جستجوی مقالات مرتبط با کلیدواژه "lattice-boltzmann" در نشریات گروه "مکانیک"

Determination of multiphase flow dynamics and thermal behavior of falling flow in a channel and around a cylinder are of importance due to its wide application in various industries. The small-scale surface tension effect plays a major role in multiphase flow behavior. So, based on simulation efficiency, precision, and stability, the mesoscopic Lattice Boltzmann method superiority has caused its broadening application. In the current study, the thermal-hydraulic behavior of subcooled falling flow in a vertical channel and around a single horizontal tube is simulated by using Lee method and Phase-Filed model, and thermal Passive Scalar model. The modified Boundary conditions for curved tube and two different boundary conditions for side boundaries are investigated. Simulations have been done for density ratio 20 and relevant viscosity and conductivity ratios of water. The film of liquid falls on a tube with a temperature of 110˚C and the outside diameter of 28.9mm. The results including contours and streamlines of the flow field, temperature, and pressure contours are presented and detailed understanding about the movement of the three-phase contact line, circulating flow and local and average Nusselt number are determined. The film thickness, thermal boundary layer variation by the film thickness, Reynold number effect on Nusselt number and mass conservation are investigated as verification. The results have shown good consistency and high effectiveness in the simulation of multiphase gas-liquid flows in the presence of a circular obstacle, and for viscosity and thermal diffusivity ratios of water.

Applying numerical methods for predicting cake formation and development in cross-flow membrane filtration has been an area of research. The solutions, which are mainly based on the development of zero, one, or two-dimensional methods for estimating filtration parameters, have always suffered from an obvious need for some calibration steps. In this paper, an independent two-way solving method is presented to determine the time variation of the geometry of the cross-flow filtration cake, so that by simultaneously solving the flow through the lattice Boltzmann (LB), it is possible to solve the convection-diffusion equation, using another mesoscopic method (LB-CA) in a two way coupling manner between flow changes and cake growth. Applying LB-CA provides it for all kinds of internal and external forces effects on particles trajectories to be explicitly taken into account. The proposed model was validated against both of theory of Romero and Davis and some experimental results. Moreover, the model was used to determine external effects which are arisen from static imposition of a DC electric field, on cross-flow filtration outcomes. The calculated results exhibits considerable improvements in flux decline curve and removing of fouling in some areas along the membrane length, as DC voltage rises. Also, optimal conditions with considering the electric poles’ size as an optimization parameter shows that with considering the maximum improvement in the flux curve as the target parameter, the electric poles’ size has an optimal value.

Applications of the wavemaker mechanisms in the experimental investigations of wave-structure interactions have attracted various researchers’ attention. Numerical simulations capable of wave generation in a water tank are appropriate substitutes for the expensive experimental studies. Due to the large values of the wave length to wave height ratio and also the water depth to wave height ratio, extremely fine grid points are generally required at the gas-liquid interface and this causes the numerical simulations to be very time consuming. In this study, a new method is proposed for numerical simulation of a piston-type wavemaker which is faster than the previous methods. The proposed method is a combination of a Lattice-Boltzmann method with multilayer moving nested grids and iWeno5 method for treating the kinematic free surface boundary condition. The numerical results of the proposed method are compared with the analytical and experimental data, where a good agreement is observed.

Present study is a numerical solution for incompressible fluid-elastic structure interaction by use of immersed boundary method. The solid phase is an elastic filament hinged on rear of a rigid cylinder in the presence of fluid flow. The purpose of this study is investigation of interaction of flexible filament and rigid cylinder. In the immersed boundary method, solid and fluid domains are solved in separated regions. For solving the flow field and momentum equations, the lattice Boltzmann equations are employed. In present study in contrast to previous studies, the elastic filament is also modeled by a mass-spring network that provides elastic properties like young’s and bending modulus. The mass of filament is discretized on nodes of spring network. These two solution regions are connected by applying suitable boundary conditions at each time step. Results show that the mass, geometry and location of filament behind the rigid cylinder have significant effect on the filament’s stability and drag reduction. Indicating and analyzing a special point behind the cylinder, where the drag is minimum, is the another purpose of this study.

