The Garfield Thomas Water Tunnel

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THE GARFIELD THOMAS WATER TUNNEL

August F. Lehman

ABSTRACT

The Garfield Thomas Water Tunnel is a part of the Pennsylvania State University. Certain early

investiga-tions at the Harvard Underwater Sound Laboratory had in-dicated that improved propeller design techniques could be achieved if the designs were made in terms of the inter-action between the propelled body and the propeller. After

the Laboratory was established at the Pennsylvania State University in 1945 to continue work started by HUSL,

con-struction of a high speed (48 knots) water tunnel with a test section of 48-inch diadeter was initiated and com-pleted in 1949. The primary purpose of the Tunnel was to serve as a research facility in the propeller field, but

its use has been extended to include a wide variety of studies on submerged bodies and their propulsors, and

re-lated research in the field of naval hydrodynamics.

The 48-inch throat diameter high speed water tunnel, which is the major test facility, is supplemented by two auxiliary facilities--a smaller high speed water tunnel and a subsonic wind tunnel, in addition to some minor facilities, a model shop and machine shops.

The 48-inch water tunnel is equipped for visual and acoustic observation of cavitation, for the acoustic obser-vation of hydroelastic vibrations, and for the measurement of forces and moments acting on models or other test bodies up to about 12 inches in diameter. The dynamometer motors used for driving the test body are instrumented to measure torque and thrust up to a total of 140 horsepower at 3600 revolutions per minute. The tunnel has been used

success-fully for testing the afterbody appendages and propeller(s) of test bodies up to 25 inches in diameter, eliminating tunnel wall interference by the use of a tunnel liner simu-lating a free stream surface about the body.

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Both water tunnels have been used for 'general investi-gations on cavitation, such as scale and roughness effects. The air tunnel serves for investigations of submerged bodies under conditions where cavitation or hydroelastic (or hydro-acoustic) observations, are not of primary importance.

INTRODUCTION

The

Garfield

Thomas -Water Tunnel is a

part

'of :the

Penn-sylvania, State University and is located on that oiMpuS. The Water-Tunmei is housed in its-OWn'building Which contains the .various

facilities

as well as offices, laboratories, and shops An 'exte'rior view-of. the tunnel building:is shown in

THE GARFIELD THOMAS WATER TUNNEL,

Figure 1.

departments of the University In addition _

advice and'aYORPrt.i4 also available

The .full-time staff at the Tunnel consists, at present,

-of

21 persons not including service employees these 21, eleven have academic rank at the University. In addition to the full-time staff, there are about ten graduate or under-graduate students averaging aboui 15 hours-per week who assist

the TUnnel-staff in the operation of the facility. Scientific ftom'the 'faculty of Other

:

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-Aka-3

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THE GARFIELD THOMAS 'WATER TUNNEL

eight consultants, well known in the field Of hydrodynamics, that-are active in reviewing and assisting in Tunnel programs.

PURPOSE .

The general purpose of. Tunnel is the advancement of the. science and art of hydrodynamic design of submerged bodies. Of specific interest are the, problems of body propulsion and control, cavitation, hydroelasticity (including hydroacoustics)

and boundary layer control. In the, solution of these hydro-dynamic problems, water tunnels are used in much the same

manner as wind tunnels are used in. the solution of aerodynamic.

problems-. The value of water. tunnel testing of models and/or

full-scale vehicles for the development of new designs is now beginning to be recognized in the field of submerged bodies.

While investigations of a basic nature require a con-siderable portion of the Tunnel effort, over half of the effort-is devoted to assisting various contractors in the solution of hydrodynamic problems where the hydrodynamic

-phenomenon being investigated is relatively unknown. In this role, the Tunnel staff lends guidance to insure the

hydrody-namic validity of the investigation.

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-4-THE GARFIELD THOMAS WATER TUNNEL

FACILITIES

Since the design and operating characteristics of the facilities are documented in detail elsewhere (1, 2)*, only the more pertinent physical and operational characteristics of each of the facilities are given here.

Large Water Tunnel

The large water tunnel is a speed, variable-pressure tunnel primarily intended for propulsion studies of body-propeller systems. It is a closed-circuit, closed-jet water tunnel in which powered models are used to drive single or counterrotating propellers. A photograph of the, tunnel and a sketch of the circuit are shown in Figure 2. The tunnel is about 100 feet long and 32 feet high. The maximum diameter of the approach to the working section is 12 feet. In this "settling section" there is a honeycomb which straightens the flow. Currently, screens are being added to reduce the turbu-lence level. The cylindrical working section is 4 feet in diameter and 14 feet long. The water velocity in the working section is continuously variable up to 80 feet per second

*Indicates References listed at the end of the paper.

