SciBud Wind Tunnel Questions

[jeffer]

Hello buddy,
I am a researcher. I have to complete thesis on it. But i am new with SciBud.
How can start it perfectly. What equipments are needed for this thesis.
Please explain it thoroughly. So that i can complete my thesis accurately.

[AerospaceGuy]

Hello Jeffer,

You are a researcher doing a thesis on wind tunnels? Please let me know a bit more about your thesis so I can be of better help to you.

What I can tell you right away is this:
*Science Buddies is a web site with information and resources for students in pre-college school--grades K through 12. If you are doing a thesis in college of any kind, then Science Buddies' resources are not of the caliber that you will need.
*To find great resources regarding wind tunnels and aerodynamics, visit the Bibliography and Credits page of my "How to Build a Wind Tunnel" guide: http://www.sciencebuddies.org/science-f ... aphy.shtml.
*For detailed explanations of how to build and use the homemade high-school level wind tunnel, you can visit my "How to Build a Wind Tunnel" guide in its entirety here: http://www.sciencebuddies.org/science-f ... -toc.shtml.

Let me know if I can be of any more help to you, Jeffer.

[r.qussous]

Hello dude =D,
My friends and I, are trying to do the same Wind tunnel project, and I would really like to know what Force sensor you used, such as model name and type, or from where we could buy such ones to be accurate for our experiment, and we also want to thank you for the time u have used to reply the posts =D

[AerospaceGuy]

Hello r.qussous,

The sensor I used was a dual-range force sensor produced by Vernier Scientific. This is the link to the specific product's page: http://www.vernier.com/probes/dfs-bta.html

As you can see from the page, these sensors are very expensive--over $100 each. This is why I suggest that you borrow sensors from teachers who already have them, unless of course you have no trouble affording them yourself.

Any sort of basic physics force sensor will do, as long as it is capable of sensing both pull and push forces, can be mounted on the threaded rod that you use to connect to your airfoil model in the test section, and that it can be easily and securely fastened down to your base, so that it doesn't move when the fan is on. In other words, any sensor just like the one I have linked to you will do just fine. Remember, you need 2--one for lift, one for drag.

I wish you and your friends good luck as you build my wind tunnel design for your project! Please feel free to come back here for help at any time. I'm happy to aid you in any way I can on Ask an Expert.

[Zues9]

Could anyone please give us guidance on the "settlement chamber" construction in the scibuddies wind tunnel? The project description on this is a bit imprecise and there isn't a photo that we can figure out. Appreciate your help.

[AerospaceGuy]

Hello,

I am the designer and builder of the wind tunnel, so I can answer any questions you may have! Please feel free to post specifics.

In general terms, the reason why there is little in the way of instructions and no photograph is because this step is simple, and up to your creativity. Basically, all that is needed is that you have two sheets of screen behind the honeycomb mesh at the entry point of the Contraction Cone. It is up to you to decide how to install those three components, since there are many different ways you can do it, depending on your materials choices, etc. In other words, I left it up to the imagination of the student, because this part of the tunnel is delicate and so the same instructions may not apply to every person's wind tunnel. Construction results vary from student to student, and so I recommend that you figure out the best way for your specific wind tunnel to have the three components attached at the Contraction Cone.

That being said, it is a bit difficult to do, so please let me know if you have any questions. I'm here to help, so if you want to run some ideas past me for advice, I'd be willing to check them out.

Also, I will search among all my photos to see if I can dig up any pictures that may be of help to you. Photos are hard to take of the Settlign Chamber because the screens and the mesh block the view of each other, but I'll see if I have anything.

[Zues9]

Thank you. I'm understanding the concept better. A photo could be helpful. We had trouble figuring out just what the honeycomb was. Would you happen to have a suggestion on what we can use for this, and where it might be available? Our initial effort on this was to simply attach a single screen to the entrance to the contraction cone, but I understand that we need to do more than that. Really appreciate your help.

[AerospaceGuy]

Hello again Zeus9,

The honeycomb mesh is the white grid that you see on the large end of the Contraction Cone. It is a product that you could find at a hardware store--I found mine at Lowe's. Look in the lighting department, where they have the large rectangular translucent panel sheets that go over light fixtures in the ceiling. You will find what you need there. If you don't, ask someone and bring a photo of the tunnel so they can know what the mesh looks like.

So, basically, the Settling Chamber of the Contraction Cone is the honeycomb mesh, behind which you have one or two screens stretched tightly. These serve the purpose of making the airflow smooth and straight ("laminar flow"), so that it's uniform and controlled.

I tried attaching a photo to this post, but it was rejected. However, there is still a good photo for you to check out that is already in the Wind Tunnel Guide--I recommend that you go back to the main page of the Wind Tunnel Guide and check out the first picture therel--the one of the wind tunnel as it is fully set up. Look closely at the Contraction Cone--notice that there is a dark square just behind the honeycomb mesh. This is a screen mounted inside the Cone.

