FEM EquationFlow
FEM EquationFlow |
Menu location |
---|
Solve → Flow equation |
Workbenches |
FEM |
Default shortcut |
None |
Introduced in version |
0.17 |
See also |
None |
This equation calculate viscous fluid flows using the Navier-Stokes equations.
For info about the math of the equation, see the Elmer models manual, section Navier-Stokes Equations.
Usage
- After adding an Elmer solver as described here, select it in the tree view.
- Now either use the toolbar button or the menu Solve → Flow equation.
- Change the equation's solver settings or the general solver settings if necessary.
Solver Settings
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 constraints 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
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).
Constraint Information
The electrostatic equation takes the following constraints into account if they are set:
- Constraint flow velocity
- Constraint initial flow velocity
- Constraint pressure
- Constraint initial pressure (introduced in version 0.21)
Notes
- Except for calculations in 2D, for all above constraints it is important that they act on a face or body. Constraints for 3D set to lines or vertices are not recognized by the Elmer solver.
- Since Constraint pressure can only be set to faces, pressure constraints cannot be used for calculations in 2D.
- If there is no Constraint pressure set, Constraint initial pressure will only be taken into account if DataGradp Discretization is set to true.
Results
The results are the velocity in and the pressure in . If there is no Constraint initial pressure and Constraint pressure constraint given, the resulting pressure will be relative not absolute. Since a pressure must act on a face, absolute pressure results cannot be obtained in 2D simulations.
- Materials: Solid, Fluid, Nonlinear mechanical, Reinforced (concrete); Material editor
- Element geometry: Beam (1D), Beam rotation (1D), Shell (2D), Fluid flow (1D)
Constraints
- Electromagnetic: Electrostatic potential, Current density, Magnetization
- Geometrical: Plane rotation, Section print, Transform
- Mechanical: Fixed, Displacement, Contact, Tie, Spring, Force, Pressure, Centrif, Self weight
- Thermal: Initial temperature, Heat flux, Temperature, Body heat source
- Overwrite Constants: Constant vacuum permittivity
- Solve: CalculiX Standard, CalculiX (new framework), Elmer, Mystran, Z88; Equations: Deformation, Elasticity, Electrostatic, Electricforce, Magnetodynamic, Magnetodynamic 2D, Flow, Flux, Heat; Solver: Solver control, Solver run
- Results: Purge, Show; Postprocessing: Apply changes, Pipeline from result, Warp filter, Scalar clip filter, Function cut filter, Region clip filter, Contours filter, Line clip filter, Stress linearization plot, Data at point clip filter, Filter function plane, Filter function sphere, Filter function cylinder, Filter function box
- Additional: Preferences; FEM Install, FEM Mesh, FEM Solver, FEM CalculiX, FEM Concrete; FEM Element Types
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