Experimental study on erosion initiation via liquid droplet impingement on smooth and rough walls

This paper presents an experimental study on erosion initiation via liquid droplet impingement on smooth and rough aluminum (A1070) walls. Experiments were conducted using a spray jet apparatus with three different orifice diameters at various nozzle pressures, which facilitated the variation of droplet characteristics, such as droplet velocity and diameter, which were measured using particle image velocimetry and a shadowgraph imaging technique, respectively. Experimental results are presented for the incubation period based on the spray flow rate, droplet diameter, impact velocity, and surface roughness. It was determined that the incubation period decreases with increasing impact velocity and surface roughness, while droplet diameter has a relatively minor effect on the incubation period. Furthermore, the incubation period based on the impact velocity and surface roughness is defined by an empirical equation for prediction. Scanning electron microscopy observations of erosion initiation on the rough walls reveal that erosion damage was initiated along crystal grain boundaries on the smooth wall, but much larger pits were generated on the rough surface based on the stress concentration effects of the roughness.