Incompressible Lattice Boltzmann Method Research Articles

A fluid-structure interaction method for soft particle transport in curved microchannels

A numerical framework is presented to predict the transport of soft elastic capsules immersed in an incompressible fluid with the aim of simulating inertial microfluidics applications. The flow evolution is modeled by a fully incompressible lattice Boltzmann method whereas a finite element model is considered for describing the dynamics of deformable structures. An immersed boundary technique is adopted to reconstruct the solution in the vicinity of the immersed surface and the time integration of the fluid-structure interaction problem is obtained by following an explicit procedure. The effectiveness of the framework is validated by means of several test cases involving: flows between two parallel plates for Reynolds numbers in the range 1÷100; capsules immersed in a fluid at Stokes regime exhibiting small and large deformations under shear; capsules migrating in a long straight microchannel with square cross-section at low-to-moderate Reynolds number. A very good agreement between the present results and literature data obtained using different numerical methods is found for all test cases. Finally, the method allowed to accurately simulate incompressible flows subjected to large pressure difference between the inlet and the outlet, characteristic of long curved microchannels, obtaining very smooth particle dynamics.

Rectangular Cylinder Orientation and Aspect Ratio Impact on the Onset of Vortex Shedding

Rectangular cylinders have the potential to provide valuable insights into the behavior of fluids in a variety of real-world applications. Keeping this in mind, the current study compares the behavior of fluid flow around rectangular cylinders with an aspect ratio (AR) of 1:2 or 2:1 under the effect of the Reynolds number (Re). The incompressible lattice Boltzmann method is used for numerical computations. It is found that the flow characteristics are highly influenced by changes in the aspect ratio compared to the Reynolds number. The flow exhibits three different regimes: Regime I (steady flow), Regime II (initial steady flow that becomes unsteady afterward), and Regime III (completely unsteady flow). In the case of the cylinder with an aspect ratio of 2:1, vortex generation, variation in drag, and the lift coefficient occur much earlier at very low Reynolds numbers compared to the cylinder with an aspect ratio of 1:2. For the cylinder with an aspect ratio of 1:2, the Reynolds number ranges for Regimes I, II, and III are 1 ≤ Re ≤ 120, 121 ≤ Re ≤ 144, and 145 ≤ Re ≤ 200, respectively. For the cylinder with an aspect ratio of 2:1, the Reynolds number ranges for Regimes I, II, and III are 1 ≤ Re ≤ 24, 25 ≤ Re ≤ 39, and 40 ≤ Re ≤ 200, respectively. The cylinder with an aspect ratio of 1:2 is found to have the ability to stabilize the incoming flow due to its extended after-body flatness. Generally, it has been found that a cylinder with an AR of 2:1 is subjected to higher pressures, higher drag forces, higher curvatures of cross-flow rotations, and higher amplitudes of flow-induced drag, as well as higher lift coefficients and lower shedding frequencies, compared to cylinders with an AR of 1:2. In Regime III, elliptic and vertically mounted airfoil-like flow structures are also observed in the wake of the cylinders.

A simple and efficient parallel immersed boundary-lattice Boltzmann method for fully resolved simulations of incompressible settling suspensions

This study presents an efficient and parallel fully resolved direct numerical simulation (FR-DNS) of settling suspensions on multiple CPU cores based on the boundary-thickening direct forcing immersed boundary method (BTDF-IBM) and incompressible lattice Boltzmann method (LBM). The simple BTDF-IBM is used to meet the no-slip and no-penetration conditions on particle boundaries, and the incompressible LBM is used to achieve the capability of large pressure fluctuations in suspensions. In addition, a theoretical force model is used to compensate for the unresolved lubrication force between the two approaching particles. A swap strategy for the streaming step is used to reduce the memory storage of the LBM particle density functions to half. A distribution and communication strategy is proposed to handle the IBM computing and complete the immersed boundary (IB) force of the particles residing in the interface region between adjacent subdomains. The developed BTDF-IBM-LBM solver “PFlows” can simulate large particle-laden flows with more than O(106) particles and with a particle volume fraction of up to 0.4. An almost linear parallel speedup and efficiency of higher than 0.8 are obtained by testing three-dimensional (3D) cases (up to 1.0 billion fluid grids and 0.45 million particles) and two-dimensional (2D) cases (up to 1.2 billion fluid grids and 2.39 million particles). Finally, the framework is applied to three large-scale real simulations involving 50,000 particles settling in 2D and 3D bounded and unbounded domains for qualitative and quantitative validations. The particle settling behaviors and disturbed complex fluid flows in the vertical channel are demonstrated. The Boycott effect in the inclined channel is uncovered by a new mechanism that combines particle sliding at the lower sidewall with fluid convection in the upper region. The hindered settling of particles in the 3D periodic domain, which is affected by the strong particle-fluid hydrodynamic interactions and particle-particle many-body interactions at a high solid volume fraction, are analyzed. The complex behaviors and statistical characteristics of the suspensions are preliminarily revealed and analyzed, which demonstrates the prospective capability of the present framework for FR-DNS of large-scale 2D and 3D suspension flows that are relevant to many industrial applications by IB-LBM.