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31 I°

SETTLING SECTOY

FLOPM---; 2 FT DIAMETER secrolts NO2'ILE -20 Fr LONG fr DIFFUSER 97' 2° itORKAG SPDV 48 INGII DI448TE4 fa7LONG 9° FT DIAMETER FVMP SETTLING SEL770N 97=7° 7° DIFFUSER SW MGM F8UR BLADE 40.4.1STNILE PITON IMPELLER

6 ^

Figure 2 The Large Water Tunnel

FIRST 7. , TURN DIFFUS9? SEC= ITURN -fro as'-77.RN FOUPTH fr." THIRD nAv

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(48 knOts) and is COhti011ed by a.95-inch diameter', four-bladed, adjustable pitch impeller driven-by

a

2000-hortepOwer electric motor. The pressure in the Working section may be reducedto

negative pressures of about 12 pounds per square inch

(0m4:

or raised to positive 'pressures of about 45 psi. Tiispermi-ts a wide range of cavitation numbers for tests. ' The water temp-erature can be varied from 40 to 120 degrees Fahrenheii. This enables a change in Reynolds number by a factor of 2 through' the change in-water temperature alone. The air content of the water in the tunnel is continlled through the use of

a

de4 .gasser., This de-gasser permits removal of air from the water

thus permitting the water in the working section to be less than air-saturated regardless of the working section pressure. This is an important aspect in cavitation

The working section is fitted with plexiglaS windows along its sides to permit visual and acoustiC observationS. Additional lighting ofthe object undergoing test is accoM= plished by means of 12 luminars located in the hatch cover on the working section. This hatch cover forms

a

large par=

tion of the top of the working section and is removable to permit installation, access to, and removal of the test bodies.

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Acoustic measurements on objects in the working section of

the tunnel can be obtained through the use of a "searchlight" system or by means of hydrophones specifically designed and positioned in the tunnel for a particular test. The search-light system consists of a hydrophone mounted in a reflector and positioned in a tank of water located on the side of the working section opposite to that used for viewing. It can be

. traversed in the longitudinal direction along the entire -length of the working section. In this manner, a particular noise source can be accurately located.

Control of the tunnel and model variables is accomplished at a console located in a glass-enclosed room facing the ob-servation side of the tunnel working section. The console operator(s) controls the tunnel water velocity and pressure as well as the speed of rotating test elements. The console room also contains equipment used for. acoustic measurements and for determining the forces and moments experienced by bodies undergoing test. A telephone and speaker communication system connects the console with various stations in the

building.

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Small Water Tunnel

The small water tunnel is used as a supplement to the large tunnel. It can be used for flow studies on all types of objects except wake-operating propellers as these cannot be manufactured accurately enough in the small sizes required

for testing in working sections of this size. The tunnel (3) is a closed-circuit type, the cross section of which is cir-cular at most points. The overall length is 26 feet excluding the drive system and the maximum height is approximately 20 feet. The working section has the same velocity and pressure range as that of the large water tunnel, i.e., a maximum velocity of approximately 80 feet per second and a working section pressure range of -12 psi to +45 psi. The pressure range in this tunnel, as in the large tunnel, is independent

of the working section velocity. A sketch of the tunnel circuit is shown in Figure 3.

One of the more unusual features of the small tunnel is

the use of interchangeable test sections. The phrase "test .section" is used here to identify the assembly forming the

upper leg of the tunnel circuit between the upper turns. There are two working sections, one having a 12-inch circular cross section and the other having a 20 by 4 1/2-inch

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FOURTH TURN HEAT EXCHANGER RECTANGIA.AR NO SEC T ION 20' 4.5'

SECOND FLOOR GRATING

FLOW

SECOND TURN

FIRST TURN

22 ID

16

8' GEAR REDUCER HYDRAULIC COUPLING ISO HP, AK/TOR

31- a

CIRCULAR

WORKING SECTKNI

I.

a

INTERCHANGEABLE TEST SECTIONS

Figure 3

,

Sketch of the

Small Water Tunnel Circuit

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rectangular cross section. Both sections are 30 inches long.

The circular working section is used to study bodies, i.e., three-dimensional flow problems, whereas the rectangular working section is used to study hydrofoils, slots, and other plane, two-dimensional flow problems.

The drive for this tunnel consists of a commercial mixed-flow pump that forms a part of the lower leg and one turn of the tunnel circuit. The pump is driven by a 150-horsepower electric induction motor through a variable-speed fluid

coupling and reduction gear. The method of cooling the tunnel water is rather unusual in that the heat exchanger is an

in-tegral part of the circuit. The exchanger is a shell and tube type. The tunnel water flows through the tubes and the cooling water flows around the tubes. Since it is placed in the cir-cuit after the pump, it acts as a honeycomb in straightening the flow from the pump and the following turn.

