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Euler-Euler modeling of non-newtonian fluid in which software ??

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Old   December 8, 2018, 08:16
Thumbs up Euler-Euler modeling of non-newtonian fluid in which software ??
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Hi everybody
I am trying to simulate a non-newtonian fluid which transfers solid particles by COMSOL and I have several problems.
First of all, it is not prepared in COMSOL to select non-newtonian fluid in Euler-Euler model.
Second, my geometry is two 3D concentric cylinder which only the interior one rotates. In Euler model the option for wall movement disappears !
Now if you are familiar with Comsol or you have experience in such a simulation in other softwares ,would you please help me to solve it or do you advise to change my software?
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Old   December 10, 2018, 09:54
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Cees Haringa
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Well, you might have to write your own code for that...

There is software that can do it, in principle. For example ANSYS FLUENT. But you are unlikely to get sensible results. In brief, bubbles will lead to accelerations (strain) at small scales (in their wake for example), which will modify your local viscosity on a scale much smaller than your grid. Non-newtonian viscosity models implemented in software such as FLUENT do not account for these small-scale strains, that may have a big impact on your rheology. Instead, it uses the strain-rates of the resolved scale, which are not representative and hence will lead to poor estimations of the true rheological behavior, and consequentially, multiphase interactions. The same applies for turbulence in non-newtonian flows, hence FLUENT has also disabled the use of non-newtonian rheology together with turbulence (the user can re-enable it, at own risk).

Apparently COMSOL chose to disable the combination of rheology and eulerian multiphase, since the models are not designed to work together and hence are highly likely giving garbage results if forced to. A lot of developments are still required to include the effects of unresolved strains originating from gas-liquid interaction and turbulence on rheology. For turbulence, some steps are being made (such as Garilov et al. 2014, turbulence model for power law fluids), but Eulerian multiphase + rheology (or better, multiphase + turbulence + rheology) is a highly unexplored field. If you are going to dive into it, do so carefully.
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Old   December 10, 2018, 16:58
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Thank you very much.
That was helpful.
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comsol, non-newtonian fluid, rotating

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