Flow analysis, design and testing of ducted propellers

This paper addresses the design and the testing of ducted propellers and illustrates how flow analysis can be used as a support. After a review of the working principles of a ducted propeller system by referring to well-known theoretical analyses, it describes developments in computational methods. In particular a numerical code simulating the viscous flow around a ducted propeller system in open water shows promising results. Since propellers in ducts are designed as quasi-open propellers, the estimation of the effective advance speed, influenced by the velocity field induced by the duct, is an important aspect. New estimates for dividing the induced flow field into a propeller and a duct contribution are given, which lead to better correspondence with experimental information. Polynomials describing the performance of the B-4-70 propeller in nozzle 19A are also provided, in addition to an empirical relation for the virtual pitch of the Ka-series propellers. Model testing of ducted propellers is evaluated against numerical simulation tools. It is concluded that, in spite of rapid developments in computational fluid dynamics, the propulsive performance of ducted propellers can still most accurately be assessed by model tests.