397 



Kd 



6 



56 



5A 



(a) 



rod 



FIGURE 13 (a) . Cavitation on the 

 hydrofoil of the 0„ profile. 



found in both cases. Even in the case of the grid 

 No. 1, much uniformity of cavitation zones can be 

 found, although some tail wisps of cavitation can 

 be found in the case of no grid, e. g. , ones 

 gathered in cores of strearawise vortices . 



4. CONCLUDING REMARKS 



Conditions and positions of inception, locations of 

 zones, and the aspect and behavior of bubbles and 

 cavities of cavitations occurring on two hydrofoils 

 with the profiles of Clark Y 11.7 and 08 in shear 

 flows made by shear grids and a uniform flow have 

 been observed and measured. They have been corre- 

 lated with measured pressure distributions on the 

 hydrofoils and the qualities of free streams, i.e. 

 turbulence levels and size distributions of cavita- 

 tion nuclei in free streams. The main conclusions 

 deduced from the results may be summarized as 

 follows . 



At attack angles small for the profile, when 

 pressure distributions have gradual chordwise 

 changes , traveling cavitations incept near positions 

 of minimum pressure and at cavitation numbers about 

 equal to absolute values of minimum pressure coeffi- 

 cients, irrespective of flow shears in free streams, 

 provided local values influenced by flow shears are 

 .used. Discrepancies between conditions and posi- 

 tions of inceptions, and pressure coefficients and 

 their distributions depend on the free stream quali- 

 ties. The sizes of traveling bubbles depends on the 

 size distribution of cavitation nuclei. 



On the hydrofoil with the Clark Y 11.7 profile, 

 having a relatively large positive pressure gradient, 

 a traveling biibble in a zone of rising pressure 

 deforms, creating a projection in shear flow, or 

 two projections in uniform flow, leaves only the 



projection and then collapses. On the hydrofoil 

 with the 08 profile having gradual pressure gradient, 

 a traveling bubble collapses after the deformation 

 caused by the instability of bubble surface. On 

 both hydrofoils, bubbles collapsing symmetrically 

 and asymmetrically, looking like micro jets forming 

 can be found. 



At attack angles larger for the profile, when 

 the pressure distribution declines steeply followed 

 by a relatively large positive pressure gradient, 

 fixed cavitations occur. Conditions and positions 

 of inception are similar to those of traveling 

 cavitations, although discrepancies of them from 

 pressure coefficients and their distributions are 

 less than those of traveling cavitations. In the 

 boundary layers on both side walls, fixed cavitations 

 occur at relatively large cavitation numbers, 

 possibly equal to absolute values of local minimum 

 pressure coefficients. They develop in both stream- 

 wise and spanwise directions even far enough beyond 

 the boundary layers to affect cavitation inceptions 

 in zones neighboring the boundary layers. Cavita- 

 tion zones on the low-speed side are larger than 

 those on the high-speed side. Fixed cavitations 

 of this kind occur in the boundary layers on both 

 sides of iiniform free streams also. 



At attack angles intermediate for the profile , 

 fixed and traveling cavitations occur at the same 

 time and tend to become fixed only on the Clark Y 

 11.7 profile. On the 08 profile, fixed cavitations 

 at the leading edge and traveling cavitations at 

 about the mid-chord appear at the same time in shear 

 flows , but only fixed cavitations occur and develop 

 at the leading edge in uniform flows. Discrepancies 

 of conditions and positions of inception from 

 pressure coefficients and their distributions are 

 the largest of the three cases mentioned on the 

 Clark Y 11.7 profile, but about the same as above 

 mentioned two cases, on the 08 profile. 



