Measurements of water flow and pressure set up by ships in motion

2N

(I) Numbers refer to bibliography at the end of the paper.

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- - AUG. 1976

_{Lab. v/}

ARCHIEF

NORTH-EAST COAST INSTITUTION OF ENGINEERS AND SHIPB

BOLBEC HALL, NEWCASTLE UPON TYNE

ADVANCE COPYSUBJECT TO REVISION

This paper is issued in advance on the understanding that neither the whole nor any portion ofit shall be published until after it has been read at a general meeting of the Institution.

It is to be read at a meeting of the Institution to be held in Newcastle upon Tyne on 5th March, 1948.

MEASUREMENTS OF WATER FLOW AND PRESSURE

SET UP BY SHIPS IN MOTION

By E. G. RICHARDSON, B.A., Ph.D., D.Sc.

5th March, 1948

SYNOPSTS.The means available for measuring water flow and pressure in the

vicinity of shipsmodel or All-scalein motion are discussed. The calibration and sensitivity of two types of recorder, i.e. the hot wire for velocity and the aneroid for pressure, are described in detail. The conditions which must be fulfilled when these instruments are required to Mow fluctuating motions are

considered.

There follow practical examples of the application of the hot-wire velocimeter to ship models in a towing tank, for recording both mean velocities set up by the general motion of the ship and the microturbulence set up by its vibration. A means of recording the flow through a screw propeller is also described.

ALTHOUGH

it

is now common practice in aerodynamics to

measure local velocities and pressures in relation to models

supported in wind tunnels andto a less extentto aircraft in

flight, the use of instruments for this purpose in relation to ships is

apparently uncommon.

It is the Author's object in presenting this

paper to exhibit the possibilities of measurements of this type in water.

In Part 1 the calibration and construction of suitable instruments are

described, while Part II illustrates some applications to ships.

The

latter were made for special purposes during the recent war and the

Author makes no claim that the results as such will be of use in ship

design. Nevertheless he hopes that they will serve as examples of what

can be done in this field with comparatively simple apparatus.

PART I

Hot-wire Velochneter

Although the well-known Pitot tube was first used by its inventor in

hydrodynamics, namely, to record the speed with which a boat was propelled

on the Seine, its usage is now almost restricted to aerodynamics. Indeed, in the

Author's experience, the Pitot is unsuited to the measurement of water flow

save in totally enclosed tunnels, since a knowledge of the local static pressure

at the orifice of the tube is required and this varies with the height of waves

produced by a surface-ship model. Venturi and Amsler meters usually occupy

too much space for model work.

There remains the measurement of velocity from point to point by the cooling

of an electrically-heated wire exposed to the flow, an instrument of frequent

use in wind-tunnel work. Much of the work described in this paper involves

applications of the hot wire to water flow.

The basis of measurement of fluid current by the cooling of a thin hot wire

exposed to the stream is to be found in a paper by King'. He established two formulae relating the heat loss per second per unit length of wire H in a flow

-

.v

.d6.1

tot.-43topoll

T

j9. A

*4

MEASUREMENTS OF WATER FLOW AND PRESSURE SET UP BY SHIPS IN MOTION

of velocity U to the radius a and temperature 0 of the wire and certain physical properties of the fluid, namely, density p, thermal capacity per unit volume s and thermal conductivity k. He gives two formulae of which the second only will concern us, relating as it does to speeds for which the natural convection from the wire is masked by the forced convection due to the motion. This formula is:

H =

[k

2-V (nksplia)] 0.

