Visualization experiments of a solid cylinder suspended by laminar flow

Abstract

The suspension of a single cylindrical particle in a square stirred tank was investigated by detailed visualization experiments. The flow pattern in the tank generated by a spinning disk is laminar (Reynolds numbers based on the disk diameter are less than 50). The cylinder’s motion and orientation were recorded by two cameras at 100 frames per second and then quantitatively analyzed. The length over diameter aspect ratio of the cylinders was varied in the range 1 – 8. The angular speed of the spinning disk at which incipient lift-off of the cylinder occurs depends on the cylinder’s diameter and its aspect ratio. Beyond an aspect ratio of about 5, this critical disk speed only weakly depends on the aspect ratio indicating that then the hydrodynamic force on the cylinder approximately scales with its length. The self-rolling as well as the azimuth sliding over the tank bottom were quantitatively identified when the cylinder approached being lifted off. The suspension phenomenon of the cylinder with aspect ratio 1 is different from other cylinders. We obtained highly reproducible results for the trajectory and orientation of the cylinder during the suspension process that can serve as benchmark data for critical evaluation of computational approaches.