Unsteady pressure boost micro-scale Laval nozzle flow characteristics

Targeting the unsteady pressure boost of the micro-scale jet when the spacecraft motion state was switched, the micro-scale Laval nozzle flow in the stepped pressure boost and linear pressure boost modes was used to simulate by direct simulation of Monte Carlo (DSMC) method, and comparative analysis of the flow characteristics in the process of change was done. Results showed that step-type pressure boost could cause a large amplitude peak-valley fluctuation in the flow characteristics, while the flow characteristics under linear pressure boost showed the characteristics of linear change; the viscous force played an important role in the unsteady pressure boost of micro-scale jet, especially in the flow field from the expansion section of the throat to the outlet; the total impulse, mass flow rate produced by the micro-scale jet and the impulse provided by unit quality working medium during the stepped pressure boost process was 59.5%, 74.7% higher, and 8.6% lower than the characteristics in linear pressure boost process, meanwhile, the volatility of the stepped pressure boost process was more obvious than the linear pressure boost process. It can be seen that the stepped pressure boost mode is suitable for system that requires large thrust to change the motion state and has sufficient propellant, and the linear pressure boost has obvious advantages when the system needs to be fine-tuned precisely or the propellant is required to produce higher efficiency. These research conclusions provide an effective reference for the design and optimization of micro-scale nozzles under different system conditions.