatially varying coefficients on general geometries. The reduction method is applied to design and implement feedback controllers for stabilisation of a 1D unstable heat equation and a more challenging 2D reaction convection diffusion equation on an irregular domain. It is shown that effective feedback stabilisation can be achieved using loworder control models.pDistributed parameter systems; multivariate splines; Galerkin s method; parabolic partial differential equations
20171101)uuid:50d5fb3ef5584076b50e7460eeac0b9aDhttp://resolver.tudelft.nl/uuid:50d5fb3ef5584076b50e7460eeac0b9aEControl of fluid flows using multivariate spline reduced order models,This paper presents a study on control of fluid flows using multivariate spline reduced order models. A new approach is presented for model reduction of the incompressible NavierStokes equations using multivariate splines defined on triangulations. State space descriptions are derived that can be used for control design. This paper considers the linearised NavierStokes equations in velocitypressure formulation. The pressure is elimi nated from the equations by using a space of velocity fields which are divergence free. The divergence free condition along with the smoothness across the domain and the bound ary conditions are imposed as a linear system of side constraints. The projection of the system on the null space of these constraints significantly reduces the dimension of the model while satisfying these constraints. The reduction method is applied to design and implement feedback controllers for stabilization of disturbances in a Poiseuille flow. It is shown that effective feedback stabilization can be achieved using low order control models.9781624103933harvest AIAA 20161821)uuid:e3108e2d070846e9bdc117a5e44cf224Dhttp://resolver.tudelft.nl/uuid:e3108e2d070846e9bdc117a5e44cf224DCleanEra: A Collection of Research Projects for Sustainable AviationDroste, B.; Van Gent, R.; Straathof, M.; Steenhuizen, D.; Kotsonis, M.; Geuskens, F.; Shroff, S.; Guerriero, G.; Gangoli Rao, A.; Lada, C.; Dewanji, D.; Yu, H.; Schroijen, M.; Hoekstra, J.; The CleanEra Team The CleanEra project was initiated with the goal of developing revolutionary ideas for civil aviation. These ideas were to offer solutions which would limit and reduce some of the negative aspects of aviation, namely: emissions and the use of resources. This book presents you with the highlights of this journey in search of new technologies for a revolutionary aircraft; an aircraft that not only offers a future of comfortable air travel for the passenger, but a future of sustainable aviation for the planet as well.&The CleanEra Project; OAFund TU Delftbook IOS PressAerospace Engineering Aerospace Structures & Materials)uuid:af74e6352843419ebb35dc2cfa5d971eDhttp://resolver.tudelft.nl/uuid:af74e6352843419ebb35dc2cfa5d971eEnergy deposition characteristics of nanosecond dielectric barrier discharge plasma actuators: Influence of dielectric material&Correale, G.; Winkel, R.; Kotsonis, M.;An experimental study aimed at the characterization of energy deposition of nanosecond Dielectric Barrier Discharge (nsDBD) plasma actuators was carried out. Special attention was given on the effect of the thickness and material used for dielectric barrier. The selected materials for this study were polyimide film (Kapton), polyamide based nylon (PA2200), and silicone rubber. Schlieren measurements were carried out in quiescent air conditions in order to observe density gradients induced by energy deposited. Size of heated area was used to qualify the energy deposition coupled with electrical power measurements performed using the backcurrent shunt technique. Additionally, light intensity measurements showed a different nature of discharge based upon the material used for barrier, for a fixed thickness and frequency of discharge. Finally, a characterisation study was performed for the three tested materials. Diele<ctric constant, volume resistivity, and thermal conductivity were measured. Strong trends between the control parameters and the energy deposited into the fluid during the discharge were observed. Results indicate that efficiency of energy deposition mechanism relative to the thickness of the barrier strongly depends upon the material used for the dielectric barrier itself. In general, a high dielectric strength and a low volumetric resistivity are preferred for a barrier, together with a high heat capacitance and a low thermal conductivity