SIMULATION OF FREE-SURFACE FLOW IN PARTIALLY FILLED INTERNAL MIXERS

Internal mixers used in rubber processing and other industries are alw ays partially filled. This results in the establishment of multiple ra ndom free surfaces in the flow field generated inside these mixers. Th erefore successful mathematical modelling of internal mixing process d epends on the development of efficient techniques for the reliable sim ulation of complex free surface flows. Various interface trucking and boundary capturing methods have been used in the past to model this ki nd of flow regimes. In particular, in has been frequently used to mode l a variety of processes involving free surface and moving boundary fl ows. Both Eulerian and Lagrangian frameworks can be adopted in the VOF scheme to simulate free surface regimes. Under realistic flow conditi ons, however, the straightforward application of the technique in both frameworks may yield inaccurate results unless elaborate solution str ategies are used to avoid errors. In many cases the use of such elabor ate schemes requires excessive computational costs and effort or the s olution scheme becomes complex and inflexible. In this paper we descri be a relatively simple free surface tracking method based on the appli cation of the VOF method in an Eulerian framework. In this scheme the flow field inside a partially filled internal mixer is treated as a tw o-phase system consisting of incompressible and compressible phases. T he sections filled with the fluid which is being mixed are always rega rded as an incompressible phase. The parts which are filled with air ( or voids in some applications) form the second phase in the present tw o-phase flow analysis. The latter phase is treated as a compressible o r an incompressible fluid (or pseudo fluid in the case of voids) depen ding on the value of the pressure calculated at each time step for the sections which contain it. We show that free surface flow of highly v iscous fluids in partially filled internal mixers can be very successf ully simulated by this method.