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Michael Amitay - One of the best experts on this subject based on the ideXlab platform.
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Comparison between Finite-Span steady and synthetic jets issued into a quiescent fluid
Experimental Thermal and Fluid Science, 2016Co-Authors: Tyler Van Buren, Michael AmitayAbstract:In this study a Finite-Span synthetic jet is compared to a steady jet with matched Reynolds number (Reo=615 and 1230). At the aspect ratios studied (AR = 6, 12, and 18) the synthetic jet flow field is very complex yielding very different flow behavior when compared to the steady jet. The entire flow volume was attained allowing for a unique three-dimensional characterization of the jets. Direct measurements of the jet momentum transport showed that the synthetic jet generated up to three times more streamwise momentum than the steady jet. The steady and synthetic jets also showed very different vorticity structures, where the synthetic jet was much more proficient in enstrophy production. Two popular velocity scales for the synthetic jet are compared throughout the article displaying that the interpretation of the results can be very different depending which scale is chosen.
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Three-dimensional interaction of a Finite-Span synthetic jet in a crossflow
Physics of Fluids, 2016Co-Authors: Tyler Van Buren, Michael Beyar, Chia Min Leong, Michael AmitayAbstract:The formation and evolution of flow structures due to the interaction of a Finite-Span synthetic jet with a zero-pressure gradient laminar boundary layer were experimentally investigated using stereoscopic particle image velocimetry. A synthetic jet with three orifice aspect ratios of AR = 6, 12, and 18 was issued into a free-stream velocity of U∞ = 10 m/s (Reδ = 2000) at blowing ratios of Cb = 0.5–1.5. The interaction was found to be associated with two sets of flow structures: (1) a recirculation region downstream of the orifice due to virtual blockage, and (2) a steady streamwise vortex pair farther downstream. These two flow structures were characterized in detail. Tube-like velocity deficits in the free-stream were evident, as well as regions of increased velocity within the boundary layer. Reducing the aspect ratio of the orifice decreased the spacing of the edgewise vortices (generated due to the Finite Span of the orifice) as well as reducing the virtual blockage of the jet. A control volume analysis of the fluid streamwise momentum indicates that there is a momentum deficit just downstream of the jet orifice and the change in streamwise momentum is proportionally similar for all cases.
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Impact of orifice orientation on a Finite-Span synthetic jet interaction with a crossflow
Physics of Fluids, 2016Co-Authors: Tyler Van Buren, Edward Whalen, Chia Min Leong, Michael AmitayAbstract:The formation and evolution of flow structures associated with a Finite-Span synthetic jet issued into a zero-pressure gradient boundary layer were investigated experimentally using stereoscopic particle image velocimetry. A synthetic jet with an aspect ratio of AR = 18 was mounted on a flat plate and its interaction with a free stream, having a velocity of U∞ = 10 m/s (Reδ = 2000) at momentum coefficients of Cμ = 0.08, 0.33, and 0.75, was studied. The effect of the orifice pitch (α = 20∘–90∘) and skew (β = 0∘–90∘) angles on vortex formation as well as the global impact of the synthetic jet on the flow field was explored in detail. It was found that the orifice orientation had a significant impact on the steady and unsteady flow structures. Different orifice skew and pitch angles could result in several types of vortical structures downstream, including: no coherent vortex structure, a single (positive or negative) strong vortex, or a symmetric vortex pair. In all cases, the velocity near the wall was increased; however, cases with higher blockage (i.e., more wall-normal, transverse orifice) resulted in a strong velocity deficit in the free stream where orifices with lower pitch angles yielded in an increase in velocity throughout. The analysis is concluded with a summary of quantitative metrics that allude to flow control effectiveness.
