Turbulent Heat Transfer Through a Highly Cooled, Partially Dissociated Boundary Layer

Abstract

SUMMARY The problem of heat transfer from high-temperature air through a turbulent boundary layer to a cold surface is con­ sidered both analytically and experimentally. Heat-transfer data obtained in shock tubes are presented and correlated by a semiempirical theory which includes the effect of atomic diffusion. The distinguishing characteristics of turbulent boundary layers with dissociation and large cooling are considered. It is shown that the equations governing such flow, after certain approximations, can be represented in a form similar to the classi­ cal equations for a turbulent boundary layer. An approximate theory is proposed for turbulent heat transfer for a highly cooled boundary layer on portions of the body where the pressure gradient is negligible in the case of blunted bodies of revolution in high-speed flight. Experimental results obtained on the cylindrical portion of a hemisphere-cylinder model are presented for conditions simulat­ ing flight speeds to 21,350 ft./sec, where up to 30 per cent of the molecules are dissociated. Reynolds Numbers of 2.5 X 10 6, based on local fluid properties external to the boundary layer, were achieved. The larger values of Reynolds Number and flight speed were not obtained simultaneously, due to structural limitations of the shock tubes; however, the experiments were conducted in such a way that the important effects of each could be determined. In the experiments the Mach Number external to the bound­ ary layer varied between 1.7 and 2.2. The corresponding Mach Number for blunted nonslender bodies in flight would have a maximum value between 2.5 and 4; however, it is shown that these differences in Mach Number are not important for such bodies.