## Fluid Compression

Here are our CFD links and discussions about aerodynamics, suspension, driver safety and tyres. Please stick to F1 on this forum.
Sorry, but most of that exhaust gas thread was filled with conjecture about increasing and accelerating mass flow with little consideration of the practicalities or the specifics. Simply saying that mass flow is increased because you are directing exhaust gases under the floor doesn't tell us anything.

Once the nonsense had died down in that thread the major practical stumbling block of blowing hot exhaust gas under the floor was pointed out - decreasing dynamic pressure and increasing static pressure (must make sure I get that the right way round!) in any way, as per Mr. Bernoulli's guidance, is obviously just not desirable. There is still a pretty large volume of hot gas going under there that will have an appreciably negative effect regardless of how quickly that gas cools and regardless of what other hypothetical benefits it might create somewhere.

Using hot gas forward of the floor or around it I can understand because the hot gas is not having any negative effect on the floor itself anywhere, but putting it under the floor? I cannot see at all that this is what Renault are trying to do and you certainly can't get that just from the direction their exhausts that you think you can see.
segedunum

Joined: 3 Apr 2007

segedunum wrote:Sorry, but most of that exhaust gas thread was filled with conjecture about increasing and accelerating mass flow with little consideration of the practicalities or the specifics. Simply saying that mass flow is increased because you are directing exhaust gases under the floor doesn't tell us anything.

Once the nonsense had died down in that thread the major practical stumbling block of blowing hot exhaust gas under the floor was pointed out - decreasing dynamic pressure and increasing static pressure (must make sure I get that the right way round!) in any way, as per Mr. Bernoulli's guidance, is obviously just not desirable. There is still a pretty large volume of hot gas going under there that will have an appreciably negative effect regardless of how quickly that gas cools and regardless of what other hypothetical benefits it might create somewhere.

Using hot gas forward of the floor or around it I can understand because the hot gas is not having any negative effect on the floor itself anywhere, but putting it under the floor? I cannot see at all that this is what Renault are trying to do and you certainly can't get that just from the direction their exhausts that you think you can see.

Sorry Seg, but there is no static pressure increase. At this speed of flow (way below speed of sound) exhaust gases and air are incompressible.

You simply can't increase static pressure of gas/fluid by blowing another gas/fluid in it until the speed is comparable to speed of sound, at which shock waves start to form.

And the reason for this behavior is simply to imagine:
At standard atmospheric pressure, the density of air is about 1.2 kg/m^3.
It means, that in 1 m^3 (1000 liters) there is actually much less then 1 liter of air molecules. You are basically blowing into empty space.
Just take a look at hot-air balloons - you can blow as much hot air into it as you will - static pressure inside this balloon remains at ambient level all the time.
marekk

Joined: 11 Feb 2011

scarbs indicated that reading SLC's posts in the forward exhaust thread will be the most enlightening as to "how it works". When I went back and re-read what he said, it does make sense and I can't type it better than SLC did, so just read what he wrote and see if it clears anything up.
volarchico

Joined: 26 Feb 2010

volarchico wrote:
zgred wrote:img

It looks like it is directed...under the floor!

It is directed under the floor now. As was said earlier, the angle can be varied.
This clearly a new floor. Before this there was a split.

But the result is still the same. If you look in the blown floor thread, it was shown that even a configuration like this the gases wont stay underneath completely.

This floor is probably an effort to tweak how much of the gases stay under and at what speeds.

Nothing new here. All predicted from the get go.

So i repeat, those gases were not staying under the center of the floor and straight out the diffuser. No matter how much is rammed under from the beginning.
They wont stay under for the full length of the car.

Where are the temp stickers this time?
For Sure!!
ringo

Joined: 29 Mar 2009

marekk wrote:
Sorry Seg, but there is no static pressure increase. At this speed of flow (way below speed of sound) exhaust gases and air are [b]incompressible[/b].

You simply can't increase static pressure of gas/fluid by blowing another gas/fluid in it until the speed is comparable to speed of sound, at which shock waves start to form.

