INFLUENCE OF GRID DENSITY AND ROTATION MODEL ON PROPELLER OPEN WATER CFD SIMULATION AND UNCERTAINTY

Abstract

To investigate and quantify the effect of grids as well as different numerical models on the propeller open water simulation results and to evaluate the confidence level of the simulation results, numerical simulation of open water and uncertainty assessment are necessary. The propeller open water performance was calculated using the SST <i>k-ω</i> method with MRF (Multiple Reference Frames) and SM (Sliding Mesh) models under different grid densities. Following ITTC (International Towing Tank Conference) (2021) procedures, CFD (Computational Fluid Dynamics) uncertainty evaluation and flow field analysis of the numerical models were carried out. The principles of the "verification" and "validation" steps were introduced. Three grids of different densities were numerically simulated to obtain the thrust coefficient <i>K</i><sub>T</sub>, torque coefficient <i>K</i><sub>Q</sub> and open water efficiency η at different advance coefficient, J. CFD calculation result uncertainty analysis was implemented. Comparisons were made of near-wall Y+ distribution, wakefield, velocity distribution, and surface pressure distribution at <i>J</i>=0.6. Results show that: 1) the trends of the three grids' results were consistent, and the SM model was more sensitive to grids, but its converged results were closer to the true value; 2) near-wall Y+ distribution, wakefield and velocity distribution showed noticeable differences due to grid discrepancies, while pressure distributions were approximate. Calculation results monotonically converged in "verification" and were validated in "validation". Thus, calculation results meet application requirements and model settings can provide an engineering reference.