A 2-COMPONENT LASER-DOPPLER SCANNING TECHNIQUE FOR THE ANALYSIS OF UNSTEADY-FLOW FIELDS AND TURBULENT STRUCTURES

A scanning measurement technique and its application to a heated free jet of air is reported. This technique uses the Doppler frequency shif t of laser light scattered in a flow field and enables fast scanning m easurements of two velocity components to be made simultaneously. The results of the rapidly acquired planar velocity vector fields illustra te that the dynamics of instability structures in the jet flow may be resolved. This holds for a frequency range up to more than 2 kHz becau se of the presently attained scanning velocity rates of about 4000 pro file pairs per second. Coherent structures in mean-velocity turbulent flows cover that order of fluctuation frequencies and are subject to t his kind of experimental analysis as well as many other cases of unste ady flows.