Mathematical modeling for the evolution of the large- and meso-scale vortex in the screw centrifugal pump with the buoyancy effect

Because of the high-speed rotating impeller and the asymmetry volute, the flow parameters are strongly nonlinear in the screw centrifugal pump runner, in which the flow is multi-scale irregular and complex; moreover, the solid–liquid two-phase flow exacerbated the degree of nonlinear. To analyze the mechanism of solid–liquid two-phase flow and the evolution of the vortex in screw centrifugal pump, the model of the large- and meso-scale vortex evolution when the solid–liquid two-phase flow layered with the buoyancy effect is established, the flow structure and the change regulation of inner flow are revealed in the screw centrifugal pump, by the means of theoretical study of the inner flow states of the screw centrifugal pump, and the calculation of the internal flow field numerical simulation was performed. The research shows that the isodensity surface and isobaric surface are oblique which lead to the change in the vorticity; with both the fluid viscosity and the baroclinicity, the working vortex maintains an orderly flow form in time and space; the form of the vortex is mainly affected by the forces of fluid field, the vortex constantly reshapes the flow structure, the low-pressure areas form the positive vortex, while high-pressure areas are inclined to forming the reverse vortex, both the positive and reverse vortices always appear in pairs, which make the fluid take on the next states continuously; it is the difference of solid and liquid proportion in the solid–liquid two-phase flow that results in the phenomenon in which the flow tends to form different concentrations and stratifications, especially in rotating machinery; these phenomena are more common. With the effect of the rotating machinery impeller, the flow field becomes the flow with the vorticity, namely, forming the rotational flow, as well as the velocity difference between solid and liquid in the solid–liquid two-phase flow, and leads to that the fluid machinery internal velocity gradient and pressure gradient change is considerably great, which induces and motivates the generation and evolution of the vortex further.