The dripping regime in the vicinity of the fluid droplet breakup is analyzed using the correlation between experiments and numerics. The evolutions of filament’s neck and its corresponding thinning velocity are described using the logistic functions. Three flow regions are observed as the relative time decreases: (1) a monotonous increase of the neck’s thinning velocity, where inertia and capillarity are balanced, (2) a transition domain characterized by the equilibrium between inertia, capillarity, and viscous forces, where the thinning velocity varies non-monotonically with the relative time and (3) the final droplet pinch-off, where velocity decreases or oscillates around a constant value. The distributions of the $$\upzeta$$ζ -coefficient (parameter related to the non-dimensional second invariant of the velocity gradient) on the filament’s surface and droplet’s profile characterize the kinematics at the interface. The regions dominated by extension, where pure elongation is located at $$\upzeta \cong 1$$ζ ≅ 1 , are determined. One main result of this study is the confirmation that distribution of the $$\upzeta$$ζ -coefficient is a relevant parameter to analyze and to quantify the breakup process. This result has the potential of developing novel techniques and more precise procedures in determining the interfacial rheology of viscous and complex fluids.

This study is concerned with the capillary-wave field generated at the base of a liquid jet impinging on a liquid reservoir. Capillary waves on laminar liquid jets are investigated in terms of the spatial damping coefficient. We find an exponential decrease of the wave crests, with the decay rate given by theory. We show that a small increase in viscosity leads to rapid suppression of the wave-like behavior. This study also emphasizes the effect of viscoelasticity, which decreases the damping coefficient. A simple dependence on the combined Weber–Deborah number is proposed for the dimensionless damping coefficient. At the impact zone, similarities are found for the decay of the free surface compared to the classic model of a meniscus climbing on a cylindrical fiber, the radial jet profile taking the shape of a catenary curve. Theoretical predictions are found to be in good qualitative agreement with the experimental data.

The evolution of an interface between two immiscible liquids in a three-branch symmetric microchannel is numerically and experimentally investigated. The main goals of the paper are to correlate the numeric data with the experimental results for the tested flow case and to assess the quality of the VOF procedure to trace the interface using the Fluent commercial code. The focus of the experiments was to characterize the dynamics of the oil–water interface formed in the vicinity of the bifurcation, at the entrance in the main microchannel of 400 microns width and 50 microns height. The oil core surrounded by water is visualized and micro-PIV measurements are performed in water. Experimental results qualitatively and quantitatively confirm the 3D numerical simulations. We propose the present investigated flow as a benchmark case for the study of the interface in a branching microchannel geometry.

This paper aims to introduce a prediction method for fluid viscosity based on fluid–air interface features in the pendant drop configuration. An automatic algorithm for interface detection, including an image processing pipeline is proposed, followed by a comprehensive study regarding the fitting method of the extracted pixels with a polynomial function. We propose interface detection based on k-means clustering algorithm followed by artifact removal and polynomial fitting and parametrization using curvature radii, minimum and maximum diameter of the droplet, droplet configuration, liquid type (viscous or viscoelastic), density, and surface tension. The radii of curvature were used to classify the liquids in viscous/viscoelastic, while all eight features were used to train a regression algorithm to quantitatively and qualitatively characterize weakly viscoelastic polymeric liquids. Viscous and viscoelastic liquids were involved in the training process, namely water–glycerin solutions and water–polyethylene oxide solutions of various concentrations. Algebraic as well as Chebyshev polynomials were comparatively implemented to provide the most accurate continuous and differentiable function of the interface.