Gas cyclones are widely used in various industrial applications. For the design of cyclones different mathematical models exist. They all describe the pressure loss and separation efficiency for particular cyclone geometries [2, 3]. For cyclones of small size all well known design models fail. Further, the flow condition in cyclones of small size is unknown. A 3-dimensional direct numerical simulation still fails in loss of time and CPU-capacity. Therefore the flow field in cyclone separators was calculated based on a 2-dimensional model assuming rotational symmetry in the flow field with very fine structured computational grid. The results indicated Taylor instabilities in the gap between the wall and the inner swirl of the fluid flow due to hydrodynamic instabilities at certain flow conditions. These simulation results were verified with 3D-CFD using Reynolds-Stress-Model as turbulence model and experiments. Based on these results new mathematical models for the stability analysis of the flow in a small scale cyclone were derived [1, 4, 5]. The appearance of Taylor instabilities was predicted correctly with the developed models. With the 2D- and the 3D-CFD simulation the operational behaviour concerning velocity distribution and pressure drop were equally determined. The Taylor instabilities could not be found with the 3D simulation while a turbulence model was used. A PIV-analysis certified the obtained results.

[1] Janoske U., Piesche M.: “Hydrodynamic Instabilities in a New Type of Cross-flow Filter”; Proceedings - FILTECH 2005, Wiesbaden. [2] König, Ch.: “Untersuchung zum Abscheideverhalten von geometrisch ähnlichen Zyklonen“; Dissertation, Universität Kaiserslautern, 1990. [3] Schütz, S., Mayer, G., Bierdel, M. und Piesche, M.: ”Investigations on the Flow and Separation Behaviour of Hydrocyclones Using Computational Fluid Dynamics”; International Journal of Mineral Processing 73 (2004), 229 - 237. [4] Taylor, G. I.: “Stability of a Viscous Liquid contained between Two Rotating Cylinders”; Phil. Trans. Roy. Soc., S. 289 - 343, 1923. [5] Zink, A., Piesche, M., Trautmann, P., Durst, M.: “Numerical and experimental investigations of a disc stack centrifuge used as an oil mist separator for automotive applications”; SAE World Congress 2004, Detroit, Paper 2004-01-0638.