Applying membranes with especial geometries and fouling characteristics has been an area of research and a subject of interest in membrane science community. While a considerable part of fouling happenings are originated from chaotic roots such as Brownian motions, the remainders can be scheduled to approach on desired filtration features. Here in this study the somehow invisible features of progressive fouling which is the case for novel micro-engineered membranes was realized in some details. The problem of progressive fouling was considered as a result of dead-ended filtration of non-colloidal particles over a vertically extended pore geometry. It was shown that, in this filtration apparatus, due to a serialized activation and deactivation of flow passages, progressive fouling can change its seat with other more flow resistive classical types of surface and pore blockings and control filtration path more apparently. Results was considered for different amounts of pore extension and porosities. It was found that employing an especial set of pore extension length and porosity make it feasible to derive manageable filtration processes with high levels of purification and permeation performances.

In this paper, a new method is proposed to reach high density ratios and low viscosities based on the Shan-Chen multiphase model in the lattice Boltzmann Method. In this new method the interaction force and as a result the pressure tensor is modified purposefully so that the density of the phases can be adjusted to coincide the corresponding values from the Maxwell equal area rule in thermodynamics. This leads to higher stability and therefore the mentioned purposes are achieved. This new method takes advantage of simplicity and the same implementing procedure in 2D and 3D problems with single or multi relaxation time collision operators. In order to validate the new method, first the coexistence densities of the phases at different subcritical temperatures are compared with those of the Maxwell rule, then the validity of the Laplace law for a droplet is evaluated, after that the spurious velocities around the droplet are evaluated, and finally the broken dam problem is simulated and its results are compared with an experimental data. Results show that the developed model is properly stable and is capable of simulating different multiphase flows at a wide range of density ratios and viscosities.

In this paper, a new immersed boundary-lattice Boltzmann method (IB-LBM) is developed to simulate heat transfer problems with constant heat flux boundary condition. In this method, the no-slip boundary condition is enforced via implicit velocity correction method and the constant heat flux boundary condition is implied considering the difference between the desired heat flux and the estimated one. The velocity correction represented as a forcing term is added to Boltzmann equation and for temperature correction, a heat source/sink term is introduced to energy equation. Elimination of sophisticated grid generation process, simplicity and effectiveness while keeping the accuracy, are the main advantages of the proposed method. Using the developed method, natural convection around a hot circular cylinder with constant heat flux in an enclosure with cold walls has been simulated at Rayleigh numbers of 103–106. Moreover, effects of diagonal position of cylinder on the flow and heat transfer patterns and local Nusselt number distribution on the surface of cylinder and walls of enclosure have been investigated. The obtained results show that the location of maximum local Nusset number is extremely depended on the diagonal position of the cylinder. According to the results of this simulation, it can be said that the present method is able to imply accurately the constant heat flux boundary condition.

In this study, the hybrid Lattice Boltzmann - Finite difference - Immersed Boundary method has been used for investigation of problems with heat transfer. For this purpose, mass and momentum conservation equations are solved by the Immersed Boundary- Lattice Boltzmann method and finite difference method has been used for solving energy conservation equation. The effect of Immersed Boundary has been shown as force and external energy source term in equations and therefor flow and heat transfer around circular cylinder and also the effect of how to move cylinder in heating of fluid inside the cavity has been studied. for this purpose four kinds of movements: circular reciprocating, normal circular, diagonal amplitude and horizontal amplitude have been considered for the cylinder and in all cases, the changes of force coefficients and Nusselt number have been discussed. It has been showed that the circular reciprocating movement has more effect on heating of fluid inside the cavity, which indeed this movement reduces the time of fluid heating about 20 percent in comparison with normal circular and diagonal amplitude movement and approximately 37 percent in comparison with horizontal amplitude movement. In all of the studied problems, the efficiency of hybrid method has been proved.

The standard Lattice Boltzmann Method, LBM, is usually able to predict the results of micro scale flows which are corresponding to the slip flow regime, while it has not sufficient accuracy for nano scale flows which are corresponding to the transition flow regime. In this paper, by improving the lattice Boltzmann method, pressure driven flow through non-porous nano channels and nano channels filled with porous media has been modeled for wide range of Knudsen numbers, Kn, covering the slip and transition regimes. The results show that the presented lattice Boltzmann model is able to predict the flow features in micro and nano scales for wide range of Knudsen numbers by modifying the relaxation time. In the presented research, the effects of the Knudsen number and porosity on the flow rate, Darcy number and pressure drop are reported. Also, for the first time, the Knudsen’s minimum effect for micro/nano channels filled with porous media is observed and evaluated. For the pressure driven flows in non-porous channels this effect occurs at Kn=1, while the results show that for the nano channels filled with porous media this effect occurs at Kn=0.1 because of the tortuosity effects.

