Binary droplet collision at high Weber number

Modelling of collisions between liquid droplets in the frame of a Lagrangian spray simulation has still many openissues, especially when considering higher viscous droplets and if colliding droplets have a large size difference. A generalisation of the collision maps is attempted based on the behaviour of characteristic points, namely the triple point where bouncing, coalescence and stretching separation coincide and the critical Weber-number where reflexive separation first occurs in head-on collisions. This is done by correlating experimental data with respect to the Capillary number with the Ohnesorge-number for the triple point and the critical Weber-number is also well described by a correlation the Ohnesorge-number. Based on these results the boundary line between stretching separation and coalescence is found by adapting the Jiang et al. (1992) correlation. For the upper boundary of reflexive separation the shifted Ashgriz and Poo (1990) correlation is used. It was however so far not possible to predict the lower bouncing boundary through the Estrade et al. (1999) boundary line correctly. The proposed boundary-line models were validated for various liquid, however still considering only a size ratio of one. With the developed three-line boundary model Euler/Lagrange numerical calculations for a simple spray system were conducted and the droplet collisions were analysed with respect to their occurrence. Droplet collision modelling is performed on the basis of the stochastic droplet collision model, also considering the influence of impact efficiency, which so far was neglected for most spray simulations. The comparison with measurements showedreasonable good agreement for all properties.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4785

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Study on high-Weber-number droplet collision by a parallel, adaptive interface-tracking method

Journal of Fluid Mechanics ◽

10.1017/jfm.2014.558 ◽

2014 ◽

Vol 759 ◽

pp. 104-133 ◽

Cited By ~ 19

Author(s):

Chih-Kuang Kuan ◽

Kuo-Long Pan ◽

Wei Shyy

Keyword(s):

Free Surface ◽

Weber Number ◽

Adaptive Mesh Refinement ◽

Droplet Size Distribution ◽

Adaptive Mesh ◽

Communication Overhead ◽

Interface Tracking ◽

Droplet Collision ◽

Deceleration Phase ◽

Adaptive Interface

AbstractWe have established a parallel, adaptive interface-tracking framework in order to conduct, based on the framework, direct simulation of binary head-on droplet collision in the high-Weber-number regime (from 200 to 1500) that exhibits complex topological changes and substantial length scale variations. The overall algorithms include a combined Eulerian and Lagrangian solver to track moving interfaces, conservative Lagrangian mesh modification and reconstruction, cell-based unstructured adaptive mesh refinement (AMR) in the Eulerian solver, and associated Eulerian and Lagrangian domain partitions to minimize communication overhead. Based on the combined computational and experimental efforts, we have resolved for the first time the free-surface instabilities of the colliding droplets at such high Weber number. We detail the characteristics of coalescence, stretch, end pinching, fingering, free-surface movement and drop breakup. The Taylor–Culick rim is present soon after the collision. Furthermore, we observe two types of longitudinal instabilities on the rim, namely, the Rayleigh–Taylor (RT)-type instability in the initial deceleration phase of the circular sheet right after droplet coalescence, and later the Rayleigh–Plateau (RP) instabilities. As the Taylor–Culick rim disintegrates in the retraction phase, fingering effect is profound and resulting in wider droplet size distribution.

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Numerical Study of Collision Behavior of Melt Drops During Fuel-Coolant Interaction

Volume 3: Student Paper Competition; Thermal-Hydraulics; Verification and Validation ◽

10.1115/icone2020-16206 ◽

2020 ◽

Author(s):

Panpan Wen ◽

Gen Li ◽

Jinchen Gao ◽

Yupeng Li ◽

Akifumi Yamaji ◽

...

