The Experts below are selected from a list of 273 Experts worldwide ranked by ideXlab platform
Eric Matlis - One of the best experts on this subject based on the ideXlab platform.
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Sensing and control of Flow Separation using plasma actuators
Philosophical transactions. Series A Mathematical physical and engineering sciences, 2011Co-Authors: Thomas Corke, Patrick Bowles, Eric MatlisAbstract:Single dielectric barrier discharge plasma actuators have been used to control Flow Separation in a large number of applications. An often used configuration involves spanwise-oriented asymmetric electrodes that are arranged to induce a tangential wall jet in the mean Flow direction. For the best effect, the plasma actuator is placed just upstream of where the Flow Separation will occur. This approach is generally more effective when the plasma actuator is periodically pulsed at a frequency that scales with the streamwise length of the Separation zone and the free-stream velocity. The optimum frequency produces two coherent spanwise vortices within the Separation zone. It has been recently shown that this periodic pulsing of the plasma actuator could be sensed by a surface pressure sensor only when the boundary layer was about to separate, and therefore could provide a Flow Separation indicator that could be used for feedback control. The paper demonstrates this approach on an aerofoil that is slowly increasing its angle of attack, and on a sinusoidally pitching aerofoil undergoing dynamic stall. Short-time spectral analysis of time series from a static pressure sensor on the aerofoil is used to determine the Separation state that ranges from attached, to imminent Separation, to fully separated. A feedback control approach is then proposed, and demonstrated on the aerofoil with the slow angle of attack motion.
E Obermeier - One of the best experts on this subject based on the ideXlab platform.
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aeromems polyimide based wall double hot wire sensors for Flow Separation detection
Sensors and Actuators A-physical, 2008Co-Authors: Ulrich Buder, Ralf Petz, Moritz Kittel, Wolfgang Nitsche, E ObermeierAbstract:Abstract A polyimide-based MEMS hot-wire sensor featuring two resistors in close proximity (200 μm) has been developed. Combining a flexible printed circuit board and a number of such MEMS wall double hot-wires, a so called hybrid AeroMEMS sensor array is established. Setup of both single double-wire sensor and hybrid array, as well as wind tunnel experiments to determine the position of Flow reattachment behind an airfoil are described. Further wind tunnel measurements on a generic two-dimensional model of a high-lift system of an airplane, consisting of a main airfoil and a flap, are presented. Evaluation of the experiments proves that the hybrid sensor array is well capable of detecting near-wall regions of Flow Separation as well as complete Flow Separation from the flap. This sensor system permits the detection of small near wall regions of Flow Separation on this specific aerodynamic configuration which were not detected by other measurement methods.
Philippe Pernod - One of the best experts on this subject based on the ideXlab platform.
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High temperature gradient micro-sensors array for Flow Separation detection and control
Smart Materials and Structures, 2019Co-Authors: Cécile Ghouila-houri, Abdelkrim Talbi, Romain Viard, Quentin Gallas, Eric Garnier, Alain Merlen, Philippe PernodAbstract:This paper reports the use of an array of calorimetric micro-sensors that perform bidirectional measurement of wall shear stress, for Flow Separation detection and control. The sensors design is hot-wire like with three parallel micro wires suspended over a micro-cavity and mechanically supported using periodic perpendicular micro-bridges. The micro-sensors were implemented on a flexible packaging and characterized in a turbulent boundary layer wind tunnel on a flat plate. An array of twelve micro-sensors were then implemented in a flap model designed for active Flow control experiments and equipped with pulsed jet actuators. The work included the design and manufacturing of appropriate miniaturized electronics. Without control, the micro-sensors successfully detected the natural Flow Separation and the Flow Separation point moving from the trailing edge to the leading edge as the angle of the flap increased. Finally, the micro-sensors characterized the efficiency of the active Flow control for avoiding Separation.
