# Opimization of a Multi-Component Propulsor

##### Background

Fast ships require efficient propulsors with low sensitivity to cavitation within their operation range. Between the usual operational velocities of conventional propellers and waterjet propulsors there is a certain range, where Multi-Component Propulsors appear to be advantageous.

The Multi-Component Propulsor regarded in this project consists of four components: rotor, hub, duct and stator, see figure 1. Aim of this project is the development of an optimisation based design-procedure for such a propulsor.

##### Approach

The duct is used to achieve a higher pressure level at the rotor-position in order to reduce the cavitation risk. Compared with the conventional propeller, the duct reduces the strength of the tip vortex and the stator helps to recover swirl energy from the rotor flow.

The geometry description as well as the interactions among the single components of the propulsor are quite complex. At the same time many design objectives have to be considered. First of all the propulsor has to fulfill thrust requirement at a certain number of revolutions. Moreover, the efficiency has to be maximized and the cavitation level to be minimized.

An appropriate technique for the design was developed which is able to consider all these demands, see figure 2. It uses a parameterized geometry description of the propulsor and automatic meshing tools. Furthermore, for the calculation of the velocity and pressure distribution at the different components of the propulsor two numerical codes are employed. The first one is an in-house developed potential flow method based on a first-order 3D-panel method. Figure 3 shows the pressure distribution calculated with potential flow theory for one geometry of the propulsor during early optimisation stage. The ANSYS-CFX code is applied to calculate the viscous flow on the propulsor. The pressure distribution on a generated geometry of the propulsor during the final optimisation stage is shown in figure 4.

The design method is coupled with an evolutionary optimisation algorithm, which was developed at the Chair of Algorithm Engineering, Department of Computer Science of the Technical University of Dortmund.

The optimised geometry of the propulsor was investigated experimentally at the Potsdam Model Basin (SVA Potsdam). Open water and cavitation tests were carried out. Figure 5 and 6 show the test model of the developed propulsor and its open water performance. The experimental data confirm that the applied numerical method provides reliable results and is suited to generate an optimized propulsor.

From the hydrodynamic point of view Multi-Component Propulsors may achieve a higher efficiency than conventional propellers at a certain speed range. According to model test results and viscous flow calculations for the full-scale case, the efficiency of an optimised geometry with good cavitation behavior can reach 73 %. In addition to that, the installation of the duct can be an advantage for ships working in extremely shallow water because the duct protects the propeller in grounding case. Another advantage of the employing of the duct is reduction of the hydro-acoustic impact on the environment.

##### Publications

Steden, M., Hundemer, J., Abdel-Maksoud, M.

Optimisation of a Linearjet

First International Symposium on Marine Propulsors, Trondheim, Norway, 2009

Steden, M., Hundemer, J., Müller, S.-B., Abdel-Maksoud, M.

Geometrische Parametrisierung und Untersuchung der Umströmung von aus Mehrkomponenten bestehenden Schiffsantrieben

102. Hauptversammlung der Schiffbautechnischen Gesellschaft, Berlin, 2007

Abdel-Maksoud, M., Steden, M., Hundemer, J.

Design of a Multi-Component Propulsor

7th International Symposium on Cavitation, Ann Arbor, USA, 2009

Druckenbrod, M., Hundemer, J., Abdel-Maksoud, M., Steden, M.

Design of a Single- and Multi-Component Propulsors

COMPIT 2010, Gubbio, Italy, 2010

##### Personnel

Dipl.-Ing. Max Steden

Dipl.-Ing. Markus Druckenbrod

Dipl.-Ing. Jochen Hundemer

Prof. Dr.-Ing. Moustafa Abdel-Maksoud

##### Cooperation Partner

Prof. Dr. Günter Rudolph, Technical University of Dortmund, Department of Computer Science, Chair of Algorithm Engineering

##### Funding

German Research Foundation (DFG)