An Experimental Study and a Numerical Simulation of the Turbulent Flow under the Vortex Finder of a Cyclone Separator

An experimental study and a numerical simulation are presented concerning the three dimensional turbulent flow of air in a cyclone separator in the region underneath the vortex finder. The computations are carried out using the Fluent CFD code. The turbulence effects on the mean flow are taken into account using the standard k-ε model and the standard Reynolds stress Model (RSM). The axial and tangential mean velocity components and the turbulence intensities are measured using Laser Doppler Anemometry. The LDA system is mounted in such a way that radial traverses at different angles of the cyclone cylindrical geometry and at different axial positions could be possible. The obtained results show interesting phenomena such as the three dimensional nature of the flow behaviour, the turbulence decay and its evolution towards an isotropic state in the quasi-free vortex region as the flow proceeds downstream in the cyclone. In the region underneath the vortex finder, the surface separating the descending and the ascending streams (set of points where the axial velocity component is nil) is located approximately in the fictitious prolongation of the vortex finder cylindrical wall. The existence of a quasi-forced vortex in the central region of the cyclone surrounded by a coaxial quasi-free vortex is confirmed. The radial distance separating the central vortex and the surrounding annular vortex, at a given angle and axial position, can be clearly defined as the distance from the axis to the point of intersection between two characteristic straight lines: the first line representing, ln Ut vs ln r, of slope +1, in the quasi-forced vortex and the second line, ln Ut vs ln r, of slope -1, in the quasi-free vortex, where Ut is the tangential component of the mean velocity.