# Rotating zones¶

Rotating zones can be used to simulate rotating systems such as turbines, fans, ventilators and similar systems. This chapter shows how a simulation with a rotating part can be set up on the SimScale platform.

## Preparation¶

Firstly, create a mesh which contains a zone around the rotor. The page Using snappyHexMesh to create a mesh for rotating geometries shows how this can be done.

## Creation of a rotating zone¶

In the tree, navigate to “Advanced Concepts” and add a rotating zone. Two types of rotating zones are supported:

### Multi Reference Frame (MRF)¶

• This approach uses a ‘rotating frame of reference’ that modifies the governing equations in the rotating zone. Additional source terms that incorporate forces in the rotating reference frame are taken into account that simulate a rotation effect in the flow.

Important

MRF is a “Steady-State” approximation of the transient rotating motion at an ‘instance’ of time. So, the body/mesh is not physically rotated. One must make sure that the problem does not include large-scale transient phenomena.

• Performing MRF simulations is computationally much less demanding than transient modeling. Hence, if the problem is setup correctly, MRF provides good approximations with less computational effort and considerably less compute times.
• MRF rotation is defined by ‘rotation center’, ‘rotation axis’, and ‘angular velocity’.

### Arbitrary Mesh Interface (AMI)¶

• In the AMI approach a mesh interface is created between the moving and stationary parts of mesh. At each time step, The rotating zone is physically rotated and quantities are interpolated at this interface to allow realistic movement of the rotating parts.

Important

AMI simulations are fully “Transient” and therefore are computationally much more expensive than MRF. They take all transient effects into account and are usually sensitive to the ‘time step length’. AMI could be specified as oscillating or full rotating motion.

The rotation is define by the following properties:

• Rotation center
• Rotation axis
• Angular velocity

Alternatively, the Rotation axis and Angular velocity could be combined into Radial velocity. The oscillating rotating motion requires an Amplitue vector instead of the Rotation axis. Once the rotation is defined, it should be assigned to the rotating zone that is created at the meshing time.

Defining a rotating zone

In this example, the rotation center is located at the middle of the rotator hub. The rotation axis points downstream towards the nacelle. The rotation speed (parameter “angular velocity”) is given in units rad/s (the value from the example gives one full revolution per second).

Finally, a cell zone for the rotation must be selected. Please switch the viewer to volume selection mode, click on the cell zone and click on “Add selection from viewer”. You can also use the check boxes to select the cell zone.

This concludes the setup of a rotating zone.