Static and Dynamic Analysis of 48″ Steel Last Stage Blade for Steam Turbine

Abstract

The 3000 rpm 48 inch blade for steam turbine has been developed with the application of new design features. The last stage moving blade was designed with integral cover, mid-span tie-boss connection, and fir-tree dovetail. Blades are continuously coupled by the blade untwist due to the centrifugal force, so vibration control and increased structural damping are provided. The last stage airfoil was optimized from view of minimization of its centrifugal force which helped to reach higher safety factors. The blade was well tuned in order to have eigen-frequencies safely away from possible excitation. Because of connection members, the number of the resonant vibration modes can be reduced by virtue of the vibration characteristics of the circumferentially continuous blades. In order to develop the 3000 rpm 48 inch blade, the latest analysis methods were applied to predict dynamic behavior of the bladed structure. Coupled rotor-blade analysis was also aim of the attention. To validate calculated results the verification measurement such as rotational vibration tests was carried out in the high-speed test rig. The test rotor was fitted with the actual full scale 48″ blades. Relation of the friction damping of the bladed structure on amount of excitation level was also monitored and evaluated.