OPTIMIZATION OF TWISTED RUDDER (With Bulb and Hub Cap)

This thesis has been carried out in close cooperation with the Fluid Engineering department of the DNV GL SE Maritime Advisory division in Hamburg. The main role of the Rudder consists not only on acting as a steering device and keep the ship on course, but also is a very signi cant energy recovery device when interacting with the wake from the propeller. Several studies have been performed in order to analyse the interaction effects between hull, rudder and propeller, assessing drag and manoeuvring characteristics from several geometries looking upon maximising the propulsive effciency. Twisted rudders in combination with rudder bulbs can improve propulsion effciency even by up to 4%. This master thesis consists in the implementation of a rudder optimization procedure with respect to overall propulsion effciency. More concretely a twisted rudder with costa bulb (and hub cap) evaluated utilizing a CFD process developed in the DNV GL SE facilities, coupling Reynolds-Averaged Navier-Stokes RANS method and Boundary Element method BEM. Solvers are the stationary OpenFOAM RANS simpleFoam and the unsteady BEM PROCAL. The use of this coupled method will reduce the computational time requirements compared to a fully RANS simulation. Thus the possibility of using an optimization routine (FS-Optmizer) to analyse different geometries for the Twisted Rudder, changing parameters in the CAD model created with CAESES Framework. The geometry is the Duisburg Test Case (DTC) which is a hull design of a typical 14000 TEU container ship in order to compare results to a real test case. A twisted rudder equipped with a Costa bulb is used, with a base symmetric pro le (NACA 0020 ); the twist goes from the top and bottom upon the bulb with a maximum angle of 15º along an axis located between 20% and 40% of the chord length. This document presents a flow work starting with the basic theoretical background, then a detailed description of the method, creation of the parametric model, mesh study followed by an initial non-twisted geometry assessment and in the end the optimization procedure description (for rudder and bulb), presenting final results, conclusions and recommendations