The basic steps for setting up a differential viscoelastic flow are as follows:
Create a sub-task for the differential viscoelastic flow problem.
Create a sub-task
Select the appropriate problem type from the Create a sub-task menu.
Differential viscoelastic isothermal flow
problem
or
Differential viscoelastic nonisothermal 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
Select the differential viscoelastic model to be used, and set the related parameters. See Choosing the Differential Viscoelastic Model for guidelines on choosing an appropriate model.
Differential viscoelastic models
Select 1-st viscoelastic model to specify the first model to be used.
1-st viscoelastic model
Select the model you want to use, and specify the relevant parameters:
Select Maxwell model to use the upper-convected Maxwell model (Equation 11–11). The inputs for this model are
(visc in
Ansys Polydata) and 
(trelax).
Select Oldroyd-B model to use the Oldroyd-B model. The inputs for this model are
(trelax) in
Equation 11–11, and the total viscosity
(visc) and
the viscosity ratio 
(ratio). By default,
is set to zero, meaning that there
is no purely viscous component of the extra-stress
tensor. To include the purely viscous component
(
in Equation 11–2), set 
to a nonzero value.
and 
will be computed from Equation 11–3 and Equation 11–4. If you do not want to include the purely viscous component, simply keep the default value of zero for
(ratio) and
will be equal to the full value of
(visc). If you want to include a purely viscous component, specify the value for
. When a multi-mode viscoelastic
model is used, the purely viscous component of the
extra-stress tensor is defined through the first
mode only; more precisely, the corresponding
viscosity will be given by the product
. See Setting the Viscosity Ratio for more information about
setting the viscosity ratio. Select White-Metzner model to use the White-Metzner model (Equation 11–12). The inputs for this model are the viscosity function for
, the relaxation time function for
, and the viscosity ratio
(ratio). For the viscosity function, choose the desired model for computing viscosity and enter the related parameters:
For a constant viscosity, select Constant viscosity and then specify the value of η (fac).
To use the Bird-Carreau law (Equation 11–14), select Bird Carreau law and specify values for
(fac),
(tnat),
(expo), and
(facinf).
To use the power law (Equation 11–13), select Power law and specify values for
(fac),
(expo), and
(tnat).
For all three methods,
and 
will be computed from Equation 11–3 and Equation 11–4. As described for the
Oldroyd-B model above, specify a nonzero value for
the viscosity ratio if you want to include the
purely viscous component of the extra stress. When a
multi-mode viscoelastic model is used, the purely
viscous component of the extra-stress tensor is
defined through the first mode only; more precisely,
the corresponding viscosity will be given by the
product 
. For the relaxation time function, choose the desired method for computing the relaxation time and enter the related parameters:
For a constant relaxation time, select Constant relaxation and then specify the value of
(facr).
To use the Bird-Carreau law (Equation 11–16), select Bird Carreau law and specify values for
(facr),
(tnatr),
and 
(expor).
To use the power law (Equation 11–15), select Power law and specify values for
(facr),
(expor),
and 
(tnatr).
Select Phan Thien - Tanner model to use the PTT model (Equation 11–17). The inputs for this model are the total viscosity
(visc), the
relaxation time 
(trelax), the
material parameters 
(eps) and
(xi), and the
viscosity ratio 
(ratio). As described in Setting the Viscosity Ratio, the PTT model requires a purely viscous component of the extra-stress tensor for stability purposes. In addition, for a single-mode PTT model,
must be at least 1/9 when
=0; it may receive a lower value
when is non-zero. See also the comments
about viscosity ratio in the description of the
Oldroyd-B model, above. Select Giesekus model to use the Giesekus viscoelastic model (Equation 11–18). The inputs for this model are the total viscosity η (visc), the relaxation time
(trelax), the
material constant 
(alfa), and
the viscosity ratio 
(ratio). As described in Setting the Viscosity Ratio, the Giesekus model may require a purely viscous component of the extra-stress tensor for stability purposes. See also the comments about viscosity ratio in the description of the Oldroyd-B model, above.
Select FENE-P to use the FENE-P model (Equation 11–19). The inputs for this model are the total viscosity η (visc), the relaxation time
(trelax), the
square of the length ratio 
(Lsqrd), and
the viscosity ratio 
(ratio).
Select POM-POM [DCPP] to use the DCPP model (Equation 11–21, Equation 11–22 and Equation 11–23). The inputs for this model are the additional parameters: additional viscosity
(visc2),
relaxation time 
(Trelax),
shear modulus 
(GO),
relaxation time for the stretching mechanism
(Tlambda),
number of arms 
(NbArms) and
the parameter controlling the second normal stress
difference 
(xi). If you want to include a purely viscous component to the extra-stress tensor, specify a nonzero value for the additional viscosity (visc2) (as per the Oldroyd-B model).
Select Leonov to use the Leonov model (Equation 11–24 – Equation 11–37). The inputs for this model are the following parameters: additional viscosity
(visc), shear
modulus 
(GO),
relaxation time 
(trelax),
initial ratio of free to trapped chains
(alpha),
coefficient 
in potential function
(beta), power
index 
in potential function
(n),
parameter 
for function of deformation
history dependence 
(m), power
index 
in mobility function
(nu),
mobility function under no debonding 
(k),
dimensionless time factor 
(q), and
yielding strain 
(gamma*). From the point of view of rheology and numerical simulation, for single-mode and multi-mode fluid models, a purely viscous contribution must be added to the total extra-stress tensor. This is largely motivated by the fact that the matrix of the discretized system can be singular when all fields are initialized to values that correspond to the solution at rest. Hence, the first or only mode will always be accompanied by a Newtonian stress contribution, which has a corresponding viscosity that receives a unit value by default. You can modify this value. It may be possible to apply an evolution to this Newtonian viscosity, which may eventually vanish.
Also, as suggested previously, a nonvanishing value k should be selected for the mobility function under no debonding. It may be possible to apply an evolution scheme in order to reduce it.
As can be seen, besides controlling the linear properties via parameters G and
, the model involves two functions
and several nonlinear parameters. In a single-mode
approach, the influence of these parameters on the
viscometric and elongational properties can be
easily identified, and appropriate values can be
selected accordingly. By default, the nonlinear
parameters are assigned values that are relevant
from the point of view of rheology. In a multi-mode
approach, corresponding nonlinear parameters should
preferably be identical for each mode, in order to
facilitate the definition of a flow case.
For nonisothermal flows, specify the temperature dependence of the viscosity.
Temperature dependence of viscosity
You can specify no temperature dependence, or select the Arrhenius law, Arrhenius approximate law, or WLF law. See Theory and Equations and Problem Setup for details.
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 convection 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.) Note that 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. For nonisothermal flows, for example, see Problem Setup for instructions.
See Computing Differential Viscoelastic Flow for suggestions about using evolution to define material properties.
Define the flow boundary conditions.
Flow boundary conditions
See Boundary Conditions for details.
For nonisothermal flows, define the thermal boundary conditions.
Thermal boundary conditions
See Boundary Conditions and Problem Setup for details.
(optional) Modify the interpolation scheme used for the stresses.
Interpolation
See Selecting the Interpolation for details.