[Ehab44]

Hi,

I am working on a 3D problem where I have a rotating impeller inside a stationary cylinder.
The impeller diameter is 93 mm and the stationary cylinder is 102 mm diameter.
I am solving this case using multiple reference of frame method. So, I divided the annulus between the rotating impeller and the stationary cylinder into two zones: a rotating zone enclosing the impeller and a stationary zone adjacent to the stationary cylinder.

I need to know how can I select the diameter of the interface dividing the two zones.

I solved the case using three different interface diameters. One at 96 mm diameter, another one at 99 mm diameter and the last one at 100 mm diameter.

I plotted the pressure, relative velocity and absolute velocity across the whole annulus and I can not see any jumps at the different interfaces except the relative velocity charts. But, this jump occurs in all the interfaces not a certain one.

I need to know if there is a criteria for selecting the interface or what should I do ?.



Yours,
Ehab

[ghost82]

Hi Ehab,
it seems that your steps are correct, imaging that you set 3 interfaces, one for the top, one for the bottom and one for the lateral faces.
Discontinuities at interfaces are known, read this from the fluent user guide:

"CFD-Post and ANSYS FLUENT display contours differently in the vicinity of a hanging node. ANSYS FLUENT takes values from cells only on one side, causing a discontinuity of contours. In CFD-Post, the hanging node is made to be a conformal node and takes values from cells on both sides, making a smoother contour."

Can't you eliminate interfaces in your mesh?
If your impeller geometry is complicated you can mesh with tetra the rotating zone, and meshing the outer zone with hexa, without create interfaces, or mesh all with hexa.

Daniele

[Ehab44]

Hi Daniele,


It seems I was not clear enough.

The diameters I talked about are for three different cases and for the circumferential interface between the impeller and the stationary cylinder.

So, lets be more clear.

- The axis of rotation of the impeller is perpendicular on the cylinder axis.
- The annulus thickness is 4.5 mm.

So I tried to solve the case three times as follows:
1- The thickness of the rotating zone is 1.5 mm and the stationary zone is 3 mm.
2- The thickness of the rotating zone is 3 mm and the stationary zone is 1.5 mm.
3- The thickness of the rotating zone is 3.5 mm and the stationary zone is 1 mm.


I hope this is clear.


Yours,
Ehab

[ghost82]

Ok, you talk about interfaces, but you mean the common faces between rotor and stator, not defined interfaces in fluent, true?
Post some picture about discontinuity.

In general, there is no advice in fluent guide about the diameter of the rotor, the guide only describes that the rotor volume must contain the rotating impeller.

Daniele

[Ehab44]

Hi Daniele,

I can not attach the files here because the capacity is restricted.

Could you send me your email ?.


Yours,
Ehab