Large-eddy simulation of separated flow over a bluff rectangular plate

The turbulent separated-reattaching flow over a bluff rectangular plate is investigated using the large-eddy simulation (LES) technique. Simulations a re presented for a Reynolds number (Re-d) of 50,000 and a blockage ratio (B r) of 5.6%. Three subgrid-scale models are used: structure function, select ive structure function and Smagorinsky models. The performance of these mod els is examined by comparing the mean flow and turbulence statistics, and t he 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 Smagori nsky model simulation, while excessive subgrid-scale dissipation is evident in the structure function simulation. Both models yield deficient mean flo w structures and turbulence statistics. The selective version of the struct ure function model, which allows a localization of the subgrid-scale contri bution, produces separated shear layer instabilities, dynamical patterns, a nd structures which are physically consistent with flow visualization. The mean flow and turbulent statistics obtained with this model are also found to be in excellent agreement with measurements. Using structure identificat ion techniques based on the vorticity modulus /omega/ and the eigenvalue la mbda(2) Of the tensor SikSkj + Omega(ik)Omega(kj), horseshoe vortices hypot hesized in earlier experimental work are clearly identified in the reattach ment region. Wavelet signal analysis reveals the persistence of scales asso ciated with shear layer flapping and the intermittent nature of the pseudo- periodic shedding of vortices in the reattachment region. (C) 2000 Begell H ouse Inc. Published by Elsevier Science Inc. All rights reserved.