جستجوی مقالات مرتبط با کلیدواژه « روش شبکه بولتزمن » در نشریات گروه « مکانیک »

In the current study, transportation of the microparticles deposition through a channel has been investigated where elliptical obstacle with constant cross sectional area but different shape factors was assumed in the channel. Numerical simulation was conducted using lattice Boltzmann method, and Lagrange method was used for particle tracking. A two-dimensional and nine-velocity model was used as the network model. A curved boundary condition was applied for the obstacle boundaries. In the designed model, particles at standard condition were injected at the inlet of the channel. Gravity force, drag force, Brownian force and Soffman lift force were applied in the motion equation of the particles. The effect of shape factor as a geometrical parameter, which was defined as the ratio of the diameters of elliptical obstacle, and the flow parameters such as Reynolds’ number was examined on the particle deposition and particle scattering. Results were examined at eight different shape factors and five different Reynolds numbers .Results revealed that the change in the shape factor varies the effect of the obstacle in the flowing stream, and also changes the flow regime. This variation was obtained at different Reynolds numbers. Furthermore, changes of the shape factor associated with variations in the flow regime and deposition mechanisms, changes the forces exerted on the particles. Generally, the effect of the mentioned parameters can be interpreted based on the number of the precipitated particles.

In this research, by using the combined lattice Boltzmann and smooth profile method, for power law non-Newtonian fluidized bed, the effect of changing the geometric and fluid on the expansion behavior of the bed has been studied. Investigations have been carried out for 7 different geometries and 4 Newtonian and non-Newtonian fluids with a power law index of 0.8 to 1. The results of the bed with Newtonian fluid show more porosity than the bed with non-Newtonian fluid. Also, increasing the index of the power law caused an increase in the porosity of the bed, and the porosity of the non-Newtonian bed decreased with an increase in the density of solid particles and the initial height of the bed. Investigating the porosity ratio in the non-Newtonian bed showed that with the increase in the diameter of the solid particles, this ratio decreases and increases with the increase in the diameter of the fluid bed. In addition, comparing the results of the bed with carboxymethyl cellulose 0.1% solution as fluid showed that the effect of reducing the particle diameter in the bed, to increase the porosity ratio is 2 times more than the effect of increasing the diameter of the bed. Finally, the output of the model showed that the porosity ratio for the bed containing solid particles with different diameters is lower than the bed containing particles with equal diameters.

In this article, the simulation methods of multiphase flow in the presence of surfactants are classified into 3 categories based on Navier-Stokes, distribution function, and based on intermolecular forces, and each one is described separately. Navier-Stokes-based methods fall into two categories: interface tracking methods and interface capture methods. Methods based on intermolecular forces act as particle-based methods with a Lagrangian perspective in dealing with the flow field. The widely used models in the methods based on the distribution function are also introduced at the end. A wide range of numerical methods has put many choices in front of researchers. Knowing and understanding the capabilities and details of these methods will help to select the most appropriate numerical method and obtain reliable and cost-effective results according to the hardware facilities.

In the present study, the entropy generated due to the conjugate heat transfer of the hybrid nanofluid inside the K-shaped chamber under magnetic field and uniform heat absorption/generation is investigated. The simulation was performed by writing computer code in Fortran language using the lattice Boltzmann method. Variations in Rayleigh number, volumetric fraction of nanoparticles, Hartmann number, heat absorption/generation coefficient, thermal conductivity ratio, chamber aspect ratio and type of magnetic field applied have been evaluated as the main variables of this study. The findings showed that the flow strength, heat transfer rate and entropy produced could be reduced by applying a magnetic field. A lower reduction of the average Nusselt number is achieved by non-uniform application of a magnetic field. Increasing the heat absorption/generation coefficient due to increasing the set temperature leads to decreasing the mean Nusselt number, which this influence increases with increasing the Hartmann number. Addition of nanoparticles to the base fluid in which the conduction of the phenomenon is predominant, increases the rate of heat transfer. Heat transfer is a function of the ratio of thermal conductivity and Rayleigh number that increasing these two parameters increases the convection effects, and in this case, the effect of increasing the Hartmann number is more pronounced. Increasing the chamber aspect ratio leads to a decline in the mean Nusselt number and entropy production, but the effect of adding nanoparticles is greater in this case. Entropy production decreases with increasing Hartmann number and increases with Rayleigh number and heat absorption/generation coefficient.

