Identification of coherent flow structures and experimental analysis of the hydroacoustic emission of a hubless propeller

Abstract

The progress in drive technology and the increasing needs for compact ship propulsion systems has brought a new class of hubless propellers into the field of operation. So far, no detailed analyses have been done concerning the unsteady flow structures which are important for the hydroacoustic emission. The objective of this paper is to analyze the unsteady flow topology and the related hydroacoustic emission of a hubless propeller with numerical and experimental methods. In order to capture the unsteady wake flow structures, a stress-blended eddy simulation (SBES) has been done. Experimental investigations in a circulating water channel provided the validation data in terms of integral quantities like thrust, wall pressure fluctuation and the hydroacoustic noise emission. The wake flow can be characterized by a multi-helix vortex system which develops from the blade root and tip region as well as from the trailing edge. The transition length of the helixes is larger compared to hub propellers in conjunction with an accelerated dissipation. The application of the proper orthogonal decomposition (POD) onto the unsteady wall pressure fields obtained from the SBES simulation was capable to assign different flow structures to the measured hydroacoustic emissions.