Rotating Zones

Rotating zones can be used to model rotating systems such as turbines, fans, ventilators, and other similar systems. This documentation page shows how simulation with rotating zones can be set up.

CAD Requirements

Simulations with rotating zones require special attention during CAD preparation. The requirements are described at length in the following knowledge base article:

How to Prepare the CAD for Simulating Rotating Zones?

Simulation Setup

In the simulation tree, navigate to Advanced concepts and click on the ‘+’ button next to Rotating zones. Two types of rotating zones are supported: Multiple Reference Frame (MRF) and Arbitrary Mesh Interface (AMI).

(MRF) Rotating Zones

The MRF rotating zone is a steady-state approximation of the transient rotating motion at an “instance” of time. Therefore, the mesh/body is not physically rotated. One must make sure that the problem does not include large-scale transient phenomena.

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. These simulate a rotation effect in the flow.

Performing MRF simulations is computationally much less demanding than transient modeling. Hence, if the problem is set up correctly, MRF provides good approximations with less computational effort and considerably less computation time.

Setup of an MRF Rotating Zone

Figure 3 shows the setup interface for a MRF rotating zone:

• Under Origin, the user should define the center point coordinates for the rotating zone;
• The Axis entry defines around which axis the rotating zone will be spinning. The direction of rotation is given by the right-hand rule;
• The final input is the Rotational velocity, given in \(rad/s\) or \(º/s\). Note that the rotational velocity can be parametrized in SimScale, as this article shows;
• Lastly, assign the rotating zone to its corresponding volume.

(AMI) Rotating Zones

AMI rotating zone 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.

In the AMI approach, a mesh interface is created between the moving and stationary parts of the 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.

Setup of an AMI Rotating Zone

Figure 5 shows the setup window for an AMI rotating zone:

• Motion type can be specified as Oscillating or full Rotating motion. An oscillating motion also requires the definition of its Amplitude;
• The Rotation can be defined as an Angular rotation or vector rotation;
• A Point on the rotation axis should be provided for the rotating zone;
• The Rotation axis needs to be defined. The right-hand rule also applies in this case;
• Lastly, the Rotational velocity should be set, and a rotating volume should be assigned. Again, the rotational velocity supports a parametric definition.

Mesh Preparation

In the mesh set up, the rotating zone volume needs to be defined as a Cell zone. The workflows to define cell zones are different, depending on the meshing algorithm. Find below the steps for each of the cases.

Standard Mesher

When using the standard mesher with physics-based meshing enabled, the algorithm automatically creates cell zones for the regions selected for any of the entries in Advanced concepts.

When Physics-based meshing is disabled, the user needs to manually define the cell zones, as in Figure 7:

Hex-Dominant Meshes

For hex-dominant meshes, the creation of a cell zone is done by adding surface refinements. When adding additional refinements in a hex mesher choose the surface refinement option.

In the settings panel, make sure Cell zone is set to ‘With cell zone’ and give a name accordingly to distinguish between multiple cell zones.

For a cell zone to be created, a closed volume (or all faces of the closed volume) needs to be assigned to the surface refinement. If successful, all cells enclosed by the assigned volume will be grouped together.

Learn more about surface refinements in our hex-dominant mesh document:

Hex-dominant

Tutorials

For a practical guide on how to set up and use rotating zones, take a look at the following tutorials:

• Advanced Tutorial: Fluid Flow Simulation Through a Centrifugal Pump
• Advanced Tutorial: Flow Simulation Through a Water Turbine

Last updated: August 13th, 2024