[k

c

/Ua]

0, ₍₁₎

Davis' has verified this formula by experiments in various liquids. Owing to the greater value of V (ks p) in liquidse.g. 0.039 in water compared to 0-000 1 l in airthe instrument is less sensitive in liquids than in gases, but this may be

offset by raising the wire's temperature further. In practice, two techniques are possible: either the temperature is maintained constant by altering the heating current to suit the different velocities in which the wire finds itself, or the heating

current is maintained while the temperature is allowed to vary and estimated

from the electrical resistance of the wire. Inserting the appropriate values of

the physical properties of water, the second operation, which the Author

prefers, leads to an expression, based on (I), which involves the heating current i, the cold resistance R0, that at temperature 02, R and a the coefficient of change of resistance of the material of the wire with temperature:

al'

RR°

Ro

k c / Lk, 0.0015 H 0.135N/Ua (2)

in water.

For sensitivity, one needs a as small as possible and 0 as large as possible but one must avoid so great a temperature excess that convection disturbs the flow which it is desired to record. To fix our ideas, the work described in Part was done with a nickel wire (a= 003) two thousandths of an inch in diameter

heated by 0-9 amp. The wire may be from II," to 1" long.

If the constants of the wire and fluid are accurately known, the calibration in the form of resistance against velocity can be predicted, but it is perhaps safer

to carry out an actual calibration by mounting the wire on a small whirling arm or beneath the carriage of the towing tank, the electrical gear being, of course, carried clear of the water. Fig. 1 shows (by the full line) a typical

calibration curve obtained in this manner.

The electrical circuit may take the form of a simple Wheatstone bridge, the

hot-wire forming one ratio arm, the other being a wire of heavy gauge of about

one ohm in order that the heating current may not raise its temperature

appreciably. The other two arms are of higher resistance, about one hundred

ohms each. For accurate measurement, the curve must be known very precisely,

so that some prefer to use a potentiometer, measuring alternately the fall of

potential across the balancing ratio armfor current verificationand the

hot-wire forkfor resistance measurement.

Fig. 2 shows a circuit of this

type, (after Tyler3).

It is an inconvenient circumstance that, as Fig. 1 and King's equations indicate, the resistance of the wire is not directly proportional to the flow in

which it finds itself. However, by feeding the potential across the wire into the

grid of a thermionic valve having a suitable characteristic, it can be arranged that the plate current in the valve is directly proportional to the velocity over a considerable range of the latter. Such a circuit, first used by Luneatri, is shown in Fig. 3 and the result on the calibration curve by the broken line on Fig. I.

The photograph (Fig. 4*) shows a form of hot-wire fork used by N. A. V.

Piercy and the Author6 for studying the flow in the vicinity of a model into the side of which the main frame members are pressed, while the micrometer head accurately locates the wire at known distances from its surface. When used in close proximity to the surface of a model, such a wire requires correction to the

" apparent " velocity which it indicates, the apparent velocity being less than

Reproduced by permission of 11. M. Stationery Office.

+

=

MEASUREMENTS OF WATER FLOW AND PRESSURE SET UP BY SHIPS IN MOTION 275

the true one. Piercy and the Author' have established this correction in air by whirling a vertical platinum wire round a circle of slightly larger radius than a fixed vertical metal cylinder and measuring the loss of heat. Results are shown in Fig. 5 from which it is apparent that the heat loss by conduction to the solid, and consequently, any velocity correction, becomes negligible beyond a certain

limiting distance--indicated by the chain linefrom the solid boundary. This

limit approaches the wall as the true speed at the wire goes up, because the heat conducted away is then blown further down stream before it strikes the cylinder and the heat lost by conduction depends inversely on the effective path length between the hot and cold bodies.

Hot-wire Apparatus fin- Direction

Direction of flow can be estimated from the fact that at a given relative

speed, the heat lost by the wire is least when it is pointing along a stream line, owing to the tendency for the after part of the wire to be warmed by that taken

from the fore part when the wire is in this position. Alternatively, a little

pyramid of three wires may be used with the vertex pointing upstream, under

which circumstance, the resistances of the three should be equal. Hot Wire in Unsteady Flow

When a heated wire is subjected to a simple periodic motion of the fluid which bathes it, the thermal inertia" prevents its following the change of velocity with exactitude at all but the lowest frequencies. If its electrical

resistance is recorded on an instrument capable of following fluctuations, such

as a string galvanometer, it is found to consist of two parts: (I), a steady fall

of resistance on which is superimposed (2), an alternating variation of twice the

frequency of the fluid motion but of amplitude less than would correspond to the full variation in each cycle. (The octave of the frequency of oscillation arises because the wire is unable to distinguish between up and down or left and right so that its resistance fluctuates twice to each period of the imposed

s.h.m.).

