Turbulence: Finding Order in Chaos | Neil Ashton | TEDxOxford

I think for most people the word turbulence is associated just with a bumpy flight it can make the difference between enjoyable start to your holiday or one of the worst experiences of your life I think we've all been there when the plane starts to move around the pilot puts the fasten seat belt sign on but normally things you know return to normal within a few minutes but maybe we've all had at least one experience of extreme turbulence where you think the planes dropping 3,000 feet even though it's probably hardly moving at all the pilot now tells the cabin crew to sit down and you know I'm an aerospace engineer I know how these planes are designed and I know the kind of safety factors that go into it but even I have a limit when I'm looking out the window and I think should the wing really be bending that much but today I want to talk about the deeper meaning of turbulence and how it defines the world around us you see turbulence shapes of planes that we fly on the cars that we drive in and even our own bodies the problem is it's quite hard to see but if you look carefully you can quite often see it in the smoke from a cigarette or a candle or even on your breath on a cold morning but what is turbulent well it really describes the way that a fluid behaves and by fluid I mean air water or even blood it's best if we see from an example so you see here the smoke coming from a candle at the beginning you see kind of a regular smooth flow that follows just one path we call this laminar flow but then you start to see these instabilities you start to see this random chaotic flow start to form that now we called turbulent flow and turbulent flow is something that really is the norm in nature it's something you see the most but all fluids can be in a laminar or turbulent state and they transition between them depending on the speed or the viscosity how sticky the fluid is or even external factors but one of the key things with turbulence is the way that it mixes things up and so if you imagine if you put like a dye trace some sort of colourful liquid into a flow in the laminar region it will just carry on going and there cannot this same path but once it gets into this turbulent region then it really starts to be mixed and turned around until that the dye is spread much wider than it was before and this is the reason that turbulence is actually desired when we want to cool down something we want to spread cooling around inside a nuclear reactor they actually design the drum tree for their the pipes which carry the coolant to promote turbulence or inside a jet engine further to cool down the turbine blades but turbulence also has some disadvantages it tends to cause more resistance more drag so if you're designing a plane or a car you want to minimize it and in general have as much laminar flow as possible this means you have less drag you can use less fuel and you're more efficient that's why usually when I ask somebody oh you know if you want to draw a car or play you tend to do something quite smooth and streamlined but if that's the case then why the golf balls have dimples probably if I asked you to design something that could go as far as possible you'd make it smooth and slick but that's where her understanding of turbulence comes into play so if we were to now look at a smooth sphere so imagine a golf ball with no dimples what I'm showing here is a visualization the flow going around that ball so what happens is the air moves over the ball imagine you just hit it and the flow starts to slow down as it goes around the sphere until you get this separated flow around the bat this wake and this wake is what's causing a resisting force of drag forces what's slowing it down but now if you put dimples on the ball you start to see that the weight is much smaller and that's because of the way that turbulence acts this mixing that we saw with the dye actually helps it to stay attached for longer the flow has more energy and momentum and so doesn't give up until later around the ball has a smaller wake and actually has almost half the drag so if you were to hit a smooth ball it would only go about half the distance to a proper golf ball will so that's kind of the interesting thing about turbulence you know it's kind of the opposite way that you'd think about how to do things but you know that's just golf I mean that's kind of interesting for some people but it's not really will changing stuff I think really the important thing all the reason that we need to know more about tournaments is actually climate change so countless studies have shown now that humans are responsible or partly responsible for climate change and you know the problem is is that it's only going to get worse and I'm talking now about the contributions from aviation and an automotive because as the emerging economies China India Brazil want to increase their use of planes - the way we do we're going to see a big increase but like so many things once you have the technology do you really want to give it up do you want to swap the ability to fly from London to LA and 10 or 11 hours we've going on a boat to cross a glam tic for five days and then a car a train of course you don't so it's the responsibility of scientists and engineers to come up with ways to reduce the impact and one of the key ways of doing that is aerodynamics because you know the planes flying through the air if we make it go through the air just that little bit more efficiently we can use less fuel less power and reduce the emissions now for it it's always good to have you know some equations in that's kind of and we've got to prove myself I have the doctor before the name and all that