On the enhancement of particle deposition in turbulent channel airflow by a ribbed wall

Abstract

The particle deposition at a vertical wall roughened by transverse square bars placed at a small spacing between them is investigated using large-eddy simulation of the turbulent flow in a ribbed channel with the gravity aligned in the flow direction together with Lagrangian particle-tracking. It is found that the particle deposition coefficient is substantially increased in the presence of roughness elements, exhibiting a weaker dependence on the variation of particle response time relative to the case of smooth channel. The enhancement ratio of particle deposition varies from three for the larger size particles to about 400 for the smaller particles examined here. The friction-weighted enhancement ratio of particle deposition is higher than unity for all particle sets, indicating that the present ribbed channel configuration efficiently increases particle deposition with respect to the increase in energy losses. The rise in the particle deposition coefficient at the rough surface is closely related to the direct inertial impaction and interception mechanisms. The population of particles depositing at the rear surface of the square bars is very small, revealing that an enlargement of the effective deposition area is not necessarily translated to a similar augmentation of particle removal.