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Dynamic stall process on a Finite Span model and its control via synthetic jet actuators
Physics of Fluids, 2015Co-Authors: Keith Taylor, Michael AmitayAbstract:An experimental study of the process by which dynamic stall occurs on a Finite Span S809 airfoil was conducted at the Center for Flow Physics and Control at Rensselaer Polytechnic Institute. Understanding the flow field around a dynamically pitching airfoil helped in controlling the dynamic stall process through active flow control via synthetic jet actuators. The three component, two dimensional flow fields were measured with a stereoscopic particle image velocimetry system. This study demonstrated that, through the introduction of periodic momentum near the leading edge of this model, the evolution of the dynamic stall vortex, which forms and convects downstream under dynamic conditions, could be delayed or suppressed in favor of the preservation of a trailing edge vortex that arises due to trailing edge separation and recirculation in the time averaged sense. This process seems to be the result of changing how the flow field transitions from trailing edge separation to a fully separated flow. In a phase-averaged sense, absent of flow control, this process is defined by the creation of a phase averaged leading edge recirculation region, which interacts with the trailing edge separation. Through the introduction of momentum near the leading edge, this process can be altered, such that the phase averaged trailing edge separation region is the dominant structure present in the flow. Additionally, a cursory investigation into the instantaneous flow fields was conducted, and a comparison between the phase averaged flow field and instantaneous fields demonstrated that while similar effects can be observed, there is a significant difference in the flow field observed in the instantaneous fields versus the phase averaged sense. This would imply that a different method of analyzing dynamic stall from PIV measurements may be necessary.
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Interaction of a Finite-Span synthetic jet near the tip of a sweptback wing
Physics of Fluids, 2015Co-Authors: Joseph Vasile, Michael AmitayAbstract:An experimental investigation was performed to study the three-dimensional flow interaction of a Finite-Span (aspect ratio of 18) synthetic jet located near the tip of a sweptback wing (cross-sectional profile of NACA 4421, aspect ratio of 4, and sweep angle of 30°) at a Reynolds number of 105 and at three angles of attack of 0°, 9°, and 15.5° (covering the range of attached to separated flow in the vicinity of the synthetic jet). Three blowing ratios were considered as 0.8, 1.2, and 2. Stereoscopic particle image velocimetry data were collected at multiple 2-D planes in the vicinity of the jet’s orifice, which were then used to reconstruct the flow volume, and the effect of the jet’s blowing ratio was analyzed using time-averaged and phase-averaged statistics. The study showed that the flow field in the vicinity of the synthetic jet orifice becomes highly three-dimensional and is governed by the streamwise structures that are associated with the Finite Span of the orifice (edge vortices). Furthermore, it...
Tyler Van Buren - One of the best experts on this subject based on the ideXlab platform.
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Three-dimensional interaction of a Finite-Span synthetic jet in a crossflow
Physics of Fluids, 2016Co-Authors: Tyler Van Buren, Michael Beyar, Chia Min Leong, Michael AmitayAbstract:The formation and evolution of flow structures due to the interaction of a Finite-Span synthetic jet with a zero-pressure gradient laminar boundary layer were experimentally investigated using stereoscopic particle image velocimetry. A synthetic jet with three orifice aspect ratios of AR = 6, 12, and 18 was issued into a free-stream velocity of U∞ = 10 m/s (Reδ = 2000) at blowing ratios of Cb = 0.5–1.5. The interaction was found to be associated with two sets of flow structures: (1) a recirculation region downstream of the orifice due to virtual blockage, and (2) a steady streamwise vortex pair farther downstream. These two flow structures were characterized in detail. Tube-like velocity deficits in the free-stream were evident, as well as regions of increased velocity within the boundary layer. Reducing the aspect ratio of the orifice decreased the spacing of the edgewise vortices (generated due to the Finite Span of the orifice) as well as reducing the virtual blockage of the jet. A control volume analysis of the fluid streamwise momentum indicates that there is a momentum deficit just downstream of the jet orifice and the change in streamwise momentum is proportionally similar for all cases.
