Simulations of the flow surrounding the Stardust Return Capsule at Mach 40 at various altitudes were used to test the validity of the ambipolar diffusion approximation. Results of direct simulation Monte Carlo (DSMC) simulations at 71 km altitude show that atomic N and O are dominant in the shock layer. The highest concentration of ions produced in the shock corresponds to , followed by , , , and . The only charged species present in the wake are , , and electrons, as , , and are formed and then depleted in the bow shock. At 100 km altitude, the influence of charged species is negligible. Simulations were also conducted in which the ambipolar diffusion approximation was not applied, and, instead, electrons were transported at the DSMC velocity. There was a net negative charge upstream from the bow shock and net positive charge in the plasma sheath adjacent to the vehicle. The magnitude of the electric field needed to maintain quasi neutrality is discussed. Results indicate that, for practical reentry flow conditions, the Debye length in the bow shock and wake is orders of magnitude smaller than the mean free path, and that invoking the ambipolar diffusion approximation is valid.
Analysis of the Ambipolar Diffusion Approximation in Hypersonic Ionizing Reentry Flows
Journal of Thermophysics and Heat Transfer ; 36 , 3 ; 734-744
01.07.2022
Aufsatz (Zeitschrift)
Elektronische Ressource
Englisch
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