coefficient in order to maximize the efficiency of the thermal energy deposition induced by an nsDBD plasma actuator.mdielectric barrier discharge; dielectric materials; dielectric thin films; electrodes; electrical resistivity&Aerodynamics, Wind Energy & Propulsion)uuid:383c1163245d47a7bd0c1f2229fb1849Dhttp://resolver.tudelft.nl/uuid:383c1163245d47a7bd0c1f2229fb1849:Flow visualization of swept wing boundary layer transitionSerpieri, J.; Kotsonis, M.In this work the flow visualization of the transition pattern occurring on a swept wing in a subsonic flow is presented. This is done by means of fluorescent oil flow technique and boundary layer hotwire scans. The experiment was performed at Reynolds number of 2:15 . 106 and at angle of attack of 3. At these conditions, three different flows are investigated: a natural transition case and two other ones where instead the transition mechanism, the stationary crossflow waves, was forced with discrete roughness elements. Previously published results on similar flows were confirmed for two of the three tested configurations (natural transition and boundary layer forcing at the wavelength of the dominant stationary mode) while, for the third one (where a subcritical wavelength was forced), some discrepancies are observed. A parametric study on the effect of the Reynolds number and the angle of attack is also presented.d3D subsonic boundary layer transition; crossflow stationary waves; oil flow visualization; hotwire Universita di Napoli Federico II.Aerospace Structures & Computational Mechanics)uuid:f0e38597a7424e20808d93cc6726669bDhttp://resolver.tudelft.nl/uuid:f0e38597a7424e20808d93cc6726669bVDesign and numerical investigation of swirl recovery vanes for the Fokker 29 propeller?Wang, Y.; Li, Q.; Eitelberg, G.; Veldhuis, L.L.M.; Kotsonis, M.Swirl recovery vanes (SRVs) are a set of stationary vanes located downstream from a propeller, which may recover some of the residual swirl from the propeller, hoping for an improvement in both thrust and efficiency. The SRV concept design for a scaled version representing the Fokker 29 propeller is performed in this paper, which may give rise to a promotion in propulsive performance of this traditional propeller. Firstly the numerical strategy is validated from two aspects of global quantities and the local flow field of the propeller compared with experimental data, and then the exit flow together with the development of propeller wake is analyzed in detail. Three kinds of SRV are designed with multiple circular airfoils. The numerical results show that the swirl behind the propeller is recovered significantly with Model V3, which is characterized by the highest solidity along spanwise, for various working conditions, and the combination of rotor and vane produced 5.76% extra thrust at the design point. However, a lower efficiency is observed asking for a better vane design and the choice of a working point. The vane position is studied which shows that there is an optimum range for higher thrust and efficiency.cmultiple circular airfoil; propellers; propulsion efficiency; swirl recovery vane; turboprop engineElsevier)uuid:e10f65c80d3e4d2c953bcf460beca025Dhttp://resolver.tudelft.nl/uuid:e10f65c80d3e4d2c953bcf460beca025[Dielectric Barrier Discharge Actuators for Flow Control: Diagnostics, Modeling, ApplicationKotsonis, M.3Scarano, F. (promotor); Veldhuis, L.L.M. (promotor)doctoral thesis)uuid:3216e2be5e6649939477e4457bb6cedc< Dhttp://resolver.tudelft.nl/uuid:3216e2be5e6649939477e4457bb6cedcbForcing mechanisms of dielectric barrier discharge plasma actuators at carrier frequency of 625 HzKotsonis, M.; Ghaemi, S.The forcing behavior of a dielectric barrier discharge (DBD) actuator is investigated experimentally using a timeresolved particle image velocimetry (PIV) system in conjunction with a phase shifting technique. The spatiotemporal evolution of the induced flowfield is accurately captured within one high voltage (HV) cycle allowing the calculation of the instantaneous velocity and acceleration. Additional voltage and current measurements provide the power consumption for each case. Four different applied voltage waveform shapes are independently tested, namely, sine, square, positive sawtooth, and negative sawtooth at fixed applied voltage (10 kVpp) and carrier frequency (625 Hz). The instantaneous flowfields reveal the effect of the plasma forcing during the HV cycle. Sine waveform provides large positive forcing during the forward stroke, with