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CFAsmo
Posts: 14
Registered: ‎03-13-2013
Accepted Solution

CFD-Model nothing flows

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03-13-2013 10:55 PM

Hello guys, 

I'm searching for some helpsters, i am a newbie in this software. To my problem: the volumetric model i have created is a part of a hydraulic valve. As boundary conditions i've set a pressure-difference between inlet and outlet. The simulation shows the pressure growth but unfortunately when i try to measure the flow on a plane it shows that there is nearly no flow at all- something like 6E-7 but the pressure seems to be correct. 

I have tried to change my flow media from hydraulic oil to water, checked the boundary conditions and so on, but at the moment i am helpless. You can see the project file in my attachments. Sorry for my bad english, i'm a german student.

 

Greetings and thanks for your help

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Product Support
wildej
Posts: 755
Registered: ‎08-25-2011

Re: CFD-Model nothing flows

03-14-2013 12:36 AM in reply to: CFAsmo

Try changing the Advection Scheme to 5 (Solve ->Soution Controls -> Advection). We should always do this where we have pressure driven flow.

 

We cannot view the file you attached, we would require a cfz (support file).

 

Regards,

Jon



Jon Wilde
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Contributor
CFAsmo
Posts: 14
Registered: ‎03-13-2013

Re: CFD-Model nothing flows

03-14-2013 03:01 AM in reply to: wildej

Hello, thank you for a quick reply!

I already tried to use ADV5 it doesn't help unfortunately. The support file is to big sth. about 4 mb, so i can't create an attachment, i'l try to upload it in a different way.

 

 

 

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Contributor
CFAsmo
Posts: 14
Registered: ‎03-13-2013

Re: CFD-Model nothing flows

03-14-2013 04:56 AM in reply to: wildej

i've just uploaded the geometry file, thanks again for support

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Product Support
wildej
Posts: 755
Registered: ‎08-25-2011

Re: CFD-Model nothing flows

03-14-2013 05:09 AM in reply to: CFAsmo

My suggestions:

 

  1. Extend the inlets and outlets by 5x diameter - having small steps near Boundary Conditions is never a good thing. Ideally we want flow over a BC to only travel in one direction, not swirl
  2. Run for more than 100 iterations - ideally until CFD converges by itself
  3. More mesh here might be wise, or simply turn on the Surface and Gap Refinment in the mesh settings (change the Gap Elements in Advanced to 3 - optimum for valves)

It does run fine as it is though, I made no changes and just pressed Solve:

 

Res.jpg



Jon Wilde
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Contributor
CFAsmo
Posts: 14
Registered: ‎03-13-2013

Re: CFD-Model nothing flows

03-14-2013 11:18 PM in reply to: wildej

Okay, i have checked it again, i measured the velocity with ctrl+shift on the plane it was a very small value, perhaps it was coming from false measuring.

Could you explain your point 1. about 5x-Diameter rule? Would appreciate!

 

best regards

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Product Support
wildej
Posts: 755
Registered: ‎08-25-2011

Re: CFD-Model nothing flows

03-15-2013 04:18 AM in reply to: CFAsmo

Ah, that is the problem them. 'ctrl shift' shows results on the solid surface, you just need 'shift' for results on a plane.

 

The 5x dia is to ensure smooth flow into and out of the analysis, to avoid and recirculation over the boundaries. Using 5 we are pretty much guaranteed this will be the case.



Jon Wilde
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