Propeller wake instabilities under turbulent-inflow conditions

The wake instabilities of a propeller operating under turbulent-inflow conditions were studied by the improved delayed detached eddy simulation method on an unstructured mesh consisting of almost 82.5 × 106 cells, capturing propeller wakes extending to the downstream distance of 9D (where D is the propeller diameter). Two turbulent-inflow cases with the turbulence intensity of 5% and 20% were considered. The mean loads and phase-averaged flow field show good agreement with experiments. As the propeller blade interacts with the turbulent inflow, a wide peak extending approximately ±10 Hz in the power spectral density of the time histories of the thrust and torque coefficient. Simulation results reveal wake instability mechanisms of the propeller operating under different turbulent-inflow conditions. The turbulence added to the inlet boundary interacts with the tip vortices, which accelerates the destabilization processes of the tip vortex system from two aspects. First, the interaction between the inflow turbulence and the tip vortex promotes the diffusion of tip vortices. Second, the interaction between the inflow turbulence and the tip vortices magnifies the instability motion of the tip vortex. The wake vortex system of the high-turbulence inflow condition loses its stability after 2.2D downstream, while the initial instability behaviors for the low-turbulence inflow condition are observed at the location of 3.4D downstream. The present study presents a deeper insight into the flow physics driving the tip vortex pairing process for a propeller operating under turbulent-inflow conditions.