A Method for Near Field Computation of Coupled Weakly Ionized Plasma Flows in Low Earth Orbit

Abstract

The problem of wake effects, particularly the near wake, from spacecraft in low Earth orbit is of increasing interest. The flow simulation reported herein combines the fully coupled effects of neutral particle flow, plasma flow, electromagnetic field effects, and spacecraft charging. The simulation necessarily allows for chemically reacting flows (associative ionization, dissociation, and chain exchange) and for thermal accommodation at a spacecraft surface. Due to the highly coupled nature of the flow physics, a full solution simultaneous approach is used. This is required due to the need for extremely high resolution results for the near wake region. In this approach, the neutral flow is modeled using a direct simulation Monte Carlo technique. The charged particles are modeled using a particle approach to solve the Poisson equation. A technique of having a separate neutral-particle grid and a charged-particle grid is used. Neutral and charged particles are allowed collisional interaction. During one time step, the neutral-particle-move process occurs separately from the charged-particle-move process which is accomplished in the presence of the electromagnetic field. A major advantage of the technique is that results may be obtained with the dominant effects of orbital flows simultaneously modeled. A major disadvantage is that the technique is computationally expensive. Flow calculations for the neutral- and charged-particle cases are compared to independent and uncoupled computational simulations to confirm their accuracy. The solution procedure and technique are presented for several types of flows at orbital altitudes of 250 and 500 km. Excellent agreement with previously verified computational algorithms has been obtained for the case of neutral particle flow and charged-particle flow. Results for the full flow simulation are presented for 250 and 500 km.