Effect of density ratio on velocity fluctuations in dispersed multiphase flow from particle-resolved numerical simulation*

Particle-resolved direct numerical simulation of a statistically homogeneous case of a dispersed multiphase flow is used to study the velocity fluctuations in the carrier phase and dispersed phase. The simulations are presented for a fixed mean slip Reynolds number (\Re_m=20) and a wide range of dispersed phase volume fractions (0.1 < \phi < 0.4) and density ratios of the dispersed phase to the carrier phase (0.001 < \rho_p/\rho_f < 1000). The velocity fluctuations are quantified by the turbulent kinetic energy (TKE) for the carrier phase and the granular temperature for dispersed phase at statistically stationary state. The results show that the granular temperature increases and then reaches an asymptotic value with decreasing density ratio. The qualitative trend of the behavior is explained by the added mass effect. The dependence of TKE on the density ratio for all volume fractions studied here is also explained. It is also shown that the low-density ratio cases are less efficient in extracting energy from mean flow to fluctuations by comparing the mixture kinetic energy for different cases.