arXiv subjects

S. A. Hosseini

Publications and source records attributed to S. A. Hosseini.

At least 19 recordsLinked to original sources

arXiv2026

Consistent lattice Boltzmann model with body force and heat source for compressible flows of generic fluids

This work presents a consistent formulation of body-force and heat-source terms within a double-distribution-function lattice Boltzmann framework for simulating compressible flows of generic fluids. The proposed approach extends a recently developed kinetic framework for non-ideal compressible fluid dynamics by incorporating external forcing and volumetric heating through shifted quasi-equilibrium states. The standard lattice Boltzmann discretization is applied with a second-order accurate integration along characteristics and product-form equilibria on nearest-neighbor lattices are employed, supplemented by necessary correction terms. This formulation ensures the consistent recovery of the Navier-Stokes-Fourier equations, including the Korteweg stress tensor, across arbitrary equations of state, while maintaining independently controllable thermodynamic and transport coefficients. The methodology is rigorously validated and applied for two different flow regimes, with ideal-gas compressible flows and non-ideal/multiphase compressible flows, respectively, where a broad hierarchy of benchmarks is employed, including non-classical shock tubes, thermal Couette flows, and force-driven Poiseuille and Womersley flows. The framework's ability to capture complex thermodynamic processes using forcing and heating is further demonstrated through Rayleigh and Fanno flows, Joule-Thomson effects, and throttling processes. Furthermore, the model is validated for multiphase phenomena, including interface consistency and liquid-vapor co-existence. The results demonstrate excellent agreement with analytical solutions and reference data, while spatio-temporal grid-refinement studies confirm the expected second-order accuracy of the scheme. This establishes the model as a robust and efficient foundation for simulating highly compressible flows of generic fluids in the presence of numerical and physical s...

physics.flu-dyn↗

arXiv2026

Vectorial lattice Boltzmann solver for compressible inviscid flows with generic equation of state

We develop a vectorial lattice Boltzmann model with a space-time adaptive relaxation coefficient, combined with adaptive time-stepping for compressible Euler dynamics with generic equation of state. The model, due to special form of the relaxation coefficient devised here is shown to converge to the Euler limit with second-order accuracy in the absence of shocks under acoustic scaling. The solver is robust and able to properly capture compressible gas dynamics for both ideal and non-ideal equations of state, including the Bethe--Zel'dovich--Thompson regime. This is verified and demonstrated through a variety of configurations of increasing complexity.

math.NA↗

arXiv2026

Local kinetic sensors for adaptive mesh and algorithm refinement

This paper presents novel refinement sensors for the application to adaptive mesh and algorithm refinement (AMAR) with kinetic models, such as discrete velocity and lattice Boltzmann methods. While refinement criteria for AMAR based on macroscopic variables can be replicated in a purely local, and therefore more scalable, way, the main advantage that can be leveraged when working with discrete velocity and lattice Boltzmann methods is the accessibility of information from the one-particle distribution function. With this accessibility, a novel palette of refinement sensors is introduced, allowing for a set of neatly tailored refinement criteria applicable to resolve characteristic flows features in many relevant domains of fluid mechanics, for instance, those emerging in compressible, turbulent, and non-equilibrium flows or non-ideal fluids. After detailed validation, novel refinement sensors are showcased for the application of adaptive mesh refinement (AMR) to a discrete velocity Boltzmann solver for compressible, viscous, and non-equilibrium flows, demonstrating promising results. The proposed sensors establish an accurate, efficient and scalable approach to kinetic simulations with AMAR, offering a valuable tool for studying complex problems in fluid dynamics and paving the way for future extensions to more specific flow problems.

physics.flu-dyn↗

arXiv2026

Effects of anisotropic confinement on droplet rebound from superhydrophobic surfaces

On flat superhydrophobic surfaces, droplet rebound is well described by a single inertio-capillary time scale, yielding a contact-time that is independent of impact energy. This single-mode response reflects the radial symmetry of flat-plate impacts. We demonstrate that an anisotropic geometric constraint, imposing a fixed spreading length along one axis, breaks this degeneracy and splits the rebound into a reciprocal pair of inertio-capillary modes. The fixed length also couples the contact-time to the Weber-dependent maximum spread, introducing an impact-energy dependence absent on the flat plate. We realize this constraint with grooved substrates, simulated using a non-ideal, entropic, multiple-relaxation-time lattice Boltzmann method and validated against the experiments of Chantelot et al. Extending their blob model from a single transverse scale to the reciprocal pair, we organize both modes through a geometric blob number and relate their time scales to the Weber number and groove width. We show that on non-wetting grooves the reciprocal modes are recovered directly, and explore the effects of finite wall affinity, using competition between the two modes to explain an observed two-branch structure in the contact-time response on mildly wetting, superhydrophobic grooves. Predictions tied to global energy balance reproduce cleanly across all conditions, while those tied to the details of the droplet's spread morphology are approximate but directionally correct. These results show that anisotropic confinement turns contact-time reduction from a question of accelerating a single rebound mode into one of selecting between conjugate inertio-capillary modes.

