Numerical Simulation of High-Temperature Gas Flows in a Millimeter-Scale Thruster

High-temperature nozzle  ows at low Reynoldsnumbers are studied numerically by the direct simulationMonte Carlo method. Modeling results are compared with the experimental data on the speciŽ c impulse efŽ ciency of a heated nitrogen  ow atRe = 1:78 £ £ 102 –4:09 £ £ 102. Good agreement between modeling and datawas observed for nonadiabatic wall conditions. The relative in uence of three major thrust loss factors— ow 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 speciŽ c impulse is 50% larger than in the cold gas case (300 K), whereas the efŽ ciency 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 signiŽ cant factor in the simulation of such  ows.