Measurement of pressures on a blade of a propeller model

%7 OKt. 1S79

ARCHEF

PAPERS

OF

March 1979

Ship Research Institute

Tokyo, Japan

Lab. y. Scheepsbouwkuruh

Technische Hogescliool

DelfiNO

₅₅

SHIP RESEARCH INSTITUTE

Measurement of Pressures on a Blade of a Propeller Model

By

* _{Received on January 11, 1979.} ** _{Ship Propulsion Division.}

Bibijotheek van de Afde!ing Schee.psbeJwzjicheepartkuflde

Techjche

_ogeschooJ

DOCUMENTATIE

r

DA TUNI

MEASUREMENT OF PRESSURES ON A BLADE OF A PROPELLER MODEL*

By

Yukio TAKEI,** Koichi KOYAMA** and Yuzo KUROBE*

Contents Abstract Introduction Propeller Measuring System 3-1 Measuring Apparatus 3-2 Pressure gauge

3-3 Location of the pressure gauges 3-4 Calibration of the pressure gauge

Experiments

4-1 Experiments in uniformflow

4-1-1 Non-cavitating condition 4-1-2 Partially cavitating condition

4-2 Experiments in non-uniform flow

Conclusions References

ABSTRACT

In designing a screw propeller, it is very important to know whether the harmfull cavitation occurres on the surface of a propeller blade or not. Pressure distributions over the surface of a blade have_{a close}

con-nection with cavitation. _{Therefore, researches on the relationship between}

cavitation and pressure distributions over the surface of the blade _have

been made.

The measurements of pressure distributions over the blade of the

propel-1er model was carried out using a new measuring _{system including very}

small pressure gauges made of semi-conductor.

The experiments were conducted under three conditions, that is, the

non-cavitating condition in the uniform flow, _{the non-cavitating condition}

in the non-uniform flow and the partially cavitating condition in the

uni-form flow.

The experimental results are compared with calculations_{by the lifting} surface theory.

1. _INTRODUCTION

In developing a new screw series of propellers, it is very important

2

to study the characteristics of cavitation, especially the harmfull cavitation that causes erosion on the blade of the propeller.

Cavitation has a relationship directly with pressure distributions over the blade of the propeller. Some researches on the relationship between

cavitation and pressure distributions have been achieved only on

two-dimensional hydrofoils, because of difficulties of measurement on the screw

propeller'.

Nowadays, however, owing to an improvement of semi-conductor, it

becomes easy to obtain a very small and high sensitive pressure gauge

which is suitable to measure pressure distributions over the blade of the

propeller model. Several researchers have reported the results of

measure-ments on pressure distributions over the blade of the propeller model2'3'4'5.

However, the more accurate results are necessary for discussing together with calculations by the lifting surface theory.

The authors carried out the measurement of pressure distributions

over the blade of the propeller model using the apparatus that was newly

made to be used in the cavitation tunnel of the Ship Research Institute. The experiments were conducted under the non-cavitating condition in

the uniform flow, the non-cavitating condition in the non-uniform flow and the partially cavitating condition in the uniform flow.

2. PROPELLER

The propeller model (M.P. No. 0123) tested is one of the series models

which have been made to develop the new series propeller suitable for

the high speed container ship.

The particulars of the propeller model and the dimensions are shown

in Table i to Table 3. Results of the open water tests on the propeller

model and of calculation by the lifting surface theory are shown in Fig. 1.

