Experimental Analysis of Turbulent Structures by Means of Rapid Two-Component Laser-Doppler Scanning

Abstract

This paper describes a dual-component scanning technique which makes use of the Doppler effect in scattered laser light in order to rapidly scan velocity profiles in a flow. The method was built up by means of doubling a previously reported one-component technique. Results are given for a measurement in the flow near the exit nozzle of a1 heated air jet. They demonstrate the dynamics of the Flow field which is absolutely unstable due to the relationship between fluid densities of the hot jet and the cold ambient air. The plotted results concern the instantaneous velocity profiles, the velocity fluctuation, their vector fields and correlation parameters as the vorticity and the Reynolds shear stresses. Up to now we scanned with a rate of about 3000 pairs of velocity profiles per second. An increased laser-light intensity would improve the measurement conditions concerning the most important experimental parameters.