Inelastic accretion of inertial particles by a towed sphere

TL;DR

This study investigates how inelastic collisions influence particle accretion onto a sphere in a flow, revealing that multiple bounces can enhance accretion but do not lead to inelastic collapse, with efficiency depending on flow parameters.

Contribution

It introduces a model for particle accretion considering inelastic collisions and demonstrates the role of multiple bounces in enhancing accretion efficiency.

Findings

Collision efficiency depends on Reynolds number via critical Stokes number.

Multiple bounces increase the likelihood of particle sticking.

Inelastic collapse does not occur without additional microphysical interactions.

Abstract

The problem of accretion of small particles by a sphere embedded in a mean flow is studied in the case where the particles undergo inelastic collisions with the solid object. The collision efficiency, which gives the flux of particles experiencing at least one bounce on the sphere, is found to depend upon the sphere Reynolds number only through the value of the critical Stokes number below which no collision occurs. In the absence of molecular diffusion, it is demonstrated that multiple bounces do not provide enough energy dissipation for the particles to stick to the surface within a finite time. This excludes the possibility of any kind of inelastic collapse, so that determining an accretion efficiency requires modelling more precisely particle-surface microphysical interactions. A straightforward choice is to assume that the particles stick when their kinetic energy at impact is below a threshold. In this view, numerical simulations are performed in order to describe the statistics of impact velocities at various values of the Reynolds number. Successive bounces are shown to enhance accretion. These results are put together in order to provide a general qualitative picture on how the accretion efficiency depends upon the non dimensional parameters of the problem.