Effect of Near Melting Temperatures on Microparticle Sand Rebound Characteristics at Constant Impact Velocity

Abstract

When gas turbine engines operate in environments where the intake air has some concentration of particles, the engine will experience degradation. Very few studies of microparticles at temperatures approaching the melting temperature of the particles are available in open literature. Coefficient of Restitution (COR), a measure of the particles’ impact characteristics, was measured for microparticles using a particle tracking technique. This study presents data taken using the Virginia Tech Aerothermal Rig and Arizona Road Dust (ARD) of 20–40μm size range. Data was taken at temperatures up to and including 1323 K, where significant deposition of the sand particles was observed. The velocity at which the particles impact the surface was held at a constant 70m/s for all of the temperature cases. The target on which the particles impacted was made of a nickel alloy, Hastelloy X. The particle angle of impact was also varied between 30° and 80°. The COR of the particles decreases slightly as some of the particles approach their glass transition point and start to become molten. Other particles, which do not become molten due to different particle composition, rebound and maintain a relatively high COR. Images were taken using a microscope to examine the particle deposition that occurs at various angles. A rebound ratio is formulated to give a measure of the number of particles which deposit on the surface. The results show an increase in deposition as the temperature approaches the melting temperature of sand.