Session: 36-01 Deposition and Erosion Effects

Paper Number: 78116

78116 - The Importance of Shape in Particle Rebound Behaviors 

An understanding of particle rebound due to surface impact is essential in predicting particle transport and engine erosion potential. Current particle rebound models are commonly informed by analysis of spherical particle impact and thus implicitly assume particle shape to be of negligible effect. Particles ingested in aero engines, however, are rarely spheres and typically feature edges and corners. Understanding the effects of particle shape on rebound behavior is essential for ascertaining the range of validity of existing models and for developing improved, physics-informed particle rebound models. Here, we report on first-principle simulations of cubical particles impacting pristine Ti-6Al-4V targets at high speed. The simulation tool and procedure were first validated by studying classical particle impact problems involving spheres and angular particles. Next, a massive parameter space, defined by the particle geometry and orientation, was systematically explored in hundreds of simulations to obtain a statistical description of principal rebound factors such as the coefficients of restitution (CoR) and impact-induced rotation.

For particles impacting a target at speeds typically found in aero engine compressors, our simulations reveal that in the case of normal impact, unlike spheres, the CoR of a cube exhibits significant scattering, and the median CoR is more than three times lower than that that observed when perfectly spherical particles are assumed. These observations align very well with data from recent experiments. We also observe that spherical geometries do not experience several modes of energy transfer seen to be significant for angular particulate. As the corners and edges of a cube become more rounded, its median CoR increases toward that of spheres with the same size. Though difficult to measure experimentally, we have seen in our simulation results that rotation and significant transverse velocity can account for ~60% of a rebounding cube's kinetic energy but are negligible modes of energy transfer in impacts involving spheres. The significant effects of particle shape on the nature of particle CoR as well as on the rotation and transverse motion of rebounding particles are discussed mechanistically by analysis of particle trajectories, stress and strain state of the target, and modes of energy transfer during impact. The results of this study suggest that the use of spherical approximations in representing angular sand particles leads to a substantial loss of fidelity in predicting particle rebound. In delineating the effects of shape on particle rebound behavior and elucidating the underlying physics, this work helps to develop physics-based, lower-order particle rebound models capable of facilitating accurate prediction of particle transport and component erosion in aero engines.

Presenting Author: Jacob Wilson Virginia Tech

Presenting Author Biography: Jacob Wilson is currently a graduate student in the Department of Mechanical Engineering at Virginia Tech. His research interest is the physical modeling of particulate behavior in turbomachinery. He received his B.S. in Physics from Georgia Tech.

Authors:

Jacob Wilson Virginia Tech
Rui Qiao Virginina Tech
Matthew Kappes Rolls-Royce Corp.
James Loebig Rolls-Royce Corp.
Rory Clarkson Rolls-Royce Plc