And the reason for this behavior is simply to imagine:
At standard atmospheric pressure, the density of air is about 1.2 kg/m^3.
It means, that in 1 m^3 (1000 liters) there is actually much less then 1 liter of air molecules. You are basically blowing into empty space.
Just take a look at hot-air balloons - you can blow as much hot air into it as you will - static pressure inside this balloon remains at ambient level all the time.

Is that so!!??
This is all wrong.
For Sure!!
ringo

Joined: 29 Mar 2009

Raptor22 wrote:
segedunum wrote:I never said it did 'blow on the front wing' , but it was clearly blowing in the arena behind the front wing, tyre and more importantly in front of the floor when you watched the car in from a standing start in testing, which seems pretty sensible given what they look as if they're trying to achieve - accelerating air and getting more volume under the car.

From the exhaust thread we never did establish what blowing hot air under the car would do other than increasing dynamic pressure and creating lift. Clearly not desirable. I simply can't see what it would achieve.

oh my ****ing word.

Go back through the Aero/chassis section and read through pages 6 and 7.

"We" did not establish anything about increasing lift. I love the way you bring "We" into it when your backs against it.

there is talk of increasing mass flow which creates lower pressure and higher pressure differential which generatesmore downforce through a lower pressure under the car. this is correct since the exhaust gas are directed under the floor.

Yes Ringo then came up with a postulation that the exhausts were blowing along the side ofthe side pods andproduced lots of great images that supported that theory, but its clear that that is not correct.

frak I give up..

Bring on Thursday.

Nothing has changed.
Notice that you are going by word of mouth. I am not.
I tested more than 1 instance of floor design, even this one, so as i said it's not a surprise, and is simply tuning the angle of the pipe since their is a relationship to speed.
You are all getting giddy over nothing. Imaginary flows and theories that make no sense. Word of Mouth and hear say.
For Sure!!
ringo

Joined: 29 Mar 2009

ringo wrote:
marekk wrote:
Sorry Seg, but there is no static pressure increase. At this speed of flow (way below speed of sound) exhaust gases and air are [b]incompressible[/b].

You simply can't increase static pressure of gas/fluid by blowing another gas/fluid in it until the speed is comparable to speed of sound, at which shock waves start to form.

And the reason for this behavior is simply to imagine:
At standard atmospheric pressure, the density of air is about 1.2 kg/m^3.
It means, that in 1 m^3 (1000 liters) there is actually much less then 1 liter of air molecules. You are basically blowing into empty space.
Just take a look at hot-air balloons - you can blow as much hot air into it as you will - static pressure inside this balloon remains at ambient level all the time.

Is that so!!??
This is all wrong.

actually he is correct. your mocking clearly shows a lack of basic understanding.
For all subsonic flows the fluid is regarded as incompressible and spped of flow creates the pressure gradient.

......but APPARENTLY you know that.

Re-run your models with the correct exhaust orientation and look at it objectively.

Also notice that SEg thinks Thermodynamics is conjecture....
Raptor22

Joined: 7 Apr 2009

ringo wrote:I tested more than 1 instance of floor design, even this one,

Sorry, when did you test the Renault design? I thought you used a made-up model from another forum member.
Just_a_fan

Joined: 31 Jan 2010

ringo wrote:
marekk wrote:
Sorry Seg, but there is no static pressure increase. At this speed of flow (way below speed of sound) exhaust gases and air are [b]incompressible[/b].

You simply can't increase static pressure of gas/fluid by blowing another gas/fluid in it until the speed is comparable to speed of sound, at which shock waves start to form.

And the reason for this behavior is simply to imagine:
At standard atmospheric pressure, the density of air is about 1.2 kg/m^3.
It means, that in 1 m^3 (1000 liters) there is actually much less then 1 liter of air molecules. You are basically blowing into empty space.
Just take a look at hot-air balloons - you can blow as much hot air into it as you will - static pressure inside this balloon remains at ambient level all the time.

Is that so!!??
This is all wrong.

