Characteristics of Plug Nozzles in Rarefied Regime Using the Direct Simulation Monte Carlo Method

An in-house code based on the direct simulation Monte-Carlo technique is used to simulate the expansion processes in microscale planar plug nozzles operating in a vacuum environment. Direct physical simulations are performed for a range of nozzle inlet flow conditions, achieved by varying the stagnation pressure and temperature values of the inlet stream. Truncation of the plug at different lengths is performed to investigate the influence of the length of the plug on the flow evolution and the thrust generation. Interestingly, it is observed that truncated plugs provide higher thrust for higher inlet pressures than a full plug at the same conditions. The near flow field of plug nozzles is critically compared with the corresponding convergent-divergent nozzles, and it was observed that the plug nozzles accelerate the flow to higher Mach numbers, which results in a higher thrust.