386 



3000 



6000 



5000 



1 1 150 



14350 



FIGURE 1. High speed water tunnel. 



inception and development of cavitation and the 

 aspect and behavior of cavitation cavities occurring 

 on two hydrofoil profiles with different cavitation 

 characteristics . 



lowering the free surface led from the top of the 

 tunnel, the maximum and minimum pressures being 

 48=<10^ Pa and -O.SxIqS pa. The flow velocity at 

 the measuring section is controlled from the measur- 

 ing station by controlling the speed of the 

 circulating pump P. 



Measuring Section 



The measuring section has a cross section 200mm 

 wide and 610mm high and its total length is SOOOmin. 

 The first upstream 1000mm has two plexiglass windows 

 in each side, and upper and lower wall. In this 

 experiment, the hydrofoil is installed through two 

 downstream-side windows in both side walls. Figure 

 2 shows the spanwise distributions of the velocity 

 and the static pressure at the position of the 

 mid-chord of the hydrofoil in the case of no grid. 

 The velocity profile is almost uniform except in 

 the 10^ the boundary layers on both side walls. 

 The static pressure, expressed as the difference 

 from that at the side wall, is constant within the 

 accuracy of this experiment. 



2. EXPERIMENTAL APPARATUS AND METHODS 



Hydrofoils 



High Speed Water Tunnel 



The water tunnel used for the experiment is shown 

 schematically in Figure 1. The tunnel contains 

 180m^ of water. The water is circulated by the 

 centrifugal pump, P, whose revolution is controllable. 

 Bubbles generated in the measuring section, the 

 duct, and the pump mainly disappear in the reservior 

 T. In the reservoir the water first flows upward 

 to the free surface at the top of the -reservoir, 

 and then down very slowly through an area of 20m 

 to the bottom. Two spaces, one at the entrance 

 corner of T and the other at the top of the tunnel, 

 separate bubbles from the water and continuously 

 remove the separated air. The water sucked up from 

 the bottom of T turns to the horizontal direction 

 through corner vanes , and enters the measuring 

 section through the honey comb, S, made of synthetic- 

 resin pipes of 26mm diameter, 5mm thick, and 450mm 

 long. Then it flows through two nozzles, Nl and 

 N2 , which contract the cross section from 2100x1400mm 

 to ISOOxlOOOmm^ and to 1200x200mm2, the room for 

 installing the shear grid, and the nozzle for 

 contracting the cross section from 1200x200mm to 

 610x200mm^. The contraction ratio is 24:1 in all. 

 The water flowing out of the measuring section flows 

 through the diffuser and back to the circulating 

 pump P. 



The tunnel pressure is controlled by introducing 

 compressed air to the top of the reservoir or by 



0.01 ~ 



o. 



• 



Two hydrofoils have been prepared for the experiment, 

 each of which has 100mm chord and 700mm span. Two 

 profiles have been selected; one is Clark Y 11.7 

 and the other 08, dimensions of which are shown in 

 Table 1. The former is selected for the purpose of 

 examining the influence of the behavior of the 

 boundary layer on the hydrofoil surfaces on the 

 inception and development of cavitation and the 

 aspects of cavitation bubbles or cavities, because 

 it has a round nose and a surface pressure distri- 

 bution rising toward the trailing edge . The latter 

 is selected as a typical profile among ones designed 

 by Numachi (1952) for high-speed flows, and has a 

 sharp leading edge and comparatively good cavitation 

 characteristics for its simple shape. 



The hydrofoil of the Clark Y 11.7 profile has 

 14 and 13 piezometer holes of 0.4mm diameter on the 

 suction and pressure surfaces respectively, and one 

 of the 08 profile has 13 and 13 piezometer holes. 



Table 1 Profile Forms of Hydrofoils 



Clark Y 11.7 



08 



0,0 0.1 0.2 0.3 0,4 0.5 OS 07 0,8 0.9 10 



y/h 

 FIGURE 2. Velocity distribution at no grid condition. 