Subsonic Wind Tunnel

The presence of a wind tunnel at a facility whose prob-lems are hydrodynamic in nature may seem somewhat strange. However, a number of publications including those by Rouse (4)

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air for evaluating cavitation potentialities. The use of low velocity air in place of water for test purposes has many inherent advantages. Among the more important are the reduction of structural requirements for models and test apparatus, the elimination of leakage problems both from. the tunnel and into the model undergoing tests, and the general simplicity of test instrumentation. In addition, turbulence measuring instrumentation for use in air is considerably more advanced than similar instrumentation for use in water.

The wind tunnel (6) is a closed-return type in which the cross section varies from an octagonally-shaped nozzle, working section and diffuser to a rectangularly-shaped return

leg. The working section is 48 inches across the flats and 16 feet long, whereas the settling section is 9 feet across the flats. The tunnel has an overall length of 60 feet and is approximately 20 feet high as shown in Figure 4. The maximum working section velocity of about 170 feet per second

is produced by a fan driven through a Vickers hydraulic speed control unit powered by a 150-horsepower synchronous motor. The axial flow fan has externally adjustable blades, and a

diameter of 70 inches. Both the impeller pitch and the drive speed are variable permitting two methods of velocity control.

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-aktainTaw;exanpl,imanscrwrinieraffirammadi

HONEYCOMB' AND

. iimi;

_ . NN,SCREEN LOCATION NOZZLE -WORKING SECTION

4-0r ,REGULAR OCTAGON le-o" LONG

POWER SECTION

FIRST TURN

...

-."4

OIL LINES

FOR HYDRAULIC DRIVE

19 II" FOURTH TURN 60' I" Figure,4 Sketch of the Subsonic Wind Tunnel Circuit THIRD .TURN SECONDS TURN

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14

-THE GARFIELD THOMAS WATER TUNNEL

The turbulence level of the tUnne-1-=itb.I.-p6r dent accbm= plished through the use of a honeycomb and screens

in

the nozzle.

Other Facilitie8

A number. Of other facilities are alsb contained in the Tunnel building'. Among these are a hydraulic system which consists

of

a -Controlled. supply Of water-having a flow rate: of 2500 galloris per minute against a total head: of About 100 feet. A number of air blowers are-aISo available-as are miscellaneous water pumps orvirloUS capacitiet

Model

Shops-The Tunnel houses a special propeller shop capable of ,manufacturing high precision blades or wing elements. Ex-tremely high precision is necessary 'because, in many cases, the experimental tests are being performed to prove .design criteria. This extreme precion is also necessary:from

cavitation considerations since even minute .deviations from

,

-the dedired shape cannot be tolerated on -the leading or trailing edges of propellers or propulsors. The precision research propellers are fabricated by the duplicate milling procest. The propellers normallY consist of individually

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machined blades assembled to a central hub. Fabrication

is

performed with a New England Model 104 Template and Pam. Machine- Shown in Figure 5 and the New England Model 102

Air-foil Milling Machine,shown in Figure -6 (7). The template and oath machine can accommodate enlarged profile sections up

to 36 inches in chord length providing

the

actual site is not

over

'8 inches. The. profile milling machine can handle shapes to

6

inches in Chord length and 16 inches in overall

This Model shop is producing propeller blades with . tolerances of ±0.002 inches as a standard procedure., These

-tolerances are for the final propeller acctimulated through the various manufacturing steps. Blades have been produced that are accdrate to about ±0.001 inch but this accuracy was attained only through extreme care. The ±0.002 inch is the maximum errOr and the average for most regions of the blade is within ±0.001 inch.

'A jig bore and several precision inspection devices,_ in addition to the usual equipment employed by tool makers, is available in this shop,.;;The.general machine shop contains lathes, milling. Machines, drill presses, power saws, grinding wheels, and other equipment' normally associated

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-Figure 5

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THE 'GARFIELD THOMAS WATER TUNNEL

equipped machine shops. A small woodworking shop is also housed ill the building and both electric arc and 'acetylene. gas welding equipment is available.

. EXPERIMENTAL TEST EQUIPMENT

Test Bodies.- Tunnel Installation - Powering. .

The test bodies normally used are 8 inches in diameter and are supported on a single pylon mount as shown in Figure 7, This mount Or strut serves as the passageway for power and instrumentation leads from the interior of-the'test body to

outside the tunnel. For studies involving pressure

distri-bution or forces on'Unpowered.yehicles, the models are usually made of wood,--For studies involving pOwered.models, electric 'motors are fastened to the central mounting unit and metal

Skins. are:slipped'over the motors to form the desired external Configuration. If body forces and moments are to be. Measured, in internal balance forming a central'unit 8 inches it

eter is fastened to the lop of the mounting

strut with

the _other equipment

then

fastened to the balance unit. For

8-inch diameter models, two 20-horsepower, variable--frequency, electric motors can be installed to power the propulsion system. For counterrotating propeller designs, one motor is used to power each propeller.

