Experimental investigation of transitional free shear layer optics

Abstract

Measurements of Strehl ratio vs downstream distance, when a beam propagates through a shear layer (Reynolds number = 810/length), reveal minimal phase distortion in the pretransition region and a sudden decrease in the Strehl ratio when transition occurs. The Strehl ratio levels off to a constant asymptotic value (which is a function of the velocity ratio) in the post-transition region. The constant Strehl ratio (in the fully developed region) is attributed to fast mixing that occurs within the core of the vortices. Measurements in the post-transition region show that the Strehl ratio takes a U-shape profile when the velocity ratio is varied from 0.4 to 0.8. Results of mathematical simulation show that coherent structures may be modeled as a sinusoidal phase plate. © 1993 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.