DESIGN AND CONSTRUCTION

OF A

WATER TUNNEL

By

Stephen C. Ko

This work has been carried out as a part of a grant from the NationalScience Foundation for the development of fluid mechanics laboratoryequipments at the Department of Ci.vi1 Engineering, Lehigh University.

Fritz Engineering LaboratoryDepartment of Civil Engineering

Lehigh UniversityBethlehem, Pennsylvania

January 1971

i

TABLE OF CONTENTS

TITLE PAGE

TABLE OF CONTENTS

TABLE OF FIGURES

1. INTRODUCTION

2. THE DESIGN OF THE WATER TUNNEL

3. THE CONSTRUCTION OF THE WATER TUNNEL

4. PERFORMANCE OF THE WATER TUNNEL

4.1 Velocity4.2 Turbulence

5. CONCLUSION

6. APPENDIX - FORCE DYNAMOMETER

7. REFERENCES

ii

i

ii

iii

1

2

11

12

1212

15

16

20

TABLE OF FIGURES

Figure

iii

l.

2.

3.

4.

5.

6.

7.

8.

9.

Water Tunnel System

Test Section

Transition Sections

Elbow No. 1

Crossection of Propeller Pump

Characteristics Curves of the Pump

Elbow No. 2 and 3.

Velocity Profile in Water Tunnel

Turbulence Profile in Water Tunnel

3

4

5

6

7

9

10

13

14

1. INTRODUCTION

A variable-pressure water tunnel which is of a facility ana­

logous to a wind tunnel, is a useful tool in the study of cavitation

or hydrodynamic characteristics of underwater bodies. Such a facility

would permit students to observe and measure cavitation, drag and lift

of submerged bodies, pressure and velocity distributions.

Since a water tunnel is a very specialized piece of equip­

ment, and is not commercially available, therefore, proposal was made

by Dr. J. B. Herbich in January 1966 to the National Science Founda­

tion to construct a water tunnel with a 4-inch diameter test section.

The proposal was approved in 1967 and the design and construction was

carried out by the author in the same year. The construction was com­

pleted in later of 1969.

-2

2. THE DESIGN OF THE WATER TUNNEL

The general layout of the water tunnel is shown in Fig. 1.

The details of each component will be discussed as follows.

The test section (Fig. 2) was made of two-inch thick trans­

parent Plexiglas. The two-inch wall thickness provides for a rigid

mounting of test objects and instruments. It was estimated that about

0.03 inch deflection of the walls would occur at a speed of 36 fps.

A four-inch hole was provided on two opposite sides of the test section.

When mounting objects, two specially designed force dynamometers

(Appendix) will fit into these holes. For mounting sensors or probes,

two plexiglas plugs will fit into these holes. There are eight t" measure

taps along the axes of the section.

Downstream of the test section is a transition section (Fig. 3)

in which the cross section is transformed from a 6 inch square into a 6

inch circle. Therefore, the flow will accelerate through this section

and minimize any disturbance that will affect upstream flow in the test

section. After the transition section is a diffuser, Fig. Ie, the dia­

meter increased from 6 inches to 10 inches within a distance of 50 5/8

inches. This gives an expansion angle of 2 degrees 16 seconds. Elbow

No.1, Fig. 4, has 6 turning vanes to minimize separation and rotation.

Originally, the turning vanes were proposed to be foil shaped, however,

due to cost, time and possibly minimal difference in performance, it

was decided to use 1/8" plate with a two-inch radius instead. The pump

(Fig. IF and Fig. 5) is a 10 inch propeller type pump by Lawrence

Pumps, Inc. The pump is driven by a 15 hp a. c. motor with a motion

CITY WATER .--

.-.

Q

p

NOT TO SCALE

L A B C

D

I

A Test SectionB Transi tionC DiffuserD Elbow No.1E Pump

H.~

Fig. 1-:-

G

F MotorG Pump DiffuserH Settling SectionI Elbow No.2J Elbow No.3

Water Tunnel System

F

K Contraction ConeL TransitionP FiltersQ Constant Head

Tank

IW

-~-4 '

FRONT VIEW

/

rI

I6"

1f,IIII

2"

'/ .