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Comparison between Finite-Span steady and synthetic jets issued into a quiescent fluid
Experimental Thermal and Fluid Science, 2016Co-Authors: Tyler Van Buren, Michael AmitayAbstract:In this study a Finite-Span synthetic jet is compared to a steady jet with matched Reynolds number (Reo=615 and 1230). At the aspect ratios studied (AR = 6, 12, and 18) the synthetic jet flow field is very complex yielding very different flow behavior when compared to the steady jet. The entire flow volume was attained allowing for a unique three-dimensional characterization of the jets. Direct measurements of the jet momentum transport showed that the synthetic jet generated up to three times more streamwise momentum than the steady jet. The steady and synthetic jets also showed very different vorticity structures, where the synthetic jet was much more proficient in enstrophy production. Two popular velocity scales for the synthetic jet are compared throughout the article displaying that the interpretation of the results can be very different depending which scale is chosen.
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Impact of orifice orientation on a Finite-Span synthetic jet interaction with a crossflow
Physics of Fluids, 2016Co-Authors: Tyler Van Buren, Edward Whalen, Chia Min Leong, Michael AmitayAbstract:The formation and evolution of flow structures associated with a Finite-Span synthetic jet issued into a zero-pressure gradient boundary layer were investigated experimentally using stereoscopic particle image velocimetry. A synthetic jet with an aspect ratio of AR = 18 was mounted on a flat plate and its interaction with a free stream, having a velocity of U∞ = 10 m/s (Reδ = 2000) at momentum coefficients of Cμ = 0.08, 0.33, and 0.75, was studied. The effect of the orifice pitch (α = 20∘–90∘) and skew (β = 0∘–90∘) angles on vortex formation as well as the global impact of the synthetic jet on the flow field was explored in detail. It was found that the orifice orientation had a significant impact on the steady and unsteady flow structures. Different orifice skew and pitch angles could result in several types of vortical structures downstream, including: no coherent vortex structure, a single (positive or negative) strong vortex, or a symmetric vortex pair. In all cases, the velocity near the wall was increased; however, cases with higher blockage (i.e., more wall-normal, transverse orifice) resulted in a strong velocity deficit in the free stream where orifices with lower pitch angles yielded in an increase in velocity throughout. The analysis is concluded with a summary of quantitative metrics that allude to flow control effectiveness.
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Vortex formation of a Finite-Span synthetic jet: effect of rectangular orifice geometry
Journal of Fluid Mechanics, 2014Co-Authors: Tyler Van Buren, Edward Whalen, Michael AmitayAbstract:The formation and evolution of flow structures of a Finite-Span synthetic jet issuing into a quiescent flow were investigated experimentally using stereoscopic particle image velocimetry (SPIV). The effect of two geometrical parameters, the orifice aspect ratio and the neck length, were explored at a Strouhal number of 0.115 and a Reynolds number of 615. Normalized orifice neck lengths of 2, 4 and 6 and aspect ratios of 6, 12, and 18 were examined. It was found that the effect of the aspect ratio is much larger than the effect of the neck length, and as the aspect ratio increases the size of the edge vortices decreases and the presence of secondary structures is more evident. Moreover, axis switching was observed and its streamwise location increases as the aspect ratio increases. The effect of the neck length on the flow structures and the evolution of the synthetic jet was found to be secondary, where the effect was only in the very near field (i.e. close to the jet’s orifice).
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Vortex formation of a Finite-Span synthetic jet: High Reynolds numbers
Physics of Fluids, 2014Co-Authors: Tyler Van Buren, Edward Whalen, Michael AmitayAbstract:The formation and evolution of flow structures of a high-speed, Finite-Span synthetic jet issued into a quiescent flow were investigated experimentally using Stereoscopic Particle Image Velocimetry for jet peak velocities up to 150 m/s. The effect of high jet Reynolds number (Re○ = 1150, 3450, and 5750, with corresponding Strouhal numbers of St = 0.215, 0.046, and 0.028, respectively) on a Finite-Span synthetic jet with aspect ratios of 18 and 24 were explored. It was found that the velocity and vorticity fields were greatly affected by the Reynolds number, with the lowest Reynolds number case producing the highest normalized peak velocities and vorticity. Moreover, for all three Reynolds numbers, axis switching was observed and its streamwise location increased as the Reynolds number increased. The Q-criterion was utilized for decoupling vortices from the vorticity concentrations in the flow field. This enabled the identification of vortices in the flow field and the reconstruction of the 3D vortex ring ...
