On the physical origin of enhanced turbulent-dispersion of inertial particles in boundary layer flows

TL;DR

This paper investigates the turbulent dispersion of inertial particles in boundary layer flows, revealing that dispersion is reduced due to settling retardation, challenging existing models that predict enhancement.

Contribution

It provides direct measurements and simulations showing the reduction of turbulent particle dispersion and explains the physical origin of this phenomenon.

Findings

Turbulent particle dispersion is reduced, not enhanced, as previously thought.

Settling retardation significantly influences particle flux in turbulent boundary layers.

Existing models overestimate dispersion by assuming quiescent water settling velocity.

Abstract

One of the most enigmatic science question concerning inertial particle transport by a turbulent boundary layer flow is the value of the turbulent Schmidt number as the ratio of particle diffusivity and turbulent eddy viscosity. Using direct acoustic measurement of turbulent particle flux profile, and two-phase flow turbulence-resolving numerical simulation, it is demonstrated that turbulent dispersion of particles is reduced rather than enhanced when predicted with existing literature model. The explanation lies in the misleading assumption of settling velocity in quiescent water to estimate the turbulent particle diffusivity while direct measurements and simulations of turbulent particle flux support the occurrence of settling retardation.