Effects of Plate Edge Thickness on Droplet Generation Caused by Water Film Breakup at the Plate Edge

Abstract

Droplets generated at trailing edges of low-pressure steam turbines strike the leading edge of moving blades, resulting in severe damage by erosion. Although the trailing edges of stationary blades employed in the steam turbine industry are often sharpened to produce fine droplets, this process requires further investigation. In this study, water film flows on a plate and breakup patterns are observed and measured to investigate the breakup behavior and the effect of the plate edge thickness. First, to determine the general characteristics of droplet formation of water film flows, the droplet diameter frequency distributions, which significantly affect erosion damage, are measured for several flow conditions. Profiles of frequency distribution of the droplet diameters exhibit on approximately linear in a semilog graph. Water lumps formed on the plate edge are expressed as a spanwise wavelength and initiate the primary breakup of the water film, while fine droplets whose diameters are similar to the critical diameter are generated and are assumed to contribute significantly to erosion damage. The effect of edge thickness on droplet diameter frequency distribution and the spanwise wavelength are observed. The plate edge thickness does not affect the frequency distributions of the droplet diameter. However, it does affect the spanwise wavelength, which is related to the intermittent discharge of water from the edge. The spanwise wavelength and discharged water period become longer when the plate edge thickness increases. Based on an experiment involving the highest airflow velocity, the discharged water frequency is similar to that generated by a general turbine rotation speed.