# Wall boundaries in a MRF rotating zone

**URL:** <https://www.simscale.com/forum/t/wall-boundaries-in-a-mrf-rotating-zone/93673>\
**Category:** Fluid Flow / CFD\
**Created:** [August 15, 2021, 8:55am UTC](https://www.simscale.com/forum/t/wall-boundaries-in-a-mrf-rotating-zone/93673 "2021-08-15T08:55:38Z")\
**Posts on this page:** 1\
**Showing post:** 2

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**Author:** ![tsite](https://www.simscale.com/forum/user_avatar/www.simscale.com/tsite/32/47909_2.png) [@tsite](https://www.simscale.com/forum/u/tsite)\
**Post date:** [August 16, 2021, 9:12am UTC](https://www.simscale.com/forum/t/wall-boundaries-in-a-mrf-rotating-zone/93673/2 "2021-08-16T09:12:21Z")

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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 🙂

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

> **[How to Prepare the CAD for Simulating Rotating Zones | SimScale](https://www.simscale.com/knowledge-base/how-to-prepare-cad-for-simulating-rotating-zones/)**
>
> For the simulation of rotating parts, one needs to prepare the CAD. This article describes everything that needs to be done in advance.

> **[Rotating Wall Versus Rotating Zone | Documentation | SimScale](https://www.simscale.com/knowledge-base/how-to-choose-between-rotating-zones-and-rotating-walls/)**
>
> How to choose between a rotating wall and a rotating zone? SimScale explains the difference and what to choose for different scenarios.

> **[How to Prepare the CAD for Simulating Rotating Zones | SimScale](https://www.simscale.com/knowledge-base/how-to-create-a-rotating-zone/)**
>
> For the simulation of rotating parts, one needs to prepare the CAD. This article describes everything that needs to be done in advance.

> [@What is the Difference between a rotating Zone and Rotating Wall?](https://www.simscale.com/forum/t/what-is-the-difference-between-a-rotating-zone-and-rotating-wall/84235):
>
> I have been attempting to simulate a ducted fan at high speed rotation 2000 rad/s, with the fan blades as rotating walls. however the result does not look correct to me. what is the What is the Difference between a rotating Zone and Rotating Wall in a steady state simulation with compressible flow? also which should I use. Thanks in advance

Best regards,  
Fillia

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