The numerical analysis of turbulent flow around off-shore structures
This study provides the physical, mathematical and numerical basis of analysis work performed for predicting the flow around three-dimensional bluff body configurations. The flow has been treated as steady, incompressible, turbulent. The predictions were made using a two-equation turbulence model, solving transport equations for turbulence kinetic energy K and the turbulence dissipation rate ε, in addition to the partial differential equations for the conservation of mass and momentum. The program used was the well tested computer code "PHOENICS-84" based on work conducted by Prof. D.B. Spalding and Co-workers. Several computations have been performed, for three models: a single cube, a pair of cubes with different spacing, and a rudimentary representation of an offshore oil platform stucture. The prediction procedure was first tested for grid refinement and optimum solution domain size until profiles at several locations for selected variables showed little change with further increase of domain size and grid points. The effect of different wind directions was investigated for the three models; in addition, different pitching conditions of the oncoming flow were also considered for the platform-model configurations. Comparisons were made with wind tunnel test results on the same three models, and some discrepancies are noted, particularly in regions of separated, recirculating flow. Also comparisons were made with certain empirical calculation procedures used for wind load estimation in maritime engineering. Overall wind loading is nevertheless reasonably well predicted. Applications of the method in the area of wind loadings on a full scale offshore oil rig is discussed, and plans for refinement and extension of the present work are outlined. It is concluded that the present method can be used as a suitable starting point for generating a platform aerodynamics simulator. However, more work is required to this end, in order to represent adequately all aspects of platform-aerodynamics phenomena.