Two-dimensional coupling issues of hybrid DSMC/Navier-Stokes solvers

A hybrid coupled Direct Simulation Monte Carlo (DSMC) / Navier-Stokes solver is developed to simulate flowfields comprised of regions of both rarefaction and continuum. The most important goal of this work is to describe possible coupling techniques and the number of pitfalls that can arise in their implementation. Moreover, the fundamental issue of the handling of scatter in the DSMC method is addressed. This is accomplished by employing an appropriate smoothing technique and investigating results of improper smoothing. Both the Marshak condition and the property interpolation technique employed in previous 1-D calculations are investigated as possible coupling mechanisms. Comparisons are made using a coupled hybrid technique, along with decoupled hybrid results, to experimental measurements of surface heat transfer rates for a blunted cone configuration with sting in a near continuum flow regime. It is shown that, for such flows, coupled approaches do not merit their cost and decoupled approaches are appropriate. Furthermore, it is found that local Knudsen number considerations by themselves for the placement of demarcation lines between continuum and rarefied regions may not lead to efficient, robust coupling schemes. Consideration should also be given to the magnitude of the fluxes along demarcation lines to avoid difficulties with the relative magnitude of the DSMC scatter. National Research Council Associate. Member AJAA. E-mail: dhash@mail.arc.nasa.gov "Professor. Associate Fellow AIAA. Copyright © 1997 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Nomenclature c particle velocity er rotational energy per mass ev vibrational energy per mass E total energy flux Er rotational energy flux Ev vibrational energy flux h° heat of formation N number flux Pn normal momentum flux Pt tangential momentum flux Y mass fraction P reciprocal of the most probable thermal speed at equilibrium p density subscripts: 1 direction normal to interface 2 direction tangential to interface D DSMC NS Navier-Stokes s species value superscripts: ' thermal component average value

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