Flow separation with reattachment is a phenomenon characterized by unsteadiness and complex turbulence that occurs in a large variety of environmental situations and engineering devices. Separated flows have been particularly challenging to predict using classical turbulence models which rely on time-averaging of the turbulent motion and its parameterization with semi-empirical models. In this paper we present two and three-dimensional time-dependent simulations using the Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS) techniques. The prototype separated-reattaching flow configuration considered is the flow over a bluff rectangular plate. Simulations are presented and discussed with a focus on the large scale dynamics and on the behaviour of the surface heat transfer coefficient-the parameter of prime interest in the design and optimization of heat transfer device. Unsteadiness and three-dimensionality are shown to play a central role in determining the structure of the thermal field and wall heat transfer rates. Simulations with long integration times are required to obtain reliable flow statistics.
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