Recent Developments in Computational Methods for the Analysis of Ducted Propellers in Open Water

Abstract

This article presents an overview of the recent developments at Instituto Superior Técnico and Maritime Research Institute Netherlands in applying computational methods for the hydrodynamic analysis of ducted propellers. The developments focus on the propeller performance prediction in open water conditions using boundary element methods and Reynolds-averaged Navier-Stokes solvers. The article starts with an estimation of the numerical errors involved in both methods. Then, the different viscous mechanisms involved in the ducted propeller flow are discussed and numerical procedures for the potential flow solution proposed. Finally, the numerical predictions are compared with experimental measurements. Ducted propellers have been widely used for marine applications. Nowadays, they may be found in tugs, trawlers, tankers, bulk ships, warships, and in dynamic positioning systems of offshore platforms or vessels. The duct may be classified as an accelerating or decelerating type. Accelerating ducts are often used to increase the efficiency and thrust of heavily loaded propellers. In the case of a decelerating duct, they are used to reduce the risk of cavitation and resulting noise. The complex interaction which occurs between the propeller and duct makes the hydrodynamic design of such systems a complicated task. For the selection of the numerical simulation tool, the designer has to choose between a simplified method that predicts the main features of the flow field around the ducted propeller, and a more complex tool that provides detailed information in problematic areas such as the gap region between propeller and duct inner surface. On the other hand, model tests in a towing tank or cavitation tunnel may be seen as an alternative, but they are usually expensive. Presently, the development of an accurate and cost-effective numerical method for the design and analysis of ducted propellers is still not complete.