Flow Characterization of a Water Drop Impinged onto a Rigid Surface at a High Speed and Normal Angle in the Presence of Stagnant Air at Ambient Conditions

Abstract

High-speed droplet impact is of great interest to power generation and aerospace industries due to the accrued cost of maintenance in steam and gas turbines. The repetitive impact of liquid droplets, that are formed due to vapor condensation in steam turbines or water injection into industrial gas turbines for evaporative cooling purposes, onto rotor blades at high relative velocities, results in the blade erosion. This is known as Liquid Impingement Erosion (LIE) and it is crucial to understand the hydrodynamics of the impact in order to identify the consequent solid response before addressing the LIE problem. The numerical study of the droplet impingement provides the transient pressure history generated in the liquid. Determining the transient behavior of the substrate, in response to the pressure force exerted due to the droplet impact, would facilitate manufacturing new types of blades that are more resistant to LIE. To that end, characterizing the impact of compressible liquid droplets impinged at very high velocities, up to 500 m/s, on rigid solid substrates and thin liquid films is the main objective of the present work. A droplet size of 500 µm, which is encountered frequently in LIE problem, and a liquid film thickness of 100 µm are simulated and a detailed analysis of the compressible flow is presented. The average pressure exerted on the solid surface due to the droplet impact is reported which can be used to model the stress in the solid and carry out the fatigue analysis of the material in order to estimate its practical lifetime.