Reduction of Resonant Stress of Turbine Blade by Use of Asymmetric Vane Spacing: Effect of Multi-resonance on Reduction of Vibratory Stress

It is well known that asymmetric vane spacing can result in decreased levels of the excitation at specific frequencies. In this paper, the resonant response reduction of turbine blades due to asymmetric vane specing is studied theoretically for the most probable asymmetric vane in which the vane count of the upper and lower half is slightly different. First, a method for predicting the vibratory stress of the blade for the asymmetric spacing vane is proposed including the effect of the multi-resonance due to the excitation force clustered around the harmonic corresponding to the number of the vane count. Secondly, a parametric study is carried out to clarify the influence of the multi-resonance on the blade resonant response reduction for typical shrouded blades of steam turbines. Experiments are also carried out to verify the effect of asymmetric vane spacing on resonant response reduction using a turbine blade of turbocharger. From these results, it is concluded that asymmetric vane spacing is very effective for reduction of resonant stresses of a shrouded blade of steam turbine.