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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
-11
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.
-12
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 -
-14
•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
-15
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
-20
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.
Recommended