Numerical Study of Dispersed Two-phase Flows

University dissertation from Fluid Mechanics

Abstract: This thesis considers the numerical study of dispersed two-phase flows.Numerical simulations have been done to investigate the particle trasportation/dispersion effect in turbulent two-phase flows. Both turbulent bubble/water flows and turbulent particle/air flows are studied. Eulerian/Eulerian approach and Eulerian/Lagrangian approachs were both used in the studies. In the Eulerian-Eulerian approach, k-epsilon model is used to model the continuous phase turbulence. The effect of interfacial forces due to mean properties and also fluctuating motions are studied in the bubbly flow simulations. In Eulerian/Lagrangian approach, Large Eddy Simulation is used to model the continuous phase turbulence, and discrete particles are tracked within the flow field predicted by LES. LES of a baffled stirred reactor in the presence of bubbles is performed. The effect of bubbles on the properties of the continuous phase are investigated. A Eulerian/Eulerian model is studied by using data obtained from LES-LPT (Large Eddy Simulation-Lagrangian Particle Tracking) of the flow in a stirred reactor. The turbulent kinetic energy of the dispersed phase and fluid-particle turbulent covariance were obtained both from direct statistics of LES simulation and closure model calculations. Results show the applicability of certain Eulerian/Eulerian models to gas-liquid reactors. Foundamental experimental studies on simulataneous two-phase DPIV are carried out. Two cameras are used to catch the information of both phases simultaneously. One camera pick up the infomationn of one phase and the other pick up the information of both phases. By post-processing, the simultaneous flow field for each phase can be obtained. LES-LPT (Large Eddy Simulation-Lagrangian Particle Tracking) is also carried out to study the same flow case. Good agreement of the results between experiment and LES-LPT shows the ability of both methods in the study of two-phase flow systems.

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