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Mo Samimy - One of the best experts on this subject based on the ideXlab platform.
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Separation Control with nanosecond pulse driven dielectric barrier discharge plasma actuators
AIAA Journal, 2012Co-Authors: Jesse Little, Munetake Nishihara, Keisuke Takashima, Igor V Adamovich, Mo SamimyAbstract:Abstract : The efficacy of dielectric barrier discharge (DBD) plasmas driven by high voltage (approximately 15 kV) repetitive nanosecond pulses approximately 100 ns FWHM) for flow Separation Control is investigated experimentally on an airfoil leading edge up to Re=1x106 (62 m/s). Unlike AC-DBDs, the nanosecond pulse driven DBD plasma actuator transfers very little momentum to the neutral air, but generates compression waves similar to localized arc filament plasma actuators. A complex pattern of quasi-planar and spherical compression waves is observed in still air. Measurements suggest that some of these compression waves are generated by discharge filaments that remain fairly reproducible pulse-to-pulse. The device performs as an active trip at high Re pre-stall angles of attack and provides perturbations that generate coherent spanwise vortices at post-stall. These coherent structures entrain freestream momentum thereby reattaching the normally separated flow to the suction surface of the airfoil. Coherent structures are identified at all tested frequencies, but values of F(subponent c, exponent +)=4-6 are most effective for Control. Such devices which are believed to function through thermal effects could be an alternative to AC-DBD plasmas that rely on momentum addition.
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flow Separation Control using nanosecond pulse driven dbd plasma actuators
International Journal of Flow Control, 2011Co-Authors: Chris Rethmel, Jesse Little, Keisuke Takashima, Aniruddha Sinha, Igor V Adamovich, Mo SamimyAbstract:This work continues an ongoing effort aimed at development and use of dielectric barrier discharge (DBD) plasma actuators driven by repetitive nanosecond pulses for high Reynolds number aerodynamic flow Control. These actuators are believed to influence the flow via a thermal mechanism which is fundamentally different from more commonly studied AC-DBD actuators. Leading edge Separation Control on an 8-inch chord NACA 0015 airfoil is demonstrated at various post-stall angles of attack for Mach numbers up to 0.26 (free stream velocity up to 93 m/s) and Reynolds numbers up to 1.15 X 106. The nanosecond (NS) pulse driven DBD is shown to extend the stall angle at low Reynolds numbers by functioning as an active trip. At post-stall angles of attack, the device is shown to excite shear layer instabilities and generate coherent spanwise vortices that transfer momentum from the freestream to the separated region, thus reattaching the flow. This is observed for all high Reynolds numbers and Mach numbers spanning th...
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flow Separation Control over an airfoil with nanosecond pulse driven dbd plasma actuators
49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 2011Co-Authors: Chris Rethmel, Jesse Little, Keisuke Takashima, Aniruddha Sinha, Igor V Adamovich, Mo SamimyAbstract:This work continues an ongoing development and use of dielectric barrier discharge (DBD) plasma actuators driven by repetitive nanosecond pulses for high Reynolds number aerodynamic flow Control. These actuators are believed to influence the flow via a thermal mechanism which is fundamentally different from the more commonly studied AC-DBD plasmas. Leading edge Separation Control on an 8-inch chord NACA 0015 airfoil is demonstrated at various post-stall angles of attack (α) for Reynolds numbers (Re) and Mach numbers (M) up to 1.15x10 6 and 0.26 respectively (free stream velocity, U∞ = 93 m/s). The nanosecond pulse driven DBD can extend the stall angle at low Re by functioning as an active trip. At poststall α, the device generates coherent spanwise vortices that transfer momentum from the freestream to the separated region, thus reattaching the flow. This is observed for all Re and M spanning the speed range of the subsonic tunnel used in this work. The actuator is also integrated into a feedback Control system with a stagnation-line-sensing hot film on the airfoil pressure side. A simple on/off type Controller that operates based on a threshold of the mean value of the power dissipated by the hot film is developed for this system. A preliminary extremum seeking Controller is also investigated for dynamically varying Re. Several challenges typically associated with integration of DBD plasma actuators into a feedback Control system have been overcome. The most important of these is the demonstration of Control authority at realistic takeoff and landing Re and M.
