Search for: large-eddy-simulation--les
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    Three-Dimensional Large Eddy Simulation of Continuous Density Currents

    , M.Sc. Thesis Sharif University of Technology Najafpour, Nategheh (Author) ; Firoozabadi, Bahar (Supervisor) ; Afshin, Hossein (Co-Advisor)
    When a fluid moves inside another fluid while they have unequal density, a phenomena occurs which is called density (or gravity) current. Therefore density difference and gravity are key factors of density current generation. Due to application in engineering and geology, it is essential to investigate and analyze the above mentioned phenomena. Dam reservoirs, sandstorm in deserts, snow slide onset and falling, ash clouds produced during eruption of a volcano, and spreading of density current due to the collapsing of reservoirs are some examples of gravity current. There are lots of methods to simulate the turbulence of density current like DNS or RANS. But DNS has high computational cost... 

    CFD Modeling of Temperature Fluctuation in Mixing of Hot and Cold Streams in a Mixing Tee

    , M.Sc. Thesis Sharif University of Technology Mirabedin, Milad (Author) ; Farhadi, Fathollah (Supervisor)
    This thesis tries to suggest a simple solution to reduce the amplitude of occurred fluctuations in mixing tees. Temperature fluctuations can induce cyclical thermal stress and thermal fatigue. In order to estimate the lifetime of pipeline material and reduce the frequency and amplitude of these fluctuations, an accurate diagnosis of these fluctuations must be conducted. For this aim, a comparison between Reynolds Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) models was carried out to show the ability of LES model in prediction of temperature fluctuations. The effect of Peclet number on the amplitude was discussed. The effect of placing simple pipe segments and orifices to... 

    Numerical Simulation of Sedimentation Tanks Using the LES Model

    , M.Sc. Thesis Sharif University of Technology Sajjadian, Mohammad (Author) ; Afshin, Hossein (Supervisor) ; Firoozabadi, Bahar (Supervisor)
    In the present study, hydrodynamics and particle sedimentation of a rectangular basin is studied numerically. Results are also validated with experimental data. Two major goals are perused in this work: First comparing LES and RNG k-ϵ turbulence models and second, investigating the accuracy of simulation of particle sedimentation by solving the concentration formula.
    In order to achieve these goals, a 2D sedimentation tank is simulated using the RNG k-ϵ model. Velocity and concentration profiles are also plotted. Comparing the results with experimental data reveals that simulating sedimentation by the mentioned method has acceptable accuracy and can be used to predict sedimentation. In... 

    Low Swirl Flame Dynamic under Vortical Flow Disturbances

    , Ph.D. Dissertation Sharif University of Technology Shahsavari, Mohammad (Author) ; Farshchi, Mohammad (Supervisor)
    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... 

    Flamelet Modeling in Large-eddy Simulation of Turbulent Premixed

    , M.Sc. Thesis Sharif University of Technology Atayizadeh, Hassan (Author) ; Farshchi, Mohammad (Supervisor) ; Salehi, Mohammad Mahdi (Co-Supervisor)
    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... 

    Large Eddy Simulation of a Low Swirl Turbulent Jet Flow using a Simple Combustion Model

    , M.Sc. Thesis Sharif University of Technology Arabnejad, Mohammad Hossein (Author) ; Farshchi, Mohammad (Supervisor)
    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... 

    Large Eddy Simulation of Continuous Density Current Impinging on Obstacles

    , M.Sc. Thesis Sharif University of Technology Abbaszadeh, Shahabaddin (Author) ; Firoozabadi , Bahar (Supervisor) ; Afshin, Hossein (Supervisor)
    Density currents as a particular form of stratified fluid motion in nature have attracted the interest of many researchers in the past decades. These flows are formed whenever a fluid with specific density begins to move through another fluid with different density called ambient fluid. Prediction of propagation of turbulent density currents, especially because of their remarkable influence on the environment, is one of the researcher’s interests in geophysics and engineering. Density currents have a lot of applications in industry and nature. Sand storm in deserts, turbidity currents in oceans and avalanches are natural examples and leakage of dense gas into the atmosphere due to reservoir... 

