Large Eddy Simulation of Expansion Wave Diffraction
A computational analysis of expansion wave diffraction was conducted using a large eddy simulation solver. The investigation was aimed at resolving particular flow features following a diffracting expansion wave which were previously identified experimentally through shadowgraph imaging but unresolved in the accompanying RANS computational analysis. The features included large-scale turbulent structures within the separation bubble at the apex, a large wake region downstream of the bubble, shear layer instability and vortex shedding. The analysis was made feasible by combining the embedded LES and wall-modelled LES hybrid RANS-LES techniques in ANSYS Fluent. The larger-scale turbulence within the separation bubble was resolved, and vortex shedding was identified in the LES solution. Evidence of the wake region was noted but remained largely unresolved due to the relatively small-scale turbulent motion. An oblique shock, found towards the rear end of the separation bubble, resolved at higher initial diaphragm pressure ratios (PR > 9) in the RANS analysis, was observed from PR = 7.7 in the LES analysis. A strong indication of this shock was seen in the shadowgraph images for PR = 7.7.