216 



-6 Y -4 



-10 -e -6-4-2 2 4 



5 20V. of U 



FIGURE 19. Velocity vectors on y-z plane (M.No.M-7, 

 Sq.St. 1/8). 



FIGURE 17. Wake distribution (M.No.M-7, Sq.St. 1/8) 



problems due to the presence of an oblique flow in 

 those experiments. It is recommended in further 

 work that the characteristics of the rotor in a 

 strong oblique flow should be studied. 



Structure of the Stern Vortices 



As stated in the previous section, the equi- 

 vorticity contours of the stern vortices can be 

 compared with plateaus in geographical contours. 

 Furthermore, in examining carefully the diagrams 

 of the vorticity distribution, there is a line of 

 concentrated vorticity on the "table of plateau," 

 which is denoted by the "Max. line" in this paper 

 and indicated in the contours. The Max. line 

 can be clearly shown in a cross section of the 

 diagrams of the contour as seen in Figures 21 and 

 22. 



The Max. line can be considered as a kind of 



a ridge on this plateau; it is steep in the forward 

 section and becomes gently sloping while shifting 

 afterward. It is noticeable that the Max. line 

 seems to show the existence of a separating vortex 

 sheet. As is well known, stream lines flow from 

 under the bottom of a hull up the boundary layer 

 at the bilge and turn into part of the vortex 

 sheet. Although the vortex sheet previously 

 mentioned has only been used as a hydrodynamic 

 description, the authors are able to show its 

 existence in the flow behind the full stern as well 

 as provide quantitative measurements. 



The development of the vortex sheet depends 

 mainly on the potential flow and the induced flow 

 from the vorticity. Its development is strongly 

 affected by each ship form, with effects of model 

 ship velocity and the Reynolds number effect 

 mainly limited to the diffusion of the vorticity. 

 In a comparison between Figure 8 and Figure 9, the 

 forms of the Max. line which correspond to a form 



-6 Y -4 -2 2 4 6 

 0.5 0.4 0.3 02 02 0.3 04 0.5 ' 



-6 - 



FIGURE 18. Wake distribution (M.No.M-4, Sq.St. 1/8). 



FIGURE 20. Velocity vectors on y-z plane (M.No.M-4, 

 Sq.St. 1/8) . 