In this paper, an efficient lattice Boltzmann method is applied for the simulation of two-phase flow problems at high density and viscosity ratios. The present lattice Boltzmann method employs the Allen-Cahn equation to model the interfacial dynamics between two phases and an appropriate collision operator is implemented to ensure the stability of the numerical solutions. The performance of the numerical algorithm is examined by studying droplet dynamics at different flow conditions. Herein, the equilibrium state of a droplet on the flat and curved walls is verified by considering the wetting properties, namely the hydrophilic and hydrophobic characteristics, for solid surfaces. The multiphase flow pattern and interfacial dynamics of an impinging droplet on a cylinder surface and a semicircular cavity are also investigated and the obtained results are compared with the available data. The present study demonstrates that the curved wall considering the wettability effects significantly affects the droplet dynamics, depending on the properties of the liquid phase and the flow conditions. This work also shows that the lattice Boltzmann method with the Allen-Cahn equation is more stable for simulation of liquid-gas systems at density ratio 1000 and viscosity ratio 100 which makes this method more suitable for predicting practical flow characteristics.

In this study, heat transfer of nanofluid in a channel with an externally–applied magnetic field and a porous obstacle is simulated and discussed. To simulate the flow field inside the obstacle, the Darcy–Brinkman–Forchheimer model is implemented in the LBM method. Thereafter, effects of influencing parameters on the heat transfer rate are analyzed utilizing the experimental design method. The results show that the nanoparticles type has the greatest effect on the heat transfer with the contribution ratio of 62.79%. The second and the third parameters are the obstacle size and the Reynolds number, with the contribution ratios of 20.71% and 7.58%, respectively. The contribution ratios of the Hartmann number and the nanoparticles fraction are estimated about 3%. However, it is found that in this problem, the influences of the porosity, type, and the Darcy number of the obstacle on the mean Nusselt number are almost negligible.

In this paper, the effect of shape and aspect ratio of wall on natural convection heat transfer of non-Newtonian fluid with power law model within two-dimensional enclosure in the presence of a uniform magnetic field by lattice Boltzmann method (LBM) is investigated. The left wall is at a constant hot temperature, while the right wall is kept on cold constant temperature and other walls are considered adiabatic. In this simulation, the flow field and temperature are calculated by simultaneously solving the flow and temperature distribution functions. The effect of various parameters such as Hartmann number, aspect ratio, different shape of the wall and power index of non-Newtonian fluid is investigated. The results show that increasing power index, aspect ratio and Hartmann number decrease the average Nusselt number. Also, the highest amount of heat transfer is generally associated with the case of a triangular wall. In addition, increasing the power index reduces the effect of the magnetic field.

In order to simulate multiphase flow in the presence of dielectric current using the Lattice Boltzmann Method (LBM), three distribution functions are used, two of which for using the He-Chen-Zhang phase field model and one for solving the potential field. Initially, the ability of the code to apply surface tension was tested using the Laplace law and the drop release test. The results show that the present numerical program is capable of modeling well the regulated surface tension force. Then, the Rayleigh–Taylor instability simulation is used to evaluate the codechr('39')s ability in applying volume forces. The results by the developed numerical program are in good agreement with the numerical results in the references. In this study, for the first time, the effect of electric field on a droplet immersed in another fluid and the presence of droplet in a porous medium is investigated by LBM. For this purpose, first the droplet motion due to the potential difference in the porous and non-porous media is investigated. After modeling the droplet motion due to the potential difference, two electric fields areapplied to the droplet to reverse the droplet deformation. Through various tests, it is shown that at a given potential difference, the droplet breaks down after much deformation and is divided into smaller droplets. The decomposition of droplets in a pre-mixed emulsion is a common technique in the production of monodisperse droplets. The presence of monodisperse droplets in an emulsion improves the physical properties of polymer science experts.

