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... 

The purpose of this study is to simulate a turbulent premixed flame with the help of the Laminar Flamelet Decomposition method. Numerical simulation is considered the main approach for studying this flame. A Bunsen-type premixed burner, which has a novel approach to making different levels of turbulence, has been used for modeling the premixed flame. To reduce the cost of numerical calculations, the Reynolds-averaged Navier-Stokes approach has been chosen for the CFD simulation. In this study, the Laminar Flamelet Decomposition model is the main combustion model for analyzing the turbulent premixed flame and with this method, the rate of reactions for all the reaction species will be... 

Industrial centrifuge fans operate in various industries, specifically heavy industries such as pelletizing plants, steel mills, and cement plants. These fans transfer process gas in the production cycle. In some cases, due to their off-design working conditions, asymmetrical wear and failure happen on one side of the impeller's blades more than the other side. The most important reason is the heterogeneity of the entrance fluid's properties. One of the many critical parameters in this issue is the asymmetric distribution of particles between the two entrances of the fan. This research investigates the asymmetric erosion problem of a specific centrifugal fan with a double-suction side... 

In most real combustion systems, flow is turbulent (e.g., diesel engines). Therefore, a reliable turbulence modeling approach is necessary to design and analyze a system with turbulent flow. Direct numerical simulation (DNS), Large eddy simulation (LES), and Reynolds-averaged Navier-Stokes (RANS) are the three most mature Computational fluid dynamics (CFD) methods for turbulent flow simulations. Because of LES’s good accuracy and acceptable computational cost. In this project, LES is chosen to simulate the turbulent flow field.Modeled turbulence subgrid scales' interaction with nonlinear flow parameters, needs modeling. In supercritical and transcritical conditions, Equation-of-state is a... 

The purpose of this study is to evaluate the performance of the optimized conditional source-term estimation approach. This model was first implemented in a computational fluid dynamics code, and then the Bernstein expansion was used to optimize it. For validation, two pre-mixed turbulent flames with different turbulence intensity and equivalence ratios were modeled with the optimized and RANS model. The results were obtained for mass fraction of the main and intermediate species, velocity and temperature examined in different sections. In the first flame, the turbulence intensity is low, and the flame is in the flamelet regimes; As a result, the results obtained with the optimized model are... 

Characterizing the dynamics dictating injection and mixing of the coaxial shear and swirl injectors is of central importance in the context of space rockets, diesel and direct injection reciprocating engines, and modern turbine gases. Sophisticated with precise thermo-physical models along with high-fidelity turbulence approaches, a computational platform –based on OpenFOAM open source code– is developed to simulate the practical injectors flow-fields under trans- and supercritical conditions. Aiming at providing a deep insight on the underlying physics, the investigations are conducted in a hierarchical manner; the flow complexities are added step-by-step to eventually construct the... 

The aim of this study was the performance analysis of the effect of guide vanes in a quasi-radial wall jet to improve the flow separation control on the wing composed of NACA4415. In order to achieve this goal, first, by examining two geometries of "quasi-radial wall jet" and "arced-shape wall jet", the effect of jet's internal flow on separation control improvement has been studied and arced-shape wall jet has been chosen as a suitable replacement for the uniform quasi-radial wall jet, which has changed the radial velocity distribution of the jet output from uniform to non-uniform. Also, increasing the radial component of the jet output velocity and improving the separation control have... 

Laminar-to-turbulent transition is very important concept in fluid dynamics due to its significant role on skin friction drag and heat transfer. It is more important in the fluid-based systems such as wind turbines. Employing computational fluid dynamics is still not efficient on prediction of flow transition, especially in complex problems such as oscillating airfoils. In one hand, flow transition models are not still suitable for general engineering flows such as oscillating airfoils. On other hand, due to the lack of experimental data, the existing flow solvers have not proven in the accurate simulation of the flow field simulation for complex problems such as oscillating airfoils. This... 

An a priori analysis is performed to assess the performances of Laminar Flamelet Decomposition (LFD) and Conditional Source-term Estimation (CSE) methods in predicting conditional and unconditional filtered production rates and mass fractions for turbulent premixed flames over a wide range of Karlovitz numbers, which is an indicator for the level of turbulence-chemistry interaction in premixed combustion.In LFD, it is assumed that a turbulent flame is composed of strained laminar flamelets. By presuming the functional form of the probability density function (PDF) of the progress variable and inverting the integral equation for the unconditional filtered mass fractions of one of the species,... 

The present thesis is devoted to deeply reconsider the anti-vortex film cooling method and its undiscovered features using numerical optimization and advanced turbulence models. In this regards, a modified turbulent heat-flux model was developed to enhance the predictions in complex flow fields with highly anisotropy and non-equilibrium flow/thermal features. Next, the model was introduced to ANSYS FLUENT 16.0 package to prepare a more accurate flow solver. Then, the solver was coupled with an in-house Differential-Evolution (DE) optimization algorithm to find the optimum configurations of anti-vortex holes for several flow and geometric conditions such as flat-plate, convex/concave surfaces... 

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... 

The Moderate or Intense Low-oxygen Dilution (MILD) combustion of liquid fuels has attracted attention to use its advantages in industrial burners and gas turbines applications. Here numerical investigation has been conducted on a research experimental MILD turbulent spray burner (Deft Spray in Hot Co-flow, DSHC). RANS approach has been adopted for modeling of the reactive turbulent flow field of continues phase with the Lagrangian approach for droplet modeling of pressure-swirl atomizer fuel spray. The EDC combustion model is used which has the ability to take into account the detailed chemical mechanisms. The accuracy of different turbulence and droplet injection sub-models are examined and... 

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... 

Turbulent combustion at supercritical condition have a considerable effect in modern high performance rocket propulsion systems, gas turbines and diesel engines. In such a reaction conditions, an abrupt changes occur in thermodynamics and transport properties of fluid. So numerically modeling of a real fluid behavior of the cryogenic propellants and the turbulent trans-critical mixing and combustion processes faces serious challenges.In this study, in order to realistically represent turbulence–chemistry interactions, detailed chemical kinetics and real-fluid thermodynamic behaviors related to the gaseous hydrogen and cryogenic liquid oxygen combustion under supercritical pressures, the... 

Reducing carbon emissions emanated from combustion of fossil fuels is a challenging problem and consumes huge amount of money that is put into research every year. Nitrogen oxides are among the most important pollutants which have been at the center of attention of industries and international environment protection organizations, especially due to their increased production by commercial aircrafts at higher altitudes of the atmosphere. Flameless is a combustion regime that has been independently discovered by different research teams while working on reducing nitrogen oxides from burning fossil fuels in the early 1990s, and afterwards has been studied for its exclusive characteristics in...