Secondary atomization of liquid columns in compressible crossflows

Abstract

The secondary atomization of liquid droplets is a common physical phenomenon in many industrial and engineering applications. Atomization in high speed compressible flows is less well understood than its more frequently studied low Mach number counterpart. The key to understanding the mechanisms of secondary atomization is examination of the breakup characteristics and droplet trajectories across a range of physical conditions. In this study, a planar shock wave impacting a cylindrical water column ($\rho_l=1000 \rm~kg/m^3$) is simulated for a range of Weber numbers ranging three orders of magnitude ($\sim 10^0-10^3$). Four different incident shock speeds are simulated ($M_s=1.47, 2, 2.5, 3$) which induce subsonic, transonic, and supersonic crossflow across the column. The flowfield is solved using a compressible multicomponent Navier-Stokes solver with capillary forces. Fluid immiscibility is maintained with an interface sharpening scheme. Overall, a diverse range of complex interface dynamics are captured across the range of physical conditions studied. Additionally, while the unsteady drag coefficient of the liquid column shows a dependence on the Weber number using the undeformed diameter, calculations using the deformed diameter significantly reduce the dependence, particularly for the supersonic cases, with implications for subgrid droplet modeling in atomization simulations. A preliminary under-resolved three-dimensional simulation of droplet breakup shows reasonable agreement with experimental data, indicating the potential of the numerical approach for future investigations.