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High Lift Airfoil Leading Edge Separation Control with Nanosecond Pulse Driven DBD Plasma Actuators
5th Flow Control Conference, 2010Co-Authors: Jesse Little, Munetake Nishihara, Keisuke Takashima, Igor V Adamovich, Mo SamimyAbstract:The efficacy of dielectric barrier discharge (DBD) plasmas driven by repetitive nanosecond (NS) pulses for flow Separation Control is investigated experimentally on an airfoil leading edge up to Re=1x10 (62 m/s). The NS pulse driven DBD plasma actuator (NSDBD hereafter) transfers very little momentum to the neutral air, but generates compression waves similar to localized arc filament plasma actuators. Experimental results indicate that NS-DBD plasma performs as an active trip at pre-stall angles of attack and provides high amplitude perturbations that manipulate flow instabilities and generate coherent spanwise vortices at post-stall angles. These coherent structures entrain freestream momentum thereby reattaching the normally separated flow to the suction surface of the airfoil. Such devices which are believed to function through thermal effects could result in a significant improvement over AC-DBD plasmas that rely on momentum addition which limits their performance at high speeds.
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High-lift airfoil trailing edge Separation Control using a single dielectric barrier discharge plasma actuator
Experiments in Fluids, 2010Co-Authors: Jesse Little, Munetake Nishihara, Igor Adamovich, Mo SamimyAbstract:Control of flow Separation from the deflected flap of a high-lift airfoil up to Reynolds numbers of 240,000 (15 m/s) is explored using a single dielectric barrier discharge (DBD) plasma actuator near the flap shoulder. Results show that the plasma discharge can increase or reduce the size of the time-averaged separated region over the flap depending on the frequency of actuation. High-frequency actuation, referred to here as quasi-steady forcing, slightly delays Separation while lengthening and flattening the separated region without drastically increasing the measured lift. The actuator is found to be most effective for increasing lift when operated in an unsteady fashion at the natural oscillation frequency of the trailing edge flow field. Results indicate that the primary Control mechanism in this configuration is an enhancement of the natural vortex shedding that promotes further momentum transfer between the freestream and separated region. Based on these results, different modulation waveforms for creating unsteady DBD plasma-induced flows are investigated in an effort to improve Control authority. Subsequent measurements show that modulation using duty cycles of 50–70% generates stronger velocity perturbations than sinusoidal modulation in quiescent conditions at the expense of an increased power requirement. Investigation of these modulation waveforms for trailing edge Separation Control similarly shows that additional increases in lift can be obtained. The dependence of these results on the actuator carrier and modulation frequencies is discussed in detail.
Jesse Little - One of the best experts on this subject based on the ideXlab platform.
