AERODYNAMIC DRAG BALANCE

Laboratory Safety

Since this instrument will be used by students in a laboratory setting certain lab. precautions has to be taken. These rules are the basic, well-known laboratory safety rules and regulation.

Absolutely no smoking, eating or drinking allowed in the lab. If you need to smoke, eat or drink, do it outside the lab.

Put safety first and do not take any chances. The lab contains expensive and potentially dangerous equipment (if not handled properly).

Ask the teaching assistant if you are unsure about anything.

Never try to force anything e.g. if something such as a valve appears to be stuck do not use excessive force, please consult the lab instructor.

The easiest way to be safe is to use your common sense.

(Note: these rules were taken form the thermal-fluids lab. webpage.)

No running in the lab.
Never operate machines that you haven’t been taught to operate.
Long hair must be tied.

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Aerodynamic Balance Safety

Since this device has no moving components, safety of inflicting harm or injuring to you or others is not very probable. But never the less, be cautious when operating the instrument. The following are some safety precautions that the instrument user has to take into account.

Never mount models in the balance that aren’t designed for this instrument.
Do not stand on the balance mounts.
Do not place heavy objects on top of the flexors.
Make sure that the forces being measured do not exceed the instruments maximum range. This will damage the load cells.
Never introduce the instrument with the wind tunnel on.
Before starting the wind tunnel check that the model is securely fasted to the balance.
In case of extreme mount, balance or model vibrations, turn the wind tunnel off. Check that all components were assembled properly.

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ASSEMBLY MANUAL

List of parts

-- 2 Aluminum flexors

--2 Load Cells

--1 Plexiglas mount

Steps for Assembly

Since the instrument is a 2 dimensional balance, and is targeted to students the assembly is very simple. We recommend that the assembly be done by two persons. The main precaution is that the person assembling the components does not try to force any piece in. The pieces are design to fit in only one way, please do not use extreme force. For the person handling the different pieces, do not step, lean or place heavy objects on top of the instruments. This will damage and deform the components increasing the calibration uncertainties. Read all steps before assembling the balance.

For the following steps you will need the mount and the two flexors.

Get the mount and connect the horizontal flexor and vertical flexor. An H (horizontal) and a V (vertical) give the direction of the flexor. You can find this symbol in the upper surface of the shaft.

Insert the flexors in their proper slots. Make sure that the letter is facing the hole.

Caution: do not over tighten the flexors, this might cause damage to the fine threads.

Get the load cells and screw them to the other end of the flexors. Make use that the proper cell is connected to the designated flexor. You can identify the cell by reading the letter at the back of the load cell. Connect the H cell to the horizontal flexor, and the V cell to the vertical cell. Caution: do not over tighten the load cells, this could damage the cells.

For the following steps you will need a screwdriver and a level.

Get the two rails. Connect the rails using the four half inch screws.

STOP!: before continuing with the next step make sure that the two rails are leveled. If this is not checked the forces measured will not be in proper alignment.

Using the clips on the back of the cells, connect the rails to the cells.
Finally, connect the mounts to the wind tunnel.

7. Mount the desired model.

Before turning on the wind tunnel: check that all the components are properly fastened, and that both rails are level.

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OPERATION MANUAL

The aerodynamic balance has three modes of operation:

Drag Mode: only the horizontal cell is turned on.
Lift Mode: only the vertical cell is turned on.
Combined Mode: both lift and drag cells are turned on.

To make the operation process explanation easier, if a step does not apply for a certain mode, we will point it out.

Connect the load cells output wires to the data acquisition hardware.
Turn on the computer and open LABVIEW software. This will be the data acquisition software.
Go to file/open. Open the drag balance archive.
Run the program.
Turn on the wind tunnel.
Turn the wind tunnel dial to the desired speed. Caution: make sure that the wind tunnel operator is familiar with the correct operation of the wind tunnel. You can find this steps in the thermal-fluids lab. webpage.

Remember: the lift or drag on the model can not exceed the maximum range of the load cell, this would cause a permanet damage to the cells. If the system starts vibrating, turn off the wund tunnel and check that all parts are properly fastened.

If a steady state reading is required, please wait for a couple of minutes to ensure that the flow around the model has stabilized.
Select the desired mode of operation.
Run the LABVIEW program.
After the experimental time interval is reached, stop the data acquisition program.
Turn down the wind tunnel.
Turn off the wind tunnel.

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LABORATORY MANUAL

Our design has to modes of operation: constant speed with different models, and varying speeds with a constant shape. We have formulated two different experiments based on these two modes of operation. Each lab. is design to introduce different, but very important fluid dynamic principles and phenomena.

Constant speed / different models

1.0 Objective

This experiment aim to demonstrate the effects of the surface shape, size and finishes on the drag and lift produced by the model being tested. In order to determine the relationship between the air velocity, drag and models, you will have to analysis the behavior of the drag and lift for different models under the same conditions..

2.0 Experimental Procedure

Choose desired model: Sphere

Cylinder (vertical, horizontal)

Cube

Polygon

Airfoil (symmetric, nonsymmetrical)

Connect model to the connector rod.
Turn on the wind tunnel counter reading to the desired speed.
If steady state condition is desired, please wait 3-4 minutes to ensure that the flow around the model has stabilized.
Turn on transducer.
Run Labview program.
Record and save the Labview output.
Turn off wind tunnel.
Connect new model.
Repeat steps 2 to 9 with the new model.

Varying speed constant shape

1.0 Objective

The objective of this experiment is to demonstrate how the drag and lift vary with the air speed is increased or decreased. During this experiment you will also determined how the location of the separation point shifts as a function of the air speed. In this experiment, you will pick one of the models provided by our package. Then the student will be asked to run this model under different conditions.

2.0 Experimental Procedure

Choose desired model.
Connect model to the connector rods.
Insert the rods to the stem.
Turn on the wind tunnel to the desired speed.
Wait 3-4 minutes to ensure that the flow around the model has reached steady state.
Turn on transducer
Run Labview program.
Record and save the Labview output.
Change the wind tunnel speed to next velocity.
Repeat steps 5 to 9.
Turn off the wind tunnel.

Conclusions

As it was mentioned above, the design was targeted for educational purpose. For this reason we tried to design a very easy to assemble, complex to operate, and a convenient to use. The data acquisition program elementary, which facilitates the interaction with the user. Enabling the student to spend all of his/her efforts in ratiocination of the experimental data, and understanding the concepts presented by the professor.

Since the actual instrument is still under construction, this manual is a ideal cease scenario. The steps of assembly are tentative. Even though that the design team thinks that the assembling steps are very clear and easy to follow, we believe that during the actual assembly, we will recheck each step. This is done in order to ensure that by adding or removing steps, the overall process would become less complicated and time consuming. The same approach will be present through each step of the way. As a result, this will be a mutable document.