Spray Combustion and Atomization

Williams, Forman A.

doi:10.1063/1.1724379

Cited by 312 publications

(200 citation statements)

References 5 publications

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“…As a result, the eventual shape of the drop is a "pancake" of uniform thickness except at the rim, where surface tension effects are significant. The thickness of the pancake is simply the height where the drop surface first collides with the boundary layer.The impact of a liquid drop onto a dry solid surface lies at the heart of many important technological processes [1,2], from the application of a thermal spray [3,4,5,6,7,8,9] to atomization of fuel in a combustion chamber [8,10,11,12]. Recent experiments revealed the splash formed when a low-viscosity liquid, such as water or ethanol, first collides with a dry smooth wall at several m/s owes its existence entirely to the presence of air [13,14,15,16].…”

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confidence: 99%

Impact of a Viscous Liquid Drop

et al. 2010

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We simulate the impact of a viscous liquid drop onto a smooth dry solid surface. As in experiments, when ambient air effects are negligible, impact flattens the falling drop without producing a splash. The no-slip boundary condition at the wall produces a boundary layer inside the liquid. Later, the flattening surface of the drop traces out the boundary layer. As a result, the eventual shape of the drop is a "pancake" of uniform thickness except at the rim, where surface tension effects are significant. The thickness of the pancake is simply the height where the drop surface first collides with the boundary layer.The impact of a liquid drop onto a dry solid surface lies at the heart of many important technological processes [1,2], from the application of a thermal spray [3,4,5,6,7,8,9] to atomization of fuel in a combustion chamber [8,10,11,12]. Recent experiments revealed the splash formed when a low-viscosity liquid, such as water or ethanol, first collides with a dry smooth wall at several m/s owes its existence entirely to the presence of air [13,14,15,16]. These results are motivating new studies on the large-scale deformations created by impact when air effects are absent as well as how a splash forms [17,18,19,20,21,22,23].Here we focus on the impact of a viscous liquid drop when air effects are absent. Recent experiments show that reducing the ambient gas pressure also suppresses the splash of a silicone oil drop. However, the form of the splash is very different. While the splash from a lowviscosity liquid develops within a few 10 µs of impact, the splash from a silicone oil develops slowly, becoming evident only after most of the liquid drop has fallen and flattened into a thin pancake [24,25]. We use an axisymmetric Volume-of-Fluid (VOF) code to simulate the impact at reduced ambient pressure [26,27,28]. Our results show that a boundary layer, corresponding to a thin region where the radial flow created by impact adjusts to the no-slip condition at the wall, is created by the impact. The boundary layer has uniform thickness. As impact nears its end, the drop surface flattens onto the boundary layer, evolving into a pancake of uniform thickness.The Volume-of-Fluid simulation solves the NavierStokes equations, together with constraint of incompressibility, for both the liquid interior and the gas exterior at reduced pressure. Physically appropriate boundary conditions, in particular the Laplace pressure jump across the surface due to surface tension, are enforced [26]. In a typical run, an initially spherical liquid drop with radius a collides with a dry, smooth solid surface at an impact speed U 0 of several m/s. The ambient air density ρ g is kept so small that 2-fold changes in in the value of ρ g have little effect on the liquid dynamics. The bottom surface of the liquid drop is not broken upon impact, which corresponds to maintaining an apparent contact angle of 180 • where the liquid rim meets the wall (Fig. 2a) [29]. We require that the velocity field inside the drop satisfies both the no-flux an...

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confidence: 99%

Impact of a Viscous Liquid Drop

et al. 2010

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“…In the Lagrangian framework, particles are treated as pointwise inclusions without explicitly resolving their surrounding flow fields. The underlying spray density function is then approximated through Dirac delta functions centred on each inclusion [43]. In the present application, the particles result from the atomization of a swirled liquid sheet.…”

Section: Injection Proceduresmentioning

confidence: 99%

Large-Eddy Simulation of Kerosene Spray Ignition in a Simplified Aeronautic Combustor

Hervo

Senoner

Biancherin

et al. 2018

Flow Turbulence Combust

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“…Probabilistic treatment of the dispersed phase The spray equation developed by Williams (1958Williams ( , 1985 represents one of the earliest attempts at a probabilistic description of sprays. Williams considered an ensemble of particles that could be characterized in terms of particle position, radius, velocity and temperature and derived a conservation equation for the particle distribution function.…”

Section: Formulationmentioning

confidence: 99%

Large-eddy simulation of particle-laden turbulent flows

2008

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A large-eddy-based methodology for the simulation of turbulent sprays is discussed. The transport equations for the spatially filtered gas phase variables, in which source terms accounting for the droplet effects are added, are solved together with a probabilistic description of the liquid phase. The probabilistic approach for the liquid phase is based on the transport equation for the spatially filtered joint probability density function of the variables required in order to describe the state of the liquid phase. In this equation, unclosed terms representing the filtered Lagrangian rates of change of the variables describing the spray are present. General modelling ideas for subgrid-scale (SGS) effects are proposed. The capabilities of the approach and the validity of the closure models, with particular with respect to the SGS dispersion, are investigated through application to a dilute particle-laden turbulent mixing layer. It is demonstrated that the formulation is able to reproduce very closely the measured properties of both the continuous and dispersed phases. The large-eddy simulation (LES) results are also found to be entirely consistent with the experimentally observed characteristics of droplet-gas turbulence interactions. Consistent with direct numerical simulation (DNS) studies of isotropic turbulence laden with particles where the entire turbulence spectrum is found to be modulated by the presence of particles, the present investigation, which comprises the effects of particle transport upon the large-scale vortical structures of a turbulent shear flow, highlights what appears to be a selective behaviour; few large-scale frequencies gain energy whereas the remaining modes are damped.

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Spray Combustion and Atomization

Cited by 312 publications

References 5 publications

Impact of a Viscous Liquid Drop

Impact of a Viscous Liquid Drop

Large-Eddy Simulation of Kerosene Spray Ignition in a Simplified Aeronautic Combustor

Large-eddy simulation of particle-laden turbulent flows

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