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The effect of a radio frequency capacitively charged plasma field on a series of axisymmetric flow-fields is investigated in this paper. Particle image velocimetry is utilized to examine the variation of compressibility on axisymm...
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The effect of a radio frequency capacitively charged plasma field on a series of axisymmetric flow-fields is investigated in this paper. Particle image velocimetry is utilized to examine the variation of compressibility on axisymmetric jets of Nitrogen gas through a series of perfectly matched converging diverging nozzles and varying pressure ratios. Mean flow velocity measurements as well as turbulent fluctuating parameters are examined to determine differences in the flow between baseline (plasma off) and plasma on. Additionally, a series of more turbulent axisymmetric flowfields, created by developing flow in a constant diameter pipe, are investigated for plasma-turbulence interactions. Finally, electrode designs are modified in an attempt to increase plasma interaction with the flowfield. Results generally indicate that the plasma interaction with the shear layer is responsible for heating the shear layer and delaying jet-core breakdown.
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The local flowfield effects of vortex generators on a supersonic axisymmetric relaxed external compression inlet have been investigated with surface flow visualization and pressure-sensitive paint measurements in the 8'x6' superso...
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The local flowfield effects of vortex generators on a supersonic axisymmetric relaxed external compression inlet have been investigated with surface flow visualization and pressure-sensitive paint measurements in the 8'x6' supersonic wind tunnel at NASA Glenn Research Center. This inlet entails a mechanically simple design for providing a high-recovery/low-distortion flowfield and low sonic boom signature. A set of vortex generators was incorporated into the design both upstream of the terminating normal shock and downstream inside the subsonic inlet diffuser for decreasing separation near the shock/boundary layer interaction and reducing radial distortion at the engine face, respectively. The inlet centerbody and downstream diffuser vortex generator regions were imaged during wind tunnel testing internally through the inlet cowl with a camera housing attached to the cowl. The surface flow visualization revealed separated regions along the inlet centerbody for large mass-flow rates without vortex generators. Upstream vortex generators did reduce separation in the subsonic diffuser, and a unique perspective of the flowfield produced by the downstream vortex generators was obtained. In addition, pressure distributions on the inlet centerbody, vortex generators, and struts were measured.
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摘要 :
The local flowfield effects of vortex generators on a supersonic axisymmetric relaxed external compression inlet have been investigated with surface flow visualization and pressure-sensitive paint measurements in the 8'x6' superso...
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The local flowfield effects of vortex generators on a supersonic axisymmetric relaxed external compression inlet have been investigated with surface flow visualization and pressure-sensitive paint measurements in the 8'x6' supersonic wind tunnel at NASA Glenn Research Center. This inlet entails a mechanically simple design for providing a high-recovery/low-distortion flowfield and low sonic boom signature. A set of vortex generators was incorporated into the design both upstream of the terminating normal shock and downstream inside the subsonic inlet diffuser for decreasing separation near the shock/boundary layer interaction and reducing radial distortion at the engine face, respectively. The inlet centerbody and downstream diffuser vortex generator regions were imaged during wind tunnel testing internally through the inlet cowl with a camera housing attached to the cowl. The surface flow visualization revealed separated regions along the inlet centerbody for large mass-flow rates without vortex generators. Upstream vortex generators did reduce separation in the subsonic diffuser, and a unique perspective of the flowfield produced by the downstream vortex generators was obtained. In addition, pressure distributions on the inlet centerbody, vortex generators, and struts were measured.
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摘要 :
Three-component, planar, stereoscopic particle image velocimetry (S-PIV) data and three-component, volumetric, tomographic PIV (T-PIV) data acquired in the near wake a Mach 2.49, axisymmetric, separated/reattaching flow field are ...
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Three-component, planar, stereoscopic particle image velocimetry (S-PIV) data and three-component, volumetric, tomographic PIV (T-PIV) data acquired in the near wake a Mach 2.49, axisymmetric, separated/reattaching flow field are modally deconstructed and analyzed using proper orthogonal decomposition (POD). The S-PIV data were analyzed throughout the entire measurable near wake, and the T-PIV data and analysis were limited to a subsection of the conical shear layer of this flow field. Analysis of the S-PIV data using POD identified high-energy turbulent mechanisms present in the flow field associated with the exchange of fluid between the shear layer and the bounded recirculation bubble corresponding to entrainment/detrainment events. The phase spectra associated with these POD modes were used in conjunction with a turbulent quadrant analysis in order to conditionally average turbulent events associated with a corresponding flow field mechanism. This analysis was able to successfully filter turbulent events to reveal the flow field dynamics occurring both in the immediate vicinity of an acting turbulent mechanism, as well as far away from where the mechanism is acting. The POD analysis of the T-PIV data revealed the presence of coherent, three-dimensional, high energy-containing turbulent structures present within the shear layer. Hairpin and counter-hairpin vortices were found to be associated with the highest energy-containing POD mode. The second POD mode identified the existence of a quasi-streamwise oriented structure that exists in the subsonic portions of the shear layer throughout the adverse pressure gradient region. The three-dimensionality of this structure was resolved and displayed using linear stochastic estimation. Many of the lower energy-containing modes exhibited similar dynamics to the turbulent structures of the higher energy modes, occurring at smaller spatial scales and/or higher spatial frequencies. This indicates that the coherent structures identified by POD are responsible for much more of the total turbulent kinetic energy present in the shear layer than just the energy contributions of the first two POD modes.
