Berkeley Fluids Seminar

January 27, 2014

Lauren Goodfriend (Civil and Environmental Engineering, UC Berkeley)

Improving large-eddy simulation on grids with refinement interfaces using explicit filtering and reconstruction

Many realistic flows, such as the urban boundary layer, are too expensive to simulate directly. Large-eddy simulation (LES) and adaptive mesh refinement (AMR) reduce the computational cost of turbulence modeling by restricting resolved length scales, but combining these techniques generates additional errors. The grid refinement interfaces in AMR grids can reflect resolved energy and create interpolation errors. This talk will explore the use of explicit filtering and reconstruction to mitigate grid interface errors in LES. I will present three case studies: decaying isotropic turbulence, half-channel, and flow around a wall mounted cube. In all cases the domain is split into two structured grids, one fine and one coarse. These simple test cases allow observation of the effects of the grid interfaces. Explicit filtering is found to reduce accumulation of resolved energy at the fine-to-coarse interface and improve the shape of coherent structures, compared to basic LES. Reconstruction of the subfilter velocity is shown to further the improvements of explicit filtering. These results inform the use of LES on block-structured non-uniform grids, such as nested grids in local atmospheric models or on more complex Cartesian AMR grids.

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Acknowledgments

Prof. Graham Fleming (Vice Chancellor for Research, UC Berkeley)

Prof. Eliot Quataert on behalf of The Theoretical Astrophysics Center and the Astronomy Department (UC Berkeley)

Prof. Philip S. Marcus on behalf of the Mechanical Engineering Department (UC Berkeley)

Prof. Michael Manga (Earth and Planetary Science, UC Berkeley)

Prof. Evan Variano (Civil and Environmental Engineering, UC Berkeley)