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Effects of Structural Motion on Separation and Separation Control: An Integrated Investigation using Numerical Simulations, Theory, Wind-Tunnel and Free-Flight Experiments
TU Braunschweig – Niedersächsisches Forschungszentrum für Luftfahrt, 2017Co-Authors: Fasel, Hermann F., Jesse Little, Hosseinverdi Shirzad, Gross AndreasAbstract:A combined investigative approach which employs high-fidelity numerical simulations, wind & water-tunnel and free-flight experiments is taken to investigate the fundamental flow physics of Separation and Separation Control for wing sections undergoing temporal motions. Detailed investigations of the underlying unsteady flow physics have been carried out for the X-56A airfoil at nominal angles of attack of 10 and 12 degrees for Re = 200k. The reduced frequency of the structural motion is k=0.7 and the plunging amplitude is 3.2% and 4.8% of the chord length. For 10deg AoA, the agreement between the measurements, simulations, and Theodorsen's theory is good even though the instantaneous angles of attack during the airfoil oscillations are outside the linear CL - AoA regime and extend into the region associated with static stall. As the angle of attack is increased to 12deg, the flow over the suction surface of the wing begins to intermittently separate and Theodorsen's theory fails. Experiments and simulations show strong qualitative agreement and both capture "bursting" of the laminar Separation bubble near the leading edge of the airfoil. Furthermore, highly resolved Direct Numerical Simulations (DNS) were performed in order to investigate the hydrodynamic instability mechanisms and transition to turbulence in swept laminar Separation bubbles.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu
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Separation Control with nanosecond pulse driven dielectric barrier discharge plasma actuators
AIAA Journal, 2012Co-Authors: Jesse Little, Munetake Nishihara, Keisuke Takashima, Igor V Adamovich, Mo SamimyAbstract:Abstract : The efficacy of dielectric barrier discharge (DBD) plasmas driven by high voltage (approximately 15 kV) repetitive nanosecond pulses approximately 100 ns FWHM) for flow Separation Control is investigated experimentally on an airfoil leading edge up to Re=1x106 (62 m/s). Unlike AC-DBDs, the nanosecond pulse driven DBD plasma actuator transfers very little momentum to the neutral air, but generates compression waves similar to localized arc filament plasma actuators. A complex pattern of quasi-planar and spherical compression waves is observed in still air. Measurements suggest that some of these compression waves are generated by discharge filaments that remain fairly reproducible pulse-to-pulse. The device performs as an active trip at high Re pre-stall angles of attack and provides perturbations that generate coherent spanwise vortices at post-stall. These coherent structures entrain freestream momentum thereby reattaching the normally separated flow to the suction surface of the airfoil. Coherent structures are identified at all tested frequencies, but values of F(subponent c, exponent +)=4-6 are most effective for Control. Such devices which are believed to function through thermal effects could be an alternative to AC-DBD plasmas that rely on momentum addition.
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flow Separation Control using nanosecond pulse driven dbd plasma actuators
International Journal of Flow Control, 2011Co-Authors: Chris Rethmel, Jesse Little, Keisuke Takashima, Aniruddha Sinha, Igor V Adamovich, Mo SamimyAbstract:This work continues an ongoing effort aimed at development and use of dielectric barrier discharge (DBD) plasma actuators driven by repetitive nanosecond pulses for high Reynolds number aerodynamic flow Control. These actuators are believed to influence the flow via a thermal mechanism which is fundamentally different from more commonly studied AC-DBD actuators. Leading edge Separation Control on an 8-inch chord NACA 0015 airfoil is demonstrated at various post-stall angles of attack for Mach numbers up to 0.26 (free stream velocity up to 93 m/s) and Reynolds numbers up to 1.15 X 106. The nanosecond (NS) pulse driven DBD is shown to extend the stall angle at low Reynolds numbers by functioning as an active trip. At post-stall angles of attack, the device is shown to excite shear layer instabilities and generate coherent spanwise vortices that transfer momentum from the freestream to the separated region, thus reattaching the flow. This is observed for all high Reynolds numbers and Mach numbers spanning th...
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flow Separation Control over an airfoil with nanosecond pulse driven dbd plasma actuators
49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 2011Co-Authors: Chris Rethmel, Jesse Little, Keisuke Takashima, Aniruddha Sinha, Igor V Adamovich, Mo SamimyAbstract:This work continues an ongoing development and use of dielectric barrier discharge (DBD) plasma actuators driven by repetitive nanosecond pulses for high Reynolds number aerodynamic flow Control. These actuators are believed to influence the flow via a thermal mechanism which is fundamentally different from the more commonly studied AC-DBD plasmas. Leading edge Separation Control on an 8-inch chord NACA 0015 airfoil is demonstrated at various post-stall angles of attack (α) for Reynolds numbers (Re) and Mach numbers (M) up to 1.15x10 6 and 0.26 respectively (free stream velocity, U∞ = 93 m/s). The nanosecond pulse driven DBD can extend the stall angle at low Re by functioning as an active trip. At poststall α, the device generates coherent spanwise vortices that transfer momentum from the freestream to the separated region, thus reattaching the flow. This is observed for all Re and M spanning the speed range of the subsonic tunnel used in this work. The actuator is also integrated into a feedback Control system with a stagnation-line-sensing hot film on the airfoil pressure side. A simple on/off type Controller that operates based on a threshold of the mean value of the power dissipated by the hot film is developed for this system. A preliminary extremum seeking Controller is also investigated for dynamically varying Re. Several challenges typically associated with integration of DBD plasma actuators into a feedback Control system have been overcome. The most important of these is the demonstration of Control authority at realistic takeoff and landing Re and M.
