Numerical study on the scale effects of two-dimensional cycloidal propellers

In this study, computational fluid dynamics (CFD) simulations were performed using commercial software StarCCM + to investigate the scale effect on the hydrodynamic performance of a single-blade cycloidal propeller.The Shear Stress Transport (SST) turbulence model was used to calculate the hydrodynamic coefficients, and a reasonable numerical scheme was determined based on the results of a convergence study with respect to the grid scale and time-step length of iterations. Accordingly, the hydrodynamic coefficients at different Reynolds numbers (Re) and scales were calculated, and the critical Reynolds number was determined. Both the distribution of vorticity and the dimensionless velocity at the vortex core were evaluated under different Re and it was found that the scale effect of cycloidal propeller differs markedly from that of conventional screw propellers. This difference leads to the invalidation of the scale effect formula recommended by the International Towing Tank Conference (ITTC). Thus, a new formula was developed based on extensive numerical simulations. The results of this study provide deeper insights into the fluid mechanism of cycloidal propeller, and can greatly accelerate their application.