Sharif Digital Repository

Multiphase flows are commonly encountered in oil and gas industries. Flow fields in production operations are often complex and include multiphase flows of gas and liquid. The prediction of pressure gradients, liquid holdup and flow patterns occurring during the simultaneous flow of gas and liquid in pipes and wellbores is necessary in designing production facilities. Previously, due to their complex nature, these flow patterns have been mostly investigated only experimentally and empirical correlations based on the experimental data. From another point of view, it is almost impossible to experimentally realize all the flowing conditions for each of the flowing patterns. Nowadays, computer... 

Vibration is one of the major problems in gas and oil pipelines. Vibrations can cause damage to the pipes, supports, valves and other equipment installed in the system. These vibrations can be caused by equipment installed on pipelines like compressors and pumps or by fluid flow in pipes and fixed equipment like connections and valves. This research investigates the dynamic behavior of fluid flow in pipelines in Karanj and Parsi oil fields located in the southern part of Iran. The pipeline is responsible for injecting gas into the field. Excessive vibrations in the system cause repeatable damage which in turn increases the operating and maintenance cost. First, the vibration of pipelines has... 

In the present work, the experiments were carried out for two types of PAM (3330 and 3630) with three distinct concentrations (25, 40 and 55 ppm) and TiO_2-water nanofluid for four concentrations (1.5, 2, 2.5 and 3 vol. %), and the Nusselt number and friction factor for each of them expressed separately. The Reynolds number was in the range from 11000 to 21000. The steady state turbulent convective heat transfer and friction factor of the combination of TiO_2-water nanofluid and polymer 3330 in the coiled tube were investigated. The effects of the Reynolds number for 2 vol. % nanoparticles which consists of 25 ppm PAM (3330) determined at the constant temperature of 24°C. It was observed... 

As a result of fission reaction in a nuclear reactor, the produced high neutron flux would affect the material of Reactor Pressure Vessel (RPV). This neutron radiation has a detrimental impact on the mechanical properties of the RPV material such as hardening (or embrittlement) while neutrons are absorbed by the material. A major concern in embrittled RPVs is propagation of critical flaw causing through-wall cracks. Some transients leading to overcooling of RPV intensify the propagation of theses cracks and result in thermal load on RPV, known as Pressurized Thermal Shock (PTS). Such situation could be created in case of Emergency Core Cooling System (ECCS) actuation which leads to injection... 

In this study, the performance of the Moss-Brooks semi-empirical model in estimating soot for six different diffusion flames with methane, ethylene, and kerosene fuels in laminar and turbulent regimes has been investigated. The results show that the model with the default constants in the laminar ethylene flame has relatively acceptable performance, but in the turbulent ethylene flame as well as the laminar and turbulent flames of methane, has a significant error. In this regard, inspired by past research and performing sensitivity analysis, the constants of oxidation and coagulation sub-models were reviewed and Improved. The results of soot volume fraction were evaluated for values of 0.015... 

It is difficult and time-consuming to calculate the reaction rate directly. For turbulence modeling methods such as RANS or LES, various statistical methods are used to model turbulence-kinetics interactions. The purpose of this study is to implement the linear eddy model in CANTERA open source-code. This code instantly simulates one-dimensional, quasi-one-dimensional laminar flames with different chemical kinetics in which the effects of viscosity and molecular diffusion are implemented like a laminar flame. The effects of turbulence are simulated by a series of stochastic processes called triple maps. This research can provide a linear eddy model in different types of one-dimensional... 

One main problem in many numerical simulations is the lack of sufficient infrastructure data to precisely model and analyze the flow through complex geometries. Since experimental procedures are generally very expensive; and sometimes impossible, it becomes necessary to find alternative ways such as numerical approaches to predict the flow behavior through complex geometries. The heat exchangers can be categorized as geometries with complex configuration and apparently expensive to solve numerically. They are widely used in different industries including the aerospace. The restrictions in design and implementation of aviation’s heat exchangers have promoted the related companies to converge... 

In the present study, an incompressible smoothed particle hydrodynamics based on the artificial compressibility method is applied for simulating the incompressible turbulent flows. The Reynolds-averaged incompressible Navier–Stokes equations using the artificial compressibility method in the Eulerian reference frame are written in the Lagrangian reference frame to provide an appropriate incompressible SPH algorithm for the turbulent flow computations. Here, the k-L_m turbulence model, which is a simplified k-ϵ turbulence model, is used and formulated in the Lagrangian reference frame. The SPH formulation implemented here is based on an implicit dual-time stepping scheme to be capable 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 research special type of jets those calls Arc-Shape Jets are studied. The meaning of this research is an effort to introduce this types of jets as a new method to film-cooling approach. In the primary section, the fitness of this scheme on a flat plate is studied. After this section, according to the results, this method is implemented on a turbine blade surface. According to the results, this method of film-cooling has suitable effectiveness in lateral direction, this has a reason of radially injection of the coolant jet. The main feature of this concept is operating by mass flow rate of much lower than other schemes. So that in a regular injection of a 45 degrees of actuator arc,... 

