Root Flexibility and Untwist Effects on Vibration Characteristics of a Gas Turbine Blade

摘要

Blade vibration is generally recognised as one of the most significant causes of high cycle fatigue failure in gas turbine engines. The blade root flexibility often cannot be determined easily in the assessment of blade vibration behaviour and exclusion of this effect may lead to a false prediction of vibration characteristics. This report outlines a study of root flexibility and aerofoil untwist effects on the vibration characteristics of a turbine blade using 3-D finite element analysis, together with laboratory testing. The vibration characteristics of the blade were analysed and the predicted results were correlated with laboratory test results at ambient temperature. The vibration characteristics of the blade assembly during engine operation were then predicted through a pre-stressed modal analysis, including the centrifugal stiffening effect, the temperature effect and the interactions between the blade and disc. The root flexibility effect due to differences in clamping condition was then investigated in detail. Untwist effects due to creep were also revealed in this analysis.