Gasdynamic approach to small plumes computation

Abstract

The semi-inverse marching characteristics scheme SIMA was extended to treat rotational flows; it is applied to computation of free plumes, starting out from non-uniform nozzle exit flow that reflects substantial viscous effects. For lack of measurements of exit flow in small nozzles, the exit plane flow is approximated by introducing a Power Law Interpolation (PLI) between the exit plane center and lip values. Exit plane flow variables thus approximated, are Mach number, pressure, flow angle and stagnation temperature. This choice is guided by gasdynamic considerations of exhaust flow from small nozzles into vacuum. The PLI is adjusted so as to obtain a match between computations and measurements at intermediate range from the nozzle. Computed plumes were found to be in good agreement with five different sets of small plume experiments. Comparative computations were performed using two alternate methods: the Boynton-Simons point-source approximation, and SIMA computation that started out from a uniform exit flow. It is demonstrated that for small nozzles having an exit flow dominated by viscous effects, the combined SIMA/PLI computational method is reasonably accurate and is dearly superior to either of the two alternate methods. 14 refs.