Rotordynamics: Eigenfrequencies of a Rotating Blade
Model ID: 9288
High rotational speed in rotating machineries can result in centrifugal forces of considerable magnitude. The forces induced by the rotation give rise to two counteracting effects: stress-stiffening and spin-softening (or centrifugal softening). The former is caused by the stationary stress field created by the centrifugal force and acts to increase the stiffness of the body, and so increase its resonance frequencies. At the same time, any radial displacement away from the axis of rotation increases the centrifugal force, while motion toward the axis decreases it. This model shows how the combined effect from stress-stiffening and spin-softening affects the fundamental eigenfrequencies of a blade attached to a rotating shaft. The eigenfrequencies obtained from this model are compared to analytical solutions.
The model also illustrates how to add the effect of Coriolis forces. Furthermore, a parametric study is performed to evaluate the effect of the angular velocity of rotation on the eigenfrequencies of the blade. The result is represented in the form of a Campbell diagram.
|Campbell diagram created from the parametric sweep output file. Notice the crossing modes, which are misinterpreted because of the sorting of the natural frequencies.|