A need exists for a seedless equivalent of laser Dopplervelocimetry (LDV) for use in low-turbulence or supersonic flows orelsewhere where seeding is undesirable or impractical. A compact laservelocimeter using heterodyne non-resonant laser-induced thermalacoustics (LITA) to measure a single component of velocity is described.Neither molecular (e.g. NO2) nor particulate seed is added tothe flow. In non-resonant LITA two beams split from a short-pulse pumplaser are crossed; interference produces two counterpropagating soundwaves by electrostriction. A CW probe laser incident on the sound wavesat the proper angle is diffracted towards a detector. Measurement of thebeating between the Doppler-shifted light and a highly attenuatedportion of the: probe beam allows determination of one component of flowvelocity, speed of sound, and temperature. The sound waves essentiallytake the place of the particulate seed used in LDV. The velocimeter wasused to study the flow behind a rearward-facing step in NASA LangleyResearch Center's Basic Aerodynamics Research Tunnel. Comparison is madewith pitot-static probe data in the freestream over the range 0 m/s - 55m/s. Comparison with LDV is made in the recirculation region behind thestep and in a well-developed boundary layer in front of the step. Goodagreement is found in all cases
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