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Guest column: Dirty air

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In addition to thrust (eng. downforce), is the resistance of the air. drag) that other aerodynamic force acting on the car on the track. IN previous article we read about how to get the most out of it downforcea from the wings, and in this article we will touch on an interesting topic of air resistance.

To simplify matters, let's take the Opel Corsa as an example. The front end of the Corsa pushes air in front of it which requires energy. That is clear to us. We can also say that a high pressure zone is created in front of the mask that pushes the car backwards - the same would be true. However, it is even more important for drag what the Corsa leaves behind - turbulent air.

Turbulent air is a set of particles that move randomly through space. However, this chaos is not completely random because the turbulent air tends to create an "eddy" (small vortex). Eddy is due to the balance between centrifugal (angular kinetic energy) and centripetal (effort to fill the lower pressure zone) force acting on each air particle. This means that when you put some energy into the air (e.g. you wave your hand while reading this) you will create a lot of eddy because air that has kinetic energy tends to fall into that state when it spins around itself. How does eddy die? He sheds his energy on some new smaller eddye, which create even less eddye and even less.

The comments on the Portal work on the same principle - globally chaotic because we often spin in a circle.

When our reference point is a Corsa that drinks 100 per hour, then the air that surrounds it (ambient air) is in the form of a laminar flow (if we focused on that ambient air we would notice that it is also turbulent, at least much weaker). Laminar flow is the opposite of turbulent flow - when fluid (in our case air) is stacked in layers that do not mix with each other.

The house eddy has the energy of closing the door from the room, and the eddy behind the Corsa has the energy of a 1.3 CDTI monster of 70 hp. We already know that air that flows faster has less pressure than air that flows more slowly (Bernoulli's principle). This means that every Corsa’s eddy is a low-pressure zone that tries to suck everything around it, and above all the car that created it. In other words, the turbulence left behind by the Corsa makes a low-pressure trailer trying to suck the car backwards.

Who follows Auto Nagazim or similar shows about cars, has heard of the notion of coefficient of resistance (eng. drag coefficient). It is a number that indicates how much resistance a body has to the fluid it is moving through. It should be noted that this value takes into account only body shape, not size. A lower drag coefficient means something is more "aerodynamic". The Corsa has a drag coefficient of 0.32 which is some average for production cars. The cube has a coefficient of 1,05, the teardrop shape only 0.04, and the ball 0.47. The Land Rover Defender, one of the most square cars, has a drag coefficient of as much as 0,59.

Try to guess the drag coefficient of one F1 car!

How to make a production car more aerodynamic? First of all, the front end should be rounded - this is what the manufacturers have been doing since the beginning of the nineties, which means that unfortunately we will probably never see rectangular beauties like the original VW Scirocco. The rear end is much more important to us for this topic. In the back, they should minimize the "turbulent trailer", and there is no better inspiration than the shape of a tear, a sanctuary for aerodynamics.

The teardrop shape is so successful because the pointed back allows the current to remain attached to the body and to separate from the body in a laminar form on the spike itself. On the car we are designing, we should strive for the laminar current to meet as soon as possible after it leaves the car. They could simply make a pointed rear end (and they would not be the first to think of it), but we’ll assume we design an SUV because it’s popular at the moment. First and foremost, let's shape the center of the car (cabin) so that the air current approaches the rear end with a certain bend - that it is already directed towards the closing of the "trailer". We will get that if we make the cabin a little rounder on the side and on the roof. Good start. Furthermore, at the place where we expect the separation of air current, we should put a spoiler (eng. spoiler, or “spoiler” because it spoils the air current). The spoiler is great because it intentionally induces turbulence and thus helps direct the laminar current downwards. Instead of spoilers, we could have the so-called "Kamm-back" - a sharply "cut" rear end that has a similar effect as a spoiler, but we will not do that because customers prefer when the rear door is non-flat. Basically, you should just avoid a rounded transition from the roof to the rear door because in that case the current will be disconnected with the most turbulence.

Basically, to go into too much detail, it is clear to us that there are options on how to reduce aerodynamic drag. The F1 car, the pinnacle of aerodynamics, certainly has a very low drag coefficient. Did you try to guess?

F1 cars reportedly have a drag coefficient of up to 1,1 which is criminal. How is that, how is that?

There are two reasons. The first has to do with the DNA of Formula 1. Throughout history, the F1 has profiled itself as a series of racing single-seater cars. single seater), and the Americans call such vehicles "open wheel". In other words, covering the wheels with armor to reduce air resistance would be "unconstitutional." The second reason, the much more important one, is the fact that thrust is very useful on all tracks of the F1 calendar. With thrust comes resistance, which is the eternal compromise that F1 engineers face.

The specific shape of the F1 car is horrible from an aerodynamic point of view. Tires are a huge source of the worst form of dirty air. Due to the fast rotation and round shape, the eddies created by the tires are very strong and unpredictable. If wheel cover in F1 wasn’t strictly forbidden, that would be the first thing teams would do. Formula E cars from the first generation had covered wheels because this greatly helped the problem they had with battery range. Furthermore, other components protruding out of the chassis (suspension, mirrors) do not help resistance. With great power comes great temperature, so we also have vents for refrigerators in sidepodes, engine intake u airbox and brake cooling vents. The driver's helmet is also not ideal for aerodynamics.

