Learning Forum

[Pollovr]

I'm currently performing a classical sloshing problem: water and air inside a tank accelerated under resonance; that gives away a free surface that is exponentially growing. So far it runs perfectly when I insert a submerged vertical baffle in the middle of the tank, but when I set up the same tank but rotate the baffle 45?, the solution get's oddly unstable (see link to another discussion where I explain in more detail the simulation https://forum.ansys.com/discussion/23824/how-does-under-relaxation-factors-urf-affect-volume-of-fluid-vof) The simulation is transientnIs it possible to use URF but just in a couple of time-steps? Maybe using a command line in the Original Settings? It should be used only in the beginning, after a few iterations, there should be any. I've been thinking that I could set them up in the beginning and then, after some iterations, set all of them to 1 (something like in this link https://forum.ansys.com/discussion/22971/fsi-volume-of-fluid-calculations-not-patching-the-water-phase ) I want to use them temporarily because my simulation is transient and I don't want them to tame or dampe the results over time.nIf anyone knows the command line please let me know!nThank youn

[DrAmine]

Sure you can use it but and more efficient and I will say more fidelity if you rather use smaller time step. Is adaptive time step something u can think about?n

[Pollovr]

Yes! I've used it before, but somewhy whenever it starts the simulations, time-steps quickly escalate to high values (although the continuity residuals are really high). I've tried to use small time-steps but it won't help. I tend to always follow the same pattern: continuity residuals start to decrease and all of a sudden they go as I as 1e2. I'm using LES and I've tried all of the pressure and momentum algorithms, but it's always the same...nI only find URF to be helpful, although they make the results smaller than they would otherwise be.n

[DrAmine]

What did you try? Why LES? Do you LES quality mesh? Which version are you using?n

[Pollovr]

I tried all of the force and pressure algorithms (PRESTO, body force weighted...). Because I benchmarked LES against experiments and it gave the best results. The mesh quality is good enough: extracted from literature, it was benchmarked and it gave a really good accuracy. ANSYS 2020R2.n

[DrAmine]

You can look in the help after vof stabilization methods. They are driven by TUI commands With 21R1 things are also accessible from GUI.nnIf you have exp data and the results are matching even with reducing urfs which might work if running outer loops every time step then it is fine.n

[YasserSelima]

You can use a UDF Define_Adjust (This function is recalled every iteration) .. and modify the URF between iterations using Set_Rp_RealnThe variables names are mom elax, and pressure elax. ntry using iterative instead of the non-iterative. Might solve the problemn