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Old   October 17, 2007, 01:46
Default Casson issue
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Hi all,

I'm using CFX11, simulating a 3D bloodflow through a stenosed artery using the Casson model. When I got my results, the wall shear stress for the casson model is around 300000pa at the stenosis compared to 120pa when using the Powerlaw model. What could of gone wrong?

Here is my casson model: LIBRARY: MATERIAL: Casson

Material Group = User

Object Origin = User

Option = Pure Substance


Option = General Material


Maximum Shear Strain Rate = 100 [s^-1]

Minimum Shear Strain Rate = 0.001 [s^-1]

Option = Casson

Viscosity Consistency = 10 [kg m^-1 s^-1.0]

Yield Stress = 100 [Pa]



Density = 1050 [kg m^-3]

Molar Mass = 1e-10 [kg kmol^-1]

Option = Value



Thanks All, CC.
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Old   October 17, 2007, 07:58
Default Re: Casson issue
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Dear CC,

The solution does not have to be the same; however, the difference is alarming at first glance.

Here are a few questions:

1 - What power law index did you use for the "powerlaw model"? The value must be consistent with the Casson model (n=1?)

2 - Have you tried running the Casson model w/o yield stress? That will rule out any problem with the yield component..

3 - Did you run the built-in power law (Ostwald de Waele) model, or your own CEL expressions?

If you think that something is still wrong, please contact ANSYS CFX help desk and request someone look into the problem.


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Old   October 17, 2007, 20:29
Default Re: Casson issue
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Hi Opaque,

I used CEL for my power-law model. Here is my CEL expression:

Mu: Mu0*(min(UpperS,max(sstrnr,LowerS))^(n-1))

where n is 0.6, Mu0 is 0.035 and the upper and lower bounds are the same as I specified in my casson CCL. How would I adapt my CEL expression for Power-Law into command editor for Casson model?

Thanks, CC.
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