All of the above are components that fall into the "necessary evil" group. Everything else is there with the goal of manipulating the air. I dare say that all the little aero elements (bargeboards, diffuser, various wings, various fins, fringes…) are made with the partial aim of reducing air resistance. The front and rear wings do the dirty work, ie they intentionally produce dirty air. The rear wing must produce as much thrust as possible by sending air upwards. upwash). It is located above the drive shaft so thrust is welcome there. Also, behind the rear wing there is nothing left that would be bothered by dirty air (other than another car, but that’s his problem). The front wing must also produce a little thrust (not too much so as not to compromise the rest of the car with dirty air), but above all it must direct the air outwards. outwash) so as to prevent turbulence from the front tire from wreaking havoc where they shouldn’t.

Outwash ipwash will make the turbulent trailer wider and taller than the front silhouette of the car - that is the reason for the criminal resistance.

In the current technical rules, the rear wing is responsible for most of the thrust and thus the resistance. The stronger the thrust we want, the wing must throw more air to us which means that only the wing must be steeper and take up more front silhouettes. When we go to Monza, then we can have a shallow rear wing that doesn’t give much resistance, but neither does downforcea.

It becomes clear to us that the best aero solutions are the ones that increase downforce without increasing resistance. One such is the vertical edge at the rear end of the wing called Gurney flap (according to driver Dan Gurney) which "lengthens" the wing without increasing the area of ​​the front silhouette.

When we monitor a GP, it doesn't matter to us exactly what the resistance of the car is and how that resistance is compared to the resistance of the Opel Corsa. The exact value of the resistance also depends on the air density, which in turn depends on the air temperature - these are variables that engineers must deal with when setupu car. We viewers should be aware of the impact of dirty air. The main features of dirty air are low pressure and forward momentum. These two features mean less air particles that "catch" the car behind, and thus all the positive aero effects are weakened. If you are driving a car that follows another, it means that you are suffering from a lack of thrust through the corners because your wings have fewer air particles to throw up. Also, fewer fresh particles enter your refrigerators so you could also have cooling problems if you race in the heat. In the age of atmospheric engines you might even feel less power because less oxygen reaches the combustion in one of the 8 cylinders.

On the other hand, in dirty air, the negative aero effects are reduced, primarily resistance. The accompanying car must push to the side / height less air particles than the one in front, and this allows it a higher maximum speed on the plane. We've all heard of slipstream, Drafting and leeward, and the most famous expression in F1 circles is tow (traction).

Dirty air and lee are one and the same, only they affect the competitiveness of the car that follows the other car in the opposite way, depending on whether it reduces the thrust through the bend or the resistance on the flat.

In this article, we read about the nature of dirty air (low pressure and turbulence) and how it affects the vehicle that creates it and the vehicle that swallows it. Along the way, we mentioned the drag coefficient and found out why almost all cars have a spoiler and almost none have a wing. We didn't explain how all those tiny wings work on an F1 car, we leave that for the next article. For the end, I would recommend a suitable music number: https://www.youtube.com/watch?v=wUTLlyv9XQY

Brazilian Mass

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Comment

15 comments

  1. It should be read several times to catch everything, especially if you are a layman but always a quality analysis 🙂



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  2. Williams Sinek Show

    cool cover illustration, I just figured it out for the third time :)
    the lyrics are good, it's a pity I don't understand more than 30%: D



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  3. Marlboro LeCrash Show

    Well explained, it is easier for us to understand when an example is given on a serial car.
    Well done.



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  4. Ferrari sisavac Donator Show

    This is already a series of columns! 👏👏
    Bravo. And I can’t wait for the next one.
    This comparison “killed” me “

    Comments on the Portal work on the same principle



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  5. Kimi Raikkonen zoka Show

    I drove an Opel Corsa, it actually goes better than a Peso 207 so it must have a smaller drag drag



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  6. Niki Lauda wapi Donator Show

    Just one small addition. The coefficient of frontal resistance is multiplied by the surface penetrating through the air.
    That area is much smaller in the case of the car than in the case of the Opel Corsa, and especially the Land Rovere or Toyota Sequoie, so all in all it is not so catastrophic.



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  7. Mclaren LH44 Donator Show

    Excessively explained: thumbs:



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  8. Pirelli Hypersoft Einspritz7 Show

    Good and interesting text, quite detailed analysis!
    However, I have one remark, when it comes to details:
    "Eddy is the result of a balance between centrifugal (angular kinetic energy) and centripetal (an effort to fill the lower pressure zone) force acting on each air particle."
    Force and energy are two different quantities, so centrifugal force cannot be kinetic energy. And especially angular, because the centrifugal force acts in a radial direction from the center of rotation outwards.



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    • Felipe Massa Braziliscanec Masa Show

      Thanks for the remarks. How should it be worded to be accurate? Instead of “angular kinetic energy” simply put “momentum”?


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      • Pirelli Hypersoft Einspritz7 Show

        Sorry I'm just answering now, but I couldn't sign up, I somehow managed now!
        Well I don't think you need to put anything, you wrote nicely that the centrifugal and centripetal forces are in balance, as well as for the centripetal that the effort is to fill the lower pressure zone (which automatically says that the centrifugal force is acting in the opposite direction)


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  9. Bravo, I've been following F1 for a long time, but I take many things for granted, ie we don't think too much about them .. the whole package is important to us.
    This column is a real refreshment ..the author writes about dry boring facts in an interesting way… .I'm waiting for the next work… and the new season will arrive faster than we thought



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  10. Sebastian Vettel 5 Crash Donator Show

    What can I say but thank you…
    Again, the top of the article, I have to google some things myself, which out of curiosity is that I don't believe you: tooth:



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