In the present study, the numerical simulation of incompressible laminar and turbulent flows using a high-order finite difference lattice Boltzmann method is presented. To handle curved geometries with non uniform grids, the incompressible form of lattice Boltzmann equation is transformed into the generalized curvilinear coordinates and the spatial derivatives of the resulting equation are discretized using the fifth-order WENO scheme. The advantage of using the WENO-LBM developed is that it needs less number of grid points and remains stable even at high Reynolds number flows. For the temporal term, the fourth-order explicit Rung-Kutta scheme is adopted for laminar flow calculations and... 

Today energy sources, in any kind, have their special situation in human’s life and we must use our knowledge to manage them for effective usage by decreasing losses and finding modern renewable sources. One of the best way to achieve this purpose is increasing efficiency and improve energy generator performances under different environmental conditions. In spite of the fact that wind turbines stall dynamics behavior is under investigation for 6 years, study of dynamic stall phenomenon especially over series blades still needed. By addition to this phenomenon, improper wind turbine arrange decreases efficiency too. As a matter of fact, scrutiny of dynamics stall of wind turbines serial... 

In this study, a new finite-element-volume (FEV) arbitrary Lagrangian-Eulerian (ALE) method is suitably extended to simulate the three-phases flows air, liquid water droplets and ice in ice accretion, i.e., over flying object surfaces. This methods benefit from the advantages of both finite-volume and finite-element methods. This method is developed for the first time to simulate three phases turbulent flows. Since the ice formation and growth needs grid movement consistant with ice boundary movement, we have used ALE approach to fulfill this requirment. In this regard, we use the linear spring analogy approach to move the hybrid triangular-rectangular mesh suitably. Facing with a chaotic... 

The most common three-dimensional flows accuring in axial turbomachineries are endwall flows. These flows, which depend on inner hub and on external surface of airfoils are called secondary flows. In modern turbines, these flows reduce turbine efficiency up to about 3 percent.Many sientists are interested in investigation such flows. In this study, turbulent endwall flows are modeled using large eddy simulation approach. Also, SIMPLE algoritm and Smagorinsky subgrid scale model are used. Non-orthogonal curvilinear coordinate system and structural grid are implemented.To verify the results, they were compared with some existing experimental data which, showed that current numerical results... 

Nowadays, hybrid LES/RANS approach is being widely used by many researchers. This approach uses the advantages of both LES and RANS approaches simultaneously. Hybrid approach is as accurate as LES, but its cost is much lower. The biggest problem of hybrid approach is transformation of data between RANS and LES regions. Before, precursor simulation and synthetic methods, such as Fourier series and synthetic eddy methods (SEM) have been used extensively to solve such problems. Precursor simulation is expensive, because of high cost of generation of data. On the other hand, Fourier series method is confined to simple geometries, while SEM has problem of programming. Interface condition in this... 

Injection of jet into cross-flow has various applications, such as film cooling of gas turbine blades, reaction control jets for missiles and aircrafts, and mixing of air and fuel in combustion chambers. Velocity ratio (blowing ratio), momentum ratio, and streamwise jet inclination angle are important correlation parameters which have been studied extensively. However, not much work has been done on the jet swirling effects. The present work investigates computational simulation of a row of swirling square jets injected normally into a cross-flow. The swirl is introduced using two injectors discharged normally into the jet. Computational simulations were performed using LES approach with... 

This work deals with the computational investigation of film cooling technique, which is one the best practical way to protect gas turbine components form high thermal loads. In this regards, previous works are extensively reviewed and most important effective parameters are classified into three general categories, as geometrical parameters, flow characteristics, and physical surface factors. Each of these categories is then divided into subcategories and more details studies of each are performed. Then, a novel near-wall flow control technique of using staggered arrangement of small injection ports near a film cooling hole (combined-triple-jet; CTJ) is introduced. The fluid injected from... 

In this study, an arbitrary Lagrangian-Eulerian (ALE) approach is incorporated with a mixed finite- volume-element (FVE) method to establish a novel moving boundary algorithm to simulate unsteady incompressible flow on non-stationary meshes. The method collects the advantages of both finite-volume and finite-element methods as well as the ALE approach in a unified algorithm capable of solving laminar, transient, and turbulent flows in fluid flow problems with moving boundaries. To enhance the robustness of the extended algorithm, we treat the convection terms at the cell faces using a physical influence upwinding scheme, while the diffusion terms are treated using bilinear finite-element... 

Numerical simulations and large eddy simulations (LES) of turbulent flow downstream of diversion dam , pool-riffle bedform in different geometrical ratios (different lengths of riffle and pool) with flow Reynolds number of 3.0 E+04 to 3.3E+04, downstream of special case study "Mill and Moghan diversion dam" with Froude number of 0.5 are presented The calculations are performed using a computational fluid dynamics model, FLOW-3D, which solves the Navier-Stokes equations in three dimensions with finite volume method. Numerical simulations are validated by comparing the numerical results of time-averaged flow patterns downstream of pool-riffle sequence with that of the experimental...