Experimental and mechanistic description of merging and bouncing in head-on binary droplet collision

Pan, Kuo-Long; Law, Chung K.; Zhou, Biao

doi:10.1063/1.2841055

Cited by 131 publications

(166 citation statements)

References 18 publications

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“…The collision influences the spray characteristics, including the distributions of droplet size and velocity, local mixing rate, and overall atomization performance. Droplet collision has been studied extensively for decades, both experimentally [19,20] and numerically [21,22]. When two droplets approach each other, the surrounding fluid is trapped between them to form a thin film.…”

Section: Droplet Collisionmentioning

confidence: 99%

Thickness-based adaptive mesh refinement methods for multi-phase flow simulations with thin regions

Chen

Yang

2014

Journal of Computational Physics

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In numerical simulations of multi-scale, multi-phase flows, grid refinement is required to resolve regions with small scales. A notable example is liquid-jet atomization and subsequent droplet dynamics. It is essential to characterize the detailed flow physics with variable length scales with high fidelity, in order to elucidate the underlying mechanisms. In this paper, two thickness-based mesh refinement schemes are developed based on distance-and topology-oriented criteria for thin regions with confining wall/plane of symmetry and in any situation, respectively. Both techniques are implemented in a general framework with a volume-of-fluid formulation and an adaptive-mesh-refinement capability. The distance-oriented technique compares against a critical value, the ratio of an interfacial cell size to the distance between the mass center of the cell and a reference plane. The topology-oriented technique is developed from digital topology theories to handle more general conditions. The requirement for interfacial mesh refinement can be detected swiftly, without the need of thickness information, equation solving, variable averaging or mesh repairing. The mesh refinement level increases smoothly on demand in thin regions. The schemes have been verified and validated against several benchmark cases to demonstrate their effectiveness and robustness. These include the dynamics of colliding droplets, droplet motions in a microchannel, and atomization of liquid impinging jets. Overall, the thickness-based refinement technique provides highly adaptive meshes for problems with thin regions in an efficient and fully automatic manner.

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Section: Droplet Collisionmentioning

confidence: 99%

Thickness-based adaptive mesh refinement methods for multi-phase flow simulations with thin regions

Chen

Yang

2014

Journal of Computational Physics

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“…At the instant of possible coalescence, this treatment is discarded so that coalescence then occurs. The time instant of coalescence is defined as the averaged value of the instants that correspond to the last cuspy contour and the first smooth contour between the two droplets [23], which are obtained from the experiment. In the simulations, one droplet with diameter D1 is initialized, colliding towards its symmetric counterpart with velocity V .…”

Section: Methodsmentioning

confidence: 99%

Experimental and Computational Investigation of binary drop collisions under elevated pressure

Reitter

Liu

Breitenbach

et al. 2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

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Spray systems often operate under extreme ambient conditions like high pressure, which can have a significant influence on important spray phenomena. One of these phenomena is binary drop collisions. Such collisions, depending on the relative velocity and the impact parameter (eccentricity of the collision), can lead to drop bouncing, coalescence or breakup. This experimental and computational study is focused on the description of the phenomenon of drop bouncing, which is caused by a thin gas layer preventing the drops coalescence. To identify the main influencing parameters of this phenomenon, experiments on binary drop collisions are performed in a pressure chamber. This experimental system allows us to investigate the effect of an ambient pressure (namely the density and viscosity of the surrounding gas) on the bouncing/coalescence threshold. Keywords drop collision, breakup/coalescence, multiphase flow IntroductionUnderstanding the collisions of drops is of interest for many fields of application. They play an important role in raindrop formation [1,2] and in the modeling of fuel combustion [3,4]. Systematic experimental studies visualizing binary drop collisions provide information allowing to construct regime maps of the collision outcomes [5,6,7]. The mechanisms of bouncing, coalescence, stretching separation, reflexive separation, and shattering are observed. These mechanisms are determined by the kinetic and geometrical parameters of the collision, as well as the properties of the drop liquids and the surrounding gas. The main kinetic and geometrical parameters are defined in Figure 1, where D1 and D2 are the drop diameters and V is the relative drop velocity. B is the distance of closest approach of the drop centers, measured orthogonal to V at the instance of the collision. Dimensional analysis reveals that the collision Weber number We = V 2 D1ρ/σ, the Ohnesorge number Oh = µ/ σD1ρ, the impact parameter X = 2B/(D1 + D2) and the drop size ratio ∆D = D1/D2 determine the outcome of the collision, if the medium ambient to the colliding drops is not varied.

