| An anisotropic turbulence model, ASM model, is implemented in CFDSHIPIOWA, which can predict the normal Reynolds stress anisotropy as well as shear Reynolds stress anisotropy. The model is first tested against benchmark cases and then applied to flows around ideal and practical geometries. For ideal geometries, the effects of free surface and external potential flow pressure gradients can be predicted individually by using the free surface condition and a symmetry boundary condition respectively. It was not impossible to predict both effects simultaneously. For practical ship hulls of KRISO tanker KVLCC2 and US navy combatant DTMB 5415, the simulation results using the new model show good agreement with the corresponding EFD results and significant improvements over the results for the isotropic models in terms of the hook-shaped axial velocity contours, cross plane velocity vectors, and the velocity profile for a horizontal line through the propeller plane. They are also as good as the best results in the context of the ship hydrodynamics workshops, typically obtained using the full Reynolds stress model. The ASM model is then extended to ASM/DES model, which combine the advantages of both models, i.e., it can predict the normal Reynolds stress anisotropy in the region close to the walls and predict more details in the LES region far away from the walls. The oblique motion of KVLCC2M with three drift angles is simulated using the ASM/DES model, which represents three regimes of the ship flow: steady flow, unsteady vortical flow, and unsteady deadwater type flow. Besides the shear layer and Karman like instabilities, the dominating frequency associated with the unsteady mode of oscillation of the aft-body bilge vortex is determined. With both resolved and modeled Reynolds stresses, the turbulent kinetic energy budget are given for the two large drift angles. |
