Effect of density ratio on velocity fluctuations in dispersed multiphase flow from simulations of finite-size particles

Abstract

Velocity fluctuations in the carrier phase and dispersed phase of a dispersed multiphase flow are studied using particle-resolved direct numerical simulation. The simulations correspond to a statistically homogeneous problem with an imposed mean pressure gradient and are presented for $${Re}_{m}=20$$ and a wide range of dispersed phase volume fractions $$\left( 0.1 \le \phi \le 0.4 \right) $$ and density ratios of the dispersed phase to the carrier phase $$\left( 0.001 \le \rho _\mathrm{p}/\rho _\mathrm{f} \le 1000 \right) $$ . The velocity fluctuations in the fluid and dispersed phase at the statistically stationary state are quantified by the turbulent kinetic energy (TKE) and granular temperature, respectively. It is found that the granular temperature increases with a decrease in the density ratio and then reaches an asymptotic value. The qualitative trend of the behavior is explained by the added mass effect, but the value of the coefficient that yields quantitative agreement is non-physical. It is also shown that the TKE has a similar dependence on the density ratio for all volume fractions studied here other than $$\phi =0.1$$ . The anomalous behavior for $$\phi =0.1$$ is hypothesized to arise from the interaction of particle wakes at higher volume fractions. The study of mixture kinetic energy for different cases indicates that low-density ratio cases are less efficient in extracting energy from mean flow to fluctuations.