Numerical analysis of a drift under crossflow for near-field behaviour of droplets

The near-field dynamic and thermal characteristics of a drift under crossflow conditions with varying Grashof numbers and velocity ratios are analyzed, employing highly resolved large eddy simulation (LES) and an Eulerian–Lagrangian approach that accounts for droplet condensation and evaporation. The development of counter-rotating vortex pair (CVP) slows down with a decreasing velocity ratio, a finding contrary to prior studies on high velocity ratios. Semi-empirical formulas for drift trajectory and drift radius are validated, and a modified semi-empirical drift radius formula is proposed, resulting in significantly enhanced predictive capability. Analysis of two-dimensional PDF of droplet temperature and diameter shows two distinctive branch-shape regimes based on the droplet ejection location. The low velocity ratio case exhibits distinct droplet evolution mechanism due to the compact and strong CVP, which increases the condensation rate and mass of the smaller droplets while stronger crossflow momentum decreases the mass of the larger droplets via mixing.