Flow tracing fidelity of scattering aerosol in laser Doppler velocimetry.

An experimental method for the determination of the flow-tracing fidelity of a scattering aerosol used in laser Doppler velocimeters was developed with particular reference to the subsonic turbulence measurements. The method employs the measurement of the dynamic response of a flow-seeding aerosol excited by acoustic waves. The amplitude and frequency of excitation were controlled in order to simulate the corresponding values of fluid turbulence components. Experimental results are presented on the dynamic response of aerosols over the size range from 0.1 microm to 2.0 microm in diam and over the frequency range 100 Hz to 100 kHz. It was observed that unit-density spherical scatterers with diameters of 0.2 mmicrom followed subsonic air turbulence frequency components up to 100 kHz with 98% fidelity.