# Particles in turbulent separated flow over a bump: effect of the Stokes number and lift force

## TL;DR

This study uses simulations to analyze how the Stokes number and lift force influence particle distribution in turbulent flow over a bump, revealing significant effects on concentration patterns especially at high Stokes numbers.

## Contribution

It provides new insights into the combined effects of Stokes number and lift force on particle behavior in turbulent separated flows with high Reynolds number.

## Key findings

- Lift force significantly alters particle concentration, especially in high vorticity regions.
- Particle distribution is highly sensitive to Stokes number, affecting recirculation and segregation.
- High Stokes number particles form high concentration layers due to inertia and flow diversion.

## Abstract

Particle-laden turbulent flow that separates due to a bump inside a channel is simulated to analyse the effects of the Stokes number and the lift force on the particle spatial distribution. The fluid friction Reynolds number is approximately 900 over the bump, the highest achieved for similar computational domains. A range of particle Stokes numbers are considered, each simulated with and without the lift force in the particle dynamic equation. When the lift force is included a significant difference in the particle concentration, in the order of thousands, is observed in comparison with cases where the lift force is omitted. The greatest deviation is in regions of high vorticity, particularly at the walls and in the shear layer but results show that the concentration also changes in the bulk of the flow away from the walls. The particle behaviour changes drastically when the Stokes number is varied. As the Stokes number increases, particles bypass the recirculating region that is formed after the bump and their redistribution is mostly affected by the strong shear layer. Particles segregate at the walls and particularly accumulate in secondary recirculating regions behind the bump. At higher Stokes numbers, the particles create reflection layers of high concentration due to their inertia as they are diverted by the bump. The fluid flow is less influential and this enables the particles to enter the recirculating region by rebounding off walls and create a focus of high particle concentration.