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The plasma flow in magnetoplasmadynamic (MPD) self-field thrusters is described by conservation equations for heavy particles, turbulence, electrons, and the magnetic field for reaction and thermal nonequilibrium. The equations are discretized on unstructured adaptive meshes. The numerical results, which are verified by experimental data, show that the newly developed finite volume code predicts the thrust well. It is found that electron pressure diffusion drives the arc out of nozzle-type MPD thrusters. The drop of density in front of a water-cooled anode is the reason for the beginning of thruster instabilities at high electric currents.

We consider a two-dimensional coupled transmission problem with the conservation laws for compressible viscous flows, where in a subdomain Ω 1 of the flow-field domain Ω the coefficients modelling the viscosity and heat conductivity are set equal to a small parameter ε > 0. The viscous/viscous coupled problem, say P ε, is equipped with specific boundary conditions and natural transmission conditions at the artificial interface Γ separating Ω 1 and Ω \ Ω 1 . Here we choose Γ to be a line segment. The solution of Pε can be viewed as a candidate for the approximation of the solution of the real physical problem for which the dissipative terms are strongly dominated by the convective part in Ω 1 . With respect to the norm of uniform convergence, Pε is in general a singular perturbation problem. Following the Vishik-Ljusternik method, we investigate here the boundary layer phenomenon at Γ. We represent the solution of Pε as an asymptotic expansion of order zero, including a boundary layer correction. We can show that the first term of the regular series satisfies a reduced problem, say P 0 , which includes the inviscid/viscous conservation laws, the same initial conditions as Pε, specific inviscid/viscous boundary conditions, and transmission conditions expressing the continuity of the normal flux at Γ. A detailed analysis of the problem for the vector-valued boundary layer correction indicates whether additional local continuity conditions at Γ are necessary for P 0 , defining herewith the reduced coupled problem completely. In addition, the solution of P 0 (which can be computed numerically) plus the boundary layer correction at Γ (if any) provides an approximation of the solution of Pε and, hence, of the physical solution as well. In our asymptotic analysis we mainly use formal arguments, but we are able to develop a rigorous analysis for the separate problem defining the correctors. Numerical results are in agreement with our asymptotic analysis.

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