Abstract:A method is presented to construct computationally efficient reduced-order models (ROMs) of three-dimensional aerodynamic flows around commercial aircraft components. The method is based on the proper orthogonal decomposition (POD) of a set of steady snapshots, which are calculated using an industrial solver based on some Reynolds averaged Navier-Stokes (RANS) equations. The POD-mode amplitudes are calculated by minimizing a residual defined from the Euler equations, even though the snapshots themselves are calculated from viscous equations. This makes the ROM independent of the peculiarities of the solver used to calculate the snapshots. Also, both the POD modes and the residual are calculated using points in the computational mesh that are concentrated in a close vicinity of the aircraft, which constitute a much smaller number than the total number of mesh points. Despite these simplifications, the method provides quite good approximations of the flow variables distributions in the whole computational domain, including the boundary layer attached to the aircraft surface and the wake. Thus, the method is both robust and computationally efficient, which is checked considering the aerodynamic flow around a horizontal tail plane, in the transonic range 0.4 < Mach number < 0.8, -3° < angle of attack < 3°.
A model of the plasma interaction with the ceramic walls of a Hall thruster chamber is presented that takes into account partial thermalization of the electron distribution function. A model of secondary electron emission with both elastically reflected and true-secondary electrons is considered. The plasma response is found to differ substantially from low to high thermalization. The different roles of the bulk and emitted populations of electrons are discussed. Plasma fluxes to the wall are independent of the thermalization level except in the very-low thermalization limit, when the tail of the distribution function of bulk electrons is highly depleted. To the contrary, energy losses to the walls and the sheath charge saturation limit depend strongly on the level of thermalization. Elastically reflected electrons affect significantly the plasma response by modifying the fluxes of primary and secondary electrons at the walls. Emphasis is put on obtaining analytical expressions for main plasma magnitudes, which can be implemented in two-dimensional models of the whole plasma discharge.
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