Direct and Refined Characterization of Rebound for Irregularly Shaped, High-Speed Particles Incident on Aerospace Grade Titanium

Abstract

The observed stochasticity in rebounding trajectories for particle-surface interactions in turbomachinery is often attributed to irregularities in particle shape. However, at higher speeds, plastic deformation of the surface can significantly influence the rebounding particle trajectory. This work explores the interaction between particle shape and surface plastic deformation at high speeds and the effect that it has on the observed spread in rebounding trajectories. Two parameters often used to characterize particle-surface interactions in turbomachinery are the coefficient of restitution (COR) and rebounding angle. A fully time-resolved two-dimensional Particle Tracking Velocimetry (2DPTV) system is employed on a high-speed free jet rig to study particle-surface interactions for 150μm−250μm crushed quartz incident on Grade 4 (Commercial) Titanium. Particle speeds range between 50m/s and 130m/s and nominal incidence angles of 30∘ and 90∘ are studied. In this work, a novel approach that couples the study of both the particle and particle-surface interactions is discussed. In addition to a full description of the experimental procedure, a source of random uncertainty stemming from particle shape coupled with rotation and inter-pixel effects is presented for both velocity and rebounding angle measurements. Moreover, the sensitivity of particle rebounding trajectories to particle shape is explored. A model from the literature is modified to include the effects that particle shape has on the normal coefficient of restitution. The sensitivity study of particle shape is then expanded to total COR and rebounding angle. It is shown that increases in plastic deformation decrease the sensitivity of the COR (both total and normal) to particle shape, reducing the spread of COR values. In contrast, the spread in rebounding angles is dominated by particle shape irregularities and incidence angle with little dependence on plastic deformation.