Sharif Digital Repository

Nowadays, the lattice Boltzmann method has been widely used by scientists and engineers as an alternative to conventional numerical solvers for the Naiver-Stokes equations. The drag force decrease on the surfaces in industrial applications special in transport industries has always been of special importance. In the current research, the effects of the drag decrease has been investigated by making some rectangular grooves on the millimeter and micrometer scale on a flat surface that has been under external laminar flow of a single-phase fluid with the uniform type. Making grooves on the surfaces usually lead to change the contact area from the solid-fluid to fluid-fluid in the grooves area.... 

Various situations of drop impact on solid surfaces occur widely in natural phenomena and industrial applications, as well as involve in the development of some new technologies, such as, 3D printers, interfacial materials, microfluidics, and biotechnology. Therefore, the relevant investigations have been increasing considerably in the last two decades. Most of these studies are related to the simple case of vertical drop impact on horizontal stationary surfaces, while in most cases vertical/oblique drop impact on horizontal/inclined stationary/moving surfaces in the absence/presence of a crossflow and their various combinations occur. One of the most important situations is drop impact on... 

Rapid preparation of a homogeneous mixture is essential for many chemical and biological applications, such as micro-scale biological-chemical agent detection, drug delivery, and DNA hybridization. Some mixing systems have a micro-scale geometry, which results in a very slow mixing process, mainly due to laminar flow in these systems. Mixing in a slow flow is performed only by molecular diffusion. In the absence of any disturbances, increased mixing is not possible simply by diffusion. Accordingly, a suitable and innovative method to improve mixing for such systems is required. Induced charge electro-osmosis is a new field of electro-osmotic flow, which performs better than conventional... 

In this research, numerical simulation of the impact of a drop on a flat surface with oblique velocity has been performed, using two-phase model of Lattice Boltzmann Method (conservative phase-field). During impact, it is important to investigate two-dimensional drop dynamics and to evaluate the effectiveness of the numerical method used. The model used here restores conservative phase field and preserves mass both locally and globally. In addition, to calculate the slope of the phase field, it calls the center points without engaging finite difference calculations. This makes it efficient for running parallel computations. A fixed dry and hard surface is considered and the drop impacts it... 

In this study, a high-order finite-difference lattice Boltzmann method (FDLBM) is used to simulate the two-dimensional incompressible flows. Here, the incompressible form of the lattice Boltzmann (LB) equation in the two-dimensional generalized curvilinear coordinates is considered and the resulting equation is discretized based on both the third- and fifth-order upwind finite-difference schemes. The time integration of the present flow solver is performed by the fourth-order Runge-Kutta method. Several incompressible laminar flow problems are simulated to examine the accuracy and performance of the developed high-order FDLBM solver. The present results are compared with the existing... 

In the present study, a high-order finite-difference lattice Boltzmann solver is applied for simulating steady and unsteady three-dimensional incompressible flows. To achieve an accurate and robust flow solver, the incompressible form of the lattice Boltzmann equation in the three-dimensional generalized curvilinear coordinates is discretized spatially based on the fifth-order weighted essentially non-oscillatory (WENO) finite-difference scheme. To ensure the stability and temporal accuracy of the flow solver, the fourth-order Runge-Kutta method is used for the time integration. To examine the accuracy and performance of the flow solver, different three-dimensional incompressible flow... 

Based on the history of computational fluid dynamics, choosing a proper method for three-dimensional investigation of two-phase flows is always challenging. In this research, the flow of atomization of a liquid jet was investigated. Also, Using GPU technique made our computations about 40 times faster. The numerical results are in good agreement with available numerical and experimental data. Based on our results, jet flow can achieve different regimes at different Weber and Reynold. Jet flow was found in dripping and Rayleigh instability regimes when Weber number was set to 1.79 and 3.10, respectively. Also, the transition between dripping and jetting was estimated at We between 2 to 3. In... 

Drop formation is an interesting field of research due to its wide-range of applications, such as drug delivery, biomedical studies, pharmaceutical industry, Lab-On-Chip (LOC) devices, etc. In recent years, researchers have used numerical studies to better understand how the process of forming and carefully examining the factors that affect quality improvement. One of the most effective methods in controlling the size and the process of drop formation is use of external force in microfluidic devices. Among the external force in this study, an electric field with oscillating current was used. Rapid methods for creating, deforming, and breaking up of drops in microfluidic applications are... 

In this research, the spectral difference lattice Boltzmann method (SDLBM) is developed and applied for an accurate simulation of two-dimensional (2D) inviscid and viscous compressible flows on the structured and unstructured meshes. The compressible form of the discrete Boltzmann-BGK equation is used in which multiple particle speeds have to be employed to correctly model the compressibility in a thermal fluid. Here, the 2D compressible Lattice Boltzmann (LB) model proposed by Watari is used. The spectral difference (SD) method is implemented for the solution of the LB equation in which the particle distribution functions are stored at the solution points while the fluxes are calculated... 

In recent years, there have been a tremendous research performed in the field of sestems containing small scales. However, besides all advantages of such systems, microfluidic systems have extraordinary difficulties and pumping liquid drops as part of some of these systems has been very important issue. An approach related to flow control is use of surface acoustic waves (SAW), which is known as acoustofluidic device. So far, most researches have only qualitatively investigated acoustic flux phenomenon. On the other hand, computational research is ongoing more emphasizing on accuracy, optimization, and obtaining more detailed physical understanding of SAW applications. Investigation of the... 