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-Figure 7

Pylon Mounting

System

Figure 8

'Pylon

Pius Bipod Mounting

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For bodies larger than 8 inches in diameter, the mounting System may also include a forward bipod strut (Figure 8) or the struts may be entirely eliminated in favor of mounting with streamlined tie rods and a long tube extending from the nose of the model to the honeycomb of the tunnel and from

there to the outside (Figure 9). In this type of installation, the tube is the passageway for the electrical power, instru-mentation, and other leads from the interior- of the model to outside the tunnel. When the model diameter is 12 inches or larger, two 70-horsepower, variable frequency, electric motors can be installed for driving the propeller(s).

In order to permit the investigation of unpowered models without the disrupting influence of struts on flow conditions over the body, a sting mounting system is currently being fab-ricated. This mounting system will be used with smaller models

(and with a smaller internal balance) to permit investigations at considerably larger angles of attack than achievable with

longer test bodies. Figure 10 is a sketch of the proposed sting mounting system.

Force and Moment Measuring Equipment

Since the principal reason for the construction of the tunnel concerned the verification of theoretical propeller

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-Figure 9

Streamlined

Tie Rod Mounting

System

Figure 10

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THE:GARFIELD THOMAS WATER TUNNEL

design with experimental test results, the determination ,of propeller thrust and torque output was an item having-the highest priority The necessity of measuring or determining

forces and moments acting on the body, as a unit, did not reach a iimilar level of necessity until the Tunnel programs had broadened to the point where the overall hydrodinamic

-characteristics of the vehicle being tested were-also prime problem areas. As a result, thrust:and power meagurements

(from which torque can be 'computed) have been successfully 'Obtained for.perhaps,Seven years, whereas body .force and

'moment Measurement's were not successfully obtained:II/Ail the

.

Fall

of 1457

Propellerthrust, power, and torque

4

The interior, or a portion of the interior, of powered bodies is

sjwipt

watertight since the variable-freqUencY' electric motors used in powering the

proOulsor do not

permit operation when submerged in water. Because of this arrange-ment, strain-gage thrust cells operating in this air-filled spice were relatively easily designed. Essentially, the pro-peller Shaft is connected to the center of a beam. The ends

of this beam are attached to a yoke which is fastened to the motor rotor. The beams are strain-gaged. Forces on the propeller shaft cause-deflections of the beam with these de-flections resulting in a change in the strain or stress

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22-THE GARFIELD THOMAS WATER TUNNEL

level of the beam which is measured by the strain gages. This system has operated extremely well with an overall accuracy of within one per cent of the design force value of the beams. A photograph of

a

thrust cell is shown in Figure 11.

Calibration Of electric motors.i6At felatively standard procedure. To permit calibration, the Tunnel has available a.70-hOrsepower'and I 10-horsepower dynamometer. 'The. ac--curacy of the power (of torque) coefficients obtained from motor calibration is estimated to be within 3 per cent

Measuring the electrical power input to the dfiving

_

motor(S) was the original Method of determining propeller power and torque.. With variable-frequency

mOteitg:con-siderable calibration:and-A:WU analyeis is neceSsary: to Obtain the actual power from the test measurements. For .thit reason, torque cell Units were designed and incor-porated in the instrumentation since the determination .of

torque (and power) then becomes a much simpler process than the one involving electrical power measurements.

The torque cells also incorporate strain-gaged members. In this unit, radial beams or spokes are fastened to the powering motor rotor. The ends of these spokes are slotted

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-Figure II

Typical

Thrust and

Torque

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as are the ends of the thrust cell yoke. Music wire is then passed from the slots of the thrust beams to the slots of the torque beams and continued around in a spiral motion. This "joining" of the ends of the thrust and torque cell beams by means of radially-wrapped music wire permits the transmission of torque but not of thrust. A torque cell and music wire joining of a thrust and torque cell is also shown in Figure 11. Accuracies are within one per cent of the design value of the cell.

Body forces and moments

The original tunnel plans included provisions for measuring body forces and moments through the use of an external balance of the type quite often employed in wind tunnel facilities. A balance of this type was constructed and tested in 1953. This balance was unsuccessful due to

its vibratory characteristics which became quite severe at tunnel flow velocities above 25 feet per second.

In 1957, program objectives were such that the measure-ments of body forces and momeasure-ments became a necessity. The success which had been obtained with strain gages in other

types of instrumentation at the facility made it logical

that a strain-gaged type of balance would be one of the first

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investigated. Because of the instability problems encoun-tered with the external type of balance, an internal type was designed and constructed. The balance system which has been in successful operation since the Fall of 1957, for measuring forces and moments on both cavitating and non-cavitating bodies, consists of an internal strain-gage type balance coupled with a strain-gaged mounting strut. This system_is shown in Figure 12.

