Improved Flow Visualization by Use of Resonant Refractivity
Final rept. 1 Mar 1974-28 Feb 1979
STANFORD UNIV CA DEPT OF AERONAUTICS AND ASTRONAUTICS
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This report discusses the experimental and theoretical work carried out associated with the use of resonance refractivity to improve flow visualization. The principal accomplishment of the present study was to verify quantitatively the feasibility of using the near-resonance spectral region around the sodium D-lines for obtaining one-to-two order-of-magnitude increase in the sensitivity of refractive methods of flow visualization such as schlieren, interferometric and shadow techniques. It is in this near region of the line wings, typically a few angstrom from line center, that the trade-off between refraction and absorption is highly favorable to permit implementation of the method with an available tunable dye laser light source. Here, the refractivity is high enough to see sound waves, weak vortices, etc. The accomplishments included a combined theoretical and experimental analysis of the near-region refractive and absorptive profile taking into account both doppler and collision broadening. The latter feature included studies to optimize the choice of collision parameters for self-broadening pure sodium vapor and for heterogeneous broadening sodium highly diluted by a carrier gas in a flow facility. Experiments with an interferometer-heat pipe arrangement using a tunable pulsed dye laser gave results which agreed with the analysis. The technique is now at the facility-design stage.
- Fluid Mechanics