How to... move global coordinate systems (reference frames) to axis of rotation Ansys Fluent

An important element of each CFD and structural simulation is the precise definition of the global coordinate system. An improperly located coordinate system can lead to many difficulties - primarily in analyzes where the movement of individual elements is defined.

Example of bad geometry position vs coordiante system 

A perfect example of a wrong definition of a coordinate system is a fan spinning around its axis. In this post I will explain the difficulties resulting from such a mistake and how to avoid it. In the first picture in the top view you can see that the axis of rotation is necessarily shifted from the correct axis of the fan subdomain. This will prevent the fan from rotating around its axis. Moving the axis will rotate the entire subdomain around the moved point.

Option to move geometry into good position 

To avoid this, the correct coordinate system should be defined at the geometry creation stage (Design Modeler, Space Claim).

The next illustration shows (red frame) how to change the position of the entire model relative to the global coordinate system. The entire path is presented on the example of Design Modeler.

By clicking on the Create menu, we choose the Body Transformation option and then Move. Then, in the Move Type option, we define the change of the model position in relation to the planes. As the Source Plane, we select the subdomain reference plane. After We select the plane of the global coordinate system as the direction of the model transfer. In the Preserve Bodies option, we choose NO because we do not want to duplicate the model. Select all model elements and press GENERATE.

And that's how we actually transferred the model to the global coordinate system. In the next steps, the position of the coordinate system, the axis of rotation and the direction of gravity (preprocessor) should be verified.The last illustration shows the properly defined coordinate system for the fan subdomain (yellow circle).

Right position of geometry for motion models in Fluent