arXiv subjects

Axel Huerre

Publications and source records attributed to Axel Huerre.

9 recordsLinked to original sources

arXiv2026

Morphology of ice structures induced by a freezing rivulet

We investigate the solidification of a water rivulet flowing over a cold inclined substrate and the resulting formation of three-dimensional ice structures. Using a controlled hydraulic and thermal setup, combined with spatiotemporal phase-shifting profilometry and infrared thermography, we characterize both the transient evolution and the final morphology of the ice. We show that a typical experiment proceeds through three stages: formation of a straight ice ridge that stabilizes the rivulet, destabilization and lateral excursions of the flow leading to rapid transverse spreading of the ice structure, and progressive thickening and smoothing of the ice block. Across a wide range of flow rates, inclinations and thermal conditions, the final morphology comprises an upstream triangular lateral envelope, followed by a downstream region of nearly constant width once the substrate edges are reached. Infrared measurements reveal that the rivulet residence time on the substrate follows a Gaussian distribution in the azimuthal angle, implying that the central region of the structure is visited far more frequently than its lateral edges. Focusing on the domain where the height has converged at the end of the experiments, we develop a two-dimensional theoretical model that couples a hydrodynamic model for the rivulet geometry with heat transport in both liquid and solid phases. In the large P\'eclet number limit, the model predicts an exponential increase of the stationary ice height along the flow direction and it shows an excellent agreement with the experimental height field. We further show how the combination of the stationary height profile and the non-uniform residence time distribution controls the angular convergence of the ice cross-sections.

physics.flu-dyn↗

arXiv2025

Free surface topography of capillary flows using spatiotemporal phase shifting profilometry

We present a novel experimental technique to characterize the free surface of capillary flows adapted from the Spatio-Temporal Phase Shifting Profilometry (ST-PSP) method introduced by Ri et al. (Journal of Optics, 2019) for solid bodies. The present study is focused on various regimes of capillary flows over inclined surfaces, including drops, rivulets, meanders, and braided films. A calibration process is carried out using a solid wedge to determine the optical distances required for the phase-to-height relationship. The optimal dye concentration necessary for accurately reconstructing the free surface of a dyed water flow is explored. The ST-PSP method is then applied to profile different liquid flows and objects, achieving large signal-to-noise ratios across all experiments. Notably, the analysis of a sessile droplet shows a promising correlation between the ST-PSP results and side-view visualizations, as evidenced by the accurate recovery of its apparent contact angle. Furthermore, free surface reconstructions of rivulet flows exhibit good agreement with the theoretical predictions of Duffy and Moffatt (The Chemical Engineering Journal and the Biochemical Engineering Journal, 1995). These results suggest that the ST-PSP method is highly effective for obtaining accurate height maps of capillary flows and objects, making it a valuable tool for validating theoretical models in the future.

physics.flu-dyn↗

arXiv2024

Deformation of hydrogel during freezing

We conducted experiments to directionally freeze agar hydrogel drops with different polymer concentrations, on a copper substrate maintained at low temperature. Unlike the water droplet studied in the literature, where the liquid part can reorganize during freezing, our droplets show a distinct deformation. This is due to the presence of the viscoelastic solid polymer matrix, which prevents deformation of the unfrozen part, leading mainly to elongation in the direction of the temperature gradient. We then derive a model describing this deformation. It assumes a flat freezing front, a change in volume at the front resulting from the Stefan condition, and a remaining volume to be frozen identical in shape to the initial one. The latter is in good agreement with experimental observations as long as water fluxes in the porous hydrogel remain negligible. It is also conclusive for different object shapes, as the hydrogel can be freely molded without a container.

cond-mat.soft↗

arXiv2024

Freezing receding contact lines

We investigate experimentally the receding of a contact line when a Peltier module is pulled out of a water bath at constant speed, while a ice layer is also growing at constant speed on the Peltier module. A steady regime is therefore reached for all the parameters used in this studied, corresponding to a dynamical stationnary meniscus. We show that the height of the meniscus provides most of the properties of the flow. For high pulling rate, it is related to the amount of liquid of the equivalent Landau-Levich (LL) film that would be extracted from the bath, which is eventually freezing as the plate is lifted upward. For smaller velocity, so that no LL film would be formed without freezing, the meniscus height is directly linked to the contact angle of water on ice in these conditions. Solving numerically the meniscus equation taking into account the solidifcation of water, our results suggest that the contact angle of water on ice should be around $6^\circ$.

