The wake of a five-bladed marine propeller at design operating condition is studied using large eddy simulation (LES). The mean loads and phase-averaged flow field show good agreement with experiments. Phase-averaged and azimuthal-averaged flow fields are analysed in detail to examine the mechanisms of wake instability. The propeller wake consisting of tip and hub vortices undergoes streamtube contraction, which is followed by the onset of instabilities as evident from the oscillations of the tip vortices. Simulation results reveal a mutual-induction mechanism of instability where, instead of the tip vortices interacting among themselves, they interact with the smaller vortices generated by the roll-up of the blade trailing edge wake in the near wake. It is argued that although the mutual-inductance mode is the dominant mode of instability in propellers, the actual mechanism depends on the propeller geometry and the operating conditions. The axial evolution of the propeller wake from near to far field is discussed. Once the propeller wake becomes unstable, the coherent vortical structures break up and evolve into the far wake, composed of a fluid mass swirling around an oscillating hub vortex. The hub vortex remains coherent over the length of the computational domain.
Bibliographical noteFunding Information:
This work was supported by the United States Office of Naval Research (ONR) under ONR grant N000141410289, with Dr K.-H. Kim as technical monitor. The computations were made possible through the computing resources provided by the US Army Engineer Research and Development Center (ERDC) in Vicksburg, Mississippi on the Cray XE6, Copper and Garnet of the High Performance Computing Modernization Program (HPCMP). The authors also acknowledge the Minnesota Supercomputing Institute (MSI) at the University of Minnesota for providing resources that contributed to the research reported in this paper. We are grateful to Dr P. Chang and Dr M. Marquardt at Naval Surface Warfare Center Carderock Division (NSWCCD) for providing us with experimental PIV data used for validation purposes.
- Turbulence simulation
- vortex interactions