Abstract
Turbine blade stress level at resonance with nozzle stimuli were studied experimentally using a developed test facility which could cause blade failure. The experiment was carried out on single blades and shrouded group of blades. Factors concerned with resonant stress were analyzed from measurement of velocity distribution across nozzle outlet, exciting forces and damping properties, and found as follows.
Exciting forces were much affected with the pitch ratio of blade to nozzle and less with the axial clearance between nozzle and blade. The damping properties varied with blade construction, stress level and vibration mode for the same material. Particularly it was noted that the 1st tangential out of phase mode vibration had smaller root damping, since it had a similar movement at blade root to a tuning fork. Blade failure could occur due to vibration at stress level near to the fatigue limit stress.
From the result an allowable design stress was discussed referring to the practice of a turbine manufacturer.
