The following conditions and limitations apply to using multiple materials in Ansys Polydata:
The task must be steady, transient, or an evolution.
The sub-task must be Generalized Newtonian (isothermal or not).
There is no PMAT dependency defined on a material property.
There is no strain dependence on viscosity, and no reinforcements.
There are no moving parts, no sliding meshes, and no bubbling.
There are no species, and there are no chemical reactions.
As soon as one of the above rules is invalid, the additional materials are inaccessible and not used. The following additional considerations and limitations also apply to the multiple-material approach:
Viscous heating, inertia, average temperature, and gravity are defined in the first material, and then applied to all other materials.
The different materials can have different viscosity laws. For instance, the first fluid can use the Bird-Carreau law, while the second fluid can use the Bingham law, etc.
The solver automatically creates and transports one species for each fluid.
The multiple-material approach is compatible with Convergence strategy for rheology/slip and the Convergence strategy for thermal flows options in the Numerical parameter menu.
Each material must enter in the flow domain by at least one inflow (and only inflow conditions). This criteria is not checked by Ansys Polydata.
You must not use other boundary conditions to allow fluid to enter the flow domain, otherwise the fluid will not be properly identified from the inlet. This criteria is not checked by Ansys Polydata.
An additional solver is used for determining the flow rate of each fluid leaving the outlet section of the flow domain. In this manner, you can check the mass conservation of each fluid.
All the materials must be defined in the same system of units.
As an extension, you can define materials that are not used by any inflow. The materials will not be used in Ansys Polydata, therefore not affecting the cost of the simulation. Note that the settings for viscous heating, average temperature, inertia, and gravity will be used for all fluids according to the selections made for the first fluid.