Keith Taylor - One of the best experts on this subject based on the ideXlab platform.
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Dynamic stall process on a Finite Span model and its control via synthetic jet actuators
Physics of Fluids, 2015Co-Authors: Keith Taylor, Michael AmitayAbstract:An experimental study of the process by which dynamic stall occurs on a Finite Span S809 airfoil was conducted at the Center for Flow Physics and Control at Rensselaer Polytechnic Institute. Understanding the flow field around a dynamically pitching airfoil helped in controlling the dynamic stall process through active flow control via synthetic jet actuators. The three component, two dimensional flow fields were measured with a stereoscopic particle image velocimetry system. This study demonstrated that, through the introduction of periodic momentum near the leading edge of this model, the evolution of the dynamic stall vortex, which forms and convects downstream under dynamic conditions, could be delayed or suppressed in favor of the preservation of a trailing edge vortex that arises due to trailing edge separation and recirculation in the time averaged sense. This process seems to be the result of changing how the flow field transitions from trailing edge separation to a fully separated flow. In a phase-averaged sense, absent of flow control, this process is defined by the creation of a phase averaged leading edge recirculation region, which interacts with the trailing edge separation. Through the introduction of momentum near the leading edge, this process can be altered, such that the phase averaged trailing edge separation region is the dominant structure present in the flow. Additionally, a cursory investigation into the instantaneous flow fields was conducted, and a comparison between the phase averaged flow field and instantaneous fields demonstrated that while similar effects can be observed, there is a significant difference in the flow field observed in the instantaneous fields versus the phase averaged sense. This would imply that a different method of analyzing dynamic stall from PIV measurements may be necessary.
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Load control on a dynamically pitching Finite Span wind turbine blade using synthetic jets
Wind Energy, 2014Co-Authors: Keith Taylor, Chia Min Leong, Michael AmitayAbstract:The feasibility of active flow control, via arrays of synthetic jet actuators, to mitigate hysteresis was investigated experimentally on a dynamically pitching Finite Span S809 blade. In the present work, a six-component load cell was used to measure the unsteady lift, drag and pitching moment. Stereoscopic Particle Image Velocimetry (SPIV) measurements were also performed to understand the effects of synthetic jets on flow separation during dynamic pitch and to correlate these effects with the forces and moment measurements. It was shown that active flow control could significantly reduce the hysteresis in lift, drag and pitching moment coefficients during dynamic pitching conditions. This effect was further enhanced when the synthetic jets were pulsed modulated. Furthermore, additional reduction in the unsteady load oscillations can be observed in post-stall conditions during dynamic motions. This reduction in the unsteady aerodynamic loading can potentially lead to prolonged life of wind turbine blades. Copyright © 2014 John Wiley & Sons, Ltd.
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The Flow Field of a Dynamically Pitching Finite Span S809 Blade and its Control
32nd ASME Wind Energy Symposium, 2014Co-Authors: Keith Taylor, Chia M. Leong, Michael AmitayAbstract:The ultimate purpose of this study is to improve the lifetime of wind turbine blades and to reduce costs associated with replacing damaged blades, such that wind energy can compete more economically. The specific goal of this paper is to understand the flow field around a dynamically pitching Finite Span wind turbine blade and subsequently reduce any unsteady loading by controlling the flow field around the blade using synthetic jet actuators. Experiments were conducted at a Reynolds number of 220,000, where the aerodynamic forces and moments were measured using a six-component load cell and the flow field was measured using Stereoscopic Particle Image Velocimetry (SPIV). Force measurements showed that unsteady loading was present during a dynamic pitch and this unsteady loading can be either enhanced (at low momentum coefficients) or reduced (at high momentum coefficients) through active flow control. SPIV measurements showed that there is a sudden change of the separation point from the trailing edge to the leading edge within a small range of angles of attack when dynamic stall happens. This phenomenon can be either delayed to a higher angle of attack or mitigated depending on the momentum coefficient. The baseline flow field around a 2-D and a 3-D model is also compared, and the flow at the mid-Span though can be considered nominally 2-D for both models; however, there are major differences in the flow fields for both cases which can be attributed to tip vibration of the 3-D model.
