Simulation Study On Operation Process And Plume Of Pulsed Plasma Thruster

The Pulsed Plasma Thruster (PPT) is a pioneer electromagnetic thruster used in space at first, which has some advantages such as small bulk, light weight, compact framework, easy controllability and high reliability, etc. Thus, it can be widely applied in attitude or orbit control propulsion system of micro-satellites, and plays an important role in the propulsion system of micro and small satellites. The PPT operation process unites many complex interactions resulted from hydrodynamics, electromechanical, plasma-physics processes. The PPT plume contains complicated species, where ionization, combination and collision processes may occur. The pulse-typed operation mode makes it difficult to master characteristics of PPT operating physics. So it is very important to do theoretical research thoroughly on PPT.In the present thesis, by means of theoretical analysis and numerical simulation, for local temperature equilibrium, one-dimension two-temperature and three-dimension two-temperature MHD (Magneto-hydrodynamic) models were built, the basic physics research on Teflon propellant parallel-plate PPT has been carried out to investigate the method to enhance performance. With the improved DSMC (the Direct Simulation Monte Carlo) /PIC (Particle in Cell) fluid hybrid method, the PPT plume was simulated to understand the formation and development process of the plume. Through the two-temperature inlet model, an analytical system was built, which can simulate the whole flow field from the operation process to plume.One-dimension time-dependent two-temperature parallel-plate PPT operation process model based on magneto-hydrodynamic was established. The operation process and performance of PPT were evaluated on different initial voltage, capacitance and electrode length. The model can provide an effective tool to evaluate the thruster performance. On the one-dimension basic model, three-dimension PPT operation process time-dependent two-temperature model based on magneto-hydrodynamic was built. The full MHD equations were proposed, and the eigenvalues system was solved. Using the three-dimension model, the processes of PPT at different parameters and geometries were simulated, the three-dimension characteristics of PPT operation process were obtained.The basic operation process of PPT was studied, the results showed that in pulse the variation of discharge current affects the flow field in thruster, interaction on discharge current and inductive magnetic field influences on velocity of plasma; propellant surface temperature has the similar variation with the discharge current, which influences plasma density and velocity in chamber; there is plasma with high temperature, high ion density and high velocity in the central area of the chamber; and around the chamber, the plasma's temperature and velocity are low, atom density is high, and atom with low velocity may bring the problem of charring.The factors affecting the performance of PPT were investigated, the results showed that in the early pulse, high-velocity plasma is the main source of thrust, in the late pulse, the late-ablation aroused by high propellant surface temperature is an important reason for low efficiency of PPT; the high-temperature propellant around makes a great deal of plasma with low velocity, which is not good for performance; long electrode is favorable for magnetism acceleration, but the little current density is not good for spout velocity; proper long gap between electrodes is useful for acceleration of plasma and propellant cooling in late pulse; the high current density, high propellant surface temperature and quick cooling in late pulse at narrow electrode are beneficial for performance; to improve performance of PPT through geometry variation, the acceleration of gas dynamic force is limited, the flow situation suitable for Lorentz force should be considered; prolonging the time with high discharge current, expansion of plasma, advancing velocity of plasma is helpful for performance; in order to optimize current, it is necessary to choose low variation of current and prolong the time of expansion of plasma based on PPT geometry and energy.The model of PPT plume was built, the DSMC/PIC fluid hybrid method is programmed, the appropriate conserving expression of shape factor for the sampling at node is corrected, potential field and electron temperature field are solved by improving GMRES algorithm to advance operation speed, for time-dependent PPT plume, one-dimension two-temperature inlet model and three-dimension two-temperature inlet model were built, the numerical researches of PPT plume were carried out.The characteristics of PPT plume were studied, results showed, in pulse, plasma plume diffuses quickly, ion diffuses more widely than atom; there are back-flow of ion and atom, ion back-flow is stronger than atom, which is the main factor of back-flow pollution; charge exchange(CEX)collision delays the axial velocity of plume, accelerates the radial velocity, which is an important influence on back-flow; the distribution of back-flow and CEX ion in plume are affected by discharge current; variations of plume are similar with different energy, under higher energy the mass-flow-rate of plume is higher, and the area of plume is more extensive.Comparing the results of different inlet models, results showed that the distribution and variation of plume were determined by thruster spout, and the correct simulation needs the inlet model based on PPT operation process model; high-velocity ion in early pulse and low-velocity neutral in late pulse can be acquired through three-dimension inlet model, which is better than one-dimension inlet model, and through which the influence of the spout angle of inlet velocity on back-flow could be effectively simulated.