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icoUncoupledKinematicParcelFoam: temperature dependent viscosity |
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March 24, 2014, 21:36 |
icoUncoupledKinematicParcelFoam: temperature dependent viscosity
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#1 |
Member
Nadish Saini
Join Date: Feb 2014
Location: Raleigh, North Carolina
Posts: 39
Rep Power: 12 |
Hello Foamers,
I am trying to compare particle trajectories with and without a temperature dependent viscosity model. For this i modified the simpleFoam solver to include temperature equation and also generated a new library file to include a temperature dependent viscosity model. Now i need to modify the icoUncoupledKinematicParcelFoam solver so that it reads the nu values from the 0 directory, generated by the above solver, instead of reading it from transportProperties directory (just like icoUncoupledKinematicParcelFoam reads U file from 0 directory of case) Can anyone please tell me how this can be done? It will be a tremendous help. Thanks |
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March 25, 2014, 02:08 |
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#2 |
Senior Member
Yogesh Bapat
Join Date: Oct 2010
Posts: 102
Rep Power: 16 |
Hello,
You can read nu as a volScalarField from 0 file very similar to U field. -Yogesh |
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March 25, 2014, 22:33 |
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#3 |
Member
Nadish Saini
Join Date: Feb 2014
Location: Raleigh, North Carolina
Posts: 39
Rep Power: 12 |
Hello Yogesh,
Thank you for your reply!! I played around with createFields.H file and was able to successfully compile a solver which takes nu file as input from 0 folder. I would really appreciate if you could help me with another question. I was using power law model for viscosity and used k value as 0.035 [Pa.s^(n)] and n 0.6 (got these values from a reference paper on blood flow). However i am getting huge time step continuity errors (simpleFoam solver, OF 2.1.1) for this k value. I searched the forum and found that some people have used very large values for k (2500). If i use such high value, the solution does converge. Can you tell me what i am doing wrong. Is k value supposed to be this high? The same issue is also reported in this post: http://www.cfd-online.com/Forums/ope...-openfoam.html |
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March 26, 2014, 09:00 |
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#4 |
Senior Member
Yogesh Bapat
Join Date: Oct 2010
Posts: 102
Rep Power: 16 |
Hello,
As you have taken k value from some paper it should be correct. What you can try is to do a few iterations with constant viscosity value so you get some flow field and then switch to power law for viscosity. This should help you in converging your case. Regards, -Yogesh |
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March 27, 2014, 00:20 |
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#5 |
Member
Nadish Saini
Join Date: Feb 2014
Location: Raleigh, North Carolina
Posts: 39
Rep Power: 12 |
Excellent Advice Yogesh. Thank you!!
I ran two time steps with constant viscosity model and then switched to power law. The solution converged. Although i don't understand clearly why this happens. Best, Nadish |
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March 27, 2014, 00:43 |
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#6 |
Senior Member
Yogesh Bapat
Join Date: Oct 2010
Posts: 102
Rep Power: 16 |
Hello ,
Reason is that power law uses velocity gradients which are not stable when you start your simulation. Doing a few iterations with constant mu helps to stabilize velocity gradients. -Yogesh |
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