Effect of Plasma Sheaths on Earth-Entry Magnetohydrodynamics

The first study of the full coupling between the aerothermodynamics, the magnetohydrodynamics (MHD), and the plasma sheaths within Earth-entry flows is here performed. The problem addressed herein is representative of a force-generating MHD patch located between the stagnation point and the aft of a capsule entering the Earth’s atmosphere at Mach 34. The reactions are obtained from the Park chemical solver and the transport coefficients from the Gupta–Yos model with modifications. The physical model fully couples the drift–diffusion model for the sheaths to the multispecies Navier–Stokes equations for the plasma flow. The Hall and ion slip effects are taken into consideration within the plasma flow and within the sheaths. The effect of the electrode material on the MHD process is studied. Using thoriated tungsten instead of graphite leads to a thirtyfold increase in the Lorentz forces and also leads to significantly reduced heat fluxes on the cathode. This is attributed to the much higher electrical conductivity of the thoriated tungsten sheath reducing by orders of magnitude the plasma electrical resistance near the surfaces.