Model for the initiation of atomization in a high-speed laminar liquid jet

Umemura, Atsushi

doi:10.1017/jfm.2014.511

Cited by 20 publications

(9 citation statements)

References 54 publications

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“…The velocity deficit along the jet interface, observed in Figure 5(a), supports the influence of the annular boundary layer of the liquid jet, formed on the nozzle wall before being injected in the stationary gas, on the development of the shear layer below the liquid interface downstream of the nozzle exit. This spatial evolution of the liquid velocity can be responsible for the initial perturbation of the liquid interface, which was proposed by Umemura [15]. Therefore, the steep increase of <V> close to the nozzle exit is the result of the initial sharp velocity gradient of the shear layer in the liquid jet.…”

Section: Resultsmentioning

confidence: 83%

“…Shinjo and Umemura [14] modelled a developing gaseous shear layer on the injecting liquid jet, and temporal tracking of the liquid surface pattern during jet injection suggested that the instability might be a Tollmien-Schlichting (TS) mode in the gaseous shear layer, which is similar to turbulent transition of solid-wall boundary layer. For case free of aerodynamic effect, Umemura [15] found that the deformation of the jet surface could be due to an instability of the thin liquid shear layer flow, which relaxes the liquid velocity profile produced by the nozzle wall. The interfacial velocity at the surface of liquid jet is important for the understanding of the atomisation process, since it may indicate the velocity of the liquid instabilities on the surface and possibly of droplets immediately after breakup.…”

Section: Introductionmentioning

confidence: 99%

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Combined Optical Connectivity and Optical Flow Velocimetry for interfacial characterisation of liquid atomisation

Wang¹,

Hardalupas²

2021

ICLASS

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The Optical connectivity (OC) technique introduces a laser beam through an atomiser nozzle and relies on total internal reflection at the liquid interface to propagate inside the continuous liquid to study the instantaneous characteristics of the disintegrating continuous liquid and its interface during the primary atomisation through imaging the emitted fluorescent intensity from the liquid flow. In the current study, time-dependent OC is used to capture the temporal evolution of the liquid interface structures along the continuous liquid jet injected by a pressure jet atomiser into quiescent air at conditions leading to breakup within the first and second wind induced regime. Optical Flow Velocimetry (OFV) is developed to measure the local velocity of the interfacial structures of the liquid jet. The results show that the liquid interface accelerates downstream of the nozzle exit. The axial and radial mean and standard deviation of the fluctuations of the velocity of the interfacial structures are quantified. The results demonstrate the significance of liquid viscosity and liquid shear on atomisation.

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Section: Resultsmentioning

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Combined Optical Connectivity and Optical Flow Velocimetry for interfacial characterisation of liquid atomisation

Wang¹,

Hardalupas²

2021

ICLASS

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“…Namely, case-by-case phenomenological parameter tuning is not needed and spray simulation can become a real predictive tool. The model proposed by Umemura [64,65] is based on the findings on atomization mechanisms derived from theoretical analysis [66][67][68], DNS [23,46,47] and pinch-off experiments [69]. By these, each physical process of surface instability, ligament formation, and droplet formation are included in the model as subgrid phenomena.…”

Section: Hybrid Eulerian-lagrangian Les With Self-closed Sgs Turbulenmentioning

confidence: 99%

Recent Advances in Computational Modeling of Primary Atomization of Liquid Fuel Sprays

Shinjo

2018

Energies

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Recent advances in modeling primary atomization in order to enable accurate practical-scale jet spray simulation are reviewed. Since the Eulerian–Lagrangian method is most widely used in academic studies and industrial applications, in which the continuous gas phase is treated in the Eulerian manner and droplets are calculated as Lagrangian point particles, the main focus is placed on improvement within this framework, especially focusing on primary atomization where modeling is the weakest. First, limitations of the conventional methods are described and then novel modeling proposals intended to tackle these issues are covered. These new modeling proposals include the Eulerian surface density approach, and the hybrid Eulerian surface/Lagrangian subgrid droplet generation approach. Compared to conventional simple yet sometimes non-physical models, recent models try to include more physical findings in primary atomization which have been obtained through experiments or direct numerical simulation (DNS). Model accuracy ranges from one that still needs some adjustment using experimental or DNS data to one which is totally self-closed so that no parameter tuning is necessary. These models have the potential to overcome the long-recognized bottleneck in primary atomization modeling and thus to improve the accuracy of whole spray simulation, and may greatly help to improve the spray design for higher combustion efficiency.

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“…The reader is referred to Portillo et al [25] and Umemura [26] for the latest experimental and theoretical research on transitional liquid jets, including detailed explanations of the transition mechanism which may be useful for nozzle design in this regime. More research is needed to explain why transitional liquid jets appear so unstable.…”

Section: Introductionmentioning

confidence: 99%

Turbulent theory of velocity-profile-induced jet breakup

Trettel¹

2019

Preprint

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Velocity profile relaxation is commonly believed to be a cause of jet breakup. This claim is critically reevaluated in this work. Contrary to common belief, laminar liquid jets with parabolic velocity profiles are actually more stable than laminar jets with flatter velocity profiles. This is shown using prior theory and experiments. For turbulent jets, the influence of the velocity profile is more difficult to determine. Previous experimentalists claimed to show that the velocity profile has an effect by varying the nozzle length. The claim is that the boundary layer thickness grows with nozzle length, and that the larger the boundary layer, the less stable the jet. In this work, nozzle length is shown to be a poor proxy for velocity profile effects because the turbulence intensity also increases as the nozzle length increases. Studies with this confounding were ignored in this work. Thinner boundary layers have greater shear, yet experiments have shown that if the boundary layer were made thinner (all else constant), the jet often is more stable. This is termed the "shear paradox". A potential resolution to the shear paradox is developed by considering that the area with shear also decreases as the boundary layer thickness is decreased, and by non-dimensionalizing the turbulent production rate by the dissipation. This theory shows an interaction between the integral scale and velocity profile relaxation which has not been previously discussed. The theoretical prediction that a smaller integral scale leads to more stable jets (due to increased turbulent dissipation) is shown to be somewhat consistent with the limited experimental and DNS data available.

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Model for the initiation of atomization in a high-speed laminar liquid jet

Cited by 20 publications

References 54 publications

Combined Optical Connectivity and Optical Flow Velocimetry for interfacial characterisation of liquid atomisation

Combined Optical Connectivity and Optical Flow Velocimetry for interfacial characterisation of liquid atomisation

Recent Advances in Computational Modeling of Primary Atomization of Liquid Fuel Sprays

Turbulent theory of velocity-profile-induced jet breakup

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