physics.flu-dyn↗

arXiv2026

Lattice Boltzmann model for non-ideal compressible fluid dynamics

We present a new kinetic model and its lattice Boltzmann realization for the simulation of compressible, non-ideal fluid flows. The method employs first-neighbour lattices and introduces a consistent set of correction terms constructed via quasi-equilibrium attractors, ensuring positive-definite and Galilean-invariant Navier-Stokes dissipation rates. This construction circumvents the need for extended stencils or ad hoc regularization, while maintaining numerical stability and thermodynamic consistency across a broad range of flow regimes. The resulting model accurately reproduces both the Euler- and Navier-Stokes hydrodynamic limits. As a stringent validation, we demonstrate, for the first time within a lattice Boltzmann framework, quantitatively accurate simulations of shock-drop interactions at Mach numbers up to 1.47. The proposed approach thus extends the applicability of lattice Boltzmann methods to high-speed, non-ideal compressible flows with a minimal kinetic stencil.

physics.flu-dyn↗

arXiv2026

Consistent kinetic modeling of compressible flows with variable Prandtl numbers: Double-distribution quasi-equilibrium approach

A consistent kinetic modeling and discretization strategy for compressible flows across all Prandtl numbers and specific heat ratios is developed using the quasi-equilibrium approach within two of the most widely used double-distribution frameworks. The methodology ensures accurate recovery of the Navier-Stokes-Fourier equations, including all macroscopic moments and dissipation rates, through detailed hydrodynamic limit analysis and careful construction of equilibrium and quasi-equilibrium attractors. Discretization is performed using high-order velocity lattices with a static reference frame in a discrete velocity Boltzmann context to isolate key modeling aspects such as the necessary requirements on expansion and quadrature orders. The proposed models demonstrate high accuracy, numerical stability and Galilean invariance across a wide range of Mach numbers and temperature ratios. Separate tests for strict conservation and measurements of all dissipation rates confirm these insights for all Prandtl numbers and specific heat ratios. Simulations of a thermal Couette flow and a sensitive two-dimensional shock-vortex interaction excellently reproduce viscous Navier-Stokes-Fourier-level physics. The proposed models establish an accurate, efficient and scalable framework for kinetic simulations of compressible flows with moderate supersonic speeds and discontinuities at arbitrary Prandtl numbers and specific heat ratios, offering a valuable tool for studying complex problems in fluid dynamics and paving the way for future extensions to the lattice Boltzmann context, by application of correction terms, as well as high-Mach and hypersonic regimes, employing target-designed reference frames.

physics.flu-dyn↗

arXiv2025

Kinetic framework with consistent hydrodynamics for shallow water equations

We present a novel discrete velocity kinetic framework to consistently recover the viscous shallow water equations. The proposed model has the following fundamental advantages and novelties: (a) A novel interpretation and general framework to introduce forces, (b) the possibility to consistently split pressure contributions between equilibrium and a force-like contribution, (c) consistent recovery of the viscous shallow water equations with no errors in the dissipation rates, (d) independent control over bulk viscosity, and (e) consistent second-order implementation of forces. As shown through a variety of different test cases, these features make for an accurate and stable solution method for the shallow-water equations.

physics.flu-dyn↗

arXiv2025

A fully conservative discrete velocity Boltzmann solver with parallel adaptive mesh refinement for compressible flows

This paper presents a parallel and fully conservative adaptive mesh refinement (AMR) implementation of a finite-volume-based kinetic solver for compressible flows. Time-dependent H-type refinement is combined with a two-population quasi-equilibrium Bhatnagar-Gross-Krook discrete velocity Boltzmann model. A validation has shown that conservation laws are strictly preserved through the application of refluxing operations at coarse-fine interfaces. Moreover, the targeted macroscopic moments of Euler and Navier-Stokes-Fourier level flows were accurately recovered with correct and Galilean invariant dispersion rates for a temperature range over three orders of magnitude and dissipation rates of all eigen-modes up to Mach of order 1.8. Results for one- and two-dimensional benchmarks up to Mach numbers of 3.2 and temperature ratios of 7, such as the Sod and Lax shock tubes, the Shu-Osher and several Riemann problems, as well as viscous shock-vortex interactions, have demonstrated that the solver precisely captures reference solutions. Excellent performance in obtaining sensitive quantities was proven, for example in the test case involving nonlinear acoustics, whilst, for the same accuracy and fidelity of the solution, the AMR methodology significantly reduced computational cost and memory footprints. Over all demonstrated two-dimensional problems, up to a 4- to 9-fold reduction was achieved and an upper limit of the AMR overhead of 30% was found in a case with very cost-intensive parameter choice. The proposed solver marks an accurate, efficient and scalable framework for kinetic simulations of compressible flows with moderate supersonic speeds and discontinuities, offering a valuable tool for studying complex problems in fluid dynamics.

