Comparative study of average sedimentation velocity: Direct numerical simulation vs two-fluid model

In this work, a comparative numerical study of sedimentation of mono-dispersed spherical particles has been performed. The results of two-fluid Eulerian modelhave been compared with direct numerical simulation results. A 3D-cubical box with periodic boundary conditions was employed as simulation domain. The aim of current research is to determine the accuracy of Eulerian two-fluid model for simulation of sedimentation. Average sedimentation velocity has been chosen as the criterion for comparison. Range of volume fraction covered varies from dilute to dense regimes for a fixed Reynolds number based on particle's terminal velocity. It is found that the average sedimentation velocity from both DNS and TFM deviates from well-known Richardson-Zaki power law at moderate Reynolds number and low particle volume fraction. For high particle concentration (greater than 0.2) the deviation becomes negligible. Both numerical methods predict particle settling velocities closer to that obtained from Richardson-Zaki power law. Since the accuracy of TFM is being tested, it can be concluded from the current study that TFM, with appropriate closures and parameters, can be used to accurately model sedimentation problems for large system sizes.

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