    Evaluation of a fourth-order finite-volume compact scheme for les with explicit filtering

    , Article Numerical Heat Transfer, Part B: Fundamentals ; Volume 48, Issue 2 , 2005 , Pages 147-163 ; 10407790 (ISSN) Elhami Amiri, A ; Kazemzadeh Hannani, S. K ; Mashayek, F ; Sharif University of Technology
    The accuracy of the large-eddy simulation (LES) of turbulent flows can be increased by using high-order numerical schemes in space and time, due to a decrease in numerical errors. This work investigates a high-order compact finite-volume scheme suitable for LES. The explicit fourth-order Runge-Kutta (RK) scheme for time marching and fourth-order compact schemes for spatial derivatives using a cell-averaged approach are implemented. Different subgrid-scale models and the effect of explicit filtering in a fully turbulent channel flow are studied. In this flow, the fourth-order compact finite-volume method in space, and fourth-order RK in time in conjunction with the dynamic Smagorinsky model... 

    Large Eddy Simulation of Excited Jet Flow

    , Ph.D. Dissertation Sharif University of Technology Ghadimi, Masoud (Author) ; Farshchi, Mohammad (Supervisor)
    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... 

    Computational Simulation of Flow over a Cylinder in Ground Effect, Using PANS

    , M.Sc. Thesis Sharif University of Technology Nirooei, Mohammad Hossein (Author) ; Taeibi-Rahni, Mohammad (Supervisor)
    Partially Averaged Navier-Stokes (PANS) turbulence approach provides a closure model for any degree of velocity field filtering, ranging from completely resolved direct numerical simulation (DNS) to completely Reynolds averaged Navier-Stokes (RANS) approach. Preliminary investigations of PANS show promising results, but there is still computational and physical issues that must be addressed. This study investigates the performance of the PANS method for turbulent flow around a cylinder in ground effect with Reynolds number of 13,200. The cylinder flow is a benchmark flow problem which has significant experimental results available for validation of PANS approach. Three different filters... 

    Investigation Methods of Simulation of Turbulent Flow over High-rise Building by Use of Large-eddy Simulation and Turbulent Modeling with OpenFOAM Software

    , M.Sc. Thesis Sharif University of Technology Moayedi, Hesam (Author) ; Kazemzadeh Hannani, Siamak (Supervisor) ; Nouri Borujerdi, Ali (Co-Advisor)
    In this study, the numerical simulation of turbulent flow using Open Source software OpenFOAM, The impact of air flow around the high-rise buildings and classification based on the height and arrangement of the buildings has been against the flow. Numerical method used, the finite volume method uses a piso algorithm, Navier-Stokes equations are solved and the speed and pressure can be obtained. Large Eddy Simulation model is a simulation model used in this software. In general tall buildings against wind loads has three types of move, move along the wind, prependicular along the wind and the twisting motion that occurs at the same time, they are, but, due to the variable nature and... 

    Computational Simulation of Turbulent Endwall Effects in Gas Turbines, Using LES Approach

    , M.Sc. Thesis Sharif University of Technology Ebrahimi, Hossein (Author) ; Tayyebi Rahni, Mohammad (Supervisor) ; Ramezanizadeh, Mahdi (Supervisor)
    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... 

    Numerical Investigation of Bidirectional Swirl Flow’s Structure in Vortex Engine

    , M.Sc. Thesis Sharif University of Technology Mehrdad, Mohammad (Author) ; Saidi, Mohammad Hasan (Supervisor)
    Numerical investigation of flow field and determination of velocity components in swirl flow are novel and important subjects in combustion chamber of swirl flow. The exact understanding of vortex phenomena and flow structures in vortex engine results in better design and control in terms of stability, geometry, cooling, and combustion efficiency. Although, numerical approaches are computationally complex, they are worthwhile and efficient. The aim of this work is to study the velocity field in a bidirectional swirl flow within the combustion chamber using numerical approaches. The investigation of flow field has been performed in the cold chamber. Four different models (RSM and LES) have... 

    Vortex Shedding Control behind Helicopter Rotor Blades, using Thin Oscillating Plates- Application to Helicopter Noise Reduction

    , M.Sc. Thesis Sharif University of Technology Mohseni, Mohammad Hassan (Author) ; Javadi, Khodayar (Supervisor)
    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... 

