A Survey of Airborne Particle Impact Characteristics Using High Speed Particle Shadow Velocimetry

Abstract

A review of the effect of particle, surface, and impact characteristics on the coefficient of restitution for quartz particles impacting an aluminum plate has been performed using highspeed Particle Shadow Velocimetry. Over one million rebounds, obtained from the analysis of approximately 2.6 million images, were analyzed. Particle impacts occurred at speeds between 0 and 100 m/s, with impact angles ranging from 0 to 90 degrees. The roughness of the target surface was varied from Ra = 0.8 – 8.0 micrometers. Observed particle sizes ranged between 150 and 1000 micrometers, with shapes ranging from roughly spherical to oblong. A code was developed that incorporated image processing, particle identification, particle tracking, rebound identification, size and shape analysis, out-of-plane velocity estimation, and calculation of restitution coefficients in a manner sufficient as to allow the efficient analysis of substantial numbers of particle images. Results match trends observed in the literature that have examined variations in impact velocity, impact angle, particle size, and surface roughness independently. The total coefficient of restitution is shown to vary strongly with both impact velocity and angle, while restitution coefficients in the normal and tangential directions are primarily functions of impact angle alone. Particle size appears to have no effect on the restitution coefficients, while the shape of the particles adds randomness to the rebound characteristics. Increased surface roughness was observed to slightly lower restitution coefficients, likely due to plastic deformation of the larger asperities.