i DESGN AND CONSTRUCTON OF A WATER TUNNEL By Stephen C. Ko This work has been carried out as a part of a grant from the National Science Foundation for the development of fluid mechanics laboratory equipments at the Department of Ci.vi1 Engineering, Lehigh University. Fritz Engineering Laboratory Department of Civil Engineering Lehigh University Bethlehem, Pennsylvania January 1971
ii TABLE OF CONTENTS TTLE PAGE TABLE OF CONTENTS TABLE OF FGURES i ii iii 1. NTRODUCTON 2. THE DESGN OF THE WATER TUNNEL 3. THE CONSTRUCTON OF THE WATER TUNNEL 4. PERFORMANCE OF THE WATER TUNNEL 4.1 Velocity 4.2 Turbulence 1 2 11 12 12 12 5. CONCLUSON 6. APPENDX - FORCE DYNAMOMETER 7. REFERENCES 15 16 20
iii TABLE OF FGURES Figure 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. NTRODUCTON A variable-pressure water tunnel which is of a facility analogous 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 equipment, and is not commercially available, therefore, proposal was made by Dr. J. B. Herbich in January 1966 to the National Science Foundation 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 completed in later of 1969.
-2 2. THE DESGN 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 transparent Plexiglas. The two-inch wall thickness provides for a rigid mounting of test objects and instruments. t 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. e, the diameter 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. F and Fig. 5) is a 10 inch propeller type pump by Lawrence Pumps, nc. The pump is driven by a 15 hp a. c. motor with a motion
.-. CTY WATER.-- Q NOT TO SCALE p L A B C D H.~ G F A B C D E Test Section Transition Diffuser Elbow No.1 Pump F G H J Motor Pump Diffuser Settling Section Elbow No.2 Elbow No.3 K L P Q Contraction Cone Transition Filters Constant Head Tank Fig. 1-:- Water Tunnel System W
-~-4 ' FRONT VEW / / /.~,- /. / @ '/. 2" f, r 6" 1 "/ / -- 5"----J... 7.5"..j... t-..-- 10" -l TOP VEW 1\,-- - ---. ;.Y DYNAMOMETER,, l\...---~ '----, ~ \ \\\\, \.\\\\\\\.\' \'\\\:\\\,\~\-r. ~~':','.'..'.'.','..\,.\,','.\\,,\.,\~\.,\,.\ \\'\,..\,.'..>.,.,\,.'.,'..'\ \.',.,\ ' \ \..\\..,.\.\\.\.,....\..'\\.' \~~\\,.,.\.\,\ \,\,\\\\\ \\\'~\,\.\\\\."",'., ~., '..>. '\\,..'\... '.., '-. ~. "..' "..' ". \. \ '.. ~ ". ~ ". \ ~ f ~ ~ ~ ~ ~~_l. \21 \21 \21 ~ -- CYLlliDER i 6" : ~ 1 '-. ',\ \.\ \.\ ' 'll'.' 'll'".. " n.. \... \. 1'\'\\\ l". \. '.' \ \. '.,'\ ~~\' \.~ " '\\ '\... \ \. '. '. \'\.\\\..,\,.\.\\ \ 11,:.'..\ 11'" '. ~. \.,'....' ''o.\ \ \ \ \\ \\ \ \. \ \ \\ \ \. '. \' r-'....., ;\ ". \... \,... "" ' '. \. " \.,... \ \ \ '. \... ' r-- J L_- 1 L l \ \' ~ ~--- 30" --.---.------...-..._.._.._... NOT TO SCALE.~--1 Fig. 2: '. Water Tunnel Test Section Details
-5 f8~"- r ~ -~ ~ '/ -<;==J ~ / ~.. [ :~.. ~, f6' SQUARE.1 t""s f 6"SQUARE - ill----~-- 1 _-+--",,6".D. 9" - Fig. 3: Transition Sections
-6 r. H 1 35" t-rt-"""'-!'j- -- 10".. Fig. 4: Elbow No. 1
~~==>l?+-- i Fig. 5: Cross Section of the Propeller Pump 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 () 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 transition 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 arrangement is to keep a constant volume of water in the system by compensating 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.
