Thursday, December 13, 2012
Project Conclusions
Taking into account the time frame, there's a wide array of factors that went unnoticed. This factors increase the room for systematical error which in return might have compromised our data. The most remarkable sources of error were mostly on the electric motor since we were not convinced how much power exactly the motor delivered. Also the rpm's might not have been exact since there was slippage between the shaft and the belt, which translates in inconsistent fan speeds. Sensors were also a big question mark because at times, the force sensors threw out numbers that did not change, giving a chance to equipment malfunction.
The construction of a wind tunnel came together as a somewhat ambitious project. The wind velocities achieved in the wind tunnel were not excessively high (less than 20 mph). The forces registered by the force sensors for lift came to be quite consistent with each other with magnitudes raging from 0.12 - 0.28N for the thick wing and 0.006 - 0.077N for the wing of thinner profile. In terms of drag force, results yielded uniform results of 0.18 - 0.19N for both wings.The wind tunnel gave us a better idea on how fluid dynamics work, giving us the big picture about principles of continuity and drag/lift forces.
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;
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.
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| Wing 1 Trial 1 |
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| Wing 1 Trial 2 |
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| Wing 1 Trial 3 |
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| Wing 1 Trial 4 (Green line is drag force) |
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| Wing 1 Trial 5 |
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| Wing 1 Trial 6 |
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| Wing 1 Trial 7 |
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| Wing 2 Trial 1 |
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| Wing 2 Trial 2 |
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| Wing 2 Trial 3 |
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| Wing 2 Upside down trial |
Wednesday, December 12, 2012
Assembly Session 2
We started by building the second diffuser with the same dimensions as the first one. Then we proceeded to build a base on which the plexi-glass would rest. The length of the plexi-glass section is 3 feet long. The plexi-glass rested on two rubber gasket strips on the base and on top of the diffusers that will held any wind leaking from the testing area.
Having the testing area completed, we proceeded to build a stand for the force sensors. We took 4 blocks of wood and screwed them together in a way to build an frame which would hold the force sensor in place. Then we added a threaded rod and screwed the structure on the testing area floor.
We constructed a mount for the fan to rest on. Support extensions were added to the drive section in order to build a frame. The fan was then mounted at the center of the cross section and joined to the electric motor through the belt. Walls were added to enclose the fan and improve air drag.
Having the testing area completed, we proceeded to build a stand for the force sensors. We took 4 blocks of wood and screwed them together in a way to build an frame which would hold the force sensor in place. Then we added a threaded rod and screwed the structure on the testing area floor.
We constructed a mount for the fan to rest on. Support extensions were added to the drive section in order to build a frame. The fan was then mounted at the center of the cross section and joined to the electric motor through the belt. Walls were added to enclose the fan and improve air drag.
The force of the wind suggested that a single sensor that would hold the
entire wing would not suffice, so we constructed a similar stand for a
second sensor. Now two sensors side to side would be attached to the test wings measuring the lift of the wing.
In order to measure the drag force on the wing, we built another force sensor stand and placed it in front of the other two aligned force sensors. A string was tied to the force sensor, and the other end of the string would be tied under the center of mass of the test wing. The string would be under low tension so that the drag force readings would be more accurate.
At first we were having trouble aligning the rods so that the wing would be leveled properly. Likewise, it was tricky to center the drag sensor. This was solved to the best of our abilities. The small apertures between the joints of the boards inside the diffusers were sealed with liquid nail to prevent air escape.
Two wings (one of them showed above) were provided by the DBF team as test subjects.
Although at the beginning we considered puting a variac to vary the voltage output from the electric motor, we dismissed this approach since we considered that the rpm delivered onto the fan was acceptable.
Assembly Session 1
During the first session of the wind tunnel construction, we focused on building the two wooden chambers that would hold in the air as it flew towards the fan. The cross sectional area of the boxes were 2 sq. ft. with a length of approximately 4 ft.
We also built supports around them to stabilize the structure and also put it on the ground safely, without compromising the internal surface of the chambers.
Once we had the first diffuser, we began building the contraction cone. In the original designs, the funnel has a conic shape, but the wood did not allow us to achieve such geometry. Instead, we build a funnel made out of four equal wood trapezoids. We joined them together by putting 2 L-brackets at each joint. As with the diffuser, a support was also built around the smaller cross-sectional area which also served as sort of a lip to mount it to the diffuser.
