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 that order):
 * 1) reduce the, see the nonlinear system settings
 * 2) increase the value for, see the nonlinear system settings
 * 3) reduce the number of used CPU cores, see the FEM preferences
 * 4) increase the mesh density (make it more fine)

Constraint Information
The electrostatic equation takes the following constraints into account if they are set:


 * [[Image:FEM_ConstraintFlowVelocity.svg|32px]] Constraint flow velocity
 * [[Image:FEM_ConstraintInitialFlowVelocity.svg|32px]] Constraint initial flow velocity
 * [[Image:FEM_ConstraintPressure.svg|32px]] Constraint pressure
 * [[Image:FEM_ConstraintInitialPressure.svg|32px]] Constraint initial pressure

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