Numerical Investigations of Unsteady Flows and Particle Behavior in a Cyclone Separator

Mechanism of particle separation in a cyclone separator is fully clarified by one-way coupled numerical simulations of large eddy simulation and particle tracking. The former resolves all the important vortical structures, while the latter inputs the computed flow fields and tracks trajectories of particles by considering Stokes drag as well as gravity. The computed axial and tangential velocities of the swirl flow in a cyclone compare well with the ones measured by particle image velocimetry (PIV). The precession frequency of the vortex rope computed for Stairmand cyclone also matches with the one measured by Darksen et al. The predicted collection efficiencies reasonably agree well with the measured equivalents for two cylindrical cyclones with different diameters and inflow conditions. Detailed investigations on the simulated vortical structures in the test cyclones and predicted trajectories of the particles have revealed that there are three major paths of trajectories for those particles that are not collected and exhausted from the cyclone. More than half of the exhausted particles are trapped by longitudinal vortices formed in the periphery of the vortex rope. Namely, the precession motion of the vortex rope generates a number of longitudinal vortices at its periphery, which trap particles and move them into the region of the upward swirl.