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Turbulence and Shear Flow Phenomena -1 First International Symposium

ISBN Imprimer: 1-56700-135-1

LARGE EDDY SIMULATION OF SEPARATED FLOW OVER A BLUFF PLATE

Résumé

The turbulent separated-reattaching flow over a bluff plate is investigated using the large-eddy simulation approach. The simulations were performed at a Reynolds number ( Ud/ν) of 50,000 and a blockage ratio of 5.7%. Three subgrid-scale models were used: structure function, selective structure function and Smagorinsky models. The performance of these models was examined by comparing the mean flow statistics and the dynamics of the flow with experimental observations. With both structure-function and Smagorinsky models, the break-up and three dimensionalization of the separated shear layer are delayed. The dynamics of the reattaching flow is altered by the persistence of small-scale structures in the Smagorinsky model simulation, while excessive subgrid-scale dissipation is evident in the structure-function simulation. Both models yield deficient mean flow structures and turbulence statistics. The selective version of the structure function model, which allows a localization of the subgrid-scale contribution, produces separated shear layer instabilities, dynamical patterns, and structure which are physically consistent with flow visualization. The mean flow and turbulent statistics obtained with the model are also found to be in excellent agreement with measurements. A preliminary wavelet analysis of the simulations reveals the persistence of scales associated with shear-layer flapping and the intermittent nature of the pseudo-periodic shedding of vortices in the reattachment region.
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