Alessandro De Rosis

Alternative formulation to incorporate forcing terms in a lattice Boltzmann scheme with central moments

Within the framework of the central-moment-based lattice Boltzmann method, we propose a strategy to account for external forces in two and three dimensions. Its numerical properties are evaluated against consolidated benchmark problems, highlighting very high accuracy and optimal convergence. Moreover, our derivations are light and intelligible.

Nonorthogonal central-moments-based lattice Boltzmann scheme in three dimensions

We present an alternative three-dimensional lattice Boltzmann collision operator consisting of a nonorthogonal basis of central moments. Our formulation is characterized by an intelligible derivation with a relatively simple and quite general implementation. It is successfully validated against several established, well-consolidated, well-defined benchmark problems, showing excellent properties in terms of accuracy and convergence. If compared to the adoption of the classical Bhatnagar-Gross-Krook operator, our model possesses superior stability.

Central-moments–based lattice Boltzmann schemes with force-enriched equilibria

This paper presents a numerical scheme to account for external forces in the central-moments–based lattice Boltzmann method. Instead of deriving additional forcing operators, here we propose to incorporate forces directly in the equilibrium populations. The resultant concise methodology is validated against established well-defined problems admitting analytical solution, showing very good accuracy and convergence rate. Moreover, it outperforms the classical BGK kernel in terms of stability.

Non-orthogonal central moments relaxing to a discrete equilibrium: A D2Q9 lattice Boltzmann model

A novel D2Q9 lattice Boltzmann scheme based on the relaxation of central moments is presented. Differently from previous efforts, here we introduce a non-orthogonal basis of moments which relax to a discrete local equilibrium. Under these choices, our proposed model recovers exactly the BGK collision kernel if a unique relaxation rate is adopted. Numerical tests involving well-consolidated canonical problems highlight the excellent properties of the algorithm in terms of accuracy, convergence and stability. Moreover, our formulation shows an intelligible derivation and a simple practical implementation.

Transport of ellipsoid fibers in oscillatory shear flows: Implications for aerosol deposition in deep airways

Abstract It is widely acknowledged that inhaled fibers, e.g. air pollutants and anthropogenic particulate matter, hold the ability to deposit deep into the lungs reaching the distal pulmonary acinar airways as a result of their aerodynamic properties; these particles tend to align with the flow and thus stay longer airborne relative to their spherical counterpart, due to higher drag forces that resist sedimentation. Together with a high surface‐to‐volume ratio, such characteristics may render non‐spherical particles, and fibers in particular, potentially attractive airborne carriers for drug delivery. Until present, however, our understanding of the dynamics of inhaled aerosols in the distal regions of the lungs has been mostly limited to spherical particles. In an effort to unravel the fate of non‐spherical aerosols in the pulmonary depths, we explore through numerical simulations the kinematics of ellipsoid‐shaped fibers in a toy model of a straight pipe as a first step towards understanding particle dynamics in more intricate acinar geometries. Transient translational and rotational motions of micron‐sized ellipsoid particles are simulated as a function of aspect ratio (AR) for laminar oscillatory shear flows mimicking various inhalation maneuvers under the influence of aerodynamic (i.e. drag and lift) and gravitational forces. We quantify transport and deposition metrics for such fibers, including residence time and penetration depth, compared with spherical particles of equivalent mass. Our findings underscore how deposition depth is largely independent of AR under oscillatory conditions, in contrast with previous works where AR was found to influence deposition depth under steady inspiratory flow. Overall, our efforts underline the importance of modeling oscillatory breathing when predicting fiber deposition in the distal lungs, as they are inhaled and exhaled during a full inspiratory cycle. Such physical insight helps further explore the potential of fiber particles as attractive carriers for deep airway targeting. Graphical abstract Figure. No caption available.

Advanced lattice Boltzmann scheme for high-Reynolds-number magneto-hydrodynamic flows

ABSTRACT Is the lattice Boltzmann method suitable to investigate numerically high-Reynolds-number magneto-hydrodynamic (MHD) flows? It is shown that a standard approach based on the Bhatnagar–Gross–Krook (BGK) collision operator rapidly yields unstable simulations as the Reynolds number increases. In order to circumvent this limitation, it is here suggested to address the collision procedure in the space of central moments for the fluid dynamics. Therefore, an hybrid lattice Boltzmann scheme is introduced, which couples a central-moment scheme for the velocity with a BGK scheme for the space-and-time evolution of the magnetic field. This method outperforms the standard approach in terms of stability, allowing us to simulate high-Reynolds-number MHD flows with non-unitary Prandtl number while maintaining accuracy and physical consistency.