International Journal of Modern Physics C

The 22nd international conference on the Discrete Simulation of Fluid Dynamics (DSFD 2013) was held on the campus of the American University of Armenia in Yerevan, Armenia on 15–19 July 2013. Approximately 60 participants took part in the conference, with discussions ranging from lattice Boltzmann and lattice-gas models of fluids, to smoothed-particle hydrodynamics and stochastic rotation dynamics. The conference presented a unique opportunity for communities of computational fluid dynamicists from the region to share their research with each other, and with an audience of some of the world's leading experts in the field.

We present a new lattice kinetic method to simulate fluid dynamics in curvilinear geometries and curved spaces. A suitable discrete Boltzmann equation is solved in contravariant coordinates, and the equilibrium distribution function is obtained by a Hermite polynomials expansion of the Maxwell–Boltzmann distribution, expressed in terms of the contravariant coordinates and the metric tensor. To validate the model, we calculate the critical Reynolds number for the onset of the Taylor–Couette instability between two concentric cylinders, obtaining excellent agreement with the theory. In order to extend this study to more general geometries, we also calculate the critical Reynolds number for the case of two concentric spheres, finding good agreement with experimental data, and the case of two concentric tori, where we have found that it is around 10% larger than the respective values for the two concentric cylinders.

We present a highly efficient lattice Boltzmann (LB) kinetic model for thermal liquid–vapor system. Three key components are as below: (i) a discrete velocity model (DVM) by Kataoka et al. [Phys. Rev. E69, 035701(R) (2004)]; (ii) a forcing term I_i aiming to describe the interfacial stress and recover the van der Waals (VDW) equation of state (EOS) by Gonnella et al. [Phys. Rev. E76, 036703 (2007)] and (iii) a Windowed Fast Fourier Transform (WFFT) scheme and its inverse by our group [Phys. Rev. E84, 046715 (2011)] for solving the spatial derivatives, together with a second-order Runge–Kutta (RK) finite difference scheme for solving the temporal derivative in the LB equation. The model is verified and validated by well-known benchmark tests. The results recovered from the present model are well consistent with previous ones [Phys. Rev. E84, 046715 (2011)] or theoretical analysis. The usage of less discrete velocities, high-order RK algorithm and WFFT scheme with 16th-order in precision makes the model more efficient by about 10 times and more accurate than the original one.

The regularized lattice BGK (RLBGK) is validated against high-accuracy spectral Chebyshev methods for lid-driven cavity flows. RLBGK is shown to provide a viable alternative to standard lattice BGK schemes, with significant enhancement of numerical stability at a very moderate computational extra-cost.

A systems of self-propelled dumbbells interacting by a Weeks–Chandler–Anderson potential is considered. At sufficiently low temperatures the system phase separates into a dense phase and a gas-like phase. The kinetics of the cluster formation and the growth law for the average cluster size are analyzed.

Many rheological properties of blood, along with transport properties of blood cells can be captured by means of modeling blood through its main constituents, red blood cells (RBCs) and plasma. In the current work, we present a fully resolved two-dimensional model for blood suspension flow, employing a discrete element model (DEM) for RBCs and coupling it to a lattice Boltzmann method (LBM) fluid solver using the immersed boundary method (IBM). We identify an efficient computationally reduced mesoscopic representation of cells and flow, still able to recover essential physics and physiological phenomena. Our model is found to agree quantitatively with experimental findings. The Fåhræus–Lindqvist effect and shear thinning is recovered, while the thickness of the cell-free layer (CFL) matches the observations. In addition, we investigate the tank-treading frequency of a single RBC in shear flow along with the transition from tumbling to tank-treading, also matching experimental data.

This paper describes the application of a single relaxation time (SRT) lattice Boltzmann scheme to the transport in porous media with large spatial variations of diffusion coefficients. Effective diffusion coefficients can vary substantially within porous media because of their dependence on porosity and tortuosity which can span over several orders of magnitude, depending on pore size and connectivity. Moreover, when mass is transported with pore-water in porous media, the hydrodynamic dispersion, which depends on Darcy's velocity, contributes additionally to the usually anisotropic variation of the dissipative term. In contrast to the traditional treatment of spatially variable diffusion coefficient by the variation of a SRT, here the variability is accommodated through the use of diffusion velocity formulation which allows for larger variabilities of diffusion coefficient. The volume averaged properties of mass transport in macroscopic porous media are resolved through the additional source term which is similar to the existing force adjusting methods. The applicability of both the proposed schemes is demonstrated on two examples. The first demonstrates that the method is accurate for the large variation of diffusion coefficients and porosities. The second example introduces mass diffusion in a real, geometrically complex system with spatially contrasting properties.

