Pressure in Aerodynamics
Part I. Calibration of Wind tunnel
1) For a wind tunnel operating frequency of 5 Hz, read the dynamic pressure from the
digital manometer on the side of the tunnel.
2) Repeat in increments of 5 Hz, up to a maximum of 30 Hz.
3) Calculate, from the dynamic pressure, the wind speed in the tunnel for each frequency.
4) Plot the curve of frequency vs. wind speed.
Part II. Pressure Distribution around a cylinder
1) Set the wind tunnel to operate at a frequency of 30 Hz.
2) When the pressure port on the cylinder is pointed directly into the free-stream (θ=90°),
read the pressure from the inclined manometer. NOTE: the U-tube manometer
measures the difference in pressure between the flow on the cylinder and the static
3) For pressure port locations ranging from 90° to 270°, in increments of 10°, record the
pressure difference from the U-tube manometer.
4) Convert these pressures to pressure coefficients and compare to the predicted behavior
for inviscid flow around a cylinder. What differences in behavior do you see? How can
you explain this from your knowledge of inviscid and viscid flow?
5) Plot the inviscid predictions of Cp versus your calculated Cp.
Part III. Pressure in the ping-pong cannon
1) Load ping pong ball using dowel rod.
2) Pressurize the chamber of the cannon to 25 psi (green dial gauge) using red handle. You
will need to let the chamber fill, then let the gauge settle to the actual chamber
3) Make sure the ball will fire DOWN the tube and that there is a pad to STOP IT at the end.
4) With the help of your TA’s make sure the oscilloscope and the photo-diodes are ready to
go. Adjust the lasers so that they are incident on the photo diodes before every run.
5) The oscilloscope should be in the triggering mode, off channel 1, triggering on a positive
slope. Set the run mode to single. Again take the help of your TA.
6) Open the firing valve.
7) With your TA’s help record the speed from the oscilloscope signal obtained.
8) Repeat Steps 1-7 for pressures ranging from 30 psi to 50 psi, in 5 psi increments.
9) Plot the velocity vs. pressure and comment in the report.
Armstrong Hall Subsonic Wind Tunnel Operation
12 inch x 18 inch test section
Maximum speed 50 m/sec
Lift and Drag Balance
Make sure Power Breaker is on (Handle up)
Press green “on” button on Allen Bradley controller
Adjust speed (motor Hz) with up and down arrow buttons
Do not exceed 30 Hz
Speed ON OFF