Experiments and large eddy simulation of swirling flow in a pipe

Swirling flows in pipes are encountered in several industrial applications for separation or mixing purposes. In this work turbulent swirling flow is generated using a new swirl generator in the form of thick-walled pipe with multi-radial holes which is lodged inside a larger cylindrical housing, called the Swirl Cage. The swirling flow exiting from the Swirl Cage feeds into a long pipe where the Reynolds number based on the pipe diameter and average velocity is equal to 40836.67. Large Eddy Simulation (LES) is used to calculate the swirling flow and explore its characteristics in conjunction with the Dynamic Kinetic Energy Subgrid-Scale model. Experiments were conducted using LDV and the results are used for validation purposes and for the discussion of the flow features. The results are discussed in relation with the mean fluid velocity and its RMS component. Profiles of the mean tangential velocity reveal a Rankine vortex swirling flow type along the whole axial distance. The core flow was slightly oscillating exhibiting a processing vortex behavior reflected by the radial velocities at the centerline. The profiles of the turbulent kinetic energy were characterized by a peak at the centerline increasing in magnitude with the axial distance. The swirl number decayed from 1.5 right at the outlet of the swirl cage to unity close to the outlet of the pipe.