Alessio Roccon

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University of Udine | UNIUD · Department of Electrical, Management and Mechanical Engineering

Surfactants are ubiquitous in our everyday life, from soap and detergents in our houses to pulmonary surfactant in our lungs, and can dramatically change the behavior of droplets and bubbles, even when present in tiny amounts. We use direct numerical simulations to shed light on the complex interplay among turbulence, interfaces, and surfactants dy...

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In this work, we propose and test the validity of a phase-field method tailored specifically for modeling boiling phenomena. The method relies on numerical solutions of the Navier–Stokes equations coupled with a phase-field method and the energy equation. The continuity and Navier–Stokes equations have been modified introducing a source term that a...

In this work, we propose and test the validity of a phase-field method tailored specifically for modeling boiling phenomena. The method relies on numerical solutions of the Navier-Stokes equations coupled with a phase-field method and the energy equation. The continuity and Navier-Stokes equations have been modified introducing a source term that a...

We use pseudo-spectral Direct Numerical Simulation (DNS), coupled with a Phase Field Method (PFM), to investigate the turbulent Poiseuille flow of two immiscible liquid layers inside a channel. The two liquid layers, which have the same thickness (h1 = h2 = h), are characterized by the same density (ρ1 = ρ2 = ρ) but different viscosities (η1 ≠ η2),...

We study the heat transfer process in a multiphase turbulent system composed by a swarm of large and deformable drops and a continuous carrier phase. For a shear Reynolds number of Re = 300 and a constant drops volume fraction of Θ = 5.4%, we perform a campaign of direct numerical simulations (DNS) of turbulence coupled with a phase-field method an...

In this work, we detail the GPU-porting of an in-house pseudo-spectral solver tailored towards large-scale simulations of interface-resolved simulation of drop- and bubble-laden turbulent flows. The code relies on direct numerical simulation of the Navier-Stokes equations, used to describe the flow field, coupled with a phase-field method, used to...

We study the problem of drag reduction (DR) in a lubricated conduit, in which a thin layer of low-viscosity (e.g., water) fluid is injected in the near-wall region and facilitates the transport of a core of high-viscosity fluid (e.g., oil). In the present investigation, the flow instance is a channel flow, and consequently we have one thin layer of...

In this work, we develop a dual-grid approach for the direct numerical simulations (DNS) of tur- bulent multiphase flows in the framework of the phase-field method (PFM). With the dual-grid approach, the solution of the Navier-Stokes equations (flow-field) and of the Cahn-Hilliard equa- tion (phase-field) are performed on two different computationa...

Heat transfer by large deformable drops in a turbulent flow is a complex and rich-in-physics system, in which drop deformation, breakage and coalescence influence the transport of heat. We study this problem by coupling direct numerical simulation (DNS) of turbulence with a phase-field method for the interface description. Simulations are run at fi...

We investigate the dynamics of turbulence and interfacial waves in an oil–water channel flow. We consider a stratified configuration, in which a thin layer of oil flows on top of a thick layer of water. The oil–water interface that separates the two layers mutually interacts with the surrounding flow field, and is characterized by the formation and...

Turbulent flows laden with large, deformable drops are ubiquitous in nature and in a wide range of industrial processes. Prediction of the interactions between drops, which deform under the action of turbulence, exchange momentum via surface tension, and that can also exchange heat or mass, are complicated due to the wide range of scales involved:...

We study the dynamics of capillary waves at the interface of a two-layer stratified turbulent channel flow. We use a combined pseudo-spectral/phase field method to solve for the turbulent flow in the two liquid layers and to track the dynamics of the liquid–liquid interface. The two liquid layers have same thickness and same density, but different...

We investigate the effect of density and viscosity differences on a swarm of large and deformable bubbles dispersed in a turbulent channel flow. For a given shear Reynolds number, Reτ=300, and a constant bubble volume fraction, Φ≃5.4%, we perform a campaign of direct numerical simulations of turbulence coupled with a phase-field method accounting f...

