Direct Monte Carlo Simulation of Small Bipropellant Engine Plumes

摘要

The prediction of rocket nozzle internal and external flowfields is an important aspect of space system design analysis, particularly with regard to exhaust plume contamination potential in the backflow region. For small engine plumes expanding into vacuum, the rarefied nonequilibrium effects both inside and outside of the nozzle render the conventional continuum method of analysis invalid in principle. To properly assess the backflow contamination flux due to inter-molecular collisions, molecular simulation of the flowfields is necessary. The objective of the present work is to subject such a simulation method to the scrutiny of a direct comparison with data taken from a simulated vacuum expansion of a 22.24N (51bf) rocket nozzle. The results of the successful application of the Direct Simulation Monte Carlo (DSMC) method to predict the mass flux density in the plume of a bipropellant engine are presented. The entire flow field starting from the nozzle throat extending to the backflow region has been calculated. Parameters varied in the simulation study include the nozzle area ratio and the internal degrees of freedom of the gas mixture. The results from DSMC calculation for all cases exhibit the same magnitude and behavior as the experimental data within expected statistical scatter. The angular mass fluxes in the backflow region are nearly independent of the parameters examined.