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High Lift Airfoil Leading Edge Separation Control with Nanosecond Pulse Driven DBD Plasma Actuators
5th Flow Control Conference, 2010Co-Authors: Jesse Little, Munetake Nishihara, Keisuke Takashima, Igor V Adamovich, Mo SamimyAbstract:The efficacy of dielectric barrier discharge (DBD) plasmas driven by repetitive nanosecond (NS) pulses for flow Separation Control is investigated experimentally on an airfoil leading edge up to Re=1x10 (62 m/s). The NS pulse driven DBD plasma actuator (NSDBD hereafter) transfers very little momentum to the neutral air, but generates compression waves similar to localized arc filament plasma actuators. Experimental results indicate that NS-DBD plasma performs as an active trip at pre-stall angles of attack and provides high amplitude perturbations that manipulate flow instabilities and generate coherent spanwise vortices at post-stall angles. These coherent structures entrain freestream momentum thereby reattaching the normally separated flow to the suction surface of the airfoil. Such devices which are believed to function through thermal effects could result in a significant improvement over AC-DBD plasmas that rely on momentum addition which limits their performance at high speeds.
Markus Abel - One of the best experts on this subject based on the ideXlab platform.
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closed loop Separation Control over a sharp edge ramp using genetic programming
Experiments in Fluids, 2016Co-Authors: Antoine Debien, Kai Von Krbek, Nicolas Mazellier, Thomas Duriez, Laurent Cordier, Bernd R Noack, Markus Abel, Azeddine KourtaAbstract:We experimentally perform open and closed-loop Control of a separating turbulent boundary layer downstream from a sharp edge ramp. The turbulent boundary layer just above the Separation point has a Reynolds number \(Re_{\theta }\approx 3500\) based on momentum thickness. The goal of the Control is to mitigate Separation and early re-attachment. The forcing employs a spanwise array of active vortex generators. The flow state is monitored with skin-friction sensors downstream of the actuators. The feedback Control law is obtained using model-free genetic programming Control (GPC) (Gautier et al. in J Fluid Mech 770:442–457, 2015). The resulting flow is assessed using the momentum coefficient, pressure distribution and skin friction over the ramp and stereo PIV. The PIV yields vector field statistics, e.g. shear layer growth, the back-flow area and vortex region. GPC is benchmarked against the best periodic forcing. While open-loop Control achieves Separation reduction by locking-on the shedding mode, GPC gives rise to similar benefits by accelerating the shear layer growth. Moreover, GPC uses less actuation energy.
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closed loop Separation Control over a sharp edge ramp using genetic programming
arXiv: Fluid Dynamics, 2015Co-Authors: Antoine Debien, Kai Von Krbek, Nicolas Mazellier, Thomas Duriez, Laurent Cordier, Bernd R Noack, Markus Abel, Azeddine KourtaAbstract:We experimentally perform open and closed-loop Control of a separating turbulent boundary layer downstream from a sharp edge ramp. The turbulent boundary layer just above the Separation point has a Reynolds number $Re_{\theta}\approx 3\,500$ based on momentum thickness. The goal of the Control is to mitigate Separation and early re-attachment. The forcing employs a spanwise array of active vortex generators. The flow state is monitored with skin-friction sensors downstream of the actuators. The feedback Control law is obtained using model-free genetic programming Control (GPC) (Gautier et al. 2015). The resulting flow is assessed using the momentum coefficient, pressure distribution and skin friction over the ramp and stereo PIV. The PIV yields vector field statistics, e.g. shear layer growth, the backflow area and vortex region. GPC is benchmarked against the best periodic forcing. While open-loop Control achieves Separation reduction by locking-on the shedding mode, GPC gives rise to similar benefits by accelerating the shear layer growth. Moreover, GPC uses less actuation energy.
