The aero-optical distortions caused by supersonic mixing layers over a flat optical window are relevant to the performance of hypersonic vehicles. Such mixing layers are typically temperature-mismatched and gas speciesmismatched due to a need to efficiently cool the optical window. To investigate the effect of the mismatched properties across the mixing layer created by blowing a cool gas over a flat window, optical measurements of an M=2 freestream air flow with a cooling two-dimensional gas jet were taken using time-resolved Shack-Hartmann WFS and Schlieren photography. To complement the optical measurements, other non-intrusive techniques, specifically acetone-based PLIF and spatially-resolved infrared thermography techniques were implemented to extract relevant fluidic properties of the mixing layer. The cooling jet gas species were air, helium and carbon dioxide (CO2). To create the temperature mismatch, the total temperature of the freestream flow was varied from 295K to 750K, while the total temperature of the cooling jet was kept constant at 295K. Results of this experimental work will be presented and discussed. Based on experimental input, a scaling method proposed in previous work was implemented in order to predict aero-optical distortions, using the mixing-dominant assumption previously applied to the helium-air and air-CO2 case.
The aero-optical distortions caused by supersonic mixing layers over an optical window are relevant to the performance of hypersonic vehicles. Such mixing layers are typically temperature-mismatched due to a need to cool the optical window. To investigate the effect of the mismatched temperature across the mixing layer created by blowing a cool air over a flat window, optical measurements of an M = 2 freestream flow with an M ≈ 0.56 cooling two-dimensional jet were taken using Shack-HartmannWFS and Schlieren photography techniques. Total temperature of the freestream flow was varied from 295K to 750K, while the total temperature of the cooling jet was kept constant at 295K. Parameters of the mixing flow were examined using optical velocity methods. A new scaling method for aero-optical distortions in a temperature-mismatched, species matched supersonic mixing layer is proposed, providing an improved linear fit compared to the previous model.
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