In this work Multi-Relaxation Time Lattice Boltzmann Method (MRT-LBM) is used to investigate the effect of the inlet air position on particle motion in a room. The sub-scale modeled room is one-tenth the scale of a full-size room with dimensions of 0.914 m×0.305 m×0.457 m and two different positions (ceiling and floor) are considered for the inlet air with dimension of 0.101m×0.101m. Large Eddy Simulation (LES) with Standard Smagorinsky model is utilized to simulate the turbulent indoor airflow. Particles with 1 and 10 micrometer sizes are selected for investigation of particle dispersion and deposition on the walls of the room. Number of deposited particles and those exiting the room show that when the inlet air is on the floor, the number of particles leaving through the exhaust register with bigger size (10µm) is more than the case for ceiling position. For smaller particles (1 µm) there is no significant difference between the floor and ceiling position of the inlet air for particles leaving the room thought the exhaust register. Results show that the gravity force significantly affect the particle deposition, as the number of deposited 10 µm particles on the floor are about 100 times that of the deposited 1 µm particles when the inlet air position is at ceiling.

In this paper for the first time, the effect of direction of wall movement on mixed convection in circle quarter porous enclosure with heat absorption/generation is investigated by LBM. The magnetic field is applied to the enclosure in uniform and periodic forms. Mixed convection is caused by the movement of walls at different angles. The results show that increasing the Richardson number, Hartmann number, heat absorption/generation coefficient and decrease the porosity coefficient reduce the average Nusselt number. With fixed all parameters the maximum value of the average Nusselt number is related to the 90 ° velocity angle, in which case the average Nusselt number is about 25% higher.  Increasing the Richardson number reduces the effect of the magnetic field. Periodic applied of a magnetic field results in about 30% more than uniform applied. Increasing the porosity coefficient also increases the effect of the Hartmann number and the angle of wall movement. It is observed that the simultaneous increase of the heat absorption/generation coefficient and the Hartmann number lead to a further decrease of the average Nusselt number.

In this paper, the effect of changing position of heat source on nanofluid heat transfer under the influence of magnetic field in the wavy channel with variable amplitude and number of oscillations is investigated by Lattice Boltzmann Method. A uniform magnetic field is applied perpendicular to the channel. The first half of the upper channel wall, wavy form with the amplitude and number of variable oscillations at constant cold temperature, and the half of the bottom channel with variable position, are at constant hot temperature. Other walls are insulated for heat and mass. In this study, the effect of parameters such as Reynolds number, nanoparticle volume fraction, Hartmann number, hot wall position and amplitude and number of wavy wall oscillations were evaluated. The results show that at a specific position location of the hot wall, the average Nusselt number increases with the increase of other parameters. The highest heat transfer also occurs when the hot wall is closer to the channel inlet that results in an average 20% increase in the Nusselt number. The effect of increasing the Hartmann number on heat transfer is greater when the hot wall is closer to the channel outlet. Increasing the percentage of nanoparticles increases heat transfer and this effect increases with decreasing Reynolds number.

In this article, the magnetic field effect on the natural convection heat transfer is simulated via LBM. The vertical wall of the left side of the cavity is at a constant hot temperature, while the vertical wall of the right side of the cavity has three different temperature boundary conditions, 1) constant cold temperature, 2) linear temperature and 3) constant hot temperature. A lozenge-shaped obstacle located in the center of the cavity is examined in four different modes, 1) cold, 2) conducting, 3) adiabatic, and 4) hot. The bottom wall of the cavity is also evaluated in three different slopes. The results show that increasing the slope of the wall and the Rayleigh number by unchanged all the parameters leads to an increase in heat transfer. Also, changing the boundary temperature of the walls and the obstacle can affect the amount of heat transfer. In addition, increasing the strength of the magnetic field reduces the average Nusselt number, which differs in different conditions.

