Download Water Tunnel Flow Visualization

Last Rev.: 7 JUL 08
Water Tunnel Flow Visualization: MIME 3470
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Grading Sheet
~~~~~~~~~~~~~~
MIME 3470—Thermal Science Laboratory
~~~~~~~~~~~~~~
Laboratory №. 12
WATER TUNNEL FLOW VISUALIZATION
Students’ Names  Section №
POINTS
PRESENTATION—Applicable to Both MS Word and Mathcad Sections
GENERAL APPEARANCE, ORGANIZATION, ENGLISH, & GRAMMAR
10
ORDERED DATA, CALCULATIONS & RESULTS—MATHCAD
DATA: FLOW RATE & READ IN FILES
PHOTO PRESENTATION (RESIZE, DISCUSS FLOW, INDICATE )
5
15
DISCUSSION OF RESULTS
FOR NEGATIVE , DRAG IS NEGATIVE. WHY IS THIS SO?
COMMENT INDIVIDUALLY ON THE 2 AIRFOILS AND COMPARE
THEM. MAKE AT LEAST 10 STRONG STATEMENTS.
USING REYNOLDS NUMBER SCALING, WHAT WOULD BE THE
VELOCITY OF AIR BE FOR THIS EXPERIMENT?
CONCLUSIONS
ORIGINAL DATASHEET
TOTAL
COMMENTS
d
GRADER—
10
40
10
5
5
100
SCORE
TOTAL
Last Rev.: 7 JUL 08
Water Tunnel Flow Visualization: MIME 3470
MIME 3470—Thermal Science Laboratory
~~~~~~~~~~~~~~
Laboratory №. 12
WATER TUNNEL FLOW VISUALIZATION
Screens
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Flow
Flow Direction
Direction 

Honeycomb
Nozzle
Nozzle
Test
Test
Section
Section
~~~~~~~~~~~~~~
LAB PARTNERS: NAME
NAME
NAME
SECTION
№
EXPERIMENT TIME/DATE:
NAME
NAME
NAME
TIME, DATE
OBJECTIVE—The objective of this exercise is demonstrate the
use of flow visualization to study complicated flows and relate the
visualizations to simple lift and drag measurements.
INTRODUCTION—The equations of flow (continuity and NavierStokes) can only be used to find solutions to a limited number of
simple flows when the boundary conditions (surface geometry) are
not too complex. Also high Reynolds number flows (i.e., turbulent
flows) are very difficult to describe. With the advent of computational fluid dynamics (CFD), the flow field can be partitioned into a
great many individual cells and the geometry and equations of flow
can be solved in matrix form for each of the cells. The success of such
solutions is dependent on the particular CFD differencing scheme
used to solve the differential equations. Such solutions may take
hundreds of hours of computer time to solve a set of matrix equations.
Further, even when a complicated flow can be described, it still
may be difficult to determine the forces that flow imparts to a
body. Thus, other tools (under the heading of experimental fluid
mechanics) are essential in investigating complicated flows.
In this experiment the student will investigate the flow over two
different models for various angles of attack, α, using both watersoluble dye to visualize the flow and a moment balance at the base
of the sting which holds the model. From the angle of attack and
the moment, lift and drag can be determined.
EXPERIMENTAL APPARATUS—The primary device utilized
in this experiment is the Model 0710 University Desktop Water
Tunnel which is shown in Figure 1. This is manufactured by the
Rolling Hills Research Corporation [1], Formerly part of Eidetics
Corp. The main components [2] of this water tunnel are as follows:
Screens—wind and water tunnel screens are normally
made of wire meshes. Screens make the flow velocity
profiles more uniform by imposing a static pressure drop
proportional to velocity squared. A screen also refracts the
incident flow towards the local normal and reduces the
turbulence intensity in the whole flow field.
Honeycomb—is effective for removing swirl (turbulence)
and lateral mean velocity variations, as long as the flow
yaw angles are not greater than about 10°. Large yaw
angles cause the honey comb to “stall,” which reduces
the effectiveness besides increasing the pressure loss.
Nozzle (contraction)—increases the mean velocity
reducing both mean and fluctuating velocity variations to
a smaller fraction of the average velocity. This assumes
that the honeycomb and screens in the low-speed region
of the tunnel have caused the flow to be fairly uniform
and straight. The honeycomb and screens need to be in a
low-speed region to reduce losses in total pressure.
Test section—region initially having a well-conditioned
uniform flow where the object to be tested is placed.
Other equipment needed for this experiment are two models with dye
injection ports, a moment balance at the base of an adjustable sting
(Figure 1d) that holds the models, a camera to capture the flow
visualization, and LabVIEW virtual instrumentation.
(a)
(a)
(b)
(b)
(c)
(c)
(d)
(d)
(e)
(e)
(f)
(f)
Figure 1— Model 0710 University Desktop Water Tunnel: (a) Screens,
(b) Honeycomb, (c) Nozzle, aka contraction, (d) Adjustable sting with
moment transducer at its base, (e) On-off switch and flow controller,
and (f) Delta-winged and (almost) 2-D test models.
THEORY—In this experiment for each angle of attack, α, the
student measure the moment at the base of the sting which
supports the model. Using a nominal 15 cm from the base of the
sting to the center of the model, a normal force on the surface of
the model can be determined. This normal force, N, can be further
broken down into lift and drag components using the angle of
attack such that the lift is L = N cosα and the drag is D = N sinα.