Keyword(s):

Contact Area ◽

Weber Number ◽

Adaptive Mesh Refinement ◽

Nuclear Reactor ◽

Numerical Study ◽

Adaptive Mesh ◽

Severe Accident ◽

Collision Dynamics ◽

Droplet Collision ◽

Refinement Method

Abstract The collision dynamics between two droplets plays an important role in various disciplines of nature and practical interests, such as fuel-coolant interaction (FCI), fuel combustion in engines, and various spraying process. FCI presents in nuclear reactor severe accident when the melt relocates into the coolant in the lower head with violent disturbance and vigorous heat transfer. The purpose of this study is to investigate the collision behavior of melt droplets during fuel-coolant interaction. The collision of two equal-sized droplets has been simulated in 3D by using the volume of fluid (VOF) and adaptive mesh refinement method. The numerical simulations of tetradecane droplet collision were carried out to validate the numerical methods. The results showed good agreement with the experiments. Furthermore, the simulations of uranium dioxide (UO2) droplets collision in coolant were carried out. The results showed that the contact area between droplets and coolant increased with time first and then decreased. With the increase of Weber number, the contact area of maximum in the droplet collision increased. Break happened in the later period and many child droplets formed. The number of child droplets increased with the increase of Weber number. In addition, the size distribution of little droplets was investigated.

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A Study on Secondary Drops Produced by Droplet Collision With a Liquid Film

Volume 2: Fora ◽

10.1115/fedsm2006-98520 ◽

2006 ◽

Author(s):

Tomio Okawa ◽

Toshiaki Mori ◽

Takuya Shiraishi ◽

Isao Kataoka

Keyword(s):

Experimental Data ◽

Liquid Film ◽

Weber Number ◽

Water Surface ◽

Total Mass ◽

Impact Angle ◽

Droplet Collision ◽

Primary Droplet ◽

Water Drops ◽

The Impact

The collision of single water drops with a plane water surface was investigated experimentally to elucidate the effect of impact angle on the amount of secondary drops. When the impact angle was not too small, the measured critical impact Weber number for the formation of secondary drops agreed with the experimental data reported in literature, provided that the absolute velocity of primary droplet was used in calculating the Weber number. The ratio of total mass of secondary drops to the mass of primary droplet increased markedly with the decrease of impact angle. Whereas, when the impact angle was too small, no secondary drops were produced within the experimental ranges tested.

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Regimes of coalescence and separation in droplet collision

Journal of Fluid Mechanics ◽

10.1017/s0022112096003722 ◽

1997 ◽

Vol 331 ◽

pp. 59-80 ◽

Cited By ~ 412

Author(s):

J. QIAN ◽

C. K. LAW

Keyword(s):

Weber Number ◽

High Impact ◽

Controlling Factors ◽

Collision Dynamics ◽

Time Resolved ◽

Droplet Collision ◽

Photographic Images ◽

Gaseous Hydrocarbons ◽

The Impact ◽

Different Gases

An experimental investigation of the binary droplet collision dynamics was conducted, with emphasis on the transition between different collision outcomes. A series of time-resolved photographic images which map all the collision regimes in terms of the collision Weber number and the impact parameter were used to identify the controlling factors for different outcomes. The effects of liquid and gas properties were studied by conducting experiments with both water and hydrocarbon droplets in environments of different gases (air, nitrogen, helium and ethylene) and pressures, the latter ranging from 0.6 to 12 atm. It is shown that, by varying the density of the gas through its pressure and molecular weight, water and hydrocarbon droplets both exhibit five distinct regimes of collision outcomes, namely (I) coalescence after minor deformation, (II) bouncing, (III) coalescence after substantial deformation, (IV) coalescence followed by separation for near head-on collisions, and (V) coalescence followed by separation for off-centre collisions. The present result therefore extends and unifies previous experimental observations, obtained at one atmosphere air, that regimes II and II do not exist for water droplets. Furthermore, it was found that coalescence of the hydrocarbon droplets is promoted in the presence of gaseous hydrocarbons in the environment, suggesting that coalescence is facilitated when the environment contains vapour of the liquid mass. Collision at high-impact inertia was also studied, and the mechanisms for separation of the coalescence are discussed based on time-resolved collision images. A coalescence/separation criterion defining the transition between regimes III and IV for the head-on collisions was derived and found to agree well with the experimental data.

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