physics.flu-dyn↗

arXiv2025

Linear stability of lattice Boltzmann models with non-ideal equation of state

Detailed study of spectral properties and of linear stability is presented for a class of lattice Boltzmann models with a non-ideal equation of state. Examples include the van der Waals and the shallow water models. Both analytical and numerical approaches demonstrate that linear stability requires boundedness of propagation speeds of normal eigen-modes. The study provides a basis for the construction of unconditionally stable lattice Boltzmann models.

math.NA↗

arXiv2024

Probing double distribution function models in the lattice Boltzmann method for highly compressible flows

The double distribution function approach is an efficient route towards extension of kinetic solvers to compressible flows. With a number of realizations available, an overview and comparative study in the context of high speed compressible flows is presented. We discuss the different variants of the energy partition, analyses of hydrodynamic limits and a numerical study of accuracy and performance with the particles on demand realization. Out of three considered energy partition strategies, it is shown that the non-translational energy split requires a higher-order quadrature for proper recovery of the Navier--Stokes--Fourier equations. The internal energy split on the other hand, while recovering the correct hydrodynamic limit with fourth-order quadrature, comes with a non-local --both in space and time-- source term which contributes to higher computational cost and memory overhead. Based on our analysis, the total energy split demonstrates the optimal overall performance.

physics.flu-dyn↗

arXiv2023

Lattice Boltzmann methods for combustion applications

The lattice Boltzmann method, after close to thirty years of presence in computational fluid dynamics has turned into a versatile, efficient and quite popular numerical tool for fluid flow simulations. The lattice Boltzmann method owes its popularity in the past decade to its efficiency, low numerical dissipation and simplicity of its algorithm. Progress in recent years has opened the door for yet another very challenging area of application: Combustion simulations. Combustion is known to be a challenge for numerical tools due to, among many others, the large number of variables and scales both in time and space, leading to a stiff multi-scale problem. In the present work we present a comprehensive overview of models and strategies developed in the past years to model combustion with the lattice Boltzmann method and discuss some of the most recent applications, remaining challenges and prospects.

physics.flu-dyn↗

arXiv2023

Thermal effects connected to crystallization dynamics: a lattice Boltzmann study

The possible impact of temperature differences during crystal growth is investigated in this study. The organic molecule considered is mandelic acid, an important component for the pharmaceutical industry. The productivity of generating pure mandelic acid crystals are largely determined by the growth process. Reaction conditions, purity of the components, supersaturation, temperature, but possibly also temperature gradients play a central role during crystal growth. In this study a numerical model based on a hybrid solver combining the lattice Boltzmann method with finite differences is developed to model the crystallization dynamics of (S)-mandelic acid (S-ma) taking quantitatively into account temperature effects. At first, the fourth-order finite-difference method used to model energy and species conservation is validated. Then, comparisons are carried out regarding temperature changes within the single-crystal growth cell. In practice, the molar heat generation at the crystal interface shows only a small effect on the temperature field in the surrounding domain, with temperature differences below $1.5$ degree. Finally, the study is extended to investigate the impact of forced convection on the crystal habits while taking into account temperature differences.

math-ph↗

arXiv2023

Towards pore-scale simulation of combustion in porous media using a low-Mach hybrid lattice Boltzmann/finite difference solver

A hybrid numerical model previously developed for combustion simulations is extended in this article to describe flame propagation and stabilization in porous media. The model, with a special focus on flame/wall interaction processes, is validated via corresponding benchmarks involving flame propagation in channels with both adiabatic and constant-temperature walls. Simulations with different channel widths show that the model can correctly capture the changes in flame shape and propagation speed as well as the dead zone and quenching limit, as found in channels with cold walls. The model is further assessed considering a pseudo 2-D porous burner involving an array of cylindrical obstacles at constant temperature, investigated in a companion experimental study. Furthermore, the model is used to simulate pore-scale flame dynamics in a randomly-generated 3-D porous media. Results are promising, opening the door for future simulations of flame propagation in realistic porous media.

physics.flu-dyn↗

arXiv2023

Entropic equilibrium for the lattice Boltzmann method: Hydrodynamics and numerical properties