Table 1. Particulars of the propeller model

MODEL PROPELLER NO. 0123

DIAMETER (m) 0.250

BOSS RATIO 0.180

PITCH RATIO 1.264 (0.7r)

EXPANDED AREA RATIO 0. 800

BLADE THICKNESS RATIO 0.050

ANGLE OF RAKE 750

NUMBER OF BLADES 6

Table 2. _{Radial distribution of breadth, thickness and pitch ratio of blade} r/R 1

Table 3. Dimension of the blade section

xli o 0.0125 0.0250 0.0500 0.0750 0.1000 0.2000 0.3000 0. 4000 0.5000 0. 6000 0.7000 0.8000 0.9000 0.9500 1.0000 YQIt 0.200 0.335 0.400 0.490 0.563 0.624 0.803 0.911 0.977 1.000 0.977 0.898 0.750 0.516 0.369 0.200 YuIt 0.200 0.120 0.100 0. 072 0.050 0.035 0.010 0.010 0.040 0.068 0. 100 3 0.9 0.6 tx 0.7 XI XL

:J /

0.8 1.0 -

II

X=r/R 0.20 0.30 0.40 0.50 0.4437 0.60 0.70 0.80 0.90 0.95 1.00

ii'/l

0.2914 0.3411 0.3940 0.4636 0.8576 0.4900 0.5298 0.5464 0.5066 0.4437 0.1655 ilL/lILT 0.3709 0.4238 0.4868 0.4900 0.4702 0.4139 0.2914 0.1821 11/10.7 0.6623 0.7649 0.9305 0.9800 1.0000 0.9603 0.7980 0.6258 tz/D 0.0406 0.0359 0.0312 0.0265 0.0218 0.0171 0.0124 0.0077 0.0054 0.0030 Px/Po.7 0.8000 0.8667 0.9333 0.9900 1.0000 1.0000

1.0

tvl.RNo.0123 0.8

C

Q 0.6 I-0.4 0.2-_1_ _l i i t I t f 0 0.5 1.0

\

1.5 J

Fig. 1. Result of open water test

The detail data of the propeller model are presented in Ref. 6).

3. MEASURING SYSTEM

3-1. Measuring apparatus

As shown in Fig. 2 and Photo. 1, the measuring apparatus is consist of the propeller driving system with the hollow shaft and the telemetring system. It can be set in the No. i measuring section of the cavitation tunnel whose section is circular of 750 mm in diameter. The propeller is

driven by 10 kw DC motor at the centre of the circular section of the

tunnel.

EXPERIMENT

(receiver)

cavitation tunnel

Fig. 2. Measuring apparatus

Photo. 1. Measuring apparatus

The number of revolution per second is measured by the hundred

tooth gear and the pulse generator. The position of the blade is detected

by the contactiess relay which is set near the shaft of the DC motor.

The telemetring system has a set of slip rings. The slip rings play two

roles, that is, conducting power of the transmitter and sending pressure signals from pressure gauges to the receivers. The pressure signals are

data- em.

Motor

6

Gain

Table 4. Characteristics of telemeter

Channel

Frequency band

Out put

Signal to noise ratio Cross talk In put impedance Allowable temperature lead 500 6 chs. DC 500Hz 37 db ±7 V 50 db 50 db loo kQ 0-50°C

modulated by multiple frequency modem. The dimensions of the transmitter

are 80 mm in diameter and 200 mm in length. The characteristics of the telemetring system are shown in Table 4.

The data recorder and the visigraph (electro-magnetic oscillograph) were used to record the pressure signals and other signals.

3.2. Pressure gauge

The pressure gauge used is the type of CT-08-1B (TOYODA). The

out view of the pressure gauge is shown in Fig. 3.

Because of the

smallness, it is suitable for measuring pressure on the blade of the

pro-peller model.

The pressure gauge is made of semi-conductor applying the solid

state diffusion. The principle of measurement is based on Piezo-resistive effect. The structure of diaphragm is shown in Fig. 4. The diaphragm

stainless steel

silicon rubber

7

95

Fig. 3. Out view of the pressure gauge

electrode(Al) gauge by diffusion

Si02 low resistance layer

2

Fig. 4. Diaphragm of the pressure gauge

is a silicon single-crystal plate of 0.1-0.2 mm in thickness, on which the

semi-conductor strain gauge is printed by diffusion of impurities.

The electronic circuit is shown in Fig. 5. Since the strain gauges

form a fully active four arms Wheatstone-bridge and have the thermal

compensating circuit as shown in Fig. 5, the thermal characteristics are excellent.

