November 22, 2019 at 6:50 amalucardz14Subscriber
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.
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)
First, why a (non-physical) spurious current is observed when using the VOF method.
Second, how to reduce this spurious currents?
November 22, 2019 at 11:32 amRobAnsys Employee
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.
November 23, 2019 at 12:12 pmalucardz14Subscriber
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.
November 25, 2019 at 6:08 amDrAmineAnsys EmployeeYou 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)
November 26, 2019 at 4:19 amalucardz14Subscriber
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.
November 26, 2019 at 6:34 amDrAmineAnsys EmployeeTry 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.
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