The Macroscopic Chemistry Method in the Direct Simulation Monte-Carlo (DSMC) method for rarefed flows

摘要

The Macroscopic Chemistry Method is a new DSMC approach to the calculation of chemical reactions in rarefied flows. MCM uses all the information available in a DSMC computation, to model the chemical reactions. It de-couples the reaction events (the replacement of simulator particles representing one species with particles representing a different species) from the collision calculations. The reaction rate is derived from the theoretical equilibrium reaction rate, consistent with the mean energy (temperature) of all the simulator particles in a cell, and is adjusted to account for the actual number of sufficiently high energy collisions which actually occur, as the result of the non-equilibrium distribution of molecular velocities. Multi-temperature reaction rates (emph{e.g.} Parku27s model which accounts for vibrational-dissociation coupling) are easily simulated. Unlike the standard total collision energy TCE method (a collision based chemistry procedure) the MCM is not restricted to a particular approximate scattering model (the VHS model) - on the contrary, any more realistic scattering law (and hence more realistic viscosity law) can be used with MCM. MCM is generally as quick or slightly quicker than standard TCE in steady flow simulations. MCM has been tested in unsteady simulations, but not compared yet for computational efficiency with TCE, in that case. Because MCM can use any viscosity law, and virtually any chemical reaction scheme used in a continuum CFD code it is much better suited for use in hybrid DSMC/continuum solvers than the TCE method.