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In this paper we propose a mesoscale model for polar fluids and numerically investigate its validity by considering well known benchmark cases: the steady and unsteady Poiseuille and the low Reynolds lid-driven cavity flow. Analytical and numerical results are compared with our numerical results and a very good agreement is found. Then we consider not yet investigated high Reynolds lid-driven cavity flow cases, obtaining consistent and interesting results, which encourage to apply the proposed model to more complex cases. [ABSTRACT FROM AUTHOR]

This paper is aimed at assessing the ability of the Lattice-Boltzmann Method (LBM) in reproducing the fundamental features of lock-exchange gravity currents. Both two- and three-dimensional numerical simulations are presented at different Reynolds numbers ( 1000 ≤ R e ≤ 30,000 ). Turbulence has been accounted for by implementing an equivalent Large Eddy Simulation (LES) model in the LBM framework. The advancement of the front position and the front velocity obtained by LBM numerical simulations are compared with laboratory experiments appositely performed with similar initial and boundary conditions and with previous results from literature, revealing that the dynamics of the gravity current as a whole is correctly reproduced. Lobes and clefts instabilities arising in three-dimensional simulations and the entrainment parameter are also analysed and comparisons with previous studies are presented. [ABSTRACT FROM AUTHOR]

We present an entropic version of the lattice Boltzmann pseudo-potential approach for the simulation of multiphase flows. The method is shown to correctly simulate the dynamics of impinging droplets on hydrophobic surfaces and head-on and grazing collisions between droplets, at Weber and Reynolds number regimes not accessible to previous pseudo-potential methods at comparable resolution. [ABSTRACT FROM AUTHOR]

Tsunami waves are generated by sea bottom failures, landslides and faults. The concurrent generation of hydro-acoustic waves (HAW), which travel much faster than the tsunami, has received much attention, motivated by their possible exploitation as precursors of tsunamis. This feature makes the detection of HAW particularly well-suited for building an early-warning system. Accuracy and efficiency of the modeling approaches for HAW thus play a pivotal role in the design of such systems. Here, we present a Lattice Boltzmann Method (LBM) for the generation and propagation of HAW resulting from tsunamigenic ground motions and verify it against commonly employed modeling solutions. LBM is well known for providing fast and accurate solutions to both hydrodynamics and acoustics problems, thus it naturally becomes a candidate as a comprehensive computational tool for modeling generation and propagation of HAW. [ABSTRACT FROM AUTHOR]

The ability to accurately and efficiently model the intrusion of salt wedges into river beds is crucial to assay its interaction with human activities and the natural environment. We present a 2D multi-layer Shallow Water Lattice Boltzmann (SWLB) model able to predict the salt wedge intrusion in river estuaries. The formulation usually employed for the simulation of gravity currents is here equipped with proper boundary conditions to handle both the downstream seaside outlet and the upstream river inlet. Firstly, the model is validated against highly accurate semi-analytical solutions of the steady state 1D two-layer Shallow Water model. Secondly, the model is applied to a more complex, fully 3D geometry, to assess its capability to handle realistic cases. The simple formulation proposed for the shear interlayer stress is proven to be consistent with the general 3D viscous solution. In addition to the accuracy, the model inherits the efficiency of the Lattice Boltzmann approach to fluid dynamics problems. [ABSTRACT FROM AUTHOR]

We present a lattice Boltzmann realization of Grad's extended hydrodynamic approach to nonequilibrium flows. This is achieved by using higher-order isotropic lattices coupled with a higher-order regularization procedure. The method is assessed for (low across parallel plates and three-dimensional flows in porous media, showing excellent agreement of the mass flow with analytical and numerical solutions of the Boltzmann equation across the full range of Knudsen numbers, from the hydrodynamic regime to ballistic motion. [ABSTRACT FROM AUTHOR]

The solution of fluid dynamics problems has recently witnessed a remarkable increase in the formulation of Boltzmann-based approaches, mainly triggered by the numerous advantages stemming from the concrete possibility of employing a low number of allowed velocities, which is the basis of the Lattice-Boltzmann (LB) methods. The field of Shallow Water (SW) modeling also took advantage of these techniques, but there are still open problems related to the practical impossibility to simulate transcritical flows while retaining the intrinsic simplicity of the LB approaches. This problem is even more crucial if one considers that transcritical flows always develop whenever a transition over dry bed occurs. Since such vertically integrated models are currently the mostly employed ones for simulating technically interesting flows, and since these flows often require the flooding of an initially dry bed, the application of LB methods seems to be facing its limits. The Gas Kinetic Method (GKM) overcomes this issue, integrating the Boltzmann equations in continuous velocity space. In this work, we formulate and extensively test a GKM-based model for solving the SW equations, which is able to manage the propagation over uneven dry bed. The benchmarking, carried out against analytical, experimental and previously proposed numerical reference solutions, shows promising results of the proposed approach. [ABSTRACT FROM AUTHOR]