@

/ .~,- /. /

/

"//

I-- 5"----J..... 7.5". .j

...t-..-- 10" -l

TOP VIEW

1\,-- - ---.; .Y DYNAMOMETER, ,

l\ ...---~ '----,\

fI 6"iI

~ II ~ I

I ~ ~ ~ ~~_lI . \21 \21 \21 ~ -- CYLlliDER II I

I: ~ I 1

'-. ',\ \.\ \.\ '···'ll'·· 'll'" n····· I l". \. '.' '.,' ~~\' \.~ " '\\ '\ .•.. \ \. '. '.\ \ .' .. " .. \ ..... \. I 1'\'\\\ \ \. \\'\.\\.. ,\,.\.\\ 11,:.' .. \ 11'" '.I ~. \.,'. . ..' ''o.\ \ \ \ \\ \\ \ \ . \ \ \\ \ \I . '. \' r-'.. ..... , ;\ ". \ .... \, .... "" ' '. \. " \., ... \ \ \ '. \ .... '

~\ \\\\, \.\ \\\\\\.\ ' \'\\\:\\\,\~\-r. ~~I':','.'..'.'.','..\,.\,','.\\,,\.,\~\.,\,.\\\'\,..\,.'..>.,.,\,.'.,'..'\ \.',.,\ ' \ \..\\..,.\.\\.\.,...•.\.. '\\.' ~., '..>. \\,.. '\ .\~~\\,.,.\.\,\ \,\,\\\\\ \\\'~\,\.\\\\."",'., '\ .. ' .., '-. ~. ". .' ". .' ". \ . \ '.. ~ ". ~ ". \

L_- 1 r-- J·

I II IL l

~---30"

\'

~

NOT TO SCALE--.---.------...-...._.._.._.... __.~--1

Fig. 2: '. Water Tunnel Test Section Details

f8~"-

r

~-~

~'/

-<;==J ~I /

~

~I..

:~ ..[

,

f6' SQUARE

.1

-5

t""s

f6"SQUARE - ill----~--

1_-+--",,6" I.D.

9" - I

Fig. 3: Transition Sections

r.H

1

35"

-6

t-rT-"""'-!'j- --

10" .. I

Fig. 4: Elbow No. 1

Fig. 5: Cross Section of the Propeller Pump

I~~==>l?+--

iiI

t......

-8

control speed V-belt drive. The pump speed can be adjusted from 795

rpm to 1700 rpm. Guide vanes are mounted tangentially with a hub

diffuser. The characteristic curves for this pump is shown in Fig. 6.

Section G in Fig. 1 is a pump diffuser with a 10 inch inlet and an 18­

inch outlet or an expansion angle of 4 degrees. The settling section

H in Fig. 1 is 63 3/4 inches long and 18 inches in diameter and follows

the pump diffuser. Both sections (I) and (J) are identical elbows with

11 guide vanes in each elbow, details see Fig. 7. The contraction cone,

section K and L, in Fig. 1, has an overall contraction ratio of 9:1.

Actually, the contraction cone consists of two sections. Section K

is a straight contraction cone which contracts from 18 inches to 8~

inches. Section L is not only a contraction section but also a tran­

sition section which transforms an 8~ inch circular section into a 6

by 6 inch square cross section.

To vary the static pressure in the water tunnel, a constant

head tank (Fig. lQ) is provided. The elevation of this constant head

tank can be adjusted ~o control the static pressure up to 20 feet of

water in the test section. Another important function of this arrange­

ment is to keep a constant volume of water in the system by compensa­

ting for water lost through the pump seal or temperature changes. Before

the water enters the water tunnel, the city water has to pass through two

cellulose fiber filters which have 5-micron rating to remove any foreign

particles. This is important for the operation of hot-film anemometer.

/56% /64%18 /70%

/H

/ /72%~~~ 12f:j /A /70%~u /'

/64%H

~8

./><A

H / 56%~0E-!

