Fundamental Eigenfrequency of a Rotating Blade

Application ID: 9288

The eigenfrequencies of a rotating blade are studied in this benchmark. It shows how stress stiffening and the combined effect from stress stiffening and spin softening affects the fundamental eigenfrequency.

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 application 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 the 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.

This model example illustrates applications of this type that would nominally be built using the following products: