Transient effects of drag coefficient in the Eulerian-Lagrangian calculation of two-phase flow

Transient effects of the drag coefficient are usually ignored in two-phase flow calculation using the Eulerian-Lagrangian method. However, this study reveals that significant errors are found in the prediction of the probability density function(PDF) of fluctuating velocity, associated with the steady drag coefficient, in the dispersed phase(u′ _pi ), particularly for large sizes. The PDF information of the dispersed phase can provide valuable information for understanding the turbulent dispersion ability of the dispersed phase. The use of the unsteady formula of drag coefficients in analysis does greatly improve the PDF prediction of u′ _pi . The limitation of the presently employed formula of the unsteady drag coefficient is also discussed.