Numerical simulation of high-temperature gas flows in a millimeter-scale thruster

High-temperature nozzle flows at low Reynolds numbers are studied numerically by the direct simulation Monte Carlo method. Modeling results are compared with the experimental data on the specific impulse efficiency of a heated nitrogen flow at Re = 1.78 × 10²-4.09 × 10². Good agreement between modeling and data was observed for nonadiabatic wall conditions. The relative influence of three major thrust loss factors - flow divergence, surface friction, and heat transfer in axisymmetric and three-dimensional nozzles - is estimated for stagnation temperatures of 300, 1000, and 2000 K and Re = 2.05 × 10². For a stagnation temperature of 1000 K, the specific impulse is 50% larger than in the cold gas case (300 K), whereas the efficiency is 10% lower as a result of heat-transfer losses of the same magnitude as friction losses. Axisymmetric conical nozzle thrust performance was studied for a hydrogen-air propellant over a range of Re = 2 × 10²-2 × 10³. It is found that vibrational relaxation could be a significant factor in the simulation of such flows.