Measuring the Velocity of a Supersonic Airflow with Laser Ionization Tagged Radar Anemometry (LITRA)
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Laser Ionization Tagged Radar Anemometry (LITRA) is a velocimetry technique which uses microwaves to follow a microplasma created within an airflow. The microplasma is generated at a point of interest via laser breakdown and is assumed to faithfully follow the flow during its lifetime. Changes in the phase of scattered microwaves result from the motion of the microplasma and also from the dynamic interaction between the microwaves and plasma. The additional phase shifts which occur independent of any motion interfere with the measurement of velocity. A differential detection system has been developed to determine and eliminate these intrinsic phase shifts and isolate the phase shift due to motion alone. Experiments to test the operation of this system have been conducted in a supersonic (Mach 2.4) wind tunnel. Velocity measurements obtained using LITRA are compared with secondary measurements obtained using a pitot tube system. LITRA velocimetry measurements deviate from the simultaneous pitot tube velocimetry measurements. It is believed that the observed deviation is a result of microwave scattering from background objects other than the plasma. Current work is aimed at identifying this and other sources of error in the LITRA measurement. Copyright © 2012 by Princeton University.
author list (cited authors)
McGuire, S., Zaidi, S., Dogariu, A., Howard, P., & Miles, R.