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-   -   Mr.Astrid Pls help me!!!! (http://www.cfd-online.com/Forums/cfx/23041-mr-astrid-pls-help-me.html)

SD September 9, 2006 01:38

Mr.Astrid Pls help me!!!!
 
Dear Astrid,

I have gone throught your VANISHING VOLUME FRACTION QUERY IN 2003. I need some help from you. I am simulating a water sprinkler used in Lawns. I have taken 2 domains(water & air).At first i have considered homogeneous model and run the analysis, i have got the same problem as yours, like VF of water in the air domain is very very low, though the stream lines are sloshing out. I couldn't get solution for this. Then i have considered inhomogeneous models as I have seen in cfx help manual, to consider inhomogeneous model to simulate Air bubbles in water column & water drops in Air domain. But when i take in to consideration the inhomogeneous model the solver terminates. The physics of the problem is inlet water velocity[inlet of sprinkler] & opening static pressure 0 [for air domain(cube)]. I feel that simulating this problem with inhomogeneous model can give a better result If you are seeing this query Pls help me!!!!!

REGARDS

SD

Joe September 9, 2006 08:22

Re: Mr.Astrid Pls help me!!!!
 
Get back to basics: Read the manual sections "Advice on flow modelling" and "Near wall meshing" and the multiphase flow best practice guide.

SD September 10, 2006 20:53

Re: Mr.Astrid Pls help me!!!!
 
Dear joe,

thnks i hav done it, as such i could come 2 this conclusion. tell me if u could throw light on some other aspect.


Joe September 11, 2006 09:26

Re: Mr.Astrid Pls help me!!!!
 
Getting good multiphase convergence in your case is never going to be simple. Strart from the simplest possible case and get convergence there, then increase the model complexitiy.

CFX 11 will offer substantial free surface robustness improvements ...

Astrid September 11, 2006 13:36

Re: Mr.Astrid Pls help me!!!!
 
Hi SD,

This is quite a long time ago. I can't even remeber what it was about. Sorry. And, CFX has changed quite a lot, so I am not sure if what I wrote there still holds.

What I would suggest is to reduce your model. You problem sounds 2D-axisymmetric. Do have a wedge-like geometry? If not, I would strongly recommend it. You can throw away a lot of elements and increase accuracy where you think it is needed.

Then, first perform a homogeneous calculation, with homogenous turbulence etc. Thereafter an inhomogeneous calculation. I have perfromed such a calculation quite recently on an atomizer. The liquid volume fraction on the inlet was 1, on the outlet it was 1e-4. I have to say that you have to be PATIENT. In total we needed 5000 iterations. We used a very small timestep as the atomizer rotated with 10000 rpm. Your problem sounds easier...

Regs, Astrid.


nhlanhla kokwe October 1, 2006 11:46

Re: Mr.Astrid Pls help me!!!!
 
I'm using Dedesign Modeler to generate a mesh,now I wanted to select all the faces of the BlantBody I'm working with here,I'm failing to select these faces and I'm getting an error saying "the location cannot overlap with the location of an existing feature, and itt refering me on to troubleshooting.


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