Analysis of Variation of Natural Frequency and Resonant Stress of Blade

A compressor blade of low aspect ratio is a typical shell-type structure and its natural frequency and vibratory stress are sensitive to a manufacturing tolerance. In designing a blade, the designer should take the variation of the vibration characteristics into account, and evaluate the mechanical strength of the blade. This paper, first, proposes an analysis method for predicting the resonant stress due to the interaction force between the vane and blade, using 3-D CFD and the modal analysis method based on 3-D FEM. Rig tests of the compressor are carried out, and the measured frequencies and vibratory stresses are compared to predicted values, and the validity of the proposed method is verified. In the second place, a practical analysis method for predicting the variation of the natural frequency and vibratory stress of the blade is proposed, where the variation of the vibration characteristics such as a natural frequency and a resonant stress is evaluated by the first order second moment method in addition to 3-D CTD and 3-D EEM. The calculated results are compared with measured ones. From the results, it is confirmed that the variation of the vibration characteristics can be predicted by the simple method proposed in this paper.