FEM EquationFlow
|
|
| Menu location |
|---|
| Solve → Flow Equation |
| Workbenches |
| FEM |
| Default shortcut |
| None |
| Introduced in version |
| 0.17 |
| See also |
| None |
Description[edit | edit source]
This equation calculates viscous fluid flows using the Navier-Stokes equations.
For information about the math of the equation, see the Elmer models manual, section Navier-Stokes Equations.
Usage[edit | edit source]
- Add an
Elmer solver.
- Select it in the Tree View.
- There are several ways to invoke the command:
- Press the
Flow Equation button.
- Select the Solve →
Flow Equation option from the menu.
- Press the
- Change the equation's solver settings or the general solver settings if necessary.
Solver Settings[edit | edit source]
For the general solver settings, see the Elmer solver settings.
The flow equation provides these special settings:
- DataDiv Discretization: To be set to true for incompressible flow for more stable discretization when the Reynolds number increases.
- DataFlow Model: The flow model that should be used. The default Full includes convection and time derivative terms in the model. No convection switches off the convection terms and the Stokes model switches off the convection terms and the (explicit) time derivative terms.
- DataGradp Discretization: If set to true pressure Dirichlet boundary conditions can be used. Also the mass flux is available as a natural boundary condition.
- DataVariable: Optional only for calculations in 2D: You can change the default of 3 to 2.
Note: In this case none of the flow velocity boundary conditions can have a specified z-component.
Equation:
- DataConvection: The type of convection to be used in the
Heat equation.
Note: For thermal flows it must be set to Computed (the default). - DataMagnetic Induction: If set to true the magnetic induction equation will be solved along with the Navier-Stokes equations.
Notes for Convergence[edit | edit source]
If the solver results do not converge, you can try these things (in the given order):
- Reduce the DataRelaxation Factor, see the nonlinear system settings.
- Increase the value for DataNonlinear Newton After Iterations, see the nonlinear system settings.
- Reduce the number of CPU cores used, see the FEM preferences.
- Increase the mesh density (make it more fine).
Analysis Feature Information[edit | edit source]
The flow equation takes the following analysis features into account if they are set:
Flow velocity boundary condition
Initial flow velocity condition
Pressure load
Initial pressure condition (introduced in 0.21)
Notes[edit | edit source]
- Except for calculations in 2D, for all above boundary conditions it is important that they act on a face or body. Boundary conditions for 3D set to lines or vertices are not recognized by the Elmer solver.
- Since
Pressure load can only be set to faces, pressure loads cannot be used for calculations in 2D.
- If there is no
Pressure load set,
Initial pressure condition will only be taken into account if DataGradp Discretization is set to true.
Results[edit | edit source]
The results are the velocity in and the pressure in . If there is no Initial pressure condition and
Pressure load given, the resulting pressure will be relative not absolute. Since pressure must act on a face, absolute pressure results cannot be obtained in 2D simulations.
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