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[ansysuser]

Hello,

In the Fluent manual, section 18.3.4, there is a discussion of different schemes for interpolating near the interface of two phases in the VOF model. For example, the geometric reconstruction, donor-acceptor, etc.  But there is no mention of how to choose one or the other and I do not see anywhere in the dialog boxes where these options are listed.

How can I choose one of these schemes in Fluent?  

 

Thanks

[Karthik Remella]

Hello,

You can pick the method from Solution Methods in Fluent. Here is a screenshot.

Hope this helps.

Best,

Karthik

[ansysuser]

I see. Thank you.

That does help, except in my drop down list I only have Compressive and Modified HRIC.  I was hoping to use Geo-Reconstruct because it looks like it will help with the phases mixing too much.  Do I need some other setting enabled before the Geo-Reconstruct is available?  Please let me know.

The problem I am having is that the phases (liquid water and incompressible air) are mixing way beyond what is physical.  Here is an example of the contour of the water phase fraction 1 second after an air bubble rises to the top of a closed container. The container is 1cm wide with 0.1mm mesh sizing. In reality, no such massive phase gradient would exist like this.  I am wondering if Coupled Level set would be a better way to go.   Any suggestions would be helpful.  

[Karthik Remella]

Hello,

These options depend on your analysis type as well as your pressure-velocity coupling. If I remember correctly, steady VoF with coupled solver will not show you Geo-Reconstruct. However, a transient analysis with SIMPLE coupling should show you the Geo-Reconstruct option.

Best,

Karthik

 

 

[ansysuser]

Thanks again, Kremella.

 

I am performing a transient analysis with SIMPLE, as shown in the SS below.

 

[Karthik Remella]

Hello,

Which version of Fluent are you using?

Best,

Karthik

[ansysuser]

I am using the version that came with Workbench 2019 R3

[Karthik Remella]

Could you please change your VoF model to Explicit and check your Solution Methods? Are you seeing all the options now?

[Keyur Kanade]

The options depend on explicit and implicit formulation. 

For your reference, 

Regards,

Keyur

 

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[ansysuser]

Thanks, Kremella. Yes, I was able to change to Geo-Recon by selecting explicit. However, the solution is now not correct.  

Thanks, kkanade. I am not sure what those plots are supposed to be, but I do see there is a difference!  

For my problem, the issue is that I am getting way too much phase mixing to be physical.  See the contour plot above.

At the start of the simulation, I have a water zone and an air zone (with patching) that have a vertical boundary between them. Then the solution starts.  Here is the difference at time step 8.  Note the implicit solution evolves into a very nice motion that looks physically correct, except the extreme amount of phase mixing. The explicit formulation gets these strange ripples.  Any suggestion would be much appreciated. (Note I had to drop the time step size to keep convergent. All other settings are the same except the Geom-Recon for the explicit formulation.)

 

[Keyur Kanade]

For explicit, geo-reconst is recommended. 

Can you please show some image with model for boundary conditions used?

Regards,

Keyur

 

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[ansysuser]

Thank you kkanade.

 

I just discovered that when I loaded the case and data files into the new Fluent module to try the explicit method, the wall contact angle was reset to the default value of 90 degrees. I am unsure why this happened, as all other settings remained unchanged.  As such, I will run with the correct contact angle and come back to start another post if needed.

 

Thanks again, I appreciate everyone's efforts.