I am doing a transient rotor stator calculation with a rotating and stationary component which rotates about the global z-axis. I set up
monitor points for the x- and y-components of the force, but they do not behave as I would expect. For example, when the blade
is parallel to the x-axis, most of the force should be in y-direction, whereas most of the force should be in the x-direction when
the blade is perpendicular to the x-axis. I don't see this type of change, however, as the x-component forces oscillates slightly about
a non-zero value as the simulation proceeds. The force components that I calculate in Post are different from the solver monitor values
and do behave as I would expect. What causes this behavior?
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In a transient rotor stator calculation, the rotating frame mesh is not really rotated during the simulation, as all meshes (stationary and rotating frames) retain their original position, although the position of the 2 profiles on either side of the transient rotor-stator interface are moved relative to each other, according to the physical time. The solver monitor values of force components therefore correspond to the initial position of the blade in the global frame. The values computed in CFX-Post are different, since the rotating components are rotated according to their physical position when read into CFX-Post, but this is done as a post-processing step. To see the true physical force components in the x, y or z directions based on the global coordinate frame, the force_x() etc. expressions used to define the Solver Monitor values must be transformed during the solver run using the real transformation (rotation) of the blade so that the force components are are reported correctly for each time step. |
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