Dept. of Applied Physics
Oregon Graduate Center
Due to advances in experimental techniques and numerical air flow modeling, there has been a need for improved instruments capable of measuring turbulence parameters in compressible (supersonic) gas flows. A great deal of work has been done in recent years in applying various optical methods as the basis for remote sensing instruments capable of measuring these parameters to a high degree of accuracy. While both active and passive techniques have been proposed and developed, passive techniques tend to require only low power light sources with resultant advantages in expense, complexity and ease of operation. The work described in this dissertation involves the application of theoretical and experimental methods first developed in the field of atmospheric optics to the problem of passive remote sensing of fluid density in the supersonic turbulent field produced in a Mach 1.8 wind tunnel. A supersonic wind tunnel at NASA Ames Research Center was first characterized using standard intrusive measurement techniques and then used to test the validity of a theory based on the extended Huygens-Fresnel (EHF) principle which has been useful in long path atmospheric propagation. Experimental results demonstrated that the extended Huygens-Fresnel-based theory may be used to model the effects of supersonic turbulence on laser radiation to a high level of accuracy. This result suggested two optical schemes for remote turbulence measurement which were explored in the wind tunnel environment with the basic instrumentation consisting of a low power (1 mW) He-Ne laser capable of providing a diffraction limited, TEM[subscript 00] beam and a simple optical system capable of focusing the beam to several waist sizes.
Emmons, Donald R. Jr., "Gaussian beam propagation in turbulent supersonic flows" (1986). Scholar Archive. 216.