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closed loop Separation Control using machine learning
Journal of Fluid Mechanics, 2015Co-Authors: N Gautier, Thomas Duriez, Bernd R Noack, Jeanluc Aider, Marc Segond, Markus AbelAbstract:We present the first closed-loop Separation Control experiment using a novel, model-free strategy based on genetic programming, which we call ‘machine learning Control’. The goal is to reduce the recirculation zone of backward-facing step flow at $\mathit{Re}_{h}=1350$ manipulated by a slotted jet and optically sensed by online particle image velocimetry. The feedback Control law is optimized with respect to a cost functional based on the recirculation area and a penalization of the actuation. This optimization is performed employing genetic programming. After 12 generations comprised of 500 individuals, the algorithm converges to a feedback law which reduces the recirculation zone by 80 %. This machine learning Control is benchmarked against the best periodic forcing which excites Kelvin–Helmholtz vortices. The machine learning Control yields a new actuation mechanism resonating with the low-frequency flapping mode instability. This feedback Control performs similarly to periodic forcing at the design condition but outperforms periodic forcing when the Reynolds number is varied by a factor two. The current study indicates that machine learning Control can effectively explore and optimize new feedback actuation mechanisms in numerous experimental applications.
Kozo Fujii - One of the best experts on this subject based on the ideXlab platform.
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unsteady shear layer flow under excited local body force for flow Separation Control in downstream of a two dimensional hump
International Journal of Heat and Fluid Flow, 2018Co-Authors: Aiko Yakeno, Taku Nonomura, Soshi Kawai, Kozo FujiiAbstract:Abstract We present a detailed numerical investigation of unsteady shear layer dynamics in downstream under an excited local body force, based on the assumption that a plasma actuator is positioned near the top of a two-dimensional hump for flow-Separation Control. A local body force works in temporal burst mode, which is homogeneous in the spanwise direction. In our previous report (Yakeno et al., 2015), the most effective frequency to cause early reattachment is f h = 0.2 , which corresponds to what Hasan (1992) and many other past studies referred to as the step mode. A periodic excitation generates two-dimensional roll vortices and other three-dimensional turbulence between downstream rolls, such as rib structures. These vortex characteristics significantly depend on the excitation frequency. In the study, we discuss these multi-scale turbulence motion separately by considering decomposition of temporal phase-locked periodic statistics of the excitation frequency and non-periodic turbulence fluctuation. At first, we found that non-periodic turbulence kinetic energy due to three-dimensional rib structure increases the most at the optimal frequency f h = 0.2 , although that frequency corresponds to the time scale that a hump-height vortex grows. It seems that non-periodic turbulence energy growth near Separation point correlates with the Control performance more than two-dimensional roll vortex increase. We operated linear hydrodynamic stability analysis on a free shear layer and confirmed that periodic phase fluctuation at high frequency grew on the Kelvin-Helmholtz instability. At low-frequency, periodic turbulence fluctuation is not reproduced with the exponential assumption, while its magnitude is large. From those results, we consider that the time and spanwise-averaged non-periodic turbulence energy becomes strong near the Separation point the most at f h = 0.2 because a hump-height vortex occurs the most times at this frequency, which is associated with a generation of the rib structure around it. Temporal-periodic momentum balance based on the decomposition is also investigated. A difference of terms contribution at high and low frequencies to the term of a pressure gradient in the wall-normal direction is discussed. Finally, we investigated how excitation position affects a total drag around a hump and found that, in some cases, two recirculation regions separately emerge in the downstream of the hump, and thus the Control performance is degraded. At f h = 0.2 , one recirculation occurs regardless of the excitation position, while the most effective position is near the inflection point of the mean velocity of the unControlled flow near the wall.