In this paper, by defining an appropriate free energy function and integrate that with a Lattice Boltzmann algorithm; a two-phase system of vapor and liquid is modeled where the flow is governed by the continuity and Navier-Stokes equations. Using the developed model, initially a planar interface is modeled and outputs are compared with theoretical results. Then a droplet which is suspended in bulk vapor is investigated and equilibrium conditions of the droplet are compared with theoretical results.

In this paper the coupled lattice Boltzmann model is developed for simulation of multi-step combustion mechanism of a methane jet diffusion flame. The lattice Boltzmann scheme employs the double-distribution-function model, one distribution function for solving flow field and another for temperature and species concentration fields. The density and temperature fields are coupled through low Mach number flow field. The solution parameters such as species properties and rate of chemical reactions adjust in every time step according to temperature and concentration of species variations. Using combustion mechanisms instead of one step fast chemistry reaction and considering effect of temperature and species concentration on solution parameters are the main advantages of the developed model. For validation of the model, a four-step reduced mechanism with six species is used for simulation of combustion in a methane jet diffusion flame configuration. Agreement between the present results and experimental data confirms that this scheme is also an efficient numerical method for more detailed combustion simulations.

In the present Paper, solution methods for simulating compressible flows and shock wave simulation by using Lattice Boltzmann Method(LBM) and simulation of shock wave in the bubble with a moving boundary is evaluated. The standard LBM is found to be incapable of predicting compressible flows and confront instabilities in high Mach number flows. But with some efforts that has been made in recent years, new models for stable solutions of the compressible equations are established. Modified Lax–Wendroff finite difference scheme that has stabale solutions has been used for discretizing Lattice Boltzmann equation. In this study models based on the compressible Euler and compressible multispeed Navier-Stokes to simulate compressible lattice Boltzmann method have been used. The dynamics of compressible bubble busing Rayleigh-Plesset equation have been obtained. Simulation of shock wave in the bubble with other computational fluid dynamics methods has been carried out, However, due to the weakness of the Lattice Boltzmann method for compressible flow, no effort to study the physic of this phenomena has been done with this method. The purpose of this simulation is to achieve a distribution of thermodynamic properties through the radius while collapsing and eventually forming the Sonoluminescence phenomena that caused by the collision of shock waves in the center of the bubble to one other,with lattice boltzmann method.

Mixed convection of free and force convection heat transfer in an inclined lid driven two dimensional enclosure is studied by using Lattice Boltzmann method (LBM) in different values of inclination angle، Richardson (Ri) and Prandtl numbers (Pr). At present case، the velocity components will be affected by inclination angle، force and free convection movements. To do this، using LBM equations are modified. Comparing present results with those of other available ones implies appropriate accuracy. Results are shown as velocity، temperature and Nusselt number profiles and contours of isotherms and streamlines. It is seen that more Pr corresponds to more heat transfer rate especially at higher values of inclination angle and Ri. As a result، to estimate the averaged Nusselt number، a correlation based on Pr، Ri and inclination angle is presented. Moreover، it is seen that the averaged Nusselt number at the upper limit of the considered range of inclination angle، Richardson and Prandtl numbers variability increases by a factor of 7.

In the present study، the motion and deformation of a red blood cell in the incompressible viscous flow is simulated using the lattice Boltzmann method combined with the immersed boundary method. The lattice Boltzmann method is used to solve the flow field، whereas the immersed boundary method is used to simulate the dynamics of the red blood cell. The red blood cell is considered as an elastic boundary immersed in the fluid domain. The main advantage of the lattice Boltzmann method is that it solves only an algebraic equation. In the immersed boundary method the fluid domain is descretized using a regular Eulerian grid، while the immersed boundary is represented in the Lagrangian coordinates. The Eulerian grid points would not necessarily coincide with the Lagrangian points. The fluid- immersed boundary interaction is modeled using an appropriate form of delta function. The effects of the no-slip condition are taken into account via a forcing term added to the Navier-Stokes Equations (here the lattice Boltzmann equation). In the present study، the tank-treading motion of a red blood cell in the viscous shear flow is simulated. The results are found to be in good agreement with the available experimental and numerical ones.