IN

OUT

)+IN

+OUT

Fig. 5. Electronic circuit of the pressure gauge

8

The diaphragm is mounted on the ceramics basement and protected by silicon rubber and stainless steel cover. Due to silicon rubber, there is little influence of bending of the blade, _{even if the pressure gauge is} mounted tightly on the blade.

The characteristics of the _{pressure gauge are shown in Table 5. It}

is clear that the pressure _{gauge has a high gain, comparing with other}

ordinary type of strain gauges.

Table 5. Characteristics of pressure gauge

3.3.

Location of the pressure gauges

Location of the pressure gauges was decided in taking account of

cavitation patterns on the propeller.

As shown in Fig. 6 five pressure gauges were mounted on the blade at 0.77 R. _{Chord-wise positions of the pressure gauges are every 20% of} the chord on the back and 40% on the face. _{They are named A, B, C, D}

and E respectively.

(A) B (C) o

0.2C-0.6 C-C (74.1mm) 0.sC

Fig. 6. Location of the pressure gauge

Pressure gauges were mounted carefully with paste made of high

molecular compound so as not to change the section of the blade. Sealing of leads of the pressure gauges on the blade were made by

the same paste as mentioned in the above. The leads were brought into

the hollow shaft through the boss of the propeller and they were sealed

by paste made from silicon.

Range Kg/cm2

i

Sensitivity mV/Vf.s. 33 Non-linearlity % f.s. 0.8 Hysteresis % f.s. 0.8 Zero-shift % f.s./10C 0.1 Sensitivity shift % f.s./1°C

0.3

Impedance KS? i Natural frequency kHz 100 Allowable temperature °C 0-40

Q) 5° ch Q) o-o

J

nrps 9

3-4. Calibration of pressure gauges

The static calibration of pressure gauges was performed by controlling

the pressure in the cavitation tunnel. In order to research an influence

of the rotation of the propeller, the dynamic calibrations were carried

out under the operating conditions. The results of the dynamic calibra-tions are shown in Fig. 7. It is clear that there is no influence of

rota-tion of the propeller.

mm Hg

loo-o lo 20 30 40 50

Reading in e.m.osci[Lo.

Fig. 7. Results of calibration of the pressure gauges

The static calibrations were performed before each experiment.

4. EXPERIMENTS

4-1. Experiments in uniform flow

4-1-1. Non-cavitating condition

The test conditions are shown in Table 6. In order to research the

influence of the rotational speed of the propeller the number of the revolu-tion was varied at the same advance coefficient.

Table 6. Test condition (uniform flow)

0.7 10 13 15 20

0.9 10 15 20

lo

The experimental procedure is as follows; First, the propeller was driven very slowly (abt. 0.4 rps) in the still water to obtain zero point of

the pressure and then the rotational speeds of both the impeller of the

tunnel and the propeller model were increased to

a desired speed. Finally, after the flow being stable the pressure signals were recorded.

Position B

--::=,

\/ \/ \./

\;7/

\:i

A _{=_}

r-\. '.

___

-C rr

-j

-f---i

t---O is

Fig. 8. Pressure signals in non-cavitating condition

(in uniform flow)

Fig. 8 shows a part of the pressure signals recorded by the

electro-magnetic oscillograph.

They look nearly sinusoidal, since the static

pressure varys with the rotation of the propeller.

The results of the tests are shown in Figs. 9 (a), (b), (c). In the figures,

the abscissa is the dimensionless chord length of the blade. The

defini-tion of Gp is as follows,

Gp =(P Po)kp W*2

where, (P P0) is the pressure difference between the pressure on the blade and the static pressure in undisturbed flow, p is density of water

and W* is inflow velocity which includes the induced velocity calculated by the lifting surface theory. Solid lines mean result of calculations by

the lifting surface theory using a conception of the equivalent blade shape7. Experimental results are presented by a mark (I) which implies a range of scattering.

