Aerodynamics Fundamentals: Basics of Vorticity
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Basics of Vorticity
05.24
| 00:00 | A term we'll often hear thrown around in the context of a race car is vortices. |
| 00:05 | Vortices are an extremely complex field of study, and something we could talk about for hours on their own. |
| 00:12 | Like many things in aerodynamics, there's no hard rules when it comes to vortices, no specific targets for strength or size to aim for, and certainly nothing that can be definitively worked out by eye. |
| 00:24 | They're probably the single most application-specific part of aerodynamics, and without wind tunnel or computational fluid dynamics testing, which we'll talk about later, it's risky to be thinking too heavily on what the vortices are doing on a club level car. |
| 00:39 | However, it is useful to have a rough understanding of what they are, even if we aren't going to be carefully tuning them. |
| 00:46 | A vortex is defined as a coherently swirling region of the flow with a high and consistent level of swirl around the streamwise direction of the flow. |
| 00:55 | Think of them a bit like a tornado or a whirlpool. |
| 00:58 | Except they're moving along the flow instead of sitting in the same spot. |
| 01:02 | Vortices are formed when we have a pressure differential over a surface that has a free tip, like at the end of a wing. |
| 01:09 | This tip is usually referred to as a shedding edge, and is any point where air can freely move laterally from a high pressure region to a low pressure region. |
| 01:18 | Consider a wing at an angle. |
| 01:20 | We have a pressure surface and a suction surface. |
| 01:23 | If there's a free tip, air can move around it. |
| 01:26 | And air will always want to flow from regions of high pressure to regions of low pressure. |
| 01:31 | So, the air will try to migrate from the pressure to the suction side. |
| 01:36 | The only way it can do that is to move sideways and work its way around the tip. |
| 01:40 | In doing so, it has to navigate quite a tight corner and turn in the opposite direction. |
| 01:46 | This results in a degree of swirling around the tip of the wing, causing the production of vortices, which then travel downstream. |
| 01:53 | This can happen any time there is a free edge with a pressure differential, such as wings, canards, or diffusers. |
| 02:01 | Vortices are shed all over a race car. |
| 02:03 | However, many people I talk to put much too much focus on them. |
| 02:07 | At the club level, we don't want to be looking too heavily at trying to predict vortices and their effects, as they're extremely hard to predict. |
| 02:16 | We're much better served by focusing on our aerodynamic fundamentals. |
| 02:20 | With that said, there are a few basic things you should know about vortices, even at this level. |
| 02:24 | The first is that vortices produce suction. |
| 02:27 | This is because they're moving in a swirling motion, so there must be a centripetal force holding all the rotation together. |
| 02:34 | This force can only be supplied by the pressure differential across the vortex, so therefore the core of the vortex must have a lower pressure than the surrounding air. |
| 02:43 | This is a useful characteristic when we produce vortices that run underneath a splitter or underneath the car's floor, as these vortices make suction, which can be used to produce more downforce. |
| 02:54 | Secondly, vortices help with flow attachment, assisting the mixing between the boundary layer and the higher-energy freestream flow. |
| 03:01 | This puts more high-energy, clean air into the boundary layer, which makes it more resistant to separation. |
| 03:07 | This is because the increased momentum from the freestream air will carry the boundary layer further through regions of adverse pressure gradient, without suffering flow reversal. |
| 03:18 | Thirdly, vortices take energy out of the flow, which will affect the flow downstream. |
| 03:23 | There's a large amount of shear through a vortex, as we have a rotating core passing along in a largely non-rotating fluid, and this shear causes viscous losses in the fluid. |
| 03:34 | Vortices can often be turbulent too, and this will result in energy losses as well. |
| 03:39 | As such, anywhere we have a vortex will typically hurt the performance of far downstream devices, because there's less energy available for them to use. |
| 03:49 | There are many other, more complicated things that vortices do and can be used for, but the reality is they're not applicable at the club-level. |
| 03:56 | For some rules of thumb with our vortices, we want them to be strong enough that they generate suction if they're being used under the floor, but we don't want them too strong. |
| 04:04 | If they are, we'll suffer with rear performance. |
| 04:07 | In practical terms, this means vortices shouldn't be made off plates or wings at massive angles to the flow. |
| 04:13 | We don't want to be casting vortices off a plate that's 45 degrees to the flow, because they'll be very strong and full of loss. |
| 04:20 | Lower angles are generally cleaner and better at the club level. |
| 04:25 | We don't want to collide them with downstream aerodevices. |
| 04:28 | For example, we don't want to put a vortex -inducing vane straight in front of a rear wing. |
| 04:34 | If you follow some of these basic rules, it should help you out with your placement and angles on aerodynamic devices. |
| 04:40 | This brings us to the end of our exploration of real-world aerodynamic influences, so let's summarize this final module to finish up. |
| 04:48 | Vortices are swirling regions of flow created by pressure differentials across surfaces with free edges, such as wings ordiffusers. |
| 04:55 | And they produce suction that can enhance downforce. |
| 04:58 | They help with flow attachment by introducing high energy air into the boundary layer, making it more resistant to separation. |
| 05:06 | However, vortices also cause energy loss, affecting downstream aerodynamic devices, and while important, their complexity makes them less relevant for club level racing compared to focusing on basic aerodynamic principles. |
