Fluid Properties
The Fluid Properties node adds the momentum and continuity equations solved by the physics interface. For the viscoelastic fluids, the constitutive relations for the extra elastic stress tensor are also added. The node also provides an interface for defining the material properties of the fluid.
Except where included below, see Fluid Properties for all the other settings.
Constitutive Relation
Viscoelastic (default), Specify dynamic viscosity and Inelastic non-Newtonian options are available. If Viscoelastic constitutive relation is selected, the Fluid Properties node also adds the variables and equations for the components of the elastic stress tensor.
For Viscoelastic constitutive relation, specify Solvent viscosity μs and select a Material model — Oldroyd-B, Giesekus, LPTT, EPTT, or FENE-P. Viscoelastic material can be described as consisting of one or more branches. For each viscoelastic branch, enter parameters in the table. See the setting for each viscoelastic model that follows.
Oldroyd-B
For Oldroyd-B enter the model parameters in the table. In each Branch raw enter the polymer viscosity μem in the Viscosity column, and the relaxation time λem in the Relaxation time column.
Giesekus
For Giesekus, in each Branch raw enter the polymer viscosity μem in the Viscosity column, the relaxation time λem in the Relaxation time column, and the mobility factor αem in the Mobility column.
FENE-P
For FENE-P, in each Branch raw enter the polymer viscosity μem in the Viscosity column, the relaxation time λem in the Relaxation time column, and the extensibility parameter Lem in the Extensibility column.
LPTT
For LPTT, in each Branch raw enter the polymer viscosity μem in the Viscosity column, the relaxation time λem in the Relaxation time column, and the extensibility εem in the Extensibility column.
EPTT
For LPTT, in each Branch raw enter the polymer viscosity μem in the Viscosity column, the relaxation time λem in the Relaxation time column, and the extensibility εem in the Extensibility column.
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Use the Add button () to add a row to the table and the Delete button () to delete a row in the table.
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Use the Load from file button () and the Save to file button () to load and store data for the branches in a text file with three space-separated columns.
Discretization
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog box. Select shape function type for the components of the auxiliary viscoelastic tensor. The default setting is Linear.
Thermal Effects
Viscoelastic properties have a strong dependence on the temperature. To model the temperature dependence, the solvent and polymer viscosities and relaxation time are modified to αTμs, αTμem, and αTλem.
Select a Thermal function — None, Arrhenius, Williams–Landel–Ferry (WLF), Exponential, or User defined. When the default, None, is kept, the thermal function αT(T) is set to unity and the viscosities and relaxation time are not modified.
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Thermal Effects
Initial Values
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog box. Enter initial values or expressions for the components of the auxiliary viscoelastic tensor. The initial values can serve as an initial condition for a transient simulation or as an initial guess for a nonlinear solver. The default values are 0 N/m2. Note, that if several branches are specified, the initial values entered above are applied to all branches.
Note: The Interior Walls boundary condition and Pair conditions are not applicable on the boundaries that are adjacent to the Fluid properties nodes with different number of branches.