Heat Transfer in a Nozzle at Supersonic Speeds

Abstract

Very few previous experiments have been done on the transfer of heat to or from a gas flowing at high subsonic or supersonic speeds in a pipe or nozzle. Since the thermodynamic effects of heat exchange and friction upon the flow may be appreciable before the flow has settled down to equilibrium distribution of temperature and velocity over the cross-section, it is essential in any experimental investigation to define precisely the condition of the flow at the entrance to the measuring section.

An example of fundamental and practical importance is the convergent-divergent nozzle with cooling at the walls, and experiments are described using a water-cooled nozzle of smooth continuous internal profile through which hot gas at 850 deg. C. (1,562 deg. F.) was passed and with the heat transfer measured at different positions along the divergent section at Mach numbers up to 1·75. The heat transfer results for the different positions are best correlated by a Reynolds number based on length from the throat, and they indicate a turbulent boundary layer, which is confirmed by temperature traverses at the nozzle end. It is concluded that transition takes place at or near the throat.

The results are somewhat unexpected since both extraction of heat and downward pressure gradient might be expected to tend to delay transition and to produce a laminar boundary layer extending well into the divergent section. The results agree remarkably well with the low velocity formula for a turbulent boundary layer along a flat plate and show no appreciable influence of Mach number.