The measuring system contained within the body permits the measurement of the body pitching moment, body rolling moment, and body lift. The strut measures body drag and body pitching moment. On the credit side of the currently-employed force and moment measuringsystem is the fact that there is a negligible amount of cross coupling between the various forces and moments. On the debit side is the fact that new beams are normally made for each test program in order to

insure the beams will operate in the stress range at which the forces and moments are expected to occur. In addition, the relatively large strut fairing that surrounds the strain-gaged strut and its subsequent effect on the flow

character:-istics about the body create problems in data interpretation. Also, looking toward the future, the single pylon strut is not particularly adaptable for the possibilities of model

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-3-10 Volts

Typical Strain Gave Bridge

ALV. Reading

Purpose - Sum Measires Body Norma/ .Force

Difference Measures Body Pitching

Mb,,Measures

Body Rolling Moment

@a@ Bridge®-Bridge® Measures Bo* Arid Force_{8,4e®-Bridge0Meastres Boa) &thing Moment}

Figure 12

Successfully Used FourComponent Balance

System

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THE-GARFIELD THOMAS WATER TUNNEL

*ciliation,- i.e., it is limited to the investigation of Steady - Stateforces.

At the time of this writing, twolnew balances have been designed And are Under construCtion.-:.One'of these balances is for use with models up to approximately 12

inches indiameter. This balance has several improvements over the one currently in use; (a). the ability. to Use

two powering Motors instead of one and thus permit testing. Of counterrotating propellers, (b)- the elimination of

non-linearities through the. exclusive use.of.tenslon members and a more flexible cOnnection

for

introducing power,

cooling, and instrumentation leads,. and (c) the incor-poration :of a drag-measuring link. The-latter-improvement

is significant since_it-eliminates,the Strain-gage strut .. with its relatively large fairing-in favor of a thinner mounting Strut.

-N

.A smaller internal balance, also operrating on the strain-gage._principle, is.being constructed.

This

balance will

measure body lilt, drag pitching, moment, and roiling moment. 'It will be Used for tests involving unpOwered mOdels * a

Sting mounting system. -This sting mOunt will-eliminate the effect of the strut on the flow pattern around the body.

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28-THE GARFIELD THOMAS WATER TUNNEL

Tunnel liners

In the testing Of any body in a closed conduit, such as the working section of a water tunnel, it is necessary to con-sider the interference between the test body and the walls co/

the tunnel. The ideal case exists when the walls are infin-itely far from the test body. Departures from the ideal case occur when the walls approach the body. The influence of the walls on the body for cases of incompressible flow can usually

be neglected, if the ratio between the diameter of the test body and the diameter of the working section is approximately 1 to 6. This ratio is, of course, not a rigid dividing line but when the ratio becomes somewhat greater than this, careful consideration of the wall effects must be taken. Body diam-eters of less than one-sixth of the-working section diameter are also necessary if accurate measurements of the drag of submerged bodies are required.

As an object moves through a fluid, the fluid moves around the object along certain stream surfaces. If the tunnel wall were to confdrm exactly to one of these stream surfaces, all forces on the object would correspond to those obtained in the free stream. It is through this approach of modifying the curvature of the tunnel wall to

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-THE GARFIELD".THOMAS _WATER-TUNNEL

conform to a free stream surface that test bodies upto, 25 inches in diameter have been successfully tested -in-the

_diameter working,, section of the tunnel.. It .Should'

be noted that for Most

test

investigations, only..the.11ow. over the afterbody

is

matched th the flgv./ 0.011.41tion of-the:

free stream since propulsor and control .appendage character-. istics.areusually the objective

of

the investigations.

The first method: used to determine the shape of' the

-thhhel7COrrectihg"linerWaS- that driginally:deVeloped:b3i von Karmari for the'caldulatiOn Of the pressure distribution over airship This' method uses'a.diStribution of line sources And'sinks along -the AkiS of the body'kefine= Merits to this Method by such means as adding an-additiohal source and" sink it the aft end of the body to simulate pro-peller action or by-thodiIyifig.the SourCe=sink strengthAlS

trihutioh near the aft end of the body to simulate the effects

of .a puthpjet

or

shrouded propeller did-hot havenoticeable

effect onthe

liner

contour.

:

I

Sinde.thiS-MethOd-of caichlating'the Shape of the

requires-a considerable amount Of effOrt, an attempt thward a simplified 'design methOd was undertaken. This simplified method' iS essentially-a Ohe;=dim4hsiohal consideration

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-30-THE GARFIELD THOMAS WATER TUNNEL

which the mean velocity of flow about the body is kept constant. The liner configurations obtained for several different bodies through the method developed by von Karman, were compared with the liner configurations obtained for the same bodies when the constant flow area principle was used. This comparison showed that if 80 per cent of the liner

thickness, calculated on the constant flow area principle, was used in the design of a liner, the final shape compared favorably with the shape obtained using the more refined mathematical approach.

