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Recent Projects
| Transitional Boundary Layer Shock Wave Interactions (Z.M. Murphree, K.B. Yuceil, N.T. Clemens, and D.S. Dolling) This aim of this study is to gain an understanding of the flow phenomena in a shock/boundary layer interaction in which the incoming boundary layer is transitional. The three-dimensional interactions are generated in Mach 5 flow with a flat plate and cylinder. Numerous techniques have been used to gain a better understanding of these interactions including surface flow visualizations, schlieren, high-speed planar laser scattering, and PIV. |
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| Physics and Control of Unstart in Supersonic Inlets and Isolators (J. L. Wagner, A. Valdivia, K. B. Yuceil, N.T. Clemens, D. S. Dolling) This study seeks to gain understanding of the physics of supersonic inlet unstart using high speed schlieren, PIV and fast response pressure measurements. ; A simplified inlet/isolator model with plexiglass sidewalls is used. ; With further understanding of unstart, passive and active control methods involving vortex generators and vortex generator jets can be investigated. |
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| Supersonic flow control using plasma actuators (J. Shin, V. Narayanaswamy, L. L. Raja, N. T. Clemens) The primary objective of this project is to develop DC glow discharge plasma actuators to produce appreciable changes to an incoming supersonic flow. An array of actuators is employed to scale the actuation over large areas. The image to the right shows a luminosity image of the plasma discharge array exposed to the incoming supersonic flow. We perform 10 kHz and 60 Hz schlieren imaging to study the plasma-flow interaction. ; We also perform optical emission spectroscopy to measure the electrothermal heating produced by the discharge. Sponsored by the AFOSR-MURI. |
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| Buoyancy effects in turbulent jet-flames in a crossflow (I.G. Boxx, C.A. Idicheria and N.T. Clemens) In this project we use a high frame-rate planar laser Mie scattering/particle image velocimetry (PLMS/PIV) system to study the effect of buoyancy on turbulent non-premixed jet-flames in a crossflow. This is done by comparing JFICF in normal gravity with otherwise identical ones in microgravity. Experiments are conducted in the University of Texas Drop Tower Facility. The image to the right shows a buoyancy-influenced, ethylene-fueled jet-flame in a crossflow. Sponsored by the Microgravity science division, NASA. |
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| Turbulent Non-premixed Jet-flames in Normal and Low-Gravity (C.A. Idicheria, I.G. Boxx and N.T. Clemens) The objective of this project is to use the low and microgravity environment to help us investigate fundamental aspects of turbulent flame structure. The low and microgravity conditions will be achieved by using the University of Texas Drop Tower Facility and 2.2 second drop tower at NASA Glenn, respectively. Our specific objective is to investigate - under varying gravity conditions - the large-scale turbulent structure and the underlying strain/vorticity fields in turbulent nonpremixed flames using high speed imaging of soot emission, planar laser Mie scattering and particle image velocimetry. An image of a turbulent propane flame in normal gravity is shown at the right. Sponsored by the Microgravity science division, NASA. |
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| Investigation of unsteadiness of shock-induced separated flows (Y.X. Hou, P.C. Bueno, R.G. Austin, S.J. Beresh, M. Comninos, S.C. Chan, N.T. Clemens and D.S. Dolling) In this project we are investigating the low frequency unsteadiness that characterizes the interaction of a shock wave with a turbulent boundary layer. This work has implications for the fatigue of structures and effectiveness of control surfaces on high speed aircraft and missiles. Our approach is to combine fast response pressure measurements with advanced optical diagnostics, such as planar laser scattering (PLS) from a condensed fog, and particle image velocimetry (PIV). An example PLS image taken in the Mach 5 wind tunnel is shown. The flow moves toward the compression ramp at the far right. The image reveals large-scale turbulent structures and their interaction with the separation shock. Sponsored by the U.S. Army Research Office. |
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| Planar laser imaging of high-speed cavity flow dynamics (Ö.H. Ünalmis, P.C. Bueno and N.T. Clemens, and D.S. Dolling) Planar laser imaging techniques are being combined with fast response pressure measurements to investigate the physics of high-speed cavity flow dynamics. Quasi-real time 'movies' obtained by planar laser scattering (PLS) and particle image velocimetry (PIV) will be used to understand the cavity oscillation cycle. The data generated in this study should prove useful in the validation of large eddy simulations (LES). Sponsored by the U.S. Air Force Office of Scientific Research. |
