Dissertation/Thesis Abstract

Large eddy simulation of crashback in marine propellers
by Vysohlid, Martin, Ph.D., University of Minnesota, 2007, 93; 3266766
Abstract (Summary)

Crashback is an important mode of operation of marine propellers, which affects maneuverability and often determines the requirements on strength of propeller blades. This work uses the large eddy simulation approach to predict and understand the unsteady flow in crashback. In a broader sense this work demonstrates the suitability of large eddy simulation to compute highly separated, complex external flows at high Reynolds numbers.

A non-dissipative, robust numerical algorithm developed by Mahesh et al. (2004, J. Comput. Phys., 197:215{240) for unstructured grids was extended to perform large eddy simulation in rotating frame of reference, and applied to flow around a marine propeller. First, flow in forward mode was computed and agreement with experiment was observed in propeller thrust and torque. Then the flow in crashback was computed and good agreement with experiment in mean value, standard deviation and power spectral density of thrust, torque and side-forces, as well as in circumferentially averaged mean velocity and turbulent kinetic energy was obtained. The dependence of unsteady performance of propeller on advance ratio was also investigated and good agreement was obtained, except for magnitude of side-forces at the lowest absolute value of advance ratio. It was shown that this disagreement was due to the effect of water tunnel geometry.

The crashback simulation shows the presence of highly unsteady, irregular recirculation region, called propeller ring vortex. The results suggest that this region be viewed as a system of several interacting vortices, and not as a single coherent ring vortex. The dynamics of the propeller ring vortex were examined, and related to the unsteady loads experienced by the propeller. A new feature of the flow was identified—spiral shape blade-root vortices, originating at the hub near the roots of the blades. Their evolution and effect on blade pressure was described.

An unsteady actuator disk model was constructed and similar modes of operation as in propeller were observed. The mode similar to propeller crashback was investigated and correspondence between the fluctuations of thrust and the behavior of the ring vortex was observed. Similarities and differences between the disk model and the real propeller were examined.

Indexing (document details)
Advisor: Mahesh, Krishnan
Commitee: Longmire, Ellen K., Strykowski, Paul J.
School: University of Minnesota
Department: Aerospace Engineering
School Location: United States -- Minnesota
Source: DAI-B 68/05, Dissertation Abstracts International
Subjects: Ocean engineering
Keywords: Crashback, Large-eddy simulation, Maneuverability, Marine propellers, Propellers
Publication Number: 3266766
ISBN: 978-0-549-05334-7
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