Numerical simulation of the dynamic stall of a freely rotating hydrofoil

Vortex shedding of freely rotating hydrofoils and the fluctuations in hydrodynamic loads are typical problems in marine engineering. Hence, the hydrodynamic mechanism should be investigated in detail. In this study, the Reynolds-averaged Navier-Stokes method is used to analyze the unsteady flow characteristics of a two-dimensional freely rotating hydrofoil in uniform flow at different Reynolds numbers. The accuracy of the numerical simulation method is verified through convergence analysis of the simulation results. According to the mechanical characteristics and flow field distributions, the effects of three Reynolds numbers from 5 x 10(4) to 1.2 x 10(6) and five rotation centers from 0.2c to 0.4c on the dynamic stall of the hydrofoil are analyzed. The results show that the rotation center considerably influences the dynamic stall characteristics of the hydrofoil. As the rotation center approaches 0.4c, the amplitudes of the drag and lift coefficients and the rotation angle of the hydrofoil clearly increase by at least 206%, 10.5%, and 185%, respectively, along with the vortex shedding frequency, which also leads to the increase in the Strouhal number by at least 17.3%. Furthermore, the recovery of the drag and lift coefficients is delayed, resulting in an evident hysteresis effect. Simultaneously, this dynamic stall results in the decrease in the velocity distribution amplitude in the wake field and the increase in the pressure difference between the upper and lower surfaces. The continuous shedding of strong vortices from the trailing edge also leads to more complicated flow field characteristics.