physics.flu-dyn↗

arXiv2024

Role of melting and solidification in the spreading of an impacting water drop

The present study reports experiments of water droplet impacting on ice or on a cold metallic substrate, with the aim of understanding the effect of phase change on the impingement process. Both liquid and substrate temperatures are varied, as well as the height of fall. The dimensionless maximum spreading diameter, $\beta_m$, is found to increase with both temperatures as well as with the impact velocity. Furthermore, $\beta_m$ is reduced when solidification, which enhances dissipation, is present, whereas fusion favours the liquid film spreading. These observations are rationalized by extending an existing model of effective viscosity, in which phase change alters the size and shape of the developing viscous boundary layer, thereby modifying the value of $\beta_m$. The use of this correction allows to adapt a scaling law existing for isothermal drop impacts to propose a universal law giving the maximum diameter of an impacting water droplet in the presence of melting or solidification.

physics.flu-dyn↗

arXiv2024

Microstructural features governing fracture of a two-dimensional amorphous solid identified by machine learning

Brittle fracturing of materials is common in natural and industrial processes over a variety of length scales. Knowledge of individual particle dynamics is vital to obtain deeper insight into the atomistic processes governing crack propagation in such materials, yet it is challenging to obtain these details in experiments. We propose an experimental approach where isotropic dilational strain is applied to a densely packed monolayer of attractive colloidal microspheres, resulting in fracture. Using brightfield microscopy and particle tracking, we examine the microstructural evolution of the monolayer during fracturing. Furthermore, using a quantified representation of the microstructure in combination with a machine learning algorithm, we calculate the likelihood of regions of the monolayer to be on a crack line, which we term Weakness. From this analysis, we identify the most important contributions to crack propagation and find that local density is more important than orientational order. Our methodology and results provide a basis for further research on microscopic processes during the fracturing process.

cond-mat.soft↗

arXiv2020

Solidification of a rivulet: shape and temperature fields

The freezing of a water rivulet begins with a water thread flowing over a very cold surface, is naturally followed by the growth of an ice layer and ends up with a water rivulet flowing on a static thin ice wall. The structure of this final ice layer presents a surprising linear shape that thickens with the distance. This paper presents a theoretical model and experimental characterisation of the ice growth dynamics, the final ice shape and the temperature fields. In a first part, we establish a 2D model, based on the advection-diffusion heat equations, that allows us to predict the shape of the ice structure and the temperature fields in both the water and the ice. Then, we study experimentally the formation of the ice layer and we show that both the transient dynamics and the final shape are well captured by the model. In a last part, we characterise experimentally the temperature fields in the ice and in the water, using an infrared camera. The model shows an excellent agreement with the experimental fields. In particular, it predicts well the linear decrease of the water surface temperature observed along the plane, confirming that the final ice shape is a consequence of the interaction between the thermal boundary layer and the free surface.

physics.flu-dyn↗

arXiv2019

Freezing a rivulet

We investigate experimentally the formation of the particular ice structure obtained when a capillary trickle of water flows on a cold substrate. We show that after a few minutes the water ends up flowing on a tiny ice wall whose shape is permanent. We characterize and understand quantitatively the formation dynamics and the final thickness of this ice structure. In particular, we identify two growth regimes. First, a 1D solidification diffusive regime, where ice is building independently of the flowing water. And second, once the ice is thick enough, the heat flux in the water comes into play, breaking the 1D symmetry of the problem, and the ice ends up thickening linearly downward. This linear pattern is explained by considering the confinement of the thermal boundary layer in the water by the free surface.

physics.flu-dyn↗

arXiv2018

Dynamic capillary assembly of colloids at interfaces with 10,000g accelerations

Extreme deformation of soft matter is central to our understanding of the effects of shock, fracture, and phase change in a variety of systems. Yet, despite, the increasing interest in this area, far-from-equilibrium behaviours of soft matter remain challenging to probe. Colloidal suspensions are often used to visualise emergent behaviours in soft matter, as they offer precise control of interparticle interactions, and ease of visualisation by optical microscopy. However, previous studies have been limited to deformations that are orders of magnitude too slow to be representative of extreme deformation. Here we use a two-dimensional model system, a monolayer of colloids confined at a fluid interface, to probe and visualise the evolution of the microstructure during high-rate deformation driven by ultrasound. We observe the emergence of a transient network of strings, and use discrete particle simulations to show that it is caused by a delicate interplay of dynamic capillarity and hydrodynamic interactions between particles oscillating at high-frequency. Remarkably, we find evidence of inertial effects in a colloidal system, caused by accelerations approaching 10,000g. These results also suggest that extreme deformation of soft matter offers new opportunities for pattern formation and dynamic self-assembly.

cond-mat.soft↗