Hi All,

I'm having trouble creating an expression for the casson model.

I inputed the following functions in CFX:

Mu: ((Eta^2*J2)^(1/4)+2^(-1/2)*Tau^(1/2))^2*J2^(-1/2) [kg*m^-1*s^-1]

Eta: Eta0*(1-H)^(-2.5)

Eta0: 0.012 [kg*m^-1*s^-1]

H: 0.37

J2: (abs(sstrnr)/2)^2

Tau: 0.1*(0.625*H)^3

CFX is giving me an inconsistent dimensions on the left and right side of the "+" error. Can anyone help with the correct syntax?

Thanks, CC.

Dear CC,

The Casson viscosity model is already built-in for ANSYS CFX 11.0. It is hidden from the GUI (will show in 12.0), but you can type the CCL for it. An example is:

LIBRARY: MATERIAL: myfluid

Material Group = User

Option = Pure Substance

Thermodynamic State = Liquid

PROPERTIES:

Option = General Material

DYNAMIC VISCOSITY:

Option = Casson

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

Yield Stress = 100 [Pa]

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

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

END

END END

The only limitation is that the input can only be "single valued CEL expressions, or constants". I wonder if your consistency is a function of H?

Hope this helps, Opaque

If you are using ANSYS CFX 10.0, then you must be careful with the J2 term because the term "(Eta^2*J2)^(1/4)" does not have units of viscosity.