Investigation of particle lift off in a turbulent boundary layer

Abstract

Entrainment and suspension of particles within turbulent flows occur widely in environmental and industrial processes. Three-dimensional particle tracking experiments are thus conducted in a water channel to understand the interaction of finite-size particles with a turbulent boundary layer. A neutrally buoyant sphere made of wax and iron oxide is first held in place on the bounding surface by a magnet before being released and tracked. The sphere is marked with dots to monitor rotation as well as translation. By setting up two pairs of cameras in a stereoscopic configuration, the trajectories of the sphere are reconstructed and tracked over a distance of $4$ to $6\delta$. Sphere diameters ranging from $40$ to $130$ wall units, initial particle Reynolds numbers of $600$ to $2000$ and friction Reynolds numbers of $500$ to $1800$ are considered. For this parameter set, the particle typically lifts off from the wall after release before falling back toward the wall. Aspects of both particle rotation and translation will be discussed.

Supported by NSF (CBET-1510154).