Write (1) in a simpler form, for steady conditions:

PR, = (c,

c2,/ U) U (la)

During the attainment of equilibrium a term in do/di intervenes. Making the same substitution of electrical resistance for temperature, we have:

dR

F,

PR (ci c2- / R Ro (3)

Roc, dt Rom

where f is the thermal capacity of the wire in joules per degree. Putting R, for the ultimate resistance as given by (la), we can combine these two equations into the form:

dR czi2Ro2 (R, R) 1

di

f

(121 R0)

T (R1

(4)

where A -

f (12,.1)

and is a temporal factor representing the thermal inertia xi' R02

of the instrument.

In a fluid oscillation of pulsatance 0,, the amplitude of the velocity indication of the wire is reduced from the true, very low-frequency value, in the reciprocal

ratio of ,V(1-1-A2w2). The phase of its response is also delayed by an angle

whose tangent is Aw

Faced with the consequences of this thermal inertia, one can adopt various

remedies. Often in wakes, one is dealing with eddying motions of a constant

periodicity; as the amplitude of response at a fixed frequency is proportional to the amplitude of the motion being recorded, one can use a measurement of the amplitude of resistance fluctuation on a vibration galvanometer without further ado. In place of the vibration galvanometer, one can put telephones, moving

the hot-wire about until the "vortex noise is a maximum. In this way, one

can trace the path of the vortices down the wake (c.f. Fig. 18 in Part II). If

one is comparing s.h.m's of different, but known, frequencies, one can calibrate

+

-- .

the hot-wire under conditions corresponding to the recording by oscillating it in still water on the prongs of a vibrating reed or tuning-fork. For overall

mixed frequencies it is

best to use an amplifier like that of Luneau and

incorporate in the output an electrical circuit having a time-factor which added to the value of to just calculated brings the instrumental lag full circle and into

phase with the water motion again. (Dryden and Kuethe'). Under such

circumstances the thermal inertia may be made to disappear, though the

compensation may not be valid for an extreme range of frequencies. Such a

doubly compensated velocimeter should give a response, i.e. anode current, proportional to the amplitude of fluctuation (for instance, in turbulent flow) independent of frequency, at the loss of a certain amount of sensitivity in comparison with the unadulterated hot-wire, (Fig. 6). The fashion in which

the electrical filter levels out the frequency response is shown in Fig. 7. Pressure Recorders

In order to record varying pressures under water, one has recourse to some form of air-filled pot with a flexible membrane for a lid. The mean pressure inside the pot must be the same as in the water outside, to keep the membrane

flat. This equalization may be performed by pumping air into the vessel

through a non-return valve, if it is attached to the hull of a ship or to be placed on the floor ofa towing tank, but

if

it is to be laid in a tideway, the principle

of the equalization chamber must be employed so that the apparatus can

reach equilibrium as to its internal pressure with the mean hydrostatic pressure outside as the tide ebbs and flows and at the same time record, with practically negligible loss, the variations in pressure due to waves and the passage of ships. The pot already mentioned may be mounted over the equalization chamber (of

capacity about 50 litres) to which it is connected *by way of a " leak " or

bleed-hole. _{The bottom of the equalization chamber is open to the sea which}

enters until an equilibrium ofpressure is reached. When a sudden excess or

deficit of pressure is applied to the diaphragm, pressure builds up in the capsule, because air cannot leak away fast enough through the bleed-hole.

