Wind energy - Blade twist

A wind turbine blade needs to present to the wind at different angles depending on which point on the blade we are looking at. Because the inside of the rotation turbine moves slower than the tip, the inside blade edge needs to look more like a bi-plane wing, and the tip needs to look more like a modern jet wing.

Try this. It wont make a wing, but it will demonstrate how we might make some twist.

Take a cardboard roll, and draw two lines along its length but on an angle, so that the lines don't quite run parallel to the sides.

Cut along the lines.

And you get this.

No great surprise, but it does show a way we might make a wing shape with a twist in it.

Our wind doesn't just need to be twisted, but it also needs to be thicker and broader in near the centre, and tapering off to thin and narrow at the tip.

That means if we draw a triangle like thing on our cardboard roll, we should get something a bit like what we need.

This should give us a bi-plane style wing at one end, a modern jet wing at the other, and everything else in between.

The little square bit at the far end is where I would bolt it onto the central hub if I was going to add 2 more blades and make a turbine.

We start to see something approaching what we need. It has a big thick wing shape near the centre, and a thin modern jet looking wing shape at the tip. It also has a twist in it so that the angle of attack reduces as we get nearer the tip. This is a good thing because the tip is travelling so much faster than the near centre. The faster it rotates, the more the apparent wind appears to be coming from  the direction of the next blade, rather than at 90 deg to the turbine.

I put some sticky tape around our new turbine blade model to try to get a reflection that might make the shape clear.

I think this captures it a bit.

Now, none of this is my idea by the way. In fact many other people have made blades like this and they seem to work OK on smaller turbines. They just don't make them out of cardboard rolls.

The best part about all this is it looks like I might be able to use PVC yet again.

I seem to have a thing for PVC.


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