Comparison of liner shapes calculated by both the sim-plified approach and the more refined mathematical approach for two significantly differently-shaped bodies showed a maximum deviation of one per cent of the liner thickness.

In the actual construction of any liner, whether de-signed on the constant flow area principle or dede-signed on the source-sink approximation, a correction equal to the boundary layer displacement thickness of the liner is made to the liner thickness.

Other Test Equipment

Acoustic measurements of various types are conducted in the working section of the water tunnel. A highly

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directional transducer utilizing an ellipsoidal reflector with a small barium titinate'element at one focus scans the working section by traversing its length. Measurements at

frequencies above 15 kilocycles per second (kc) are conducted using this mechanism. Other types of hydrophones'and vibra-tion-sensing instruments are installed either in the tunnel or on the body undergoing test depending upon the test ob-jective and frequency range of interest.

The recording and analysis system into which the pres-sure or vibration data is fed may also be varied. Data can

be recorded using a 7-channel magnetic tape recorder or if output level versus time data is desired, a sound level re-corder can be used. Either amplitude or frequency modulation recording methods may be employed.

Analysis of the data may take place directly or from magnetic tape records. Direct analysis can be made with variable bandwidth fixed filters having a minimum bandwidth of 2 cycles.per second (cps) or through a 1/3-octave system In analysis of the magnetic tape records, the tape drive speed may be varied, resulting in either frequency multipli-cation or division, in order to extend the frequency range.

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A visual trace of the output spectrum can be obtained using a cathode ray tube presentation of a narrow band hetro-dyne filter system. The trace of this panoramic analyzer covers a frequency range of 200 cps to 20 kc. The screen may be photographed if permanent records are desired.

Photography work up to the present time has consisted primarily of single exposures taken with a Graphic View II 4" by 5" camera using Strobolume flash units.

Manometer banks for use with mercury as well as other liquids are available. Pitot tubes, wake rakes, and similar

instrumentation are normally constructed for a particular test investigation.

Constant temperature hot wire anemometer equipment is available for studies involving turbulence in the wind tunnel.

TEST AREAS AND RESEARCH CAPABILITIES

There are essentially five areas in which the Tunnel is principally concerned in terms of research and test investi-gations. These areas are those involving propulsors, cavi-tation, stability and control, hydroelasticity (including bydroacoustics), and boundary layer flow. An indication of the capabilities under each of these areas is listed.

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Propulsors (includes both propeller and pumpjet designs)

Design of propulsors and consultation on design problems including the introduction of empirical modifications.

Theoretical and experimental studies of hydro-dynamic interaction of components with the pro-pulsor.

Complete and accurate testing with propulsors on powered models or full-scale prototypes.

Free stream testing of experimental propulsors up to diameters of 18 inches with power requirements up to 140 horsepower.

Cavitation

1. _{Cavitation investigations on entire models or}

proto-types up to a maximum of about 25 inches in diameter (with the use of a tunnel liner) or on the components of submerged bodies such as propulsors, control sur-faces, and other appendages, including both the effects of protuberances and indentations.

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-34-THE GARFIELD THOMAS WATER TUNNEL'

Cavitation studies of hydrofoils,

3--Researth on vortex' and Surface cavitation inception.

Stability and Control

.

Research onOrobleins bOncerning:the stability and control of submerged bodies,

Theoretical and experimental studies on hydrodynamic interaction of components suth as bodies, appendages, propulsors, etc.'I

Researa-and.testS determining the Static, hydrody-namit derivatives of modelt of undetWater Vehicles.

Hydrdelasticity (Including Hydroacoustics)

HydrOdnamically inducecilvihrafions; a matter of well-recognized importance in the field of bigh.

.

speed submerged bodies. According to the present incomplete state of knowledge in the field, the vibrations may fall into the following categories:

a. Vibrations due to the unsteady interaction

be-tween the propeller blades and nearby control surfaces.

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Vibrations induced by the shedding of an

un-steady wake (reminiscent of a von Karman vortex street) from the trailing edge of propeller blades, control surfaces, or other appendages. This type of hydroelastic vibration is usually referred to as "singing".

Vibrations induced by the flow past an opening in the hull whereby the body of the fluid be-hind the opening may be excited.

Vibrations of the outer skin of the vessel in-duced by unsteady flow phenomena in the boundary layer such as boundary layer transition, large scale turbulence, or separation.

Vibrations that are excited by cavitation.

Spectrum analysis of underwater noise from approxi-mately 1 cps to 100 kc, if level is above tunnel background.

Modulation analysis of detected noise from 10 to approximately 150 kc if level is above the tunnel background.

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Boundary Layer Control

Research and experimental tests involving boundary layer control through various means such as suction.

Tests involving drag reduction through vehicle con-figuration.

Other Hydrodynamic Areas

In addition to the main areas listed above, other in-vestigations of hydrodynamic phenomena have also been per-formed and will continue to be perper-formed on the following:

General subsonic wind tunnel testing up to speeds of 170 feet per second.