The agreement between the results of the experiments and of the

calculations by the lifting surface theory becomes better as the advance

coefficient increases.

4-1-2. Partially cavitating condition

Table 7. Test condition (Cavitation) 11 -0.5 -0.4 -0.3 J = 0.7 -0.2 o-o

I

o- _-0.1 3. L) 0.0 0.5 C/C. 1.0 L.E. T E. 0.1 0.2 (a)

0.3

-= 0.9 -0.2

I

o-

I

C-) -0.1 -0.5 C/Co 1.0 0.0 L . E TtE 0.1 -(b) J = 1.1 -0.2

I

-0.1

-3. L)

-

1.0 0.0 I 0.15 C/C0 0.1

-

_(c)

Fig. 9. Pressure distribution at 0.77 R in non-cavitating condition

(in uniform flow)

j

Vm/s n rps

0.5 2.52 20.0 16.9_9.1 13.5_8.6 10.3

12

constant velocity of the water and the constant revolution of the propel-1er, various cavitating conditions were realized. The test conditions are shown in Table 7. The conditions were selected in the case that the

rear end of the cavitation reached near each pressure gauge, monitering

by a stroboscope.

Photo. 2. Partially cavitating propeller

Photograph taken under the condition J=O.7, rv=5.l is shown in

Photo. 2. The photograph shows that the sheet cavitation on the blade

is stable. Extension of the sheet cavitation under the each condition is illustrated by dotted lines on the right side in Figs. 10 (a), (b).

A part of the pressure signals recorded on the electro-magnetice

oscillograph is shown in Fig. 11. Under the non-cavitating condition the

signals appear to be nearly sinusoidal curves as shown in Fig. li (a).

Fig. il (b) shows that pressure gauge A was in cavitation, B was located

at the rear end of cavitation area and C was out of the cavitation. In

the case of Fig. 11 (c), A and B were covered with cavitation and the

signals were very stable such as A in Fig. 11 (b). However, the signal

from C located in the vicinity of the rear end of cavitation has large

fluctuation. Its frequency agrees with the number of the revolution of

the propeller. The lower side value of the signal was nearly equal to the vapour pressure and the upper side value of the signal presented a

little higher pressure than the stagnation pressure.

Pressure distributions over the blade are shown in Figs. 10 (a), (b).

Dotted lines

are not obtained from calculation but from estimation

using experimental results. As mentioned before, the solid line with

0. L) -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 -0.5 -0.1

--LE. = 0.5 V -IX (a) -Xi 0.5 C/C0 t t I I Non-cavitation(Exp.) Calculation byL.S.T. 0V 0W = (P - e)4 pV2 ow* (P - e)/J- pW'2 J = 0.7 I Non-cavitation(Exp.) Calculation by L.S.T 0V 0W 11.0 ---... T.E. 0.5 C/C0 1.0 0.0 T.E. 0.1 - (b)

Fig. 10. Pressure distributions in partially cavitating condition

(in uniform flow)

of calculations by the lifting surface theory under non-cavitating codi-tion.

Figs. 10 (a) and 10 (b) show that cavitation on the back of the blade did not influence on the pressure distributions over the face of the blade.

On the back of the blade, it can be said that cavitation did not give

re-markable influence on the pressure distributions in downstream, except

near the rear end of cavitation.

o 5.1 0.42 3.7 11.30 D 3.1 0.24 16.9 0.72 Q 13.5 0.58 V 10.3 0.43 D 9.1 0.38 ) 8.6 0.35 -0.4 --0.3 -0.2

14 1.0 0

---c

-.

yt_

-,;ç

B 0.05s (a)

J = 0.5

Non-cay. A B lower side

--kF--tA,

L_ .

