Vodafone McLaren MP4-27 Mercedes

[hardingfv32]

So, could the exhaust expand? Yeah, like I said, maybe, but I don't think so, depends.

My ballooning muffler system on the end of my dyno says there is serious pressure wanting out.

You need to spend a little time near a Top Fuel dragster when they fire it up in the pits. Idle output on alcohol will be enough to set you straight.

Brian

[Pup]

Top fuel at idle - that's rich.

Can't we talk about mercury switched W-ducts or something like the other threads?

[hardingfv32]

Consider why it's slowing – because it's losing energy, this should give you a hint about whether it's expanding or contracting.

So that is why EVERYONE wanted to route the exhaust near the rear diffuser. The exhaust flow creates a low pressure zone all by itself.

I say it expands. I do not remember all the rules, being 40 years out of school, conservation of mechanical energy, etc., to prove it with making some kind of misstatement that would upset some.

Brian

[Pup]

Consider why it's slowing – because it's losing energy, this should give you a hint about whether it's expanding or contracting.

So that is why EVERYONE wanted to route the exhaust near the rear diffuser. The exhaust flow creates a low pressure zone all by itself.

Yes, actually.

[hardingfv32]

Can't we talk about mercury switched W-ducts or something like the other threads?

Sure anything that you can stick with 'tapping' out.

Brian

[Pup]

I don't know what that means.

[AdamCarpenter]

I know what it is. It is how it is implemented that we need more 'detailed' knowledge of to know if it applies here. I brought up the side-pod example because it would seem relevant, yet you do not see it brought up in the aero literature. There is a reason we are overlooking.

I am up for learning something new today.

Brian

It isn't implemented, it's utilised. Coanda effect isn't something that only works when an engineer designs something that uses it, it happens all the time, even when a person walks or runs, the curvature of their head/shoulders/torso/arms/legs will create a small (very small) amount of Coanda effect. The reason I believe its relevance to sidepods isn't in aero literature is because people tend to write about new or exciting ideas that are being used. At the time that the first team figured out that they could get more airflow to the rear of their car with rounded sidepods i'm sure it was talked about, but nowadays everyone's doing it so it's old news. Same reason people don't talk about semi auto gearboxes, or carbon fibre chassis in F1 any more, everyone's got them.

[Owen.C93]

higher velocity = lower pressure

Forced exhaust gas will be high pressure though.

With ref to the above quote, I wouldn't imagine the exhaust gas would maintain high pressure for long, I thought pressure only really exists when there is something to oppose flow, once the exhaust gas is out of the pipe and into free air i dont see how it would stay at a high pressure?

I'm not too sure, I know that increasing air speed of a car will decrease the pressure, which is why you want some nice fast flow under the floor. But would an exhaust gas (which has quite a bit of force) still be lower pressure than atmospheric air at 150mph?

[strad]

Just for the record..IF one cylinder,just one, on one bank of a funny car engine quits firing the difference in force/pressure from the exhaust makes it so the driver has to turn hard in the opposite direction the keep the car going straight..worse yet if it's the side near the wall.

[dan_f1]

Two links for everyone to read.

http://en.wikipedia.org/wiki/Back_pressure

http://en.wikipedia.org/wiki/Ideal_gas_law

to put it simple this system is to complex to explain with simple anecdotes and references to simple formulas/theories. Fluid dynamics and thermal dynamics must be taken into account, and I question if any team is actually doing that.

[strad]

and I question if any team is actually doing that.

I don't think they leave any stone unturned

[dan_f1]

I don't think they leave any stone unturned

Don't be so sure, adding thermal dynamics into the mix drastically changes the number and complexity of the differential equations involved in the model.

[NoDivergence]

I don't think they leave any stone unturned

Don't be so sure, adding thermal dynamics into the mix drastically changes the number and complexity of the differential equations involved in the model.

Are you serious? You do know that current F1 cars are some of the most complex advanced human made objects ever made, right?

[Raptor22]

brian, I think that we are not sharing the same basic ideas. If I find a good article on coanda effect with reference to round jets, I will post the link and we will start from that.
I have some doubts to iron ou about coand for myself; for example I remember reading somewhere that the classic example of the spoon being attracted to the tap water is wrong.

In the mentime, let me draw your attention to one thing: why do both mclaren and ferrari sport a convex ramp after the mandated circular exit of the exhaust pipe?
On the f2002 of 10 years ago that ramp was straight...

On the F2002 though they were trying to aim the gasses just above the suspension arms; on the current McLaren and Ferrari they're trying to aim it at the floor.

That exactly what I was pointing at, for which Pup has given a nice demo.
If there is a convex suface there, then there is the aim to make the plume follow that curve.
Great pictures Pup!

Indeed. It will result in the expansion plume being displaced in the direction of the curvature of the surface it is expanding over. This is not a bell housing for a rocket motor.

We also need to remember that an F1 engine runs rich and that the exhaust gas contains a fair percentage of unburnt HC emissions. Those particles have mass, charge and will therefore behave in a manner where their resultant displacement is a factor of velocity mass, thermodynamic considerations and molecular interaction.

Yes the plume is expanding.
Yes the inner portion of the plume is contracting
Yes the plume if flowing closely enough to a surface will follow the shape of that surface to a degree.

you're all right. The ide is to place the hot air in the appropriate space so that by the time it is cooling and contracting violently it can draw in additional air into a space where that can be used to aid with generating downforce.

[beelsebob]

Consider why it's slowing – because it's losing energy, this should give you a hint about whether it's expanding or contracting.

So that is why EVERYONE wanted to route the exhaust near the rear diffuser. The exhaust flow creates a low pressure zone all by itself.

I say it expands. I do not remember all the rules, being 40 years out of school, conservation of mechanical energy, etc., to prove it with making some kind of misstatement that would upset some.

No, the reason why EVERYONE wanted to do that is because it causes the air around it to expand and accelerate, while it itself contracts and decelerates