Then the lift and drag coefficients, CL and CD, can be computed
from the relations
L
D
(1)
CL 
CD 
1
1
2
  U   S
   U 2  S
2
2
where,
 – fluid density
U – free-stream fluid velocity
S – plan-view surface area of the model
EXPERIMENTAL PROCEDURE—
1. Fill the water tunnel to the top of the screens and make sure that
all air bubbles are out of the honeycomb.
2. Attach the model of choice to the sting and attach dye hoses. Set
the angle of attach to zero.
Last Rev.: 7 JUL 08
Water Tunnel Flow Visualization: MIME 3470
3. Turn on SCXI box and open the LabVIEW program. There is a
PowerPoint presentation to explain the operation of LabVIEW.
This can be found in the same folder at the LabVIEW program.
4. Click on the “initialize data acquisition” button to synchronize
the eye-balled zero angle of attack with LabVIEW.
5. Turn on the water flow at the box in Figure 1e and adjust the
flow to a flow rate to around 4in/s and record the flow rate.
6. Set the pressure gauge on the dye-injection system to a small
value—just enough to cause the dye to flow.
7. Take plan-view measurements of the triangular, delta-wing
model and the rectangular, 2-D airfoil.
8. Set up the camera. Check through the view finder that it is not
tilted to the left or right.
9. For angle of attack, , varying from –2° to 32° in 2° increments,
perform the steps below.
a. Photograph the flow about the model. Be sure there is some indication of the angle in the photo; e.g., a Post-It note with the
nominal angle written on it stuck to the viewing window of the
water tunnel. This will later be cropped from the photo.
b. Record LabVIEW data for the particular angle of attack.
Not all photos are needed in the report! Use photos to indicate
general phenomenon over a range of data points or to show a
transition in the flow between two data points.
For the Report
This is an exercise in formatting. Your boss’ life will be made easier
if s/he does not have to flip pages to compare photos and plots.
1. The student has been provided with the programming which plots
lift and drag coefficients for the two models vs. angle of attack. He
or she should enter the appropriate flow rate and their file names to
be read. Instead of doing Mathcad programming, here the student
will format their data such that appropriate photos (not all photos)
and the calculations with plot all are presented on one page.
When finished, the presentation will look similar to Figure 2.
click on the picture and if the picture
toolbar (see right) does not appear, choose
SHOW PICTURE TOOLBAR. Now
when one right clicks the picture select the
icon that looks like
. This tool is used to
grab the handles of the picture to hide the
parts of the picture that are not desired. The
PictureToolbar
result is shown in Figure 4.
e. Finally, size the picture for the presentation format already
prepared for you. Right click on the picture, choose SIZE,
and set the width to 1.6 inches (see formatting dialog box below)
For each photo used, describe below it what of interest is happening in the boundary layer. Also indicate the angle of attack.
Figure 3—Photo inserted in line with text with a border added
Figure 4—Cropped photo
Figure 2— Sample presentation of photographic data,
calculations, and combined plot
2. To prepare photos, do the following:
a. Insert the photo into this document. INSERT / PICTURE /
FROM FILE (if using MS Word 2003).
b. Right click on the picture. Select FORMAT OBJECT. Choose
the tab LAYOUT and select IN LINE WITH TEXT.
c. Right click on the picture and choose BORDERS AND
SHADING. Select the BORDERS tab, click on BOX, and
choose DARK BLUE as the color. Figure 3 has had these steps
performed on it.
d. In the picture, one wants to see only the model and dyeenhanced flow. Thus the photo needs to be cropped. One might
use a photo editor; but, the following is easy and quick. Right
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Figure 5—Resizing the photo
Last Rev.: 7 JUL 08
Water Tunnel Flow Visualization: MIME 3470
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ORDERED PHOTOGRAPHIC AND NUMERICAL DATA, CALCULATIONS, and RESULTS
2-D AIRFOIL
Nominal Particulars:
Length
= 11cm
Width
= 16.5cm
RECTANGULAR
Flow Closely Following Surface
 = 0°
Text Box
FLOW RATE:
DENSITY:
in
Uoo  4.05 
s
  998 
m
AIRFOIL DATA
DELTA-WING MODEL
INDEX:
kg
Nominal Particulars:
Length = 13.5cm
Width = 12.5cm
TRIANGULAR
i  0  17
3
DELTA-WING DATA
M 
M  
Surface S  11  16.5  cm
Area:
 0
Attach   M
Angle:
 2
Lift:
L  M
 3
Drag:
D  M
Lift
Coeff:
CL 
Drag
Coeff:
CD 
2
2 L
2
S  
13.5  12.5
2
 0
   M 
 2
L   M 
 3
D  M 
CL. 
  Uoo  S
2 D
2
  Uoo  S
CD. 
 cm
2
2  L
2
  Uoo  S 
2  D
2
  Uoo  S 
6.163
CL
Mathcad
Object 
i
CL.
i
CD
i
CD.
i
0
5
      
i
i i
i
32.145
Text Box
Last Rev.: 7 JUL 08
Water Tunnel Flow Visualization: MIME 3470
DISCUSSION OF RESULTS
For negative angles of attack, the drag is negative even though
common sense says it should be positive. Why is this so?
Answer:
Comment individually on the two airfoils and compare them.
You should be able to make at least 10 strong statements.
Answer:
Using Reynolds number scaling, what would the velocity of air
be for experiment?
Answer:
CONCLUSIONS
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Last Rev.: 7 JUL 08
Water Tunnel Flow Visualization: MIME 3470
DATA SHEET FOR WATER-TUNNEL FLOW VISUALIZATION
Time/Date:
_______________________
Lab Partners:
_______________________ _______________________ _______________________
_______________________ _______________________ _______________________
Flow Rate:
______________(________)
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