Cavitation tests on Hydrofoil of Simple Form Report 6: On three profiles of 3,5 percent thickness ratio

Cavitation Tests on Hydrofoil of Simple Form/Report 6

(On Three Profiles of 3.5 Per Cent Thickness Ratio)

F. NUMACHI2 and I. CHIDA'

Synopsis

edft Univenzity of Technology Ship Hydromectanics Laboratory

Library

Mekelweg 2 - 2628CD Detft

The Netherlands

Phone: 31 15 786373 - Fe= 31 1578183S

Forty hydrofoil profiles to be used for blade elements of ship propellers,

axial-flow turbines and pumps were deviced and all simplified in form with a view to facilitating their machining. The series of cavitation tests have been carried out

on these hydrofoils. The present paper forms the first report of the tests on the hydrofoil profiles of thickness ratio 3.5 per cent among them.

1. Introduction

Thin hydrofoil profiles of 3 to 4 per cent thickness ratio are much utilized in designing the cross sections nearer the periphery of blades for axial-flow turbines and pumps, and ship propellors, and thin profiles with superior performance are

in demand for reference in design of these hydraulic machines. Little information

is however available on thin profiles, since such varieties are not very useful for aircraft design, and their performance under cavitation is practically unknown.

The present study follows on that of the Report 3 of the series ( 1 ), and

concerns tests on three new profiles of simple form with 3.5 per cent thickness ratio. One of the results is a clarification of the effect of wash-back. Though no new forms of superior all round characteristics were found, one of the profiles

tested yielded the best performance of any so far, in the domain of very high

speeds (k> 0.35).

Report No. 86 (in European language) of the Institute of High Speed Mechanics,

Thhoku University. Read at the Meeting in Sendai District of the Japan Society of

Mechanical Engineers, on December 10, 1949.

Professor, Faculty of Engineering, concurrently Director of the Institute of High

Speed Mechanics, T0hoku University.

Assistant of the Institute.

(1) Numbers in brackets refer to the Bibliography at the end of the paper.

1

.1.

2.. 3.

90 Rep. Inst. High Sp. Mech., Japan, Vol. 9 (1958), No. 86

2. Experimental Method and Test Specimens

The method of experiment was that

and will not be repeated here. The

out-line forms of the profiles taken up are

given in Fig. 1, and the procedure for

drawing these outlines and pertinent

dimensions given in Tables 1 and 2.

It will be seen that the profile 0.13.5 is provided with a very slight wash-back,

at the tail end, the 01, with wash-back

at both ends, and the OIL at the head

end only, similarly to the 01,, of Report 3 1D, though less pronounced.

fully described in the previous paper ( 2 ),

Trailing Edge 03 3,-1 o 6 0 .c X

Fig. 1. Specimen Profiles

Table 1. Dimensional Proportions for Drawing Profiles with Annexed Key Diagramme Leading Edge 10 Profile L t n R, R.2 R3 R4 R5 w, w, 11 1, t,

t

1., 100 3.50 50.00 390.50 443.33

38.07 7 0.145 0.53 75.29 0.29 70.29

01, 70 2.45 35.00 273.35 310.33

26.65 V 0.1

_{0.37 73.70 0.20 70.20}

100 3.50 50.00 531.49 443.33 64.57 38.07 28.57 0.86 0.53 8.57 5.29 0.29 0.57 0.29 0;., 70 2.45 35.00 372.04 310.33 45.20 26.65 20.00 0.60 0.37 6.00 3.70 0.20 0.40 0.20 100 3.50 50.00 531.49 390.50 64.57 28.57 0.86 0.145 8.57

,

0.29 0.57 0.29 01, 70 2.45 35.00 372.04 273.35 45.20 20.00 0.60 0.1 6.00 0.20 0.40 0.20 5 I

F. NUMACHI and I. CHIDA, Cavitation Tests on Hydrofoils / 6 91

Table 2. Dimensional Proportions of Profiles

The characteristics of the wash-back applied to the different profiles tested may be tabulated as follows:

3. Results

Mode of Cavitation Occurrence.