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摘要 :
Three-component, planar, stereoscopic particle image velocimetry (S-PIV) data and three-component, volumetric, tomographic PIV (T-PIV) data acquired in the near wake a Mach 2.49, axisymmetric, separated/reattaching flow field are ...
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Three-component, planar, stereoscopic particle image velocimetry (S-PIV) data and three-component, volumetric, tomographic PIV (T-PIV) data acquired in the near wake a Mach 2.49, axisymmetric, separated/reattaching flow field are modally deconstructed and analyzed using proper orthogonal decomposition (POD). The S-PIV data were analyzed throughout the entire measurable near wake, and the T-PIV data and analysis were limited to a subsection of the conical shear layer of this flow field. Analysis of the S-PIV data using POD identified high-energy turbulent mechanisms present in the flow field associated with the exchange of fluid between the shear layer and the bounded recirculation bubble corresponding to entrainment/detrainment events. The phase spectra associated with these POD modes were used in conjunction with a turbulent quadrant analysis in order to conditionally average turbulent events associated with a corresponding flow field mechanism. This analysis was able to successfully filter turbulent events to reveal the flow field dynamics occurring both in the immediate vicinity of an acting turbulent mechanism, as well as far away from where the mechanism is acting. The POD analysis of the T-PIV data revealed the presence of coherent, three-dimensional, high energy-containing turbulent structures present within the shear layer. Hairpin and counter-hairpin vortices were found to be associated with the highest energy-containing POD mode. The second POD mode identified the existence of a quasi-streamwise oriented structure that exists in the subsonic portions of the shear layer throughout the adverse pressure gradient region. The three-dimensionality of this structure was resolved and displayed using linear stochastic estimation. Many of the lower energy-containing modes exhibited similar dynamics to the turbulent structures of the higher energy modes, occurring at smaller spatial scales and/or higher spatial frequencies. This indicates that the coherent structures identified by POD are responsible for much more of the total turbulent kinetic energy present in the shear layer than just the energy contributions of the first two POD modes.
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摘要 :
The coherence of three-dimensional turbulence in the compressible mixing layer of an axisymmetric, Mach 2.49, separated flow field is investigated experimentally by means of non-time-correlated tomographic particle image velocimet...
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The coherence of three-dimensional turbulence in the compressible mixing layer of an axisymmetric, Mach 2.49, separated flow field is investigated experimentally by means of non-time-correlated tomographic particle image velocimetry (tomo-PIV) measurements. Validation of the tomo-PIV data is performed by comparison with reliable data of the same flow field acquired using stereoscopic PIV and laser Doppler velocimetry. Statistical evidence of both hairpin vortex structures as well as counter-hairpins within the mixing layer was found by conditionally averaging the flow field measurements utilizing linear stochastic estimation. The dependence of the streamwise and transverse spatial location within the mixing layer, as well as the effect of flow field recompression on these structures is presented. The size, coherence, and angular orientation of the conventional-hairpins are shown to be strongly dependent on both the streamwise coordinate, as well as the onset of the adverse pressure gradient induced by recompression. For the counter-hairpins, however, only a mild dependence of the streamwise coordinate or the onset of recompression was found until the flow field approached the point at which low momentum fluid is turned to be recirculated upstream. These structures were found to commonly exist throughout the mixing layer and occur statistically in conjunction with one another throughout a significant transverse extent of the mixing layer. Distinct regions within the mixing layer that are statistically dominated by either conventional or counter-hairpins are identified and their implications discussed. Additionally, the dynamics of the counter-hairpin structures suggest a mechanism of potentially effective flow control which, if feasible, could have a profound impact on the net vehicle drag of a blunt-faced cylindrical body in supersonic flight.
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摘要 :
The coherence of three-dimensional turbulence in the compressible mixing layer of an axisymmetric, Mach 2.49, separated flow field is investigated experimentally by means of non-time-correlated tomographic particle image velocimet...
