The Rotating Machinery, Fluid Flow Interfaces
Moving Mesh
The Rotating Machinery, Fluid Flow interfaces rely on ALE (arbitrary Lagrangian–Eulerian) moving mesh functionality for their rotating domain and free surface implementation.
Rotating Domains
When a Rotating Machinery, Fluid Flow interface is added using the Model Wizard, a Rotating Domain node is added automatically in the Model Builder under the Definitions > Moving Mesh node. It contains settings for specifying the rotation of one or several domains. By default, All domains are selected. Under the Rotating Domain, you can exclude any nonrotating fluid domains. For both 3D and 2D components, the Rotation type should be set to Specified rotational velocity.
Select a Rotational velocity expression — General revolutions per time (the default), Constant revolutions per time, General angular velocity, or Constant angular velocity.
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For Constant revolutions per time or General revolutions per time, enter a value or expression respectively in the Revolutions per time input field and optionally an Initial angle. The angular velocity in this case is defined as the input multiplied by 2π.
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For Constant angular velocity or General angular velocity enter a value or an expression respectively in the Angular velocity input field and optionally an Initial angle.
3D Components
For 3D components, select the Rotation axis base point, rax. The default is the origin. Select the Rotation axis, urot, the z-axis is the default. If the x-axis is selected, it corresponds to a rotational axis (1, 0, 0) with the origin as the base point, and correspondingly for the y-axis and z-axis.
2D Components
For 2D components, enter coordinates for the Rotation axis base point, rax. The default is the origin (0, 0).
Deforming Domain
When using the Free Surface feature, a Deforming Domain must first be added in the Model Builder under the Definitions > Moving Mesh node. Within the Deforming Domain, the mesh position is solved for to match the current position of the free surface. On exterior boundaries not defined as a free surface, the mesh is constrained to move only in the tangential direction. On boundaries which are internal with respect to the fluid (separating deforming domains from ordinary fluid domains), the mesh is constrained to its initial position.
If there is more than one deforming domain, these must not intersect. Also a deforming domain cannot intersect with a rotating domain.
Mesh Smoothing Type
This setting controls the method used to solve for the mesh displacement within deforming domains. The Mesh smoothing type can be chosen to be Laplace, Winslow, Hyperelastic, or Yeoh (the default) smoothing. Note that the equations used for each smoothing type have different properties. For the Yeoh mesh smoothing type, also specify a Stiffening factor (default: 10). See Smoothing Methods in the COMSOL Multiphysics Reference Manual for more information.
Free Surface