Propeller crashback

Office of Naval Research          Graduate Student: Martin Vysohlid

 

                   

Propeller crashback refers to the sudden reversal of rotation by marine propellers. This maneuver is performed under emergency conditions, and results in large fluctuating forces that affect required propeller blade strength and maneuverability. Simulation methods that are adequate for propellers under design conditions are unable to predict crashback, and yield errors as high as 110% in the thrust and torque coefficients. Also, these computations do not reproduce unsteadiness in the blade forces as observed by experiments. We are performing three-dimensional, unsteady simulations of a marine propeller in crashback. Preliminary simulations show low frequency unsteadiness similar to that observed by experiment, and torque and thrust coefficients that are substantially closer to experimental values. More detailed simulations are in progress. This project demonstrates the potential of our simulation methodology to predict off-design conditions in marine environments. The figures show contours of axial velocity from the simulations. Note the ring-vortex and regions of reverse flow.

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