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“…Gotaas et al [12] have studied the effects of viscosity on droplet-droplet collision outcome. The dynamics of head-on collision between two identical droplets was experimentally and computationally investigated by Pan et al [13], who emphasized on the transitions from merging to bouncing and to merging again as Weber number increases. Although experimental studies can monitor the evolution of the complex collision geometry by employing fast-speed digital cameras, the flow processes inside the drops can hardly be accessed.…”

Section: Introductionmentioning

confidence: 99%

“…Since most fuels are Newtonian fluids, experimental studies on droplet collision are mainly limited to such fluid [9][10][11][12][13]. Ashgriz and Poo [9] performed extensive experiments to interpret water droplet collision mechanisms, and obtained a transition curve between coalescence and separation regimes based on collision outcome.…”

Section: Introductionmentioning

confidence: 99%

“…For numerical simulations of binary droplet collisions, several numerical methods have been used for tracking the liquid-gas interface, including the Marker-And-Cell (MAC) method, the front tracking method, Lattice Boltzmann (LB) method, Level-Set (LS) method, Smoothed Particle Hydrodynamic (SPH) method and VOF method [7,8,[12][13][14][15][16][17][18][19][20]. Dupuy et al [15] have simulated the binary head-on collisions at high pressure using the LB method, and explained the stochastic behavior of low inertia coalescence at high pressure.…”

Section: Introductionmentioning

confidence: 99%

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Numerical Simulation on Head-On Binary Collision of Gel Propellant Droplets

Liu

et al. 2013

Energies

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Binary collision of droplets is a fundamental form of droplet interaction in the spraying flow field. In order to reveal the central collision mechanism of two gel droplets with equal diameters, an axi-symmetric form of the Navier-Stokes equations are firstly solved and the method of VOF (volume of fluid) is utilized to track the evolution of the gas-liquid free interface. Then, the numerical computation model is validated with Qian's experimental results on Newtonian liquids. Phenomena of rebound, coalescence and reflexive separation of droplets after collision are investigated, and structures of the complicated flow fields during the collision process are also analyzed in detail. Results show that the maximum shear rate will appear at the point where the flow is redirected and accelerated. Rebound of droplets is determined by the Weber number and viscosity of the fluid together. It can be concluded that the gel droplets are easier to rebound in comparison with the base fluid droplets. The results also show that the alternant appearance along with the deformation of droplets in the radial and axial direction is the main characteristic of the droplet coalescence process, and the deformation amplitude attenuates gradually. Moreover, the reflexive separation process of droplets can be divided into three distinctive stages including the radial expansion, the recovery of the spherical shape, and the axial extension and reflexive separation. The variation trend of the kinetic energy is opposite to that of the surface energy. The maximum deformation of droplets appears in the radial expansion stage; in the case of a low Weber number, the minimum central thickness of a droplet appears later than its maximum deformation, however, this result is on the contrary in the case of a high Weber number. OPEN ACCESSEnergies 2013, 6 205

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Experimental and mechanistic description of merging and bouncing in head-on binary droplet collision

Cited by 131 publications

References 18 publications

Thickness-based adaptive mesh refinement methods for multi-phase flow simulations with thin regions

Thickness-based adaptive mesh refinement methods for multi-phase flow simulations with thin regions

Experimental and Computational Investigation of binary drop collisions under elevated pressure

Numerical Simulation on Head-On Binary Collision of Gel Propellant Droplets

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