    Numerical Simulation of Particle Settling in Sedimentation Basins using the LES Model

    , M.Sc. Thesis Sharif University of Technology Sattari, Reza (Author) ; Firouzabadi, Bahar (Supervisor) ; Kazemzadeh Hannani, Siyamak (Supervisor)
    Sedimentation basins are one of the most important and costly processes of water treatment, in which the process of particle settling takes place using gravity. There are two types of sedimentation basins namely, primary and secondary basins. In the primary basins, due to the low concentration of particles, in simulation, it is possible to ignore the effect of particles on the equation of motion. But in the secondary type because of buoyancy forces (which is dependent on particle concentration), the particles affect the flow field. So far, various studies have been done on the simulation of sedimentation basins with numerical methods, but a comprehensive research on the simulation of... 

    Numerical Investigation of Turbulent Flow Inside De-Oiling Hydrocyclones Using Large Eddy Simulation Approach

    , M.Sc. Thesis Sharif University of Technology Saeedi, Maysam (Author) ; Farhanieh, Bijan (Supervisor)
    Hydrocyclones are used for separating different materials from liquids in a variety of applications. Compactness, efficiency, reliability and low maintenance costs are their noteworthy characteristics. Dewatering and deoiling hydrocyclones used for refining crude oil or oily waste water in offshore platforms are examples of liquid-liquid hydrocyclones. Separation process in hydrocyclones is based on the fact that swirl flow induces a centrifugal force and leads to separation due to density difference. The density difference in liquid-liquid mixtures is smaller than solid-liquid types and trying to separate one liquid from another takes much more effort than the other type. Increase of... 

    Numerical Simulation of Incompressible Film Cooling, Using Compound Triple Jets and Large Eddy Simulation Approach

    , M.Sc. Thesis Sharif University of Technology Farhadi Azar, Roozbeh (Author) ; Taeibi-Rahni, Mohammad (Supervisor) ; Ramezanizadeh, Mahdi (Co-Advisor)
    The interactions between jets and cross flows appear in many engineering applications (such as film cooling) and thus their study is of great importance. In film cooling, the coolant fluid is transferred from the compressor to the surface of the turbine blades via small holes. An increase of about 170⁰C of the engine working temperature increases the engine efficiency about 5%. To reach higher temperatures of the inlet air flow, one tries to have the least amount of interactions between the film cooling jets and the the cross flow. In this work, we computationally studied turbulent film cooling of a flat plate, in which we used the combined triple jet and investigated the effects of density... 

    Computational Simulation of a Pre-swirl Incompressible Turbulent Jet-into-Cross-Flow Problem, Using LES Approach

    , M.Sc. Thesis Sharif University of Technology Banyassady, Rayhaneh (Author) ; Taeibi Rahni, Mohammad (Supervisor) ; Ramezanizadeh, Mahdi (Co-Advisor)
    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... 

    Drag Reduction by Blowing and Creating a Film of a Secondary Lower Viscosity Fluid-Large Eddy Simulation

    , M.Sc. Thesis Sharif University of Technology Ghaffarian, Ali (Author) ; Taeibi Rahni, Mohammad (Supervisor) ; Ramezanizadeh, Mahdi (Supervisor)
    Drag reduction is one of the most important topics in aerodynamics. Several techniques have been represented to reduce this force, such as surface roughness reduction, blowing, suction, cooling the fluid, etc. Blowing and creating a film of a secondary lower viscosity fluid is the technique used here. In our computations, we used large eddy simulation approach considering viscosity ratio variations effects. Investigations were performed for multiple squared cross sectional jets inclined normally into a turbulent cross flow. Each jet generates a pair of counter rotating vortex pair (CRVP) at its downstream while entering the cross flow. Two horseshoe vortices and a couple of wake vortices... 

    Large Eddy Simulation and Design of the Three phase Immiscible Oil/Water/Solid Particles flow Separation System based on Vortices Generation

    , M.Sc. Thesis Sharif University of Technology Akrami, Ehsan (Author) ; Roshandel, Ramin (Supervisor) ; Ashjari, Mohammad Ali (Supervisor)
    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...