Sharif Digital Repository

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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 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... 

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... 

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... 

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... 

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... 

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 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... 

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... 

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... 

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...