Which one of those statements is wrong ?
marekk

Joined: 11 Feb 2011

Just curious - maybe this hard 4-core SuperComputer CFD work will provide us with something groundbreaking regarding dynamics of fluids ?
marekk

Joined: 11 Feb 2011

marekk wrote:
ringo wrote:
marekk wrote:
Sorry Seg, but there is no static pressure increase. At this speed of flow (way below speed of sound) exhaust gases and air are [b]incompressible[/b].

You simply can't increase static pressure of gas/fluid by blowing another gas/fluid in it until the speed is comparable to speed of sound, at which shock waves start to form.

And the reason for this behavior is simply to imagine:
At standard atmospheric pressure, the density of air is about 1.2 kg/m^3.
It means, that in 1 m^3 (1000 liters) there is actually much less then 1 liter of air molecules. You are basically blowing into empty space.
Just take a look at hot-air balloons - you can blow as much hot air into it as you will - static pressure inside this balloon remains at ambient level all the time.

Is that so!!??
This is all wrong.

Which one of those statements is wrong ?

Well i have done fluid dynamics as part of my degree, so i don't where he got that BS from.
Water is incompressible not air!!! I guess a turbo charger can't compress air since it's incompressible.

density plot.
http://s1010.photobucket.com/albums/af226/duckants_bucket/?action=view&current=Animation2.mp4

Ignorance is bliss. Some things you can't learn from hear say. You have see it.

Gas ..... incompressible. heh heh.
For Sure!!
ringo

Joined: 29 Mar 2009

ringo wrote:Well i have done fluid dynamics as part of my degree, so i don't where he got that BS from.
Water is incompressible not air!!! I guess a turbo charger can't compress air since it's incompressible.

density plot.
http://s1010.photobucket.com/albums/af226/duckants_bucket/?action=view&current=Animation2.mp4

Ignorance is bliss. Some things you can't learn from hear say. You have see it.

@Ringo: Do your study one more time, you missed something.
And this funny movie isn't about static pressure, is it ?

BTW: water is compressible, it's bulk modulus elasticity is 2.15 N/m2.
marekk

Joined: 11 Feb 2011

Yes it is, but no one is going to do a pen to paper fluid calculation with the consideration that water is compressible. It's not practical.

Amazing though, how one can think water is compressible but yet air isn't. Makes you wonder how an engine has a compression ratio.

These kinds of reasoning only confirms what people actually know about the R31 exhaust. I'll hold to my conviction; it's safer that way.

I know what is happening, i see the flow, i see the density changes, I see the temperature stickers on the Renault control arms and end plates.

Plenty of evidence available as opposed to hear say.

This new floor is simply a tuned version, aimed at managing the flow between the top and bottom, but it doesn't change that most of it will curl over the top as it goes along the length.
But i'll withdraw; let the madness of incompressible air continue.
For Sure!!
ringo

Joined: 29 Mar 2009

ringo wrote:Amazing though, how one can think water is compressible but yet air isn't. Makes you wonder how an engine has a compression ratio.
But i'll withdraw; let the madness of incompressible air continue.

@Ringo: just read seg's post and my answer to it, do not comment on part it, taken out of context.

Remove valves from your engine and check compression ratio in your CFD.
marekk

Joined: 11 Feb 2011

marekk wrote:
ringo wrote:Amazing though, how one can think water is compressible but yet air isn't. Makes you wonder how an engine has a compression ratio.
But i'll withdraw; let the madness of incompressible air continue.

@Ringo: just read seg's post and my answer to it, do not comment on part it, taken out of context.

Remove valves from your engine and check compression ratio in your CFD.

It will compress to some degree, as small as it may be. The valve holes are still restrictions aren't they?
If you exert a force on air, ie if you accelerate it by any amount, it will compress or expand. If you change the temperature it will change in density as well. Air is elastic.

No matter how small the change in density, or how small the force causing it. There is a change.

A change in temperature of 20 degrees is enough to change density considerably.

+35 1.1455
+15 1.2250

This is just 20 degrees celcius. The exhaust from the r31 cools to about 55 degrees celcius by the time it reaches the tyres.
That is over 800 degrees drop in less than a few feet. You can imagine the density change with that.
For Sure!!
ringo

Joined: 29 Mar 2009

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