Cover Page for Lab Report – Group Portion
Flow Visualization in a Water Channel
Prepared by Professor J. M. Cimbala, Penn State University
Latest revision: 17 February 2012
Name 1:
___________________________________________________
Name 2:
___________________________________________________
Name 3:
___________________________________________________
[Name 4:
___________________________________________________ ]
Date:
_______________________________
Section number:
ME 325._____
Group letter: (A, B, ...) _____
Score (For instructor or TA use only):
Lab experiment and results, plots, tables, etc. - Procedure portion
Discussion
Neatness & grammar
TOTAL
Comments (For instructor or TA use only):
_____ / 45
_____ / 15
_____ / 10
______ / 70
Procedure and Presentations of Results
A.
Operation of the Water Channel
To fill up and run the water channel, follow this procedure:
1.
Set the Plexiglas cover plate containing the sting mount for the sphere models onto the top of the channel test
section.
2. Close both large drain valves  one on the bottom left side of the water channel, and the other on the PVC pipe to
the right of the pump. Also, be sure the small brass drain valve on the clear Plexiglas end of the channel is
closed.
3. Open the water channel fill valve (located adjacent to the drain valve).
4. Turn on the fill valve that supplies the fill garden hose. (This valve is located on the north wall of the room, to the
left of the sink. Do not turn the valve on the right side of the sink – that one should stay open at all times.)
5. You should both hear and see the water channel begin to fill. Note that the right side of the channel is clear
Plexiglas, and you can watch the water fill the channel. Never leave the room while the channel is filling!
6. Let the water rise until it just starts to lift up the Plexiglas cover plate at the top of the test section. Close the fill
valve quickly so that the water does not overflow. The channel operates best if the water level is about a quarter
inch above the top cover plate (i.e. the top cover plate should be completely submerged).
7. Turn on the cooling fan behind the motor. Run the fan throughout the experiment to prevent the motor from
overheating. The low setting is typically good enough.
8. Turn on the pump motor controller circuit breaker switch (to the left of the water channel). Rotate the black
handle ¼ turn clockwise so that it points vertically to ON.
9. Push the “RUN” button on the Toshiba frequency controller. The water should start flowing. You can adjust the
speed with the control pad “up” and “down” arrow keys. A digital display on the frequency controller indicates
the approximate freestream velocity (in m/s) in the water channel test section.
10. Run the channel at high speed (at a reading of around 1.0 on the control panel) for a few minutes to purge the
water channel of air bubbles. Open the bleed valve on top of the channel to let some trapped air escape.
11. To shut off the flow at any time, simply push the “STOP” button on the Toshiba frequency controller.
To drain the water channel (Not now – do this when finished with your experiment):
1.
2.
3.
4.
5.
6.
B.
Push the “STOP” button on the Toshiba frequency controller.
Turn off the pump motor controller circuit breaker. Rotate the black handle ¼ turn counter clockwise to the OFF
position. Never drain the system with the motor running.
Open both drain valves. The channel will slowly begin to drain. Wait several minutes until the water is nearly all
drained from the channel. (You can monitor the draining progress from the large Plexiglas cover on the far right
side of the water channel.)
Open the small brass valve on the far end of the water channel (clear Plexiglas end) to allow the trapped water to
drain into a bucket.
Turn off the wall-mounted fill valve that supplies the fill garden hose.
Briefly open and then close the water channel fill valve to release the pressure in the garden hose.
Operation of the Laser Velocimeter
1.
The LV (Laser Velocimeter), which is sometimes also called an LDV (Laser Doppler Velocimeter) is used to
measure the freestream velocity for this lab. Verify that the fiber optic LV head is located near the very start of the
test section, where the flow is uniform and uninfluenced by the dye probe or by any models. The LV head should
be close to the vertical centerline of the test section (i.e. at a reading of around 16 or 17 cm on the vertical
traverse), and approximately 3.5 inches away from the front Plexiglas panel of the test section. If the LV system is
already on and operating, all you will need to do is open the laser shutter, which is the “shutter” dial on the black
box labeled “FlowLite” on the top of the electronics rack, and carefully remove the lens cover. Verify (visually)
that the laser is on, then skip steps 2 through 4 below. Do NOT look directly into the laser beam! Serious eye
damage will result! Special laser goggles that filter out laser light are available in the lab for your protection.
