Exhaust Blown Floor - Forward Exhaust Exit

[horse]

=D>

Thanks Ringo, that's very interesting and informative. It's pretty clear that there are numerous benefits including better mass flow at the floor leading edge and better utilization of the undertray (a wider effective area, if you like).

The only downside I can think of is the decrease in pressure behind the rear wheels. I believe the wheels are useful for "sucking" the diffuser due to the low pressure there. So, as you said, this would lead to having a more "spread out" pressure distribution possibly with less focus on the diffuser. I wonder then, if this would hamper developing a mighty front wing, like the RBR?

[marekk]

@ringo: interesting, can you provide exhaust angle, speed, temp and rotational speed of the wheels in this simulation ?

[ringo]

Some plots along a line i placed in the exhaust stream.





for some reason it plotted the exhaust exit as the end of the line at 2.4m instead of the other end at zero, but it's no biggie.

Just read the graph right to left. The right side at 2.4 being where the exhaust flows out flowing towards length of zero which is at the rear wheel center line as it goes along the car.

wheel rotation is road speed of 70m/s / 0.66m. It doesn't change much in this case aerodynamically anyway.

pipe angle is 45 degrees from horizontal and 45 to car center line.

And this velocity is indisputable. I only entered mass flow, i made sure not to enter velocity to make it clear and unbiased.
The program calculated the velocity from the pipe area and gas density, and it's where we expect; very fast.

I used a temperature of 950 degrees because that is the only documented temperature we have. So it was best to use what is reported to keep things objective.

[bot6]

Ringo -> I agree with you on the effect, that's pretty much what I described as the "virtual low bargeboard" in the Renault thread, as it acts more like a deflector at the front of the floor than as a "virtual skirt" along the whole length.

I do think though that their exhaust does curl back a bit more closer to the end of the car, as their diffuser probably is more efficient than that of your model.

But this will change a lot with flow speed, so I suppose at slow speeds the exhaust will go outwards more, and at high speeds it will be sucked in by the diffuser more.

Any chance you can run the simulation for three speeds (say 100, 180 and 250kph)?

[ringo]

this is at 252 kph.
So with this floor and this pipe angle it wont turn to the diffuser at a lower speed.
252 kph is a reasonably high cornering speed as well.

I think most of the flow going to the diffuser at cornering speeds is only the case if the pipes were facing backward completely.

It will be very artificial if we try to force the flow to do something that it simply wont do by itself.
A little went to the diffuser in earlier models but this was with an inaccurate floor design, and it wasn't really convincing as a genuine diffuser blower. Too much lost energy to the tyres.

It seems more can be learnt by strictly copying the geometry instead of trying to achieve a certain expectation.

If it goes to the diffuser, it will lose the effect of increasing the floor size, and will lose most of the drag reduction capability.

It's hard to believe that the r31 is not blowing the diffuser, but it seems reasonable enough.

So until we get direct confirmation from the team we wont know. As for direct
evidence it would be nice if anyone on F1T has video of qualifying 1 with petrov coming out of the pits. The car shot a flame in Q1 and a screen capture would be helpful.

[bot6]

I'm not debating that. I'm just thinking that the exhaust flow will be further outwards at low speeds and further inwards at high speed, and I'm just wondering what kind of effect that has on pressure distribution, hence aero balance, when the speed changes. Just thought it might be interesting to try.

[marekk]

@ringo:

Can you try to run it once more with pipes angle to car's axis of about 65-70 degree, 0 degree horizontal and reshape slightly this airfoil in front of pipe to something like this:

__
  \
   \_________

I'm slightly confused with this plot along a line placed in the exhaust stream - looks like it's on ambient temp just after 60-70 cm, where is this 300kW of energy gone ?
Can you plot temp for the area of the car plus 1m outside of it on the reference plane ?

Wheels rotational speed should be 70m / 2,07m for 26" wheel IMO - can you put this into this simulation ?

[nipo]

So... Under braking, drag at the wheels resumes and there's less down force?

Overall doesn't that make the R31 even more sensitive to throttle control than other cars?

[Fil]

Nipo, you're probably right on the mark. The R31 has the most aggressive off-throttle exhaust overlap of any car in the field. By far.

It gurgles & burbles like nothing else out there. Even when the driver is priming the throttle through the constant radius corners, the R31 splutters & spits when others already have the usual F1 whine. It all sounds incredibly rough & crude (i loved it!). Obviously the Renault setup requires a certain amount of flow at all times.

[void1]

My god have you got the contact patches wrong or what! It will have a rather large effect when you have corrected this..

[ringo]

Ok mr Pirreli P zero. You know all about the tyre behavior.

Large effect. What effect?

large, small, medium, super sized with extra fries?

[Fil]

'Mr Pirelli P Zero' may have a point you know.

In your images on the previous page, the contact patches are only horizontal lines (and by my understanding, the front-most part of the tyre's contact).

With an actual contact patch at least 4-5x this length, would this not create a much more pronounced, or (at the very least) a later occurring low pressure zone off the front wheels?
And wouldn't this then interact more significantly with the barge boards, sidepods, floor edge & subsequent front exhaust effect?


Oh, and he did specify 'rather large'. So, hold the fries!

[strad]

So until we get direct confirmation from the team we wont know. As for direct
evidence it would be nice if anyone on F1T has video of qualifying 1 with petrov coming out of the pits. The car shot a flame in Q1 and a screen capture would be helpful.

If you point me closer I will do that. I looked quickly before work and didn't see it..early...late? Q1 right?

[nipo]

Nipo, you're probably right on the mark. The R31 has the most aggressive off-throttle exhaust overlap of any car in the field. By far.

It gurgles & burbles like nothing else out there. Even when the driver is priming the throttle through the constant radius corners, the R31 splutters & spits when others already have the usual F1 whine. It all sounds incredibly rough & crude (i loved it!). Obviously the Renault setup requires a certain amount of flow at all times.

OK... If so, what about fuel consumption - does that not put them in a disadvantage, or the effect is actually quite small?

[ringo]

So until we get direct confirmation from the team we wont know. As for direct
evidence it would be nice if anyone on F1T has video of qualifying 1 with petrov coming out of the pits. The car shot a flame in Q1 and a screen capture would be helpful.

If you point me closer I will do that. I looked quickly before work and didn't see it..early...late? Q1 right?

i can't remember, i'm not in the UK so i don't have access to bbc.
It was the beginning of a q session i believe.