A computational study of an atomizing liquid sheet

Abstract

Linear instability predictions of liquid sheets injected into a gas medium are well established in the literature. These analyses are often used in Lagrangian-Eulerian spray simulations, a prominent simulation method, to model the dynamics occurring in the near-nozzle region. In the present work, these instability predictions are re-examined by first generalizing the treatment of interfacial conditions and related assumptions with a two-phase Orr-Sommerfeld (OS) system, and second, by employing highly resolved-Volume-of-Fluid (VoF) simulations. After presenting some validation exercises for both the VoF and OS solvers, the OS predictions are compared to earlier studies from the literature leading to reasonable agreement in the limit as the boundary layer thickness tends to zero. Results from VoF simulations of liquid sheet injection are used to characterize the range of scales of the liquid structures immediately before atomization. The mean value in this range is found to be approximately two to three orders of magnitude larger than the corresponding predictions from previous studies. A two-phase mixing layer under the same physical conditions is used to examine this disparity, revealing that within the linear regime, relatively good agreement exists between the VoF and OS predicted instability mechanisms. However, the most unstable mode in the linear regime is too small to cause a fracture or atomization of the liquid sheet and hence cannot be directly responsible for the atomization. The generation of a much larger mode, which emerges well beyond the linear regime, is the one causing breakup.

Experimental and Computational Investigation of Subcritical Near-Nozzle Spray Structure and Primary Atomization in the Engine Combustion Network Spray D

“…If computational design tools are to be used to guide the use of direct injection strategies for cleaner and more fuel-efficient engines, accurate representation of the fuel spray within an engine simulation is essential. However, the spray formation process is challenging to model in the Reynolds and Weber number regimes relevant to fuel sprays [4], and for atomization processes driven not only by linear instabilities, but also by non-linear instabilities, as recently determined in [5,6]. In particular, the near-nozzle region is characterized by high mass loadings of the liquid phase and large momentum exchanges, therefore requiring specialized numerical techniques that are the subject of much ongoing research [7,8].…”

Evaluation and validation of large-eddy simulation sub-grid spray dispersion models using high-fidelity volume-of-fluid simulation data and engine combustion network experimental data

“…This is to compare LES and VoF data in the same breakup regime where breakup of liquid core and dramatic increase in gas-liquid interface area occur. In the VoF calculations, 20,48 this occurs in the region between the upstream initial instability development and downstream dispersed droplets. In LES, this region is modeled by the concept of the breakup length in the stochastic KH-RT model.…”

Extraction of Droplet Genealogies From High-Fidelity Atomization Simulations

“…High-fidelity models have recently started to become increasingly popular. With the increasing popularity of these models many different geometries and simulation parameters have been modeled and validated against experimental results [25], [7], [11], [3], [18], [19], [1].…”

“…7 shows all the droplets that took five splitting events to reach their final size shown inFig. 3.4.…”