2.
Turn on the LV acquisition system with the switch located on the piece of equipment labeled “BSA F60 Flow
Processor” located below the computer on the electronics equipment rack. If the laser is not already ON, turn it
ON with the key on the piece of equipment labeled “FlowLite” located above the computer, and turn the shutter
switch below the key to OPEN. Finally, remove the lens cover on the fiber optic probe head, being careful not to
scratch the lens.
3.
Verify (visually) that the laser is on. You should see two laser spots reflected from the Plexiglas side of the
channel. Or you may see the two beams reflected off particles in the water channel. Do NOT look directly into
the laser beam. Serious eye damage will result. Special laser goggles that filter out laser light are available in
the lab for your protection.
4.
Turn on the lab computer if it is not already on. Double click on BSA Flow Software V4.50 on the desktop. If the
icon is not on the desktop, start the program using the Start → All Programs menu. If this is the first time you
have run this program under your unique log-in ID, continue. If you have run this program under your ID
previously, skip to step 6.
5.
You may see a message saying “BSA software to run for the first time.” This is normal. A window will appear
asking if you wish to register the software now. Click “No”.
6.
In the “Getting Started” window, choose “Browse for an existing project”. Then choose the directory C:\ME325.
In this directory, choose the project: “RLSProject.lda”. If you have run this program under your ID previously,
skip to step 8.
7. When the software is done loading, you will see several windows on the screen. In the window titiled “Device
List”, R-click on Processor. In that menu, click on Device Configuration. This will start the Auto-Configuration
Wizard. (If it does not start automatically, choose “Auto” in the window that comes up.) The Wizard will present
a series of steps:
a. Choose “Next”
b. Message says: “Searching for Processors”. Then “Found Processor”. Choose “Next”.
c. Message says: “Connected to Processor”. Choose “Next”.
d. Message will ask about a traverse. “None” should be selected. Choose “Finish”.
e. If necessary, choose “Close” in the next message.
8.
In the Device List window, R-Click on Processor. Choose “Connect to Processor”.
9.
A new window should appear at the lower right called “System Monitor”. If it does not, R-click on Processor
again, and choose “System Monitor”.
10. In the Device List window, click on “Optical PDA System”.
11. In the “Properties” window (lower left), under “Beam System-U1” click on “Wavelength”. The wavelength of the
laser of this system is 632.80 nm. If this number is not displayed as the current wavelength, use the downward
pointing button and select “632.80 nm” from the drop-down list.
12. In the same window, click on “Focal Length”. Use the downward pointing button to select “160.0 mm” from the
drop-down list.
13. In the same window, under “PDA Receiver” click on “Receiver Focal Length”. Use the downward pointing button
to select “160.0 mm” from the drop-down list.
14. Click on “View” in the toolbar at the top of the screen. Click on “Start Page”, which will bring that window to the
front. Close that window to reduce clutter. Now click at the upper right to enlarge the software to Full Screen.
15. Examine the windows on the screen. You should see: Project Explorer, Device List, a Histogram graph,
Properties, a Data List, a Moments List, the System Monitor, and Messages. Note that the Data List has columns
for Arrival Time (AT), Transit Time (TT), and LDA1 (velocity in direction 1). Look at the columns in the
Moments List and note there is a column for LDA1 Mean. This is where the mean velocity in direction 1 will be
reported for each data acquisition period. Currently, the set up is such that data are taken for 10 seconds. Each
“burst” of LDV signal which results in a measured velocity during that period will be reported in the Data List.
The mean velocity for that period will be reported in the Moments List under LDA1 Mean.
16. Change the data format and precision: in the toolbar at the top, click on “Tools”, then “Options”. Choose the tab
labeled “Data Formats”. Then:
a. Highlight “Velocity”.
b. Click “Change”.
c. Change the Unit to “m/s” and change the Precision to “4”.
d. Click OK. Click OK again on the Options dialog box. A message box appears. Click OK.
