Numerical Analysis of Liquid Droplet Impingement on Pitted Material Surface with Water Pool of Various Depth

Abstract

Liquid droplet impingement erosion occurs at the elbows in steam pipes where droplets impinge at high speed. In the actual pipe wall which numerous droplets always impinge, it is predicted that both a liquid film exists on a pipe wall surface and, on the other hand, this surface is also eroded by repeated droplet impingement. Therefore, the liquid film and roughness on the material surfaces are considered to exist mixed on the actual impinged point of droplets. In this study, by using an in-house fluid/material two-way coupled numerical method that considers reflection and transmission on the fluid/material interface, the numerical analysis of the phenomenon of liquid droplet impingement on a pitted surface with a water pool is conducted. From the analysis results, the impinged pressure at the moment of impingement is reduced by a water pool. However, as the cavitation bubbles are generated in the bottom and top of the droplet after the impingement and then the cavitation bubble of the bottom side collapses, the collapse pressure which greatly exceeds the pressure of the droplet impingement occurs, and the equivalent stress also increases greatly there. Therefore, this analysis result may indicate one reason why the erosion progresses deeply at the pit part in an actual pipe wall thinning.