As shown in Figs. 2 to 4, cavitation was observed in all three profiles in zones

I, II and III. It was observed in zone IV only in the 01, and 035.5, with tail-end wash-back.

Variation in Lift and Drag.

The variation in lift and drag coefficients according to cavitation coefficient is shown in Figs. 5 to 10.

In all three profiles, maximum (with large incident

angles) or minimum (with negative incident angles) values occur in the lift

co-efficient in relation to I?,

Performance Curves.

Individual polar diagrammes are not reproduced here, but detailed values are given in Tablse 3 to 5. Profile di., x Profile 01, Profile ()(_{. .5} yo _{Yu Yo Yu} x _Yo Y. 0 0 0 7.14 1.14 0.00 8.57 1.88 0.00 8.57 1.88 0.00 21.43 2.45 0.00 21.43 2.73 0.00 21.43 2.73 0.00 35.71 3.24 0.00 35.71 3.31 0.00 35.71 3.31 0.00 50.00 3.50 0.00 50.00 3.50 0.00 50.00 3.50 0.00 64.29 3.27 0.00 64.29 3.27 0.00 64.29 3.24 0.00 78.57 2.58 0.00 78.57 2.58 0.00 78.57 2.45 0.00 94.71 1.24 0.00 94.71 1.24 0.00 92.86 1.14 0.00 100.00 100.00 i 100.00 Profile

Wash-back at head Wash-back at tail

11/ 1..% w,/t % 12/ L 0 0 15 5.3 25 8.6 15 5.3 = lOwilL = 10 wi/L (4.5 25 8.6 0 0 25 2.5 0 0 Cavitation.

(1)

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92 Rep. Inst. 'High Sp, Mech., Japan, Vol. 9 (1958), No. 86

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it Relation to Incidence Angle am; Value of kr, at which Incipient

Cavitation Occurs, as well as Values of X// for Growing Cavitation.; Ranges, of Erosion and Vibration Danger (Profile 033.5)

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F. NUMACHI and I. cHIDA, Cavitation Tests ,on Hydrofoils 6

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Fig. 8. Variation of Drag Coefficient C, for Various Incidence Angle a with

Changing Values of Cavitation Coefficient k, (Profile 0'3.5)

402

0,02

F. NUMACHI and I. CHIDA, Cavitation Tests on Hydrofoils / 6 95

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Table 3.

Variation with Cavitation Coefficient 'p, of Lift and Drag Coefficients Ca

and Cu; (Profile 033:5)

