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[hardingfv32]

Ringo, does the CFD system accurately model the pulse nature of exhaust gases? Or does it make the, not unreasonable in light of the computational limitations, assumption that the gas flow is uniform over time and across the flow regime?

I'd bet that even the wind tunnel model, whilst using heated flow to represent the exhaust, doesn't include the pulse nature of the flow. These little things can have a disproportionate affect on the outcome.

I would claim that the pulsation actions of the exhaust have a cooling affect. As such there is no reason that the teams to not have accurate test data of exhaust temps at various distances from the exhaust tip. Both CFD and wind tunnel activities could be made to correlate with these measurements.

Take away from the sim what you wish. It is all we have at this point and do not plan on a lot more being made available.

Brian

[hardingfv32]

As per Scarbs' post, teams are trying to get the exhaust gases to exit in as flat a plane as possible, ie not uniformly across the surface of the exhaust port. This is (just) one area where the posted CFD diagram falls flat, as it assumes a uniform exit.

Can someone expand on this. The flat plane is horizontal or vertical?

What is a uniform exit mean?

Brian

[hardingfv32]

Having a rollercoaster of an exhaust path is how you'd achieve this, probably coupled with fins inside the pipe? This is why teams bodywork is singing in funny places, the exhaust is now not optimised just for engine characteristics but also for exit plume shape and velocity.

The primaries have contorted like this for a decade. In the past there were no fins in the primaries.

Placing the collector where you want can be done without trauma to the exhaust tuning. The volume of the collector place a big role. You vary the size against the length.

Brian

[ringo]

Ringo, does the CFD system accurately model the pulse nature of exhaust gases? Or does it make the, not unreasonable in light of the computational limitations, assumption that the gas flow is uniform over time and across the flow regime?

You see, CFD is a representation of reality predicated on a number of assumptions that are chosen in order to reduce the computational resource overhead whilst hopefully not affecting the overall accuracy of the result.

It is an approximation based on a guess. It is an important tool, no doubt, but it has its limitations and should never be held up as "the answer" in any ngiven situation.

I'd bet that even the wind tunnel model, whilst using heated flow to represent the exhaust, doesn't include the pulse nature of the flow. These little things can have a disproportionate affect on the outcome.

And what is someone's opinion compared to all that you have stated?

Pulse nature doesn't change the "shape" of the exhuast. CFD is fully capable of mimicking that to anyway.

[ringo]

All they are trying to do is ram the exhaust between the wheel and under the diffuser as fast as is possible.

Expand on this for me. Is ramming the exhaust between the wheel and under the diffuser:

a) Strengthening the vortex formation in this area and reduce pressure under the diffuser?

b) Speeding up the flow under the diffuser?

Brian

B is more like it. A is true as well. It's basically trying to do what the blown exhausts were doing last year, just that it's much much weaker. In fact i am not sure if these coanda exhuasts are worth much. May not even mean the difference between making a Q2 team turning into a Q3 team.

[Vasco]

Looks like they are using they are not using the snowplough.

[myurr]

Looks like they are using they are not using the snowplough.

They weren't expected to, it's been discussed quite a bit after they took it off the car for the final test. The team had also publicly discussed it and said they weren't going to be using it although they may revisit it later in the season if they can get more rear end downforce on the car.

[Raptor22]

at 18000 rpm from a V8 engine the exhaust gas pulses can be considered to be a uniform, continuous flow

[beelsebob]

As per Scarbs' post, teams are trying to get the exhaust gases to exit in as flat a plane as possible, ie not uniformly across the surface of the exhaust port. This is (just) one area where the posted CFD diagram falls flat, as it assumes a uniform exit.

You say CFD falls flat and you take someones opinion to be more substantial?
The exhaust exits as you see it in the CFD. There is no other way it will physically exit.
And where is this evidence of what the teams are trying to do?

The pipe is cylindrical, the only thing that has an influence on the "shape" outside of the pipe is the external airflow and the sidepod cut out, and even that wont "flatten" it.

All they are trying to do is ram the exhaust between the wheel and under the diffuser as fast as is possible.

You're right ringo – no amount of manipulating how air flows and using specific shapes will cause a high pressure area in one place and a low pressure area in another. That's why all the teams ignore aero and go straight for engines. A cylindrical outlet will always produce a cylindrical flow because you can't manipulate that flow at all with the shapes that it flows over.

[Raptor22]

All they are trying to do is ram the exhaust between the wheel and under the diffuser as fast as is possible.

Expand on this for me. Is ramming the exhaust between the wheel and under the diffuser:

a) Strengthening the vortex formation in this area and reduce pressure under the diffuser?

b) Speeding up the flow under the diffuser?

Brian

B is more like it. A is true as well. It's basically trying to do what the blown exhausts were doing last year, just that it's much much weaker. In fact i am not sure if these coanda exhuasts are worth much. May not even mean the difference between making a Q2 team turning into a Q3 team.

Correct, I don;t believe the coanda effect is worth much since we're dealing with fairly hot gas, expanding in a cone shape behind the exit. There is momentum of gas to consider but mostly the momentum is imparted to unburnt fuel.
This year the trick with the exhaust is to either get it to speed up the flow in the diffuser (not under it) or create a higher mass flow above the rear floor while minimising flow going under the car into the diffuser i.e. a bigger pressure differential.

[Raptor22]

All they are trying to do is ram the exhaust between the wheel and under the diffuser as fast as is possible.

Expand on this for me. Is ramming the exhaust between the wheel and under the diffuser:

a) Strengthening the vortex formation in this area and reduce pressure under the diffuser?

b) Speeding up the flow under the diffuser?

Brian

B is more like it. A is true as well. It's basically trying to do what the blown exhausts were doing last year, just that it's much much weaker. In fact i am not sure if these coanda exhuasts are worth much. May not even mean the difference between making a Q2 team turning into a Q3 team.

Correct, I don;t believe the coanda effect is worth much since we're dealing with fairly hot gas, expanding in a cone shape behind the exit. There is momentum of gas to consider but mostly the momentum is imparted to unburnt fuel.
This year the trick with the exhaust is to either get it to speed up the flow in the diffuser (not under it) or create a higher mass flow above the rear floor while minimising flow going under the car into the diffuser i.e. a bigger pressure differential.

[okayplayer]

I found this image on AMuS page and somehow the exhaust layout seems akward to me. Is there going to be an u-bend added? why not pointing it directly rearwards. or is it for layout reasons?

[beelsebob]

I found this image on AMuS page and somehow the exhaust layout seems akward to me. Is there going to be an u-bend added? why not pointing it directly rearwards. or is it for layout reasons?

That was posted a page or two ago, and yes there's a U bend to go on there. It's packaged like that because they want the exit to be only barely further back from the engine, but they still need to get the correct length of pipework in to get a nice resonation down it. Red bull package their exhaust in pretty much the same way.

[myurr]

I found this image on AMuS page and somehow the exhaust layout seems akward to me. Is there going to be an u-bend added? why not pointing it directly rearwards. or is it for layout reasons?

That was posted a page or two ago, and yes there's a U bend to go on there. It's packaged like that because they want the exit to be only barely further back from the engine, but they still need to get the correct length of pipework in to get a nice resonation down it. Red bull package their exhaust in pretty much the same way.

That routing also helps keep the side pods tightly packaged.

[RichardF1]

McLaren running the extended pylons now? If not blame the reflection