SIMPLIFIED METHOD TO MEASURE UNSTEADY FORCES ACTING ON THE VIBRATING BLADES IN CASCADE.

Abstract

In measuring the aerodynamic damping characteristics of a cascade, when the air velocity is so high that the compressibility of the air can not be ignored, the vibration frequency becomes very high in order to keep a certain value of reduced frequency, and it is difficult technically to make all the blades in the cascade vibrate at the same time at so high frequency. In the method described, only the center blade in cascade is vibrating amnd the others are at rest, and the unsteady forces induced on the vibrating blade and other neighboring blades at rest are measured and they are linearly combined with arbitrary interblade phase angle, thus the unsteady forces are equivalent to the one in the case when all the blades in cascade are vibrating at the same time with arbitrary interblade phase angle.