Under floor flow & diffusers

[chuckdanny]

The real picture of the underside of an f1 is not seen just by looking at it from the side and seeing a rake and more rake in the shape of a diffuser. In reality you've got to see the decreasing section as seen from the top, actually there are two throat on each side beteween rear wheels and the central skid plank !

[chuckdanny]

Maybe i'm wrong but that's the flow structure for me.



Otherwise it make no sense why would the air accelerate at the diffuser/extractor edge ?

[chuckdanny]

Well it's not true, both effect are important, acceleration by section reduction end allowable volume expansion of the air which has a speed, internal energy that is allowed to develop streamwise when there is room to do that, i know it's not very scientific but it's a boltzmann many particles interaction way of seeing the phenomenon.

[turbof1]

A diffuser is pure bernoulli principle. It isn't thay the diffuser is filled with high pressure (the air on top of the diffuser is), but the diffuser is there to lower the velocity by letting the airflow expand. The pressure does increase, but you have to see as a pressure difference between floor and diffuser. This creates a suction effect right at the edge between floor and diffuser, which accelerates the velocity of the air underneath the floor, which increases its downforce.

The diffuser on its own in isolation should be more looked like a wing. Low pressure beneath, high pressure above= downforce.

[chuckdanny]

That's like at the front of the floor, why on earth would air accelerate ? it's almost a splitter so air should split nicely over and under the floor whitout disturbation, the floor is so thin, sharp like a knife ?
Well there is a boundary layer phenomenon that shape the knife quite differently first and furthermore it's not just a splitter, it has a wing leading edge kind of shape that create a section reduction.
Second, underneath the Tea tray the transition between the plank and the floor is aerodynamically shaped so that it violently disturbe the air laterally and vertically and then accelerate on each side.

[NoDivergence]

Because you have rake...

[Moose]

Because you have rake...

That would decelerate the air, not accelerate it.

[AlainProst]

Have you noticed the amount of the rear wing of the RB11 come from Mercedes W05 (and W06) with just twoi slits contrary to others teams ?

[AlainProst]

Because you have rake...

That would decelerate the air, not accelerate it.

Yes, you deccelerate the air, it's the Bernoulli principle who says that the air accelrates in a narrower area and deccelerates in a wider area

[timbo]

One of the main benefits of higher rake is lowering of FW.

[ForMuLaOne]

Bernoulli`s law can be applied in a closed system with pressure gradients. It really is a difference to have moving car through an airmass that is basically standing still. Actually you have higher airspeeds and lower static pressures underneath the car. As a result air will be sucked to this region also from the side of the car, increase the pressure and decrease airspeeds. To prevent these spillover effects, red bull had their exhaust ramp with the holes sucking off the air above the floor. Vortices can of course seal the floor as you create high energetic airflows that show more stability due to predetermined trajectory of the air molecules before they interact with the following surfaces of the car.Thats why the floorshave sculpted edges behind the front wheel.

[OO7]

http://www.mulsannescorner.com/diffuser.htm

[hollus]

If a difusser decelerates the air back to the external stream's velocity, it follows that the same air had been accelerated beforehand. Think about it.

[NoDivergence]

^Exactly. Correct logic.

The wake of the car is lower pressure than ambient. The diffuser as we all know, increases pressure though itself by increasing area. So clearly, the flow velocity upstream of the diffuser must be accelerated.

Rake essentially reduces the area of flow under the splitter/teatray. This results in flow acceleration due to the change in area. Acts just like a upside down wing or a flat plate at negative angle of attack where you have a huge suction peak on the low pressure side. In fact, it's enhanced due to the proximity to the ground.

[Moose]

If a difusser decelerates the air back to the external stream's velocity, it follows that the same air had been accelerated beforehand. Think about it.

While I think that's a reasonable way to think about it, I don't think your assumption is correct. The reason that cars following other cars get aero disturbances is because the air is not travelling at the same velocity as the external stream. One thing for example that changes is that the air's velocity (in large part at least) has a large upward component that it didn't have before. Newton tells us that the only way you get downforce is by throwing something else (air) upwards.

So basically, while I'm sure they do accelerate the air under the floor through a variety of techniques, I don't think your logic dictates that they must, simply because your premise is flawed.