In this research, surface reaction phenomenon in porous media has been numerically simulated in pore scale. The main interesting part in this kind of physics is surface reaction exposed to a flow field. In this regard, an in-house code, based on LBM was developed. To speed-up our simulation, parallel computing was used on a GPU platform leading to a significant speed-up. Also, to model a real complex geometry, X-CT and MRI medical imaging technique were used to accurately model several complex 3D geometries. While, image processing technique was used to model our 2D geometries. The basic equilibrium equation of isopropanol dehydrogenation was considered to simulate and to analize chemical... 

In recent years, lattice Boltzmann method (LBM) has been developed to be used as an alternative and promising computational technique to simulate various flows. It originates from classical statistical physics. The ability to simply solve complex flows, simulating of multiphase and multi-component without need to follow the boundaries of different phases, and the inherent ability of parallel processing are notable features of this approach. On the other hand, finite element method (FEM) is widely used in many practical engineering fields, especially in solid mechanics. In this study, in addition to simulating flow over a rigid body, flow over an elastic body is also simulated with a... 

The goal of the present study is to simulate the compressible rarefied gas flow by using a high-order finite-difference lattice Boltzmann method. Here, a weighted essentially non-oscillatory lattice Boltzmann method (WENO-LBM) is applied for the solution of the compressible form of the LB equation with the Kataoka-Tsutahara model. The solution procedure is based on the discretization of the convection terms of the LB equation using the fifth-order finite-difference WENO scheme and the temporal term using the third-order explicit total variation diminishing Runge-Kutta scheme for both the continuum and rarefied gas flows. The treatment of implementing the no-slip and slip boundary conditions... 

Formation and detachment of drops are of fundamental importance in studying two-phase flows, such as ink jet printing, emulsion, and spray. Drops are formed under the effects of surface tension forces. After formation, forces like gravity detach the drop from the rest of the fluid. The flow rate is varied from dripping to jetting regime. In this project, formation and detachment of drops were simulated, using LBM with phase field model, which can simulate flows with high-density ratios and is a robust method for applying wetting condition on the walls. Results were validated using single-phase and two-phase flows. After code validation, the oscillations caused by formation and detachment of... 

In the this study, a numerical simulation of two-dimensional incompressible sloshing flow in a rectangular tank with baffle(s), using Lattice Boltzmann Method (LBM) is presented. Finite difference LBM and two-phase "Lee" model were used. The potential form of intermolecular forces is utilized to guarantee the stability of the numerical scheme and the discretization of the solution domain is performed by a two dimensional structured grid. Two different distribution functions are applied to obtain pressure, momentum, and composition of the particles. Furthermore, the Boltzmann transport equation is discretized, by using standard D2Q9 method. The "dropl" test case is simulated by the present... 

In recent years, LBM has shown to be a suitable computational method for most flow simulations. Its simplicity, adaptability for complex geometries, and capability in parallel processing are among many reasons for broad implementation of LBM these days. In this research, we have tried to take advantage of these features in the simulation of a turbulent flow over a moving circular cylinder at low CPU cost. In order to use LBM in a high Reynolds number incompressible flow over a moving solid body, one needs to pay special attention to grid quality, curved solid wall boundary condition, turbulence model, moving boundary, etc. In order to obtain a suitable practical LBM computer code, the... 

In this study, two finite-difference lattice Boltzmann methods (FDLBM) are applied and assessed for the simulation of two-phase liquid-vapor flows with high density ratios. For this aim, the He-Shan-Doolen type lattice Boltzmann multiphase model is used and the spatial derivatives in the resulting system of equations are discretized by using the second-order central difference and modified Lax-Wendroff schemes. Suitable numerical dissipation terms and filters are applied to regularize the numerical solution and remove spurious waves generated by flow nonlinearities in smooth regions and at the same time to remove the numerical oscillations in the interface region of the two phases.Three... 

Bubble cluster has attracted the interests of many researches since the early twentieth century. Despite its easy generation and numerous occurrences, its study is extremely complex. Describing the dynamical behavior of bubble clusters is possible when quite a few simplifying assumptions are utilized. In other words, one can observe that with current approaches, the relevant theoretical researches are not very valuable. In this research, however, lattice Boltzmann method, a rather recent mesoscopic approach, was used to study the behavior of bubbles in a bubble cluster. Of course, this is only the beginning and there is a long way before getting close to experimental results. However, there... 

With advances in technology, production and propagation of sound waves in the air has become very important. One of the main goals of study of these waves is controlling them. The environment plays the most important role in sound propagation. Therefore, the properties of the environment and their effects should be studied. One such concern studied widespread previously, is porosity and porous media effects on the properties of a fluid flow and sound waves through it. An important application of this study is sound proofing systems. In this project two-dimensional numerical simulation of aeroacoustic waves passing through a porous media is carried out, using Lattice Boltzmann Method. The aim... 

In the present study, the simulation of incompressible Electro-Magneto-hydrodynamic flows is performed using a finite volume lattice Boltzmann method (FVLBM). The Boltzmann transport equation is solved using a cell-centered finite volume method on structured meshes. A central difference scheme is used to discretize the spatial derivatives and the fourth-order numerical dissipation term is added to stabilize the solution. To discretize the temporal derivative, the fourth-order Runge-Kutta time stepping scheme is applied. The standard collision-streaming lattice Boltzmann method has been used to simulate EMHD flows in the literature, however, it has several deficiencies such as the...