Species weighting scheme in direct simulation Monte Carlo applied to jet plume simulations

In the conventional Direct Simulation Monte Carlo (DSMC) method, large density variation among the flow species involves an enormous quantity of numerical particles representing the denser species to enable the simulation of the trace ones. In this work, a Species Weighting Scheme method is used to define different ratios between numerical and physical particles depending on the species they represent, and simulate both major and trace species accurately while reducing the computational time and the memory cost. Collision momentum, energy conservation, and flow transport properties, are verified by comparing them with conventional DSMC on one cell, Couette and Fourier flow simulations. The novelty of this study is to evaluate the influence of the species weight settings and the use of enhanced pair collision selection methods using academic and more complex cases involving nozzle free jet expansion and jet impingement into a conical surface. The Species Weighting Scheme shows excellent agreement with conventional DSMC for a major to trace species numerical particle ratio of 10 and deviation below this threshold. Furthermore, using enhanced pair collision selection allowed us to obtain accurate results even for low ratios down to 2 or 1, leading to a significant computational time reduction by a factor of 7.