Water temperature tu,---7(19.6-21.6) deg. C,

Reynolds number R--T(5.8-10.4) 105,

Degree of air content alqs-- 10,

4 tx.-Incidence angle gF1- rt-0.15 0.2 0.25 0.3 0.4 0.5 0.6

-0.7 0,8 0.9 1.0 1.1 1:2 1,4 1.6 . 1.8 2.0 2.5 --3° Ca -0.047 -0.069 -0.124 -0.189 -0.310 -0.397 --0.331 Cu.,--= 0,0195 0.0215 0.0243 0.0268 0.0315 0.0332 0.0336 -0.275 0.0316 -0.255 0.0311 -0,231 0.0305 -0.230 0.0303 -0.229 0.0301 -0.229 0.0300 -0.229 0.0300 -0.229 00300 -0.230 0.0305 -0.230 -0.230., 0.0299 0.0300 on -""+,- 2° ,==-0.034 -0.053 -0.090 -0.189 -0.296 -0.313 -0.130 0.0181 0.0183 0.0196 0.0213 0.0257 0.0226 0.0228 -I0.123 0.0215 -0.118 0.0213 -0.118 0.0212 -0.117 0.0210 -0t117 0.0210 -0.117 0.0210 -0.117 0.0210 -0.117 0.0210 70.117 0.0218 -0.117 0.0209 -0.117 0.0209 191 =0.022 -0.012 -0.009 -0.050 -0.108 -0.010 -0,009 -0.010 -0.010 -0.010 -0.011 -0.011 -0.011 -0.012 -0.015 -0.019 -0.020 -0.024 0.0160 0.0171 0.0162 0.0159 0.0168 0.0170 0.0169 0.0169 0.0168 0.0167 0.0167 0.0167 0,0167 0.0165 0.0165 0.0163 00164 0.0160 0° 0.061 0.099 0.092 0.089 0089 0.099 0.099 0.099 0.099 0.099 0.099 0.099 0.099 0.099 0.100 0.100 0.100 0.099 0.0153 0.0145 0.0145 0.0147 00146 0.0146 0.0146 0.0145 0.0147 0.0146 0.0144 0.0144 0.0145 0.0145 0.0144 0.0147 0.0145 0.0145 1° 0.086 0,167 0.223 0.203 0.195 0:193 0.193 0.0180 0.0163 0.0147 0.0148 0.0147 0.0148 0.0146 0.192 0.0146 0.193 0.0146 0.193 0.0146 0.193 0.0146 0.193 0.0145 0.193 0.0145 0.193 0.0143 0.195 0.0140 0.195 0.0138 0.196 0,0138 0.198' 0.0135

a.

0.100 0.174 0.235 '0.250 0.297 0.330 0.342 0.308 0.302 0.298 0.298 0.298 0.298 0.298 0.297 0.297 0.297 0,297 0.0210 0.0180 0.0175 0.0185 0.0197 0.0200 0.0170 0.0162 0.0162 0.0162 0.0163 Q.0163 0.0163 0.0162 0.0160 0.0160 0.0160 0.0155 .11 V 0.110 0.170 0.228 0.280 0.390 0.483 0.497 0.0274 .0.0200 0.0215 0.0233 0.0262 0.0290 0.0220 0.428 0.0196 0.425 0.0202 0.417 0.0202 0.401 0.0203 0.401 0.0203 0.400 0.0203 0.400 00202 0.399 0.0202 0.3-98 _'0.0201 0.398 0.0201 0.398 0.0206, 4° 0.124 0.172 0.229 0.289 0.401 0.513 0.571 0.550 0.548 0.547 0.529 0.529 0.510 0.509 0.508 0.506 01506 0.506 00 0.0335 0.0238 0.0261 0.0292 0.0343 0.0390 0.0320 0.0283 0.0290 0,0313 0.0303 0.0289 0.0289 0.0285 0.0285 0.0285 00285 0.0290 5° 0.181 04232 0.290 0.395 0,500 01597 0.652-0.711 0.710' 0.677 0.659 0.639 0.620 0.610 0.608 0.608 0.608 0.0274 000318 0.0360 0.0440 0.0499 0.0520 0.0515 0t0508 0.0488 0.0445 1:00425 0.0409 0.0390 0.0388 0.0390 0,0390 0.0398 6° 0.192 0:239 0.291 0:386 0.490 0.618 0.768 0.900 0.893 0.826 0.780 0356 0.725 0.710 0.706 0.708 0.706 0.0311 010380 0.0440 0.0555 0.0606 0.0765 0.0813 0.0769 0.0665 0.0592 0.0553 0.0550 010517 0:0509 0.0517 0.0517 0.0530 2°

Table

41-Variation with 'Cavitation Coefficient k, of Lift and Drag Coefficients C. and Cm (Profile 053.5).

