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Change fluid properties - non newtonian flow
Posted 14 ott 2011, 05:48 GMT-4 Fluid & Heat, Computational Fluid Dynamics (CFD), Materials, Parameters, Variables, & Functions Version 4.2, Version 5.2 2 Replies
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Hi,
I need to simulate a turbulent fluid flow in a pipe with viscosity function of fluid velocity or shear rate. The viscosity has an expression this type: viscosity = a*u^b, where b<0.
In comsol I am doing
Global Definitions -> Variables -> Vis = a*mod1.spf.U^b,
where a and b are defined in Global Definitions -> Parameters -> a=0.01 and b=-0.15.
When compute the problem I get the following error:
The following feature has encountered a problem:
- Feature: Dependent Variables 1 (sol1/v1)
-Error: Failed to evaluate expression.
When b>0 the simulation goes well without error, the problem appears when b>0.
When I try: Turbulent Flow -> Fluid Properties -> Dynamic viscosity: non-newtonian power law I get the same error. When I define that n=1 and the problem then it is newtonian I get the same error.
Someone can help me?
Carla
I need to simulate a turbulent fluid flow in a pipe with viscosity function of fluid velocity or shear rate. The viscosity has an expression this type: viscosity = a*u^b, where b<0.
In comsol I am doing
Global Definitions -> Variables -> Vis = a*mod1.spf.U^b,
where a and b are defined in Global Definitions -> Parameters -> a=0.01 and b=-0.15.
When compute the problem I get the following error:
The following feature has encountered a problem:
- Feature: Dependent Variables 1 (sol1/v1)
-Error: Failed to evaluate expression.
When b>0 the simulation goes well without error, the problem appears when b>0.
When I try: Turbulent Flow -> Fluid Properties -> Dynamic viscosity: non-newtonian power law I get the same error. When I define that n=1 and the problem then it is newtonian I get the same error.
Someone can help me?
Carla
2 Replies Last Post 17 ott 2011, 04:21 GMT-4
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Posted:
1 decade ago
When b is negative COMSOL cannot evaluate the expression if spf.U is zero (or negative). Instead try (spf.U+epsilon)^b where epsilon is a small positive number.
Nagi Elabbasi
Veryst Engineering
Nagi Elabbasi
Veryst Engineering
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Posted:
1 decade ago
Hello Nagi,
Thanks for your replying. I did your suggestion in COMSOL and the simulations now are Ok.
Carla
Thanks for your replying. I did your suggestion in COMSOL and the simulations now are Ok.
Carla