Numerical research on the instabilities of CLT propeller wake

Optimising contracted and load tip (CLT) propellers has proven difficult due to the lack of research on flow fields. In this study, the hydrodynamics and wake of the P1727 propeller, a CLT propeller, are investigated using large eddy simulation for three advance coefficients. Fluctuations in the thrust and torque are minimal, with a frequency of up to 1000 Hz, as indicated by the simulations, which are verified based on experimental data and study on spatial and temporal convergences. Instantaneous, phase-averaged, and azimuthal-averaged flow fields are used to analyse propeller wake, including the tip vortices of endplate, secondary tip vortices, merged and trailing sheet vortices and the hub vortex. Based on previous works, we present a novel mutual inductance mechanism for the instabilities in CLT propeller wake. The merged vortices formed by merging between the tip vortices of endplate and the secondary tip vortices are strengthened, stretched by the outer trailing vortices that are caused by the crack of trailing sheet vortices, then the reinforced merged vortices trigger the leapfrogging phenomenon and induce the outer instabilities. While the inner trailing vortices, or root vortices, remain coherent, they undergo contraction and approach the hub vortex. Thereafter, they intertwine with the spiraling hub vortex, acting as the dominant mutual inductance mode of the inner CLT propeller wake.