A -= 71 Water temperature tw (19.7,*.211) deg. C; Reynolds number 1?-1=7 (5.9-10,2).105,

a.=

Degree of air content al as

Incidence angle ka 0.2 0.25 0.3 0.4 05 0.6 0.7 0.8 '0.9 11,0 1.1 1.2 14 116 1.8 2.0 2.5 3° -W090 0.0144 -0.137 0.0179 -0,197 0.0200 -0.314 0.0245 -0.290 0.0225 -0.230 -0.212 -0.207 0.0186 0.0186 0.0170 =0.207 0.0170 -0.204 0.0168 -0.199 0.0158 -0.200 0.0157 -0.200 0.0150 -0,194 =0.200 0.0149 0.0149 -0.199 0.0149 -0.200 0.0165 -0087 -0.132 -0.185 -0.144 -0.103 -0.090 -0.092 -0.090 -0.081 -0.082 -0.084 -0.090 -0092 =0,095 - 0,095 -0.087 -0.087 x 00105 0.0127 0.0140 0.0122 0.0115 0.0118 0.0115 0.0115 0.0115 030115 0.0115 0.0116 040114 0,0113 0.0113 0.0117 0.0133 'E54 03025 0.006 0.009 0.015 0/9,18, 0,018 0.018 0.015 0.012 01011 0.010 0.008 0.005 0.004 01003 0.003 0 rPt-, 030071 0,0071 0.0079 0.0082 00085 0,0089 mug 0.0090 0,0092 0.0093 0.0095 0i0096 0.0089 0.0096, 010096 0.0094 0.0088 0.9 01117 040076 0.107 0.0077 0.110 030085 0.112 0.0092 0.107 0,0093 0.107 0.110 0.114 0.0096 010097 0.0098 0.113 0.0097 01111 _0.0097 0.107 0.0098 0.107 0.0100 0.107 0.0100 0.107 0.103 0.0099 0.0099 0.105 0.0098 0.107 0.0107 1=6) 17' 01161 010105 0.215 110113 0272 0.0112 0.223 0,0090 0.222 0.0094 0222 01220 0.222 000g8 '00100 0.0101 0.221 0.0100 0.223 00100 0.222 0.0098 0.218 0:0100 0,213 0:0100 0.222 0221 0.0099 00099 0L222 0.0097 '0.220 110095 17D3 0.140 0.200 0.268 0,316 0.345 0.362 0,359 0.345 0.335 0.335 0.327 0.332 0.323 0.322 0.322 0.324 0.334 0.0122 0.0150 0.0163 0.0180 0.0190 0.0192 0.0140 .0.0134 Q.0134 0.0134 0.0132 0.0139 0:0123 0.0121 0.0132 0.0133 0.0121 0.126 0.180 0.253 0.387 0.477 0.557 0.498 0.453 0.446 0.435 0.435 01437 0,421 0.421 0.422 0.421 0.435 0.0157 010185 0.0222 0.0268 0.0305 0.0307 010219 0.0207 0.0207 0.0207 0.0205 0.0219 0.0198 0.0197 0.0197 00198 010207 0. 0.129 0.181 0.250 0.377 0.488 0.582 0.600 0.593 01593 0.592 0.572 0.550 0.534 0.521 0.520 0.521 0.534 0 0.0187 0.0226 0.0270 0.0350 00411 0.0440 0.0368 0.0362 0.0380 0,0340 0.0330 0.0314 0.0300 0.0300 0.0300 0.0312 0.0312 0. 5,0 0.144 0.0213 0.193 0.0267 0.250 0.0312 0.354 0.0420 0.475 0,0513 0.578 0.671 0.743 0.0571 0.0606 0.0611 0.758 0.0600 0.747 0.0545 0.721 0.0515 0.685 00483 0.610 0.0144 0.622 0.621 0.0438 '0.0436 0.622 0.0444 0.630 0.0443 6° 0.180 0.238 0.250 0.333 0.460 0.570 0.715 0.883 0.916 0.900 '0.868 0.818 0.742 -,0.720 0.720 0.722 0.725 0.0240 0.0308 0.0350 '0.0480 0.0608 0.0706 0.0934 0.1040 010955 0.0895 0.0793 0.0742 0.0653 0.0600 0.0600 0.0600 0.0623' Ca = -2° -1° 2° 3° 4°

Table 5.

