Lattice Boltzmann models for non-ideal fluids with arrested phase-separation

The effects of mid-range repulsion in Lattice Boltzmann models on the coalescence/breakup behaviour of single-component, non-ideal fluids are investigated. It is found that mid-range repulsive interactions allow the formation of spray-like, multi-droplet configurations, with droplet size directly related to the strength of the repulsive interaction. The simulations show that just a tiny ten-percent of mid-range repulsive pseudo-energy can boost the surface/volume ratio of the phase- separated fluid by nearly two orders of magnitude. Drawing upon a formal analogy with magnetic Ising systems, a pseudo-potential energy is defined, which is found to behave like a quasi-conserved quantity for most of the time-evolution. This offers a useful quantitative indicator of the stability of the various configurations, thus helping the task of their interpretation and classification. The present approach appears to be a promising tool for the computational modelling of complex flow phenomena, such as atomization, spray formation and micro-emulsions, break-up phenomena and possibly glassy-like systems as well.Comment: 12 pages, 9 figure

notes on the hybrid urans les turbulence modeling for internal combustion engines simulation

Abstract In the past 20 years, Large Eddy Simulation methods have continuously increased their popularity among the Internal Combustion Engines modeling community, due to their intrinsic potential in the description of the unsteady and randomly generated in-cylinder flow structures. Such capability has gained further relevance in the simulation of modern turbocharged GDI engines, where the high-fidelity resolution of cycle-to-cycle variability phenomena is crucial for the evaluation of the engine performance and emission trends. Nonetheless, even after many years of development the application of standard LES methods to full-scale engine geometries is still not straightforward, due to: the need for specific, turbulence-generating boundary conditions at open ends; more severe grid resolution/quality and time step requirements compared to unsteady RANS; the need for high-order (at least second-order accurate) numerical schemes. Therefore, a viable alternative might be found in hybrid URANS/LES turbulence modeling, which has the potential to achieve adequate scale-resolving levels wherever actually needed, but mitigating at the same time some of the aforementioned concerns. In the present work we discuss the current status and perspectives of URANS/LES hybrids in the ICE field, based on the scientific literature state-of-the art and on a series of previous computational studies made by the authors. Outcomes from this study essentially confirm that this class of methods deserve further attention and will likely support URANS and standard LES in the near future as an effective computational tool for the ICE development and optimization

Shear Banding from lattice kinetic models with competing interactions

Soft Glassy Materials, Non Linear Rheology, Lattice Kinetic models, frustrated phase separation} We present numerical simulations based on a Boltzmann kinetic model with competing interactions, aimed at characterizating the rheological properties of soft-glassy materials. The lattice kinetic model is shown to reproduce typical signatures of driven soft-glassy flows in confined geometries, such as Herschel-Bulkley rheology, shear-banding and histeresys. This lends further credit to the present lattice kinetic model as a valuable tool for the theoretical/computational investigation of the rheology of driven soft-glassy materials under confinement.Comment: 8 Pages, 5 Figure

Modern Lattice Boltzmann methods for multiphase micro-flows

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.During the last decade, the Lattice Boltzmann (LB) method has captured an increasing attention as an efficient tool for the numerical simulation of complex fluids, particularly multi-phase and multi-component flows. In this paper, we revisit the basic features of two modern variants of lattice Boltzmann models for non-ideal fluids, which offer promising perspectives for the numerical simulation of complex micro- flows.This study is funded from the European Project INFLUS, NMP3-CT-2006-031980

A mesoscopic model for microscale hydrodynamics and interfacial phenomena: Slip, films, and contact angle hysteresis

We present a model based on the lattice Boltzmann equation that is suitable for the simulation of dynamic wetting. The model is capable of exhibiting fundamental interfacial phenomena such as weak adsorption of fluid on the solid substrate and the presence of a thin surface film within which a disjoining pressure acts. Dynamics in this surface film, tightly coupled with hydrodynamics in the fluid bulk, determine macroscopic properties of primary interest: the hydrodynamic slip; the equilibrium contact angle; and the static and dynamic hysteresis of the contact angles. The pseudo- potentials employed for fluid-solid interactions are composed of a repulsive core and an attractive tail that can be independently adjusted. This enables effective modification of the functional form of the disjoining pressure so that one can vary the static and dynamic hysteresis on surfaces that exhibit the same equilibrium contact angle. The modeled solid-fluid interface is diffuse, represented by a wall probability function which ultimately controls the momentum exchange between solid and fluid phases. This approach allows us to effectively vary the slip length for a given wettability (i.e. the static contact angle) of the solid substrate

