The basic steps for setting up a generalized Newtonian flow are as follows:
Create a sub-task for the generalized Newtonian flow problem.
Create a sub-task
Select the appropriate problem type from the Create a sub-task menu.
Generalized Newtonian isothermal flow problem
or
Generalized Newtonian non-isothermal flow
problem
When prompted, specify a name for the sub-task.
Specify the region where the sub-task applies.
Domain of the sub-task
Define the material properties.
Material data
Define the shear-rate dependence of the viscosity.
Shear-rate dependence of viscosity
Select the viscosity law you want to use, and specify the relevant parameters:
Select Constant viscosity to specify a constant (Newtonian) viscosity. The only input required is the value of
in Equation 10–6 (referred to as fac in Ansys Polydata).
Select Bird-Carreau law to use the Bird-Carreau viscosity law. The inputs for this law are
(referred to as fac
in Ansys Polydata), 
(referred to as
tnat), 
(expo), and
(facinf) in Equation 10–8. Select Power law to use the power law for viscosity. The inputs for this law are
(referred to as fac
in Ansys Polydata), 
(expo), and
(tnat) in Equation 10–7.
The default value for tnat is 1, which
results in the classical expression for the power law.
Select Bingham law to use the Bingham viscosity law. The inputs for this law are
(referred to as fac
in Ansys Polydata), 
(referred to as
ystr), and 
(gcrit) in Equation 10–11. Select Herschel-Bulkley law to use the Herschel-Bulkley viscosity law. The inputs for this law are
(referred to as fac1
in Ansys Polydata), 
(referred to as
fac2), 
(expo), and
(gcrit) in Equation 10–13. Select Cross law to use the Cross law for viscosity. The inputs for this law are
(referred to as fac
in Ansys Polydata), 
(referred to as
tnat), and 
(expom) in Equation 10–9.
Select Log-Log law to use the log-log law for viscosity. The inputs for this law are
(referred to as fac
in Ansys Polydata), 
(referred to as
gcrit), and the coefficients
, 
, and 
in Equation 10–15. Use the mixed-dependence law for the temperature dependence of viscosity if you choose to use the log-log law for a nonisothermal flow.
Select modified Bingham law to use the modified Bingham law for viscosity. The inputs for this law are
(referred to as fac
in Ansys Polydata), 
(referred to as
ystr), and 
(gcrit) in Equation 10–12. Select modified Herschel-Bulkley law to use the modified Herschel-Bulkley law for viscosity. The inputs for this law are
(referred to as fac1
in Ansys Polydata), 
(referred to as
fac2), 
(expo), and
(gcrit) in Equation 10–14. Select Carreau-Yasuda law to use the Carreau-Yasuda law for viscosity. The inputs for this law are
(referred to as fac
in Ansys Polydata), 
(referred to as
tnat), 
(facinf),
(expo), and
(expoa) in Equation 10–16. Select modified Cross law to use the modified Cross law for viscosity. The inputs for this law are
(referred to as fac
in Ansys Polydata), 
(referred to as
tnat), and 
(expom) in Equation 10–10.
For nonisothermal flows, define the temperature dependence of the viscosity.
Temperature dependence of viscosity
Select the law you want to use, and specify the relevant parameters:
Select No temperature dependence if you do not want the viscosity to be temperature-dependent (that is,
in Equation 10–17). No further inputs are required. Select Arrhenius approximate law to use Equation 10–20 with temperatures at constant shear rate. The inputs for this law are
and 
. Select Arrhenius law to use Equation 10–18 with temperatures at constant shear rate. The inputs for this law are
, 
, and 
. To specify 
as an absolute temperature, set the
temperature shift 
to 0. Otherwise, set
to the appropriate temperature shift and
then specify 
relative to 
. Select Arrhenius approximate shear stress law to use Equation 10–20 with temperatures at constant shear stress. The inputs are the same as for Arrhenius approximate law.
Select Arrhenius shear stress law to use Equation 10–18 with temperatures at constant shear stress. The inputs are the same as for Arrhenius law.
Select Mixed dependence to use the mixed-dependence law (Equation 10–24). The inputs for this law are
, 
, 
, and 
. Important: The mixed-dependence law is available only if you have selected the log-log law for shear-rate dependence. It is the only law for temperature dependence that can be used with the log-log law.
Select Fulcher dependence to use Equation 10–21. The inputs for this law are
, 
, and 
. Select WLF dependence to use the WLF equation (Equation 10–22) based on shear rate (that is, with only a vertical shift in the
- 
diagram). The inputs for this law are
, 
, 
, and 
. The default values for 
and 
are appropriate for many polymer
processing applications. Select WLF shear stress dependence to use the WLF equation (Equation 10–22) based on shear stress (that is, with a vertical and horizontal shift in the
- 
diagram). The inputs are the same as for
WLF dependence.
If inertia, heat convection, or natural convection are to be taken into account in the calculation, define the density, inertia terms, and gravity. (By default, density is equal to zero, inertia terms are neglected, and gravitational acceleration is equal to zero.) For many processing applications, the Reynolds number is so low that inertia terms can safely be neglected. Even in the absence of inertia terms, however, it may be necessary to assign nonzero values for density and gravitational acceleration, since they influence heat capacity and buoyancy forces, respectively.
Set the density.
Density
Select Modification of density and enter a new value.
Enable the inertia terms in the momentum equations.
Inertia terms
Select Inertia will be taken into account to enable the inertia terms. To disregard the inertia terms, you can select Inertia will be neglected, the default setting. The option to take inertia into account will not be available if the density is equal to zero. You will need to specify a nonzero density first, in order to enable the inertia terms.
Set the gravitational acceleration.
Gravity
Select Modification of gx and set the gravitational acceleration in the
direction. Repeat for the 
and 
components.
Set any other appropriate material properties (such as thermal conductivity, heat capacity, or thermal expansion coefficient). For nonisothermal flows, for example, see Problem Setup for instructions.
See Using Evolution to Compute Generalized Newtonian Flow for suggestions about using evolution to define material properties.
Define the flow boundary conditions.
Flow boundary conditions
See Boundary Conditions for details. See also Using Evolution to Compute Generalized Newtonian Flow for suggestions about using evolution to define boundary conditions.
For nonisothermal flows, define the thermal boundary conditions.
Thermal boundary conditions
See Boundary Conditions and Problem Setup for details.
(optional) Modify the interpolation schemes used for the momentum and incompressibility equations.
Interpolation
See Controlling the Interpolation for details.