## Fluids

Topics relate to Fluent, CFX, Turbogrid and more

#### Melting a warm object through ice

• Paco Sheeran
Subscriber

Hi,

I'm a newbie to fluent. I am trying to model the melting of a warm object through a block of ice and see how fast it will melt said ice and get to the bottom based on the temperature at the surface of the object. When I simulate this in fluent using solidification/ melting, the liquid fraction shows that ice is melting below the object, but it is not moving, it's basically floating. I checked that gravity is on but it still doesn't move. Is this simulation possible with fluent and if so what is the procedure for it? Thank you

Paco

• Rob
Ansys Employee

Read how the solidification model works: it won't melt to give you floating ice.

• Paco Sheeran
Subscriber

I’m sorry I might not have explained it very well, or I am not quite understanding your explanation sadly. I’m not exactly looking to simulate ice floating. More so trying to simulate a warm object melting through the stationary ice. The warm object I simulated in the ice stays in position even when the ice around it has melted. It should be falling down with gravity if there is no ice holding it up. At least that was my assumption.

I believe it is possible for Ansys fluent to do this because I have seen the concept published in journal articles such as the one linked below

Does this make sense, thank you

• Rob
Ansys Employee

Ah, so a falling solid?  OK. Still not easy, but have a look at the 6DOF (possibly 1DOF) solver and moving mesh.

• Paco Sheeran
Subscriber

Hi again,

I tried that 6 dof solver and moving mesh and I think I made some progress, thank you. I just keep running into what appears to be a common error which is negative cell volume detected. I have tried what appears to be the typical problem which is too big of a mesh and timesteps too fast but neither of those really seem to work. I attached a picture of the setup. Do you have any thoughts on why this may be happening when trying to do melting/solidification simulations? The other solutions I have found on other forums don't really seem to work and most of those solutions are not for melting/solidification. Thank you

• Rob
Ansys Employee

I can't remember if full remeshing is availble for hex/quad elements. Check the documentation, you may want to retry with tet/tri.

• Paco Sheeran
Subscriber

Ok I tried with both Triangles and Tri and does not seem to be changing anything. Could there be any other source of the error? Thanks

• Rob
Ansys Employee

The above are hex cells, so I assume you also tried with tri as asked. If you work out the motion speed how many time steps does it take to cross a cell?

• Paco Sheeran
Subscriber

Yeah so I have tried it with all the possible mesh types I see in mesh, I showed the tri on this one I think.

So the motion speed is sort of what I am trying to find with the simulation in the first place so I am not entirely sure how to calculate it. If I do the same simulation without 6dof on though I find that after 5000 time steps of 0.001s the liquid/solid boundary layers appears to have moved about 1.5 cells. So knowing that I am assuming it would take about 3333 times steps to get across the cells currently. Is that a reasonable way to assume that?

• Rob
Ansys Employee

More-or-less. However, if you move more than one cell length the risk is you turn the cells inside out: the nodes can't reconnect (remesh) before they're corrupted.