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| High Repetition Rate Rayleigh Scattering Measurements in Turbulent Nonpremixed Jet Flames (G.H. Wang, N.T. Clemens and P.L. Varghese) The objective of this study is to make high-quality, high-repetition rate (10 kHz), two-point laser Rayleigh temperature measurements in a weakly co-flowing turbulent nonpremixed jet flame at a Reynolds number of 15,200, with high signal-to-noise ratio (~50 in room air) and where the finest scales of turbulence are spatially and temporally resolved. These two-point temperature data were used to obtain temperature power spectra and detailed statistics of the thermal dissipation rate. Sponsored by the National Science Foundation. |
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| Plasma ignition of solid propellants (M.D. Ryan, J.U. Kim, J.M. Kohel, L.K. Su, P.L. Varghese and N.T. Clemens) A study is being conducted of plasma-induced ignition of solid propellants. Work to date has included the characterization of a pulsed plasma jet resulting from a capillary discharge. An image of the visible emission of the plasma jet, as captured by a fast shuttering intensified camera, is shown at right.Sponsored by the Army Research Office and Institute for Advanced Technology. |
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| Flowfield imaging of the fine scales in gas-phase turbulent jets (M.S. Tsurikov and N.T. Clemens) The structure and dynamics of the fine scales in gas-phase turbulent jets were investigated in the Fine Scale Turbulence Facility. Simultaneous PIV and PLIF measurements were made in an axisymmetric turbulent jet where the Kolmogorov scale was 0.6 mm. The image at right shows the scalar dissipation field for one sample image, plotted as a logarithmic contour plot. Results indicate that the mean finest scales in the velocity and scalar fields are 4 and 3 classical Kolmogorov scales, respectively. Sponsored by the National Science Foundation. |
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| Simultaneous PIV/OH PLIF measurements in planar nonpremixed turbulent flames (P.S. Kothnur, J.E. Rehm and N.T. Clemens) The aim of this work is to directly investigate the relationship between the reaction zone structure and the underlying strain and vorticity fields in planar turbulent nonpremixed jet flames using simultaneous PIV and PLIF of the OH radical. The image shows vorticity contours (left) and principal compressive strain (right) superimposed on simultaneous OH PLIF of a highly strained flame sheet with local extiction. Sponsored by the National Science Foundation. |
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| Heat release effects in planar, non-premixed turbulent flames (J.E. Rehm and N.T. Clemens) This project involves a fundamental study of the differences in structure between non-premixed planar flames and non-reacting jets. Two example images are shown of hydrogen flames taken in the planar jet/flame facility. Each image shows the two-dimensional particle concentration field (in gray scale) which marks the fuel jet, on which is superimposed the OH radical concentration field (yellow), which marks the reaction zone. The particle and OH concentration fields were obtained through simultaneous planar laser Mie scattering and planar laser-induced fluorescence (PLIF), respectively. Sponsored by the National Science Foundation. |
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| Mixing in gas-phase planar turbulent jets (L.K. Su and N.T. Clemens) Simultaneous, two-plane Rayleigh scattering from propane and planar laser-induced fluorescence (PLIF) from acetone are used to provide three-dimensional scalar field information in a turbulent planar jet. A sample Rayleigh scattering image is shown at right. Resolution is sufficient to permit differentiation of the results in all three spatial dimensions.This access to the three-dimensional scalar gradient field will provide useful insights into areas which are highly dependent on molecular mixing processes, such as nonequilibrium reacting flows and reacting flow pollutant formation. Sponsored by the National Science Foundation. |
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| Temperature and pressure imaging of a supersonic wake (E.R. Lachney, M.F. Smith and N.T. Clemens) Quantitative measurements of temperature and pressure in a complex supersonic flow are being made, with potential application in CFD code validation. An example image of the mean pressure field of a Mach 3, thick trailing edge wake is shown. The measurements are obtained through planar laser-induced fluorescence (PLIF) from nitric oxide (chosen for its strong fluorescence signal) seeded into the main flow. Using an appropriate model of the fluorescence process, the PLIF signal can be related to the thermodynamic state of the gas. Sponsored by the Institute for Advanced Technology. |
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