Analysis of the Backflow Recirculation in Flow Blurring Nozzles via Lagrangian Coherent Structures

The liquid atomization process relies on the disturbance of the liquid surface by various forces. In the case of “flow-blurring” (FB) atomization, this is achieved by inducing turbulence near the liquid channel exit. In this study, we analyze the underlying dynamics of these coherent turbulent structures and their role in the primary atomization within the FB regime. For that purpose, Smoothed Particles Hydrodynamics (SPH) simulations have been conducted using the geometry of an FB atomizer, which was also studied experimentally. An in-house developed visualization and data exploration platform (postAtom) was used to capture the time-resolved, Lagrangian coherent structures ($\mathrm{LCSs}$) via the finite-time Lyapunov exponent ($\mathrm{FTLE}$) fields. The results indicate that the design of the mixing chamber can trigger an oscillatory behavior at the nozzle exit, which has a direct impact on the evolution of the micro-ligaments and the consecutive primary atomization. It is further shown how the $\mathrm{FTLE}$ fields can be used as a guide to optimize the nozzle geometry.