Abstract:

The large eddy simulation (LES) technique for turbulent flows have become a standard tool of academic research, but has yet to really make an impact on the engineering design and analysis process in more applied situations. The talk will identify a range of reasons for this situation, and will describe recent work towards solving two of the main obstacles: the need for robust and accurate wall-models in LES, and the need for a solution-driven approach to grid-adaptation in LES.

The proposed approach to wall-modeling is based on the multi-scale nature of turbulent boundary layers and on the need for showing grid-convergence in numerical simulations. These considerations naturally lead to a number of criteria on wall-modeled LES, and a simple method that satisfies these criteria is presented. This is then shown to lead to excellent accuracy on a number of test cases, including supersonic boundary layers and shock/boundary-layer interactions. A simple method that enables predictions of laminar-to-turbulence transition is presented and tested on a boundary layer and a multi-element airfoil at flight Reynolds number.

The talk will end by discussing a proposed approach to automatically find a near-optimal grid in LES of wall-bounded flows. A directional error indicator is introduced, which measures the level of kinetic energy at scales near the grid-spacing in a directional manner; this then enables the grid to be adapted to resolve the turbulence in a more balanced way. The method is tested on turbulent channel flows with very reasonable results.

Biosketch:

Johan Larsson is an Assistant Professor at the University of Maryland where he works on multiple problems in the field of computational turbulence, including shock/turbulence interaction, wall-modeling for large eddy simulation at very high Reynolds numbers, turbulent combustion, grid-adaptation for turbulence simulations, and uncertainty quantification for turbulence problems.
He earned his PhD at the University of Waterloo, Canada, in 2006, and then worked at the Center for Turbulence Research at Stanford University as a postdoctoral fellow and Research Associate for 6 years before joining the University of Maryland in 2012.