Development of an experimental device for a pod fitted with contra-rotating propellers

In present paper the development of a device for testing a pod fitted with contra-rotating propellers is presented. The device was realized in order to be mounted on the University of Genoa Cavitation Tunnel to investigate both global performances and cavitation phenomena. Although standard cavitation tunnels have in some cases the capability of testing contra-rotating propellers, the whole propulsive efficiency of the pod is rarely determined. This was one of the objectives of the developed device, designed in the framework of a research project in cooperation with Zf Marine, whose final aim is to develop a design procedure for contra-rotating propellers. One of the objectives of present study was the simplicity of the device, in order to minimise costs, searching for a compromise between testing accuracy and device complexity, as described in the paper. A first application of the testing equipment is then described, showing results obtained for a couple of propellers, which were tested alone and in contra-rotating configuration. Despite the practical problems which had to be overcome to keep the measuring system as simple as possible, results were rather satisfactory, allowing to measure usual propeller coefficients and to have an insight into the complex cavitating behaviour of this kind of propulsors.