Experimental investigation on the aero-optical effects of supersonic gas films with various cooling fluids

Despite the fact that a supersonic cooling gas film can efficiently insulate aerodynamic heating, its interaction with the mainstream generates a sophisticated flow structure which may cause significant aero-optical ramifications. This study aims to analyze the fluid structure and wavefront distortion of supersonic gas film when subjected to varying nozzle pressure ratios (NPR) by employing two distinct cooling refrigerants, namely C O ₂ and air. Within the NPR range of 0 to 2, a linear relationship exists between the wavefront distortion of both C O ₂ and air films, while the C O ₂ film exhibits higher wavefront distortion than the air. Additionally, the influence of condensation on the discrepancies in aero-optical effects of the two refrigerants is discussed.