Aerodynamics Fundamentals: Ducting & Rules of Thumb
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Ducting & Rules of Thumb
04.39
| 00:00 | As we discussed in the previous module, the way to have effective cooling through heat exchangers is to have air flowing through them. |
| 00:06 | This requires two things, high energy air to be ducted in, and low energy air to be allowed to exit the back of the heat exchanger. |
| 00:14 | This second part is really critical, and it's one of the things I see most commonly forgotten on club level cars. |
| 00:20 | Air in, air out is our friend when it comes to cooling. |
| 00:24 | To be as effective as possible, the cooler should have inlet ducting that is present between the free air stream all the way up to the face of the cooler. |
| 00:32 | This ducting should be as well sealed as possible to the bodywork and the cooler so that air can't move around it and must pass through it to reach the cooler. |
| 00:41 | This is because the fins on the cooler provide quite a bit of restriction to the oncoming flow, which will bring about a pressurize in front of the core of the cooler. |
| 00:50 | This high pressure region will mean the entire inlet duct is pressurized with respect to its surroundings, so air will be trying to leak out. |
| 00:58 | We don't want this air to leak out, as it will hurt the performance of our aerodynamic devices on the car, and we also want as much of this air going to the cooler as possible, and as high a pressure in front of the cooler as possible to drive mass flow through the cooler. |
| 01:11 | This is why we want to make sure that the inlet duct is well sealed and drawing air from a clean, high energy location. |
| 01:18 | In terms of inlet duct geometry, this should have smooth curvature to minimize the risk of any separations. |
| 01:24 | As we touched on in the previous lesson, having air traveling as fast as physically possible through the radiator is not terribly efficient. |
| 01:31 | We want to slow the air down a little bit to reduce losses. |
| 01:35 | This means that on the inlet side, we'll have an expanding duct with an inlet smaller than the radiator core. |
| 01:42 | There's no hard rules on what expansion ratio to use, but let's look at some very quick examples. |
| 01:47 | First, a very low speed car, like an autocross car for example, in this case we may want to be close to 1 to 1 as our ratio. |
| 01:55 | Whereas a medium speed club car with end of straight speeds around 200 k's per hour, we may want 2 to 1. |
| 02:01 | And a high speed car with end of straight speeds around 270 k's per hour, we may be looking at 3 to 1, or much more for higher end cars with large radiators. |
| 02:11 | A lot of the time, our duct will be dictated by what can physically be packaged in there. |
| 02:15 | But when doing duct work, we should generally err on the side of a larger inlet until we know how our cooling system is performing. |
| 02:23 | This means that if we have plenty of cooling in hand, we can shrink down the inlet a little bit more. |
| 02:29 | Outlet ducting is a more interesting one, because there's so many ways to play it. |
| 02:33 | The most straightforward and generally effective way is to have a dedicated duct picking up off the back of the cooler, and this duct should have smooth curvature. |
| 02:43 | If we're connecting to a hood, we want a nice smooth transition onto the hood with no abrupt angles that may cause separations. |
| 02:51 | Generally speaking, our outlet duct will also have an exit that's smaller than the heat exchanger core. |
| 02:57 | With that said, in some cases we may find ourselves with outlet ducting not being an option. |
| 03:02 | A prime example would be a case that the radiator is too close to the engine. |
| 03:06 | In this situation, we need to try and seal up the engine bay as much as possible to prevent air spilling into the wheel wells. |
| 03:13 | It's also important to have an exit path that's open from the engine bay with louvers to control any excessive flows of low energy air from the coolers out the top, which will travel downstream and may impact rear wing performance. |
| 03:25 | There's an important note in here in regards to sealing the engine bay. |
| 03:29 | It's all too common to see people running what's called a V-mount setup with their radiator and intercooler in an arrangement where one exits out the hood and the other exits below the engine. |
| 03:39 | If aerodynamic performance is important, we should definitely not run a setup like this, as it just results in a huge amount of low energy cooling air being directed to the underfloor, which hurts the performance of the car both at the front splitter and at the rear diffuser. |
| 03:54 | Let's quickly summarize what we've learned about ducting before moving on. |
| 03:58 | Effective cooling in race cars requires high energy air ducted in and low energy air allowed to exit from every heat exchanger. |
| 04:06 | The inlet duct should be well sealed to prevent air leakage, ensuring high pressure in front of the cooler to drive airflow through it. |
| 04:14 | The duct's geometry should expand smoothly to slow down the air before it hits the radiator, with larger expansion ratios required for higher speed cars. |
| 04:23 | For outlet ducts, smooth curvature and controlled exit paths are crucial, while poorly designed setups like a V -mount that dumps low energy air under the car can severely impact aerodynamic performance. |
