Hypersonic turbulence wake modeling from rarefied to continuum regimes

Hypersonic flows over a cylinder are studied to investigate the unsteady characteristics of rarefied and continuum turbulent wake flows. To do this end, an open-source DSMC solver, SPARTA, is used to capture large gradients associated with shock expansion waves separation region interactions especially in the wake region. Conversely, continuum simulations are carried out using an open-source continuum non-equilibrium solver, SU2-NEMO, for relatively low-pressure rarefied nature of flows with a freestream pressure of up to 100 Pa. Comparisons were made using SPARTA and SU2-NEMO at moderately low freestream pressures of 100 Pa for NS and very good agreement is achieved using continuum and rarefied solvers, indicating that DSMC and continuum numerical parameters are accurately selected. Numerical probes are inserted at various locations to study the temporal and turbulence characteristics by performing ensemble averaging each time step of DSMC. Consistent with previous numerical studies, x-velocity, y-velocity, and cross-velocity fluctuations are mostly dominant in the wake, bow, and tail shock region. For higher pressure cases, temporal characteristics of residuals are reported to calculate the frequency of oscillations seen in the wake with various Reynolds numbers (Re). The frequency of oscillations is found to be in relatively good agreement with previous experimental measurements and tends to increase with Re.