Data formats will change once data acquisition has begun.
17. Turn on the water channel to some medium flow rate (around 0.4 m/s on the readout of the frequency controller).
18. Position the optical probe head so that the laser focal volume (also called measurement volume – where the beams
cross) is near the cross-stream centerline of the channel.
19. In the Device List window, Click on “Processor” so it is highlighted. In the top tool bar, select the icon that looks
like a black arrow tip (►); this is the “Run” button. A dialog box will come up – Click on “Run—Create New
Data”. Another dialog box will appear. Click on “Acquire”. You should see “Running” at the bottom of the
screen. Data acquisition will continue for 10 seconds. Observe the System Monitor window. You should see
frequent “bursts” representing LDV signals from the measurement volume. As data are being taken, results
should be posted in the Data List. In the “Run” mode, data acquisition will stop automatically after the 10 second
period.
20. Wait for acquisition to stop. In the top tool bar, select the icon which resembles two arrows in a circle ( . ). This
starts the “Repetitive Mode” so that data are continually updated and displayed. Whenever you wish to quit, click
on the black square icon (■) on the top tool bar to stop acquisition.
21. Record the LDV reading of the average freestream velocity. Vavg = ___________ m/s.
22. NOTE: When the LDV is not being used, restore the lens cover to the LDV fiber optic head, and turn the shutter
dial to “closed”. Leave all the electronics ON. You will use the LDV system again later in this lab.
When completely finished with the lab, close the BSA Flow Software program. Restore the lens cover to the
LDV fiber optic head, and turn the shutter dial to “closed”. Leave all the electronics ON. Also turn off the
water channel. If the water is colored with dye, drain the water from the system.
To prevent eye injury, it is advisable to turn the shutter to “closed” whenever you are viewing the sphere or
airfoil. Open the shutter only when a velocity measurement is required.
C.
Operation of the Dye Injector System
One container of dye is mounted on a vertical pole. If the dye reservoirs are nearly empty, ask your Instructor or TA to
fill them with more dye. A valve (one for each reservoir) controls the flow rate of dye into the dye injection needle. This
flow rate should be adjusted as water channel speed changes to give the best possible dye streak. If the valve is not open
enough, the dye streak will be too weak. If it is open too much, the dye itself will form a jet which disturbs the flow. The
orientation of the dye probe is also critical to the quality of the dye streak.
(4)
1.
Install the dye injection needle into the top cover plate. Remove any spheres from the sting mount. Experiment
with the dye injection system with the water flowing at various speeds, and with the dye valve adjusted to various
flow rates. Rotate the dye injection needle to determine the best orientation for injection.
2.
Turn on the backlight (push and hold in the switch at the bottom of the light box for a couple seconds). The
backlight should make the dye streak more visible.
3.
Which orientation yields the best dye streak at very low water channel speeds (around 0.1 or 0.2 m/s)?
Does this agree with your intuition?
How about at higher speeds (around 1.0 m/s)?
Include sketches of the dye streaks at both low and high speeds in the space below:
4.
As the water slowly turns color, the dye streak will become more difficult to see. If the water gets too colored, you
will have to drain and re-fill the water channel.
D.
Visualization of Flow over Spheres
(15)
1.
Study the flow over the various sphere models (golf ball, baseball, smooth yellow ball, and roughened yellow
ball) at various speeds. Be careful that you don’t damage the dye injection needle as you change models. Do not
over-tighten the model onto the sting mount. Most of the results in this lab experiment are qualitative, but be sure
to record the freestream velocity (as obtained from the LV system) for each case so that you can calculate
effective Reynolds numbers. Note that the LV has a rather slow response time at low velocities, so make sure you
wait for the velocity reading to settle down before recording its value. Pay particular attention to the location
where the boundary layer separates off the surface of the spheres, and the Reynolds number at which the drag
crisis occurs (if at all). Record your observations neatly in the space below, including some sketches. Attach extra
pages if necessary. Note that you can move the dye injection needle up or down until the dye streak hits the sphere
exactly where you want it to hit. For each sphere, look for the three Reynolds number regimes: laminar,
transitional, and fully turbulent. Ask your instructor or TA for assistance if you are not sure which regime is being
seen. Hint: The best results are obtained when the flow over the bottom of the sphere is observed.
