On the instability mechanisms of ship propeller wakes

This paper evaluates the propeller wake characteristics of the benchmark ship propeller INSEAN E779A using large eddy simulations and identifies instability mechanisms that lead to wake breakdown. The effects of propeller blade loading on wake stability are considered by conducting simulations at different advance coefficients (J = 0.85, J = 0.65 and J = 0.45). The hydrodynamic results capture the propeller wake vortical structures and flow features from the onset and evolution of the instability to the far wake. The simulation results are verified and validated against experimental measurements from the literature. A new instability mechanism concerning mutual interaction among adjacent helical vortex sheets in the transition region is identified. Further, the formation of short wave instabilities in the vortex filaments is found to be initiated by the same mutual interactions among sheets. Lastly, it is shown that interaction of sheets with the preceding tip vortex induces the onset of tip vortical filaments breakup, mutual-interaction and long wave instability.