Structural design of blade root and strength evaluation in low pressure steam turbine blade

Abstract

Increase of the power demands and the environmental condition has made the design newlineof the steam turbines undergo tremendous changes in recent years. The steam path newlinecomponents like geometry, shape of the airfoil, blade roots and shape of the low pressure newlinecasing are the critical components in the structural design of low pressure blades. Earlier, the newlineeffort to increase overall turbine efficiency was mainly focused on the high pressure and newlineintermediate pressure sections. It has become essential to increase the efficiency and life in newlinelow pressure sections by optimizing the variables like fillet radius, root width, land height and newlineso on. Simulation is carried out with scaled models for design optimization. newlineThe criticality lies in establishing the contact between the blade tang and disk crown newlineacross the circumference. Estimating the butting forces at the tang region is an another newlinechallenge. The von Mises stresses are high at the tang which leads to crack growth and leads newlineto fracture near the tang. In the present work one such effort is made in eliminating the tang newlinewith minor modifications at the blade root butting area in the blade and disk root fillet newlinethrough linear, bilinear stress and fatigue analysis using 2D models. newlineIn the first part of the work, the baseline and proposed models of HP bladed disk are newlineanalysed using FEA to estimate the von Mises stress and the same is compared with the newlinetheoretical values obtained from the basic equations and Peterson s Stress Concentration newlineFactor chart. Peterson s chart is effectively utilized to modify the blade root by reducing the newlinestress concentration factor in the proposed model. The stress concentration reduction in the newlineblade root fillet for high pressure cycle is examined using FEA in plane stress condition.