Approved for public release; distribution unlimited. 1 Rotational and Vibrational Nonequilibrium in a Low Diffusion Particle Method for Continuum Flow Simulation

A low diffusion particle method for simulating compressible low Knudsen number gas flows is modified for application to flows involving nonequilibrium distributions in rotational and vibrational energy modes. This method is closely based on the direct simulation Monte Carlo (DSMC) method, and has been developed for use in a strongly coupled hybrid scheme with DSMC. In simulations employing this hybrid scheme, the proposed modifications allow greater consistency with DSMC and reduced information loss along continuum breakdown boundaries when significant internal energy nonequilibrium effects exist within continuum flow regions. Two different approaches for rotational and vibrational nonequilibrium are proposed; the first provides greater efficiency and reduced sensitivity to time step size, while the second utilizes standard DSMC energy exchange procedures and should be easier to implement in an existing DSMC code. Both approaches are evaluated through comparison with DSMC for a set of homogeneous relaxation problems, and capabilities of the hybrid scheme are demonstrated in simulations of a hypersonic flow over a cylinder. I