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Abstract:
This report describes fluid-optic interaction research at the University of Notre Dame. When a laser beam propagates through a variable-index- of-refraction, turbulent fluid, its wavefront becomes aberrated, reducing associated optical-system performance. For flight Mach numbers above 0.6 Mach, "compressibility" effects in the flow past the aircraft become important in aberrating wavefronts (aero-optics). This report presents experimental validation for the mechanism responsible for these aberrations in high, subsonic-Mach, free shear-layer flows, the so-called Weakly-Compressible Model. The data collected for this validation clearly shows that deep static pressure wells form in the coherent structures naturally present in shear layers. The presence of these static pressure wells overturns the previously-held belief that static-pressure fluctuations in shear layers are negligible. Results of a study using Proper Orthogonal Decomposition (POD) are also presented. These results suggest that POD methods can be extremely useful in solving some of the high-speed wavefront sensing issues associated with mitigating shear-layer induced aero-optical effects.
| Limitations: |
 APPROVED FOR PUBLIC RELEASE |
| Description: |
Final rept. 15 Nov 1999-14 Nov 2002 |
| Pages: |
28 |
| Report Date: |
10 FEB 2003 |
| Contract Number: |
F49620-00-1-0025, FQ8671-00-0- |
| Report Number: |
A352214 |
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