Water drop erosion on turbine blades : Numerical framework and applications

When small droplets are formed in the wet steam stage of a steam turbine, they may impact the blade surface at a high velocity and repetitive impacts cause water drop erosion, which emerges as one of the primary reliability concerns of the turbine. We propose an effective numerical framework that couples fluid mechanics with solid mechanics. The movements of water drops in a blade channel are analyzed based on the solution of the flow field of water steam in turbine, and impact statistics such as impact frequency, velocity, and position are obtained as the working condition and particle size are varied. A nonlinear wave model is established for high velocity liquid-solid impact, from which the characteristic impact pressure in liquid and peak impact stress in solid are obtained; the solutions are then superimposed with the pathways of water particles, and a fatigue analysis is carried out to elucidate the mechanisms of water drop erosion. The lifetime map on a blade surface with two different materials ( 1Cr13 and Ti-6A1-4V) under typical working conditions are obtained, in terms of operation hours, and the most dangerous water drop erosion regions and operating conditions of the steam turbine are deduced. © 2008 The Japan Institute of Metals.