Multi-scale analysis of simulated capillary instability

Dumouchel, Christophe; Aniszewski, Wojciech; Vu, Trung-Thanh; Ménard, Thibaut

doi:10.1016/j.ijmultiphaseflow.2017.03.012

Cited by 13 publications

(22 citation statements)

References 38 publications

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“…6-a), e3(0,t)Dj/2 increases up to a local maximum at around t/tBU = 0.5 and then decreases before increasing again when the breakup is approached. The first increase corresponds to the deformation of the cylindrical jet caused by the growth of the swells (as for the Newtonian case [11]) and the subsequent decrease occurs during the evolution of the BOAS pattern. This indicates that the evolution of the BOAS is an interface reduction mechanism.…”

Section: Figure 4 Presents the Temporal Evolution Of V(t) The Averagmentioning

confidence: 99%

“…The scale d4 for which the derivative is a minimum is a characteristic scale. It has been demonstrated ( [11] for instance) that the specific behavior of the derivative in the small scale range (d < d1) in Fig. 2 denotes the presence of a thinning cylindrical ligament.…”

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confidence: 90%

“…Third, the surface-based cumulative scale function E2(d,z) of the jet portion delimited by the analyzing window was measured. Introduced in several previous works (see [9][10][11] for instance), the measurement of this function is inspired from the Euclidean Distance Mapping method to determine fractal dimension [12] and consists in applying successive erosion operations at a scale d ranging from 0 to infinity. The erosion operation consists in removing a strip of width d/2 around the whole system.…”

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confidence: 99%

“…Between these two scales, E2(d,z) monotonously increases. A more detailed definition of the cumulative scale function is available in [9][10][11]. At each z position, the measurement was performed on 204 images and an average cumulative function was calculated.…”

mentioning

confidence: 99%

“…In the case where 3D system information is available, the 3D generalization of the 2D multi-scale description summarized above is straightforward (see [11,13] for applications). The system is characterized by its volume and the erosion operation removes the peripheral volume of a d/2 thickness from the system boundary.…”

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confidence: 99%

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Behaviour of free falling viscoelastic liquid jets

Tirel

Renoult

Dumouchel

et al. 2017

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

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In a recent work, a protocol to measure the relaxation time of dilute polymer solutions, known to be challenging, has been established [1]. This protocol is based on a 2D multi-scale description of free-falling low velocity viscoelastic liquid jets. Although the relaxation time reached an asymptotic value for high jet velocities, a significant dependence with the jet velocity is observed for low velocities. The present work reconsiders these previous experimental data using a 3D multi-scale analysis in order to identify the origin of the dependence between the relaxation time and the jet velocity. The 3D analysis demonstrates the importance of a velocity-dependent coalescence mechanism in the jet behaviour. Thanks to a simple model of jet deformation it is demonstrated that this coalescence mechanism prevents the elasto-capillary contraction of the smallest scales from occurring when the jet velocity is reduced. KeywordsDilute polymer solutions, Viscoelasticity, Jet break-up, Multi-scale analysis IntroductionContrary to Newtonian fluids, the atomisation of a cylindrical jet of a viscoelastic solution presents long life time cylindrical ligaments connecting spherical beads, the so called beads-on-a-string (BOAS) structures [2]. These structures are observed at times prior jet breakup. It is well known that the thinning evolution of the ligaments diameter is controlled by the elasticity of the liquid [3]. The decrease is exponential, with a relaxation time depending only on the physical properties of the liquid. The measurement of this relaxation time is also known to be particularly challenging for dilute polymer solutions [4] for which the relaxation time is very short (micro-second or under). Previous studies [5][6][7][8] have investigated the possibility to use a cylindrical jet to measure this quantity, a method that could be suitable to probe very short times [4]. Yet, it was shown that the relaxation time obtained with this method depends on the jet operating conditions, i.e. the jet velocity, the amplitude and the frequency of the initial disturbance [6][7][8], thus limiting the development of this experimental method. Until recently, new results [4] suggest that an operating domain where these dependences vanish may exist. In this context, a multi-scale analysis of the behaviour of free falling jets of a dilute viscoelastic solution was performed, allowing measurements of the relaxation time [1]. The dynamics of the smaller scales was monitored and an exponential decrease was observed from which a relaxation time was extracted. It was found that the measured relaxation time decreases with increasing jet velocity, reaching a plateau for sufficiently high velocities. This behaviour was related to the influence of the initial amplitude disturbance as reported in [6][7][8]. The higher jet velocity was imposed, the larger initial amplitude was observed on jet images and the lower relaxation time was measured in agreement with [6][7][8]. To date, the dependence of the relaxation time with the jet veloci...

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Section: Figure 4 Presents the Temporal Evolution Of V(t) The Averagmentioning

confidence: 99%

mentioning

confidence: 90%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Behaviour of free falling viscoelastic liquid jets

Tirel

Renoult

Dumouchel

et al. 2017

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

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Measurement of extensional properties during free jet breakup

2020

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This paper reports an experimental method for extracting the extensional properties of viscoelastic liquids during atomization. As a first approach, lowvelocity free jets are considered. Such jets of viscoelastic liquids break with the formation of a beads-on-a-string pattern composed of quasi-spherical beads and quasicylindrical ligaments. The liquid extensional properties, i.e., the relaxation time and the terminal extensional viscosity, are measured by analyzing the ligament thinning. This analysis uses a statistical multi-scale description tool whose principle is explained for an ensemble of thinning cylinders. The tool is applied to free jets of dilute polymer solutions for several polymer concentrations, liquid flow rates and nozzle dimensions. Results show a correlation between the terminal extensional viscosity and the relaxation time in good agreement with the literature. The relaxation time is found to depend on an equivalent nozzle deformation rate. This behavior is due to polymer mechanical degradation in the nozzle. Because of its statistical nature, the method also returns the diameter distribution of the ligaments seen at each position along the jet. Ligament diameter distributions observed in more energetic atomization processes can thus be measured. The extensional properties can also be inferred from a temporal monitoring of these ligaments.

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Where does the droplet size distribution come from?

Canu

Puggelli

Essadki

et al. 2018

International Journal of Multiphase Flow

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This study employs DNS of two-phase flows to enhance primary atomization understanding and modeling to be used in numerical simulation in RANS or LES framework. In particular, the work has been aimed at improving the information on the liquid-gas interface evolution for modeling approaches, such as the Eulerian-Lagrangian Spray Atomization (ELSA) framework. Even though this approach has been already successfully employed to describe the complete liquid atomization process from the primary region to the dilute spray, improvements are still expected on the derivation of the drop size distribution (DSD). The main aim of the present work is the introduction of a new framework to achieve a continuous description of the DSD formation during the atomization process. The attention is here focused on the extraction from DNS data of the behavior of geometrical variable of the liquid-gas interface, such as the mean (H) and Gauss (G) surface curvatures. The use of a Surface Curvature Distribution is also proposed and studied. A Rayleigh-Plateau instability along a column of liquid and a droplet collision case are first of all considered to analyze and to verify the capabilities of the code to correctly predicting the curvature distributions. A statistical analysis

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Multi-scale analysis of simulated capillary instability

Cited by 13 publications

References 38 publications

Behaviour of free falling viscoelastic liquid jets

Behaviour of free falling viscoelastic liquid jets

Measurement of extensional properties during free jet breakup

Where does the droplet size distribution come from?

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