Learning Forum

[Dubey92]

I am modelling Selective Laser Melting(SLM) in FlUENT using Explicit VOF. One phase is inert gas and the other is metal. I am applying Laser over the particle bed using a UDF. The solution starts and initially the convergence is very good. Then after some time steps, the continuity equation does not converge. Other equations converge. There is a oscillatory behaviour in the convergence of the equations. I have attached the image. Any help is much appreciated. I am using Explicit VOF with a Courant number 0.05 and the Global courant number is 0.1.

[Rahul Kumar]

Hello, 

Have you setup any monitors to see how the simulation is behaving? If not, I would suggest you to do so. You might also want to reduce the URFs to check if it would help. Check this link for solution strategies : 22.8. Solution Strategies for Multiphase Modeling (ansys.com)

[Dubey92]

Hello Rahul, thanks for your reply. I have not set up any monitors. I am new to this type of modelling. Can you please suggest some parameters which I can monitor? As for the URFs, I am using a URF of 0.6 for the momentum, 1 for density and 1 for body forces. I am attaching the figure which shows my model domain. The laser starts but it does not move forward as the continuity equation is not converging smoothly.

[Rob]

Check the local velocity. If the material has/is melting are you still respecting the local courant number? I'd also review the temperature field, why have you got randomly scattered facets at 2500K or so in the image?

[Dubey92]

Rob, thanks for your suggestion. I am using a very small courant number for VoF(0.05). I am applying the Laser source on on the top interfacial cells between the gas and the metal. The temperature values are in the range what I expect. The issue is only with the convergence of continuity equation. I haven't checked the velocity values yet but will do.

[CKS]

Hi Dubey92, I'm having the same issue as well. I managed to run 75% of the VOF simulation for the SLM process and suddenly the continuity doesnt converge.

Can you drop me an email (chun.sit@monash.edu) where I can show you some of my (incomplete) simulation results?

[Dubey92]

 

Hi. You can mail me at Edited as requested Rob

 

[Rob]

I would usually delete email addresses, and will do so once you (Dubey) let me know you're in contact. In return, please post any resolution/notes that will help others with this application. 

[CKS]

I have got Dubey's response. Yo may proceed to deleting the emails. Thanks and I may open a new ticket for my specific issues later.

[Rob]

While we're waiting for Dudley, check the flow field just before the model diverges. Is anything changing or about to change? Ie is the model flow timescale about to shorten for some reason?