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Dynamic Load Control on a Finite Span Wind Turbine Blade Using Synthetic Jets
50th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 2012Co-Authors: Keith Taylor, Chia M. Leong, Michael AmitayAbstract:The feasibility of active flow control to mitigate hysteresis loop due to a dynamically pitching Finite Span s809 blade was investigated experimentally at a Reynolds number of 220,000. Under normal operating conditions, hysteresis loop and tip vibrations exist, which with extended exposure would cause blade fatigue and eventually translate to a reduced lifetime of wind turbines. In this regard, active flow control via arrays of synthetic jet actuators was explored as a means to control flow separation over the Finite Span blade, which can lead to mitigation of these undesired unsteady loads. In the present work, a six-component load cell was used to measure the aerodynamic loading of lift, drag and pitching moment. Stereoscopic Particle Image Velocimetry (SPIV) measurements were also performed to understand the effects of synthetic jets on flow separation during dynamic pitch, and to correlate these effects to the forces and moment measurements. It was shown that active flow control could delay or minimize dynamic stall through the reduction of the hysteresis loop of the aerodynamic loads. This implies less unsteady aerodynamic loadings on the blade, which can potentially lead to prolonged life of wind turbines.
John Farnsworth - One of the best experts on this subject based on the ideXlab platform.
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Vortex ring bifurcation and secondary structures in a Finite-Span synthetic jet
Journal of Fluid Mechanics, 2020Co-Authors: Joseph Straccia, John FarnsworthAbstract:An experimental investigation using stereo particle image velocimetry (SPIV) was performed to study the vortex dynamics of an aspect ratio 13 rectangular orifice synthetic jet issuing into quiescent fluid. Data were obtained on the orifice centreline planes for four Reynolds numbers and five Strouhal numbers, ranging from 298 to 731 and 0.039 to 0.100, respectively. At one condition, SPIV data obtained on parallel planes distributed across the width of the jet were used to reconstruct the three-dimensional, three-component velocity field. The results reveal that the axis switching deformations of the non-circular vortex rings give rise to several types of secondary structures. Before the primary vortex ring completed its first axis switch, the anti-parallel sides of the ring collided, resulting in vorticity reconnection. Consequently, the elongated vortex ring bifurcated into two circular vortex rings which propagated off along independent paths. The development and structure of vortex ring bifurcation in addition to the bifurcation's effect on the jet shape, momentum and entrainment are presented. The bifurcation process captured in the synthetic jet experiment is similar in many ways to computational simulations of isolated vortex rings. Despite these similarities and the fact that vortex ring bifurcation was detected for all conditions tested, it is shown that the bifurcation process is sensitive to the unique conditions in synthetic jets, specifically the proximity of other vortex rings as indicated by the Strouhal number. Finally, the results at different jet conditions are discussed in relation to prior studies of synthetic jets.
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Developing a reduced order model from structural kinematic measurements of a flexible Finite Span wing in stall flutter
Journal of Fluids and Structures, 2017Co-Authors: Ethan C. Culler, Thomas Mclaughlin, Jurgen Seidel, Casey Fagley, John FarnsworthAbstract:Abstract Experiments were conducted on a flexible, Finite-Span cyber–physical wing model in the wind tunnel to study the structural kinematics for a wing undergoing stall flutter. The wing model was designed to be weak in torsion and stiff in bending to exhibit stall flutter oscillations. The physical deformation of the wing surface was mapped at 38%, 58%, 78%, and 98% Span using a stereo vision motion tracking system. From these measurements, the wing motion is decomposed and shown to consist of a principally torsional (pitching) oscillation consistent with the first mode for a cantilevered beam in free vibration. A two equation empirical model of the wing motion was then developed and compared to the measured stall flutter motion.
