# Momentum Sources

Momentum sources can be used to simulate fans, ventilators and other similar devices without having to model the exact geometry and motion of the device. For instance, one may want to model an axial fan whose dimensions and output velocity are known. With this feature it is possible to assign the velocity output to a cylinder with the same cross section as the fan.

## Preparation

• Momentum sources can be used in every analysis type, except Compressible and Multiphase.
• Momentum source must be assigned to a volume, defined through a geometry primitive (cartesian box, sphere and cylinder) or a cell zone.
• It is recommended to refine the mesh in the vicinity of the source (e.g. refinement region downstream of the source), in order to better capture the dynamics of the flow.

## Creation of a momentum source

• In the simulation tree, navigate to Advanced Concepts and add a Momentum Source.
• Simscale currently supports only the Average velocity momentum source. This simulates a linear momentum defined by a velocity vector $$\vec{u} = [u_x u_y u_z]$$.