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Flow Visualization of a Turbulent Shear Flow using an Optical Wavefront Sensor.
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH
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The research reported here investigated the use of a shearing interferometer SI wavefront sensor to determine the effects of shear-layer turbulence on an optical wavefront. A collimated helium-neon laser beam was propagated through a plane shear-layer produced by mixing helium and nitrogen at different velocities. Since the gases have different indices of refraction, the optical wavefront was distorted by different amounts by each gas. The SI measured the wavefront slope across the sampled area of the wavefront. The shear-layer was viewed from two orthogonal directions. This document contains shadow graphs, interference patterns imaged by each of the SIs six cameras, interferograms containing fringes with separation proportional to the wavefront slope, and phase maps showing the shape of the perturbed optical wavefronts. The side view showed an area of steep slope along the mixing area of the two gases. The slope gradually changed as the distance from the mixing layer region increased. For the top view, the peaks and valleys grew as they propagated away from the shear-layer turbulence generator. The results also indicated that the interference patterns recorded by the SI cameras provide a simple way to visualize turbulence in a manner that provides phase information about the wavefront.
APPROVED FOR PUBLIC RELEASE