Wind turbines inspired by Whales
Kat - When you see a whale, it probably doesn't make you think of wind turbines, but our next guest, the very aptly named Professor Frank Fish from West Chester University in the states was inspired by the fins of a humpback whale to design a better wind turbine. So we're joined by Frank. Hello...
Frank - Hi. How are you doing?
Kat - Hi. Good. Now, tell us about the story behind this because I understand that you saw a picture of a whale and it set off your train of thought.
Frank - Actually, it wasn't a picture. It was a little bit more three-dimensional than that. It was a sculpture of a humpback whale and I saw that it had, aside from very long flippers, these very curious bumps along the leading edge, the front edge of the flipper. And I was quite embarrassed because I actually started saying that "this is impossible" until I did see a picture, and then tried to figure out why it have these curious bumps that you just don't see on anything else.
Kat - It does seem counter intuitive. You'd think that bumps would interfere with the action of the fin. So, what are the bumps doing?
Frank - Well, what it appears is that they modify the flow. So, if you have a wing-like structure - like taking your hand and putting it out of a car window and playing aeroplane - what will happen is a wing will modify the flow of air. It'll push it down and as a result, you get a lift force as you raise the angle of the wing. And that occurs up to a particular point, in which case the hand or the wing will go through what's called 'stall' if the angle is too big because the air flow or water flow can't move around it in a nice controlled fashion. Stall is something you don't want to happen. It's awful when it happens in aeroplane, but for every humpback whale, what the bumps do is that they can increase the angle at which you can have that flipper directed into the flow, without stalling.
Kat - So you can have a sharper angle and get more drive from the wind?
Frank - Exactly. So, the whole idea is that, because you can raise it at a higher angle, what's called an angle of attack, you can then place it into a wind or water flow and you can get more lift out of it, and thus, more energy if you're putting it into a windmill. You can also have a safety factor; a big problem with windmills is that you get gusts of wind from any direction and that sometimes exceeds the stall angle, and the result is that the windmill becomes unstable. It starts to vibrate and can even blow apart. With this, you can actually have a higher angle, get more energy out of the wind and in the same way, also protect the windmill because it's less likely to form these vibrations.
Kat - So how have you been applying these kind of bumpy fins to wind turbines? Have you got large scale ones or is this kind of just small scale work at the moment?
Frank - Well, I work with a company and we've had a test windmill up in Canada and it was about a 30-kilowatt windmill, test windmill, and what we found is that under moderate air speeds, you could actually get a 20 percent increase in the amount of energy that we could produce with the windmill.
Kat - That sounds absolutely phenomenal. Why have people not thought of making bumpy wind turbines before?
Frank - Well again, it's sort of counterintuitive. I mean, whenever you see wing-like structures, we always think that they need a nice sharp, clean leading edge, so aeroplanes or car spoilers or windmills, or fans, anything like that. So this is a bit counterintuitive that you wouldn't think of putting these bumps along the leading edge. Part of the argument has been that, if you do that, you're going to disrupt the flow in another way and that is, you're going to increase the amount of resistance that wing will go through the air or through the water with. What we have found with the bumps is actually - there is no penalty for having these bumps along the leading edge. They don't increase the resistance. And additionally, as you go up to higher and higher angles, there's actually a reduction in the amount of resistance compared to a wing that doesn't have the bumps, simply because the wing isn't stalling. When it stalls, the amount of resistance goes up quite a bit. So we can operate at higher angles with less resistance than if we didn't have the bumps.
Kat - That sounds brilliant. We've had a question in from Silverwing Benoir in Second Life; he says, is this similar to the dimples on golf balls? Is it a similar function that's going on?
Frank - It has similarities, but there are distinct differences. What a golf ball does by having the dimples on it is to turbulise the air over the surface of the golf ball. So normally air will move in nice, even layers over a surface, and that's what we call laminar flow. The trouble with laminar flow is it's not very stable. You can't maintain it at very high speeds or with very large entities. And so, by having the dimples that turbulise the flow over the golf ball, which means that the flow will continue over more of the surface, and as a result, there's less resistance, and the ball travels further when it's hit. With the tubercles, or these bumps along the leading edge, what they do is they do create a different flow regime, but not necessarily turbulising the flow. What they do is they produce large swirling masses of flow, what are called vortices. These vortices interact over parts of the wing to actually help to speed up the flow over say, the bump itself and keep that flow attached over the entire surface of the wing, so that again, you don't stall out.
Kat - So, at the moment, you are testing this wind turbine up in Canada. How long might it be until this starts to be adapted more widely as turbine technology?
Frank - Well, I think it's ready to go. The big problem is that there's always a large capital investment in redesigning structures such as windmill turbine blades, especially when you're talking about very large wind turbines. We have had success in actually putting these on ventilation fans and there again, we're seeing that there's an improvement for the manufacturer because they can push as much or more air with fewer blades, by having these bumps on the fan blades. And so, what that means for the producer is that there's less material cost. Then the actual fan operates with greater efficiency, which means for the end-user, they're going to pay less in their electric bills to ventilate some area using the fans with the bumps.
Kat - Fantastic! That sounds like a great example of stealing from nature to make something that's greatly improved. So, thank you very much, Frank. That's Professor Frank Fish from West Chester University, explaining how the bumps on the edge of a whale's fins have inspired him to make new, better wind turbines.