Strongly Swirling Turbulent Sink Flow Between Two Stationary Disks

Abstract

The steady, incompressible turbulent sink flow developing between two stationary disks under the influence of strong swirl was numerically investigated. The simulations were made using the FLUENT 6.2 software. The purpose of the study is to first validate the method and then proceed in identifying the origin of some key known flow features, such as the appearance of a toroidal recirculation zone in the central flow region, the saddlelike behavior of the tangential velocity, and the two radial velocity kinks near the two end plates. The simulations are found to be in good accord with earlier experiments. Centrifugal force is shown to be the prime culprit for all of the previous flow manifestations. The overpowering centrifugal force compels the fluid to drain mainly through the end-plate boundary layers where its value is the minimum. The buildup of the recirculation zone is a natural response by the fluid to account for the local flow inactivity. This buildup is also responsible for the evolution of a weak reversed flow in the midchannel plane that, along with turbulence and the nonslip condition on the disk surface, produces the until-now unexplained saddlelike shape of the tangential velocity profile. The growth of the radial velocity spikes near the disks is due to the synergetic action of the boundary-layer development and the reduction of the local flow area. Finally, the simulations have also unveiled a previously unknown tangential velocity undulation inside the vortex core triggered by vortex transition from laminar to turbulent conditions.