Wall boundaries in a MRF rotating zone

Hello,

I want to simulate the flow through a centrifugal pump (steady-state). Do I need to assign a rotating wall boundary to walls of the impeller in the rotating zone? If not, would it be wrong (result wise) to do so?

Additionally, what do I do with stationary walls (e.g. casing walls) that are also located in the MRF volume that is necessary for the rotating zone? Do I need to assign a rotating wall boundary condition with a zero velocity (rad/s) to it?

Thank you so much in advance!

Hi there!

When using an MRF region, everything that is inside the cell zone that you created will be rotated, so it is important that you can create a zone that only includes the rotating parts.

Also, there is no need to assign the rotating faces to Rotating Wall, let them be automatically modelled as No-slip walls by leaving them unassigned :slight_smile:

Have a look at the following documents to use as reference:

Best regards,
Fillia

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Hi Fillia,

thank you for your detailed answer. Last week I watched the SimScale webinar about Turbomachinery. As far as I’m aware your US colleague aunni created a rotating zone for a centrifugal pump that also cuts through the stationary casing walls of the pump. Additionally, he defined a rotating wall boundary conditions to all the rotating walls inside the rotating zone.

Is this workflow specific to the new Simerics solver in SimScale?

Best regards!

Hi, just quickly adding some notes:

Anything inside a rotating zone will be rotating - you can verify this by plotting velocities on the post-processor and analyzing the velocities on the walls. In short, if you leave walls inside a rotating zone with “No-slip”, they will already be rotating (as Fillia mentioned).

The second case, where we have a wall that should not rotate but is inside the rotating zone requires caution. Only in this case it’s necessary to define a rotating wall boundary condition with zero angular velocity, otherwise the portion of the wall inside the rotating zone will rotate.

This procedure is covered in section 2.2.3. from the water turbine tutorial:

To answer your question: at the moment it’s necessary to define the walls as rotating walls for the subsonic analysis. There will be a patch soon, to apply this condition automatically, so it works exactly like in the OpenFOAM solvers.

Hope this helps.

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