Atherosclerosis is responsible for almost 35% of annual deaths in developed countries. The disease could be due to an artery blockage by the interaction of an externally second phase (air bubbles, medicine carrying capsules) with a particle which is entered to the bloodstream. The effect of some most important affecting parameters on the blockage time of a microchannel due to the impact of a particle and a second moving second phase is investigated using lattice Boltzmann method and with programming Fortran90. The authors tried to mimic the physic of the flow of a small artery by generating the same geometry and changing geometrical and physical parameters. Lee and Lin Lattice Boltzmann multi-phase model is used beside the immersed boundary method. It is investigated the small changes in Capillary flow has no meaningful effect on the interaction of second phase and particle. But, the ratio of particle size to the channel width affects the blockage time in the microchannel. In fact, the blockage time will increase by an increase in the size of the particle. The initial size of the second phase to particle size ratio has the highest effect on the blockage time.

In this paper natural convection of nanofluid around a hot obstacle simulates in a square cavity with east and west cool walls and an adiabatic wall in north and a hot wall in south by Lattice Boltzmann Method. Flow is quiet and non-compressible and nanofluid is water-Tio2. We use D2Q9 LBM for velocity and fluid temperature. The purpose of this study is investigation of heat transfer around a hot obstacle in a square cavity and the effect of Rayleigh number, obstacle dimension, volume fraction of nanofluid, cavity dimensions, surface ratio and various models of computing heat transfer conductivity coefficient and viscosity coefficient on Nusselt number. This investigat is done for the first time. The results show that, by increasing of Rayleigh number and volume fraction, average of Nusselt number will increase. The average of Nusselt number will increase when obstacle dimensions increase to 0.5L but it will decrease when the obstacle dimensions increase to 0.7L. Vortexes will create in 0.8L and it causes to increase of heat transfer. By reduplicating the obstacle width heat transfer is better than reduplicating the obstacle length. The average of Nusselt number increases by increasing of cavity’s length and it will decrease by increasing of cavity’s wide. All results are equal in Hamilton-crosser and Maxwell- Garnett model when the surface ratio is one. But heat transfer will increase by decreasing surface ratio. The average of Nusselt Number in Wang model is less than Nusselt Number in Brinkman model.

In this study, the liquid-solid fluidized bed was simulated using a combination of Lattice Boltzmann and smoothed profile method and then by changing the geometrical parameters contains of, particles diameter, width of the bed, initial bed height and the placement of the particles in non-uniform particles bed, their effects on porosity are studied. The hydrodynamic model of the flow is based on the LBM and SPM is adopted to enforce the no-slip boundary condition at the liquid-solid interface. The kinematics and trajectory of the discrete particles are evaluated by Newton's law of motion. Comparison of numerical and empirical results for porosity at different velosities showed acceptable accuracy. Also, Simulations indicate that an increase in width of the bed and particles diameter increased porosity and an increase in initial bed height decreased the porosity of the bed. Finally, the effect of placement of particles in none uniform fluidized bed showed the highest porosity accurse where particles with a small diameter stay on particles with a large diameter, also where the particles are mixed together the lowest porosity was accrued.

