
[Sponsors] 
HerschelBulkley nonNewtonian viscosity model has term with sign error 

LinkBack  Thread Tools  Display Modes 
March 1, 2011, 19:31 
HerschelBulkley nonNewtonian viscosity model has term with sign error

#1 
New Member
Paul Bryant
Join Date: Feb 2011
Posts: 13
Rep Power: 8 
Sponsored Links
return (min(nu0_,(tau0_ + k_* rtone *( pow(tone * sr(), n_) + pow(tone*tau0_/nu0_,n_))) / (max(sr(), dimensionedScalar ("VSMALL", dimless/dimTime, VSMALL))))); Note that the stress and viscosity are both given in kinematic form (i.e. divided by the density). The factors tone and rtone are both equal to unity but have dimensions of time and inverse time and are included to get the units correct for the result. The CORRECTED VERSION with the sign change is: return (min(nu0_,(tau0_ + k_* rtone *( pow(tone * sr(), n_)  pow(tone*tau0_/nu0_,n_))) / (max(sr(), dimensionedScalar ("VSMALL", dimless/dimTime, VSMALL))))); Note that when sr=tao0/nu0, the two pow() functions will now cancel out and give the expected result nu=tao0/sr. Without the indicated sign correction, tao0 has no obvious physical interpretation, as it is neither the stress at the transition point between the two forms nor is it the stress that would occur if the power law form was used as the shear rate approaches zero. The correction will have little effect in cases when the value of nu0 is set to a very large value to approximate infinity. 

Sponsored Links 
May 6, 2011, 06:46 

#2 
Senior Member
Robert Sawko
Join Date: Mar 2009
Posts: 117
Rep Power: 15 
This is just to say: you're absolutely right! Thanks for sharing.


May 7, 2011, 02:58 

#3 
Senior Member
Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,910
Rep Power: 28 
FYI, this was fixed some time ago: http://www.openfoam.com/mantisbt/view.php?id=153
__________________
Alberto Passalacqua GeekoCFD  A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats. OpenQBMM  An opensource implementation of quadraturebased moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using. 

November 4, 2011, 05:01 
HerschelBulkley validation

#4 
Senior Member
Albrecht vBoetticher
Join Date: Aug 2010
Location: Zürich, Swizerland
Posts: 214
Rep Power: 10 
It seems like the HerschelBulkley viscosity model gets more and more applied in OpenFOAM. Did somebody already run a validation test case to compare the OpenFOAM implementation with the results of another CFD? I currently finish my PhD were I model shallow landslides and debris flows with the HerschelBulkley rheology law, all results fit the experiments but only if I choose the yield stress tao0 and consistency factor k exactly a hundred times smaller that recommended by the literature.


November 14, 2011, 09:47 

#5 
Senior Member
Albrecht vBoetticher
Join Date: Aug 2010
Location: Zürich, Swizerland
Posts: 214
Rep Power: 10 
...sorry that was a mistake in the preprocessor changing from [lb/ft^2] to [Pa]. Actually, the HerschelBulkley looks fine :)


June 18, 2013, 23:53 

#6  
Senior Member
Dongyue Li
Join Date: Jun 2012
Location: Torino, Italy
Posts: 752
Rep Power: 10 
Quote:
This is where I cannot get it, just see the image: The red line is nu, black one is tao. Is this what you said? so is there anything wrong with my equation? but my equation is not implemented in openFOAM. THANKS! 

Tags 
herschelbulkley, nonnewtonian, viscosity models 
Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
CGNS Compiling  Diego  Main CFD Forum  17  December 21, 2014 02:40 
CGNS lib and Fortran compiler  manaliac  Main CFD Forum  2  November 29, 2010 07:25 
groovyBC  sega  OpenFOAM Running, Solving & CFD  12  February 17, 2010 10:30 
compile errors of boundary condition "expDirectionMixed"  liying02ts  OpenFOAM Bugs  2  February 1, 2010 21:11 
Regarding Implementation of Hershel Bulkley Model in Viscosity correlation  Pathak  FLOW3D  0  August 24, 2009 06:34 
Sponsored Links 