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janko-hrasko January 26, 2012 11:49

Reciprocating compressor_help
Hi guys,
I am student in the last year of my study at the university and now I have to make a cfd simulation of rec. compressor for my diploma thesis. I am working with CFX for a while, but so far I have solved only simple tasks, so I am not very familiar with moving body/mesh.

So far I have figured out piston movement with mesh displacement (+sinus function). I tried to use rigid body option for valves motion (or FluidStuctureInteraction as one of valves is being deformed by pressure, but that's not effecting my problem) but the problem is closing of the valves. How can I do that in CFX? (or CCM+ - not very familiar with)

I have read some posts that it is very complicated with fully closed valve and there is better way to leave there a small gap between valve and outside wall. The other solution here on CFD forum was to use KIVA soft, but I have only access to CFX (CCM+).

Can someone help me please?
(if you have any tutorial how to solve the problem, I would highly appreciate it)

Thanks to all respons in advance.

ghorrocks January 26, 2012 17:30

What type of compressor? If you are talking about valves then I assume you mean a reciprocating compressor.

What are you trying to achieve with the simulation of the compressor? Do you want to know the heat transfer? Or the losses? Or optimise the design? Or just some pretty pictures?

Closing valves in CFX is tricky. Your main options are to use moving mesh (and possibly remeshing) to move valves to almost shut, at least to where the flow is insignificant, then snap the valve shut and have two unconnected domains.

The second option is you can use GGI interfaces to do the motion and they handle the valve closing with no problem, but you need a geometry where you cna put the sliding GGI interfaces in and that may require geometric modification or it could be impossible.

For an example of this have a look at the ball valve tutorial, but the stuff I discuss above goes beyond that tutorial.

janko-hrasko January 27, 2012 11:31

Thank you Glenn for you answer,

I was talking about reciprocating compressor (the name of the thread)
I thought it is not going to be easy , I am going to try the first option you suggested. Close the valve as much as possible and than somehow use zero velocity or wall function for the gap.
I didn't figure out how to use GGI interface for moving body, maybe after more tutorial studying i will understand the point of that...

Does anyone has any tutorial of how to set conditions for combustion engine? I think IC engine and Rec. compresor are very similiar in this.

ghorrocks January 29, 2012 06:22

I did my PhD in IC engine modelling, and there definitely was no tutorials in how to do it back then :)

But I think there will be some tutorials on this now for CFX as it is such a big area of focus for them. I would contact CFX support and ask for some automotive tutorials. There might also be some on the ANSYS community website.

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