The Viscoelastic Flow Interface
The Viscoelastic Flow (vef) interface () is used for simulating single-phase flows of viscoelastic fluids. The physics interface is only suitable for incompressible flows.
The equations solved by the Viscoelastic Flow interface are the continuity equation for conservation of mass, the Navier–Stokes equations, augmented by an elastic stress tensor term, and a constitutive equation that defines the extra elastic stress contribution.
The Viscoelastic Flow interface is available for stationary and time-dependent analyses. The main feature is Fluid Properties, which adds the Navier–Stokes equations, continuity equations, and the constitutive relations between the extra elastic stress term and the velocity gradient. The Fluid Properties feature provides an interface for defining the fluid material and its properties. Viscoelastic, Newtonian, and Inelastic non-Newtonian constitutive relations are available. The boundary conditions are essentially the same as for the Laminar Flow interface. When this physics interface is added, the following default nodes are also added in the Model Builder:
Fluid Properties
Initial Values
Wall
Then, from the Physics toolbar, add other nodes that implement, for example, boundary conditions and volume forces. You can also right-click Viscoelastic Flow to select physics features from the context menu.
Settings
The Label is the default physics interface name.
The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.
The default Name (for the first physics interface in the model) is vef.
Physical Model
This node specifies the properties of the Viscoelastic Flow interface, which describe the overall type of fluid flow model.
Include Gravity
When the Include gravity check box is selected, a global Gravity feature is shown in the interface model tree.
Also, when the Include gravity check box is selected, the Use reduced pressure option changes the pressure formulation from using the total pressure (default) to using the reduced pressure. For more information, see Gravity.
Dependent Variables
The following dependent variables (fields) are defined for this physics interface:
Velocity field u and its components
Pressure p
If the Viscoelastic constitutive relation is selected, the Fluid Properties node also adds as variables the components of the elastic stress tensor.
For all other settings, see The Laminar Flow Interface.
Flow of Viscoelastic Fluid Past a Cylinder: Application Library path CFD_Module/Single-Phase_Flow/cylinder_flow_viscoelastic