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burst mode frequency effects of dielectric barrier discharge plasma actuator for Separation Control
AIAA Journal, 2017Co-Authors: Satoshi Sekimoto, Taku Nonomura, Kozo FujiiAbstract:The various Separation Control mechanisms of burst-mode actuation with a dielectric barrier discharge plasma actuator were experimentally investigated in this study. The Control of the separated fl...
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burst mode frequency effects of dielectric barrier discharge plasma actuator for Separation Control
AIAA Journal, 2017Co-Authors: Satoshi Sekimoto, Taku Nonomura, Kozo FujiiAbstract:The various Separation Control mechanisms of burst-mode actuation with a dielectric barrier discharge plasma actuator were experimentally investigated in this study. The Control of the separated flow around a NACA 0015 airfoil at a Reynolds number of 6.3×104 was investigated using a plasma actuator mounted at a distance from the leading edge of 5% of the chord length. A parametric study on the nondimensionalized burst frequency was conducted at three poststall angles of attack and various input voltages using time-averaged pressure measurements and time-resolved particle imaging velocimetry (PIV) results. The measurement results of the trailing edge pressure, which was selected as the index of Separation Control, indicate that the optimal burst frequency varies with the angle of attack. Several flow fields are discussed in detail in this paper, and two flow Control mechanisms were observed: the use of a large-scale vortex and the promotion of turbulent transition. With regard to the first mechanism, the p...
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an effective three dimensional layout of actuation body force for Separation Control
International Journal of Aerospace Engineering, 2012Co-Authors: Ittetsu Kaneda, Satoshi Sekimoto, Taku Nonomura, Kengo Asada, Akira Oyama, Kozo FujiiAbstract:We conducted large eddy simulations of the Control of separated flow over an airfoil using body forces and discuss the role of a three-dimensional vortex structure in Separation Control. Two types of cases are examined: (1) the body force is distributed in a spanwise uniform layout and (2) the body force is distributed in a spanwise intermittent layout, with three-dimensional vortices being expected to be generated in the latter cases. The flow fields in the latter cases have a shorter Separation bubble than those in the former cases although the total momentum of the body force in the latter cases is the same as or half of the former cases. In the flow fields of the latter type, the three-dimensional vortices, which are not observed in the former cases, are generated by the body force downstream of the body force distributed. Thus, three-dimensional vortices are considered to be effective in Controlling the separated flow.
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effects of plasma actuator layouts on a flow Separation Control over a wing theory and function of localized fluid flows and their physics
Transactions of the Japan Society of Mechanical Engineers. B, 2007Co-Authors: Daisuke Tsubakino, Yoshiteru Tanaka, Kozo FujiiAbstract:Effective location of plasma actuators for a flow Separation Control over a NACA 0012 airfoil is investigated by computational simulations. Single plasma actuator is located at 5%, 10% or 20% chord from the leading edge. The results indicate that the actuator located near the Separation has a better capability to Control flow Separations. Separation is once avoided when a single actuator is located near the Separation, another Separation occurs from the trailing edge. This motivates to use multiple actuators and the Separations are carried out for two actuators. The result shows the possibility that appropriate layouts of actuators can achieve high Control performance with relatively low input voltage.
Flint O. Thomas - One of the best experts on this subject based on the ideXlab platform.
