Renault R31

[horse]

Thanks for that SLC, it's the most convincing argument so far, I think. My arguments for the benefits of hotter gases all stem from the excitement of the upper surface of the diffuser with the blown system, however, I'm willing to accept your argument that this is minor in comparison to just injecting mass at front of the floor - a cold exhaust would be just as good?

It's funny, this made me think of the suction cars where the opposite was going on! Remember the big fans?

By increasing the mass flow over the floor LE you end up with a stronger initial suction peak (where the air is accelerated around the allowed 50mm radius coming off of the step plane), and this sets the baseline pressure for the forward half of the floor.

Could you elaborate on the above a bit, please? I haven't quite got what is going on initially. Are the exhaust gases deflecting flow to generate this effect - it hasn't quite clicked for me yet? Is it because the velocity of the exhaust generates a local low pressure there?

[SLC]

Thanks for that SLC, it's the most convincing argument so far, I think. My arguments for the benefits of hotter gases all stem from the excitement of the upper surface of the diffuser with the blown system, however, I'm willing to accept your argument that this is minor in comparison to just injecting mass at front of the floor - a cold exhaust would be just as good?

It's funny, this made me think of the suction cars where the opposite was going on! Remember the big fans?

By increasing the mass flow over the floor LE you end up with a stronger initial suction peak (where the air is accelerated around the allowed 50mm radius coming off of the step plane), and this sets the baseline pressure for the forward half of the floor.

Could you elaborate on the above a bit, please? I haven't quite got what is going on initially. Are the exhaust gases deflecting flow to generate this effect - it hasn't quite clicked for me yet?

The suction cars were working on a very similar principle - by forcing mass flow out of the floor system (at the rear of the floor) they were, in turn, increasing the mass flow at the front of the floor. The exhaust is now directly inserting more mass flow into the system.

Yes, a cold exhaust would give a similar effect. There are temperature related effects, of course (flow is at what, near 1,000K!), but I don't think they are overly significant.

The floor LE is just a curved surface - depending on the incidence of the oncoming flow and the exact shape of the curvature it will generate a pressure gradient (just think LE of an aerofoil). Blow more air onto it and the overall circulation increases - ie, a larger pressure gradient and a higher peak suction level.

[Raptor22]

There will be a thermal benefit, it cannot be ignored but agree, the big gain is from the increased expansion and thus lower pressure under the car.

[HungryHebbo]

I've finally found a video with R31. We can here it there

http://www.youtube.com/watch?v=FnU2GSmisxU

It doesn't really sound much - if any - different to the other cars with retarded ignition through that microphone.

[horse]

The floor LE is just a curved surface - depending on the incidence of the oncoming flow and the exact shape of the curvature it will generate a pressure gradient (just think LE of an aerofoil). Blow more air onto it and the overall circulation increases - ie, a larger pressure gradient and a higher peak suction level.

Ah, OK, thanks. I didn't realise there was some profiling at this part of the car (I was under the impression that it just 'began', as it were). I think I am getting closer to grasping it. By just putting the exhaust there you are forcing its extra mass under the car, which will effectively increase the velocity of the flow under the car, increasing DF.

Any risk of 'choking', I wonder, with such a system?

( F1 makes fluid dynamics so much fun! )

[SLC]

The floor LE is just a curved surface - depending on the incidence of the oncoming flow and the exact shape of the curvature it will generate a pressure gradient (just think LE of an aerofoil). Blow more air onto it and the overall circulation increases - ie, a larger pressure gradient and a higher peak suction level.

Ah, OK, thanks. I didn't realise there was some profiling at this part of the car (I was under the impression that it just 'began', as it were). I think I am getting closer to grasping it. By just putting the exhaust there you are forcing its extra mass under the car, which will effectively increase the velocity of the flow under the car, increasing DF.

Any risk of 'choking', I wonder, with such a system?

( F1 makes fluid dynamics so much fun! )

The rules allow for up to a 50mm radius coming off the step plane (which is the outboard portion of the floor, effectively). So you can't actually profile it, it has to be a perfectly circular section (measured perpendicular to the extremity of the surface defined on that step plane).

Well choking in itself is only a supersonic phenomenon, so no, you can't "choke" the floor. The limiting factor will however be the amount of expansion provided by the diffuser (whose main purpose is to increase the pressure of the air under the car back to atmospheric). If you try to "over-work" the floor by pushing mass flow in at the LE, the rear of the floor will become overly lossy if the diffuser ramp is unable to provide the necessary expansion. You will end up with a rapid over-expansion at the diffuser TE, and this will mean a bunch of lossiness. The flow will always seek a route of least resistance, and thus, will try to find another path around the car (like through the sidepod undercut above the floor).

[horse]

That's diffuser stall right? This diagram from Katz (2006) shows it coming on with reduced ride height. I was just wondering if you might bring this effect on quicker with the Renault system?



I'm sorry, I think 'choke' was the wrong word.

[SLC]

That's diffuser stall right? This diagram from Katz (2006) shows it coming on with reduced ride height. I was just wondering if you might bring this effect on quicker with the Renault system?



I'm sorry, I think 'choke' was the wrong word.

No not really - diffuser stall occurs when the flow deattaches/separates at the diffuser kink line (the point where the diffuser ramp starts). In an F1 car this usually happens because the ride height decreases below some critical value at which point the effective acceleration/expansion that you are asking the air to go through between the ground and the kink line becomes too great.

If anything, blowing the front of the floor will help prevent/delay the onset of diffuser stall because you've increased the kinetic energy of the flow below the car.

[horse]

If anything, blowing the front of the floor will help prevent/delay the onset of diffuser stall because you've increased the kinetic energy of the flow below the car.

I shall just do a very rubbish post and say that's very interesting. It's almost a surprise that it hasn't been tried previously!

[747heavy]

[Blackout]

Last year Fw but with new endplates

The spltter has wider inlets than the 2010 version

[mith]

Well, that wing's already massively developed.

[imightbewrong]

[BreezyRacer]

from f1fanatic link above: http://www.f1fanatic.co.uk/2011/02/01/r ... /_jle0965/

Well guys, to me it looks like the exhausts are meant to IMPED flow to the under tray, similar to what teams having been doing with the fronts of the under trays and barge boards to send airflow AWAY from entering the under floor area, thus creating a low pressure area under the car, as far forward as possible.

Nice idea .. I hope Renault get some mileage out of their innovative setup. Along with Red Bull, they have had the best handle on getting the most from diffuser/under tray performance in 2010. The new aero team there seems to be a pretty creative bunch and it seems that they are listened to there as well ..

[BreezyRacer]

That's diffuser stall right? This diagram from Katz (2006) shows it coming on with reduced ride height. I was just wondering if you might bring this effect on quicker with the Renault system?



I'm sorry, I think 'choke' was the wrong word.

Horse,
Keep in mind that diffuser angles are largely controlled in F1 thru it's interaction with the beam and rear wings. The wing "pull" allows for very steep angles without breaking the flow into turbulence. once you get turbulent flow in the diffuser it's not working anymore. The 50 mm stepped floor pretty much eliminates the idea that the floor is ever going to get close to ground to choke off the diffuser .. that was the reason for the stepped floor design in the first place. Thank Senna, who paid the ultimate price to make the point that we cannot let these cars choke off the diffusers ..