Variation with Cavitation Coefficient k, of Lift and Drag Coefficients Ca and C. (Profile 05)

Water temperature

(19.4-20.7) deg. C,

Degree of air content alas

1.0

Reynolds number R---7 (5.7-10.2)

105,

a.= Incidence angle

0.15 0.2 0.25 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.4 1.6 1.8 2.0 2.5 Ca - -0.062 -0.083 -0.143 -0.203 -0.265 -0.205 -0.160 -0.143 -0.135 -0.135 -0.135 -0.135 -0.140 -0.138 -0.138 -0.138 -0.138 -0.135 Cu,-0.0189 0.0200 0.0230 0.0253 0.0280 0.0250 0.0225 0.0216 0.0206 0.0200 0.0198 0.0195 0.0195 0.0187 0.0185 0.0183 0.0183 0.0180 C/Q -0.040 -0.080 -0.126 -0.125 -0.020 -0.018 -0.020 -0.020 -0.020 -0.020 -0.023 -0.025 -0.028 -0.028 0.0172 0.0170 0.0170 0.0176 0.0160 0.0155 0.0150 0.0150 0.0150 0.0148 0.0148 0.0147 0.0147 0.0147 -0.030 0.0147 -0.030 -0.030 0.0147 0.0147 -0.033 0.0147 cr; 0.048 0.100 0.112 0.110 0.103 0.103 0.100 0.095 0.095 0.095 0.093 0.090 0.085 0.080 0.077 0.073 0.070 0.063 0.0135 0.0126 0.0127 0.0130 0.0140 0.0140 0.0138 0.0134 0.0135 0.0130 0.0130 0.0131 0.0133 0.0134 0,0137 0.0139 0.0140 0.0145 c o 0.062 0.175 0.198 0.195 0.185 0.185 0.184 0.184 0.182 0.182 0.182 0.180 0.180 0.180 0.177 0.177 0.177 0.177 0.0153 0.0152 0.0138 0.0137 0.0140 0.0140 0.0140 0.0140 0.0140 0.0138 0.0133 0.0132 0.0132 0.0130 0.0130 0.0128 0.0129 0.0126 0.155 0.210 0.255 0.298 0.342 0.297 0.288 0.285 0.285 0.285 0.285 0.285 0.278 0.278 0.278 0.278 0.278 0.285 0.0165 0.0160 0.0160 0.0166 0.0152 0.0150 0.0150 0,0153 0.0153 0.0153 0.0153 0.0153 0.0153 0.0153 0.0152 0.0150 0.0150 0.0150 0.163 0.215 0.268 0.315 0.400 0.420 0.430 0.430 0.413 0.395 0.387 0.387 0.382 0.375 0.375 0.375 0.375 0.375 C 0.0181 0.0190 0.0200 0.0220 0.0235 0.0225 0.0210 0.0195 0.0192 0.0192 0.0192 0.0192 0.0192 0.0192 0.0191 0.0190 0.0190 0.0190 <.0 0.160 0.210 0.260 0.307 0.407 0.495 0.575 0.645 0.540 0.517 0.500 0.498 0.490 0.483 0.483 0.480 0.480 0.475 0.0195 0.0236 0.0255 0.0280 0.0333 0.0353 0.0363 0.0290 0.0275 0.0260 0.0260 0.0257 0.0257 0.0257 0.0255 0.0252 0.0252 0.0250 0.154 0.210 0.250 0.300 0.405 0.513 0.637 0.715 0.665 0.653 0.635 0.622 0.610 0.600 0.595 0.595 0.593 0.590 0.0215 0.0277 0.0308 0.0343 0.0425 0.0473 0.0520 0.0485 0.0453 0.0445 0.0445 0.0425 0.0387 0.0367 0.0360 0.0358 0.0358 0.0358 0.210 0.235 0.290 0.400 0.515 0.630 0.730 0.785 0.825 0.805 0.758 0.737 0.710 0.690 0.690 0.680 0.690 0.0317 0.0356 0.0404 0.0510 0.0582 0.0660 0.0733 0.0743 0.0743 0.0670 0.0585 0.0545 0.0510 0.210 0.220 0.280 0.400 0.510 0.600 0.722 0.895 1.000 0.960 0.885 0.855 0.810 0.0500 0.770 0.0493 0.0493 0.765 0.760 0.0493 0.755 cr, 0.0360 0.0400 0.0468 0.0590 0.0690 0.0795 0.0890 0.0985 0.0985 0.0843 0.0750 0.0695 0.0695 0.0685 0.0665 0.0665 0.0665 I

