Applying a hybrid DSMC/Navier–Stokes frame to explore the effect of splitter catalyst plates in micro/nanopropulsion systems

In this study, we apply a hybrid direct simulation Monte Carlo (DSMC)/Navier–Stokes (NS) frame to simulate the effects of catalyst or splitter plates in propulsive efficiency of micro/nanopropulsion systems. Our hybrid frame uses the local Knudsen number based on the gradient of the flow properties (KnGLL) to distinct the continuum and molecular regions. This frame also uses the state-based coupling (Dirichlet–Dirichlet boundary-condition coupling) to transfer the information between the two regions. We simulate typical micro/nanopropulsion systems consisting of channels, catalyst or splitter plates, and convergent–divergent nozzles. According to the KnGLL, we apply the NS solver to the channel including the splitter plates and the convergent part of the micro/nanopropulsion system and the DSMC solver to the divergent part of the system. In microscales, we find that the nozzle geometry can affect the system propulsive efficiency considerably. Additionally, the catalyst splitter plates can enhance the stagnation temperature upstream of the nozzle inlet and subsequently increase the overall specific impulse of the propulsion system. Furthermore, the inlet channel and the overall system sizes can affect the propulsive efficiency of the system, thrust force, and the specific impulse. However, a high viscous force in nanoscale propulsion systems does not permit the flow to meet the chocking condition at the nozzle throat. This limit decreases the propulsive force per unit area in the nanopropulsion systems considerably.