Towards PR-DNS of scour around a wall-mounted cylinder in turbulent open channel flow

TL;DR

This study uses particle-resolved direct numerical simulation to investigate how a wall-mounted cylinder affects turbulence, particle distribution, and wall shear stress in turbulent open channel flow.

Contribution

It demonstrates the impact of a cylinder and wall roughness on turbulence structures, particle accumulation, and wall-normal particle transport in open channel flow.

Findings

Cylinder induces intense vortical structures and enhances turbulence.

Particle concentration varies with wake region, showing accumulation and depletion.

Wall roughness increases particle entrainment far from the wall.

Abstract

Particle-resolved direct numerical simulation (PR-DNS) is performed for turbulent open channel flow over a smooth horizontal wall with a vertical cylinder and a dilute set of mobile, heavy, spherical particles. At the chosen parameter point (which matches a previous study without a cylinder) the particles are mostly translating in the horizontal plane while remaining in contact with the wall. It is shown that the presence of the cylinder leads to the generation of intense vortical structures, enhanced turbulence intensity in the wake region, and to strong modifications of the local wall shear stress. These cylinder-induced perturbations have direct consequences for the average particle concentration: preferential accumulation/depletion in different parts of the wake region occurs, while the wall-normal transport of particles (against gravity) is significantly enhanced. A second simulation which adds roughness elements on the wall reveals an additional effect upon the wall-normal distribution of particles. It turns out that the configuration with wall-roughness and a wall-mounted cylinder features the largest fraction of entrained particles, even far from the wall.