Multiphase flows occurring in circular curved pipes exhibit important physical phenomena.They are characterized by a large pressure drop and are composed of different phases. In the past, erosion–corrosion was measured through the use of experimental methods. Today numerical simulation models provide a more in depth look into the problem of erosion. Solid particle erosion is of major concern in the industrial engineering sector. In this study, erosion occurring in a (90)-degree elbow has been simulated. The generated two-dimensional data was done through the use of the Commercial software ANSYS Fluent. The primary idea comes from the petrochemicals industry. To overcome this problem, counter measures are proposed in this paper to the piping setup in order to protect pumps from unwanted excessive sand concentrations. Note that the physical properties of the simulated fluid mixture are taken the same as for the real-studied sample.

The so-called "Yard-Sale Model" of wealth distribution posits that wealth is transferred between economic agents as a result of transactions whose size is proportional to the wealth of the less wealthy agent. In recent work [B. M. Boghosian, Phys. Rev. E89, 042804 (2014)], it was shown that this results in a Fokker–Planck equation governing the distribution of wealth. With the addition of a mechanism for wealth redistribution, it was further shown that this model results in stationary wealth distributions that are very similar in form to Pareto's well-known law. In this paper, a much simpler derivation of that Fokker–Planck equation is presented.

This paper validates three-dimensional (3D) simulation results of electron beam melting (EBM) processes by comparing experimental and numerical data. The physical setup is presented which is discretized by a 3D thermal lattice Boltzmann method (LBM). An experimental process window is used for the validation depending on the line energy injected into the metal powder bed and the scan velocity of the electron beam. In the process window, the EBM products are classified into the categories, porous, good and swelling, depending on the quality of the surface. The same parameter sets are used to generate a numerical process window. A comparison of numerical and experimental process windows shows a good agreement. This validates the EBM model and justifies simulations for future improvements of the EBM processes. In particular, numerical simulations can be used to explain future process window scenarios and find the best parameter set for a good surface quality and dense products.

Stretching dynamics of polymers in microfluidics is of particular interest for polymer scientists. As a charged polymer, a polyelectrolyte (PE) can be deformed from its coiled equilibrium configuration to an extended chain by applying uniform or nonuniform electric fields. By means of hybrid lattice Boltzmann (LB)-molecular dynamics (MD) simulations, we investigate how the condensed counterions (CIs) around the PE contribute to the polymer stretching in inhomogeneous fields. As an application, we discuss the translocation phenomena and entropic traps, when the driving force is an applied external electric field.

The Gauss–Laguerre quadrature method is used to construct three-dimensional thermal Lattice Boltzmann models that exactly recover integrals of the equilibrium distribution function over Cartesian octants of the momentum space. We illustrate the capability of these models to exactly implement the diffuse reflection boundary conditions by considering the Couette flow at various values of the Knudsen number.

This paper deals with the simulation of water entry problems using the lattice Boltzmann method (LBM). The dynamics of the free surface is treated through the mass and momentum fluxes across the interface cells. A bounce-back boundary condition is utilized to model the contact between the fluid and the moving object. The method is implemented for the analysis of a two-dimensional flow physics produced by a symmetric wedge entering vertically a weakly-compressible fluid at a constant velocity. The method is used to predict the wetted length, the height of water pile-up, the pressure distribution and the overall force on the wedge. The accuracy of the numerical results is demonstrated through comparisons with data reported in the literature.

Nonparticulate continuum descriptions allow for computationally efficient modeling of suspension flows at scales that are inaccessible to more detailed particulate approaches. It is well known that the presence of particles influences the effective viscosity of a suspension and that this effect has thus to be accounted for in macroscopic continuum models. The present paper aims at developing a nonparticulate model that reproduces not only the rheology but also the cell-induced velocity fluctuations, responsible for enhanced diffusivity. The results are obtained from a coarse-grained blood model based on the lattice Boltzmann (LB) method. The benchmark system comprises a flow between two parallel plates with one of them featuring a smooth obstacle imitating a stenosis. Appropriate boundary conditions are developed for the particulate model to generate equilibrated cell configurations mimicking an infinite channel in front of the stenosis. The averaged flow field in the bulk of the channel can be described well by a nonparticulate simulation with a matched viscosity. We show that our proposed phenomenological model is capable to reproduce many features of the velocity fluctuations.

We show that a hyperbolic system with a mathematical entropy can be discretized with vectorial lattice Boltzmann schemes using the methodology of kinetic representation of the dual entropy. We test this approach for the shallow water equations in one and two spatial dimensions. We obtain interesting results for a shock tube, reflection of a shock wave and nonstationary two-dimensional propagation. This contribution shows the ability of vectorial lattice Boltzmann schemes to simulate strong nonlinear waves in nonstationary situations.