P.Satyanarayana, Subramanyam Pavuluri, Dr. A.Siva Kumar
The present paper deals with a issue of steam turbine blade efficiency. Based on the theory of vibration of mechanical structures, the dynamic behavior of a turbine blade, blades or the blades disc assembly can be predicted. The evaluation of a blade design is made by combining the dynamic behavior with the nature of the fluctuating forces. The basic design consideration is to avoid or to minimize the dynamic stresses produced by the fluctuating forces. Since these forces are periodic one has to consider a several number of these harmonics coincides with any of the natural frequencies of the blades. Generally a Campbell diagram is drawn to ascertain this. In this connection an attempt is made on estimate the dynamic behavior of a blade and the stresses occurring in the blade of steam turbine in the last stage due to centrifugal force. The stresses occurring at the disc groove where it gets in contact with root are analysis natural frequencies and mode shapes were obtained and Campbell diagram were plotted and verified with the experimental data. Since the blade is long and twisted it needs a lot of input to accurately define the complete geometry. Blade geometry is defined by giving different profile data at different heights. The results and conclusions are presented for a study concerning the durability problems experienced with steam turbine blades.
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