Björn Regnström

A Procedure for Optimizing Cavitating Propeller Blades in a Given Wake

Abstract The blade geometry of a cavitating propeller in a given wake is optimized to maximize propeller efficiency and minimize propeller induced pressure fluctuations. The Keller criterion, the cavity volume and other constraints are considered in the optimization process. Such constraints are cavity area, cavity length and face side pressure. These are switched on separately or simultaneously to investigate their influence on cavitation and efficiency. The optimization starts from a near optimum propeller as well as from an off-design propeller. Results indicate that the present optimization technique can yield higher efficiency and lower pressure amplitude with tolerable cavitation for a cavitating propeller in a given wake.

Numerical optimisation of propeller-hull configurations at full scale

Optimisation of propeller/hull configurations based on the Reynolds-Averaged Navier-Stokes (RANS) equations has been very rare so far due to the large computational effort required. Virtually no such optimisation has been carried out at full scale, where only a few RANS methods are at all applicable due to stability problems. The present paper introduces a newly developed RANS solver especially designed for stability and this solver is shown to work well at full scale. Through a link to a commonly used propeller analysis code, predictions of the viscous flow around the full scale ship with an operating propeller may be made. This is utilised in the work reported here, where the flow codes are introduced into a system for automatic optimisation. It is shown that even well designed propellers may be further improved, both in a fixed wake and in the wake behind a fixed hull.

Wake Survey of a Yacht Keel for CFD Validation and Flow Analysis

Abstract The wake behind an America’s Cup keel model is studied experimentally and numerically. A RANS code is validated against the data from wind tunnel tests with generally good agreement. The wake measurements are also used for analysing the flow case. Differences in the performance of design alternatives are explained by studying the wake. Force-estimates based on wake integration methods applied to the computed wake are proven to be equally or slightly less accurate than integration of surface forces. The drag force is decomposed by applying wake integration methods to the computed wake. The result is compared with the drag components computed with a potential flow/boundary layer code. The comparison points out the difference between vortex drag and induced drag. Finally, the measured wake is used to validate the lift distribution along the winglets computed with a RANS code and a potential flow code.