Effect of Shaft Inclination on the Flow Field around two Marine Propellers

The objective of the present study is to investigate, by means of veloci- metric measurements, the flow field generated by two marine propellers running with inclined shaft configuration. The two propellers represent two alternative designs for the same application, mostly differing for the radial load distribution adopted. The presence of shaft appendages is considered as well, thus simulating a typical twin screw vessel configura- tion. Measurements have been carried out on two different scaled model of the propellers in the cavitation tunnel of UNIGE using Laser Doppler Velocimetry (LDV) and the acquired data have been post-processed ap- plying the ensemble average technique. The tests have been performed with and without propellers in order to characterize the propeller inflow and the effects of the struts and shaft on the incoming flow field. The complete 3-D flow field has been measured considering one transverse section downstream of the propeller, focusing on the near field wake and a longitudinal plane containing the propeller shaft as well. Acquisitions have been made at longitudinal plane extending from -0.25D till 1D. Re- sults allow analysing the main characteristics of the flow field, including the evolution of its main structures. The effects of non-uniform inflow conditions caused by the oblique flow and the appendages are analysed focusing on the axial and tagential velocity of the flow field.