Evoluzione quaternaria del bacino di Leonessa (Rieti)

Il bacino di Leonessa è una delle maggiori depressioni tettoniche intermontane dell’Appennino Centrale. A differenza dalle altre depressioni, disposte in direzione appenninica con la faglia bordiera principale sul lato orientale, il bacino è orientato in senso WNW - ESE ed ha la faglia bordiera principale sul suo margine sud-occidentale. Il più antico deposito di origine continentale che riempie la depressione non è affiorante ed è stato rinvenuto solo in alcuni sondaggi. E’ costituito da alternanze di sabbie-argillose e ghiaie (attribuite da GE.MI.NA. ad un generico Pliocene). I sedimenti affioranti sono stati distinti in sintemi. Quello stratigraficamente più basso è il Sintema di Villa Pulcini, costituito da un alternanza di argille, argille torbose, marne e sabbie argillose di ambiente deposizionale da lacustre a piana a canali intrecciati (braided plain), attribuibili alla parte alta del Pleistocene inferiore. Il Sintema di Villa Pulcini è parzialmente coperto dal Sintema di Leonessa, costituito da depositi di conoide alluvionale (conoide della Vallonina) a ovest e da depositi lacustri a est, ambedue contenenti, nella parte alta, intercalazioni di vulcaniti risedimentate. Il ritrovamento di un molare di M. (M.) trogontherii all’interno di depositi alluvionali consente di riferire al Galeriano (U.F. Slivia - ? U.F. Fontana Ranuccio) la porzione basale del sistema. I due sintemi precedenti sono coperti a tratti da sabbie e sabbie argillose rossastre (Sintema di Terzone), con spessore che raramente supera i 5 metri, ricche di elementi vulcanici rimaneggiati. Nella parte più meridionale del bacino, all’interno della profonda incisione del Fosso Tascino, sono localmente presenti due ordini di terrazzi alluvionali. Attualmente il Fosso Tascino mostra un tipico esempio di letto a canali intrecciati (braided), con una piana che supera i 100 m di larghezza. Nella zona di raccordo tra il versante NE del Monte Tilia e i Sintemi di Leonessa e di Terzone, sono stati riconosciuti due ordini di conoidi alluvionali sovrapposti, costituiti in prevalenza da sedimenti ghiaiosi con una minore componente sabbiosa, poggianti in discordanza sui sedimenti più antichi. La definizione degli eventi erosivo-deposizionali che hanno contraddistinto l’evoluzione del paesaggio nel bacino di Leonessa costituisce un passo ulteriore verso un più preciso inquadramento temporale dell’attività tettonica distensiva, del sollevamento regionale e dei cambiamenti climatici che hanno portato all’attuale assetto geomorfologico dell’Appennino Centrale

Geomorphic signatures of recent normal fault activity versus geological evidence of inactivity: case studies from the central Apennines (Italy)

