Abstract: Accurate simulation of plume flowfield is the basis of plume effects assessment of space thrusters. Both continuum and rarefied flow regimes are contained in the plume flowfield of thrusters，therefore，decoupled Navier-Stokes(N-S)and Direct Simulation Monte Carlo(DSMC)method is usually employed to simulate this kind of flow problem. To ensure both high accuracy and high efficiency when using decoupled N-S/DSMC method to solve vacuum plume flowfield of thrusters，the DSMC inflow and nozzle wall boundary conditions are investigated. By detailed comparing with the experimental data for the plume flows of a low-total-pressure thruster in literature，reasonable methods for setting boundary conditions，including the location of DSMC inflow boundary，reflection type of nozzle wall and wall temperature，are set up. When using these methods to simulate practical high-total-pressure thrusters，computational efficiency reduces seriously. Series of numerical tests are conducted，which show that the DSMC inflow interface can be set by starting from the nozzle exit and laying along the KnGL contour line of 0.05，meanwhile in the practical cases，wall temperature setting makes little influence on the simulation results.

Key words: Decoupled N-S/DSMC method；Vacuum plume of thrusters；Boundary condition；DSMC method

摘要： 准确模拟羽流流场是合理评估空间推力器真空羽流效应的基础。因羽流流场同时包含连续和稀薄两种流动机理，通常采用解耦方式的Navier-Stokes(N-S)方程和直接模拟蒙特卡罗(DSMC)混合方法对其进行模拟。为保证解耦N-S/DSMC方法应用于羽流计算时的准确性并尽量提高其计算效率，对计算中的DSMC入口和喷管壁面等边界条件设置问题开展了研究。通过与文献中低总压工况的羽流试验数据比较，确定了合理设置DSMC入口边界位置、壁面反射类型、壁温等边界条件的方法。针对将此方法应用于实际推力器工况计算时效率过低的问题，通过多种数值试验，表明从喷管出口处开始沿KnGL为0.05的等值线作为DSMC入口界面可同时保证仿真精度和较高的计算效率；并证明实际工况下壁温设置对羽流场仿真结果影响不大。

关键词: 解耦N-S/DSMC方法；推力器真空羽流；边界条件；DSMC方法