Numerical Simulation of Nitrogen Nozzle Expansion Using Kinetic and Continuum Approaches

Kurzfassung

Attitude control of satellites is often accomplished by expanding a gas through the nozzle of small thrusters. The very low background pressure leads to a heavily underexpanded plume, which may impinge on the surrounding surfaces causing contamination, thermal loads and unwanted forces. A thorough understanding of the plume expansion is thus of high importance for the design of a spacecraft and its mission and numerical support of experimental investigations is needed. In a first step towards the development of an efficient numerical methodology that allows for simulation of gas flows over a wide density range, a detached downstream coupling approach of a continuum solver (applicable in regions of high density) and a kinetic particle solver (efficient in regions of low density) has been applied to the problem of nitrogen gas expanding through a nozzle into vacuum. It was found that the approach followed is not sufficient in the investigated flow scenario, as it produces a density discontinuity across large parts of the coupling interface. The reasons for failure of this approach are discussed. The numerical results in the highly rarefied far field of the flow do however agree well with experimental findings.