Measurements of heat transfer from fine wires in supersonic flows

Results of an experimental investigation of the heat loss of fine heated wires immersed in a supersonic stream at right angles to the flow direction are presented. The measurements show that the heat loss of the wire is independent of the free-stream Mach number for values of the latter between 1.3 and 4.5. Since the wire is always in the wake of a detached shock wave, the streamlines in the neighbourhood of the wire pass through a normal shock wave. The Reynolds number Re2 based on conditions behind a normal shock, thus becomes the characteristic parameter for the heat transfer. The measurements covering a Reynolds number range of 3 to 220 show the existence of two flow regimes. For Re2 > 20 the Nusselt number is a linear function of the square root of the Reynolds number, and the equilibrium temperature is nearly independent of Re2 < 20 the Nusselt number decreases more slowly, and the equilibrium temperature rises sharply with decreasing Reynolds number.