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The coherence of three-dimensional turbulence in the compressible mixing layer of an axisymmetric, Mach 2.49, separated flow field is investigated experimentally by means of non-time-correlated tomographic particle image velocimetry (tomo-PIV) measurements. Validation of the tomo-PIV data is performed by comparison with reliable data of the same flow field acquired using stereoscopic PIV and laser Doppler velocimetry. Statistical evidence of both hairpin vortex structures as well as counter-hairpins within the mixing layer was found by conditionally averaging the flow field measurements utilizing linear stochastic estimation. The dependence of the streamwise and transverse spatial location within the mixing layer, as well as the effect of flow field recompression on these structures is presented. The size, coherence, and angular orientation of the conventional-hairpins are shown to be strongly dependent on both the streamwise coordinate, as well as the onset of the adverse pressure gradient induced by recompression. For the counter-hairpins, however, only a mild dependence of the streamwise coordinate or the onset of recompression was found until the flow field approached the point at which low momentum fluid is turned to be recirculated upstream. These structures were found to commonly exist throughout the mixing layer and occur statistically in conjunction with one another throughout a significant transverse extent of the mixing layer. Distinct regions within the mixing layer that are statistically dominated by either conventional or counter-hairpins are identified and their implications discussed. Additionally, the dynamics of the counter-hairpin structures suggest a mechanism of potentially effective flow control which, if feasible, could have a profound impact on the net vehicle drag of a blunt-faced cylindrical body in supersonic flight.
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Turbulent mixing layers of varying compressibility (M_c = 0.19, 0.38, 0.54, and 0.89) are experimentally studied using flow visualization and velocimetry techniques. The experiments are conducted in a wind tunnel facility at the U...
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Turbulent mixing layers of varying compressibility (M_c = 0.19, 0.38, 0.54, and 0.89) are experimentally studied using flow visualization and velocimetry techniques. The experiments are conducted in a wind tunnel facility at the University of Illinois at Urbana-Champaign that is capable of five different convective Mach numbers. Inflow conditions are documented in the form of PIV measurements of the incoming boundary layers in both streams. Schlieren and Mie scattering images show that increased compressibility in the shear layer tends to elongate the rounded 2-D rollers that are extensively documented in the incompressible case. In addition, instantaneous three-component SPIV measurements are made on the spanwise-central plane. Mean velocity results confirm the reduction in growth rate with increasing M_c that has been widely agreed upon. Turbulence statistics results show that the streamwise normal Reynolds stress remains constant, while spanwise normal, transverse normal, and primary shear Reynolds stresses all decrease with increasing M_c. The Reynolds stress anisotropy tensor is also fully characterized with all three normal components. Anisotropy values near the shear layer center remain constant for each case. As mixing layer compressibility increases, the streamwise normal stress anisotropy increases, the transverse and spanwise normal stress anisotropics decrease, and shear stress anisotropy remains constant.
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摘要 :
Turbulent mixing layers of varying compressibility (M_c = 0.19, 0.38, 0.54, and 0.89) are experimentally studied using flow visualization and velocimetry techniques. The experiments are conducted in a wind tunnel facility at the U...
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Turbulent mixing layers of varying compressibility (M_c = 0.19, 0.38, 0.54, and 0.89) are experimentally studied using flow visualization and velocimetry techniques. The experiments are conducted in a wind tunnel facility at the University of Illinois at Urbana-Champaign that is capable of five different convective Mach numbers. Inflow conditions are documented in the form of PIV measurements of the incoming boundary layers in both streams. Schlieren and Mie scattering images show that increased compressibility in the shear layer tends to elongate the rounded 2-D rollers that are extensively documented in the incompressible case. In addition, instantaneous three-component SPIV measurements are made on the spanwise-central plane. Mean velocity results confirm the reduction in growth rate with increasing M_c that has been widely agreed upon. Turbulence statistics results show that the streamwise normal Reynolds stress remains constant, while spanwise normal, transverse normal, and primary shear Reynolds stresses all decrease with increasing M_c. The Reynolds stress anisotropy tensor is also fully characterized with all three normal components. Anisotropy values near the shear layer center remain constant for each case. As mixing layer compressibility increases, the streamwise normal stress anisotropy increases, the transverse and spanwise normal stress anisotropics decrease, and shear stress anisotropy remains constant.
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The interaction of an underexpanded jet and a nearby adjacent compliant surface is considered in an effort to gain insight into the relevant fluid-structure interaction. High-quality simultaneous flowfield and surface-deflection d...
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The interaction of an underexpanded jet and a nearby adjacent compliant surface is considered in an effort to gain insight into the relevant fluid-structure interaction. High-quality simultaneous flowfield and surface-deflection data were obtained in this high-Reynolds number flow using non-intrusive, fullfield, optical diagnostics (planar particle image velocimetry and stereo/3D digital image correlation, respectively). Both experimental setups were rigorously validated in terms of their measurement resolution and accuracy, both individually, and in a combined manner. The fullfield surface deflection data indicate that the surface has a predominantly quasi-static response characterized by a 'standing-wave' type contour along the jet axis. A large jetward deflection, on the order of 10 plate thicknesses, was observed near the first shock cell region, which is consistent with previously obtained rigid-surface case surface pressure measurements. The compliant-surface flowfield was analyzed and compared to the rigid-surface case results in key regions: the initial expansion region, through the shock/boundary-layer interaction (SBLI), the SBLI separation region, the shock cell structure of the remainder of the jet plume, the near-wall boundary layer, and the farfieId conditions. Notable differences were observed before, within, and after the SBLI region, as well as within the boundary layer, and in the shock-cell structure.
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