On the effects of density ratio on droplet-laden isotropic turbulence

Our objective is to determine the effects of varying the droplet- to carrier-fluid density ratio ($\rho_d/\rho_c$) on the interaction of droplets with turbulence. We performed DNS of 3130 finite-size, non-evaporating droplets of diameter approximately equal to the Taylor lengthscale and with 5~\% droplet volume fraction in decaying isotropic turbulence at initial Taylor-scale Reynolds number Re$_\lambda=83$. We varied $\rho_d/\rho_c$ from 1 to 100 while keeping the Weber number and dynamic viscosity ratio constant, We$_\mathrm{rms}$=1 and $\mu_d/\mu_c$=1. We derived the turbulence kinetic energy (TKE) equations for the two-fluid, carrier-fluid and droplet-fluid flow. These equations allow us to explain the pathways for TKE exchange between the carrier turbulent flow and the flow inside the droplet. We show that increasing $\rho_d/\rho_c$ increases the decay rate of TKE in the two-fluid flow. The TKE budget shows that this increase is caused by an increase in the dissipation rate of TKE and a decrease in the power of the surface tension. The underlying physical mechanisms for these behaviors will be presented.