Exhaust Blown Floor - Forward Exhaust Exit

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mep
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Re: Exhaust Blown Floor - Forward Exhaust Exit

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Nice idea they brought there. I am surprised they didn't try to hide it for longer time. They can lose their advantage when other teams copy the idea until season opener.

It's interesting they rather try to seal the floor.
I am wondering if there is any gain when you "full blow" (longitudional) the floor.

I guess due to the reduced cross section on the exit of the diffusor it does not make much sense to push even more air trough the floor because you can accelerate it anymore to get a significant pressure droop. So it’s better to seal the floor to get the "natural air" you have under the floor accelerated.
Btw. have you ever thought about the reduced diffusor area to cause a slightly reduction in ride high of the car to get optimum downforce?
Last edited by mep on Wed Feb 02, 2011 6:04 pm, edited 1 time in total.

nacho
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Re: Exhaust Blown Floor - Forward Exhaust Exit

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To me it looks like that the pipe will blow 100% under the floor.

RichardHH
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Re: Exhaust Blown Floor - Forward Exhaust Exit

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I also believe that the exhaust is directed primarily (if not totally) beneath the floor. Don't forget the flow of air comming from the forward velocity of the car pushing the exhaust further to the rear where the bulge (for lack of a better word) is higher?.

I just have another question about this. Noone has considered the flow of air from both exits simultaneously. Doesnt the double outward motion in itself cause a drop of air pressure in between raising the overall efficiency of the downforce?

Also, I see no necessity (or simply just don't understand) of high temperature air above the floor plate. I understand the will to bring hot air to the underside of the diffuser as in 2010, but bringing hot air to both sides seems kind of counter productive to me.

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ringo
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Re: Exhaust Blown Floor - Forward Exhaust Exit

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Raptor22 wrote:from the renault r31 thread
n smikle wrote:
It has energy in the form of speed and temperature. When you impede it's motion or diffuser it the pressure will rise. Naturally it is going to drop to atmospheric after some time outside the pipe, but for example if ones uses their hand to block the pipe and you will see the pressure can get high.

There was a pdf on a CFD analysis of the blown diffuser floating around the internet. the pressure behind the exhaust was higher. I do not know how much higher though, but it can be significant if the exhaust is impeded.

Sorry but thats not correct at all. What you are feeling is the pressure rise against your hand not the exhaust pressure. When thehot gas leaves the boundary of the pipe it moves to atmospheric pressure instantaneously. Your hand is feeling pressure due to the velocity of the gas and is not a pressure that will be felt by the underside of the car.

The airflowingunder the car will be accelerated by the faster moving exhaust gas. It is this acceleration of the normal airflow due to the added kinetic energy and thermal energy loss to expansion that accelerates the air flow under the car. That drops the pressure under the car increasing downforce under the stepped bottom.
it is this alone that is doing the magic, nothing else.

Using a exhaust exit in or near the diffusor is slightlyless effective because you impart less kinetic energy to the freestream due to loss of knetic energy due to skin friction. Both concepts allow for accelerating the air flow under the car.

Lotus Renaults solution may have a slightly higher expansion ration resulting a few kilo more downforce but that expansion is now taking place over a much bigger surface area which could negate the benefit.
It doesn't move to atmospheric instantly, if it's presented with an obstruction the pressure will increase. Keep in mind the mass flow of the air and Newton's third law. The pressure rise against your hand is equal and oppossite to the pressure of the gas. The exhuast drops to atmospheric with some time, but would only be instant with a propper diffuser on the pipe.
The exhuast is pointed sideways indicating it's intentions are not to fully go under the car. The uncoming air would have to be almost of equal energy and mass flow to turn the gasses right under the car.

That's the thing with this concept as well, it doesn't work the same way at all speeds. It probably has a speed where it works perfectly. The team might be able to angle it for different tracks.

One weakness is that a car can pull up beside robert or Vitaly and affect one side of their car by interacting with the flow field of the exhuast.
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manchild
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Re: Exhaust Blown Floor - Forward Exhaust Exit

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I've never wrote 50/50. It is logical that main part goes under and small one over the floor. Most of the gasses will go below, but part of them will go above too.

It can be see on newer pics that it is the case, since metal shield is burnt above too.

