387 



Table 2 Positions of Piezometer Holes 



Clark Y 11.7 



1 



2 



3 



4 



5 



6 



7 



8 



9 



10 



11 



12 



13 



14 



Upper 

 X % 







3 



6 

 10 

 15 

 20 

 30 

 40 

 50 

 60 



Lower 

 X % 



70 .4 

 80 .3 

 85 .0 

 90 .2 



15 

 16 

 17 

 18 

 19 

 20 

 21 

 22 

 23 

 24 

 25 

 26 

 27 



3 

 6 

 10 

 14 

 20 

 30 

 39 

 50 

 60 

 69 

 79 



.0 

 .1 

 .1 

 .8 

 .1 

 .1 

 .9 

 .0 

 .0 



89 .6 



^^iJ-liJ°V-.,. 



^ 



,45 6 7 8 9 10 



m 



I5'l7 I 19 20 21 22 23 24 25 I 27 

 16 18 26 



^^ 



] _ I " r ^ ;'igi3 



III I I I I I III 



I4I16 lis 19 20 21 22 23 24l 26 

 15 17 25 



as are shown in Table 2. The holes are inclined to 

 the direction of the free streams as to have no 

 influence on the pressures measurements of each other. 

 Pressures are measured by using a mercury-water 

 manometer. 



For measurements of pressure distributions, the 

 hydrofoil is shifted spanwise so as to allow the 

 piezometer holes to cover the whole 200mra span. 

 For observations of cavitations, the part of hydro- 

 foil having no piezometer hole is used. 



Shear Grids 



In order to examine the influence of shear flow, 

 the free stream at the measuring section has been 

 made to have the simplest shear, that is, uniform 

 shear. The grids for creating uniform shear flow 

 are composed of straight rods arranged perpendicular 

 to the free stream and the hydrofoil span with non- 

 uniform spacings calculated by using the theory of 

 Owen and Zienkiewicz (1957) . The spaces near both 

 side walls were modified according to Liverey and 

 Turner, (1964) and Adachi and Kato (1973) and are 

 shown in Table 3. In order to make two different 

 free streams having the same shear but different 

 turbulence, two grids were made, composed of rods 

 with different diameters, 20mm for No. 1 and 15mm 

 for No. 2. 



TABLE 3 Rod Spacings of Shear Grids 



The shear grid is installed at a position 1500mm 

 upstream from the mid-chord of hydrofoil, where 

 the cross section of the duct is about twice as 

 great as that of the measuring section so as to 

 keep the grid free from cavitation. 



Measurement of Velocity and Static Pressure at the 

 Measuring Section 



Spanwise distributions of the velocity and the static 

 pressure are measured at the position of the mid- 

 chord of the hydrofoil in the absence of the 

 hydrofoil, by using a Prandtl-type Pitot tube of 

 3mm diameter. They corresponded to the difference 

 of static pressures at the inlet and exit of the 

 second nozzle, N2 , and the static pressures at the 

 exit of the nozzle and the position 530mm upstream 

 and 170mm below the position of the mid-chord of 

 hydrofoil. 



It has been pointed out by Lighthill (1957) that 

 total pressures measured by using a Pitot-tube in 

 a shear flow exhibit larger values than real ones 

 due to displacement effects of a Pitot-tiabe. The 

 displacement thickness of the boundary layer on 

 the Pitot-tube used in this experiment, having a 

 ratio of outer to inner diameters of 0.6, is 

 calculated as about 0.54mm by use of the empirical 

 equation presented by Yound and Mass (1936) and 

 Macmillan (1955) . The error in this experiment 

 caused by the displacement thickness is the order 

 of 0.08mm/s for a shear factor of 0.15 in the core 

 of the shear flow so that it can be neglected, 

 except in the boundary layers . There the shear 

 factor, on which the error is proportional, is 

 considerably large, especially near both side walls. 



The static pressure at the measuring section is 

 limited due to the following two reasons : at the 

 upper limit, by the strength of the differential 

 piezometer used for detecting the velocity at the 

 measuring section; and at the lower limit by the 

 need to prevent the shear grid from cavitating. 

 The prescribed velocities at the measuring section 

 are determined so as to keep the static pressure 

 at the measuring section within the above-written 

 limits for obtaining the inception and development 

 of cavitation corresponding to the angles of attack 

 of the hydrofoils, as shown in Table 4. 



Measurement of Turbulence 



Spanwise distributions of the components of turbu- 

 lent velocity in the directions parallel to the 

 free stream and perpendicular to the free stream 

 and the hydrofoil span are measured at the position 

 of the mid-chord of hydrofoil (in the absence of it) 

 by using the Laser-Doppler velocimeter, DISA 55L 

 Mark II. Each component of turbulent velocity is 



Rod Number 



Gria No. 1 

 1 2 



distance from low-speed 



side wall (mm) 20.1 59.9 103.4 153.3 



TABLE 4 Velocity and Pressure at the Test Section 

 on Cavitation Experiments 



oi(rad) Velocity (m/s) 



Pressure (105 pa) 



Rod Number 



Grid No. 2 



12 3 



distance from low-speed 



side wall (mm) 16 47.4 81.5 118.4 161.2 



-0.64 - -0.45 



-0.65 ~ -0.35 



-0.60 - -0.11 



-0.33 ~ +0.40 