Lengthwise, the diffuser-contraction cone surpassed the 8 feet mark.
This is what half of the assembly of the wind tunnel looked like. It's worth mentioning that the joints haven't been sealed up to this point. Stands were added to the diffuser.
We also built supports around them to stabilize the structure and also put it on the ground safely, without compromising the internal surface of the chambers.
Once we had the first diffuser, we began building the contraction cone. In the original designs, the funnel has a conic shape, but the wood did not allow us to achieve such geometry. Instead, we build a funnel made out of four equal wood trapezoids. We joined them together by putting 2 L-brackets at each joint. As with the diffuser, a support was also built around the smaller cross-sectional area which also served as sort of a lip to mount it to the diffuser.
Lengthwise, the diffuser-contraction cone surpassed the 8 feet mark.
This is what half of the assembly of the wind tunnel looked like. It's worth mentioning that the joints haven't been sealed up to this point. Stands were added to the diffuser.
Criteria for Success
1. Build a functional wind tunnel of realistic proportions with a small budget in mind.
2. Attempt to minimize the sources of error such as excessive turbulence, wind leaking and faulty
data collection.
data collection.
3. Have a wind tunnel modest enough to use it for DBF wing testing, and/or future Physics classroom
experiments.
4. Generate interest in the study of Aerodynamics.
Bill of Materials
The following is a list of the projected costs of the materials used for the assembly of the wind tunnel:
-Plywood boards = 4 * $20
-2x2 wood pieces = 4 * $1
-Plexiglass chamber = Free
-Fan = Free
-Electric motor = Borrowed from an SPS member
-Plastic engine belt = Free
-Variac = Property of the Physics department
-Metal rods = Free
-Force sensors = Property of the Physics department
-Rubber gasket strips = Free
-String = Free
-L-brackets = 8 x $1.50
-Box of screws = $7
-Anenometer = Provided by Prof. Mason
-Scrap wood = Free
Most of the materials that we got for free were donated/borrowed by fellow DBF teammates on the understanding that such project is an investment for the DBF project in the future.
-Plywood boards = 4 * $20
-2x2 wood pieces = 4 * $1
-Plexiglass chamber = Free
-Fan = Free
-Electric motor = Borrowed from an SPS member
-Plastic engine belt = Free
-Variac = Property of the Physics department
-Metal rods = Free
-Force sensors = Property of the Physics department
-Rubber gasket strips = Free
-String = Free
-L-brackets = 8 x $1.50
-Box of screws = $7
-Anenometer = Provided by Prof. Mason
-Scrap wood = Free
Most of the materials that we got for free were donated/borrowed by fellow DBF teammates on the understanding that such project is an investment for the DBF project in the future.
PERT Chart
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Project Name: Wind Tunnel
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Team Member: Jesus Oropeza
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Team Member: Manuel Castaneda
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Task
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Task Lead
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Thu Nov 8th
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Tue Nov 13th
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Wed Nov 14th
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Fri Nov 16th
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Sat Nov 17th
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Mon Nov 19th
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Tue Nov 20th
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Wed Nov 21st
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Thu Nov 22nd
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Fri Nov 23rd
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Mon Nov 26th
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Tue Nov 27th
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Wed Nov 28th
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Mon Dec 3rd
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Thu Dec 6th
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Mon Dec 10th
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Thu Dec 13th
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Obtain Turbine
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Jesus
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X
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Final Proposal
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Jesus/Manuel
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X
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Tunnel design/Mechanism
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Manuel
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x
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x
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x
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Tunnel Materials
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Manuel
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X
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Wing prototypes
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Jesus
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x
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X
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x
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Measurement parameters
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Jesus
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x
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x
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Assembly/Bill of materials
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Jesus/Manuel
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x
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x
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Preliminary Testing I
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Jesus/Manuel
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x
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Preliminary Testing II
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Jesus/Manuel
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x
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Wing revision
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Manuel
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x
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X
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Quantitative set up/ data
gathering
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Manuel/ Jesus
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X
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x
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x
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Project update
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Manuel
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x
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Final Wing Testing I
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Manuel
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x
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x
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Final Wing Testing II
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Jesus
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X
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Data Analysis
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Manuel/Jesus
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x
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Work on Powerpoint
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Manuel
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x
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Presentation
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Jesus/Manuel
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x
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