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turbulent boundary layer Separation Control with single dielectric barrier discharge plasma actuators
AIAA Journal, 2010Co-Authors: David M. Schatzman, Flint O. ThomasAbstract:An experimental study was conducted to determine the effect of single dielectric barrier discharge plasma actuators on turbulent boundary-layer Separation Control. Two-component particle image velocimetry and laser Doppler velocimetry measurements showed the effect of plasma actuators on ambient air, a canonical zero-pressure gradient turbulent boundary layer, and a two-dimensional turbulent boundary-layer Separation from a convex ramp section. Different actuator configurations and Control strategies were implemented. Spanwise actuators were operated in both steady and unsteady modes. Plasma streamwise vortex generators were also used to enhance boundary-layer mixing. Flow visualization using a high-speed camera captured the temporal aspects of the Separation Control process and helped discern the physical mechanisms associated with each actuation strategy. The steady spanwise actuation produced a wall jet effect that augmented near-wall momentum and reattached the separated boundary layer. The streamwise oriented actuators also showed effective Control authority by creating counter-rotating vortices within the boundary layer that promote mixing of high and low momentum fluid.
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Turbulent Boundary Layer Separation Control with Plasma Actuators
4th Flow Control Conference, 2008Co-Authors: David M. Schatzman, Flint O. ThomasAbstract:An experimental study was conducted to determine the effect of single dielectric barrier discharge pl asma actuators on turbulent boundary layer Separation Control . Two component PIV measurements showed the effect of plasma actuators on ambient air, a canonical zero pressure gradient turbu lent boundary layer, and a two -dimensional turbulent boundary layer Separation from a convex ramp section. Different actuator configurations and Control strategies were implemented. Spanwise actuators were operated in both steady and unsteady modes . Plas ma streamwise vortex generators were also used to enhance boundary lay er mixing . Flow visualization using a high speed camera captured the temporal aspects of the Separation Control process and helped discern the physical mechanisms associated with each actuation strategy. The steady spanwise actuation produced a wall jet ef fect which helped reattach the separated boundary layer . The streamwise oriented actuators also showed effective Control authority by creating counter -rotating vortices with in the boundary layer which promote mixing of high and low momentum fluid .
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unsteady plasma actuators for Separation Control of low pressure turbine blades
AIAA Journal, 2006Co-Authors: Junhui Huang, Thomas Corke, Flint O. ThomasAbstract:This is a continuation of our work on the use of single dielectric barrier plasma actuators for Controlling flow Separation on turbine blades in the low-pressure turbine stage at low Reynolds numbers typical of high-altitude cruise. This used a linear cascade of Pratt & Whitney "PakB" shaped blades to provide generic low-pressure turbine conditions. The flow over one of the blades was documented through surface pressure, laser-Doppler velocimetry, and hot-wire measurements. These were used to define the location and size of the separated flow region on the suction side of the blade. Both steady and unsteady plasma actuators were implemented and found to be effective in Separation Control. For the unsteady actuators, there was an optimum excitation frequency to reattach the flow that corresponded to a Strouhal number, based on the length of the separated zone and the local freestream velocity, equal to unity. The unsteady actuator was more effective than the steady actuator in reattaching the flow while also requiring less power. It was suggested by the experimental results that the mechanism for the steady actuators was turbulence tripping, whereas the mechanism for the unsteady actuators was to generate a train of spanwise structures that promoted mixing.
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plasma actuators for Separation Control of low pressure turbine blades
AIAA Journal, 2006Co-Authors: Junhui Huang, Thomas Corke, Flint O. ThomasAbstract:This work involves the documentation and Control of flow Separation that occurs over turbine blades in the low-pressure-turbine (LPT) stage at the low Reynolds numbers typical of high-altitude cruise. We utilize a specially constructed linear cascade that is designed to study the flowfield over a generic LPT cascade consisting of Pratt and Whitney Pak B shaped blades. The center blade in the cascade is instrumented to measure the surface-pressure coefficient distribution. Optical access allows laser-Doppler-velocimetry measurements for boundary-layer profiles. Experimental conditions were chosen to give a range of chord Reynolds numbers from 10 4 to 10 5 , and a range of freestream turbulence levels from u'/U∞ = 0.08 to 2.85%. The surface-pressure measurements were used to define a region of Separation and reattachment that depends on the freestream conditions
