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Carreau or Carreau-Yasuda model

Posted 26.05.2015, 11:35 GMT-4 Fluid & Heat, Computational Fluid Dynamics (CFD), Modeling Tools & Definitions, Parameters, Variables, & Functions Version 5.0 4 Replies

James Sparkes
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Hi,

Is there an easy way to use the more general CY model in COMSOL 5 rather than the carreau model?
4 Replies Last Post 10.06.2015, 21:41 GMT-4
Steve Conrad
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Posted: 10 years ago 09.06.2015, 11:22 GMT-4
I think Carreau and Carreau-Yasuda are used interchangeably and refer to the same. COMSOL uses for former term.

One has the option of selecting a user-defined model if the built-in models don't meet your needs.

--
Steven Conrad, MD PhD
LSU Health
I think Carreau and Carreau-Yasuda are used interchangeably and refer to the same. COMSOL uses for former term. One has the option of selecting a user-defined model if the built-in models don't meet your needs. -- Steven Conrad, MD PhD LSU Health
James Sparkes
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Posted: 10 years ago 10.06.2015, 06:40 GMT-4
I have solved this problem using a user defined viscosity:

eta_0*(1+(lambda*spf.sr)^a)^((n-1)/a)

The Carreau model, with a=2, is a specific form of the more general carreau-yasuda model.
I have solved this problem using a user defined viscosity: eta_0*(1+(lambda*spf.sr)^a)^((n-1)/a) The Carreau model, with a=2, is a specific form of the more general carreau-yasuda model.
Himanshu Khandelwal
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Posted: 10 years ago 10.06.2015, 10:04 GMT-4
Can you tell me how can I add herschel-bulkley parameters or Bingham Plastic properties?
Can you tell me how can I add herschel-bulkley parameters or Bingham Plastic properties?
Steve Conrad
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Posted: 10 years ago 10.06.2015, 21:41 GMT-4
James, thanks for the clarification

Himanshu, you can provide any equation that provides a dynamic viscosity value, and you have the COMSOL variable spf.sr available for the shear rate.

I have not worked with Bingham fluids, but here are my thoughts. Consider using a very large limiting viscosity for a shear rate (spf.sr) under a given value (to simulate the yield stress), and the characteristic plastic viscosity above that value. The COMSOL if() function can be used to select the value based on shear rate. The result will have to be smoothed with a Heaviside function to eliminate the discontinuity.

This can be extended to the Herschel-Bulkley model by applying a shear thinning/thickening coefficient such as spf.sr^(n-1). The article at en.wikipedia.org/wiki/Herschel–Bulkley_fluid gives an even more generalized approach based on shear rate.

If anyone sees any problem with this approach, please advise!

--
Steven Conrad, MD PhD
LSU Health
James, thanks for the clarification Himanshu, you can provide any equation that provides a dynamic viscosity value, and you have the COMSOL variable spf.sr available for the shear rate. I have not worked with Bingham fluids, but here are my thoughts. Consider using a very large limiting viscosity for a shear rate (spf.sr) under a given value (to simulate the yield stress), and the characteristic plastic viscosity above that value. The COMSOL if() function can be used to select the value based on shear rate. The result will have to be smoothed with a Heaviside function to eliminate the discontinuity. This can be extended to the Herschel-Bulkley model by applying a shear thinning/thickening coefficient such as spf.sr^(n-1). The article at http://en.wikipedia.org/wiki/Herschel–Bulkley_fluid gives an even more generalized approach based on shear rate. If anyone sees any problem with this approach, please advise! -- Steven Conrad, MD PhD LSU Health

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