In one form of the apparatus, devised by the Author, the difference of pressure

between the upper capsule and the equalization chamber was recorded by

a sylphon bellows of the type used in barometers, whose expansion cut off more or lessofthe light reaching a photoelectric cell within the pot, connected to a

galvanometer inshore. This apparatus was used for recording the pressure on the sea bed due to waves and has been fully described elsewhere'.

In a later form of pressure recorder, which the Author thinks better adapted for measurements inboard of ships or in towing tanks, the movement of the

membrane over the pot was measured electrostatically. The general build of the pot (Fig. 8) is similar to that used on the aneroid device aforementioned.

The upper plate of an electrical condenser is formed by a thin brass plate (P1) which is clamped to the rubber diaphragm (R) at its centre and so moves with it. The lower plate (P2) is fixed. Both are insulated, the central boss and the circular groove round the diaphragm being covered with Chatterton's compound,

The lower plate has a thin paper strip stuck to its upper surface to prevent its making electrical contact with the other under excessive deflection. The

deflection up or down of the diaphragm under varying water pressure causes

changes in the capacitance of the condenser, the plates of which are connected

through as short a length as possible of concentric cable to the grid circuit of

a valve amplifier. The anode potential of the latter, modified by the pressure-induced signal, is fed to a cathode-ray oscillograph. (If the cable is lengthy, its capacitance swamps that of the manometer, which makes this recorder unsuitable

for use on the sea bed without a pre-amplifier in the pot.)

Both types of pressure recorder are calibrated by having known steady and rhythmic alternations of hydrostatic pressure applied to them, e.g. by raising

and lowering the pot in a deep tank or water tower. Other things being equal, the movement of the diaphragm and consequent reduction in the separation of the plates for a given increase of pressure depends directly on the volume of the

MEASUREMENTS OF WATER FLOW AND PRESSURE SET UP BY SHIPS IN MOTION

pot and inversely on the static pressure. Packing pieces of wood (B, Fig. 8)

can be inserted to alter the internal volume of the pot togive a desired sensitivity.

These recorders were built in 1941.

Later a more compact form of

electrostatic recorder was developed at the Admiralty Experiment Works, Haslars for use in the towing tank and a somewhat similar apparatus built at the Royal Aircraft Establishment was used by the Author in a study of the impact forces on the hulls of flying boats when alighting on water. There is

no reason why similar recorders should not beattached to the hulls of ships to

measure impact pressures in rough seas, though, as far as the Author knows,

this has never been done.

PART II

The experiments now to be described on the flow of water under ships in

motion were carried out while the Author was attached to the

Admiralty Mine Design Department in 1940 and 1941. Thelocales were the fairway at

Spithead for full-scale experiments and the towing tanks of the Admiralty Experiment Works at Haslar (by arrangement with the Superintendent and the Director of Naval Construction) for model experiments.

At the time when the Author joined the staff of the former establishment, Mr.

R. W. L. Gawn, Superintendent of the Admiralty Experiment Works, had

already made some qualitative measurements of pressures under surface models

by means of static tubes, at the suggestion of the late Prof. B. P. Haighof the

Royal Naval College, Greenwich, and in fact, as we learned later, some

measurements by the same rather rough method had been made elsewhere in

1917 in respect of a model submarine. These had shown that beneath the passage of a full-scale ship at cruising speed in a moderate depth of water,

pressure fluctuations of the order of a few inches of head were to be expected.

Using the aneroid recorder mentioned in Part I, the Author confirmed this

under ships passing up and down Spithead in March 1941 and later in the same year recorded the sea-bed pressures due to Channel waves and swell in a more exposed site off Ventor, I.o.W. (It is not proposed to refer further to these here as they have already been published7). Mr. Gawn has also quoted later

results obtained by his staff at A.E.W. of the pressures under model ships

using an electrostatic device.'

