Finite element analysis of dynamic characteristics for steam turbine interlocked blades with integral shroud

Abstract

Integral shroud construction is an advanced technique to improve reliability for steam turbine blades. The Chinese-built 1029mm freestanding blade is remodeled to interlocked blade with integral shroud based on design principle of interlocked blade of steam turbine. Models and methods used to calculate contact tightness between adjacent shrouds are developed. With the aid of FEA software ALGOR, twist-back angle of blade and contact tightness of adjacent shrouds are analyzed and calculated; natural frequencies and mode shapes of freestanding blade and interlocked blades are mainly investigated, and the relationship between the natural frequencies of interlocked blade and rotating speed is investigated; and also the resonant rotating speed chart (Campbell chart) of the interlocked blade is presented. The interlocked blades are examined for the "3-coincide point" resonance under nodal diameter number m≤6 within rotating speed range of 2850∼3090 rpm. As compared with freestanding blade, the dynamic characteristics of integrally shrouded blade are improved greatly, so the operation security and reliability of blades are enhanced. The achievements gained in the paper have provided a variety of effective numerical method for studying dynamic and static characteristics of steam turbine blade, and will find important engineering application in development and modification design of the integrally shrouded blades.