Learning Forum

[Rusbel.Ayala]

Greetings, I am trying to simulate water droplets with a high contact angle rolling along a plate (wall), induced by incoming air velocity. I have achieved decent results with fixed quad mesh but now I am looking to adapt the mesh as the droplets roll into one another. Unsure how to properly edit mesh over each timestep. 

I am aware that the newest versions of Fluent have Predefined Criteria with multiphase-VOF, in addition to General Apation Controls. 2019 R3 is currently at my disposal. 

Current mesh domain elements: 2e-5 m 

Key Fluent settings: 

• Transient, pressure-based, gravity enabled
• Model: VOF, explicit formulation, implicit body forces on
• Surface tension force modeling: on, continuum surface force on, wall adhesion on, surface tension coe: 0.072 (water/air [n/m])
• water contact angle: 155°
• viscous model: k-omega sst 
  • Interest in LES model - Bounded Second Order Implicit Transient Formulation not available with VOF 

[Danica]

Hi,

Have a look at using automatic mesh adaptation to define a refinement criterion and coarsening criterion with a cell register within a certain region that is characteristic to the edge of the bubbles. This will allow for an automatic mesh adaptation for your predefined timesteps specific to the cell register criteria.

Take a look at 33.2. Refining and Coarsening (ansys.com)

[Rusbel.Ayala]

I found that some Field Variable options (Derivative and Scaling Options) cause Fluent to instantly crash. I am currently getting some mesh adaption, but the CFL number exceeds 250. With the droplet boundary causing some unusual flame like results.

Any recommendation as what ‘Minimum Edge Length’ or ‘CellVolume’ (I have a 2D case) should be?

Finally, when I try to use Model: LES (currently using SST K-Omega with mesh adaption), none of the options for mesh adaptation work.  Causing an instant crash. I am aware that SST k-omega is the preferred model for VOF/Multi-Fluid VOF applications. 

Cheers!

[not.lah.enough]

Hi Danica,

Sorry if I cut into the discussion all the sudden since I have more or less similar issue regarding adaptive mesh. I'm using v2023 R2 and despite the VOF multiphase already chosen, the adaptive VOF can't be chosen. Been using adaptive mesh a few times using different releases in the past, I've never encountered this problem until now. I posted the problem in another topic elsewhere in the forum (to no avail so far), so is there anything I missed or is this even a bug? Thanks in advance.

[Rob]

Give us a chance - you posted "overnight" UK time! Danica's no longer with Ansys so there may be a delay in her answering....

[not.lah.enough]

No worries! I think the team can address it any time - not that much of a stress on my side.

[Danica]

Hi,

A possible way of improving this issue is to use turbulence damping, see screengrab below. However, this is only available in the newer updates so you may want to update your version to try this