Hot wire turbulence measurements in air.

Wake surveys and studies for essentially axi-symmetric bodies.

General hydraulic research involving controlled flow of water in conduits up to 45 feet long, flow rates up to 2500 gallons per minute.

Research and tests involving visual observation of flow phenomena in air and water.

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EXAMPLES OF RESEARCH

Of the five research areas previously mentioned, the most note*orthy contributions have been made An the areas invol-ving propulsors and'cavitation: This is due to the fact that these two fields were initial areas of highest Priority.' Some contributions have been made in the fields of stability and control and hydroelasticity, but the area involving

boundary layer control has not, at.thiSwritingreceived

extensive consideration. Certainly, much of the success achieved in the 'propulsion and cavitation fields has been due to the fact that tunnel testing permits accurate

control

-of the test' mediumand the test vehicle variables for reta-'.tivelY indefinite periodsof time: This fact cOUpled,

with

the opportunity for visual observation of the

flow

field, through the aid of Strobotac-type lights, PermitS the detailS.

_

of propeller action to be viewed not only at design conditiOns but it cOnditions other thin

design

both with and without the influence of cavitation.

Acoustic observation of the: body- under test

It also

possible and While Such information is of considerable value,

it does have certain limitationsfrom the hydrodynamicists

standpoint in terms of correcting or eliMinating Cavitation

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noise sources. _{It is well known that an acoustic level} re-sulting from several areas of cavitation only shows a signi-ficant decrease with the disappearance of the last bit of cavitation. Thus, in testing a pair of counterrotating propellers, acoustic observation only indicates when cavi-tation has disappeared from the propeller _{set, whereas the} designer is actually interested in the disappearance of cavi-tilation from each of the propellers in addition to the type, formation, and location of cavitation. _{Therefore, visual} observation of cavitation is indispensable.

Theoretical methods have been developed for the design and analysis of wake-adapted propellers (7). _{From the} re-sults of controlled tests of accurately machined propellers as well as subsequent application of the design principles

to prototype design, it is concluded that the _theoretical methods that have been developed predict satisfactorily the performance of propellers over a wide _{range of} opera-ting conditions. _{This conclusion is intended to apply not} only to the thrust and torque characteristics of _the pro-peller, but also to the incipient cavitation characteris-tics. It is true that the thrust and torque design re-quirements are more easily satisfied with the first testing

of a new design or prototype. _{Usually some minor modifications}

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are necessary to the blade configuration in order to satisfy the predicted cavitation performance. It is through the use of tunnel observation that very local areas of cavitation can be observed and relatively minor changes incorporated

in the configuration resulting in a considerable improvement in the cavitation performance of the propeller.

In the field of cavitation, both theoretical and dk-perimental work has been done on the inception of cavita-tion on isolated surface irregularities imbedded in a turbulent boundary layer (9). The principal variable was the relative height of the roughness to the boundary layer

thickness in the vicinity of the roughness. The results show that when the boundary layer thickness is 70 times greater than the height of a triangular irregularity, the

incipient cavitation number can still be as great as 0.3. Thus, the incipient cavitation number for a very smooth, streamlined body would be increased very significantly when such an irregularity is located in the region of minimum pressure. A study of approximate methods indicates that an estimate of the incipient cavitation number of an

isolated slikface irregularity can be made by assuming the

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velocity at the height of roughness characterizes the flow in the boundary layer.

Also, in the field of cavitation, a joint experimental program on cavitation scale effect was conducted at the Water Tunnel and at the Hydrodynamics Laboratory, California

Institute of Technology (10). It was found that in spite of differences in the test facilities, the measurements for incipient cavitation obtained at both facilities showed good agreement. The dependence of the incipient cavitation number upon free stream velocity and model size was verified. In addition, the results showed that for cavitation tests of small models, it is not correct to assume that the incipient cavitation number equals the negative of the minimum pressure coefficient.

In the field of turbomachinery, the unsteady wake inter-action and its effect on cavitation has undergone some inves-tigation (11). Here, the influence of the non-steady pressure perturbations on a blade row due to periodic wakes shed from an upstream blade row were predicted theoretically and then

compared with experimental results. While the experimental values were somewhat lower than the predicted values, the observed influence of wake width and wake spacing was in substantial agreement with the theory.

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nolds_numbers were quite high and led to further

experi-mental.work

the wind tunnel to see if periodic shedding

could exist at the higher Reynolds numbers.

_Urging A hot

wire probe

It was determined that periodic disturbances

existed in the wake Cd,.a flat plate at Reynolds numbers as

high as 780,000.

_Other types of investigations undertaken at the Tunnel.

include such subjects as electrolytic methods for measuring

,Ater velocity (13), flow visualization techniques in.a high.

