Flow visualization by elastic light scattering in the boundary layer of a supersonic flow
National Aeronautics and Space Administration, Langley Research Center, 2000 - Science - 23 pages
We demonstrate instantaneous flow visualization of the boundary layer region of a Mach 2.5 supersonic flow over a flat plate that is interacting with an impinging shock wave. Tests were performed in the Unitary Plan Wind Tunnel (UPWT) at NASA Langley Research Center. The technique is elastic light scattering using 10-nsec laser pulses at 532 nm. We emphasize that no seed material of any kind, including water (H2O), is purposely added to the flow. The scattered light comes from a residual impurity that normally exists in the flow medium after the air drying process. Thus, the technique described here differs from the traditional vapor-screen method, which is typically accomplished by the addition of extra H2O vapor to the airflow. The flow is visualized with a series of thin two-dimensional light sheets (oriented perpendicular to the streamwise direction) that are located at several positions downstream of the leading edge of the model. This geometry allows the direct observation of the unsteady flow structure in the spanwise dimension of the model and also allows the indirect observation of the boundary layer growth in the streamwise dimension.
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7.6 cm downstream Aeronautics and Space airflow amount of H2O boundary layer height boundary layer region boundary layer thickness camera pixel condensation dark current delta wing dew point elastic light scattering estimate farther downstream field of view five locations flow density flow field flow medium flow structure flow visualization gray level ICCD illustrated image of figure impurity instantaneous flow Langley Research Center laser beam laser light sheet laser sheet layer interaction model leading edge lower plate Mach mole fraction molecular NASA STI Program observation particles perpendicular Plan Wind Tunnel position probe Raman data Rayleigh scattering REPORT scattered signal scattering cross section Scattering Species scientific and technical secondary vortices seed material setup shock impingement point shock wave/boundary layer show eight shown in figure side view stagnation temperature STI Program Office stream streamwise direction streamwise locations supersonic flow surface technique uniform Unitary Plan Wind upstream UPWT facility vortex wavelength