A preliminary study of optical properties of inhomogeneous shear layers

Fluid mechanical and optical properties of two-dimensional, subsonic shear layers with zero velocity ratio have been investigated. Experimental measurements of shear layer growth rates and laser beam degradation for propagation normal to the turbulent interface are presented. From schlieren photographs and long exposure interferograms taken parallel to the shear layer, growth rates were found to decrease with increasing Mach number. Coherent structure was observed at jet Mach numbers of 0.1, while the shear layer structure appears to be more random at jet Mach numbers of 0.6 to 0.9. Interferograms taken normal to the shear layer show that the greatest beam degradation is for a helium jet since the net index of refraction difference across the shear layer is the largest. The helium jet also produced larger shear layer growth rate than the others. The least beam degradation was observed for a jet of a helium and argon mixture with a small refractive index change across the shear layer.