Learning Forum

[Timothée Levionnais]

Hello,

I am currently trying to make a simulation with a rotating fan and an obstacle near it. The fan is in a rotating fluid zone to simulate the rotation of the fan and the body is in a stationary fluid.

There is then 4 zones in the model : The environment (fluid), the rotor zone (fluid zone inside of the environment), the fan (dead zone inside of rotor zone), the body (dead zone inside of environment)

The problem I am facing is that when describing geometry in Fluent meshing and selecting that the geometry consists in fluid regions and solid regions and/or voids, the boundary between the two fluid regions is detected as non fluid-fluid interface and changed automatically from "internal" to "wall", not allowing the fluid to move freely from one zone to another like it should be the case. However, when describing it as only fluid regions, the boundaries are defined correctly.

I would like to know if I am understanding the description of the geometry wrongly or if it is indeed "fluid and solid and/or voids" that should be selected. If it is, how could I avoid the problem of having my boundaries changed automatically ?

Thanks in advance for any help you could give me,

[Federico]

Your understanding of the Geometry description is correct. Fluent will attempt to assign boundary types automatically based on boundary names and their topology relative to the rest of the domain.

You can try providing descriptive names to the relevant boundaries prior to bringing into Fluent Meshing. Fluent will recognize words like "internal", "wall", "inlet", for example.

You can also change the boundary type in the Update Boundaries taks.

[Timothée Levionnais]

Hello,

Thanks for your answer. However my problem is that even after changing the boundary types to internal in Update Boundaries task, Fluent automatically changes it to wall because it detects it as a non fluid-fluid interface even though I haven't described the types of the zones yet. Is there any way I can force it to be internal ?

[Rob]

Check the zone settings in Fluent Meshing - are they assigned as fluid or solid? 

[Timothée Levionnais]

They're not yet referenced, the choice of zones is after the choice of boundaries, and changing the two zones on the two sides of this boundary to fluid doesn't adjust the boundary back to internal

[Rob]

You can set the cell zone types in Fluent Meshing too. The connecting surface shouldn't be walls unless you weren't very careful with the boundary labels. 

[Timothée Levionnais]

I am indeed setting the cell zone types in Fleunt Meshing and the name of the faces on the interface is "rotor int" and "rotor ext", which shouldn't cause any problems... Also the thing that is weird is that it works great when I select "only fluids" option when describing the geometry, and I can even put some zones as dead zones when the geometry is described this way

[Rob]

Did you click the "walls between fluid zones" option by accident? Is the mesh conformal between the rotor & stator? 

[Timothée Levionnais]

I do not see this option, all I can select is "Will you cap openings and extract fluid rgions ?" set on NO, and "Change all fluid-fluid boundary types from wall to internal ?", also on NO. I have tried with and without those options but the problem I face happens before and is not corrected by the definition of the zones that comes after

[Rob]

"Change all fluid-fluid boundary types from wall to internal ?", also on NO.    YES! 

[Timothée Levionnais]

Ok, the problem seems to be solved, I don't have the automatic change of boundary anymore. I would then like to know why did it work to put some dead regions in the geometry when it was described as containing only fluid regions ?

[Rob]

Possibly something in the geometry labels or domain space. I can't see what you've done, or the settings you've used so it's difficult to diagnose.