The outbreak of the COVID-19 pandemic highlighted the importance of accurately modelling the pathogen transmission via droplets and aerosols emitted while speaking, coughing and sneezing. In this work, we present an effective model for assessing the direct contagion risk associated with these pathogen-laden droplets. In particular, using the most r...

Significance Violent expiratory events like coughs and sneezes represent an important route for the spread of respiratory viruses, such as SARS-CoV-2, the virus responsible for COVID-19. We use finely resolved experiments and simulations to quantify how the turbulent cloud of moist air exhaled during a sneeze largely increases the airborne time and...

After the Spanish flu pandemic, it was apparent that airborne transmission was crucial to spreading virus contagion, and research responded by producing several fundamental works like the experiments of Duguid [J. Hyg. 44:6, 1946] and the model of Wells [Am. J. Hyg., 20:611–18,1934]. These seminal works have been pillars to past and current guideli...

Turbulent flows laden with large, deformable drops or bubbles are ubiquitous in nature and in a number of industrial processes. These flows are characterized by a physics acting at many different scales: from the macroscopic length scale of the problem down to the microscopic molecular scale of the interface. Naturally, the numerical resolution of...

In this work we investigate flow topology modifications produced by a swarm of large surfactant-laden droplets released in a turbulent channel flow. Droplets have the same density and viscosity of the carrier fluid, so only surface tension effects are considered. We run one single-phase flow simulation at Reτ=ρuτh/μ=300 and ten droplet-laden simula...

In this work, we compute numerically breakage/coalescence rates and size distribution of surfactant-laden droplets in turbulent flow. We use direct numerical simulation of turbulence coupled with a two-order-parameter phase-field method to describe droplets and surfactant dynamics. We consider two different values of the surface tension (i.e. two v...

In this work we study the deformation of clean and surfactant-laden droplets in laminar shear-flow. The simulations are based on Direct Numerical Simulation of the Navier–Stokes equations coupled with a Phase Field Method to describe interface topology and surfactant concentration. Simulations are performed considering both 2D (circular droplet) an...

We propose a physically sound explanation for the drag reduction mechanism in a lubricated channel, a flow configuration in which an interface separates a thin layer of less-viscous fluid (viscosity $\unicode[STIX]{x1D702}_{1}$ ) from a main layer of a more-viscous fluid (viscosity $\unicode[STIX]{x1D702}_{2}$ ). To single out the effect of surface...

The phase field method has emerged as a powerful tool for the simulation of multiphase flow. The method has great potential for further developments and applications: it has a sound physical basis, and when associated with a highly refined grid, physics is accurately rendered. However, in many cases, especially when dealing with turbulent flows, th...

In this work, we propose and test the validity of a modified Phase Field Method (PFM), which is specifically developed for large scale simulations of turbulent flows with large and deformable surfactant-laden droplets. The time evolution of the phase field, ϕ, and of the surfactant concentration field, ψ, are obtained from two Cahn–Hilliard-like eq...

In this work we study the turbulence modulation in a viscosity-stratified two-phase flow using Direct Numerical Simulation (DNS) of turbulence and the Phase Field Method (PFM) to simulate the interfacial phenomena. Specifically we consider the case of two immiscible fluid layers driven in a closed rectangular channel by an imposed mean pressure gra...

In this work, we examine the influence of viscosity on breakup and coalescence of a swarm of large drops in a wall-bounded turbulent flow. We consider several values of surface tension and a wide range of drops to fluid viscosity ratios λ=ηd/ηc (with ηd the viscosity of the drops and ηc the viscosity of the carrier fluid), from λ=0.01 to λ=100, whi...

In this work we use Direct Numerical Simulation (DNS) to study the turbulent Poiseuille flow of two immiscible liquid layers inside a rectangular channel. A thin liquid layer (fluid 1) flows on top of a thick liquid layer (fluid 2), such that their thickness ratio is . The two liquid layers have the same density but different viscosities (viscosity...