Investigations of Transonic Flow over a Hemisphere using DES and hybrid RANS/LES Turbulence Models

This research effort addresses the use of numerical simulations to predict the flow physics over an airborne turret, represented by a hemisphere. Computational fluid dynamics codes, Loci-Chem, Kestrel and OVERFLOW were used in this study with different high fidelity turbulence models, including DES, DDES, D-MS and hybrid RANS/LES, to determine their capabilities of predicting these complex flow features. These numerical simulations were compared against the experiment conducted at Auburn University, in terms of wall-pressure data, instantaneous density contour images, and optical path difference (OPD). Among the three codes, Loci-Chem using the hybrid RANS/LES turbulence model was able to capture the unsteady flow structures, such as shear-layer fluctuations, and the rolling motions of the vortex shedding. Both Kestrel using DDES+SST and OVERFLOW using the DES, DDES, and D-MS turbulence models were able to predict certain levels of shear-layer oscillations; however the presence of the vortex motions behind the wake region were not fully captured. Therefore, the results from Kestrel and OVERFLOW predicted limited OPD values as compared to the experimental data. Since the solution from Loci-Chem was able to produce the vortex shedding, the OPD analysis was able to follow the most of the trends, except that under-predicted the vortex motion shown in the experiment.