Sharif Digital Repository

The Computational fluid dynamics (CFD)–discrete element method (DEM) numerical simulation may be applied to predict the hydrodynamic behavior of dense particle–fluid flows. The main drawback of this simulation is the long computational time required owing to the large number of particles and the minute time-step required to maintain a stable solution. In this work, a new method to improve the efficiency and accuracy of CFD–DEM simulations is presented. The particle stiffness coefficient is used as a flexible parameter to improve the accuracy and efficiency of the model. The particle concentration distribution results are compared with experimental one’s to derive the optimum effective... 

The Computational fluid dynamics (CFD)–discrete element method (DEM) numerical simulation may be applied to predict the hydrodynamic behavior of dense particle–fluid flows. The main drawback of this simulation is the long computational time required owing to the large number of particles and the minute time-step required to maintain a stable solution. In this work, a new method to improve the efficiency and accuracy of CFD–DEM simulations is presented. The particle stiffness coefficient is used as a flexible parameter to improve the accuracy and efficiency of the model. The particle concentration distribution results are compared with experimental one’s to derive the optimum effective... 

The Computational fluid dynamics (CFD)–discrete element method (DEM) numerical simulation may be applied to predict the hydrodynamic behavior of dense particle–fluid flows. The main drawback of this simulation is the long computational time required owing to the large number of particles and the minute time-step required to maintain a stable solution. In this work, a new method to improve the efficiency and accuracy of CFD–DEM simulations is presented. The particle stiffness coefficient is used as a flexible parameter to improve the accuracy and efficiency of the model. The particle concentration distribution results are compared with experimental one’s to derive the optimum effective... 

Heat generation from Very Large-Scale Integrated (VLSI) circuits increases with the development of high-density integrated circuit technology. One of the efficient techniques is liquid cooling by using a microchannel heat sink. Numerical simulations on the microchannel heat sink in the literature are mainly two dimensional. The purpose of the present study is to develop a three-dimensional procedure to investigate flow and conjugate heat transfer in the microchannel heat sink for electronic packaging applications. A finite volume numerical code with a multigrid technique, based on an additive correction multigrid (AC-MG) scheme, which is a high-performance solver, is developed to solve the... 

An improved vorticity-based gridding technique is presented and applied to create optimal non-uniform Cartesian coarse grid for numerical simulation of two-phase flow. The optimal coarse grid distribution (OCGD) is obtained in a manner to capture variations in both permeability and fluid velocity of the fine grid using a single physical quantity called "vorticity". Only single-phase flow simulation on the fine grid is required to extract the vorticity. Based on the fine-scale vorticity information, several coarse grid models are generated for a given fine grid model. Then the vorticity map preservation error is used to predict how well each coarse grid model reproduces the fine-scale... 

The present study focuses on the numerical simulation of cavitation around the NACA 0015. The unsteady behaviors of cavitation which have worthwhile applications are investigated. The cavitation patterns, velocity fields and frequency of the cavitating flow around hydrofoil is obtained. For multi phase simulation, single-fluid Navier-Stokes equations, along with a volume fraction transport equation, are employed. The bubble dynamics model is utilized to simulate phase change. SIMPLE algorithm is used for velocity and pressure computations. For discretization of equations the finite-volume approach written in body fitted curvilinear coordinates, on collocated grid, is used. In this study,... 

This paper develops a two dimensional Green element simulator based on a "compatibility-equation" algorithm for simulation of counter-current spontaneous imbibition (COUCSI) process. The Green element method is a novel computational approach based on the boundary integral theory, which is regarded as a hybrid combination of both boundary and finite element methods. The superiority of the Green element method in modeling of two phase water/oil flow is at the core of this paper. The developed simulator within the context of this proposition is explored to predict the oil recovery from a one dimensional single matrix block. The results are then compared with the experimental data, and they... 

In this article, a v2f model is employed to conduct a series of computations of incompressible flow in a periodic array of square cylinders simulating a porous media. A Galerkin/least-squares finite element formulation employing equal order velocity-pressure elements is used to discretize the governing equations. The Reynolds number is varied from 1000 to 84,000 and different values of porosities are considered in the calculations. Results are compared to the available data in the literature. The v2f model exhibits superior accuracy with respect to κ - ε results and is closer to LES calculations. The macroscopic pressure gradients for all porosities studied showed a good agreement with... 

Production logging is used to evaluate wells production performance. Interpretation of production log data provides velocity profile and contribution of each zone on total production. In multi-phase flow conditions, production log interpretation can be challenging since producing fluids do not have similar densities and travel with different speed depending on fluids properties and wellbore deviation. Production log interpretation in multi-phase producing wells requires identifying downhole flow regimes and determining velocity profile for each phase. There are different flow regimes and velocity models available, which are being used in production log interpretation to determine wells flow... 

Decision on the location of new wells through infill drilling projects is a complex problem that depends on the reservoir rock and fluid properties, well and surface facilities specifications, and economic measures. Conventional approach to address this is a direct optimization that uses the numerical flow simulation. However, this is computationally very extensive. In this study the authors use a hybrid genetic algorithm (HGA) optimization technique based on the genetic algorithm (GA) with helper functions based on the polytope algorithm and the neural network. This hybridization introduces hill-climbing into the stochastic search and makes use of proxies created and calibrated iteratively... 