Numerical simulations of incompressible fluid flow in synthetic fractures using lattice Boltzmann method

The effect of the geometrical complexity on the fluid flow through single fractures is the subject of this study. Synthetic self-affine fractures with different waviness and local roughness are generated by SynFrac. Several fracture profiles were sliced from the generated fractures for 2D simulations. An incompressible lattice Boltzmann method with non-equilibrium extrapolation method was used to simulate the fluid flow through the generated rough fractures by solving the full Navier-Stokes equations. The results indicate that the scaling irregular nature has a great influence on the fluid flow through single fractures. The tortuosity and the randomly distributed stagnated areas had been confirmed as the reasons for the deviation from local cubic law both theoretically and numerically. The tortuosity tends to have a linear relationship with the standard deviations which represent the amplitude of the waviness on the large scale, and a second-order dependence on the fractal dimensions which presents the degree of local roughness. The recirculation zones were formed in the troughs of rough fractures even when the flow was a creeping one with the Reynolds number below 1. These stagnated areas were observed to have an intuitive influence on the local effective advective aperture. An effective volume ratio was defined to quantify this effect of eddies on the hydraulic aperture which had been related to the local roughness of the fractures. The tortuosity of the fluid flow and eddies formed along the fractures combined together to make the permeability deviate from the local cubic law.

Numerical research of the infinitely wide wedge flow based on the lattice Boltzmann method

A new computational fluid dynamics method, the incompressible lattice Boltzmann method (LBM) is utilized to simulate fluid flow of the infinitely wide wedge in this paper. Compared with the traditional method, LBM is a mesoscopic scale method and some characteristics can be described more clearly with LBM. In this article, three kinds of model .i.e. linear type, parabolic type and harmonic type wedge models are built. The streamline and velocity contour in the fluid field are described. The pressure distribution of different types wedge is studied in LBM. The results manifest that, for the same bottom boundary velocity, the parabolic type and harmonic type wedges are easy to form a vortex, and the load capacity in the harmonic type wedge model is the largest. This paper is ready to investigate the microscopic lubrication mechanism of journal bearing in the future.

Solid wall and open boundary conditions in hybrid recursive regularized lattice Boltzmann method for compressible flows

Complex geometries and open boundaries have been intensively studied in the nearly incompressible lattice Boltzmann method (LBM) framework. Therefore, only few boundary conditions for the high speed fully compressible LBM have been proposed. This paper deals with the definition of efficient boundary conditions for the compressible LBM methods, with the emphasis put on the newly proposed hybrid recursive regularized D3Q19 LBM (HRR-LBM) with applications to compressible aerodynamics. The straightforward simple extrapolation-based far-field boundary conditions, the characteristic boundary conditions, and the absorbing sponge layer approach are extended and estimated in the HRR-LBM for the choice of open boundaries. Moreover, a cut-cell type approach to handle the immersed solid is proposed to model both slip and no-slip wall boundary conditions with either isothermal or adiabatic behavior. The proposed implementations are assessed considering the simulation of (i) isentropic vortex convection with subsonic to supersonic inflow and outflow conditions, (ii) two-dimensional (2D) compressible mixing layer, (iii) steady inviscid transonic flow over a National Advisory Committee for Aeronautics (NACA) 0012 airfoil, (iv) unsteady viscous transonic flow over a NACA 0012 airfoil, and (v) three-dimensional (3D) transonic flows over a German Aerospace Center (DLR) F6 full aircraft configuration.

Hydrodynamic stability and turbulent transition with the Vreman LES SGS and a modified lattice Boltzmann equation

For the evaluation of a broad range of Re in incompressible flows, particularly unsteady and transition regimes, the Vreman subgrid scale model is studied within the framework of a modified lattice Boltzmann equation. A unique multiple relaxation time form which recovers the fully incompressible unsteady Navier-Stokes equations is derived for the D3Q19 lattice. Solutions to the 3D-driven cavity are compared to a number of lattice Boltzmann and Navier-Stokes solutions. Initial simulations demonstrate the vanishing nature of eddy viscosity in the steady laminar regime. Onset of unsteadiness is found between Re 1900 and 1950, matching well with the wealth of literature. At Re 6000, velocity history and complex vortex structures show a transition to turbulence near the domain bottom and front walls while the centre of the domain retains laminar characteristics. By Re 8000 intermittent turbulence has progressed to the domain centre. This range of Re for transition and the flow characteristics are in agreement with the general ranges in literature, with further observations being added here. The Vreman model with an incompressible lattice Boltzmann method is found to be a promising tool for laminarto- turbulent simulation.

