RAPID MEASUREMENT OF VELOCITY PROFILES WITH A DOPPLER-SHIFT CONTROLLED INTERFEROMETER

A scanning device is described for the rapid acquisition of velocity profiles in unsteady flow fields. It uses the Doppler effect on scattered laser light which is analyzed by a Laser-Doppler Velocimeter, Type ISL. This is a Doppler shift compensating interferometer of the Michelson type. The instrument's features permit an increase in scanning rates relative to systems which use conventional methods of Doppler signal analysis. Scanned profile frequencies of more than one thousand per second are achieved by means of a specially developed optomechanical scanner. The measurement examples discussed concern the exit flow fields of a nozzle and of a sudden expansion pipe flow.