Predictions are reported of the two-dimensional turbulent flow around a square cylinder with rounded corners at high Reynolds numbers. The effects of rounded corners have proved difficult to predict with conventional turbulence closures, and hence, the adoption in this study of a two-equation closure that has been specifically adapted to account for the interactions between the organized mean-flow motions due to vortex shedding and the random motions due to turbulence. The computations were performed using openfoam and were validated against the data from flows past cylinders with sharp corners. For the case of rounded corners, only the modified turbulence closure succeeded in capturing the consequences of the delayed flow separation manifested mainly in the reduction of the magnitude of the lift and drag forces relative to the sharp-edged case. These and other results presented here argue in favor of the use of the computationally more efficient unsteady Reynolds-averaged Navier-Stokes approach to this important class of flows provided that the effects of vortex shedding are properly accounted for in the turbulence closure.

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Computations were performed to determine the optimal conditions for the suppression of vortex shedding from circular cylinders at high Reynolds number by means of splitter plates. Previous studies of this mechanism for vortex-shedding control have largely been confined to two-dimensional flows at low Reynolds number, and to a single ratio of splitter plate width to cylinder diameter. In this study, we consider fully-turbulent, three-dimensional flows at high Reynolds number, and investigate the dependence of vortex-shedding suppression on two geometric parameters; namely the ratio of splitter-plate width and height to cylinder diameter and length. The computations were performed with the OpenFOAM software using a well-validated turbulence closure that considers the effects of the organized mean-flow unsteadiness on the random turbulent fluctuations. Comparisons were made with experimental data, and the validated method is used to perform a systematic study to determine the effectiveness of vortex suppression. To aid in the analysis, two-point correlations of forces along span of cylinder were obtained to determine uncoupling conditions of sectional oscillations. The results obtained indicate that splitter plates provide a practical method for vortex suppression at high Reynolds number, and the degree of suppression can be maximized by optimal geometric configuration.

a b s t r a c tOpenFOAM is an open-source finite-volume solver in the public domain. In recent years, its use for fluidflow simulations has grown very rapidly due to its flexibility and extensive capabilities. However, to date, its application in ocean engineering has been very limited. The main purpose of this paper is to evaluate this tool for use in this field. Simulations were hence performed of the flow field around a full-scale Tension-Leg Platform (TLP) in steady current at high Reynolds number. Of particular interest was assessment of OpenFOAM's ability to accurately predict the unsteady hydrodynamic loads due to vortex shedding. Turbulence was accounted for using the k À ε model. It was found that this model, which remains the model of choice in engineering practice, fails badly in this respect. A modification that has been shown to improve this model's performance in flows with vortex shedding was then implemented into OpenFOAM and checked against two benchmark flows namely around a single cylinder and around two cylinders in tandem. Application of the modified solver to the TLP flow convincingly demonstrates the suitability of this open-source tool, when used with the appropriate turbulence closure, for use in applications of interest to the ocean engineering community.

The use of the Lattice Boltzmann Method (LBM) for fluid-flow simulation has been the subject of several recent studies where it was reported that the method offers many advantages such as high accuracy coupled with computational efficiency. In this paper, we report on the use of this method, in conjunction with Large-Eddy Simulations, to study an interesting phenomenon related to the suppression of vortex shedding from circular cylinders. Specifically, it has been observed in experiments that vortex shedding from a cylinder can be drastically reduced by the injection of a fluid jet into the approach flow. We first present results for a cylinder without jet injection in order to quantify the suitability of the LBM for use in such flows. Thereafter, we present results for the case with jet injection where we consider the case where Re = 55,440. Preliminary results conclusively demonstrate that the presence of jet injection does indeed lead to substantial reduction in the magnitude of lift forces on the cylinder. This strongly argues in favor of further research to understand the dynamics of this phenomenon, and the range of parameters needed to maximize its beneficial effects.