Specify Wall Motion

If you select Real Wall as the boundary condition type, with Wall Motion you can simulate tangential motion of a wall by specifying the motion direction and the velocity. The available motion types are translation (for cylindrical surfaces) and rotation (for surfaces of revolution). The moving wall is treated by Flow Simulation as the tangential velocity boundary condition at the wall.

You can simulate the translational motion of the wall along an axis or curve. If the wall does not change its geometry relative to the surrounding fluid, you can specify simultaneous translation and rotation of the wall.

Procedure

Select Coordinate System, Axis or Curve defining the motion direction or axis of rotation:
- Reference Axis
  
  In the flyout FeatureManager design tree, select a reference Axis. To create an axis, go to Insert > Reference Geometry > Axis.
  
  For the Translation motion type, the direction of the axis defines the direction of the wall motion (if the velocity value is positive). For the Rotation type of motion, the selected axis is assumed to be a rotational axis and the angular velocity obeys the right-handle rule. The axis direction is indicated by the axis name that is shown near the axis origin.
- Axis of Coordinate System
  
  In the flyout FeatureManager design tree, select a reference Coordinate system (or keep the default Global Coordinate System Reference axis, select an axis of this coordinate system which either defines the motion direction for the Translation type (if the velocity value is positive), or the rotation axis for the Rotation motion type (the angular velocity obeys the right-handle rule). To create a reference coordinate system, go to Insert > Reference Geometry > Coordinate System.
  
  Note:
  The reference axis and coordinate system specified under Selection are only used to define a Dependency and must not be confused with the coordinate system and axis selected under Wall Motion and used for specification of the motion direction.
- Tangent to Curve
  
  In the flyout FeatureManager design tree, select a Curve coinciding with the surface profile curve to define motion of a cylindrical surface along the profile curve.
Define the type of motion and specify the translation or angular velocity, or both:
- To specify the translational motion of the wall, enter the value of Translation Velocity .
  
  The translation type of motion can be applied to any cylindrical surface, i.e. a surface created by linear translation (along the generatrix) of a profile curve, to simulate motion along the curve (or along a line in case of a flat face). For a flat wall, the wall motion direction is denoted by the selected reference axis or the axis of the selected coordinate system. For a non-flat cylindrical surface, the surface motion direction is specified as tangent to the profile curve.
  
  Figure 1. Translation Motion: 1) origin, 2) motion direction, 3) curve, 4) generatrix.
- To specify rotation of the wall, enter the value of Angular Velocity .
  
  The rotational type of motion can be applied to any surface of revolution, i.e. a surface created by the rotation of a curve, e.g. a cylinder or cone.
- If the wall is located within a rotating reference frame, you can select Absolute to specify the velocity values relative to the non-rotating reference frame or select Relative to rotating frame to specify velocity values relative to the rotating reference frame (see “Relative to rotating frame” for details).