Effects of geometry design on micro nozzle's performance

The Direct Simulation Monte-Carlo method is applied to simulate the flow in micronozzles with conical, bell, and trumpet shaped diverging sections, and the variations of each nozzle' s performance under different inlet temperature and pressure. The internal energy relaxation model and Cercignani-Lampis-Lord (CLL) molecule surface reflection model are applied in the simulation, which are extraordinary similar to real molecule collision process. The study indicates that the thrust performance of bell nozzle is apparently lower than that of trumpet and conical nozzle because of the influence of circumfluence region in the diverging section, while the difference of thrust performance between conical nozzle and trumpet nozzle is insignificant. The thrust produced by the three nozzles declines as the temperature of inlet flow increases, however, the thrust coefficient of nozzles increases accordingly. In general, the inlet pressure variations have considerable influence on the thrust of the nozzle. While the influence of inlet pressure variations on the thrust coefficient of the nozzle is insignificant.