Application of the test-particle statistical method for the simulation of rarefied plume in a vacuum

Abstract

The article substantiates the important role of the problem of the supersonic jet outflow into a vacuum to control the motion of the center of mass, orientation, and stabilization of the spacecraft’s position in space. The types of low-thrust engines and microrocket engines viewed have plumes that can pass through all regimes from continuum to free-molecular. In zones where motion is described at the molecular-kinetic level, statistical methods are most often used. The statistical Test Particle Method (TPM) has so far been used only in rarefied homogeneous flows. The aim of this work is to develop the TPM for numerical modelling plume flows. Below are the basic tenets of the TPM and changes in its algorithm.             The initial drawing of the trajectories of molecules is carried out either from the nozzle exit (in the absence of a dense core) or from the initial surface, which is the virtual border of the continuity zone. Determining the distributions over the surface of the drawing of the coordinates of the start and the mass velocity of the plume flow is decisive for obtaining adequate results. Among the considered launch options, the most realistic one is uneven, with a concentration on the plume axis. The calculation of the mass velocity of the plume flow at the initial surface can be performed using numerical methods of continuum aerodynamics or using approximate methods.              The testing of TPM in the far field of a rarefied nitrogen plume was carried out by comparing the relative density distribution with the data of the approximate method. The results obtained in the presence of the initial sphere and in its absence agree with each other. The TPM testing in the area adjacent to the nozzle was carried out by comparing the isolines of relative density and Mach numbers with the results of direct Monte Carlo simulation for the experimental conditions of helium outflow from a low-thrust engine into a vacuum. Satisfactory agreement has been obtained between the numerical simulation data of the TPM and the compared data.