We have here analysed two normal faults of the central Apennines, one that affects the south-western slopes of theMontagna dei Fiori–Montagna di Campli relief, and the other that is located along the south-western border of the Leonessa intermontane depression. Through this analysis, we aim to better understand the reliability of geomorphic features, such as the fresh exposure of fault planes along bedrock scarps as certain evidence of active faulting in the Apennines, and to define the Quaternary kinematic history of these tectonic structures. The experience gathered from these two case studies suggests that the so-called ‘geomorphic signature’ of recent fault activity must be supported by wider geomorphologic and geologic investigations, such as the identification of displaced deposits and landforms not older than the Late Pleistocene, and/or an accurate definition of the slope instabilities. Our observations indicate that the fault planes studied are exposed exclusively because of the occurrence of non-tectonic processes, i.e. differential erosion and gravitational phenomena that have affected the portions of the slopes that are located in the hanging wall sectors. The geological evidence we have collected indicates that the Montagna dei Fiori–Montagna di Campli fault was probably not active during the whole of theuaternary, while the tectonic activity of the Leonessa fault ceased (or strongly reduced) at least during the Late Pleistocene, and probably since the Middle Pleistocene. The present lack of activity of these tectonic structures suggests that the fault activation for high magnitude earthquakes that produce surface faulting is improbable (i.e.Mw5.5–6.0, with reference to the Apennines, according toMichetti et al. [Michetti, A.M., Brunamonte, F., Serva, L.,Vittori, E. (1996), Trench investigations of the 1915 Fucino earthquake fault scarps (Abruzzo, Central Italy):geological evidence of large historical events, J. Geoph. Res.,101, 5921–5936; Michetti, A.M., Ferreli, L., Esposito, E.,Porfido, S., Blumetti, A.M., Vittori, E., Serva, L., Roberts, G.P. (2000)]). If, according to the current view, the shifting of the intra-Apennine extension towards the Adriatic sectors is still active, the Montagna dei Fiori–Montagna di Campli fault might be involved in active extensional deformation in the future

Herschel-Bulkley rheology from lattice kinetic theory of soft-glassy materials

We provide a clear evidence that a two species mesoscopic Lattice Boltzmann (LB) model with competing short-range attractive and mid-range repulsive interactions supports emergent Herschel-Bulkley (HB) rheology, i.e. a power-law dependence of the shear-stress as a function of the strain rate, beyond a given yield-stress threshold. This kinetic formulation supports a seamless transition from flowing to non-flowing behaviour, through a smooth tuning of the parameters governing the mesoscopic interactions between the two species. The present model may become a valuable computational tool for the investigation of the rheology of soft-glassy materials on scales of experimental interest.Comment: 5 figure

Optimized modeling and design of a pcm-enhanced h2 storage

Thermal and mechanical energy storage is pivotal for the effective exploitation of renewable energy sources, thus fostering the transition to a sustainable economy. Hydrogen-based systems are among the most promising solutions for electrical energy storage. However, several technical and economic barriers (e.g., high costs, low energy and power density, advanced material requirements) still hinder the diffusion of such solutions. Similarly, the realization of latent heat storages through phase change materials is particularly attractive because it provides high energy density in addition to allowing for the storage of the heat of fusion at a (nearly) constant temperature. In this paper, we posit the challenge to couple a metal hydride H-2 canister with a latent heat storage, in order to improve the overall power density and realize a passive control of the system temperature. A highly flexible numerical solver based on a hybrid Lattice Boltzmann Phase-Field (LB-PF) algorithm is developed to assist the design of the hybrid PCM-MH tank by studying the melting and solidification processes of paraffin-like materials. The present approach is used to model the storage of the heat released by the hydride during the H-2 loading process in a phase change material (PCM). The results in terms of Nusselt numbers are used to design an enhanced metal-hydride storage for H-2-based energy systems, relevant for a reliable and cost-effective "Hydrogen Economy". The application of the developed numerical model to the case study demonstrates the feasibility of the posited design. Specifically, the phase change material application significantly increases the heat flux at the metal hydride surface, thus improving the overall system power density

Power vs. capacity performances of thermally integrated MH-PCM hydrogen storage solutions: current status and development perspectives

The present work focuses on two particular performance indicators for hydrogen storage solutions based on the thermal integration of metal hydrides (MH) with phase-change materials (PCMs): i) the (specific) discharge power and ii) the system-level volumetric capacity. The paper first condenses available literature data from modelling and experimental activities, and then analyses a basic numerical benchmark of a low-temperature MH-PCM system. Findings from the literature review show that, due to the interrelation between efficient thermal management and hydrogen desorption rate, the selected performance indicators are not independent one from another. It is also confirmed that simultaneously achieving high-power (flexibility) and specific capacity (compactness) is a challenging goal for such kind of hydrogen storage systems. The parametric analysis of the numerical benchmark system suggests that, for a given MH operating pressure-temperature envelope, special care should be given in the PCM accurate characterisation and selection, as well as in the quantification of the optimal trade-off between the PCM volume and desorption kinetics performance. Furthermore it is found that the geometrical distribution of the MH and PCM volumes have a larger than expected impact on the specific discharge power