Turbulent flow field and resulting noise induced by hub-less propellers
The underwater noise which is generated by ship propulsion systems becomes a more and more growing environmental problem nowadays. A new promising design concept for the reduction of emitted underwater noise is the usage of hub-less propellers in conjunction with an electrical ring drive. Detailed research with respect to this new propulsion system, especially in terms of the turbulent flow field in and behind a hub-less propeller and the resulting sound field, has not been carried out so far. Main focus of the proposed project will be the investigation of the overall topology of the wake flow, the transition and collapse of the tip vortices, the topology of the horseshoe vortices at the blade hub and the radiated hydro acoustic sound field. Time resolved stereo PIV experiments in the wake flow of a hub-less propellers and time synchronous measurements of the fluctuating surface pressure in combination with fully transient DES computations of the turbulent flow field will be core elements of the planned research work.For the numerical prediction of the hydro-acoustic pressure field a fourth order Expansion over Incompressible Flow (EIF) approach will be developed based on a finite volume formulation. The approach for the analysis of the experimental data, numerical data and for the identification of coherent flow structures will be the Proper Orthogonal Decomposition procedure (POD). Moreover it will be complemented with vortex core extraction methods. Due to the usage of the POD method, conclusions to the acoustics of different coherent flow structures will be possible for the first time. In the outlook of this project, first design rules for the reduction of hydro-acoustic sound emissions might be reasoned.