Expansion of gasses where exhaust ends doesn't look like water flowing down the pipe. Gasses have inertia, but they expand equally.

hecti
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Re: Exhaust Blown Floor - Forward Exhaust Exit

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nacho wrote:To me it looks like that the pipe will blow 100% under the floor.
Yea this is true but that little flick up next to the vertical wing nest to the entrance of the side pod creates a vortex, thus forming the "exhaust side skirt"

BreezyRacer
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Re: Exhaust Blown Floor - Forward Exhaust Exit

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I agree pretty much with Ringo's assessment except that imagine almost all the exhaust flow is under the car .. the exhaust flow acts as a barrier to KEEP FORWARD AIR FROM GOING UNDER THE CAR .. thus more low pressure area under the car, and low pressure created as far forward in the chassis as is possible.

The exhaust flow will exit nearly perpendicular to the car and interrupt the forward air off the the sides of the under tray.

You want LESS airflow under the car to create as much low pressure as is possible .. at least until you get so little airflow that there is no flow :P

The now familiar splitter inlets on the sides of the center splitter/tea tray provide a highly charged amount of airflow under the car just for this .. to provide the highest charge of airflow to the undertray. Then they are using the inlet radius rules and barge boards to channel forward airflow to the outer sides. They have been doing this for the last few seasons .. it's no secret. This exhaust placement just creates a great way to exaggerate that effect.

And BTW, if you didn't build this into your tub before crash testing (already complete of course) you'll have a damn hard time finding room for it IMO. Kind of like McLaren with the F duct last year ..

manchild
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Re: Exhaust Blown Floor - Forward Exhaust Exit

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BreezyRacer wrote:I agree pretty much with Ringo's assessment except that imagine almost all the exhaust flow is under the car .. the exhaust flow acts as a barrier to KEEP FORWARD AIR FROM GOING UNDER THE CAR .. thus more low pressure area under the car, and low pressure created as far forward in the chassis as is possible.

The exhaust flow will exit nearly perpendicular to the car and interrupt the forward air off the the sides of the under tray.

You want LESS airflow under the car to create as much low pressure as is possible .. at least until you get so little airflow that there is no flow :P
The exhaust doesn't block the air from entering below sidepods since it is leveled up with the floor and most of the air passes below exhaust pipe.

Also, the idea isn't to reduce the flow under the car but to increase it. The more air you get under without bottoming the better (the greater difference in pressure between the air on top and below the better = greater downforce).

Skirts, both real ones as well as these virtual serve to prevent air from spilling sideways, since spilling reduces it's amount and speed, decreasing downforce.

andrew
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Re: Exhaust Blown Floor - Forward Exhaust Exit

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Looking at the pictures of the Lotus on the Lotus thread, they have these small fences in front of the rear wheels also. Certainly a renault idea and ties in Forty Two's theory on the first page of this thread.

Can't see the exhaust outlets on the Lotus due to the barge boards being in the way but I'll wager they have the same exhaust configuration.

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forty-two
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Re: Exhaust Blown Floor - Forward Exhaust Exit

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andrew wrote:Looking at the pictures of the Lotus on the Lotus thread, they have these small fences in front of the rear wheels also. Certainly a renault idea and ties in Forty Two's theory on the first page of this thread.

Can't see the exhaust outlets on the Lotus due to the barge boards being in the way but I'll wager they have the same exhaust configuration.
Or maybe they have at least allowed space in their sidepods to route the pipework there in the future should they feel the need! I notice that the area in the corner of the floor on the Lotus (where the bargeboard attaches) is similarly "lumpy" perhaps this is indeed hiding something?

I've been looking for some decent images of the floor at the back of the Lotus for precisely this reason actually, did you find any good shots Andrew?
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andrew
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Re: Exhaust Blown Floor - Forward Exhaust Exit

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Havn't found any good shots yet but I'll keep looking.

imightbewrong
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Re: Exhaust Blown Floor - Forward Exhaust Exit

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Image

Richard
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Re: Exhaust Blown Floor - Forward Exhaust Exit

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That fence in front of the rear wheel was on the R30, so not a new feature for the forward exhaust

http://www.formula1.com/news/technical/ ... 2/763.html

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forty-two
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Re: Exhaust Blown Floor - Forward Exhaust Exit

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richard_leeds wrote:That fence in front of the rear wheel was on the R30, so not a new feature for the forward exhaust

http://www.formula1.com/news/technical/ ... 2/763.html

Image
Interesting, but I guess that it doesn't mean they haven't been working on this for a while now. Putting the fence there last year might well have taught them important lessons about the flow in general, even without the exhaust blowing there.

Remember Mclaren running an "always on" f-duct at Monaco 2009?
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andrew
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Re: Exhaust Blown Floor - Forward Exhaust Exit

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Would the fence not be of use anyway to help channel air around the rear suspension?

I agree that it may be something that Renault have been experimenting with for a while.