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Calibri 83ffff̙̙3f3fff3f3f33333f33333.TU Delft Repositoryg Xuuidrepository linktitleauthorcontributorpublication yearabstract
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departmentresearch group programmeprojectcoordinates)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 ReynoldsOrr 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 instabilityenjournal articleAerodynamics)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: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, Srikar (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 th< e 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.conference paperAIAA
20190201)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: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 wind< tunnel 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: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 the first experimental observation of the secondary instability structures under natural flow conditions.2Boundary layer stability; boundary layer structure
20180201)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 wa<s 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 IIAerospace Engineering.Aerospace Structures & Computational Mechanics
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