Technique: this is the use of diffusers

Posted on 03-10-2015 14:04 by mauritsh – 50 Comments”

Of constructors in motorsport to tuners: they use almost all diffusers for a variety of reasons. It comes to these things so not for purely aesthetic reasons, but why? Autoblog explains.

A word in advance

In the motorsport are diffusers all used for decades, but also car manufacturers and tuners find it but what is interesting to models (not post) with such a gaping hole on the back rest. You see the term ‘diffuser’ than in many article voorbijfietsen, what for this writer the occasion was to take in to diving and to explain where those things are exactly for.

Please note: I have no degree in physics or mathematics. Aerodynamics is, however, very complex and it is almost impossible to include all relevant matters in one article to explain. The explanation will, therefore, be a basic representation of reality, but we can be a good ride. Just look on.

The Law of Bernoulli

For an understanding of the operation of diffusers is the bitter necessity to some physics involved. You are still sweating awake thanks to those formulas in the article about CW-values? Have no fear, we let them this time out.

This law of Bernoulli is the following: the faster a flowing medium flows, the lower the pressure is. When physicists jump the tears in the eyes of this explanation, but that forgotten we now, for convenience, equally. This phenomenon is also sometimes expressed as the Venturi Effect.

The following diagram clarifies this effect. In the thick section, the flow rate is lower and the pressure is higher (see the filled tube). In thin section, the flow velocity is higher and pressure is lower (see the slightly less-filled tube).

That low pressure is exactly what manufacturers are looking for, if they make use of diffusers. Time to explain why that is.

Flat bottoms

Low pressure under the car, it means that this as it were to the surface to be sucked. According to the Law of Bernoulli, the flow rate of the air under the car so up.

The level of the soil is already a good start. Suspensions, gearbox, oil sump and other things that are at the bottom of the car from the stitches can disrupt the air flow. Therefore, more and more automobiles are equipped with a flat bottom, that the air under the car is not obstructed in any way. That’s not only good for creating downward pressure, but of course also for the aerodynamic resistance. Check out below the bottom of a Gumpert Apollo. Da’s are indeed flat.

The air under this Apollo does not encounter any obstacles on the way to the back of the car and flows only, therefore all the faster, which results in lower pressure. In addition, the air can not escape through holes and cracks in the bottom of the car.

Diffusers

The flat bottom we have covered, to what it’s all about in this special. The diffuser is so shaped that the air under the car is further accelerated. How do those things that? See below first for a schematic view of the diffuser and the corresponding air velocity. For the good order: the rear of the car is located on the right of the picture.

As you can see is the diffuser, a slanted ascending plane under the rear of the car, which, as it were, a gap creates. This gap is filled by the flow of air under the car goes through, allowing the same air flow is further accelerated. We tackle the Law of Bernoulli it, then it means that the pressure under the car thus becomes lower.

This ‘vacuum’ sucks the car to the road surface, thereby, for example, harder through a turn can, et voilà: that’s the great utility of diffusers. Long story short: the diffuser has a suction effect on the air flow under the car. This is therefore accelerated, causing the pressure under the car is reduced and this to the surface is sucked. This results in grip, causing cars to higher g-forces can handle. Also applies (to some extent, see comments): the larger the diffuser, the greater the suction effect.

A big advantage of generating downforce through diffusers is that the aerodynamics are not to suffer. Large wings such as on Formula 1 cars result in CW-values where even a Hummer H2 not yet near, but the diffusers do not know this disadvantage. Incidentally generates a F1 car as about 50% of its downforce with the aerodynamics under the car, so the diffuser and the flat bottom.

We tackle there is still a picture, we can see that there are several vertical baffles are placed in the diffuser of this Formula 1-racert. That bulkheads serve really only one purpose and that is in the right direction, direction of air, so this is no free game has and the suction effect is increased. Without divisions, there would be possible turbulence may arise, in relation to the operation of the diffuser does not benefit.

Excesses in motorsport.

This may be beautifully illustrated by a few beautiful examples from the past. The Brabham BT46 below, had a huge fan at the tail of the car, which supposedly was meant to have hot air from the engine compartment to suck.

That was a fopje of designer Gordon Murray to the competition and the FIA with huddled the cane to steer, because the raison d’être of this misshapen monstrosity had everything to do with the air under the car. The rotation speed of this fan depending on the speed and sucked the air therefore even harder under the car.

Result: lower pressure under the car, which is still harder to the tarmac was lifted and a much higher G-forces pulled the rest of the field. The technique worked like a charm, and was therefore immediately banned. So once again, in the Formula 1. By way of illustration, that the fansnelheid was dependent on the rpm, means the car’s still down popped up as soon as the gas was pressed.

Another example is the frankly bizarre Chaparral 2J. This CanAm car worked on the same principle as the Brabham and drove out also the competition on a pile. Unfortunately threw away the faulty mechanics regularly, the soot in the food, so this separate but progressive creation no real winner was.

More recent examples

If we are talking about diffusers, allowed the creations of Brawn and Red Bull in the Formula 1, of course, not be forgotten. In the highest (broken regulated) class of racing, it is important to understand the loopholes in the rules to be found, that offer scope for imaginative solutions.

Thus it was Brawn GP in 2009 with a ‘double diffuser’ on the stuff, that have a significant advantage offered. Jenson Button was even champion. Red Bull dominated a few years later, racing with their blown diffuser, that, through the use of exhaust gases to the suction effect increased.

Splitters

We have now diffusers to the rear of cars be fitted, but the front is also done the necessary on the aerodynamic plane. So-called splitters are horizontal plates that the air, as it were, split (hence the name…). It goes too far to the functioning of these parts will now describe them in detail, but it boils down to the following.

The air is, as I said split into two streams. The pressure in one flow is higher (because lower flow rate) and in the other lower (because higher flow rate). Thus works a splitter, so in a similar way as a diffuser. Check for a nice example of this Audi RS6 DTM, which once belonged to Jon Olsson.

Finally

Needless to say, but this story is just a very brief explanation for the effect of diffusers to clarify. Complete? Not even a little bit. Scientifically justified? Even if not. We hope only that the concept of ‘diffuser’ in the future no hollow term more, to the extent applicable, of course, was.