In this work, a numerical assessment of the suitability of a Single Relaxation Time (SRT) Lattice Boltzmann Method (LBM) model to simulate axisymmetric gravity currents is carried out. The model results are compared with both experimental data and other numerical models. The particular SRT formulation employed is known to converge, in the limit of low Knudsen number, to the two-layer 2D Shallow Water Equations (SWEs) set with a viscosity term featuring a closed theoretical formulation. Even with the lowest viscosity achievable by the method, its effect is shown to become important in most of the cases analysed, thus posing some serious constraints on possible application of the single relaxation time LBM method to simulate the lock-release generated-type gravity currents analysed here. The comparison with classical numerical models shows that the the viscous effects in the LBM model can be well reproduced employing coefficients derived from the above-mentioned theoretical formulation. [ABSTRACT FROM AUTHOR]

The Lattice Boltzmann Method (LBM) is a mesoscopic method founded on the kinetic theoryof Boltzmann and has been proven to describe successfully flows of hydraulic interest such asturbulent, multicomponent and multiphase flows. The main advantage of the LBM, comparedto more traditional methods of the Computational Fluid Dynamics, are: the simplicity of theset of explicit algebraic equations forming the computational algorithm, the ease ofdescription of complex boundaries and the proneness of the LBM to provide unprecedentedparallel scalability on a large number of architectures. Thus, the computational resourcesavailable nowadays make the employment of 3D models feasible to study large-scaleproblems as well. In this work, a fully 3D LBM model is developed and applied to the simulation of freesurface impulsive flows. The evolution of the free surface is here tracked by means of a 3Dinterface tracking model and coupled to the traditional LBM algorithm. Dam-breakevents are simulated and LBM numerical results are compared to both analytical andexperimental reference results. The latter are relative to symmetrical dam-break,asymmetrical dam-break, dam-break over a triangular obstacle, dam-break with anisolated building and the laboratory model of the Toce river test case. The accuracy ofthe model is assessed by comparing depth and velocity values, when available,at some gauge locations. The study shows that the LBM provides a remarkablyaccurate description of the phenomena. The results are very promising for futureapplications of this kind of models for the study of realistic hydraulic problems. [ABSTRACT FROM AUTHOR]

We investigate the accuracy and performance of the regularized version of the single-relaxation-time lattice Boltzmann equation for the case of two- and three-dimensional lid-driven cavities. The regularized version is shown to provide a significant gain in stability over the standard single-relaxation time, at a moderate computational overhead. [ABSTRACT FROM AUTHOR]

Free-surface flows play an important role in many environmental hydraulic problems. Owing to their characteristic large spatial and temporal scales, reduced complexity models, such as depth-integrated shallow water (DI-SW) models, have so far been largely preferred to three-dimensional (3D) approaches. Even if they can reproduce water levels satisfactorily, DI-SW models do not natively provide flow velocity at the bed, which is pivotal for estimating scour effects induced by impulsive flows, such as those resulting from dam breaks. However, resort to fully 3D modeling is often impractical due to the high computational demand required; nonetheless, recent works have shown impressive performance of the lattice Boltzmann method (LBM) compared to classical numerical methods while proving to be as accurate in many fields, suggesting LBM makes such computations affordable on desktop computers. So far, a comprehensive assessment of a LBM-based, fully 3D, free-surface model is still lacking. In this work, a LBM model is compared to data from a large series of dam-break-flow experiments, in terms of water levels and, where available, flow velocities. Comparisons with available DI-SW models are also carried out. Results show that the LBM model can correctly simulate both water levels and velocity distributions, the latter often being inaccurately reproduced by DI-SW models. To provide guidelines for the correct modeling of such flows, considerations are also given to opportunities to use either no-slip or free-slip boundary conditions, the latter being preferable if underresolved boundary layers are present. [ABSTRACT FROM AUTHOR]

Nowadays the Lattice Boltzmann Method (LBM), thanks to its mesoscale approach, is a powerful tool when dealing with upscaling problems in Fluid Dynamics. In this study a numerical investigation on the flow through fractured porous media has been performed, based on a three dimensional LBM model developed at the Engineering Department of the Roma Tre University. Two different kinds of porous matrices, consisting of deterministic and random arrays of spheres, have been considered. The formers have been arranged both as a primitive and body centred cubic system. The latters are characterized both by monodisperse and by polydisperse diameters. In order to calculate the permeability of every considered porous medium, the Darcy's experiment has been simulated. Then a channel has been considered in every porous matrix, giving raise to different fractured porous media. The Darcy's experiment has been repeated with the fractured porous media and the LBM has been used as a numerical lab to verify the ranges of validity of upscaled models based on the analytical solution of flow in equivalent porous media. It has been found that numerical and analytical results are in good agreement when a fractured deterministic porous medium is considered. In this case the order of magnitude of the relative error, defined as the absolute value of the percentage difference between the numerical and analytical velocity on the axis of the channel, is equal to few percents. Moreover, the error decreases with the permeability: the greater the permeability, the smaller the error. LBM numerical results obtained considering random fractured porous media are characterised by a relative error larger than that corresponding to numerical results obtained considering deterministic fractured porous media, being equal permeability and hydrodynamic conditions. Future work is addressed to the understanding of how the parameters characterizing the random fractured porous media affect the results obtained by applying the LBM model and the difference with the reference results. [ABSTRACT FROM AUTHOR]