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Aeroelastic Response of a Finite Span NACA 0018 Wing Part 1: Experimental Measurements
53rd AIAA Aerospace Sciences Meeting, 2015Co-Authors: John Farnsworth, Stuart Corbett, Jurgen Seidel, Thomas MclaughlinAbstract:A rectangular planform Finite Span NACA 0018 wing section was machined from three different materials to experimentally quantify the steady aeroelastic response of the wing section. This study was done to provide a baseline model for future flow control experiments and to assist with verification and validation of computational simulations being run in parallel. Measurements from both a six component force/moment balance and a stereo vision system were collected simultaneously to match the wing deformation to the aerodynamic loads. A solid aluminum wing was utilized as a rigid comparison to the flexible plastic materials that were tested. Each of the flexble wings displayed significant wing bending, but negligible wing twisting was observed. As a result the aerodynamic lift and drag profiles showed minimal influence from the aeroelastic response of the wings. Finally, from the force and moment measurements, an estimate of the wing Spanwise lift distribution was made and the bending deformation profile was calculated to compare with the stereovision measurements. The estimated bending profiles matched the measured within 1 mm across the wing Span of 600 mm for a maximum tip deflection of 25 mm.
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Interaction of a Finite-Span Synthetic-jet and Cross-flow over a Swept Wing
2010Co-Authors: Joseph Vasile, Michael Amitay, Yossef Elimelech, John Farnsworth, Kenneth E. JansenAbstract:An experimental investigation was performed to study the three-dimensional flow structures and interactions of a Finite-Span synthetic jet with the flow over a Finite and swept back wing (cross-sectional profile of the NACA 4421, AR=4, sweep angle of 30 deg), at a Reynolds number of 10 5 and zero angle of attack. Two momentum coefficients were considered, corresponding to two blowing ratios of 0.8 and 1.2. Stereoscopic PIV data was collected around the center jet in the mid-Span section. The effect of the momentum coefficient (or blowing ratio) was analyzed based on the three-dimensional flow field using time-averaged and phase-averaged statistics. The study showed that, similar to the interaction of a synthetic jet with the flow over an unswept wing, the flow field in the vicinity of the synthetic-jet orifice becomes highly three-dimensional and is governed by the superposition of two kinds of flow structures: (1) streamwise structures that are associated with the Finite Span of the jet (edge vortices), and (2) Spanwise flow structures that are generated along the orifice due to the vortex pairs that are formed by the synthetic jet. Nevertheless, over a swept wing these three-dimensional flow structures evolve almost immediately downstream to the synthetic-jet orifice and evolve into a very complex 3-D flow field.
Chia Min Leong - One of the best experts on this subject based on the ideXlab platform.
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Three-dimensional interaction of a Finite-Span synthetic jet in a crossflow
Physics of Fluids, 2016Co-Authors: Tyler Van Buren, Michael Beyar, Chia Min Leong, Michael AmitayAbstract:The formation and evolution of flow structures due to the interaction of a Finite-Span synthetic jet with a zero-pressure gradient laminar boundary layer were experimentally investigated using stereoscopic particle image velocimetry. A synthetic jet with three orifice aspect ratios of AR = 6, 12, and 18 was issued into a free-stream velocity of U∞ = 10 m/s (Reδ = 2000) at blowing ratios of Cb = 0.5–1.5. The interaction was found to be associated with two sets of flow structures: (1) a recirculation region downstream of the orifice due to virtual blockage, and (2) a steady streamwise vortex pair farther downstream. These two flow structures were characterized in detail. Tube-like velocity deficits in the free-stream were evident, as well as regions of increased velocity within the boundary layer. Reducing the aspect ratio of the orifice decreased the spacing of the edgewise vortices (generated due to the Finite Span of the orifice) as well as reducing the virtual blockage of the jet. A control volume analysis of the fluid streamwise momentum indicates that there is a momentum deficit just downstream of the jet orifice and the change in streamwise momentum is proportionally similar for all cases.
