Large amounts of tiny microparticles are ingested into gas turbines over their operating life, resulting in unexpected wear and tear. Knowledge of such microparticle behavior at gas turbine operating temperatures is limited in published literature. In this study, Arizona road dust (ARD) is injected into a hot flow field to measure the effects of high temperature and velocity on particle rebound from a polished 304 stainless steel (SS) coupon. The results are compared with baseline (27 mis) measurements at ambient (300 K) temperature made in the Virginia Tech Aerothermal Rig, as well as previously published literature. Mean coefficient of restitution (COR) was shown to decrease with the increased temperature/velocity conditions in the VT Aerothermal Rig. The effects of increasing temperature and velocity led to a 12% average reduction in COR at 533 K (47m/s), 15% average reduction in COR at 866K (77m/s), and 16% average reduction in COR at 1073 K (102 m/s) compared with ambient results. The decrease in COR appeared to be almost entirely a result of increased velocity that resulted from heating the flow. Trends show that temperature plays a minor role in energy transfer between particle and impact surface below a critical temperature.
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 such microparticles approaching their melting temperatures are available in open literature. The coefficient of restitution (COR), a measure of the particles' impact characteristics, was measured in this study of microparticles using a particle tracking technique. Part II of this study presents data taken using the Virginia Tech Aerothermal Rig and Arizona road dust (ARD) of 20–40 μm size range. Data were 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 70 m/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 deg and 80 deg. Deposition of particles was observed as some particles approach their glass transition point and became molten. Other particles, which do not become molten due to different particle composition, rebounded and maintained a relatively high COR. Images were taken using a microscope to examine the particle deposition that occurs at various angles. A rebound ratio was formulated to give a measure of the number of particles which deposited on the surface. The results show an increase in deposition as the temperature approaches the melting temperature of sand.
Many gas turbine engines operate in harsh environments where the engines ingest solid particles. Ingested particles accelerate the deterioration of engine components and reduce the engine's service life. Understanding particle impacts on materials used in gas turbines at representative engine conditions leads to improved designs for turbomachinery operating in particle-laden environments. Coefficient of restitution (COR) is a measure of particle/wall interaction and is used to study erosion and deposition. In this study, the effect of temperature (independent of velocity) on COR was investigated. Arizona road dust (ARD) of 20–40 μm size was injected into a flow field to measure the effects of temperature and velocity on particle rebound. Target coupon materials used were Stainless Steel 304 (SS304) and Hastelloy X (HX). Tests were performed at three different temperatures: 300 K (ambient), 873 K, and 1073 K. The velocity of the flow field was held constant at 28 m/s. The impingement angle of the bulk sand on the coupon was varied from 30 deg to 80 deg for each temperature tested. The COR was found to decrease substantially from the ambient case to the 873 K and 1073 K cases. The HX material exhibits a larger decrease in COR than the SS304 material. The results are also compared to previously published literatures. The decrease in COR is believed to be due to the changes in the surface of both materials due to oxide layer formation which occurs as the target material is heated.
Erosion and deposition in gas turbine engines are functions of particle/wall interactions and Coefficient of Restitution (COR) is a fundamental property of these interactions. COR depends on impact velocity, angle of impact, temperature, particle composition, and wall material. The current study attempts to characterize the fundamental behavior of sand at different impact angles. A PIV system is used in the Virginia Tech Aerothermal Rig to measure velocity trajectories of microparticles. A novel method is used that solves for impact velocity in a forced flowfield by numerical methods. Two sizes of Arizona Test Dust and one of Glass beads are impacted into a 304 Stainless Steel coupon. Free jet velocity is 27m/s at room temperature. Impact angle varies from almost 90 to 25 degrees depending on particle. Mean results compare favorably with trends established in literature. This utilization of this technique to measure COR of microparticle sand will help develop a computational model and serve as a baseline for further measurements at elevated, engine representative air and wall temperatures.
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.
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