-e--', __A

t/ +±r

---

-+-4--j---

_r-+

r-____t-±i

'-t-upper side\

(c)

J =0.5

v = 10.3

Fig. 11. Pressure signals in cavitating condition

(in uniform flow)

(b)

J=0.5cv1.5

'f r/ ro 0.912 0.7 60 0.624 0.504 300 360 6deg

4-2. Experiments in non-uniform flow

To obtain the pressure fluctuation on the blade in non-uniform flow,

mesh screen method was used to reproduce a wake distribution in the

-C

240

0 60 120 180

BOTTOM

cavitation tunnel. The wake distributions are shown in Fig. 12.

The test conditions are shown in Table 8. velocity of the water is

averaged in the propeller disk area. Advance coefficient J is calculated from the averaged velocity of the water.

-70 -60

50

-40

i 30

E E -20 û--1 0 o 10

Table 8. Test condition (non-uniform flow)

J (mean) n rps

0.7 13.9

0.9 10.8

V (mean) V (max.)

rn/s m/s

T.No.70 Np 10.Orps J = 0.9 Position A

Fig. 13. Pressure signal in non-uniform flow (in non-cavitating condition)

I i J

0 60 120 180 240 300 360

BOTTOM G ¡n deg

Fig. 14. Pressure fluctuation (Position A)

15

16

The pressure fluctuation recorded on the electro-magnetic oscillograph

is shown in Fig. 13. The pressure fluctuations recorded using the data

recorder were digitized using an A-D converter and were processed using

a computer.

-60

50

mmHg (0 Shaft tent re)

n 10.8 rs J =0.9 / 0000 o

B-1 0 o 10 20 - 60 40 a'

I

0* C 00000 . ..cc0e 00 00 e.. I J J I I I 0 60 120 180 240 300 360 BOTTOM e deg.

Fig. 15. Pressure fluctuations (Position B and E)

n o 10.ßrps J = 0.9 Colculoted 000 Experiment 50 E 0 000 E 3 0 00 00 0 0 0 0 0 0000e o o.. 0Q0 00 00 00 ₀ OOQO 000 0 000

20 -

000 000 000 000 00 0 000 10 0000 O I i i i I 0 60 120 180 240 300 360 BOTTOM _{e in deg.}

Fig. 16. Pressure fluctuation (position C)

40

3 0

1.0 0000 Calculated o I I I 0 60 120 180 240 300 360 80110M _{e in deg.}

Fig. 17. Pressure fluctuation (position D)

Pressure fluctuation at each position in the case of J=O.9, is shown together with results of calculations in Fig. 14 to Fig. 178.

It can be said that, the experimental results

_{agree well with the} results of calculations concerning amplitudes and phase _{of the pressure}

fluctuations. _{However, in the case of position C and D, there exist}

dis-crepancies concerning phases.

As pressure gauge B is just back to back with E, it is easy to obtain

the pressure difference, that is, the lift.

Fig. 18 shows the fluctuation of the lift _{obtained from experiments.}

-

CaLculated °° Experiment n=10.8rps J=0.9 0 00 000 Experiment n = 10.8 rps J o 0.9 I I I I I 0 ₆₀ 120 180 240 300 360 BOTTOM 9deg,

Fig. 18. Fluctuation of the lift.

17 D - 50 -40 U)

30

D-

00;00

20

30

C 0 0.5 O

18 0.4 C -J 0.2 0.1 o Culculatod

Fig. 19. Fourier coefficients of the lift.

The Fourier coefficients are shown in Fig. 19. The experimental results

agree well with the calculations.

5. CONCLUSIONS

Measurements of the pressure distribution over the blade of the propeller model were carried out successfully under three conditions, that is the non-cavitating condition in uniform flow, the non-cavitating

con-dition in the non-uniform flow and the partially cavitating concon-dition in uniform flow.

It is found that the very small pressure gauge made of semi-conductor is suitable for measuring pressures on a blade of a propeller model.

In the case of the non-cavitating condition in the uniform flow, the agreement between the results of experiments and of calculations by

the lifting surface theory became better as the advance coefficient in-creased.

