An Experimental Study of the Effect of Mass Injection at the Stagnation Point of a Blunt Body

Abstract

An experimental study of the effect of the injection of nitrogen and helium coolant gases at the stagnation point of a blunt body was carried out in the GALCIT Hypersonic Wind Tunnel at a Mach number of 5. 8. The gases were injected straight out of the stagnation point and also tangential to the body surface. The model was also fitted with flow separation spikes. The injection of the coolant gas resulted in a marked reduction in the model equilibrium temperature, and this cooling effect persisted over the entire length of the model. For the same mass flow, helium was a better coolant than nitrogen. The average heat transfer near the nose of the body was reduced almost to zero by injecting a mass flow of helium as small as 1/2 per cent of the mass flow of free-stream air contained in the "capture" area πR^2 of the spherical nose. Separation near the spike tip was observed up to a ratio of spike length to spherical nose diameter of 1.78 and a free-stream Reynolds number based on nose diameter of 2.84 x 10^5, resulting in a value of the foredrag coefficient which was one-third the value with no spike attached. The average heat transfer near the nose of the body was reduced almost to zero by attaching a spike having a ratio of spike length to hemispherical nose diameter of 1.07.