Exhaust Blown Floor - Forward Exhaust Exit

[marekk]

and we see that even the "jet" deflects due to the perpendicular flow. It has some ballistic trajectory though which is consistent and relevant to this discussion

You can find trajectory numbers and figures in this previously posted research study.

For our discussion the most relevant thing is, that for exhaust/external speed ratio of 1,5 this jet hardly reaches about 5 times pipe's diameter. If we take into account that exhaust is not perpendicular to external flow, and our jet is hot, even less.

which tends to support my ascertion that the exhaust is not really a jet but just expanding hot air.

I also think the boundary layer flow is relevant since the flow beneath the car is almst perpendicular to the exit flow.

If you take a look into this linked research study, you will see that external flow goes around "jet" flow for first few pipe's diameters, contrary to what i used to believe. For me this is enough to use term jet.

Regarding exhaust to external flow angle - i meant exhaust bend to the rear will help to flatten the trajectory and to keep resulting mixed flow under the floor. Once attached to the flow under the car, it finds it's way to diffuser, even if exhaust flow is 3 times quicker then external flow.

[WhiteBlue]

http://www.racecar-engineering.com/news ... more-fuel/

Renault blown floor uses 10% more fuel
By Sam // April 6, 2011

Renault R31
Renault Sport F1 has revealed that during the Australian Grand Prix Red Bull and Renault used 10% more fuel than normal. The blown floors prevalent in the field this year mean that engine and exhaust management is even more crucial than in previous seasons. To power a blown floor effectively and generate additional downforce, an engine must produce significant amounts of exhaust gas. Simply put, the more fuel burned, the more exhaust is produced and potentially more downforce. “Since the RS27’s fuel consumption rate is extremely good, the Renault-equipped teams were able to burn 10% more fuel than normal during the Australian Grand Prix without running out of fuel, therefore giving more exhaust flow to its partners using the blown diffuser” a Renault release revealed.

The Ferrari 056 is thought to have the highest fuel consumption in Formula 1.

I think that 10% more fuel consumption is considerable. It is not in the interest of the sport to increase fuel consumption. I expect that something will be done about it in the future.

[ringo]

let me interject.

This second one is not related to what we are discussing, since this is flow in the boundary layer. The boundary 2cm, is bigger than the exhaust diameter 3mm , so this is way way off and should not be refereed to.

Carry on.

I know, ringo. But i've seen on the other thread you started to talk about supersonic exhaust flow on R31, so this second video is specially for you.

I did not say that.
I said trans-sonic flow, there's a big difference with supersonic.

@ raptor, the boundary layer on an F1 car floor is nowhere near the diameter of the pipe at that the front of the car.

And these videos only confirm that the flow does not all go under the floor to the diffuser.

If it's a jet or not, it's not a bother. It could be laser beam.
I think you are right in saying it is not a jet, since you say you deal with roxkets and such.
But this flow does not bend under the floor.

[ringo]

Regarding exhaust to external flow angle - i meant exhaust bend to the rear will help to flatten the trajectory and to keep resulting mixed flow under the floor. Once attached to the flow under the car, it finds it's way to diffuser, even if exhaust flow is 3 times quicker then external flow.

How do you come to this conclusion ?

[Pingguest]

http://www.racecar-engineering.com/news ... more-fuel/

Renault blown floor uses 10% more fuel
By Sam // April 6, 2011

Renault R31
Renault Sport F1 has revealed that during the Australian Grand Prix Red Bull and Renault used 10% more fuel than normal. The blown floors prevalent in the field this year mean that engine and exhaust management is even more crucial than in previous seasons. To power a blown floor effectively and generate additional downforce, an engine must produce significant amounts of exhaust gas. Simply put, the more fuel burned, the more exhaust is produced and potentially more downforce. “Since the RS27’s fuel consumption rate is extremely good, the Renault-equipped teams were able to burn 10% more fuel than normal during the Australian Grand Prix without running out of fuel, therefore giving more exhaust flow to its partners using the blown diffuser” a Renault release revealed.

The Ferrari 056 is thought to have the highest fuel consumption in Formula 1.

I think that 10% more fuel consumption is considerable. It is not in the interest of the sport to increase fuel consumption. I expect that something will be done about it in the future.

A downforce limit - preferably to quite a low level - would be the solution. Teams should than have to focus on drag reduction only.

[marekk]

How do you come to this conclusion ?

I can visualize flows like Newey

Ringo, lets face it.

Exhaust speed is comparable too external flow's speed under the car in medium to quick corners. Can be 2 times slower or quicker, but comparable.

This research: https://aem.umn.edu/people/faculty/mahe ... caling.pdf shows real world experimental numbers, and for "jet" flow 1,52 times quicker then external flow, trajectory of mixed flows is almost parallel to external flow's direction at 5 x pipe diameter.

