Investigation of Magnetic Heat Shielding in Weakly Ionized and Completely Ionized Plasma Regimes

Recent developments in spaceflight and High Temperature Super conductor technologies raise the prospect of developing reusable heat shields for atmospheric entry. The plasma sheath formed around blunt bodies due to high speed can be severely altered by interaction of strong magnetic fields. However, the effect of ionization fraction on such flow fields is not much explored. This thesis investigates the effect of a magnetic field on different flow parameters associated with re-entry in different ionization regimes. The study includes low Knudsen number flows ranging from partially ionized to fully ionized flow corresponding to re-entry scenarios. The initial part of the study devised and validated a magnetohydrodynamic (MHD) compressible solver in a finite volume platform (CMFoam). CMFoam is then used to study the blunt body exposed to the fully ionized plasma regime. Later, a study specifically for the partially ionized flow regime is conducted across various altitudes for 0T and 2T magnetic field. Different altitude re-entry conditions are selected from the weakly ionized regime studies. A finite-volume open-source code hy2Foam is used to simulate the weakly ionized regime. It is observed that as the altitude increases, the ionization also increases. To understand the effect of higher conductivity on the plasma, a 70km altitude case is emulated with 10 times higher electrical conductivity. Further, a maximum ionization condition corresponding to the bow shock condition at 70km is chosen as the initial condition for a fully ionized study by CMFoam. This condition was selected because it represents the point of maximum ionization without violating the continuum hypothesis among the chosen altitudes. Non-dimensional analysis of parameters is carried out to initialize similar conditions for fully ionized test cases by CMFoam and hy2Foam. The flowfield shock stand-off distance is analysed for different ionization regimes for a magnetic field of 2T. The shock stand-off distance increases due to the increase in interaction parameter at higher altitude. Next, the wall heat flux is evaluated for different altitudes using conduction models and Fay & Riddell correlations. The peak heat flux occurs at 65km altitude for the particular geometry selected for study. The peak heat flux reduces when a magnetic field is imposed. The reduction in wall heat flux reaches a maximum at 70km altitude. The emulated fully ionized test case shows overestimated heat flux reduction, compared to a fully ionized condition case by CMFoam and hy2Foam. Further, the mole fraction and ionization fraction for different altitudes with and without a magnetic field is studied. A shift in reaction regime is observed, corresponding to the shift in the non equilibrium region. The higher the altitude, the wider the non equilibrium regime that is observed. Also, higher mole fractions of ions and electrons are observed at higher altitudes. Finally, the flowfield vorticity is studied for different altitudes and magnetic field. The presence of a magnetic field increases net vorticity at higher altitudes due to shock curvature, while concurrently decreasing vorticity in the wake region.