minimal but still positive forcing during the backward stroke. Square waveform provides strong and concentrated positive and negative forcing at the beginning of the forward and backward stroke, respectively. Positive sawtooth provides positive but weak forcing during both strokes while the negative sawtooth case produces observable forcing only during the forward stroke. Results indicate the inherent importance of negative ions on the force production mechanisms of DBD s. Furthermore, the revealed influence of the waveform shape on the force production can provide guidelines for the design of custom asymmetric waveforms for the improvement of the actuator s performance.actuators; discharges (electric); plasma devices; plasma diagnostics; plasma dielectric properties; plasma transport processes; power consumption; spatiotemporal phenomenaAmerican Institute of PhysicsAerodynamics & Wind Energy)uuid:b3422eaa651a4076afbd9607d22ad9adDhttp://resolver.tudelft.nl/uuid:b3422eaa651a4076afbd9607d22ad9adONumerical Study on Control of TollmienSchlichting Waves Using Plasma Actuators+Kotsonis, M.; Giepman, R.; Veldhuis, L.L.M.A numerical investigation on the use of plasma actuators for transition control is presented. The numerical framework involves the solution of the full unsteady 2D incompressible Navier Stokes equations using a finite volume formulation. The set of equations is formulated by solving for the perturbations in the flow while a mean laminar boundary layer flow is considered fixed and superimposed. The effect of the plasma actuator is represented as an imposed unsteady body force distribution derived from experimental measurements. Furthermore, an adaptive control system based on the filteredx LMS algorithm is implemented directly into the flow solver. The control system uses pressure signals at the wall in order to compute the frequency, phase and amplitude of the plasma body force which minimizes the intensity of the propagating TS waves. Results show large reductions in wave amplitude for both single and multi frequency cases.9American Institute of Aeronautics and Astronautics (AIAA))uuid:225874e4dda647ceb5f45983aacb5419Dhttp://resolver.tudelft.nl/uuid:225874e4dda647ceb5f45983aacb54193A twoparameter method for eN transition predictionVan Ingen, J.L.; Kotsonis, M.bA correction to the eN method for transition prediction, that at present is in use at Delft University, is developed and tested. The existing method is based on solutions of the FalknerSkan similar boundary layer equation without suction or blowing. The correction is based on additional solutions of this equation with suction and blowing. For the development of the method an OrrSommerfeld solver is used for the calculation of the stability diagrams for several series of FalknerSkan ows with suction or blowing for fixed shape factor (H). This results in differences in the velocity profile curvature near the wall. A correction based on only one additional parameter has been devised using these results. A co< mparison between the corrected eN method and direct stability calculations for several nonsimilar ows with and without suction shows good agreement.)uuid:32b4ed4af4e8485299fbfd405aa7da6aDhttp://resolver.tudelft.nl/uuid:32b4ed4af4e8485299fbfd405aa7da6aMOn the mechanical efficiency of dielectric barrier discharge plasma actuatorsGiepman, R.H.M.; Kotsonis, M.The mechanical power production and electrical power consumption of the dielectric barrier discharge plasma actuator is investigated for different operating conditions. The ratio of these two values delivers the mechanical efficiency of the actuator as a flow acceleration device. The general trend is that higher carrier frequencies and voltages lead to higher values of the efficiency. The values that were found for the mechanical efficiency are very small, the highest recorded value is only 0.18%.Fdischarges (electric); plasma applications; plasma transport processes)uuid:d68a55f007584c788fd5797b316a51e1Dhttp://resolver.tudelft.nl/uuid:d68a55f007584c788fd5797b316a51e17Measurement of the body force field of plasma actuators5Kotsonis, M.; Ghaemi, S.; Veldhuis, L.; Scanorano, F.A novel technique is proposed and investigated for the estimation of the body force field resulting from the operation of a dielectric barrier discharge plasma actuator. The technique relies on the measurement of the spatiotemporal evolution of the induced velocity field using highspeed particle image velocimetry (PIV). The technique