Associated with the pressure variations accompanying the passage of a ship

are varying movements of the water which it is the main purpose of this section

of the paper to record. The origin of both these effects may be sought on the

one hand in the bodily displacement of water by the hull as

it passesand

therefore equally relevant to a fish or a submarineand on the other hand to

the wave motion which a surface ship sets up-and therefore equally applicable

to a hydroplane. When a (surface) craft is moving slowly, the first aspect is more rational but the latter is more appropriate to a fast vessel. On these

bases, theories may be built to calculate the suction or velocity of the water, at least as to their amplitudes. The " displacement theory due to Sir Geoffrey

Taylor is to be found in an appendix to Gawn's paper but the latter involves a difficult calculation from the wave pattern of ships such as those derived by

Prof. T. H. Havelock. It is not proposed to elaborate these further, since this

is a paper of practical measurement, than to point out that the motions in

question are complex functions of the amplitude of water displacement A, the

length and draught of ship, its speed U and the depth h to the place of

measurement. In the simplest case of a system of plane waves of length /, the

pressure amplitude p on the bed works out as:

2rfp,1

U2 sinh274 I

Model Experiments on the Flow Beneath a Moving Ship

Nickel wires 0.001 inch and 0.002 inch diameter and 1.5 inch long were used for model experiments on the flow beneath a moving ship. They were mounted on a fork attached to an insulated base weighted with lead to rest on the floor of

the main Haslar tank with the wire horizontal and broadside to the track of the ship. Eventually the thinner wire was discarded owing to frequent breakages. _A

current of 0.9 amp. in the thicker wire was found to give adequate sensitivity.

The holder was intended to give two alternative positions, respectively 1 in. and

3 in. above the base, but in the event only the higher position _{was employed}

(Fig. 9).

The hot-wire was connected into a circuit of the type already described

(Fig. 3), the galvanometer recording if need be continuously on a moving strip of paper in a camera. _{Calibration of the velocimeter was effected by mounting} the fork upside down under the towing carriage so that the wire lay submerged,

running the carriage at known speeds and observing the deflection of the

galvanometer. In such a calibration run the recording gear had to travel with

the carriage but when models were being run, leads from the fork _{on the bed of} the tank were taken to the recording gear stationary in the walking way alongside the tank.

Fig. 10 gives the flow signatures beneath the track of a model (A) 20 ft. long and 1/39 scale, the bed being 5 ft. below the water surface. The three records are obtained at scale speeds of 4, 6 and 12 knots respectively. These all show

the characteristic double hump associated presumably with the wave crest at

stern and stern. _{These maxima do not, however, increase in size as the speed}

directly owing to interference and their location in regard to bow and stern

changes with speed. Fig. 11 shows another type of signature less common among our records, in which one hump predominates. These were obtained

with a model (D) 18+ ft. long and 1/13 scale so that the draughtwas relatively greater, the upper pair with a depth of 5 ft. at 12 and 10 knots respectively, the

lower pair with a depth of 7+. ftby removing the false bottom from the tank at 12 and 8 knots respectively. _{Though the pattern preserves its similarity,} the flow induced by the vessel at the greater depth is less for thesame speed. (The width of the tank is 40 ft.)

Fig. 12 is for a model (B) 14 ft. long and 1/14 scale at a speed of 8 knots when the instrument was moved successively to one side of the track. The

record is of the more usual type and it will be seen that the ship's passage is

still registered though less markedly, 4.5 beams to one side of the track. There is also a progressively increasing lag in the arrival of the disturbance to stations to one side of the track. The bottom of the tank for this set lay at 7+ ft. below the surface. Finally, to simulate sea conditions, the apparatus was moved to

the smaller Haslar tank in which waves of nominal length and height can be set

up at the same time as the model is towed from the carriage. Three typical records of the flow due to model waves are shown in Fig. 13 together with one

in which another model (C), 13 ft. long, 1/15 scale, travelled through thewave

system at 8 knots. The passage of the model is disclosed by a pair of peaks of abnormal height and wave-length followed by a wake which "interferes

with the prevailing waves. (This tank is 20 ft. wide and 8+ ft. deep.)

