Sharif Digital Repository

In the process of extraction and refining of crude oil, a considerable amount of waste water are produced and if they are not removed, they would become one of the most hazardous environmental factors. Furthermore, purification and separation of such wastewaters are extremely costly, which with an increase in separation efficiency can lead to a decrease in valuable product loss. On the other hand, in the extraction process from oil reservoirs, because of porous and permeable nature of them, solid particles may be added to the extracted crude oil, which can result in an obstruction in pipelines and transport equipment.The most conventional method for separating a mixture of water, oil, and... 

The main purpose of the current study is to control the boundary layer of the flow passing over the wing and the lift force enhancement. In this research has been tried to introduce a new generation of passive flow control and use bumpy surface structures to control the separated flow and increase the aerodynamic efficiency. Therefore, the wing with the hawk bird’s airfoil section has been designated. Then, assuming a viscous, incompressible flow and a low Reynolds number range (about 2 × 105), the flow formation and boundary layer development on this wing has been investigated. Subsequently, bump structures have been settled on the upper surface of this wing. The numerical simulations have... 

This research investigates the use of baffles in sector jets for film cooling of turbine blades. The goal of this study is to compare the cooling performance in three conditions: sector jet without baffles (one 90-degree arc), with one baffle (two 45-degree arcs), and with two baffles (three 30-degree arcs). The effect of using this type of cooling is also compared to the crossflow jet, which is the simplest type of cooling jet. In all conditions, the mass flow ratio is constant and equal to 1. The problem is solved for a turbine blade with the “AGTB-B1” airfoil. The problem is first solved with the Transition SST turbulence model, and the results are used as the initial conditions for the... 

Boundary layer control has long been and still is considered to reduce drag. In this research, the effect of quasi-spherical structures on the control of boundary layer is investigated. First, flow over a NACA0015 airfoil was investigated. Then, flow over the same airfoil with quasi-spherical bumps on its upper surface was numerically simulated and the result of these two situations were compared. The dimensions and numbers of the bumps in longitudinal and lateral directions (different case studies) were chosen using trial and error. The three-dimensional, incompressible, and turbulent flow governing equations were numerically solved, using FVM and the OpenFOAM software. To get preliminary... 

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 limitations of metals in tolerating thermal stresses is one of the main obstacles in increasing temperature of combustion products. In addition, strong desires to use higher temperatures than are allowed for metals, have led to use of different cooling methods for protecting surfaces adjacent to hot gases. Previous valid studies show that more than 25% of research in the field of gas turbine is related to their blades cooling. On the other hand, one of the very important methods of cooling such surfaces is film cooling. The results of this and previous researches conducted by the team of this thesis’ supervisors can for instance help designers to predict more suitable positions for... 

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... 

Increasing the kinetic energy of the near-wall fluid by exciting shear layers is known as an effective method for flow separation control. So far, choosing the proper approach to apply excitations has been a challenging issue in the field of flow control. This work investigates flow control of airfoils in static stall and flutter conditions, employing shear layer excitation technique and plasma actuators. This research introduces a novel flow separation control, namely dual-point excitation of shear layers and compares its performance with the conventional single-point excitation method. Two airfoils (NACA 4415 and NACA 0015) have been considered as the baseline test-cases. In the first part... 

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... 

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... 

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... 

The purpose of this study is to investigate the efficiency of a flamelet method along with the LES1 approach in the modeling of a turbulent premixed flame behind the bluff-body. In this flame ,because of the high turbulence intensity and fuel dilution, there is a significant interaction between the turbulence and chemical kinetics. In this study, first, the cold flow is modeled using LES and RANS2 approaches. Then, using the Flame-Generated Manifold (FGM) model and a presumed PDF model, the turbulent reacting flow is simulated.Comparison of the results of the LES and RANS showed that the accuracy of the LES method in simulating the physics of turbulent flow is much higher than RANS, but its... 

In the present work, large eddy simulation approach was employed to investigate flows such as backward facing step and internal channel flow, using Smagorinsky and explicit algebraic subgrid-scale models (EASSM) in OpenFOAM software. For this purpose, an explicit algebraic subgrid-scale model was added to OpenFOAM. Coupling pressure and velocity fields were applied to the PISO-SIMPLE (PIMPLE) algorithm. The focus of the present study was to assess various subgrid scale models, in order to predict the behavior of several flows, as well as their extensive numerical study. The results were compared to available experimental data showning that the EASSM results were more accurate than... 

Lean premixed combustion is highly susceptible to thermoacoustic instabilities. Such instabilities are compounded in low swirl flames by the fact that low swirl flames are stabilized aerodynamically at a relatively considerable distance downstream of the burner rim, such stabilization mechanism makes the flame more prone to both vertical and acoustic perturbations. The main objective of the present thesis is to evaluate effects of acoustic and hydrodynamic perturbations on low swirl flame features. To such aim, first, low swirl flame characteristics and stabilization mechanism are studied using large eddy simulations along with thickened flame combustion model. The obtained results show that... 

The interaction of the vortices and helicopter’s blades is the most significant source of generating the main rotor’s noise, especially in landing and rising. The kind of this noise is broadband and it is produced because of establishing the vortices behind the forward blade, their interaction with backward blade, changing their structures and creating turbulency loading. The known method for modeling of the interaction of the vortices structures and solid surfaces is the simple compounding the rod and airfoil. In this project, by using this method, the noise of the interaction of vortex and blade is modeled in the Reynolds number of 48000 with LES and FW-H Analogy as a hibrid method in... 

Excited jet flow has many physical and industrial applications, e.g. in aeroacoustics and the combustion instability. Analysis of this type of flow needs an accurate simulation of flow dynamics. This work presents the large eddy simulation of this type of flow. The numerical method used in the large eddy simulation must have low numerical dissipation and high order of accuracy. Compact methods which satisfy these requirements and have high resolution of frequency, are favorable ones for the large eddy simulation. A fourth-order compact finite volume method which had been developed in the MSc thesis of the author is extended and completed in the present work. This extension includes the... 

Wall systems are an essential part of the buildings and their capacity should be properly considered in their design. However, the seismic behavior of building systems with in-filled walls and their interaction is a very complex issue, yet to be understood. Using the in-filled walls in the buildings without including them in the design process changes the whole behavior of the structural system as well as their failure mechanism under earthquake excitations. On the other hand, there have been extensive researches on rehabilitation of the structures with in-filled walls or designing them as the main or one of the lateral load carrying systems against seismic input. In this research, first the... 

In this thesis, isothermal and reactive low swirl flow are investigated using the large eddy simulation (LES) method. In contrast to high swirl burner, in low swirl burner stability mechanism is not related to central recirculation zone and a detached flame stabilizes in a place where the flow velocity and flame speed are matched. Although lots of efforts have been devoted to simulate swirl flow, much of the previous simulations investigated high swirl flow in different configurations. The current research is conducted for co-annular swirl flow, isothermal low swirl flow and reactive low swirl flow. Simulation of co-annular swirl flow is performed to investigate the performance of...