Learning Forum

[alucardz14]

 

My problem description:

I'm trying to solve the problem about the interface between water and air in a microchannel.

Bubble is stayed at the cavity and water is injected through the inlet.

Surface tension force is dominant rather than inertia and viscous forces.

 

Numerical results:

Inlet velocity is 0.01 m/s.

However, The numerical results show that the spurious velocity of 0.2 m/s at the interface near the wall.

 

Please see the attached *.cas and *.dat files.

 

 1) zoomed area (vectors of velocity components)

2) entire domain (contours of velocity magnitude)

Questions:

First, why a (non-physical) spurious current is observed when using the VOF method.

Second, how to reduce this spurious currents?

  

 

[Rob]

You may find refining the mesh and reducing the time step to work. Also have a look in the Release notes and documentation: there are some numerics that can help but I can't remember which version they're in. 

[alucardz14]

Thanks for your information. As far as I know, small time step with finer mesh can be the reason that spurious currents are getting worse. (Brackbill's aritcle, https://doi.org/10.1016/0021-9991(92)90240-Y)

I already did some simulations to check the effect of mesh and time step. It did not help with convergence and accuracy.

 

 

[DrAmine]

You are right.
You probably need to look into beta feature after interracial dissipation. Other trick is to increase the number of smoothing steps for surface tension (docu)

[alucardz14]

Some tests were performed by adjusting smoothing steps  (solve>set>surface-tension options in the TUI).

The magnitude of the velocity was decreased by increasing smoothing step, however, the spurious currents (vortex) was maintained.

So, numerical results have still non-physical behaviors.

[DrAmine]

Try the other suggestion too. Spurious velocity is an evergreen topic for all multiphase codes.
Make a sensitivity run without st force and with st stress instead of Brackbill force.