Union College
Lab 2
Me331 – Fluid Mechanics
Lab #2b: Measuring Wind Tunnel Velocity
The purpose of this experiment is to learn how to measure velocity using a pitot probe and to calibrate
wind tunnel motor frequency to test section velocity.
Pre lab Assignment:
Bring your pressure transducer calibration curve and serial number to lab!
Procedure:
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Connect your pressure transducer to the computer in the wind tunnel room (S&E N007) using
the data acquisition system.
Setup the data acquisition software to take 100 measurements at a rate of 10 readings per
second.
Mount the pitot probe in the wind tunnel as shown in Figure 1. Make sure that the pitot probe
is lined up with the flow direction.
Connect the stagnation pressure probe to the high side of your transducer. Connect the static
pressure probe to the low side.
Figure 1. Schematic Representation of ME WindTunnel (Courtesy of Rob Powell, ME ’09)
Acquire Velocity Data:
Turn on the wind tunnel and set the motor frequency to 3 hz. Use the computer to record the pitot
probe pressure difference (100 readings). Calculate the average and standard deviation in your
transducer reading and convert the average volts to pressure using the transducer calibration that
you measured last week in lab. Now calculate the test section velocity using Bernoulli’s equation
along a streamline:
V
Winter 2013

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2 ( Po
P )

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Professor Anderson
Union College
Lab 2
Me331 – Fluid Mechanics
Where V is the velocity of the fluid, Po is the stagnation pressure, P is the static pressure and 
is the fluid density. Note: You will need the conversion 1”H20 = 248.8 Pa. Use the
temperature in the test section and the ambient pressure (101.3 kPa) to calculate density.
Increase the motor frequency by 2 hz and repeat the measurement. Continue to increase the
motor frequency in 2 hz intervals until your transducer is saturated (i.e.p > 1.0” H20)
After you acquire your data, save your file and move to another computer so that the next
group can use the wind tunnel.
Data Analysis
1. Calculate the uncertainty in your velocity measurement. Include the uncertainty in pressure
difference, P (from your calibration data), and the uncertainty in air density which you can
estimate assuming the uncertainty in the temperature measurement is 1 oC and the uncertainty
in pressure is 3%.
2. Plot motor frequency versus velocity, including uncertainty bars. Compare your results to the
manufacturers supplied data in Table 1 below.
Table 1. ME Windtunnel Performance Data.
Motor
Frequency
(hz)
3
5
10
15
20
25
30
35
Velocity
(m/s)
1.99
3.42
7.43
11.93
16.23
21.88
24.8
29.41
The Lab MEMO Report
In this part of the lab I have asked you to measure the velocity in the wind tunnel test section and
compare it to the manufacturer’s specifications. To summarize this lab you will revise your memo
report from last week to include your finding on wind tunnel velocity.
Winter 2013
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Professor Anderson