has the advantage of providing spatial distribution of the body force vector field. A full Navier Stokes term decomposition is applied on the evolving field along with additional closure norms in order to decouple the pressure gradient and body force terms. Results are compared with loadcell measurements of the direct reaction force and also momentum balance calculations based on the PIV field. Agreement between the different methods is observed. The data can easily be incorporated in computational flow solvers and also be used for validation and calibration of numerical plasma models.IOP Publishing(Aerodynamics, Wind Energy and Propulsion)uuid:9769545ed0de4660b341e3d9b6ef63f7Dhttp://resolver.tudelft.nl/uuid:9769545ed0de4660b341e3d9b6ef63f7TExperimental study on dielectric barrier discharge actuators operating in pulse modeKotsonis, M.; Veldhuis, L.An experimental investigation is performed on the operation of dielectric barrier discharge plasma actuators used as manipulators of secondary and unsteady flow structures such as boundary layer instabilities or shedding vortices. The actuators are tested mainly in pulse mode. High sample rate hotwire measurements of the induced velocity field downstream of the actuator are taken for the cases of pulse actuation in still air as well as in a laminar boundary layer. Complementary voltage and current measurements are taken to calculate power consumption. Additionally, a study on the influence of the pulse frequency and duty cycle of actuation is performed. Results show the effectiveness of plasma actuators in inducing fluctuating components of velocity when operated in pulse mode. Spectral analysis reveals the connection between the actuator driving signal and the induced flowfield. The magnitude as well as the consistency of the resulting fluctuating field are dependent on both the duty cycle and the pulse frequency. An empirical operational envelope based on phenomenological observations is proposed, for the use of the actuators at specific flow and operational conditions given in the paper.boundary layers; discharges (electric); flow control; flow instability; flow measurement; fluctuations; laminar flow; plasma devices; vortices)uuid:8bf4cb4f60c94164b396d867f5938d9bDhttp://resolver.tudelft.nl/uuid:8bf4cb4f60c94164b396d867f5938d9bTExperimental Study on the Body Force Field of Dielectric Barrier Discharge Actuators;Kotsonis, M.; Ghaemi, S.; Giepman, R.H.M.; Veldhuis, L.L.M.9An experimental investigation on thrust and body force of Dielectric Barrier Discharge (DBD) /plasma actuators aim<ed at low power flow control applications is presented. A parametric study on thrust is conducted for a wide range of geometrical configurations as well as several electrical operational conditions. Direct measurements of the induced thrust are taken using a highly sensitive load cell. Simultaneous readings of current and voltage are also performed, providing the power consumption. Furthermore a novel technique for determination of the spatial distribution of the bodyforce is proposed, developed and tested. The technique involves the use of a highspeed PIV system to resolve all terms of the NavierStokes equation representation of the flow field including body force. Results reveal the existence of an explicit relation between voltage, thrust and consumed power. Furthermore the influence of the geometrical configuration of the actuator on the thrust is shown. The body force obtained with the proposed technique agrees well with the thrust measurements.)uuid:cdaadcdcf5d94459bd5dad6a58d05af8Dhttp://resolver.tudelft.nl/uuid:cdaadcdcf5d94459bd5dad6a58d05af8Plasmas for Transition Delay$Kotsonis, M.; Boon, P.; Veldhuis, L.This paper describes the experimental investigation of the properties of Dielectric Barrier Discharge (DBD) actuators aimed at transition delay techniques. A wide range of geometrical configurations are tested as well as several electrical operational conditions. For the majority of the measurements statistical data for the induced flow field are obtained and for a limited selection of actuators, high samplerate time resolved measurements are also conducted. All measurements are made in still flow in order to eliminate freestream effects on the induced velocities. Results show the formation of a thin nearwall jet which could be used as a flow control device.Pplasma actuators; experimental study; active wave cancellation; transition delay
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