-3°

-2'

-1° 0° 1° 2' 3° 4' 5° 6°

F. NUmACHI and I. CHIDA, Cavitation Tests on Hydrofoils / 6 99

( 4 )

Comparative merits of the three profiles.

( a ) Performance curves-: For the different profiles are represented in

com-parison to each other in Figs. 11 to 16, together with the curves for the

03,5 of

Report 3, reproduced here for reference. The present series of profiles have been developed for use at relatively low lift coefficients, and so, arranged in the sequence of superiority under such conditions, the order according to cavitation coefficient is:

08 Ca 00 02 0 -02

77

4.1I off 2'2' =2,5 _A=20 i° 04T r\M'Arqt; 6,35-civ so.-3° <DT a02 u,'N 0 02 0;86 tov /9,5-21,6°C -R4 (e58--X)11-001

Fig. 11. Comparison on Polar Diagrams of Profiles at Various Values of Cavitation Coefficient (k, - 2.5, 2.0, 1.8)

tw-af--21,1°C

c,

Fig. 12. Ditto with Fig. 11 (k, = 1.6, 1.4, 1.2)

8,08

408

100 'Rep. Inst. High Sp. Mech., Japan, Vol. 9 (1958), -No. 86 ae +g

LJ

'Or

r

I 12;

AO=

WI

kci=e9

R W-40400

MEM

03, 0 2° 0 -3° 0 OR

00 0

40i

11111101..i

11/11/11

Ca 4.7 kd=a9 7 3

3/r

,tr-mr /,' Vftk` ,0:71 Ogs-0 ajs kci=a5 tprifc-216T

"

R4(8,58-187) fe Ow QS ag -a

Fig. 13. Ditto with Fig. 11 (kd = 1.1, 1.40,,, 0

- 002 -3' ag, 0 002

-OA ggz 118#'age 308 we,

'Fig.

Cv

Drtfci With Fig. 11 (kd '0.8, 0,7,105)

A n7.6--4)-!

MIEN

Ill

Egfa

8,3, -3' g4( 4,01. Q.08 e' 5. LIM -92 4. 001 14. = 40 98

!Ca

a?

a

F. NUMACHI and I. CHIDA, Cavitation Tests on Hydrofoils / 6 '101

ao2 vs/ a / / 4/-'Ir 9. UK _{Of/ , 3} 11° _

bgt k -nc

d--\ I Nb 0.7

0,

-71 3° Of

Fig. 15. "Ditto, with Fig, 11 (k6=0.5.. 0.4, 0.3; 0,.25)

Pig. 16, Ditto with Fig. 11 (ka=0.2, 0'.15)

For kd= : When Ca 0.45

'For kd = 1.4-0.8 : When Ca <,0.5

For kd = 07 Wheti Ca < 01.5

For k a -= 0,6 When Ca < 0.35,,

For k'd = 01.5 When Ca.< 03,

For tkd = When Ca '< 0.25,

t

6w="9,1-21, °C " (6;11-4,#)101, 03

e

7Off lii111111

Mill

07

(All inferior to 0i3.5)

053.5 Oxt 0L5

infrior ta 015)