Assuming your prediction of pipe's diameter = 2,5" is correct, that means most of the flow is already 85 degree bended after 31 cm.

And considering we start already with some bend (about 15 degree in my view) towards car center line, our jet is less dense (3-4 times) and has less momentum, and exhaust's speed profile is far from elliptical after going through pipe's bend and built-in separator, it will bend even quicker.

At about 2:10 in this video of real honda F1 car CFD you will see (almost) real flow lines under the floor. Most of the flow at floor's leading edge goes to the diffuser.

[youtube]http://www.youtube.com/watch?v=1SpOnitU ... detailpage[/youtube]

[shelly]

I find it interesting (if I have seen well in the videos) that exhaust "jet" keeps a certain definite shape for some lengths outside, and the external flow has to deviate around it.

About behaviour of the floor under the floor, I think we all accept (in this thread, at least), that there are two low pressure zones on a f1 diffuser: flat floor leading edge and diffuser kink line.

If we watch pathlines from below, they will be heart-shaped; after the peak on the laeding edge they tend to diverge outside, and this sets the pressure level on a big part of the flat floor.
The more you can keep those pathlines narrow, the more downforce you will get.

[marekk]

The more you can keep those pathlines narrow, the more downforce you will get.

I'm not quite sure about this one.
As long as flow stays under the floor, longer paths should give us for a given pressure gradient more flow's acceleration and more speed acting on bigger area, so more nett downforce. But that's just assumption.

You was definitely right in regards to exhaust forming sort of "almost solid tube" for first few inches.

[raymondu999]

Wow! Apparently the ignition overrun means that the cars use 10% more fuel for the Renault RS27 http://www.racecar-engineering.com/news ... more-fuel/

[ringo]

@ MArekk Let's face what?
What you are saying is simply not true and not supported by any relevant facts.

That research is supporting the idea that the flow does not turn a dead 90 degrees and go backwards under the floor.

I don't know where anything in that paper is agreeing with what your position is.

Secondly the flat surface in this experiment is in a perpendicular plane, while on the F1 car there are 2 planes, the ground and the floor which a parallel.

Have you read the paper?

you said this:

shows real world experimental numbers, and for "jet" flow 1,52 times quicker then external flow, trajectory of mixed flows is almost parallel to external flow's direction at 5 x pipe diameter.

^^ This is completely and utterly false; the complete opposite of what the paper is saying. And is just a ploy to fool those who wont read the full paper. Are you just seeing what you want to see?

5 times pipe diameter is 317mm anyway. You run out of floor area with that.

I know what is going on so let me lay it out, and add an example for the R31 to boot:

velocity ratio, r = {(PjUj^2)/(PcfUcf^2)} ^0.5

0.3*220^2/ 1.2*70^2 = 1.57 , r= 1.57

this is at 70m/s but changes as the car slows or speeds up

now that we have r and know d, an equation to get the average trajectory:

y/rd = A (x/rd) ^ B where A is 1.2<A<2.6 and 0.28<B<0.34



Here's the knock out punch, I've entered the equations into excell and scaled the graphs to fit the r30 car. And this is why you should understand what you are postig. Yoiu'll get knocked out in the argument.
You are grossly misinterpreting that paper.

I ran the data at 70m/s.
And what do i get?

To make it even more unbiased i used the range of values for A & B and the median value.




keep in mind this is to scale, all measurements in meters.

All this posting is useless because the CFD is founded on all the research you think you can bring up; which doesn't support your view anyway. And it will only act to reinforce the CFD results.
The flow does not go under the floor!!

Still no change.

[ringo]

This shows even more why the flow wont go under. It's being screened of by the fast moving inflow comming in from the splitter.
The flow radiates outward from the centre of the car and only bows back in when it reaches the wheel.
The flow lines from the exhuast cannot go across these lines or influence them to go straight down the center.
The exhaust simply has to go outwards of the floor.

[PlatinumZealot]

where is that image from? And is that exhaust or regular deflected free stream air?

[ringo]

youtube video posted by marekk, it's a honda with no FEE.

[shelly]

@marekk: imagine you focus your attention on the flow section normal to floor /ground, positioned where the suction peak on the leading edge is.
If, starting form this section, pathlines diverge laterally, the downstram section of your streamtube will increase, and as a consequence you will loose speed and get higher pressure.

[rjsa]

http://www.racecar-engineering.com/news ... more-fuel/
I think that 10% more fuel consumption is considerable. It is not in the interest of the sport to increase fuel consumption. I expect that something will be done about it in the future.

Nobody there cares.

They have a limited tank size and as long as they finish the race they will burn all the fuel possible.

Mark Webber parking right after the finish line in OZ stile.

Let just hope someone will not start handing points for fuel left on the tank.

Dear god I said it.