Three-Dimensional Simulations of Backflows from Ion Thruster Plumes Using Unstructured Grid Refinement

Abstract

Ion thruster plumes are simulated under a framework that was recently developed to take advantage of the large scalability of unstructured grids using adaptive mesh refinement. Momentum and charge-exchange collisions occurring between neutral and ion species, as well as the induced electric field due to ions, have been performed using multiple adaptive mesh refinement meshes to study the backflow of an ion thruster to a spacecraft surface. Furthermore, the ions and neutral species are directly coupled, which is found to have a 15% effect on the neutral species velocity profiles. The backflow for ions is found to occur when charge-exchange and momentum-exchange collisions are present, and then it is strongly enhanced when the induced electric field is considered. The ion energy distributions in the backflow region are obtained, and it is found that the inclusion of the electric field modeling is the most important factor in determining its shape. The plume backflow structure is also examined for a triple-thruster three-dimensional geometry case, and it is found that the ion velocity in the backflow region appears to be roughly independent of the number of thrusters. Finally, the influence of solar cell panel voltage on backflow fluxes is evaluated using a combined commercial software-generated potential with the induced potential, and the influence of gas–surface interactions is studied.