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Unique holographic measurements of viscous interactions in hypersonic air flows are presented. These results are part of a research project conducted in the 96 inch hypersonic shock tunnel at the Calspan-UB Research Center, Buffalo, New York. Flow visualizations of both 2D flat plate and axisymmetric boundary layer separations induced by compression turns, and 2D flat plate boundary layer separation resulting from an external shock impinging on the boundary layer are shown. Holographic interferometric measurements for the turbulent boundary layer flow upstream of the 2D compression-ramp separation case are presented for a free stream flow with a Reynolds number of 35 million per meter, and a Mach number of 11, nominally. The interferometric measurements for the 2D rectilinear fields are influenced by edged effects and refraction which make accurate calculation of the density distributions difficult. Further, the high compression of the flow in the regions of boundary layer reattachment produce a correspondingly strong optical refraction which obliterates definition of the flow and distinction of the wall. Different ways for correcting the interferometric measurements to account for the edge effects are suggested. Means of coping with the edge effects downstream of separation, and means for improving the distinction of the flow near reattachment seem remote for these studies. Thus far, the flow visualizations are the primary contribution of this holographic application, because they show the qualitative details of the shock structures throughout the separation regions with a clarity that surpasses all previous measurements. The few quantitative results presented here are unique, and while they offer new information as well as a potential to obtain density measurements in other types of hypersonic flows, they reveal concerns which need to be resolved before the interferometric data can be claimed to be accurate measurements of these fluid densities.
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