MES: Równanie przepływu

From FreeCAD Documentation
Revision as of 13:10, 22 November 2023 by NewJoker (talk | contribs) (Created page with "Dla ogólnych ustawień solvera zobacz konfigurację solvera Elmer.")

MES: Równanie przepływu

Lokalizacja w menu
Rozwiąż → Równanie przepływu
Środowisko pracy
MES
Domyślny skrót
brak
Wprowadzono w wersji
0.17
Zobacz także
brak

To równanie analizuje przepływ płynów lepkich przy pomocy równań Naviera-Stokesa.

Informacje o teorii stojącej za tym równaniem można znaleźć w dokumencie Elmer models manual, w sekcji Navier-Stokes Equations (równania Naviera-Stokesa).

Użycie

  1. Po dodaniu solvera Elmer zgodnie z opisem na stronie solvera, zaznacz go w widoku drzewa.
  2. Teraz wciśnij przycisk lub wybierz opcję Rozwiąż → Równanie przepływu z menu.
  3. Zmień ustawienia solvera dla równania lub ogólne ustawienia solvera jeśli to konieczne.

Ustawienia solvera

Dla ogólnych ustawień solvera zobacz konfigurację solvera Elmer.

The flow equation provides these special settings:

  • DANEDiv Discretization: To be set to true for incompressible flow for more stable discretization when the Reynolds number increases.
  • DANEFlow 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.
  • DANEGradp Discretization: If set to true pressure Dirichlet boundary conditions can be used. Also the mass flux is available as a natural boundary condition.
  • DANEVariable: 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:

  • DANEConvection: The type of convection to be used in the Heat equation.
    Note: For thermal flows it must be set to Computed (the default).
  • DANEMagnetic 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):

  1. Reduce the DANERelaxation Factor, see the nonlinear system settings.
  2. Increase the value for DANENonlinear Newton After Iterations, 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:

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 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 DANEGradp Discretization is set to true.

Results

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.