Cavitation on Hydrofoils in 

 Turbulent Shear Flow 



H. Murai, A. Ihara, and Y. Tsurumi 

 Tohoku University, Sendai, Japan 



ABSTRACT 



Conditions and positions of inception, locations of 

 zones , and aspects and behaviors of bubbles and 

 cavities of cavitations occurring on two hydrofoils 

 with the profiles of Clark Y 11.7 and 08 in shear 

 flows and a uniform flow have been observed and 

 measured, and correlated with measured pressure 

 distributions on the hydrofoils and turbulence 

 levels and size distributions of cavitation nuclei 

 in free streams. 



At attack angles small for the profile, traveling 

 cavitations begin near positions of minimum pressure 

 and at cavitation numbers about the same as absolute 

 values of minimum pressure coefficients, irrespective 

 of flow shears in free streams provided local values 

 are used. Discrepancies between conditions and 

 positions of inceptions and pressure coefficients 

 and their distributions, and sizes of traveling 

 bubbles depend on qualities of free streams. 



On the hydrofoil with the Clark Y 11.7 profile, 

 a traveling bubble 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 08 profile, a traveling bubble collapses after 

 the deformation caused by the instability of the 

 bubble surface. On both hydrofils, bubbles collaps- 

 ing symmetrically and asymmetrically, looking like 

 micro jets forming, can be found. 



At attack angles large for the profile , fixed 

 cavitations occur. Conditions and positions of 

 inception are similar to those of traveling cavita- 

 tions . In the boundary layers on both side walls , 

 fixed cavitations occur at relatively large 

 cavitation numbers, possibly equal to the absolute 

 values of local minimum pressure coefficients, and 

 even develop beyond the boundary layers . Cavitation 

 zones on the low-speed side are larger than those 

 on the other side, and those occurring in the 

 boundary layers of uniform free streams are of an 

 intermediate size. 



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. 



1 . INTRODUCTION 



Many researches on the cavitation characteristics 

 of hydrofoil profiles have been published, and the 

 appearance, the degree, and the effects on the 

 hydrodynamic behavior of hydrofoil of the incipient 

 and developed cavitations occurring on hydrofoils 

 have been discussed by Numachi (1939, 1954) , Daily 

 (1944, 1949) , and Kermeen (1956a, 1956b) . Recently, 

 the effects of the behavior of boundary layers and 

 the turbulence in the free stream on the inception 

 and development of cavitations on hydrofoils were 

 reported by Casey (1974), Numachi (1975), and Blake 

 et al. (1977). Although they have been concerned 

 with cavitation occurring on hydrofoils in a free 

 stream of uniform velocity, actual blades of 

 hydraulic machines, including ships' propellers, 

 work mostly in nonuniform flow, and the effect of 

 nonuniformity might have to be examined as well. 



Investigations on cavitation occurring in shear 

 layers have been made by Daily and Johnson (1956) 

 in a zone of wall shear turbulence, by Keirmeen and 

 Parkin (1957) in a wake behind a circular plate 

 and by Rouse et al . (1950) and Rouse (1953) in 

 submerged jets. But research concerning the cavita- 

 tion occurring on hydrofoils laid in a free stream 

 with a shear is not available as far as the authors 

 are aware . 



The present report is intended to clarify the 

 influence of the spanwise shear, uniform in the 

 core and the accompaning boundary layers on both 

 sides of the free stream and its turbulence on the 



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