Thermal Effects on a Transpiration Cooled Hemisphere

Abstract

An approximate method is used to obtain the injec­ tion distribution which would exist on an isothermal, transpiration-cooled hemisphere in a supersonic stream. This distribution is the same for both air and helium injection, and is independent of the blowing level. A model having this distribution was tested in the Naval Supersonic Laboratory wind tunnel at a Mach number of 3.53. It is concluded that the design technique is reasonably accurate. Data taken near the nose are compared with the theories for air and helium injec­ tion. The agreement in the case of the reduction in heat-transfer coefficient is good. The values of in­ sulated wall temperature obtained near the nose with helium injection are 8 percent above the local stagna­ tion temperature, and largely independent of injection rate. It is believed that this phenomenon may be attributed to the thermal diffusion of the helium within the boundary layer. Air injection causes a slight re­ duction in the insulated wall temperature. It is shown that injection of either air or helium at the hemisphere nose considerably reduces the heat flux at the surface. The additional reduction in heat flux resulting from helium injection as opposed to air injection, and pre­ dicted by existing theory, is largely absent.