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Non-Newtonian Rheology Model Units Inconsitency |
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#1 |
New Member
Mitch
Join Date: Jun 2024
Posts: 1
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Hello,
The computation of non-newtonian viscosity seems to be inconsistent in units. For example, the Herschel-Bulkley model is set up to provide a kinematic viscosity below the yield stress threshold, while calculating a dynamic viscosity above the yield stress threshold: nu = min ( nu0, (tau0 + k*gamma_dot^n)/(gamma_dot)) The output is specified as kinematic viscosity units, so clearly the equation is not correct if tau0 units are N/m^2 and gamma_dot units are s^-1. https://www.openfoam.com/documentati...8C_source.html The documentation I can find online seems to ignore this inconsistency when describing input parameters: https://doc.cfd.direct/openfoam/user...sport-rheology Unless I'm missing something, the solution should be providing the tau0 and k parameters already divided by density. If true, this is straight forward but lacking/unclear in the documentation. I am hoping to confirm this with the community before I implement. Cheers |
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#2 |
Senior Member
Marcin
Join Date: May 2014
Location: Poland, Swiebodzin
Posts: 313
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There is the inconsistency in units for non-Newtonian viscosity calculations in the Herschel-Bulkley model. The inconsistency arises because the model expresses shear stress (tau) in units of N/m^2 (Pascals), while the shear rate (gamma_dot) is in units of s^-1 (reciprocal seconds).
More at https://howtooansys.blogspot.com/202...es-in-non.html
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Tags |
inconsistencies, rheology, units |
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