215 



FIGURE 14. Vorticity distribution of M.No M-7 at 

 Sq.St. A. 



holes 25°) is shown in Figure 16 and the wake 

 distributions and the velocity vectors by the five- 

 hole Pitot tube are shown in Figures 17, 18, 19 

 and 20 respectively. ' ' 



020 % of u 



FIGURE 15. Velocity vectors on y-z plane due to stern 

 vortices (M.No. M-7, Sq.St. 1/4). 



FIGURE 16. Vorticity distribution measured by 5-hole 

 pitot tube (M.No. M-7, Sq. St. 1/8). 



4. DISCUSSIONS AND APPLICATIONS OF THE RESULTS 

 Remarks on Vorticity Measurements 



The rotor-type vortexmeter performed as expected. 

 As seen from a comparison between Figures 8 and 16, 

 the rotor-type vortexmeter is more sensitive and 

 can be used to obtain a finer vorticity distribu- 

 tion contour than the five-hole Pitot tube, while 

 both vorticity distribution diagrams appear to have 

 a similar shaped vortex core, they have fairly 

 different values. The distinguishing difference 

 IS mainly in the pattern of the distribution. Al- 

 though the plateau-type distribution would be the 

 expected form of the typical vortex cores in the 

 vorticity distribution obtained by the vortexmeter, 

 the plateau- type is broken in Figure 16. It can be 

 said that the difference between these results 

 indicate the usefulness of the vortexmeter ' s resolv- 

 ing ability. 



Contrary to the general opinion that a geometry 

 of the stern vortices is fluctuating, in the 

 authors' measurements, the vorticity and geometry 

 of the stern vortices were generally quite stable. 

 However, there is an unstable vorticity-zone at 

 the top of the main vortex core indicated in 

 Figures 8, 9, and others. Through these experi- 

 ences, it can be shown that the dynamic character 

 of the vortexmeter is one of its prominent features. 



While the present diameter of the vortexmeter ' s 

 rotor was selected for maintaining its accuracy in 

 measurement, it is possible that the rotor diameter 

 is too large for the 4m geosim model (M.No.M-4) . 

 Furthermore, it appears that there were some 



