From High-Fidelity Numerical Simulations of a Liquid-Film Atomization to a Regime Classification

Abstract

High-fidelity numerical simulations of spray formation were conducted with the aim of improving fundamental understanding of airblast liquid film atomisation. The gas/liquid interaction in the near nozzle region is investigated for a multitude of operating conditions in order to extrapolate phenomenological and breakup predictions. To reach this goal, the Robust Conservative Level Set (RCLS) method has been used. For a fixed prefilmer geometry, we performed a parametric study on the impact of various liquid and gas velocities on the topological evolution of the liquid interface. The behaviour and development of the liquid film is found to be influenced mainly by the relative inertia of the gas and the liquid, the liquid surface tension and interfacial shear stresses. Preliminary regime maps predicting the prefilming liquid-sheet atomisation behaviour are constructed based on our numerical results. Three distinct types of "regime" are reported: accumulation, ligament-merging and 3-D wave mode. In addition, these results also show the influence of vortex action and rim-driven dynamics on the breakup mechanism at the atomiser edge. An increase in liquid injection speed leads to the generation of smaller droplets whereas an increase in air velocity does not point to one simple conclusion.

Detailed numerical simulations of primary atomization of airblasted liquid sheet

“…On the other hand, the planar configuration of airblast atomization has different breakup physics compared to its cylindrical counterpart. Many experimental [9,19,20,21] and numerical [22,23,24,25] works have investigated this configuration to understand the breakup physics and the atomization characteristics such as drop size distribution (DSD) and drop velocity distributions (DVD). Many of the past experimental studies have found that the aerodynamic forces play a significant and key role in the droplet sizes; specifically, the increase in the mean air velocities resulted in reduction in the droplet sizes [26,27,28,29] while a reduction in the Sauter Mean Diameter (SMD) has been observed with the increase in the surface tension of the liquid fuel [26,27].…”

“…Recently, Agbaglah et al [32] studied the destabilization of the air/water planar liquid sheet and found an excellent agreement between experiments and simulations for liquid cone length, spatial growth of primary instability, and maximum wave frequency. The investigations by Bilger and Cant [23] performed simulations of planar airblast atomization with a laminar inlet velocity profile for the gas phase and developed a regime diagram for the atomization process using the liquid and gas phase velocities as the abscissa and ordinate, respectively.…”

“…Many of the previous studies on experimental [19,20,9,21] and numerical [22,23,24,25] investigations of airblast atomization of liquid sheet have focused entirely on the primary atomization. However, it is physically and statistically possible that the atomized drops produced from various breakup mechanisms can undergo secondary atomization within the computational domain.…”

“…They are then stretched to their limit due to the aerodynamic forces from the high speed gas flowing above and below the pre-filmer plate and then breakup into droplets. In the past studies, the quantitative data extracted from the simulations [23,24,42] and experimental measurements [29,28,30] pertain mainly to the far downstream quantities such as DSD and DVD. In a recent study [9], the data in the near-field region of the injector pertaining to liquid ligaments have been extracted.…”