Decision on the location of new wells through infill drilling projects is a complex problem that depends on the reservoir rock and fluid properties, well and surface facilities specifications, and economic measures. Conventional approach to address this is a direct optimization that uses the numerical flow simulation. However, this is computationally very extensive. In this study the authors use a hybrid genetic algorithm (HGA) optimization technique based on the genetic algorithm (GA) with helper functions based on the polytope algorithm and the neural network. This hybridization introduces hill-climbing into the stochastic search and makes use of proxies created and calibrated iteratively... 

In this study, we use direct simulation Monte Carlo method to simulate subsonic flow in nanochannels and micro/nanoscale backward-facing (BF) step considering a wide range of Knudsen number regimes. The nanochannel flow simulation indicates that the nanoscale flow through the nanochannel resembles unique features such as encountering negative pressure deviation behavior and observing flat velocity profiles at higher Knudsen number regimes. On the other hand, the micro/nano BF step flow simulations demonstrate that the length of separation region considerably decreases as the flow becomes more rarefied and approaches the transition regime. Meanwhile, the variations in the flow properties are... 

This Paper presents the simulation of electroosmotic flow in nanochannels using the dissipative particle dynamics (DPD) method. Most of the past electroosmotic phenomenon studies have been carried out using the continuum flow assumptions. However, there are many electroosmotic applications in nanoscales NEMS and microscales MEMS, which need to be treated using non-continuum flow assumptions. We simulate the electroosmotic flow within the mesoscopic scale using the DPD method. Contrary to the ordinary molecular dynamics method, the DPD method provides less computational costs. We will show that the current DPD results are in very good agreement with other available non-DPD results. To expand... 

We investigate heat transfer between parallel plates separated by liquid argon using two-dimensional molecular dynamics (MD) simulations incorporating with 6-12 Lennard-Jones potential between molecule pairs. In molecular dynamics simulation of nanoscale flows through nanochannels, it is customary to fix the wall molecules. However, this approach cannot suitably model the heat transfer between the fluid molecules and wall molecules. Alternatively, we use thermal walls constructed from the oscillating molecules, which are connected to their original positions using linear spring forces. This approach is much more effective than the one which uses a fixed lattice wall modeling to simulate the... 

Reservoir flow simulation involves subdivision of the physical domain into a number of gridblocks. This is best accomplished with optimized gridpoint density and a minimized number of gridblocks, especially for coarse-grid generation from a fine-grid geological model. In any coarse-grid generation, proper distribution of gridpoints, which form the basis of numerical gridblocks, is a challenging task. We show that this can be achieved effectively by a novel grid-generation approach based on a background grid that stores gridpoint spacing parameters. Spacing parameter (L) can be described by Poisson's equation (▽2L = G), where the local density of gridpoints is controlled by a variable source... 

Reservoir flow simulation involves subdivision of the physical domain into a number of gridblocks. This is best accomplished with optimized grid point density and minimized number of gridblocks especially for coarse grid generation from a fine grid geological model. In any coarse grid generation, proper distribution of grid points, which form basis of numerical gridblocks, is a challenging task. We show that this can be effectively achieved by generating a background grid that stores grid point spacing parameter. Spacing (X) can be described by Poisson's equation (∇2 L = G) where the local density of grid points is controlled by a variable source term (G). This source term can be based on... 

Domed roofs have been used in Iran and many other countries to cover large buildings such as mosques, shrines, churches, schools. They have been also employed in other buildings like bazaars or market places in Iran due to their favorable thermal performance. The aim of this research is to study about domed roofs thermal performance in order to determine how they can be helpful in reducing the maximum air temperature of inside buildings during the warm seasons considering all parameters like air flow around them, solar radiation, radiation heat transfer with the sky and the ground as well as some openings on the building. The results of the study show that the thermal performance of the... 

This paper presents a new combined method for accurate upscaling of two-phase displacements in highly heterogeneous reservoirs. The method has the capability to retain its high performance for various flow regimes, from viscous to gravity dominant displacements, without the need for further modifications and computational steps. Two different grids are incorporated for simulation. The grid on fine scale is used to recognize the complicated physics of flow which depends on dominated driving forces and their interaction with heterogeneity. However, to achieve a fast simulation, the global flow calculation is performed on the coarse scale grid using upscaled equivalent properties. The... 

Overall turbine analysis requires large CPU time and computer memory, even in the present days. As a result, choosing an appropriate computational domain accompanied by a suitable boundary condition can dramatically reduce the time cost of computations. This work compares different geometries for numerical investigation of the 3D flow in the runner of a Francis turbine, and presents an optimum geometry with least computational effort and desirable numerical accuracy. The numerical results are validated with a GAMM Francis Turbine runner, which was used as a test case (GAMM workshop on 3D computation of incompressible internal flows, 1989) in which the geometry and detailed best efficiency... 

Presence of fracture roughness and occurrence of nonlinear flow complicate fluid flow through rock fractures. This paper presents a qualitative and quantitative study on the effects of fracture wall surface roughness on flow behavior using direct flow simulation on artificial fractures. Previous studies have highlighted the importance of roughness on linear and nonlinear flow through rock fractures. Therefore, considering fracture roughness to propose models for the linear and nonlinear flow parameters seems to be necessary. In the current report, lattice Boltzmann method is used to numerically simulate fluid flow through different fracture realizations. Flow simulations are conducted over a...