Sections of the models used in these trials are given in Fig. 14.

Subsonic Emission from Ships

The hot-wire holder of Fig. 9 was mounted on a sinker and surrounded by an open-mesh wire cage to prevent objects falling on it and then used in sea trials alongside the pressure gauge. A nickel wire of 0.003 in. was used fed

by 15 amp. and the supporting pillars were encased in rubber sleeves to prevent,

as far as possible, leakage of current through the sea. (The extent of this

leakage may be gauged from the observation that if the wire broke the remaining

current through the leads to the sea path was 04 amp. instead of zero as in

fresh water.) _{This wire responded to the passage of a ship by a change in its}

resistance, though this never reached the stagnant-water value owing to tidal

flow. It was noted when using a galvanometer not critically damped that there

was some oscillation of low frequency picked up from the ship and this was confirmed by replacing this instrument with a vibration galvanometer of "

MEASUREMENTS OF WATER FLOW AND PRESSURE SET UP BY SHIPS IN MOTION 279

frequency 25 c. /sec. At this frequency the general tidal background picked up

in Spithead gave a deflection of 1-2 cm., which on the passage of a ship rose to 7-10 cm.*

In order to study these " subsonic' vibrations, apparentlyemitted by a ship, in more detail, a subsonic source was built and used in a bay of the Haslar tank against the hot-wire as detector. This consisted of a floating raft 3 ft. 6 in. square, on which was mounted a h.p. motor with a pair of eccentric

axle loads, the corners of which were tied by loose strings to a

wooden frame-work which could straddle the dock and leave the raft free to vibrate under

the action of the motor while preventing it from driftingfree (Fig. 15a). The

hot-wire was then traversed along the central plane of the dock at various depths

beneath the raft and the deflections of a vibration galvanometer in a

simple-bridge circuit noted. From these records contours of equal deflection were

plotted, Fig. 15b shows a set of such contours and Fig. 16 the experimental traverses from which the field is derived, at a frequency of 30 c. /sec., a previous calibration of the bridge having shown that the response of the galvanometer is

proportional to the amplitude of subsonics at this frequency, at least up to a

deflection of 8 cm.

In the light of these experiments, it is concluded that the hot-wire, usedin this way, can respond to the hull vibrations of a ship. This was confirmed by laying

the hot-wire once more on the false bottom of the larger towing

tankat a

depth of 7 ft. 6 in.while a gunboat model of 1/8 scale was being run, and noting the vibration signature both with and without its propeller running.

Fig. 16 shows a typical record, wherein the initial disturbance before the arrival

of the model is probably transmitted from the motion of the towing carriage through the structure of the tank. The enhanced disturbance after the model

has gone ahead of the recorder about 20 ft. is evidently emitted by the model.

The following table records these runs:

Remarks

1 2 cm. average deflection after peak

'value.

Prolonged deflection

of 4 cm.

average.

Peak 25" behind stern.

Prolonged deflection of 4 cm. after

peak.

Control run of carriage without

model.

It appears then that the " subsonics - recorded by the wire are not noise

emitted by the propeller so much as microturbulence set up in the water by the hull. This is confirmed by the fact that the peak of response of the detector

invariably occurs some seconds after the hull has passed over the unit, indicating

that the disturbance was propagated at quite a low velocity and certainly not

at the speed of sound as propeller noises are.

Plotting Velocity Fields in the Vicinity of Models

To show how the existence of periodic fluctuations in the wake of a model may be detected and followed by the hot-wire, a figure is included in which

contours of equal velocity-fluctuation are recorded with the hot-wire connected

to a string galvanometer° (Fig. 18. The numbers attached to the curves are

Only records of flow in the model tanks can be exhibited in this paper, as the records from the sea and most of the apparatus used for these sea trials were destroyed when an enemy bomb fell on the inshore hut in May, 1941.

