Motion of Submicron Particles in Supersonic Laminar Boundary Layers

Abstract

Submicron-particle motion in laminar boundary layers is present in many practical applications. Some important findings on this issue have been achieved during the last decades, but many mechanisms in this process still remain unclear. In the present work, a model has been developed to describe the motion of the submicron particles in supersonic laminar boundary layers above an adiabatic plate along with the mainstream. In this model, the Lagrangian method is used to track the particles and calculate their trajectories, and the Eulerian method to calculate the flowfield. The effects of the entering position, Mach number, and the size and density of the particles were investigated. It is concluded that there are three particle-motion patterns when they enter the supersonic boundary layer, which are departure pattern, equilibrium pattern, and deposition pattern. The drag force and Saffman lift force were discovered to play dominating roles in deciding the patterns, and thermophoretic force and Brownian force are of less importance. A dimensionless number to describe these three patterns is suggested. This work was intended to provide an insight into the submicron-particle motion in the supersonic laminar boundary layer, which can be guidance for industrial applications involving this phenomenon.