Research on the effect of nozzle pressure ratio on tangential supersonic film cooling of hypersonic spherical windows

In a hypersonic flight environment, optical windows face severe aerodynamic heating challenges, leading to window overheating, which can drown out infrared signals and even damage the windows. This paper proposes a spherical window cooling method based on tangential supersonic gas film. We conducted heat flux measurement in a hypersonic (Ma infinity = 7.1) shock wave wind tunnel to obtain the impact law of Nozzle Pressure Ratio (NPR = P c / P infinity , 2 = 0, 0.059, 0.106, 0.148, 0.206, 0.313, 0.345, defined as the static pressure of the jet outlet to the total pressure of the spherical stagnation point) on the tangential supersonic gas film cooling of the spherical. Combined with the flow information near the window obtained by the numerical simulation method of Reynolds average Navier-Stokes, the internal mechanism of NPR to the tangential supersonic gas film cooling law of the spherical window is revealed. The results indicate that as the NPR increases, the surface heat flux on the spherical window decreases significantly. The momentum of the supersonic gas film increases, improving the ability of gas film to resist mainstream mixing, expanding the effective cooling zone (denoted by the central angle theta of the heat insulation ( eta >= 1 )), enhancing the film cooling efficiency markedly. Therefore, the increase of NPR improves the ability of the gas film to isolate the mainstream. Furthermore, a higher NPR reduces the angle at which the supersonic gas film is compressed inward. The gas film expands outward. At the same central angle theta , resulting in an accelerated flow within the gas film flow, decreasing the static temperature of the gas film, thereby intensifying the heat dissipation effect against the high-temperature mainstream flow. Thus, the increase of NPR also improves the effect of the gas film cooling main stream, resulting in a nonlinear growth in the relationship between the unit volume gas film momentum and the effective cooling range ( eta >= 1 ) with the varies of NPR.