_speed water tunnel (14) a study of the minimum pressure in

In the field of hydroelasticity, some investigations

undertaken repeat the work by Gongwer (12), while other

in-vestigations.involved the vibratory characteristics of fixed

Wings having different materials.

These tests indicated

that.a periodic shedding of flow irregularities similar to

_

a von Kaman vortex street is the exciting

force.

Since

these tests were undertaken in the water tunnel, the Rey-

_ .

-,

a trailing vortex system (15), and a study

of incompressible

turbulent boundary layers (16).

These examples in no way-supply detailed

information

on my of therfieldia-diScUssed nor7do.they express the-range

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-THE GARFIELD:ITIOMAS WATER TUNNEL

of research-work at the Tunnel. They only serve

as

indica-, tions of the type of research which has-been and is-being performed.

CONCLUSIONS

The Garfield Thomas Water Tunnel is a key facility in

the field of hydrodynamic research.' It is basically a facility in which hydrodynamics is an applied science. Its efforts are aimed at 'improvingthe submerged performance of equipment which operates at least a portion of its life

in

a completely SUbmerged condition.

The knowledge of the physical laws and the behavior of fluid as a body moves through the fluid must be understood if the .hydrodynamic operating characteristics Of the body are to be an optimum. The end Objective ofthe programs

undertaken at the Tunnel is to-add to this field of knowledge.

With the availability of a -large and small, high speed Water tunnel, a subsonic Wind tunnel plus supporting equip-f' Ment and indtrUtentation Covering flow ranges from subsonic Hair to water at velocities of 80.feet per second oVer pressure

ranges. of .3 to 6 peundS per Square inch absolute,

apossible types of fluid,-flew investigations are very large.

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-43-However, investigations are stressed in the areas of pro-pulsion, cavitation., stability andcontrol, hydroelasticity, and boundary. layer-research.

AFL:ditg

January29, 1959..

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REFERENCES

"Garfield Thomas Water Tunnel Operations," by R. B. Power, J. M. Robertson, Donald Ross, and the Water Tunnel Staff, GTWT.Report, May 1, 1951.

"New Hydrodynamic Research Facilities at the Garfield Thomas Water Tunnel," A. F. Lehman, Paper presented at the Ninth

Underwater Ballistics Conference, July 1952.

"The Design of a Small Water Tunnel," by Roger L. Steele, M. S. thesis, The Pennsylvania State College Graduate School, Department of Mechanical Engineering, June 1951.

"Use of the Low Velocity Air Tunnel in Hydraulic Research," by Hunter Rouse, Proceedings of the Third Hydraulics

Con-ference, June 10-12, 1946, Edited by J. W. Howe and J. S. McNown, University of Iowa Studies in Engineering Bulletin No. 31.

"Model Tests Using Low Velocity Air," by James W. Ball, Proceedings of the American Society of Civil Engineers, Volume 7, June 1951, Sep. No. 76.

"The Design of a Subsonic Wind Tunnel," by Girard L. Calehuff, M. S. thesis, The Pennsylvania State College, Graduate School, Department of Engineering Mechanics, June 1952.

"A Study of Propellers - Part I," by B. W. McCormick, J. J. Eisenhuth, J. E. Lynn, GTWT Report, March 30, 1958.

"Calculations of Pressure Distribution on Air Ship Hulls," by Th. von Karman, NACA TM #574, July 1930.

"The Effect of Surface Irregularities on Incipient Cavi-tation," by J. W. Holl, GTWT TM 5.3410-03, June 2, 1958. "Incipient Cavitation Scaling Experiments for Hemispherical and 1.5-Caliber Ogive-Nosed Bodies," A Joint Study by the Hydrodynamics Laboratory, California Institute of Technology

and the Garfield Thomas Water Tunnel, The Pennsylvania State College, by B. R. Parkin and J. W. Roll, GTWT Report,

May 15, 1953.

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11. "The Unsteady. Wake Interaction

in

Turbomachinery and Its

Effect onCavitation,"

by

Hsuan Yeh

and

J.

EisOnhuth

ASME Paper No.-58, AT114,july-3I, 1958,

-"A Study of Vanes Singing in Water," by C. A. Gongwer, Aerojet Engineering-Corporation,Azusa, California,

"Electrolytic Methods for Measuring Water Velocities," by W. E. Ranz, GTWT TM- 19.8854-5, February 20, 1957.

"Flow Visualization Techniques in a Nigh Speed Water' Tunnel," by G. B. Gurney and A. F. Lehman, GTWT.TN

19:6103-03, July 15, 1958. _

"A Study of Minimum Pressure in a Trailing Vortex System," by Barnes W. McCormick, Jr., Ph.D thesis, The Pennsylvania State University Graduate School, Department Of Aeronautical Engineering, June 1954.

"A Study of Incompressible Turbulent Boundary iayek-0," by Donald Ross, Ph.D. thesis, The Harvard University Graduate School, 1953.