Large Eddy Simulation of Ducted Propeller Tip Vortex Interactions with Application to Cavitation Inception*

Large-Eddy Simulation (LES) is performed to study the tip vortex flow in a ducted marine propulsor geometry replicating the experiments of Chesnakas and Jessup (ASME FEDSM 2003) and Oweis et al. (J. Fluids. Eng. 2006). Inception of cavitation in these marine propulsion systems is closely tied to the unsteady interactions between multiple vortices in the tip region. LES is used to shed insight into the structure of the tip vortex flow across a range of operating conditions. Simulation results are able to predict propeller loads within experimental scatter and show agreement with LDV measurements of the mean flow in the blade wake at design advance ratio, J = 0.98.

Results show the pressure differential across the blade produces a primary leakage vortex which separates off the suction side blade tip upstream of the trailing edge. The separation sheet aft of the primary vortex separation point is shown to produce a complex arrangement of unsteady vortices co- and counter-rotating with the primary vortex. Separation sheet vortices oriented parallel to the leakage flow are seen to produce instantaneous low-pressure regions wrapping helically around the primary vortex core. The rollup of the leakage flow duct boundary layer behind the trailing edge is also seen to produce counter-rotating vortices which interact with the primary leakage vortex further downstream. Likely cavitation inception locations predicted by the LES are examined through statistics of instantaneous low pressure events below the minimum mean pressure.