Numerical Prediction of Unsteady Sheet Cavitation on Marine Propellers

摘要

This document describes the theory and numerical methods used in the propeller analysis program CAVITY for the prediction of periodic back sheet cavitation on marine propellers operating in a ship's wake. Sheet cavitation chordwise extents and thickness distributions can be predicted at up to 60 blade angular positions per revolution for a given propeller geometry, operating condition and ship wake inflow in the propeller rotation plane. The procedures used in CAVITY are based on lifting surface methods as an extension of the PUF-2 code for predicting both steady and unsteady propulsive performance characteristics of marine propellers. The original procedures for the prediction of back sheet cavitation are reviewed and some modifications concerning chordwise distributions of singularities and propeller wake modelling are described. These changes are incorporated to improve predictions of leading edge cavitation development as well as results obtained at off-design operating conditions. Numerical extents obtained with CAVITY are compared to available experimental data. Provided that representative ship wake data are used, the predictions to data for back sheet cavitation show good agreement with experimentally observed extents developing on thin blade sections.