Run Speed knots Screw revs/min. Maximum deflection 1 9 3,000 5 2 ,, 0 4 3 12-5 0 6 4 ,, 3,000 6 5 ,, 3,250 4 6 7 ,, 0

_

8 1 I

-proportional to the deflection). The shedding of periodic eddies is quite obvious in the lee of the cylinder, to which this method is applied, by the peak deflection which can in fact be traced quite a distance down the wake. Using

the wire as a "stethoscope for turbulence" (c.f. Part I) the region of vortex

noise was also delineated and is recorded on the same figure.

By traversing a wire of the type shown in Fig. 4 along normals to a hull profile and connecting it into a bridge for steady or mean velocities, one can

derive from these corresponding contours of mean velocity, such as those shown in Fig. 19 for an airship hull at a low Reynolds number". _{Unfortunately, the}

Author has no records for the hull in water and the measurements of both Figs. 18 and 19 refer to air as ambient medium. There seems no reason to

anticipate any difficulties in making such measurements round a model hull in

water, provided that the detector is located where no part of it can project

above the free surface.

Finally, a word or two about plotting the flow round model screws. For this again only data on air are yet available. Fig. 20 shows a scheme used by the Author" about twenty years ago to explore the flow round an airscrew. _The

hot-wire W occupies a fixed position in a wind tunnel. The velocity relative

to the propeller at a fixed point varies with the rotation of the blades so that a continuous record of the resistance of W would be vitiated by thermal lag.

To overcome this difficulty, the electric current was supplied to the wire for a short

epoch once in each revolution, by means of the metal slip ring B on the insulated

boss of the propeller, wiped by two leads to the battery. The rotation was sufficiently fast for a balance of the resistance on a Wheatstone bridge to be

attained under these conditions. The device was calibrated by rotating the boss alone at the same speed, with the blades removed, and the channel wind suitably

varied. In this way, a series of traverses of velocity with phase anglereckoned

as zero when the trailing edge of the one blade exactly covers the wire in the

military sensewas obtained and plotted on Fig. 21.

This shows well the

impetus given to the fluid as the blade passes. An alternative method, which

a student of King's College, Newcastle, has proposed for the corresponding study of the flow produced by a water screw, is to fix the hot wire by suitable bracing to the blade, with which it rotates, and to convey electric current to it

by slip rings. It thus remains at constant phase angle relative to the blade and

should record a steady velocity, though the design of the braces to avoid

interference with the flow may involve difficulties.

Acknowledgments

The work on ships described in Part 11 of this paper is published by permission of the Chief of the Royal Naval Scientific Service and the Director of Naval Construction. The Author wishes to give his best thanks to Mr. R. W. L. Gawn and his staff for their helpful collaboration while the work was being done at Admiralty Experiment Works. He also wishes to record his appreciation of his colleagues in the section of the Mine

Design Department dealing with new weapons for their willing assistance, often

continued under the stress of enemy action, in 1940-42. _{Their names were: Drs. S.}

Holmes, C. H. Mortimer, H. L. Penman, N. W. Robinson, H. C. Wright. Not all took part in the experiments here recorded, but it is a pleasure to recall, in less hectic times, a very pleasant association.

REFERENCES I. King, L. V., Phil. Trans., 214A, 373 (1914).

Davis, A. H., Phil. Mag., 44, 930 and 940 (1922).

Tyler, E. Journ. Scient. hist, 6, 310 (1929); Phil. Mag., 11, 849 (1931). Luneau, Aeronautique, 15, 232 (1933)

Piercy, N. A. V. and Richardson, E. G., Aero. Res. Comm. R. & M. 1224 (1938). Dryden, H. L. and Kuethe...., Nat. Advis. Comm. Aero. Rep. 320 (1929) Richardson, E. G., Phil. Mag., 37, 25 (1946).

