Unstructured LES_DNS of a Turbulent Boundary Layer over a Gaussian Bump


Wall-resolved large eddy simulation (WRLES) is often thought to have mesh resolution requirements that grow at the same asymptotic rate as direct numerical simulation (DNS), but WRLES actually does grow slower than DNS, even if the near-wall region is resolved to DNS resolution. In this paper, a new simulation concept dubbed LESDNS is undertaken, where the near-wall and inflow resolution of a WRLES is taken down to DNS levels. The primary advantage of this approach is that it removes the need for sub-grid models in the highly-anisotropic near-wall region, where they are the least mature. When combined with the use of unstructured grids that coarsen in all three directions outside of this near-wall region, significantly higher Reynolds numbers may be simulated for wall-bounded flows relative to traditional DNS. In this work, LESDNS is applied to the zero pressure gradient flat plate boundary layer and Gaussian bump problems. The new concept was found to be effective for both cases tested. In particular, LESDNS of the Gaussian bump was able to closely match DNS results at a fraction of the cost despite the complex physics involved with the problem. It is found that the new concept is effectively able to provide the sub-grid stress model with a "perfect wall model". Because of this "perfect wall model", deficiencies in the standard dynamic sub-grid stress model were identified in the outer region of the boundary layer in the Gaussian bump case.

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