. 4

o ' 4 8 12 16 20 24 28

Q, IN HUNDRED GALLONS PER MINUTE

Fig. 6: Characteristic Curves of a PumpI\0

-10

10"--------ia-f

IIIII

r::::::> IIIIII

_L I

3/16"

l===':!~jl-_-_--=-- ~_-__=__-_-_-___>.__J

24 ] 8"

Fig. 7: Elbow Nos. 2 and 3

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3. THE CONSTRUCTION OF THE WATER TUNNEL

The fabrication of the water tunnel was done by Fuller Company

and galvanized by Lehigh Structural Steel Company, both are local firms.

The installation and test runs were completed in late September 1969.

From the date of design to the day of completion was one year and nine

months. The total cost of the water tunnel, including labor and materials,

was $8,441.93. The original proposed price in 1966 was $4,500.

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4. PERFORMANCE OF THE WATER TUNNEL

4.1 Velocity

The velocity in the water tunnel can be varied from 17 fps.

to 35 fps. The velocity profile at the mid-section of the test section

is shown in Fig. 8. The Reynolds number, based on test section dimen­

sion, maximum velocity and at 700 F, ranges from 8 x 105 to 1.6 x 106

.

4.2 Turbulence

The turbulence characteristics were measured by a constant

temperature anemometer with a parabolic quartz coated probe. The anemo-

meter is a Heat Flux System Model 1000A, built by Thermo-Systems, Inc.

This unit has a probe power computer which takes the values of bridge

voltage and probe resistance and with squaring circuit, amplifier, and

voltage dividers computes the actual electrical power of the probe.

Therefore, all the free stream measurements were in terms of power out-

put, in watts, instead of voltages. The power computer has a manufac-

turer's claimed accuracy of 1.5% of power output. Detailed descriptions

of the model are given in the manufacturer's manual, Heat Flux System

Model 1000A Instruction Manual.

The turbulence intensity profile obtained at a centerline

velocity U = 18.07 fps. (Fig. 9) At the center portion of the test

section, t~e turbulence intensity u' ~~ = -1.488% which is very good

when compared with similar size wind tunnel.

1.0

0.8

~ ~_::!----~-:---T--....-~•

0.6

• U = 17.9 fpsc

0.4

+ U = 22.5 fpsc

0.2

0.60.50.40.30.20.1

O...-- L..- ---i'-- ---' --J. ....

o

y

DI'.....w

Fig. 8: Velocity Profile in the Water Tunnel

14

12 -

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•L•Ie

u = 18.07 fps

D = .6 inches1 e

e

\e

Q%U' •

6

4

. 2

e

e-e------ e--e--_.

o 1 2 3 4 5

Fig. 9: Turbulence Profile in a Water Tunnel

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5. CONCLUSION

A 6" x 6" water tunnel has been constructed. The water tunnel

has a velocity range from 17 fps to 35 fps. The static pressure in

the test section can be adjusted up to 20 feet of water. Turbulence

intensity at the center portion of the test section is, 1.488%. Both

velocity and turbulence profiles were determined.

-16

6. APPENDIX - FORCE DYNAMOMETERS

The force dynamometer for the water tunnel is shown in Fig.

10, and its construction and function were based on the dynamometer

constructed by Silberman et a1. (1962). The force dynamometer consists

of one aluminum plug which fits into the 4-inch hole in the test section

of the water tunnel, see Fig. 2, three force plates, eight force beams

(four lift beams and four drag beams), and one Plexiglas housing which

encloses all the force beams. The construction and function of the

force dynamometer are described as follows. The three force plates

are the bas~ plate, the drag force plate, and the lift force plate.

The base plate is fixed to the aluminum plug which in turn is fitted

into the hole on the test section. The lower ends of the drag force

beams are fixed to the base plate, two of these are seen in Fig. 10

indicated as (A) and (B), while the upper ends of the four drag beams,

two of these are seen in Fig. 10 indicated as (C) and (D), hinged to

the drag force plate. On the remaining sides of the drag force plate

four lift force beams are fixed on it, two of these are seen in Fig.

