Turbulence Sphere Method: Evaluating Wind Tunnel Flow Quality

1. Preparation of turbulence sphere in the wind tunnel

1. Connect the wind tunnel pitot tube to port #1 on the pressure scanner, and connect the static pressure port to port #2 on the pressure scanner.
2. Lock external balance.
3. Fix the sphere strut to the balance support inside the wind tunnel.
4. Install the sphere with 6 in diameter.
5. Connect the leading-edge pressure tap to port #3 on the pressure scanner, and connect the four aft pressure taps to port #4 on the pressure scanner.
6. Attach the air supply line to the pressure regulator, and set the pressure to 65 psi.
7. Connect the manifold of the pressure scanner to the pressure line.
8. Start up the data acquisition system and pressure scanner. Make sure to turn them on at least 20 minutes prior to the test.
9. Estimate the maximum dynamic pressure based on the free-air critical Reynolds number for a smooth sphere: . See Tables 1 and 2 for recommended test parameters.
10. Define the dynamic pressure test range from 0 to q_max and define the test points by dividing the range in 15 intervals.

Table 1. Parameters for the first test.

Sphere diameter (in)	qMin [in H2O]	qMax [in H2O]
4	4	6
4.987	2	3.4
6	1	2.4

Table 2. Parameters for the second test.

Sphere diameter (in)	qMin [in H2O]	qMax [in H2O]
4	3.4	7.2
4.987	1.3	5.1
6	--	--

2. Conducting stabilization and pressure scan measurement

1. Read the barometric pressure and room temperature and record the values.
2. Apply the corrections to the barometric pressure using equations provided by the manometer manufacturer.
3. Setup the data acquisition software and connect it to the pressure scanner, setting the proper IP address.
4. Insert the following commands pressing enter after each command.
   >calz
   >set chan1 0
   >set chan 1-1..1-4
   >set fps 10
5. Check that the test section and wind tunnel are free from debris.
6. Close the test section doors.
7. Set the wind tunnel speed dial to zero.
8. Turn on the wind tunnel and wind tunnel cooling system.
9. With the wind speed at 0 mph, start recording data, then insert the following command to scan the pressure:
   >scan
10. Record the wind tunnel air temperature.
11. Increase the wind speed up to the next test point dynamic pressure as defined in step 1.10.
12. Wait until the airspeed stabilizes, then repeat steps 2.9 - 2.11 until the last test point is executed.
13. Slowly reduce the airspeed to zero.
14. When all the points have been measured, replace the 6 in sphere with the next sphere following steps 1.2 - 1.5.
15. Repeat steps from 2.3 - 2.14 to repeat the stabilization and pressure scan experiments.
16. Wait the wind tunnel to cool down after the test is executed for all three spheres.
17. Turn off the wind tunnel and data acquisition software.