FEM ConstraintFlowVelocity/de

Beschreibung
Applies a flow velocity as boundary condition to an edge in 2D or to a face in 3D.



Anwendung

 * 1) Either press the button   or select the menu.
 * 2) Select the target Edges or Faces.
 * 3) Press the  button.
 * 4) Uncheck Unspecified to activate the necessary fields for edition.
 * 5) Set the velocity values or  specify a formula.

Formulas
It is possible to define a velocity by specifying the velocity profile as formula. In this case the solver sets the velocities at the different positions according to the profile.

To specify for example the velocity profile

$$\quad v_{x}=6\left(y-1\right)\left(2-y\right) $$

for $$y\in[1;2]$$ (assuming that e.g. a pipe has the wall at y = 1 m and y = 2 m)

enter this to the Formula field:

This code has the following syntax:
 * the prefix Variable specifies that the velocity is not a constant but a variable
 * the coordinate the velocity profile is based on is Coordinate 2, meaning Y
 * the velocity values are returned as Real (floating point value)
 * MATC is the prefix for the Elmer solver that the following code is a formula
 * tx is the variable in the formula

Hinweise

 * Any vector component that should be the result of the solver must be set as Unspecified.
 * If the target face or edge is not aligned with the main Cartesian coordinate system, it is possible to set the option Normal to boundary.
 * If Normal to boundary is checked, the normal vector to the selected edge or face is X and it will be oriented away from the mesh domain.
 * For example, if a flow of 20 mm/s of air should enter the domain, then with Normal to boundary one must input -20 mm/s in the Velocity x field.


 * For a wall with non-slip condition, set all velocity components to 0.
 * For a symmetry condition, set the the flow to 0, Unspecified, Unspecified) if Normal to boundary is checked.