The entropic lattice Boltzmann framework proposed the construction of the discrete equilibrium by taking into consideration minimization of a discrete entropy functional. The effect of this form of the discrete equilibrium on properties of the resulting solver has been the topic of discussions in the literature. Here we present a rigorous analysis of the hydrodynamics and numerics of the entropic. In doing so we demonstrate that the entropic equilibrium features unconditional linear stability, in contrast to the conventional polynomial equilibrium. We reveal the mechanisms through which unconditional linear stability is guaranteed, most notable of which the adaptive normal modes propagation velocity and the positive-definite nature of the dissipation rates of all eigen-modes. We further present a simple local correction to considerably reduce the deviations in the effective bulk viscosity.

physics.flu-dyn↗

arXiv2023

Lattice Boltzmann for non-ideal fluids: Fundamentals and Practice

This contribution presents a comprehensive overview of of lattice Boltzmann models for non-ideal fluids, covering both theoretical concepts at both kinetic and macroscopic levels and more practical discussion of numerical nature. In that context, elements of kinetic theory of ideal gases are presented and discussed at length. Then a detailed discussion of the lattice Boltzmann method for ideal gases from discretization to Galilean invariance issues and different collision models along with their effect on stability and consistency at the hydrodynamic level is presented. Extension to non-ideal fluids is then introduced in the context of the kinetic theory of gases along with the corresponding thermodynamics at the macroscopic level, i.e. the van der Waals fluid, followed by an overview of different lattice Boltzmann based models for non-ideal fluids. After an in-depth discussion of different well-known issues and artifacts and corresponding solutions, the article finishes with a brief discussion on most recent applications of such models and extensions proposed in the literature towards non-isothermal and multi-component flows.

physics.flu-dyn↗

arXiv2022

Low Mach number lattice Boltzmann model for turbulent combustion: flow in confined geometries

A hybrid lattice Boltzmann/finite-difference solver for low Mach thermo-compressible flows developed in earlier works is extended to more realistic and challenging configurations involving turbulence and complex geometries in the present article. The major novelty here as compared to previous contributions is the application of a more robust collision operator, considerably extending the stability of the original single relaxation time model and facilitating larger Reynolds number flow simulations. Additionally, a subgrid model and the thickened flame approach have also been added allowing for efficient large eddy simulations of turbulent reactive flows in complex geometries. This robust solver, in combination with appropriate treatment of boundary conditions, is used to simulate combustion in two configurations: flame front propagation in a 2-D combustion chamber with several obstacles, and the 3-D PRECCINSTA swirl burner. Time evolution of the flame surface in the 2-D configuration shows very good agreement compared to direct numerical and large eddy simulation results available in the literature. The simulation of the PRECCINSTA burner is first performed in the case of cold flow using two different grid resolutions. Comparisons with experimental data reveal very good agreement even at lower resolution. The model is then used, with a 2-step chemistry and multi-component transport/thermodynamics, to simulate the combustor at operating conditions similar to previously reported experimental/numerical studies for $ϕ$=0.83. Results are again in very good agreement compared with available large eddy simulation results as well as experimental data, demonstrating the excellent performance of the hybrid solver.

physics.flu-dyn↗

arXiv2022

Mandelic acid single-crystal growth: Experiments vs numerical simulations

Mandelic acid is an enantiomer of interest in many areas, in particular for the pharmaceutical industry. One of the approaches to produce enantiopure mandelic acid is through crystallization from an aqueous solution. We propose in this study a numerical tool based on lattice Boltzmann simulations to model crystallization dynamics of (S)-mandelic acid. The solver is first validated against experimental data. It is then used to perform parametric studies concerning the effects of important parameters such as supersaturation and seed size on the growth rate. It is finally extended to investigate the impact of forced convection on the crystal habits. Based on there parametric studies, a modification of the reactor geometry is proposed that should reduce the observed deviations from symmetrical growth with a five-fold habit.

physics.flu-dyn↗

arXiv2022

Entropic multi-relaxation-time lattice Boltzmann model for large density ratio two-phase flows

We propose a multiple relaxation time entropic realization of a two-phase flow lattice Boltzmann model we introduced in earlier works arXiv:2112.01975 S.A. Hosseini, B. Dorschner, and I. V. Karlin, arXiv preprint, arXiv:2112.01975 (2021). While the original model with a single relaxation time allows us to reach large density ratios, it is limited in terms of stability with respect to non-dimensional viscosity and Courant--Friedrichs--Lewy number. Here we show that the entropic multiple relaxation time model extends the stability limits of the model significantly, which allows us to reach larger Reynolds numbers for a given grid resolution. The thermodynamic properties of the solver, using the Peng--Robinson equation of state, are studied first using simple configurations. Co-existence densities and temperature scaling of both the interface thickness and the surface tension are shown to agree well with theory. The model is then used to simulate the impact of a drop onto a thin liquid film with density and viscosity ratios matching those of water and air both in 2-D and 3-D. The results are in very good agreement with theoretically predicted scaling laws and experimental data.

physics.flu-dyn↗