Comparison of Hexa-Structured and Hybrid-Unstructured Meshing Approaches for Numerical Prediction of the Flow Around Marine Propellers

In this paper we present a comparison between hexa-structured and hybrid-unstructured meshing approaches for the numerical prediction of the flow around marine propellers working in homogeneous flow (Open Water Conditions). The objective was to verify if the accuracy of the predictions based on structured meshes is significantly better than predictions based on hybrid meshes to justify the more difficult and time-consuming meshing strategy. The study was performed on two five-bladed propellers in model scale. Simulations were carried out with a commercial RANS solver, using a moving frame of reference approach and employing the SST (Shear Stress Transport) two equation turbulence model. Computational results from both meshing approaches were compared against experimental data. The thrust and torque coefficients were used as global quantities. Circumferentially averaged velocity components and root-mean square values of the turbulent velocity fluctuations, avaiable for one of the propellers, were used to indagate the local flow field. The computational results of global quantities for both meshing approaches were very close to each other and in line with experimental data. Also the local values of the flow were in line with the experimental data, exept for turbulent velocity fluctuations wich were underpredicted, especially in the case of the hybrid approach, where higher diffusivity was observed. The overall results suggest that for the prediction of the propulsive performances of marine propellers, at model scale, there are no significant differences, in term of accuracy, between structured and hybrid meshes but for a detailed study of the flow, the structured mesh seems to offer a better resolution.