H ~ ~ ~ 12 /56% /64% 18 /70% / /72% f:j / A /70% ~ u H ~ >< A H ~ 0E-! 8. 4 / /'./ /64% / 56% o ' 4 8 12 16 20 24 28 Q, N HUNDRED GALLONS PER MNUTE Fig. 6: Characteristic Curves of a Pump \0
-10 10" --------ia-f r::::::> _L 3/16" l===':!~jl-_-_--=-- ~_- _= -_-_- >. J 24 ] 8" Fig. 7: Elbow Nos. 2 and 3
-11 3. THE CONSTRUCTON 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. to 35 fps. The velocity in the water tunnel can be varied from 17 fps The velocity profile at the mid-section of the test section is shown in Fig. 8. The Reynolds number, based on test section dimension, maximum velocity and at 70 0 F, ranges from 8 x 105 to 1.6 x 10 6. 4.2 Turbulence The turbulence characteristics were measured by a constant temperature anemometer with a parabolic quartz coated probe. The anemometer is a Heat Flux System Model 1000A, built by Thermo-Systems, nc. 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 output, in watts, instead of voltages. The power computer has a manufacturer'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 nstruction 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 ~ ~_::!----~-:---T--...-~ 0.8 0.6 U = 17.9 fps c 0.4 + U = 22.5 fps c 0.2 O...-- L..- ---i'-- ---' --J.... o 0.1 0.2 0.3 0.4 0.5 0.6 y D '... w Fig. 8: Velocity Profile in the Water Tunnel
-14 14 L e 12-1 e e \ u = 18.07 fps D =.6 inches Q % U' e 6 4 e. 2 e-e------ e--e--_. o 1 2 3 4 5 Fig. 9: Turbulence Profile in a Water Tunnel
-15 5. CONCLUSON 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. APPENDX - 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, J, 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. f a force in the direction of the flow, i.e. normal to
-17 ( DRAG FORCE PLATE -+-+---+:.+-- PRESSURE TAP 1 STRAN GAGE TERHNALS PLEXGLASS HOUSNG eeeeeeee 1 3-3/8 inches (, DRAG" FORCE BEi\t!~t--t--...-~. ---. " " --_..._--~ LFT FORCE PLATE -+--f~'-'--'--t----'---j!;~---1--'+-=-lft FORCE B-EAL'1S! 1 '- '... -'. -. "1-- ALUMNillli PLUG BASE PLATE... -. ", -'. " ". ". ~", ". '. '".....2 inches...- l1l;;;;_----- inches ROD FO ATTACHNG TQ MODEL... 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. f 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. f 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.
1.4 1.2 1.0 lbs. 0.8 0.6 0.4 0.2 0 0 100 200 300 400 500 600 700 t-' 6., MCRONS \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 - Review of Literature". Report Nord 7958-139, Ordnance Research Lab., The Pennsylvania State College, State College, Pennsylvania, May 16, 1949. 2. Robertson, J. M. and Ross, D. "Water Tunnel Diffuser Flow Studies, Part - Experimental Research". Report Nord 7958-143, Ordnance Research Lab., The Pennsylvania State College, State College, Pennsylvania, July 8, 1949. 3. Robertson, J. ~1. and Turchetti, A. J. "Water Tunnel Vaned-Turns Studies". Ordnance Research Laboratory External Report Nord 7958 64, The Pennsylvania State College, State College, Pennsylvania, September, 1947. 4. Ross, D. "Water Tunnel Working Section Flow Studies". Report Nord 7958-97, Ordnance Research Laboratory, The Pennsylvania State College, State College, Pennsylvania, June 15, 1948. 5. Smith, R. H. and Wang, C. T. "Contraction Cones Giving Uniform Throat Speeds". J. Aero. Sci., Vol. 11 (1944) pp. 356-360. 6. Silberman, E. and Daugherty, R. H. "A Dynamometer for the Two Dimensional, Free-Jet Water Tunnel Test Section". St. Anthony Falls Hydraulic Laboratory, University of Minnesota, 1962. 7. Tsien, H. S. "On the Design of the Contraction Cone for a Wind Tunnel". J. Aero. Sci., Vol. 10 (1943), pp. 68-70.