High velocity measurements of particle rebound characteristics under erosive conditions of high pressure compressors

Abstract

Ingested sand particles may lead to severe erosion in aero engine compressors resulting in performance deterioration. Predicting particle trajectories through a turbo machine requires accurate estimation of the particle rebound. The experimental investigation of particle impact is a challenging task with high demands on measurement equipment due to the combination of small particle sizes with high impact velocities. Therefore high velocity impacts with a realistic combination of both, impact velocity and particle size, have not been investigated experimentally yet. In this work high velocity impacts have been measured for 60 μm sized quartz particles impacting stainless steel (1.4301) and Ti6Al4V targets. The experiments were conducted in a sand-blast type erosion test rig designed to meet compressor specific boundary conditions representative for a third stage axial compressor of civil jet engines. Particle Shadow Velocimetry is used to measure the particle velocities in the test rig. A dimensional analysis of normal impact is presented to discuss the effect of particle size and impact velocity on the rebound characteristics. It was found that the widely used approach to implement the energy loss via a simple curve-fit that solely depends on the impact angle is not valid throughout the broad range of possible impact events in aero engine compressors. In addition, for a realistic combination of particle size and impact velocity, particle fracture was observed. The fracture alters the Stokes Number of the particles and with that the particle trajectory after first impact. Hence the accurate prediction of the particle-wall interaction includes not only the change of particle direction and velocity upon impact but the treatment of the particle fracture. This is especially relevant for high impact velocities and high normal impact velocities.