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Secondary instability in thin film flows under an inclined plane: Growth of lenses on spatially developing rivulets
Full text linkImpact of renewable energy integration: a numerical study of atmospheric flow around models of agrivoltaic farms
Full text linkAgrivoltaic systems combine solar energy harvesting with crop cultivation. Here, we leverage Computational-Fluid-Dynamics simulations to investigate their impact by analyzing airflow patterns, temperature distributions, and moisture transport across the panels. The panel configuration affects temperature and heat exchanges, with implications for crop growth and energy harvesting. An increase in spacing or height lowers temperatures within crops and affects moisture distribution. These findings could be employed to suggest design guidelines to balance energy efficiency and agricultural productivity, e.g., by tuning the spatial arrangement
Instability of a thin viscous film flowing under an inclined substrate: steady patterns – CORRIGENDUM
Full text linkInstability of a thin viscous film flowing under an inclined substrate: steady patterns
Full text linkThe flow of a thin film coating the underside of an inclined substrate is studied. We measure experimentally spatial growth rates and compare them to the linear stability analysis of a flat film modelled by the lubrication equation. When forced by a stationary localized perturbation, a front develops that we predict with the group velocity of the unstable wave packet. We compare our experimental measurements with numerical solutions of the nonlinear lubrication equation with complete curvature. Streamwise structures dominate and saturate after some distance. We recover their profile with a one-dimensional lubrication equation suitably modified to ensure an invariant profile along the streamwise direction and compare them with the solution of a purely two-dimensional pendent drop, showing overall a very good agreement. Finally, those different profiles agree also with a two-dimensional simulation of the Stokes equations
Dripping down the rivulet
Full text linkThis paper is associated with a video winner of a 2018 American Physical Society's Division of Fluid Dynamics (DFD) Milton van Dyke Award for work presented at the DFD Gallery of Fluid Motion. The original video is available online at the Gallery of Fluid Motion, https://doi.org/10.1103/APS.DFD.2018.GFM.V0070
Instability of a thin viscous film flowing under an inclined substrate: The emergence and stability of rivulets
Full text linkWe study the pattern formation of a thin film flowing under an inclined planar substrate. The phenomenon is studied in the context of the Rayleigh-Taylor instability using the lubrication equation. Inspired by experimental observations, we numerically study the thin film response to a streamwise-invariant sinusoidal initial condition. The numerical response shows the emergence of predominant streamwise-aligned structures, modulated along the direction perpendicular to the flow, called rivulets. Oscillations of the thickness profile along the streamwise direction do not grow significantly when the inclination is very large or the liquid layer very thin. However, for small inclinations or thick films, streamwise perturbations grow on rivulets. A secondary stability analysis of one-dimensional and steady rivulets reveals a strong stabilization mechanism for large inclinations or very thin films. The theoretical results are compared with experimental measurements of the streamwise oscillations of the rivulet profile, showing a good agreement. The emergence of rivulets is investigated by studying the impulse response. Both the experimental observation and the numerical simulation show a marked anisotropy favouring streamwise-aligned structures. A weakly nonlinear model is proposed to rationalize the levelling of all but streamwise-aligned structures
Transport across thin membranes: Effective solute flux jump
Full text linkA model to describe the transport across membranes of chemical species dissolved in an incompressible flow is developed via homogenization. The asymptotic matching between the microscopic and macroscopic solute concentration fields leads to a solute flux jump across the membrane, quantified through the solution of diffusion problems at the microscale. The predictive model, written in a closed form, covers a wide range of membrane behaviors, in the limit of negligible Reynolds and Péclet numbers inside the membrane. The closure problem at the microscale, found via homogenization, allows one to link the membrane microstructure to its effective macroscopic properties, such as solvent permeability and solute diffusivity. After a validation of the model through comparison with the corresponding full-scale solution, an immediate application is provided, where the membrane behavior is a priori predicted through an analysis of its microscopic properties. The introduced tools and considerations may find applications in the design of thin microstructured membranes
Instability of a thin viscous film flowing under an inclined substrate: the emergence and stability of rivulets – CORRIGENDUM
Full text linkFlow dynamics in a model of a dilated thoracic aorta prior to and following prosthetic replacement
Full text linkWe numerically investigate the flow dynamics in a model of a dilated thoracic aorta, and compare the flow features with the case of a prosthetic replacement in its ascending part. The flow is characterized by an inlet jet which impacts the aortic walls and sweeps toward the aortic arch. Secondary flows generated by the transvalvular jet evolve downstream into a helical flow. The small curvature radius at the end of the aortic arch induces flow separation and vortex shedding in the initial part of the descending aorta, during the systole. The implantation of a prosthesis determines several modifications in the global and local flow patterns. An increase of the pulse wave velocity in the aorta leads to larger pressures inside the vessel, due to the geometrical and rigidity modifications. The sweeping jet is more aligned along the axial direction and propagates faster along the aortic arch. Consequently, a stronger separation of the flow downstream of the aortic arch is observed. By also exploiting manifold analysis, we identify regions characterized by near-wall disordered flows which may present intense accumulation and drop of concentration of biochemicals. These regions are localized downstream of the prosthetic replacement, in the aortic arch, and may be more prone to a new emergence of vessel dilation
Homogenization theory captures macroscopic flow discontinuities across Janus membranes
Full text linkJanus membranes, thin permeable structures with chemical and geometrical asymmetric properties, show great potential in industrial separation processes. Yet the link between the micro- and macro-scale behaviours of these membranes needs to be established rigorously. Here, we develop interface conditions to describe the solvent-solute flow across Janus membranes within a homogenization-based framework. Upstream and downstream spatial averages are introduced to account for discontinuities induced by the microstructure. The homogenized model quantifies the macroscopic jump, across the membrane, in the solvent velocity and stresses, and in the solute concentration and fluxes through coefficients obtained via closure problems at the micro-scale. The model paves the way towards a better understanding of fundamental interface phenomena such as osmosis and phoresis via homogenization
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