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Impact of orifice orientation on a Finite-Span synthetic jet interaction with a crossflow
Physics of Fluids, 2016Co-Authors: Tyler Van Buren, Edward Whalen, Chia Min Leong, Michael AmitayAbstract:The formation and evolution of flow structures associated with a Finite-Span synthetic jet issued into a zero-pressure gradient boundary layer were investigated experimentally using stereoscopic particle image velocimetry. A synthetic jet with an aspect ratio of AR = 18 was mounted on a flat plate and its interaction with a free stream, having a velocity of U∞ = 10 m/s (Reδ = 2000) at momentum coefficients of Cμ = 0.08, 0.33, and 0.75, was studied. The effect of the orifice pitch (α = 20∘–90∘) and skew (β = 0∘–90∘) angles on vortex formation as well as the global impact of the synthetic jet on the flow field was explored in detail. It was found that the orifice orientation had a significant impact on the steady and unsteady flow structures. Different orifice skew and pitch angles could result in several types of vortical structures downstream, including: no coherent vortex structure, a single (positive or negative) strong vortex, or a symmetric vortex pair. In all cases, the velocity near the wall was increased; however, cases with higher blockage (i.e., more wall-normal, transverse orifice) resulted in a strong velocity deficit in the free stream where orifices with lower pitch angles yielded in an increase in velocity throughout. The analysis is concluded with a summary of quantitative metrics that allude to flow control effectiveness.
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Load control on a dynamically pitching Finite Span wind turbine blade using synthetic jets
Wind Energy, 2014Co-Authors: Keith Taylor, Chia Min Leong, Michael AmitayAbstract:The feasibility of active flow control, via arrays of synthetic jet actuators, to mitigate hysteresis was investigated experimentally on a dynamically pitching Finite Span S809 blade. In the present work, a six-component load cell was used to measure the unsteady lift, drag and pitching moment. Stereoscopic Particle Image Velocimetry (SPIV) measurements were also performed to understand the effects of synthetic jets on flow separation during dynamic pitch and to correlate these effects with the forces and moment measurements. It was shown that active flow control could significantly reduce the hysteresis in lift, drag and pitching moment coefficients during dynamic pitching conditions. This effect was further enhanced when the synthetic jets were pulsed modulated. Furthermore, additional reduction in the unsteady load oscillations can be observed in post-stall conditions during dynamic motions. This reduction in the unsteady aerodynamic loading can potentially lead to prolonged life of wind turbine blades. Copyright © 2014 John Wiley & Sons, Ltd.
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Modification of the near wake behind a Finite-Span cylinder by a single synthetic jet
Experiments in Fluids, 2012Co-Authors: Edward P. Demauro, Chia Min Leong, Michael AmitayAbstract:Modification to the flow field about a Finite-Span cylinder of low-aspect ratio (AR = 3) by a single synthetic jet, mounted normal to the cylinder axis, was studied experimentally using surface-mounted pressure taps, stereoscopic particle image velocimetry (SPIV), and constant-temperature anemometry. The synthetic jet altered the circulation about the cylinder and created a large Spanwise change to the surface pressure, much greater than the dimensions of its orifice. SPIV measurements in the near wake showed that the synthetic jet enhances mixing of the downwash from the cylinder free end with the wake deficit, vectoring and narrowing the wake. The synthetic jet penetrates through the streamwise vorticity, enhancing mixing within the wake and reducing the power associated with the shedding frequency, St = 0.155, except below the vortex dislocation, where the shedding frequency was increased to that corresponding to a quasi-two-dimensional cylinder, St = 0.22.