Make sure that you re-read the small section of instructions regarding the Settling Chamber in the Contraction Cone portion of the Wind Tunnel Guide. Having seen the image, and read my answers, the instructions should make much more sense to you now.

I hope that those two images have clarified things for you! If not, please feel free to ask what questions you have left. Good luck!

[Zues9]

This is very helpful, and just what we needed. Thank you.

[epwaotl]

I was reading this thread and I saw this:

Your question is a very good one, by the way. The collection chamber does in fact serve to increase wind speed in the test section. This is part of what I meant about the differences between the math and actual data you would collect: the collection chamber is much more voluminous than the test section so that a large volume of air is collected and compressed to fit into the test section volume. By the continuity and Bernoulli equations, the effect produced is that the wind speed in the test section increases without the need of power. In other words, the fan draws air into the tunnel, which speeds up as it is compressed into a smaller volume.

This got me wondering if the same principle would work for a push through wind tunnel rather than a draw through wind tunnel. My wind tunnel is a pusher. The way it is set up there is a fan which lows air into a contraction zone, then a settling chamber, and then the test chamber. I was wondering if adding a large collection chamber upstream of the fan would increase the airspeed in the test chamber. If I made this modification air would flow through the large collection chamber before entering the fan and the rest of the wind tunnel.

Thanks for the help.

[AerospaceGuy]

Hi epwaotl,

The principle works for both types of tunnels: draw-through fans and push-through fans. The reason that the Science Buddies tunnel is a draw-through fan is because push-through fans tend to create more turbulence because they are blowing air in. Drawing air into the settling chamber makes it easier to straighten the flow into a laminar flow.

Adding a cone upstream of the fan will not really do anything for you--the fan is open at the back and is drawing air from the surroundings to blow downstream of itself. Adding a cone will only restrict the volume of air from which the fan may draw. It won't really produce any helpful effect for you.

If you want to learn more about this, I recommend that you do a science project about the best wind tunnel configuration. That would be a great project!

If you are simply looking for advice, I suggest that you build a draw-through tunnel like the Science Buddies wind tunnel design. It's simple and will produce the least amount of turbulence.

[linhely]

I have started building the wind tunnel and have a question concerning the threaded rod that goes from the Vernier sensor to the airfoil in the test section. I purchased a #6-32 threaded rod which screws into the sensor. This rod seems very flexible. The project recommends a rod that does not respond to just the airflow in the tunnel but this rods seems like it will bend with little air flow.


[Edited by Science Buddies administrators.]

[AerospaceGuy]

Hello linhely,

Your concern addresses a very important component of the design--the rod has to be of a metal material strong enough to resist bending caused by the airflow. The air will push back on the model and cause the rod to bend unless it is made of a stronger material. What sort of rod are you using? You will want to use something like steel if you can get it.

[acoggan]

Hello,

Using your plans as a general guide, I am in the process of building a similar wind tunnel. Based on theoretical calculations and your students’ data, I was expecting/hoping to achieve wind speeds of ~8 m/s. However, a calibrated vane anemometer installed in the diffuser reads only ~5 m/s without the test chamber in place, and only 3-4 m/s with it attached (I haven’t finished the contraction yet to be able test the tunnel as a whole).

I assume that this is because the gable fan I purchased off Amazon to save a few dollars can’t/doesn’t deliver the claimed CFM of 1620 when used in such a manner. In looking at your write-up, though, I cannot determine the exact make/model/size of fan that you used. The plastic shroud makes me think it is a Vent Air as they sell at, e.g., Lowes, but they all measure >17” in diameter (including the shroud), which isn’t consistent with your Figure 2C.

If you could provide a few more details re. the fan, I would greatly appreciate it!

[AerospaceGuy]

Hello acoggan,

At the moment, I cannot find a record of the exact make and model of the fan I used in the example wind tunnel, as I was trying to be general at the time and didn't make specific product recommendations. I will see if I can pay a visit to the high school which now uses that wind tunnel and take a look at the fan to determine the information you need.

In the meantime, I recommend that you construct the contraction cone and use the anemometer to test the entire wind tunnel as a whole. The point of the cone is to contract incoming air, and thus accelerate it, and so perhaps that is the missing element you need to achieve the calculated theoretical airflow you desire. The test chamber brings your number down because it limits the open quantity of available air to draw through the diffuser. Once you have attached the cone, however, that quantity will increase markedly because the cross-sectional inlet of the cone is 7X greater than that of either the test chamber or the diffuser.

If you are still having trouble with the wind speed once you have connected the cone, then we can conclude that either the fan or the wind tunnel itself are causing a loss of flow rate. I'll get the fan info if I can, and you test the full wind tunnel design, so we can go after two possibilities at once.