Numerical investigation of swirling flow in cylindrical cyclones

Abstract

Abstract This paper constitutes a preliminary study of the two-phase flow in a Gas–Liquid Cylindrical Cyclone (GLCC © 1 1 GLCC – Gas–Liquid Cylindrical Cyclone – Copyright, The University of Tulsa, 1994. ) separator. A GLCC consists in a vertical pipe with a downward inclined tangential inlet. The incoming flow forms a swirling motion producing a centrifugal force. The gas and liquid are thus separated due to both centrifugal and gravity forces. Therefore the separation efficiency is higher than for conventional vessel type separators, allowing more compactness. In this study, the aim is to better understand the swirling hydrodynamics of this separator via CFD simulations. Therefore, the single-phase hydrodynamics is calculated for swirling flows generated by means of tangential injection(s) in a straight pipe. Geometry and flow conditions are chosen according to the experimental study of Erdal (2001a), who performed local measurements of the axial and tangential velocities. RANS, URANS and LES simulations are carried out using different turbulence models and different near wall treatments. Among the Reynolds Averaged Navier–Stokes (RANS) models, the high-Reynolds realizable k– ϵ model performs the best for predicting the local mean axial and tangential velocities. Its results are as good as the LES ones when the fluid is injected through only one inlet, while LES predicted flow is closer to the experimental one for two inlets. Numerical results also show that, contrary to the common approximation of the literature, the radial velocity magnitude is not negligible. The vortex core precession is well predicted by the simulations, which show that its direction is the opposite of the swirl one. We think that the growth of the turbulence kinetic energy in the core of the flow is directly linked to this phenomenon. Finally computations are conducted to investigate the effect of the inlet geometry on the cyclone hydrodynamics. According to simulations, the rectangular inlet performs better than a circular one, since it reduces the vortex distortion, which is supposed to improve the separation efficiency.