[OldEngineer]

ANSYS-CFX Free suface model.


The simulation es very simple: Box with water and air; no movement.



CFX-Pre: Homogeneous model, free surface model standard, isothermal, laminar, fluid bouyancy model: density difference, surface tension mode: none, interface transfer: free surface.


Initial conditions are: zero velocity, volume fraction of water and air and pressure. Steady state.


InitialZ (height of water): 0 [m]
initial water volume fraction: if((z<InitialZ), 1, 0)
initial air volume fraction: 1 - OceanoVFAgua
initial pressure: if((z<InitialZ), ((997 [kg m^-3] - 1.185 [kg m^-3])*g*(InitialZ-z)), 0 [Pa])


After run, the results are:
hidrostatic pressure OK
low or very velocities (1e-3 m/s), but they must be zero
and
Normalised Imbalance Summary |
+--------------------------------------------------------------------+
| Equation | Maximum Flow | Imbalance (%) |
+--------------------------------------------------------------------+
| U-Mom-Bulk | 1.2143E+06 | 0.0000 |
| V-Mom-Bulk | 1.2143E+06 | 0.0000 |
| W-Mom-Bulk | 1.2143E+06 | -0.0005 |
| P-Vol | 2.9663E-04 | -100.0000 |
+----------------------+-----------------------+---------------------+
| Mass-Water | 1.6829E-15 | -100.0000 |
+----------------------+-----------------------+---------------------+

Does anyone know if this is correct? Why these imbalances?



Thanks in advance.
Best regards.

[Gert-Jan]

Mass imbalance is based on amount of inflow. If there is no inflow, then there is no reference and mass imbalance is 100% in your case.

[OldEngineer]

Thank you very much for your help, Gert-Jan.