CE06 - Polymères, composites, physique et chimie de la matière molle, procédés

Impact of non-Newtonian drops on liquids – INNpact

Submission summary

The impact of non-Newtonian fluids (polymer microgels, suspensions, emulsions etc.) on free liquid surfaces represents a fundamental and scarcely explored topic in interfacial hydrodynamics and soft matter rheology directly related to extremely important environmental and industrial situations, such as pesticides deposition, inkjet printing, coating, motor jets, ceramic beads and non-spherical particles production, as well as encapsulation processes.
Typically, multiphase impact flows involve a falling non-Newtonian drop passing through a liquid-air interface and forming an air cavity, which later retracts, while the non-Newtonian material penetrates the liquid. During the penetration, the drop undergoes deformations as a consequence of the impact on the liquid surface and its interactions with the aforementioned air cavity, inducing different final shapes. These final morphologies can vary from pears to capsules, passing through Mexican hats and bowls, depending on the impact velocity and the rheological properties of the drop. Since non-Newtonian fluids can present an extremely rich rheological behaviour (which may include shear-rate-dependent viscosity, yield-stress, normal stress differences, elasticity, shear localization etc.), the drop final shapes are difficult to predict and to control. In addition, since, to our knowledge, only very few attempts to highlight this problem have been reported up to now, the physical connections between the drop rheology and the instabilities induced by it during the penetration process remain unknown, which ultimately retains progress in predicting and controlling drop final shape.

The goal of the proposed research is to highlight the physical mechanisms that drive the impact of non-Newtonian drops on liquids. In this connection, we analyse the referred problem through a unique approach combining experiments and three-dimensional numerical simulations. In order to tackle this ambitious challenge, we propose a progressive three-step method that will be developed in the Computing and Fluids team (CFL), a mixed numerical/experimental research group devoted to Fluid Mechanics at CEMEF, MINES ParisTech. In a first step, experiments on the impact of different elasto-viscoplastic drops on different water-glycerol solutions will be carried out via particle tracking techniques, in order to identify physical signatures of the phenomenon (scaling laws, cavity dynamics, drop final morphologies etc.) depending on the drop rheology. In addition to the impact velocity, a wide range of rheological properties can be explored by selecting several non-Newtonian fluids, such as Carbopol microgels (moderate elasto-viscoplasticity), alginate suspensions (moderate elasto-viscoplasticity), black carbon gels (moderate elasto-viscoplasticity), alumina suspensions (high viscoplasticity), and carrageenan gels (high elasticity). Second, supplemental details concerning the velocity/pressure field within the drop, the water-glycerol solution, and the air, as well as the elastic microstructural field will be provided by three-dimensional numerical simulations based on an adaptive variational multi-scale method for these three materials with surface tension. The non-Newtonian drop will be rheologically described via the implementation of an elasto-viscoplastic framework that recovers the usual Oldroyd model for viscoelastic fluids when the yield-stress is null, up to a Hershel-Bulkley (viscoplastic) constitutive law, which emerges in the rigid limit. Furthermore, a Level-Set function will be used to provide the precise position of the fluid interfaces. Finally, a satisfactory quantitative matching between experiments and numerical simulations carried out in a third step will allow us to properly describe the energy distribution within both the drop and the water-glycerol solution during the penetration process and, thus, to precisely highlight the relevance of each rheological ingredient during the drop deformation.

Project coordination

Anselmo PEREIRA (Centre de Mise en Forme des Matériaux)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

CEMEF Centre de Mise en Forme des Matériaux

Help of the ANR 152,880 euros
Beginning and duration of the scientific project: - 36 Months

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