Particle Bounce Stick Behavior in the Rotating Frame of Reference

Abstract

Particle deposition is a major damage mechanism for gas turbine components, especially in the secondary air system. Predicting the transport and deposition of ingested atmospheric contaminants is of great interest in component-level simulations. Bounce stick models predict deposition upon collision with a wall during Lagrangian particle tracking; they consider a range of physical phenomena, including van der Waals forces and plastic deformation. The effect of the rotating frame of reference on particle collision physics has thus far been neglected in the literature despite the significant centrifugal (CF) loads experienced by many components of interest for deposition studies, for example, turbine blades. The collision physics of the rotating frame are discussed here using low-order models and Monte Carlo style simulations. The present work aims to provide a conceptual framework for the inclusion of CF forces in collision physics. No significant effect was found on the rebound velocities of particles experiencing “worst case” CF forces. However, differences were observed in the sticking probability between concave and convex rotating surfaces, where the CF forces act in opposing directions to either push the particle into the surface or detach it. A force-based analogy of the popular critical velocity model was developed to study the phenomenon. It was used in a Monte Carlo style simulation of a rotor disk, finding that the variation of critical velocity due to CF forces was likely to bias deposition toward concave surfaces. The collision physics of the rotating frame were found to be unintuitive, with complex implications for modeling deposition in gas turbine components. However, they were consequential in determining the distribution of deposition through the system, hence should be included in particle deposition simulations in computational fluid dynamics (CFD).