topic Re: Car exhaust pipe simulation in CFD Forum

Car exhaust pipe simulation

valEM2GF — Sun, 27 Nov 2022 21:07:13 GMT

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?

Re: Car exhaust pipe simulation

marwan_azzam — Mon, 28 Nov 2022 11:54:22 GMT

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

Re: Car exhaust pipe simulation

valEM2GF — Mon, 28 Nov 2022 15:51:28 GMT

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.

Re: Car exhaust pipe simulation

marwan_azzam — Mon, 28 Nov 2022 17:00:54 GMT

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

Re: Car exhaust pipe simulation

valEM2GF — Mon, 28 Nov 2022 17:08:01 GMT

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

Re: Car exhaust pipe simulation

marwan_azzam — Mon, 28 Nov 2022 17:23:08 GMT

@valEM2GF ,

Excellent. Thanks for confirming.

Marwan

Re: Car exhaust pipe simulation

valEM2GF — Mon, 28 Nov 2022 18:14:29 GMT

So my set up should work?

Re: Car exhaust pipe simulation

marwan_azzam — Mon, 28 Nov 2022 18:20:57 GMT

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

Marwan

Re: Car exhaust pipe simulation

valEM2GF — Mon, 28 Nov 2022 18:23:00 GMT

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

Re: Car exhaust pipe simulation

marwan_azzam — Mon, 28 Nov 2022 18:41:35 GMT

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

Marwan

Re: Car exhaust pipe simulation

valEM2GF — Mon, 28 Nov 2022 22:27:13 GMT

Here is the file

Re: Car exhaust pipe simulation

marwan_azzam — Tue, 29 Nov 2022 13:30:19 GMT

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

Re: Car exhaust pipe simulation

valEM2GF — Wed, 30 Nov 2022 16:34:49 GMT

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.

Re: Car exhaust pipe simulation

marwan_azzam — Thu, 01 Dec 2022 14:55:04 GMT

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