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

Abstract

Abstract The turbulent separated-reattaching flow over a bluff rectangular plate is investigated using the large-eddy simulation (LES) technique. Simulations are presented for a Reynolds number (Red) of 50,000 and a blockage ratio (Br) of 5.6%. Three subgrid-scale models are used: structure function, selective structure function and Smagorinsky models. The performance of these models is examined by comparing the mean flow and turbulence 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 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 identification techniques based on the vorticity modulus |ω| and the eigenvalue λ2 of the tensor S ik S kj +Ω ik Ω kj , horseshoe vortices hypothesized in earlier experimental work are clearly identified in the reattachment region. Wavelet signal analysis 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.