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April 30, 2014, 07:40 
Accessing information about Volume Fraction of Phases

#1 
Senior Member
Paritosh Vasava
Join Date: Oct 2012
Location: Lappeenranta, Finland
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I want to write a new viscosity model where viscosity is also a function of volume fraction of one of the phases in a multiphase flow.
I have played a bit with CrossPowerLaw. I made some minor modifications and everything was nice. I understood that this piece of code does is the main equation for the viscosity model. Code:
Foam::tmp<Foam::volScalarField> Foam::viscosityModels::NewCrossPowerLaw::calcNu() const { return (nu0_  nuInf_)/(scalar(1) + pow(m_*strainRate(), n_)) + nuInf_; } My C++ skills are way too basic so you would also have to explain about changes in the header file. Thanks!! PS:


April 30, 2014, 12:06 

#2  
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Andrew Somorjai
Join Date: May 2013
Posts: 77
Rep Power: 5 
Quote:
Code:
Foam::tmp<Foam::volScalarField> Foam::viscosityModels::NewCrossPowerLaw::calcNu() const { return (nu0_  nuInf_)/(scalar(1) + pow(m_*strainRate(), n_)) + nuInf_; } nuInf_ so you would create it (volume fraction) double vol_frac = function_for_calculation_of_vol_frac(); and then plug it into the code Code:
Foam::tmp<Foam::volScalarField> Foam::viscosityModels::NewCrossPowerLaw::calcNu() const { double vol_frac = function_for_calculation_of_vol_frac(); return (nu0_  nuInf_*vol_frac)/(scalar(1) + pow(m_*strainRate(), n_)) + nuInf_*vol_frac; } For the header file you would need to add the function for function_for_calculation_of_vol_frac() if not then you would need to include the volume fraction calculation within the function Foam::viscosityModels::NewCrossPowerLaw::calcNu() and there's no need to change any header file. Last edited by massive_turbulence; May 1, 2014 at 15:24. 

May 2, 2014, 01:17 

#3 
Senior Member
Paritosh Vasava
Join Date: Oct 2012
Location: Lappeenranta, Finland
Posts: 682
Rep Power: 15 
Thanks for your response.
This code as I mentioned is from CrossPowerLaw. I have included this code just for illustration. Right now I do not know how to include the information about the volume fraction of a phase. 

May 2, 2014, 11:45 

#4 
Member
Andrew Somorjai
Join Date: May 2013
Posts: 77
Rep Power: 5 
How is the 'volume fraction of the phase' calculated though, surely there's a simple formula (I think I remember something about this from thermo)? You might be able to read data from a dat file using fstream although if time dependence is necessary or some other variable changes then the function call would get more difficult to implement.
Last edited by massive_turbulence; May 2, 2014 at 16:31. 

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openfoam, viscosity models 
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