053,5

03..5035

Ô5

of which 053,5. is superior to 035) 6. 7 0 53:,1 o53., '03.5, 03.5 03,5 063.5 01, 3 03_, oL, 015 however, inferior to 015) 06,5 o3.53 05. 0.33,5 0365. 6° or ,fd=e2.3-id=4.3 .0- _{'1 7r} fi41/41 For k'd 0.4 When Ca < 0.25 0/1--/76 1 02 403 15-16°C 4/2 2.5-1.6 < (All, = (All 0.3-0.15:

102 Rep. Inst. High Sp. Mech., Japan, Vol. 9 (1958), No. 86 It follows from the above that :

( i ) The provision of wash-back at either head or tail (cf. 033.5, 0.'3.5) is not in itself conducive to better performance ;

(ii) A favourable combination of head and tail wash-back seems however to

have been the key to the success of the 0,

(b) Mode of cavitation occurrence : With the object of determining which

of the profile forms are more apt to involve cavitation, the a.ka curves for

cavitation inception given in Figs. 2 to 4 are gathered together in Fig. 17 for

7

-2°

as

Fig. 17. Comparison of Profiles with Regard to Manner of Cavitation

Occurrence

comparison with each other. The sequence, in the order of lateness in cavitation

inception, is as follows:

from which it appears that wash-back at the tail end only (015) inhibits cavitation

in zones I and III.

(c) Incident angle for minimum drag lift ratio : The incidence angle cr.,,Thm

according to the minimum value of Go/Ca may be obtained from the Tables 3 to 5. The relation between and le, is given for the three profiles in Fig. 18 in

comparison with each other. The sequence according to imperturbability of this

angle to changing cavitation coefficient is:

063.5 053.5

01,

R.(a57-10)/01

pon (D

ff-ZeRe

mir

Mr

_gm

m

es 04 a/= /O ..44411f 1111

NM

draw

mm. MU al, val

midirm'momenrairmicasommr---11370,--,

MIN11111111w-i'll,

0.11

mew , ...---migamrogi

_{-..., ...s} -IME 0,7,- 01111

Nil

info/ewe of

Ion

ilia.

---1-Zone Coe

RIM

off evi 4

..,4, ,

ih.

1,,

4f

oy, ifizzo/tna, al 1-70,0'ar,v

11

-100.1.(E)

k

In zone I : 015 053.5 In zone II : 035.5 015 In zone III: 03.5

0

031.5 1,8 za

where the O5 compares with O. and O, with this angle susceptible to change

in kd beyond kd = 0.6.

ao0

F. NUMACHI and I. CHIDA, Cavitation Tests on Hydrofoils / 6 103

Fig. 18. Variation with Changing Cavitation Coefficient k, of Incidence Angle for Minimum Drag-Lift Ratio

4. Conclusion

( 1 ) With profiles of forms such as the present series, the provision of

wash-back at the head or tail does not in itself constitute a contribution towards better performance (cf. 0, 043,0

( 2 ) Good performance may obtained by a favourable combination of head

and tail wash-back (cf. 053.5)

( 3 ) At extreme high speeds, a less pronounced wash-back (0.5) does better

than a more pronounced one.

In conclusion, the valuable assistance provided by Mr. S. Nakayama, technical

officier of the ex-Japanese Navy, in developing the profiles and in preparing the

test specimens must be acknowledged.

The able assistance in the experiments

provided by Mr. K. Tsunoda, Technical Official of the institute, is appreciated.

5. Bibliography

(1]

F. Numachi, K Tsunoda and I. Chida, Cavitation Tests on Hydrofoil

Profiles of Simple Form / Rep. 3 (On Four Profiles of Thickness Ratio 3.5 Per Cent), Rep. Inst. High Sp. Mech., Japan, Vol. 9 (1958), p. 35. 2 ) E Numachi, Kraftmessungen an vier Fliigelprofilen bei Hohlsog, Forsch.

Ing.-Wes., Bd. 11 (1940), S. 303.