A Model of the Motion of Erosion-Hazardous Droplets in Steam Turbines’ Interblade Channels

Abstract

A model is discussed describing the interaction of liquid droplets with interblade channel walls in condensing steam turbines. It is based on the experimental data on the impact of individual droplets on a surface that are presented in the form of statistical models with free empirical parameters. The motion of liquid particles is simulated using individual streams of droplets under the action of aerodynamic drag force from the steam. Their interaction with the interblade channel surface is determined by the kinetic energy of impingement affecting the subsequent process. The proposed numerical approach deals with two droplet impact cases, i.e., a droplet deposits on the profile of the blade airfoil or becomes a source of secondary moisture leaving the surface. Liquid droplets formed in the latter case are also simulated using streams. The empirical coefficients of the model were selected based on the results of experimental investigation of the motion of liquid particles in a flat vane cascade. Parameters of wet steam flow in an interblade channel were determined using a laser flow diagnostic system and the particle tracking velocimetry (PTV) method implemented on its basis. The investigations were performed in a two-dimensional flow. The measured patterns of liquid particles’ motion were compared with predicted ones. The velocity distributions of primary and secondary droplets were examined in six characteristic regions of the flat cascade. Causes responsible for disagreement between the experiment and the predictions were outlined. It has been found that the angle at which droplets impinge on the interblade channel wall has a considerable effect on characteristics of the formed secondary droplets. Verification of the model demonstrated a satisfactory agreement of the experiment with the predictions.