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Comparison of Large Eddy Simulation, Detached Eddy Simulation and Unsteady RANS Numerical Predictions of Flow Past a Bottom River Cavity

Author(s): Kyoungsik Chang; George Constantinescu; Seung-O Park

Linked Author(s): George Constantinescu

Keywords: No Keywords

Abstract: The three-dimensional incompressible flow past a rectangular two-dimensional (2D) shallow cavity in a straight channel is investigated using Large Eddy Simulation (LES), Detached Eddy Simulation (DES) and Unsteady RANS (URANS). This problem is relevant for studying the flow processes encountered in flow past cavity-like geometries present on the bottom of rivers or lakes. The interest in DES is motivated by the fact that it is computationally less expensive than LES and can be used for predictions at much higher Reynolds numbers, closer to the ones encountered in rivers. The aspect ratio (length/depth) of the cavity is L/D=2 and the Reynolds number defined with the cavity depth and the mean velocity in the upstream channel is 3, 360. The flow past the cavity is strongly dependent on the inflow conditions. For instance, highly resolved LES simulations show the presence of large scale quasi-regular shedding of large spanwise roller structures in the case where the thickness of the incoming boundary layer is relatively small. However, these coherent structures are absent in the case in which the incoming flow is fully turbulent and the incoming thickness of the boundary layer is large. Using experimental measurements and the data from LES, the capabilities of SA and SST based DES and URANS to predict the mean flow and turbulent kinetic energy (TKE) are investigated. In particular, the effect of presence of turbulent fluctuations in the incoming flow on the accuracy of the DES and URANS predictions is studied. The presence of inflow fluctuations in DES is found to break the large coherence of the vortices shed in the separated shear layer present in the DES simulations with steady (fully turbulent) inflow conditions and to generate a wider range of threedimensional eddies inside the cavity, similar to LES. The predictions of the mean velocity profiles from URANS and DES are found to be close. However, URANS predictions show poorer agreement with LES and experiment compared to DES for the TKE


Year: 2007

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