Investigation on the multiphase sink vortex Ekman pumping effects by CFD-DEM coupling method

The gas-liquid-solid multiphase sink vortex is a complex turbulent mechanical phenomenon, in which the
pumping effects of Ekman boundary layer involved in the above process has the important scientific value and engineering significance. To address the matter, a coupled Computational Fluid Dynamic and Discrete Element Method (CFD-DEM)method for the simulation of the multiphase sink vortex is proposed based on the realizable k-ε turbulentmodel and the soft spheremodel. The suction and extraction regularities of gas-liquid coupling process are analyzed to reveal the matter transfer mechanismof Ekman boundary layer. Then, the phenomenon for the particle sucked by sink vortex is investigated to obtain the Ekman pumping effects. Finally, the influences of Ekman pumping effects on particles with respect to different densities are studied to verify the validity and reliability of the proposed method. Numerical results demonstrate that the suction and extraction intensities constitute a data set that is dependent on the initial disturbance components; there is an apparent upwelling phenomenon in the liquid boundary layer, which is caused by the spiral coupling structure of Ekman boundary layer. The Ekman pumping process for particles has three typical stage: Ekman suction-extraction state, Ekman horizontal pumping state, and Ekman upwelling state,wherein the flowpatterns are dominated by the initial disturbance and appear a complex nonlinear turbulence features;with the particle density increasing, the effects of Ekman suction-extraction state and horizontal pumping state are enhanced, but the Ekman upwelling effect for particle has apparent decreased.