Car exhaust pipe simulation

[valEM2GF]

I set up the Exhaust pipe inside a wind tunnel as made of air then the exit surface (exhaust outlet) as velocity. I know the exhaust flow speed: 95 mph at 8000 rpm/2L racing engine.

Is this correct?

[marwan_azzam]

Hi @valEM2GF ,

What are you trying to achieve with your analysis.

Your description above does not provide much details to say if it's correct or not.

Please elaborate.

Marwan

[valEM2GF]

Simulate a racecar in a wind tunnel with the exhaust pipe pointing at the rear wing (called "blown wing"). I tried what I described, and it did not produce credible results. The speed in the wind tunnel was 60 mph, it should have increased the DF of the wing.

[marwan_azzam]

So what you are saying is that the flow of the wind in the wind tunnel (at 60 mph) produces a certain DownForce on the wing.

In addition to that, you are introducing the exhaust air (at 95 mph) directed at the wing and you are expecting the DownForce to increase as a result but it's not. Is that correct?

Marwan

[valEM2GF]

Yes. Many racecars use this method but many years ago it was banned from Indy cars because at their speeds it can be dangerous to have DF depending on the engine RPM

[marwan_azzam]

@valEM2GF ,

Excellent. Thanks for confirming.

Marwan

[valEM2GF]

So my set up should work?

[marwan_azzam]

I can't answer the question because we've not really seen the setup.

Marwan

[valEM2GF]

What do I need to post to make the setup clear?

[marwan_azzam]

Zip the support share file (*.cfz) of your model and post it.

Marwan

[valEM2GF]

Here is the file

[marwan_azzam]

Hello @valEM2GF ,

Thank you for posting  the model.

I would:

1- suppress volume 11. Not right to have a velocity BC on an internal surface like that. Besides, there's nowhere to suck the air at the other end. Suppress volume 11 and the boundary condition will be on volume 63.

2- Simplify the velocity boundary conditions by making them Normal instead of Component.

Let us know how that works out for you.

Marwan

[valEM2GF]

It worked brilliantly but I have another question triggered by your solution. If you look at the file I sent under materials/silicon rubber you will see multiple replicas of the same tire for example. I declared them all silicon rubber, Correct?

The same happened with all the parts imported from the CAD file.

[marwan_azzam · Accepted solution]

Hi @valEM2GF ,

I'm glad it is working now.

Yes, it's OK to have all those materials set to Silicon Rubber. These are not multiple replicas. For some reason each tire is split into multiple volumes and that's why the 4 tires end up being 11 volumes. I's how the CAD model was built.

Marwan