but really the it's because if we want to design better planes cars we've got to understand turbulence we've got a really bill to try and model it visualize it so about 200 years ago two mathematicians came with the navier-stokes equations and these if solved can exactly represent the motion of any fluid we can get out its speed its direction and the force it imposes on the body that it goes through or around but the problem is even though these might look quite simple they're not they're very complicated and nonlinear such that you cannot solve them by hand analytically so instead we have to use numerical methods to approximate them and we'll use supercomputers if we can do this then we can start to visualize the flow so here's an example of a simulation that I ran a couple of months ago solving these equations on a supercomputer and here we see the flow around a racing bike the red is the fast-moving flow fast-moving air and the blue is the slowest like we saw on the golf ball now here you can actually see the turbulence you can see these structures coming off the back of the helmet back of the rider and you can see how this company can change the shape of their bike to reduce these regions it's also why you see cyclists go into that tuck position because it reduces the amount of separation behind but to do all this we have to use supercomputers but what is a supercomputer well I think most people tend to think of a supercomputer is some kind of big fast version of their own PC or laptop and that's not strictly true it's best to really think of it more as a collection of computers or working together in parallel and here's an example of a computer in Barcelona it's called Maron Ostrom it's actually held within this beautiful chapel and you can see all the different rows of machines which essentially are those collections of your own PC but just working together but sometimes it's hard to understand how they used so the way I like to think about it is if I asked you to try and no write a book and I give you a thousand pages of handwritten notes and I ask you to type it up now it might take one of you I don't know three weeks a month to type up a thousand pages but instead how about instead of asking one person how about I ask a thousand people but just to write one page now it might take one person to write a page half an hour or now so if the thousand people are doing this simultaneously then instead of one person taking a month it's only going to take the time it takes one because they're all doing at the same time they communicate it back to me and this is exactly how supercomputers work it's essentially splitting up the task into little little problems and letting the supercomputer to it basically we have tried to understand turbulence we're trying to adapt the flow but nature's beaten us to it you know a lot of the reason why we look the way we do or or animals and facial mammals is because they need to be able to deal with with turbulence it's it's all around us so for awhile if you look carefully you can see on that side of the fin there are these cubicles these kind of undulations and for a long time we didn't really know what they did and it's only really once we have this power of supercomputing and understanding turbulence we figured it out and so they act a little bit like a golf ball does in it they generate these vortices this flow that move over if at a laser pointer I could show you they move over the the fin and allow it to stay attached for longer it stays more efficient and what that means to the whale is that it can maneuver more easily under the water but what's for me really interesting as somebody used to work in Formula one is how these designs have inspired engineers to try and take it into their own so if you look carefully here in between the two words of a sponsor that I can't say you can see that these little undulations that's try to do exactly the same thing that the whale is doing for the Formula One car it tries to give lower dragon and more lift or more downforce so this is 100 more examples of the way the animals inspired engineering now so I hope the next time that you're on a plane and you experience that bit of turbulence that you start to perhaps understand a bit more what's going on you see the turbulence that you experience on a plane it is quite often being generated by the flow coming over a whole mountain range so you just as we saw on the bike the flow went over the back of the guys helmet and then separate at the back and we saw this slow flow the same can happen up a mountain range the flow comes over and for miles and miles miles you have this turbulent - chaotic random flow and so of course if a plane flies into that the plane is not really operating in there in the right conditions or what it's designed for but it's not happening exactly in the same place at the same time over the wing so what you tend to find as it loses a little bit of its lift which means it drops a bit but because it's doing it in different parts of the wing that's what creates that kind of bumpiness feeling you have as soon as the pilot manages to to move out of that region things return to normal so I hope that you've managed to get some deeper understanding of turbulence and the way that it shapes our world it's not just about the turbulence we experience on a plane and I hope that you'll maybe now start to see turbulence in places that you didn't expect to see it before so thank you very much you

Channel: TEDx Talks

Views: 33,393

Keywords: TEDxTalks, English, United Kingdom, Science (hard), Computers, Engineering, Nature, Physics, Science, Software, Space, Technology

Id: ePwVPmynMV0

Length: 12min 52sec (772 seconds)

Published: Fri Apr 29 2016