ABSTRACT

Results of an installed marine propeller wake survey, performed by means of stereo-PIV and LDV techniques, are presented. Measurements were carried out in phase with the propeller angular position along a transversal section of the wake, located in the close vicinity of the blade trailing edge. Both the techniques allow a suitable reconstruction of the propeller wake features and of the strong and complex interactions between the propeller itself and the hull wake. The present work is mainly focused in pointing out the capability of the measurement techniques in resolving the propeller wake especially for the application of Stereo PIV.

INTRODUCTION

The accurate experimental investigation and assessment of the flow field downstream of an installed propeller plays a fundamental role in the naval field, where the propeller performances are largely dependent upon the upstream wake. Non-uniform inflow induces variable radial and angular fluid dynamic loads along the blade and hence thrust and torque distribution, which change during the revolution. These changes lead to propeller-induced vessel vibration, unsteady cavitation and noise generation. The increased complexity of the propeller blade geometry, due to the demanding requirements for reduced noise levels and for lower propeller-induced structural vibrations, enhances the interest in detailed measurements of the propeller flow field. Such measurements are useful to check the conformity with the design requirements, for instance by using the deduced blade section drag coefficients and bound circulation distribution as in Kobayashi (1982) and Jessup (1989), as well as to acquire information for a completely new design. Furthermore, the experimental investigation provides baselines to improve and integrate theoretical forecast and to develop and validate numerical codes. The occurrence of strong vortex structures, turbulent fluctuations, three dimensional boundary layer and marked velocity gradients (Hoshino & Oshima, 1987), puts rather strict requirements into the choice of the measurement technique.

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