E.
(5)
Visualization of Flow over a Model Car
1.
Carefully remove the dye injection needle and gently set it down on the cover of the settling chamber.
2.
Carefully lift up the cover plate with the sting mount, and replace it with the cover plate that supports the model
car.
3.
Carefully re-install the dye injection needle on the new cover plate.
4.
Use the dye to study the flow over the model car. Pay particular attention to the flow over the top (roof) of the car,
around the back side, and into the wake region. Does the flow separate or not? Draw some sketches.
F.
(2)
Visualization of Airfoil Stall
1.
Carefully remove the dye injection needle and gently set it down on the cover of the settling chamber.
2.
Carefully lift up the cover plate with the model car, and replace it with the cover plate that supports the airfoil.
3.
Carefully re-install the dye injection needle on the new cover plate.
4.
The airfoil angle of attack can be increased by turning the brass knob counterclockwise. Use the protractor
mounted on the back of the test section to monitor the angle. Set the airfoil at zero degrees angle of attack. Turn
on the water flow at a fairly slow speed (around 0.25 m/s). Record the freestream velocity (as obtained from the
LV system). Calculate Reynolds number in a similar manner as was done for the spheres. Define Rec = Vc/
where c is the chord length of the airfoil (4.0 inches). Since the airfoil is thin, it is not necessary to correct for
blockage effects here. Vary the channel speed up to the maximum. Showing sample calculations in the space
provided below, calculate the Reynolds number of this airfoil at the various channel speeds, and fill in the table:
Sample calculations of Reynolds number:
Reynolds number range for the airfoil:
Water channel speed setting
(reading on the control pad)
0.25
0.50
0.75
1.0
(3)
5.
Freestream velocity V measured
by the LDV instrument (m/s)
Reynolds number, Red
For this available range of Reynolds numbers, do you expect the boundary layer to be laminar or turbulent? (Note:
assume the airfoil surface is smooth.) Justify your answer.
To save time in the steps which follow, you may use the above table to estimate Reynolds number as a function of
channel speed setting. Even when you change angle of attack, you may assume that the Reynolds number remains
constant; i.e. it is not necessary to re-measure velocity and recalculate Re at each different angle of attack.
(5)
6.
Set the water channel speed to about 0.25 m/s. With dye injection, slowly increase the angle of attack of the airfoil
from 0 to about 20, and record sketches of your observations. If the flow separates off the upper surface of the
airfoil, indicate the separation point on your sketch. Does the separation point move with increasing angle of
attack?
(2)
7.
Based on your observations with the dye streaks, at what angle of attack  does the airfoil stall at this speed?
(3)
8.
Turn off the dye injection, and repeat the experiment, watching the tufts instead. When stall occurs, the tufts
should change direction, as discussed above. Based on your observations with the tufts, at what angle of attack 
does the airfoil stall at this speed?
(5)
9.
Now repeat the experiment for the other three water channel speeds (approximately 0.5, 0.75, and 1.0 m/s). Use
either the dye streak or the tuft flow visualization method to determine the stall angle. Describe your results in the
space below and on additional sheets of paper if necessary. Specifically, determine stall angle as a function of
Reynolds number. Some sketches may be helpful.
10. Drain the water channel and turn everything off. Restore the channel to the same condition it was in when you
started.
Discussion
(5)
1.
Were you able to observe a drag crisis on any of the spheres? Why or why not? Discuss what you learned about
drag crisis and flow separation. Has flow visualization helped you to understand this concept better?
(5)
2.
Did you observe flow separation at the back of the model car? If so, where does the flow separate? Discuss how
flow separation may influence the aerodynamic drag on an automobile.
(5)
3.
Describe what you learned about the process of airfoil stall. In your experiment, did the airfoil stall angle depend
on Reynolds number? Why or why not?