Cover Page for Lab Report – Group Portion

Boundary Layer Measurements

Prepared by Professor J. M. Cimbala, Penn State University

Latest revision: 23 February 2017

Name 1: ______

Name 2: ______

Name 3: ______

[Name 4: ______]

Date: ______

Section number: ME 325._____ Group # _____

Score (For instructor or TA use only):

Lab experiment and results, plots, tables, etc. - Procedure portion / _____ / 45
Discussion / _____ / 15
Neatness & grammar / _____ / 10

TOTAL

/ ______/ 70

Comments (For instructor or TA use only):


A. Operation of the Water Channel

To fill up and run the water channel, follow this procedure (7-10 minutes):

1.  Remove the top Plexiglas cover plate and set aside safely. Note: If using one of the horizontal model insert, put this insert in before filling water channel (see Figure 4a)

Caution: The plexiglass has a perfect seal that can create a high pressure within the system as air would not be able to flow out. This will slow filling time and can even completely stop the filling up processes if pressure stays too high.

  1. Close large drain valves - one on the bottom right side of the water channel Also, be sure the small brass drain valve on the clear Plexiglas end of the channel is closed. See Figure 3a for correct configuration.
  2. Open the water channel fill valve (located adjacent to the drain valve).
  3. 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.) See Figure 3b for valve location and correct configuration
  4. 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!

Caution: As water nears the top wall of the water channel, the water level will RISE QUICKLY

  1. Let the water rise until it just about reaches at the top of the test section where the bottom of the plexiglass cover should be See Figure 4b. Close the fill valve quickly so that the water does not overflow. The channel operates best if the water level essentially filled to its max.
  2. Place the plexiglass back on top and if water is too high, cautiously drain some of the water to an appropriate level. If the water level is too low, cautiously add open the fill valve and the bleed valve (the brass valve at the top right of the water channel, see Figure 5a) to let air out while filling and prevent pressure build up.
  3. Once satisfied, close all valves including the bleed valve and the water filter inlet on the wall.
  4. Turn on the pump motor controller circuit breaker switch (to the left of the water channel). Rotate the red handle ¼ turn clockwise so that it points vertically to ON.
  5. 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. Note: A digital display on the frequency controller is merely approximate freestream velocity reading. Use the flow rate meter on the side, then divide it by 5 for a better approximation (in m/s) of the freestream velocity in the water channel test section (See Figure 5b). That is a reading of 54.4 means flow is moving at approximately 1m/s.

Caution: run the filter pump when dye visualization is in use to prevent accumulation of dye in the system. The switch is located on the right side of the main system circuit breaker handle and ensure that the filter drain valve is See Figure 6a and b

  1. Run the channel at high speed (at a reading of around 1.0 m/s) 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.
  2. To shut off the flow at any time, simply push the “STOP” button on the Toshiba frequency controller.

Figure 1: a) Fill and drain values location in an open fill & closed drain orientation. b) Water inlet located on the wall in the open position.

Figure 2: a) Max. water level to insert horizontal models. b) Max. water fill level for the water channel before spill occurs

Figure 3: a) Brass bleed valve located on the top of the channel. b) Sample flow meter reading of 5.04 m/s in the pump outlet but the freestream is wider and so flow is actually 5.04/5 = 1.008 m/s approx.

Figure 4: a) the filter pump switch. b) the recirculating filter pump valve in the open position.

To drain the water channel (Not now – do this when finished with your experiment):

1. Push the “STOP” button on the Toshiba frequency controller.

2. Turn off the filter pump first (see Figure 6a), then it is safe to turn of the pump motor controller circuit breaker. Rotate the red handle ¼ turn counter clockwise to the OFF position.

Caution: Never drain the system with the motor running.

3. Remove the top plexiglass and open the drain valve marked in Figure 3. The channel will slowly begin to drain. Wait several minutes (15 minutes if complete drain is required) 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.)

Caution: Removal of the top plexiglass is critical to prevent creation of a partial vacuum/ low pressure within the system. If the plexiglass is already sucked tight, open the bleed air flow to balance the pressure.

4. 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.

5. Turn off the wall-mounted fill valve that supplies the fill garden hose.

6. Briefly open and then close the water channel fill valve to release the pressure in the garden hose.

B. 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 “1D LDA with Traverse.lpd” from the “Project Templates” section. 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 titled “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 LDA 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. 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.

14. 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 setup 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.

15. 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.

16. Turn on the water channel to some medium flow rate (around 0.5 m/s or around 30 Hz on the readout of the frequency controller).

17. 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.

18. 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.

19. 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.

20. Record the LDV reading of the average freestream velocity. Vavg = ______m/s.

21. 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. Measurement of the Laminar Boundary Layer