Impact of Nozzle Separation on the Plumes of Two Parallel Thrusters

Abstract

Two identical, interacting plumes emanating from model thrusters with parallel axes separated from 50 to 150 throat diameters are studied numerically. The nozzle throat Reynolds number is set to nearly 15; 000 to match that of a small bi-propellant attitude control thruster, but the simulated gas is nitrogen with a stagnation temperature of 300K. The near-isentropic, dense plume core is computed with the DLR Navier-Stokes solver TAU and the conditions at a suitably defined interface are then used on the inflow boundary of a separately conducted direct simulation Monte Carlo (DSMC) simulation. The results are shown to agree favorably with particle flux measurements performed in the DLR high-vacuum plume test facility for chemical thrusters (STGCT). Varying the nozzle separation distance alters the degree of rarefaction in the interaction plane, and by tagging DSMC particles according to their origin, the effect on the individual plume may be investigated. The impact of nozzle axis separation on mass flux along the line formed by the intersecting planes of symmetry is compared to the case of two equal superposed (i. e. non-interfering) plumes.