A MULTI-FLUID STAGNATION-FLOW PLASMA MODEL WITH SELF-CONSISTENT TREATMENT OF THE COLLISIONAL SHEATH

A two-temperature, multi-fluid model of a plasma in stagnation flow ag ainst a cooled, electrically biased surface is presented in this paper , The model couples bulk fluid motion, species diffusion and convectio n, electron and bulk energy equations, and net finite-rate ionization with Poisson's equation for the electric field in a generalized formul ation. Application of the model to argon pow reveals important interac tions between thermal, hydrodynamic, chemical and electrical boundary- layers, with implications to current-limiting regimes of arcjet operat ion. Our analysis also examines the response of a planar, Langmuir pro be in contact with a collisional, flowing plasma. Determinations of cu rrent-voltage behavior compare well to simple theory, including depend ence on incident plasma velocity. Departures from this theory arise fr om boundary-layer perturbations near the electrode surface, away from free-stream conditions. The computational model incorporates a finite- rate catalytic recombination of ions and electrons at the electrode su rface together with a specified current. These boundary conditions det ermine electron and ion fluxes at the surface consistent with mass and charge conservation. While the value of the net recombination rate is unknown, the dependence of calculated sheath strength on this rate is discussed.