How do I determine the exact shape of an airfoil blade for my wind turbine?

[Frankie.S]

I'm currently doing a project in my tech class where a partner and I have to create a wind turbine. We've decided that we are creating a vertical axis wind turbine, that we are creating the base out of PVC, and using three airfoil shaped blades that will be created via cnc milling. I have a few questions about the blade design process. It seems that airfoil blades are the most effective for what we are doing with the resources that we have. How exactly does an airfoil work? I've heard that the common explanation that the wind moving across the top of the blade must move faster causing a pressure difference is incomplete. Also, how should we go about figuring out the exact shape of the blade? Finally, how exactly is wind created? As I understand it, the Earth is unevenly heated causing pressure differences that result in wind, but why exactly is it that the Earth is heated unevenly?

 

[berkeman]

Welcome to the PF.

I'm currently doing a project in my tech class where a partner and I have to create a wind turbine. We've decided that we are creating a vertical axis wind turbine, that we are creating the base out of PVC, and using three airfoil shaped blades that will be created via cnc milling. I have a few questions about the blade design process. It seems that airfoil blades are the most effective for what we are doing with the resources that we have. How exactly does an airfoil work? I've heard that the common explanation that the wind moving across the top of the blade must move faster causing a pressure difference is incomplete. Also, how should we go about figuring out the exact shape of the blade?

There is a good PF Insights article about this: https://www.physicsforums.com/insights/airplane-wing-work-primer-lift/

Finally, how exactly is wind created? As I understand it, the Earth is unevenly heated causing pressure differences that result in wind, but why exactly is it that the Earth is heated unevenly?

Can you post links to the reading you've been doing on this question? Please show your effort, so we can provide some tutorial help.

 

[rootone]

...
... how exactly is wind created? As I understand it, the Earth is unevenly heated causing pressure differences that result in wind, but why exactly is it that the Earth is heated unevenly?

Tilt of the Earth's rotation axis, Sea generally absorbs more heat, land tends to reflect it, and local weather can be strongly affected by local geography.

 

[albertov123]

When I was designing a Kaplan (hydraulic) turbine, I chose a couple of airfoil profiles which are extensively used in turbine blade design, i created 3D models of them and made CFD analyses for each, in order to understand which one would yield the maximum torque at given conditions.

You calculate turbine's certain values (blade angles, rotor and turbine wheel radius etc.) by empirical-based relations and equations.

 

[Mark Eaton]

Yes vertical axis method allows for any wind direction as long as you have at least three towers or section 120 degrees apart to cover all 360 degrees for start up.
Also a big improvement is to block the wind from the side that is apposing the wind, not aiding in the wind force.
I feel a great blade design would look like a sharp angled long bow tie. The side that opposes the wind has much less area of trapped air than the other side will catch.
The wind will be displaced much easier on the opposing angle side, opposed to the. aiding side.
You must also consider rpm and efficient levels, that should be well matched for your rpms.. And weight, causing different amounts of possible wanted momentum that you might want for periods of wind speed flux. It is easier to start a light weight blade or design, though also easier to stop the devise also. Though you still would be better off, blocking or funneling the air, or wind to the aiding side.

 

[Mark Eaton]

The opposing force is what I call, Interactive Momentum, it causes friction, and is in opposition to force or momentum. This is what you want to try to eliminate, .on the opposing side of the blade or scoop.

 

[Frankie.S]

I apologize, I meant to say horizontal axis wind turbine. Our turbine will be tested directly facing a fan, so wind direction is not an issue. I'm going to find some of the information we've found on blade design and post it here later when I have more time.

 

[imsmooth]

I built a wind turbine, but I do not know if this is what you wanted. I put up a whole tutorial a while back.
http://www.mindchallenger.com/wind

 

[berkeman]

I built a wind turbine, but I do not know if this is what you wanted. I put up a whole tutorial a while back.
http://www.mindchallenger.com/wind

Looks like a fun and challenging project. Did you eventually connect your system to the grid? Did you get your local utility to sign off on the connection? What did you use for the interface to the grid, with the "island" feature?

 

[imsmooth]

I bought an Aurora grid-tie inverter and was connected for about 4 years before one of the wire couplers failed. This was the mercury switch that allowed the turbine to spin 360 but still connect to stationary wires within the pole. Because I still had a significant amount of trees I did not want to repair this. The unit was able to produce a solid 1.5kw when it got a good wind. Unfortunately, with the trees I did not have enough constant winds. It was a great project, though.

 

[Frankie.S]

My project is simpler than the one that you did. I don't have to worry about converting the mechanical energy into potential energy. I will be given the equipment to do that when my turbine is being tested. I also have a very limited amount of time. This turbine will probably be about 1-2ft tall. That does seem like an interesting project though. I might have to do something like that on my own time after I complete this one. Here is some of what I've found and have been looking at so far.

https://en.m.wikipedia.org/wiki/Wind_turbine_design
http://centurionenergy.net/types-of-wind-turbines
https://en.m.wikipedia.org/wiki/Angle_of_attack
http://learn.kidwind.org/sites/default/files/windturbinebladedesign.ppt
http://www.thomasnet.com/about/cnc-milling-51276103.html

So far, I have decided to create a model for an airfoil blade in inventor and get 3 made via cnc milling in order to create a horizontal axis wind turbine. I've contacted somembody that has access to the equipment required to do this, and have been permitted to use it. I've also decided to create a simple base out of pvc.

Now I need to design a blade on auto desk inventor, get three of them made, find or create a rotor, and put it all together. This is what I'm having trouble with. I'm not finding much information showing me how to determine the exact shape of my blade. I was hoping to make the blade in a way so that angle of attack can be adjusted, so that I don't have to worry about that until I'm able to test the turbine. I'm also still having trouble with the explanation of the airfoil. From looking into it, I've read that both the Newtonian and the Bernoulli explanation are correct. They are just different ways of looking at the same thing. I don't understand this. If that's true, then how does the Bernoulli explanation explain planes with flat wings flying? Also how would a plane fly with wings that have an angle of attack of 0 degrees according to the Newtonian explanation?