Gawn, R. W. L., I.N.A., 88, 148 (1946).

Piercy, N. A. V., and Richardson, E. G., Phil. Mag., 6, 970 (1928) Richardson, E. G. and Tyler, E.. Phys. Zeits., 32, 509 (1931) Richardson, E. G., Journ. Roy. Aero. Soc., (1927).

-5.

.6.

20

111EASUREMENTS OF WATER FLOW AND PRESSURE SET UP BY SHIPS IN MOTION' 281

Fig. 3Amplifier Circuit giving

Linear Response

tanelard cell Weston)

Hot Wire (s0 alems) dabv

Fig. 4-Hot- Wire Fork for Use in Vicinity of Model Boundary

""hms

Ammeter Fig. 2- Wheatstone Bridge

for Hot Wire

VELOC.Jrf

Fig. 1- Calibration Graphs

for Hot Wire

2.0

7.5 (211=0075

aU=0.06

aU=0-05

aU=0-03

fig. 9Hot- Wire Instrument used in Towing Tank

Distance of centre from wall

Radius of wire

Fig. 5Heat Loss from Wire in Vicinity of Solid Boundary

Input

2?

Fig. 6 Amplifier Circuit giving Response Independent of Frequency

of

1

Compensated Wire

0

0

250

500

750

Frequency

/c01.12Pei7sated

_Wire

Fig. 7Effect

of

Compensation on Hot-Wire Response

v 1111'

\MSC.

IMMO. WM Pu, I PSI _UI 111,151

Fig. 8Apparatus for recording Underwater Pressures For Fig. 9 see opposite page

}Output

0.8

0-6

>t,

0-4

tsk,

02

1000

(cisec.)

.7ated

20

10

Fig. 10-Records of Flow wider Model A at Several Speeds

t5 1,4E (5E,B).

TIME5(S(..0 5).

Fig. 1 1-Records of Flow under Model D at two Speeds and Depths

20

10

MEASUREMENTS OF WATER FLOW AND PRESSURE SET UP BY SHIPS IN MOTION 285

ram E (SECS) 15

Fig. 12Records of Flow under Model Hat Various Distances Abeam

2 6 ILMEAUC.L0 Q.462 R TRACK 5 CT F206% TRA0,1, FT FIZOM -MACK ao

Fig. 13Records of Flow due to Waves, with Ship Passage

WAVE LENGT. 3.7FT.

keIe.T51.1.

WNIE LEN6T4 5 eFT.

NEIGAT 5 w/61E. /...21.1,,,T14 6sFT. HEIGHT 61N wAVE .:NSTEM WITh5442PS PA55AGE

-0

Fig. 14Sections of Model Ships

UT WooDEN ...7,-"FivamE on+ TANK.

ECC. %NT$:ZIG L-0A0

ij _{banIMIMMENI.."}

Mara

.111=11111

1111"..'111011111 111111111111111 5 ONO 3 a 1-6oPizoN-rp..,_ 018 TAN CE (F-1").

Fig. 15Records of Subsonics due to Vibrating Raft

Ohi ,#4000C.4

RAT.

TARE ADS

a

HORIZONTAL DISTANCE (-r)

1 6 - Co nioursof Subsonics due to Raft

Fig. 1 7Subso n ics due to PassageofModel over Unit

AUDIBLE LIA11_7"?.. ---OVER 60

- AUDIBLE MAX

ONO

Fig. 1 8- Con to ursof Velocity Fluctuation in WakeofCylinder

i 0 2

5Q

V w u. 5 ow 10 2 Ak.. t 401 40 20 60 40 50

----I

1.50

V

/00

Fig. 20Apparatus for Exploring Flow through Screw Propeller

7crn ,afro

-30 ° 30 6o

Pit(15t Artgit

Fig. 21Traverses of Flow across Planes at various Distance,

behind Propeller Disc