Physics 4C Wind Tunnel Project Fall 2012: Data Collection/Analysis

There are two important elements that are to be measured in the wind tunnel: wind velocity traveling across the test area and the forces in contact with the wing.

The velocity of the wind at the different secctions of the wind tunnel can be obtained using the continuity principle or flow velocity

A1V1 = A2V2, where A is the cross sectional area and V is the velocity of a fluid, in this case wind.

Our focus will be on the drive and testing sections of the wind tunnel;

AdriveVdrive = AtestVtest, where we can measure V drive as the wind velocity from the fan.

	Dimensions		Area
Testing Chamber	23,13/16 inches x 24, 5/16 in	(0.6048 x 0.6175) +/- 0.002 m	0.373 +/- 0.0017 m^2
Fan Area	25 inches x 23, 13/16 in.	(0.6350 x 0.6175) +/- 0.002 m	0.392 +/- 0.0018 m^2

Testing Data
Trial	Wind Velocity (Drive Section)		Wind Velocity (Test area Section)
1	15 mph	6.7056 +/- 0.003 m/s	7.05 + /- 0.045 m/s
2	26.4 mph	11.8019 +/- 0.002 m/s	12.41 +/- 0.080 m/s
3	20.2 mph	9.0302 +/- 0.005 m/s	9.49 +/- 0.061 m/s
4	15 mph	6.7056 +/- 0.001 m/s	7.05 +/- 0.045 m/s
5	19.5 mph	8.7173 +/- 0.004 m/s	9.16 +/- 0.059 m/s
6	20.5 mph	9.1643 +/- 0.002 m/s	9.63 +/- 0.062 m/s
7	21.2 mph	9.4772 +/- 0.002 m/s	9.96 +/- 0.064 m/s

2nd wing (wider thinner one)
Trial	Wind Velocity (Drive Section)		Wind Velocity (Test area Section)
upside down	15 mph	6.7056 +/- 0.004 m/s	7.05 +/- 0.045 m/s
1	16 mph	7.1526 +/- 0.003 m/s	7.52 +/- 0.049 m/s
2	17 mph	7.5997 +/- 0.002 m/s	7.99 +/- 0.052 m/s
3	16.5 mph	7.3762 +/- 0.003 m/s	7.75 +/- 0.050 m/s

Next we will measure the forces on the surface of the wing: lift and drag forces.

The two parallel sensors will measure the magnitude of the force at which the wing would be elevated. The readings on each of the sensors will be averaged and added up to find the total lift.

The sensor with the tied string will measure the drag force. Such sensor will measure the tension of the string. In order to find the actual drag force, trigonometry will be used to find the tension in the x-direction.

We can disregard the weight of the wings because at every trial, we made sure we zero'd out the force sensors; therefore, we always started at readings of about 0.001 N.

length of the string: 24.5 in		0.6223 +/- 0.002 m	Angle between string and test area floor
height of the wing: 14 inches		0.3556 +/- 0.003 m	θ = 34.85 +/- 2.63 degrees

x-component of Fdrag
Fd = Fav drag * cos θ = Fav drag (0.820650855 +/- 0.052441316)

Wing 1

	Av. Force 1, N	Av. Force 2, N	Total Av. Lift Force, N	Av. Drag Force	Av. Drag Force (x-dir)
Trial 1	0.008801704	0.142621863	0.151423567	-	-
Trial 2	0.009557088	0.152211019	0.161768107	-	-
Trial 3	0.010082532	0.126034313	0.136116845	-	-
Trial 4	0.025633385	0.095053882	0.120687266	0.022678596	0.019 +/- 0.0012
Trial 5	-0.006802365	0.277639954	0.27083759	0.02155324	0.018 +/- 0.0011
Trial 6	-0.002359967	0.291803081	0.289443114	0.021768195	0.018 +/- 0.0011
Trial 7	-0.007184506	0.231735183	0.224550676	0.023320645	0.019 +/- 0.0012

Wing 2

	Av. Force 1, N	Av. Force 2, N	Total Av. Lift Force, N	Av. Drag Force	Av. Drag Force (x-dir)
Upside down trial	-0.027309775	-0.010491441	-0.037801215	0.021690002	0.018 +/- 0.0011
Trial 1	0.006914956	0.070443325	0.07735828	0.021908227	0.018 +/- 0.0011
Trial 2	-0.00017855	0.028765995	0.028587446	0.022768046	0.019 +/- 0.0012
Trial 3	-0.00550465	0.012238367	0.006733717	0.022696394	0.019 +/- 0.0012

An interesting variation occurs when collecting data for the upside down trial. The total lift force comes up to be negative. This means that this force is actually a 'push down' force. This phenomena is better known as downforce, which is when air pushes down on a wing instead of lifting it up. This downforce effect is very desirable in auto racing while taking sharp corners, making race cars to better adhere to the track.