219 



Effect on Propeller Operation Due to Tangential 

 Stern Vortex Flow 



In the previous section, the authors have mainly 

 discussed the structure of the stern vortices 

 obtained from the towing experiments. As was 

 reported by Hoekstra (1977) it can be considered 

 that the structure and geometry of the stern 

 vortices is strongly affected by the flow induced 

 propeller thrust. However, the authors have studied 

 the forces and moments on the working propeller as 

 a preliminary problem, assuming the structure of 

 the stern vortices is not changed by the influences 

 of the propeller suction. 



The forces and moments on the propeller are 

 remarkably related to the pattern of the flow 

 distribution at the propeller disk location. The 

 flow distribution relevant to the present problem, 

 is composed of the wake component, V /U, and the 

 tangential components, V /U, which were obatained 

 by the five-hole Pitot tube. The authors assumed 

 that the tangential components could be further 

 decomposed into the component obtained by the 

 vortexmeter, V /U, and other components. Although 

 each component has already been shown in previous 

 figures, for convenience the circumferential dis- 

 tributions of V /U, V /U, and V /U at 90%, 70%, 



X T TV 



and 50% of the disk radius are shown respectively 



in Figures 26, 27, and 28. Furthermore, the authors 

 have included the tangential velocity vector com- 

 ponent, V /U, in Figure 29. 



In order to determine the propeller forces and 

 moments induced by the stern vortices, the authors 

 have performed the following calculations using 

 the unsteady lifting surface theory developed by 

 Koyama (1975) . The authors thus calculated the 

 thrust and torque of the propeller, along with the 

 vertical and horizontal forces and moments imparted 

 by the propeller shaft of the working propeller 

 with and without stern vortex flow. The definitions 

 concerning the forces and moments are shown in 

 Figure 30. 



The authors have assumed for the calculation that 

 the tangential flow obtained from the subtractive 

 procedure (V /U - V /U) simulates one eliminating 

 the effect of the stern vortices, and a common 

 wake flow can be used for both calculations with 

 and v:ithout the stern vortices. 



Since the results of the calculation for M.No.M-4 

 are quite similar to the results of M.No.M-7, only 

 the results of M.No.M-7 are shown in Figures 31 and 

 32. Figure 31 indicates a comparison of the torque 

 and thrust on a blade of the propeller with and 

 without the stern vortex flow. Total torque, 

 thrust, and other forces and moments on the pro- 

 peller (indicating propeller turning angle 0° to 



0,2 







-02 



Vt/U tongefiTial velocity component 

 obtotned by five -hole Pilot tube 



Top 



Storboord side 



180 

 (deg I 



Top FIGURE 27. Circumferential dis- 

 tribution of tangential flow on 

 propeller disk, Vrp/U. 



360 



-03 

 0.2 



= 

 -0.2 



Vtv/U longentiol velocity component r/R ■ 0.50 



obtoined by vortexmeter 



Top 



Storboord side 



180 

 e (deg ) 



Top 



FIGURE 28. Circumferential dis- 

 tribution of tangential flow on 

 360 propeller disk (induced flow) , 



Vtv/U- 