10 indicated as (E) and (F). The lower ends of these four lift beams

are hinged on the lift force plate, two of these are seen in Fig. 10

indicated as (G) and (H). An attaching rod, IJ, is threaded on the lift

force plate and extended into the water tunnel to attach to the cylinder.

There are two strain gages (Type EA-06-125AD-120) on each beam; on the

tension, and on the compression sides. The force beams are made of

aluminum plates 1/8-inch thick and ~-inch wide. The drag force beams

are 2~ inches long and the lift force beams are 2 inches long.

The function of the force dynamometer may be described as

follows. If a force in the direction of the flow, i.e. normal to

-17

(

PRESSURE TAP

STRAIN GAGE TERHINALS 1

ROD FO ATTACHING TQ MODEL

....- l1l;;I;;_-----

!

II

II1

PLEXIGLASSHOUSING

13-3/8 inches

'- '... -'. - .

"1--ALUMINilll i

PLUG I.2 inches

'. '" .............

-'. "". ".~", ".

....

inches

-+--f~'-'--'--t--I--'---j!;~---1I--'+-=-LIFTFORCEB-EAL'1S

",

............... - .

eeeeeeeeDRAG FORCEPLATE -+-+---+:.+--

" "

BASEPLATE

LIFT FORCE

PLATE

DRAG"FORCE BEi\t!~t--t-- .......-~__. ---.

--_...._--~( ,

NOT TO SCALE

'.- .

("Fig. 10: Force Dynamometer for the Water Tunnel

-18

Fig. 10, is applied to the cylinder, the drag force beams and only the

drag force beams act as cantilevers in the direction of drag. If a

force normal to the direction of flow, i.e. parallel to the paper

(Fig. 10), is applied, then only the lift beams act as cantilevers and

drag beams are inoperative. If a force other than parallel or normal

is applied to the cylinder, the drag force and lift force beams deflect

accordingly. Therefore, not only can lift and drag forces be measured,

but also the moment on the cylinder can be determined. The force beams

and force plates are enclosed in a transparent Plexiglas housing. During

operation the dynamometer is completely filled with water, and the pressure

in the housing is equalized with the pressure in the test section by

connecting the top of the housing to the free-stream in the water tunnel

test section. All terminals can be removed in a few minutes. The

calibration curve obtained by applied dead weights is shown in Fig. 11.

lbs.

1.4

1.2

1.0

0.8

0.6

0.4

0.2

00 100 200 300 400 500 600 700

It-'

6., MICRONS \0

Fig. 11: Dynamometer Calibration Curve for the Water Tunnel

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7 • REFERENCES

1. Robertson, J. M. and Ross, D. "Water Tunnel Diffuser Flow Studies,Part I - Review of Literature". Report Nord 7958-139, OrdnanceResearch Lab., The Pennsylvania State College, State College,Pennsylvania, May 16, 1949.

2. Robertson, J. M. and Ross, D. "Water Tunnel Diffuser Flow Studies,Part II - Experimental Research". Report Nord 7958-143, OrdnanceResearch Lab., The Pennsylvania State College, State College,Pennsylvania, July 8, 1949.

3. Robertson, J. ~1. and Turchetti, A. J. "Water Tunnel Vaned-TurnsStudies". Ordnance Research Laboratory External Report Nord 7958­64, The Pennsylvania State College, State College, Pennsylvania,September, 1947.

4. Ross, D. "Water Tunnel Working Section Flow Studies". ReportNord 7958-97, Ordnance Research Laboratory, The Pennsylvania StateCollege, State College, Pennsylvania, June 15, 1948.

5. Smith, R. H. and Wang, C. T. "Contraction Cones Giving UniformThroat Speeds". J. Aero. Sci., Vol. 11 (1944) pp. 356-360.

6. Silberman, E. and Daugherty, R. H. "A Dynamometer for the Two­Dimensional, Free-Jet Water Tunnel Test Section". St. AnthonyFalls Hydraulic Laboratory, University of Minnesota, 1962.

7. Tsien, H. S. "On the Design of the Contraction Cone for a WindTunnel". J. Aero. Sci., Vol. 10 (1943), pp. 68-70.