Learning Forum

[Samira Nazari]

Hello everyone, I would like to simulate the impact of a water droplet onto a surface with a contact angle of 110° and might also need a dynamic contact angle. I aim to define the interface boundary condition between the water and air zone. I tried to simulate it with Ansys CFX and Ansys Fluent but I could not get any results. As I turned on the surface tension model to add contact angle it considered the contact angle between air and water and the droplet changed its shape in the same spot instead of dropping down to the surface. I would appreciate it if anyone can help me. 

 

 

 

[Rob]

What happened when you tried to run the model? Have you looked at the various VOF examples in Help and Learning? 

[Samira Nazari]

Hi Rob,

In Ansys CFX, I defined two different domains (air and water). As I turned on the surface tension model (a), the droplet stayed at the same spot, just changing the shape(b). I tried different numbers of elements and also decreased and increased the timestep to see any changes, but nothing happened. I got good results when I did not turn on the surface tension model.

In Ansys Fluent, I used the same geometry, defined two domains, and allocated the interface boundary condition between them. In the "mesh interface" window, "matching" was selected. The gravity direction is downward, and I obtained this result (c) with the multiphase setting of wall adhesion (d). I also selected Pressure outlet and Pressure inlet boundary conditions to see if they will change or not.

Then, I tried another method in Ansys Fluent with just having one domain and using the "Cell registers" part. I got good results; however, I am looking to have the interface boundary condition to get more accurate results. I searched, and I could not find anything. I would appreciate it if you have some ideas or some links to help me in this regard.

[Rob]

For Fluent use ShareTopology in the geometry tool or Fluent Meshing. You really want an interior at that location. Interface will work, but it's overkill for this application. 

Registers work well, but turn on the smoothing when patching in the liquid. That should smooth out the initial surface to a reasonable level (assuming the mesh is sufficiently well refined).  You may also want to review the automatic mesh refinement (adaption) for VOF. 

[Samira Nazari]

Thank you so much Rob.

[Yogesh Tope]

And using jump adhesion instead of wall adhesion 

Hello, I’m working with the droplet bouncing mechanism on hydrophobic surface with contact angle ranging from 110 to 150 degrees and it’s asking for cell based smoothing for surface tension and how to I do it. Can anyone help

 

[Rob]

No, it's telling you that is what Fluent has set. 

 

[Yogesh Tope]

So should I continue my work without any changes in settings or procedure?

[Rob]

For that bit of the model, yes. I can't comment on any other settings. 

[Yogesh Tope]

Ok thnx for reply