In this work, natural convection in a two-dimensional enclosure with different shapes filled nanofluid with heat generating/absorbing in the presence of a magnetic field is simulated by LBM. The left vertical wall of the enclosure is examined in two modes: constant temperature heating and linear temperature heating and the cold wall of the enclosure in three different forms (a) diagonal, (b) curved and (c) smooth. The effect of parameters such as Hartmann number, nanoparticle volume concentration, heat generation/absorption coefficient, cold wall shape and type of wall heating on the nature of flow and heat transfer is evaluated. The results show that in all cases, increasing the Hartmann number and heat generation/absorption coefficient decrease the Nusselt number. The effect of Hartmann number in different states is different. The highest heat transfer also occurs when the vertical wall has a constant temperature. The effect of the magnetic field is greater when the cold wall is smooth. The effect of adding nanoparticles to the base fluid on decreasing or increasing the average Nusselt number depends on the Hartmann number and heat generation/absorption coefficient.

In this paper, for the first time, natural convection heat transfer of a nanofluid in the presence of a uniform magnetic field inside a parallelogram shaped cavity with two triangular obstacles with different boundary conditions is simulated by using lattice Boltzmann method. The right vertical wall of the cavity is assumed to be adiabatic and the inclined walls are kept at constant cold temperature, while the left vertical walls are kept at constant hot temperature. The flow and temperature field is calculated by solving lattice Boltzmann equations for velocity and temperature distribution functions simultaneously. D2Q9 lattice arrangement for each distribution function is used. The results have been validated with available results in the literature. The effects of different parameters such as Rayleigh number (103-105), Hartmann number (0-90), nanoparticle volume fraction (0-0.05) and different boundary conditions at triangular obstacles on natural heat convective heat transfer are investigated. The results show that, at a constant Rayleigh and Hartmann number, the average Nusselt number takes its maximum and minimum value when the triangular obstacles are kept at constant cold and hot temperatures, respectively. For all cases, it is found that the average Nusselt number increases with enhancement of Rayleigh number. Also, increasing of Hartman number decreases the flow velocity and heat transfer rate. Furthermore, increase of volume fraction of nano particles enhances heat transfer rate, however its changes for different Rayleigh and Hartman numbers are not the same.

In this paper the Multi Relaxation Time Lattice Boltzmann Method in conjunction with the Large Eddy Simulation model was used to study the particle deposition in a room  with various diameters (10nm-10µm)and the effect of buoyancy, drag and Brownian forces to particle deposition on the different walls of the room has been investigated.  The sub-grid scale turbulence effects were simulated through a shear-improved Smagorinsky model. To simulate the particle deposition in the room, the particle injection process was initiated with 144 particles injected uniformly at the inlet with the same velocity as the airflow at every 0.05s; particle injection was stopped after 30s. Therefore, a total of 86400 particles were injected into the room. The present simulation results for the airflow showed good agreement with the experimental data and the earlier numerical results. The simulated results for particle dispersion and deposition showed that the numbers of deposited particles on the walls increases by augmentation of the time. When the particle injection started the concentration in the inlet jet region is more than other zones and that increases in the region far from the inlet by time. Present results will be interesting for designing air condition systems in the office and hospitals rooms.

In this work numerical simulation of magneto hydrodynamics (MHD) natural convection in a three dimensional square cavity has been considered by new means of the Lattice Boltzmann method with double Multi-Relaxation-Time (MRT) model utilizing cu/water nanofluids. D3Q19 and D3Q7 models have been used to solve the momentum and energy equations, respectively and the effect of different Grashof numbers (Gr=1e3 _1e5) and various Hartmann numbers (Ha=0-100) for volumetric fraction of the nanoparticles between 0 and 12% have been investigated. The results have been shown at different planes and lines of the 3-D enclosure and based on the results the double MRT-LBM method is a proper method for simulating the complex 3-D flows. Also, the results show that augmentation of the Hartmann number decreases the heat transfer for base fluid and the maximum reduction of Nusselt number with increasing Hartmann number from 0 to 100 has been observed as 71% for Gr=1e4. While increasing the Grashof number and volumetric fraction of the nanoparticles enhance the heat transfer rate for all Hartmann number. The highest effect of nanoparticle is obtained at Gr=1e4 and Ha=50 as with increasing 12% of volumetric fraction of the nanoparticles Nusselt number enhances 43% .