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

Abstract

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 (LCSs) via the finite-time Lyapunov exponent (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 FTLE fields can be used as a guide to optimize the nozzle geometry.

Review of Flow Blurring Atomization: Advances and Perspectives

“…It is therefore inevitable that for a full understanding of the near-field atomization zone from FB injectors, more complex imaging methods will be required (e.g., ballistic imaging) to truly reveal the physical behavior of the spray. Recent efforts in the modeling of FB atomization ,− may also help to reveal fundamental phenomena; however, there remains a scarcity of literature on that topic.…”

“…This review has highlighted the sensitivity of FB atomization to the orifice geometry, and this is because this atomization mode (unlike air-blast atomizers) is heavily driven by internal turbulent mixing inside the nozzle. Slight variations in the redirection of air inside the nozzle have the potential to result in substantial changes to subsequent atomization behavior, 65 which may be the cause of variable results presented between different research groups. In the authors' view, designs of more fundamental experiments to better image the internal nozzle region and external primary atomization zone simultaneously are crucial.…”