Large-eddy simulation of compressible transitional boundary layer

Compressible large-eddy simulation (LES) is applied to the bypass transition of a compressible boundary layer over a flat plate. Simulated time-averaged and statistics flow properties and analyses of flowfields and flow spectra reasonably demonstrate that compressible LES with the adequate grid resolution and numerical scheme ensures qualitative discussions for the compressible transitional turbulent flowfields. The interactions of relatively large-scale coherent structures, such as backward flow streaks, pair of clockwise and counter-clockwise rotating longitudinal vortices and hairpin vortices play key roles in determining the behavior of the transition. Grid resolution and numerical scheme which can directly resolve the large-scale coherent structures are required for LES to properly simulate the physics of the bypass transition. Much finer grid resolution than that required to resolve the large-scale coherent structures is required to resolve the small structures at the latter part of the transitional zone. However, when the large-scale coherent structures are adequately resolved, the underresolution of the small structures has little influences to the results.