Aerodynamics Fundamentals: Flow Energy & Loss
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Flow Energy & Loss
04.34
| 00:00 | In the previous module, we briefly touched on the concept of dirty air, and in this module we're going to dive deeper and talk about energy in our flows. |
| 00:08 | You may already have some experience with dirty air from your own racing, or from watching series like Formula One. |
| 00:15 | When we're following a car, we sit in the low energy air that's cast off the back of the car in front. |
| 00:21 | This dirty air, also known as a wake, will effectively supply less energy and flow velocity to all our aerodynamic devices on our car. |
| 00:30 | This is what drives the slipstream effect, whereby we have less drag on the car when it's following as a consequence of having a weaker headwind. |
| 00:38 | It also causes all our aerodynamic devices to produce not as much downforce, as they're effectively receiving less air velocity. |
| 00:46 | In recent years, regulations in Formula One have heavily focused on reducing the amount of dirty air off the back of cars by attempting to narrow the car's wake, and to reduce the flow energy lost in the wake itself. |
| 01:00 | If these objectives are achieved, the car behind will have more energy available to it from the oncoming flow, and thus will have more downforce than if it was driving in a larger, lower energy wake. |
| 01:12 | As we've discussed before, in air flows, we can encounter boundary layers and separated regions. |
| 01:18 | And these are regions of low energy. |
| 01:21 | The reason for the flow losing energy here is that at a microscopic level, the action of viscosity causes loss of energy. |
| 01:27 | This causes kinetic energy to be removed from the flow, and transferred into the fluid in the form of heat. |
| 01:33 | The energy transfer required to drop the kinetic energy in these regions isn't that large, so we don't see too much in the way of temperature rise, but it is occurring, ever so slightly. |
| 01:45 | When we have a boundary layer with a bunch of shear in it, we'll have losses from viscosity in which kinetic energy goes into heat. |
| 01:52 | When we have a turbulent flow, it's formed from lots of small eddies. |
| 01:57 | These eddies break down at a microscopic level, at which point viscosity will turn kinetic energy into heat. |
| 02:04 | Fundamentally, this reduces the available energy and total pressure available to use in the flow. |
| 02:09 | And we call this phenomenon loss, which is when the total pressure is reduced from the free stream as a result of how we are working the air. |
| 02:18 | In general, the harder we work the air, the more loss we'll create. |
| 02:22 | Large surfaces with thick boundary layers, aggressive wings, and where we work the boundary layer hard, or any sort of separation at all, will introduce losses into the flow. |
| 02:33 | Boundary layers can also be swept up into structures shed off wings and similar devices, and this will create blobs of loss which will travel downstream and interact with other aerodynamic devices. |
| 02:44 | Loss is pretty much always a bad thing on a club level car. |
| 02:47 | We want to minimize its production where we can. |
| 02:50 | More loss means more drag on the car, as the energy has to come from somewhere, and that's from pushing the car through the air. |
| 02:57 | If you impact loss onto a downstream element, it'll reduce its performance. |
| 03:02 | For example, if I put a wing in flow with 10% less energy in it, the wing will make 10 % less downforce. |
| 03:09 | So, whenever we put a front downforce device on a car, we have to be mindful that it could be creating loss that'll hurt the rear of the car. |
| 03:17 | However, there's a balance to strike. |
| 03:19 | If we aren't producing any loss, we probably haven't been producing any downforce, as we haven't been working the air very hard. |
| 03:26 | So, we've got to be careful. |
| 03:27 | With every car, we need to accept that loss is an inevitable consequence of our downforce production, but still try to minimize it where possible. |
| 03:35 | Essentially, all over the car, different parts will be producing their own little wake regions. |
| 03:41 | When it comes to professional series like Formula One, a huge amount of effort is put into managing the locations and strengths of all these wakes. |
| 03:49 | However, the detailed management of these is a bit too complex to attempt on a club level car. |
| 03:55 | So, we really on simple approaches and minimizing wake production in the first place, which we'll talk about more in some upcoming modules. |
| 04:04 | Let's summarize before moving on. |
| 04:06 | Loss in airflow occurs when kinetic energy is converted to heat due to viscosity, reducing total pressure and available energy. |
| 04:14 | This is particularly prevalent in boundary layers, turbulent flows, and separated regions, where energy is lost and results in increased drag. |
| 04:22 | While some loss is inevitable when generating downforce, minimizing it is crucial to make sure the car is maintaining overall aerodynamic efficiency and reducing drag. |
