Hybrid particle-particle numerical algorithm for high speed non-equilibrium flows

A new hybrid kinetic particle-particle numerical method is presented that combines the Direct Simulation Monte Carlo (DSMC) method and Collision Limiter (CL) method to simulate high-speed non-equilibrium flows. To this end, a 2D parallel multi-species hybrid solver is developed based on kinetic particle based the DSMC and Collision Limiter methods. The hybrid particle-particle solver can solve non-equilibrium multi-scale flows with length scales ranging from continuum to rarefied. The present hybrid solver uses the cell-based Knudsen number and Kolmogorov-Smirnov statistical test as continuum breakdown parameters. Based on the continuum breakdown parameter, DSMC is utilized where non-equilibrium flow regions are encountered, while the Collision Limiter approach is used where flow regions are found to be in near-equilibrium state. The Collision Limiter scheme employs less number of collisions per cell at every time step. The hypersonic flow of nitrogen flow over an aerospike and supersonic flow of argon through a micronozzle are simulated in the present work and results are compared with the regular DSMC method. A good agreement is achieved between the DSMC and the hybrid DSMC-CL method, with significant savings in the computational cost.