Simulation of hypersonic flows using a particle-based ellipsoidal statistical Bhatnagar-Gross-Krook method

To reduce the computational costs related to direct simulation Monte Carlo (DSMC) computations for low Knudsen number flows, a new par-ticle method, based on the ES-BGK model of the Boltzmann equation, is investigated. In this method, a fraction of the computational particles in a cell is selected for velocity reassignment from the local Max wellian distribution based the local collision frequency and an even smaller fractionis selected for internal mode energy reassignment based the rotational and vibrational relaxation rates. A scaling algorithm is used to decrease there quired number of particles per cell and to guarantee that the energy and momentum are conserved in each time step. The accuracy and efficiency of the ES-BGK method are tested in three different test cases and the results are compared to the DSMC solution and experiment as well. The ES-BGK approach is found to provide good agreement with DSMC solutions how-ever a factor of two speed up compared to DSMC is only achieved when the collisions frequency is sufficiently high.