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DIRECT NUMERICAL SIMULATIONS OF TURBULENT FLOWS GENERATED BY REGULAR AND FRACTAL GRIDS USING AN IMMERSED BOUNDARY METHOD

Sylvain Laizet
Turbulence, Mixing and Flow Control Group, Department of Aeronautics Imperial College London, London, SW7 2BY, United Kingdom

John Christos Vassilicos
Turbulence, Mixing and Flow Control Group, Department of Aeronautics Imperial College London, London SW7 2AZ, United Kingdom

Abstract

Two turbulent flows, one generated by a regular grid and the other by a fractal square grid are studied by means of Direct Numerical Simulations (DNS). An innovative approach which combines high order compact schemes, Immersed Boundary Method and an efficient domain decomposition method is used in this study. Turbulent statistics such as Reynolds stresses are investigated with the objective to analyse the two different regions (production and decay regions) downstream from the grid, as already observed in the experimental results of Hurst & Vassilicos (2007). The main goal of this numerical study is to identify the physical mechanisms implicated in the generation of turbulent flows, especially when generated at different scales, but also to compare the different levels of turbulence intensity generated by each grid.