Learning Forum

[farzad pour]

Hi, 
Problem: Free falling of a disk in water
I want to simulate the free falling of a disk in a water tank located under the free surface. The disk diameter is 5 cm, the tank is 30*30 cm, and the height of the tank, which is filled with water, is 1m. I used the 6-DOF method; I simulated the case as the working fluid was air without any problem.! But as I changed it to water, I couldn't get any converged solution. I tried both the overset mesh method and dynamic mesh, but still, I can't solve this case! Also, I used the VOF model to consider the air and free surface, (primary fluid is air, and operation density was considered 1.225 (air), also 0 was tried). By the VOF model, there is a relatively good convergency, but during the solution, it will diverge even the CFL number is less than 0.01 (time step size about 10^-5).
I tried the SIMPLE and Couple methods for pressure and velocity field coupling, but they didn't work; it seems due to the high viscosity and density of water, which are higher than air, some points are need to be considered in the simulation.
Could you help me? Do you have any suggestions/comments?

[SRP]

Hi,

Can you please the setting that you have applied during VOF and with 6DOF?

Did you tick implicit body force during setting vof model?

Ensure that the properties of air and water are correctly defined in their respective regions.Since you are using the VOF model, make sure that you have set up the interface capturing parameters appropriately. This includes refining the mesh near the free surface and employing a sharp interface capturing method.

[farzad pour]

Thanks for your reply. 

yes. I have activated body force and the properties of air and water are correctly defined.

About the free surface: indeed, the disk is fully submerged. It releases inside of the water, 5 cm below the free surface.