Exhaust Blown Floor - Forward Exhaust Exit

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ringo
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Joined: 29 Mar 2009, 10:57

Re: Exhaust Blown Floor - Forward Exhaust Exit

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

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! :lol:
He's free to calculate it if he pleases. :mrgreen: I'm not going to up and do it becuase he thinks it has a big effect.
I think rain will affect the effectiveness of the FEE or even driving beside another car, am i goin to even try to figue that one out? No :D
There are a million and 1 things that anyone can consider, and it's easier to say it than to do it.

The contact patch doesn't change the fact that there is over 640mm, or so, of tyre left in the free flow.
Thus the general flow wont change much, just that square patch will increase in size and a little change in drag, lift etc; it wont add a revelation to the discussion.
I've done the spinning wheels plenty of times and the effect is noticable but minute.

The patch size is really an unnecessary at this level of discussion, and is probably extremely tedious to calculate without even knowing what downforce the r31 has or even the pirelli tyre behavior itself; much less at speed.

These things have an effect yes (i don't know why it has to be large), but that would be taking the thread too far into another realm.
For Sure!!

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strad
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Joined: 02 Jan 2010, 01:57

Re: Exhaust Blown Floor - Forward Exhaust Exit

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Ringo: Since he was first out in Q1 I watched that closely and even in slo-mo and haven't seen it..not sayin it aint there,,just that I can't see it.
To achieve anything, you must be prepared to dabble on the boundary of disaster.”
Sir Stirling Moss

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ringo
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Joined: 29 Mar 2009, 10:57

Re: Exhaust Blown Floor - Forward Exhaust Exit

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then it must be practice 3 then. Don't worry if you can't find it. It was a flash from the exhausts so it may be difficult to spot.
For Sure!!

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strad
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Joined: 02 Jan 2010, 01:57

Re: Exhaust Blown Floor - Forward Exhaust Exit

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Hmmmmmmmm got rid of practice.
To achieve anything, you must be prepared to dabble on the boundary of disaster.”
Sir Stirling Moss

marekk
marekk
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Joined: 12 Feb 2011, 00:29

Re: Exhaust Blown Floor - Forward Exhaust Exit

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Found this one on youtube, from author's description really close to our FFE, should give us an idea about real exhaust flow behavior:

[youtube]http://www.youtube.com/watch?v=KnLCbEn1 ... detailpage[/youtube]

Raptor22
Raptor22
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Joined: 07 Apr 2009, 22:48

Re: Exhaust Blown Floor - Forward Exhaust Exit

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what was the perpendicular flow speed?

marekk
marekk
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Joined: 12 Feb 2011, 00:29

Re: Exhaust Blown Floor - Forward Exhaust Exit

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Raptor22 wrote:what was the perpendicular flow speed?
Subsonic, external flow/jet speed = 4, no more details i'm afraid.
Hot air jet, cold external flow.

Another one, supersonic CFD, but nice looking:

[youtube]http://www.youtube.com/watch?v=U7xpwfYQ ... detailpage[/youtube]

Some serious research on this topic: https://aem.umn.edu/people/faculty/mahe ... caling.pdf

shelly
shelly
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Joined: 05 May 2009, 12:18

Re: Exhaust Blown Floor - Forward Exhaust Exit

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Very intersting videos! Also the "top view" (clickable afetr seeing the first) is relevant to our discussion I think.

I am not sure why the inside off the transverse jet is black: is it blowing through an annular orifice?
twitter: @armchair_aero

marekk
marekk
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Joined: 12 Feb 2011, 00:29

Re: Exhaust Blown Floor - Forward Exhaust Exit

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shelly wrote:Very intersting videos! Also the "top view" (clickable afetr seeing the first) is relevant to our discussion I think.

I am not sure why the inside off the transverse jet is black: is it blowing through an annular orifice?
We see just outside part of the jet - that's where smoke fluid was introduced into flow IMO.

Raptor22
Raptor22
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Joined: 07 Apr 2009, 22:48

Re: Exhaust Blown Floor - Forward Exhaust Exit

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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

marekk
marekk
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Joined: 12 Feb 2011, 00:29

Re: Exhaust Blown Floor - Forward Exhaust Exit

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Raptor22 wrote: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.

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ringo
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Joined: 29 Mar 2009, 10:57

Re: Exhaust Blown Floor - Forward Exhaust Exit

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marekk wrote:
Raptor22 wrote:what was the perpendicular flow speed?
Subsonic, external flow/jet speed = 4, no more details i'm afraid.
Hot air jet, cold external flow.

Another one, supersonic CFD, but nice looking:

[youtube]http://www.youtube.com/watch?v=U7xpwfYQ ... detailpage[/youtube]

Some serious research on this topic: https://aem.umn.edu/people/faculty/mahe ... caling.pdf
let me interject.

The first video, the ten second one, shows that gas turning 90 degrees right out the pipe wont happen. There is a turning radius dependent on the momentum between the free stream and the gas.

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. :mrgreen:
For Sure!!

marekk
marekk
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Joined: 12 Feb 2011, 00:29

Re: Exhaust Blown Floor - Forward Exhaust Exit

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ringo wrote: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. :mrgreen:
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.

Raptor22
Raptor22
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Joined: 07 Apr 2009, 22:48

Re: Exhaust Blown Floor - Forward Exhaust Exit

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marekk wrote:
Raptor22 wrote: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.

shelly
shelly
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Joined: 05 May 2009, 12:18

Re: Exhaust Blown Floor - Forward Exhaust Exit

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Raptor22 wrote: which tends to support my ascertion that the exhaust is not really a jet but just expanding hot air.
Can you explain better this point?
twitter: @armchair_aero