FUNDAMENTAL TURBULENCE MEASUREMENTS BY RELIEF FLOW TAGGING

The observation of small-scale velocity structures in high Reynolds number turbulent flowfields is important for the understanding of energy scaling and dissipation phenomena. The Raman excitation plus laser-induced electronic fluorescence (RELIEF) technique is shown to be a promising tool to observe these scales. Lines on the order of 100 thick and 1 cm long are written into a contained turbulent jet and observed with a resolution on the order of tens of microns. The images that are recorded give instantaneous velocity profiles if very short time delays between tagging and interrogation are used. This time-of-flight approach is a direct measure of velocity, so approximations such as constant density, constant temperature, or the Taylor hypothesis are not required. The velocity data are analyzed to yield the velocity profile, the turbulence intensity, the lateral correlation function, and the lateral second-order structure function. At 35 jet exit diameters downstream, a slope of 0.669 is measured through the inertial subrange portion of the ln-ln plot of the second-order structure function. 1993 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

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