Modeling of submicron particle filtration in an electret monolith filter with rectangular cross-section microchannels

ABSTRACTElectret monolith filters have the advantage of low pressure drop and high filtration efficiency. In such filters, the filtration of submicron aerosol particles occurs as air passes through millions of microchannels. This article investigates the flow and filtration mechanisms in a representative rectangular microchannel of an electret monolith filter. An improved incompressible lattice Boltzmann method with Bhatnagar–Gross–Krook (traditionally shortened as LBGK) and lattice velocity D3Q15 model is employed to simulate no-slip and slip flows in the rectangular microchannels of a monolith filter. We considered mono-disperse submicron particles and one-way coupling (particle motion was affected by the flow, but the presence of particles did not affect the flow). Based on flow computations, the effects of key dimensionless parameters (Reynolds number, Knudsen number, Stokes number and the dimensionless length of the channel) on the total capture efficiency of mono-disperse submicron particles were in...

Numerical investigations on the vortex-induced vibration of moving square cylinder by using incompressible lattice Boltzmann method

Vortex-induced vibrations (VIV) phenomena related to self-excited energy harvesters consisting of square cylinders have been investigated numerically by using the BGK incompressible lattice Boltzmann method. In the present work, such a harvester is placed inside a channel flow and is allowed to oscillate without a structural restoring force in a direction normal to the flow. Currently the half-way bounce-back boundary and interpolations method are being used to model the moving boundary. The numerical results of the periodical and non-periodical oscillations and the frequency content of the longitudinal and lateral forces acting on the square cross section harvester are discussed in detail. The numerical technique was validated by computing the flow around a fixed cylinder. The results are compared favorably with the results obtained by classical CFD methods.

非圧縮型格子ボルツマン法による自由表面流れ解析の計算安定化

非圧縮型格子ボルツマン法による自由表面流れ解析の計算安定化

Lattice Boltzmann simulation of flow around two, three and four circular cylinders in close proximity

Cross-flows around two, three and four circular cylinders in tandem, side-by-side, isosceles triangle and square arrangements are simulated using the incompressible lattice Boltzmann method with a second-order accurate curved boundary condition at Reynolds number 200 and the cylinder center-to-center transverse or/and longitudinal spacing 1.5D, where D is the identical circular cylinder diameter. The wake patterns, pressure and force distributions on the cylinders and mechanism of flow dynamics are investigated and compared among the four cases. The results also show that flows around the three or four cylinders significantly differ from those of the two cylinders in the tandem and side-by-side arrangements although there are some common features among the four cases due to their similarity of structures, which are interesting, complex and useful for practical applications. This study provides a useful database to validate the simplicity, accuracy and robustness of the Lattice Boltzmann method. Lattice Boltzmann method, curved boundary condition, cross-flow around cylinders

Numerical simulation of flow past rectangular cylinders with different aspect ratios using the incompressible lattice Boltzmann method

This paper presents a numerical study of a uniform flow past a rectangular cylinder using the incompressible lattice Boltzmann method (ILBM). Firstly, we use the ILBM to simulate the flow past a square cylinder symmetrically placed in a two-dimensional channel and results are validated against the well-resolved results obtained using finite-difference method and finite-volume method. Secondly, the effects of the aspect ratio defined as R = width/height on the fluid forces, vortex shedding frequency and the flow structures in the wake are investigated. Aspect ratios ranging from 0.15 to 4.00 and four Reynolds numbers Re = 100, 150, 200 and 250 are selected for the investigation. The results show that the effects of aspect ratio on physical quantities such as drag and lift coefficients, Strouhal number and the vortex shedding mechanism are very notable in the range between 0 and 2. In general, the drag coefficient decreases with the aspect ratio and the decreasing rate is more distinct in the range of 0.15 ≤ R ≤ 2.0. There is no local maximum found at around R = 0.6 in the drag coefficient as reported for higher Reynolds numbers in the literature. However the root-mean-square value of the lift coefficient shows a maximum value at R ≈ 0.5 for all Reynolds numbers selected. The variation of Strouhal number with R appears to be different for four selected Reynolds numbers. Especially for Re = 250, a discontinuity in St, as has been observed for higher Reynolds numbers, is observed at around R = 1.45 where multiple peaks are found in the result of Fourier spectrum analysis of the lift force and irregular vortex shedding behavior with no fixed shedding frequency is observed from the instantaneous vorticity contours. Such discontinuity is not observed for Re = 100, 150 and 200. The present results using the LBM are compared with some existing experimental data and numerical studies. The comparison shows that the LBM can capture the characteristics of the bluff body flow well and is a useful tool for bluff body flow studies.

Simulation of Thermal Convection in a Rotating and Strarified Fluids by the Lattice Boltzmann Method

Three-dimensional flow of thermal convection contained in cubic and rectangular vessel placed in a rotating field is simulated by the incompressible Lattice Boltzmann method using two types of particles, that are red and blue ones. The gravitational force and the Coriolis force introduced in the local equilibrium distribution function. In this model, the gravitational force acts on the blue particles only and the Coriolis force acts both the particles. The results proved that the present method simulates the structure of flow and the mechanism how the stratification and the Coriolis force affects on the spread of flow and temperature.