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The Analysis of Blade Vibration due to Random Excitation

This Report gives an account of the experimental measurement of the power spectra of wave-forms derived from vibrating blades in axial compressors under running conditions. This enables the damping factor of the blades to be found, and these damping factors agree reasonably well with theoretical estimates of the aerodynamic damping. There is no significant decrease in the damping factor when the blades stall. The Report includes theoretical estimations of the length of data which has to be examined to get accurate measurements of the R.M.S. amplitude and the power spectrum. The amount of data required is much greater for the power spectrum, but even for the R.M.S. amplitude it is surprisingly long. The Report also includes a theoretical prediction of the effect of variations of air density and blade material density under otherwise similar conditions.