FEM EquationFlow

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

 * 1) After adding an Elmer solver as described here, select it in the tree view.
 * 2) Now either use the toolbar button [[Image:FEM_EquationFlow.svg|24px]] or the menu.
 * 3) 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:
 * : To be set to true for incompressible flow for more stable discretization when the Reynolds number increases.
 * : 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.
 * : If set to true pressure Dirichlet boundary conditions can be used. Also the mass flux is available as a natural boundary condition.
 * : 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:
 * : The type of convection to be used in the [[Image:FEM_EquationHeat.svg|24px]] Heat equation. Note: For thermal flows it must be set to Computed (the default).
 * : 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):
 * 1) Reduce the, see the nonlinear system settings.
 * 2) Increase the value for, see the nonlinear system settings.
 * 3) Reduce the number of CPU cores used, see the FEM preferences.
 * 4) Increase the mesh density (make it more fine).

Analysis Feature Information
The flow equation takes the following analysis features into account if they are set:


 * [[Image:FEM_ConstraintFlowVelocity.svg|32px]] Flow velocity boundary condition
 * [[Image:FEM_ConstraintInitialFlowVelocity.svg|32px]] Initial flow velocity condition
 * [[Image:FEM_ConstraintPressure.svg|32px]] Pressure load
 * [[Image:FEM_ConstraintInitialPressure.svg|32px]] Initial pressure condition

Results
The results are the velocity in $$\rm m/s$$ and the pressure in $$\rm Pa$$. 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.