In the case of the partially cavitating condition in uniform flow, the cavitation on the back of the blade did not give remarkable influence

on the pressure distribution over the blade except near the rear end of

the cavitation.

In the case of the non-cavitating condition in non-uniform flow,

the experimental results agreed well with the results of calculations by

the lifting surface theory concerning the amplitude and the phase of the pressure fluctuation except phase at positions C and D.

The investigation dealt with in this paper has been performed as a

part of development of a new series of screw propeller for high speed

container ships. 0.5 _{n = 10.8 rps} J = 0.9 Experiment 6 2 3 4 5

REFERENCES

Miyata, S., Tamiya, S. and Kato, H., "Some Characteristics of a Partially Cavitating Hydrofoil", Journal of the Society of Naval Architects of Japan, Vol. 132, 1972. Maviudoff, M. A., "Measurement of Pressure on the Blade Surface of Non-cavitating

Propeller Model", Proceedings of the 11th TTTC, 1965.

Kato, H., "An Experimental Study of the Pressure Fluctuation on a Propeller", Proceedings of Symposium on Hydrodynamics of Ship and Off-shore Propulsion, Oslo,

1977.

Ito, Y. and Araki, S., "On Measurement of Surface Pressure of an acting Model

Propeller (ist report)", Technical Note of the Shipbuilding Research Centre of Japan,

Vol. 4, 1976.

Ito, Y. and Araki, S., "On Measurement of Surface pressure of an acting Model

Prop-eller (2nd report)", Technical Note of the Shipbuilding Research Centre of Japan, Vol. 5, 1977.

Kadoi, H., Kokubo, Y., Koyama, K. and Okamoto, M., 'Systematic Test on the SRI. a-Propeller", Report of Ship Research Institute, Vol. 15, No. 2, 1978.

Koyama, K., "A Numerical Method for Propeller Lifting Surface Theory of a Marine Propeller", Journal of the Society of Naval Architects of Japan, Vol. 132, 1972.

Koyama. K., "A numerical Method for Propeller Lifting Surface Theory in Non-uniform

Flow and Its Application'. Journal of the Society of Naval Architects of Japan, Vol. 137, 1975.

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23

Takahashi, March 1973.

No. 45 Life Distribution and Design Curve in Low Cycle Fatigue, by Kunihiro lida and Hajime moue. July 1973.

No. 46 Elasto-Plastic Stress Analysis of Rotating Discs (2nd Report: Discs subjected to Transient Thermal and Constant Centrifugal Loading), by Shigeyasu Amada and Akimasa Machida, July 1973.

No. 47 PALLAS-2DCY, A Two-Dimensional Transport Code, by Kiyoshi Takeuchi,

November 1973.

No. 48 On the Irregular Frequencies in the Theory of Oscillating Bodies in a Free

Surface, by Shigeo Ohmatsu, January 1975.

No. 49 Fast Neutron Streaming through a Cylindrical Air Duct in Water, by Toshimasa Miura, Akio Yamaji, Kiyoshi Takeuchi and Takayoshi Fuse, September 1976. No. 50 A Consideration on the Extraordinary Response of the Automatic Steering

Sys-tem for Ship Model in Quartering Seas, by Takeshi Fuwa, November 1976.

No. 51 On the Effect of the Forward Velocity on the Roll Damping Moment, by Iwao

Watanabe, February 1977.

No. 52 The Added Mass Coefficient of a Cylinder Oscillating in Shallow Water in the Limit K-.O and Koc, by Makoto Kan, May 1977.

No. 53 Wave Generation and Absorption by Means of Completely Submerged Horizontal

Circular Cylinder Moving in a Circular OrbitFundamental Study on Wave Energy Extraction, by Takeshi Fuwa, October 1978.

No. 54 Wave-power Absorption by Asymmetric Bodies, by Makoto Kan, February 1979.

In addition to the above-mentioned reports, the Ship Research Institute has another

series of reports, entitled "Report of Ship Research Institute". The "Report" is