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MEMS calorimetric transducers for Flow Separation detection and control
2019Co-Authors: Cécile Ghouila-houri, Romain Viard, Quentin Gallas, Eric Garnier, Alain Merlen, Talbi Abdelkrim, Philippe PernodAbstract:Robust micro machined high temperature gradient calorimetric (HTGC) transducers were developed for Flow Separation control. Based on thermal principle, the transducers measure the mean and fluctuating bidirectional shear stress that is particularly useful for Flow Separation detection. More than a hundred micro-sensors were simultaneously micro-machined using MEMS technology. A flexible array of calorimetric micro-sensors was implemented with miniaturized electronics on a flap model also equipped with pulsed jet actuators. Flow control experiments were successfully conducted as the natural Separation occurring on the model was detected the HTGC micro sensors and controlled by pulsed jet actuation.
Yuxuan Yang - One of the best experts on this subject based on the ideXlab platform.
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Interpretation of Four Unique Phenomena and the Mechanism in Unsteady Flow Separation Controls
Energies, 2019Co-Authors: Guoping Huang, Jinchun Wang, Yuxuan YangAbstract:Unsteady Flow Separation controls are effective in suppressing Flow Separations. However, the unique phenomena in unsteady Separation control, including frequency-dependent, threshold, location-dependent, and lock-on effects, are not fully understood. Furthermore, the mechanism of the effectiveness that lies in unsteady Flow controls remains unclear. Thus, this study aims to interpret further the unique phenomena and mechanism in unsteady Flow Separation controls. First, numerical simulation and some experimental results of a separated curved diffuser using pulsed jet Flow control are discussed to show the four unique phenomena. Second, the bases of unsteady Flow control, Flow instability, and free shear Flow theories are introduced to elucidate the unique phenomena and mechanism in unsteady Flow Separation controls. Subsequently, with the support of these theories, the unique phenomena of unsteady Flow control are interpreted, and the mechanisms hidden in the phenomena are revealed.
Alan Tassin - One of the best experts on this subject based on the ideXlab platform.
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A two-dimensional analytical model of vertical water entry for asymmetric bodies with Flow Separation
2019Co-Authors: Romain Hascoet, Nicolas Jacques, Yves-marie Scolan, Alan TassinAbstract:The vertical water entry of asymmetric two-dimensional bodies with Flow Separation is considered. As long as there is no Flow Separation, linearised Wagner's theory combined with the Modified Logvinovich Model has been shown to provide computationally fast and reliable estimates of slamming loads during water entry. Tassin et al. (2014) introduced the Fictitious Body Continuation (FBC) concept as a way to extend the use of Wagner's model to separated Flow configurations , but they only considered symmetric bodies. In the present study, we investigate the ability of the FBC concept to provide accurate estimates of slamming loads for asymmetric bodies. In this case, Flow Separation may not occur simultaneously on both sides of the body. During an intermediate phase, slamming loads are governed by a competition between the local drop in pressure due to partial Flow Separation and the ongoing expansion of the wetted area. As a first benchmark for the model, we consider the water entry of an inclined flat plate and compare the FBC estimates with the results of a nonlin-ear model. Then, we consider the case of a foil and compare the FBC results with Computational Fluid Dynamics predictions. In both cases, we find that the FBC model is able to provide reliable estimates of the slamming loads.
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An analytical model of vertical water entry for 2D asymmetric bodies with Flow Separation
2019Co-Authors: Romain Hascoet, Nicolas Jacques, Yves-marie Scolan, Alan TassinAbstract:The vertical water entry of asymmetric two-dimensional bodies with Flow Separation is considered. As long as there is no Flow Separation, linearised Wagner's theory combined with the Modified Logvinovich Model has been shown to provide computationally fast and reliable estimates of slamming loads during water entry. Tassin et al. (2014) introduced the Fictitious Body Continuation (FBC) concept as a way to extend the use of Wagner's theory to separated Flow configurations, but they only considered symmetric bodies. In the present study, we investigate the ability of the FBC concept to provide accurate estimates of slamming loads for asymmetric bodies. In this case, Flow Separation may not occur simultaneously on both sides of the body. During an intermediate phase, slamming loads are governed by a competition between the local drop in pressure due to partial Flow Separation and the ongoing expansion of the wetted area. As a first benchmark for the model, we consider the water entry of an inclined flat plate and compare the FBC estimates with the results of a nonlinear model. Then, we consider the case of a foil and compare the FBC results with Computational Fluid Dynamics predictions. In both cases, we find that the FBC model is able to provide reliable estimates of the slamming loads.
