Sharif Digital Repository

The present research deals with the effect of steam injection to gas turbine engines. First, a comparison is made across the possible positions in the gas turbine for steam injection. Commercial software is used to investigate the pros and cons. Second, the investigation is focused on an industrial 4 MW gas turbine engine. Classical cycle and sensitivity analysis are performed and the operating envelope of the gas turbine engine with steam injection at various operating states as well as different environmental conditions is determined. Finally, a simulator based on Matlab Simulink is developed to examine the impact of different design and thermodynamic conditions of steam injection to the... 

Currently, the relatively long time of the turbine life passes and their parts and equipment damage are different, that loss optimum performance and thus reducing their efficiency and may lead to faults and other unexpected stops in their production cycle. Process used to estimate the remaining life of the various components of this turbine is an important tool for improving the efficiency of these units to perform preventive maintenance. In the present thesis, the types of damages in different parts of gas turbines and various methods for detection of critical points, particularly finite element method, high cycle fatigue, modal analysis, methods to estimate the lifetime of a gas turbine... 

Typical thermoacoustic systems deal with the conversion of heat energy to sound energy and vice versa. Recent advances in the field of thermoacoustics have altered the working mechanism of many conventional heating and cooling devices. These systems have three highlighted advantages: first, they have simple structure, no moving parts, low cost of manufacture, and high reliability; second, by using inert gases as working fluid, they are environmentally friendly; and finally, heat driven thermoacoustic devices can be driven by low quality energy sources such as waste heat and solar energy.
The main focus of the present thesis is on the application of the thermoacoustic technology in the... 

In this thesis, turbine disk thermo elastic and creep stresses has been extracted and the turbine disk cross-section is optimized. Gas turbine disks are used at high temperature and high rotational speed. Due to high temperatures gradients, the mechanical properties vary along the radius of the disk. Most of the stresses in the gas turbine are exerted by centrifugal force and thermal strains. At first, thermo elastic and creep equations for these disks are derived, assuming plane stress and axisymmetry. The resulting differential equations are nonlinear and can not be solved using analytical solutions. Two methods are used to solve the equations which finally are verified employing the... 

A new one-dimensional, time dependent aerothermodynamic mathematical model and computer simulation of the gas turbine engine has been developed and is introduced herein. This code simulates the transient and dynamic operation of the gas turbine engine bye solving conservation equations, expressed as one dimensional, time dependent Euler equations, with turbomachinery source terms. The various component models, which provide the turbomachinery source terms to Euler equations, are described. Bye incorporating both explicit and implicit equation solvers, transient simulation of the gas turbine engine can be conducted efficiently while maintaining the capability of simulating dynamic events.... 

Turbochargers are industrial devices that widely are used in aviation, marine and automotive industry. Manufacturing cost and technology of their components vary according to their application fields. One of the most important components of these devices is turbine wheel, which needs to be solid, strong and have a high resistance in critical extraordinary conditions. In these days, it can be seen that superalloys are used remarkably in manufacturing of turbine wheels. When this part of turbine is damaged due to some different reasons, turbine wheel must be quit of circle Process according to repair instructions. In these conditions either turbine must be repaired or replaced by a new one;... 

Axial compressor design is a very complex and expensive process. In general, for design and development of a new axial compressor, manufacturing companies usually intend to employ an existing and successful axial compressor as an starting point and modify and upgrade it. In this regard, dimensional scaling is a common method for derivative axial compressors. The goal of dimensional scaling is to get a different capacitywhile minimizing the development time and cost. In this thesis, theNASA eight stage transonic axial flow compressor is chosen as the base model for dimensional scaling to lower and upper size of its original dimension. The scaled compressor is analyzed with a quasi 2-D code.... 

This study develops an aerodynamic shape optimization code using parallel processing capability based on a gradient-based adjoint method. Calculation of the gradient of the objective function with respect to design variables is the most costly part of the gradient-based optimization algorithms. Applying adjoint methods, gradients can be calculated with solving some additional equations known as the "adjoint equations", instead of direct calculation. In this study, the blade shape optimization is performed by inverse design method and using steepest descent optimization algorithm. The objective function of inverse design problem is the desired blade surface pressure distribution. In each... 

Today, the material selection process plays an important role in all engineering design branches. Generally, in transition from concept design to detail design, designers and engineers need to find specific materials to optimize performance of the systems. There are introduced nearly 80000 engineering materials up to now, i.e. metallic alloys, composite materials, plastics, ceramics, glass and etc. These large amounts of materials and the wide range of manufacturing processes causes engineers always seek new material selection methods. In material selection it’s require to consider advantages, restrictions, necessities of method and this phenomenon appear because of design problem that... 

The objective of the current work is to investigate the application of tandem blade rotor for possible improvements of a transonic fan. A near term application of tandem blade rotor could be either in the last stages of a high pressure compressor or in the fan section. The present research is motivated by evaluating the tandem configuration for transonic fan of high bypass ratio turbofan engines. The main idea is to achieve higher overall blade loading and at the same time lowering the flow separation tendency by shifting the boundary layer growth to the rear rotor. A computational fluid dynamics code, solving the Navier-Stokes equations based on a flexible multiple-block grid discretization... 

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... 

An experimental investigation of unsteady boundary layer over a wind turbine blade conducted in a subsonic wind tunnel. The experiment performed at different positions along the airfoil chord. Model was oscillated with amplitude of ±5 cm. Reynolds number, based on airfoil chord, ranged 3˟105 upto 6.5˟105 and the reduced frequency ranged from 0.0055 to 0.0981. Velocity profile measured with a total pressure rake. The data were reduced via a low-pass filter. Increasing the reduced frequency, the velocity profile increases the level on turbulence fluctuation and becomes more attached to the surface.

 

Application of wind energy and specially wind turbines as a green source of energy is getting more popular and as a result, the knowledge of wind energy has been improved dramatically. The purpose of this research is to determine the flow characteristics in the boundary layer profile over an airfoil which is used in a wind turbine blade. The model is sinusoidally oscillated in pitch. For the present study, the critical cross section of the wind turbine blade has been selected and the boundary layer velocity profiles over its airfoil have been investigated experimentally. Dynamic motion is produced with sinusoidal oscillator and the reduced frequency is varied in the range of 0.054 to 0.1.... 

Flameless Combustion was experimentally studied. In this combustion mode, inlet air is preheated and products are recirculated inside the chamber. Therefore, the reaction zone is spread from a limited front to a wider area with that of a lower peak temperature and very lower Nitrogen Oxides (NOx) production. Controllable parameters are preheating temperature, equivalence ratio, and fuel and air mass flow rates. Applying similar conditions, the flameless combustion was compared to the diffusion flame. Measurable parameters are exhaust temperature and composition, including NOx. Reaction zone homogeneity is observed by photographing inside the combustion chamber through its visual access... 

An improvement of thermal efficiency of modern gas turbines is achieved by increasing turbine inlet temperatures. One of the methods of turbine cooling is to form a film layer on the external surfaces of the blades, so that they can work at high temperatures. Most of the studies concentrate on flat plate geometries with injection through slots or rows of holes. Turbine blade surfaces usually have curvatures which seem to alter the flow field significantly on the film-cooled surfaces. However, there are few reports which investigate the effect of curvature on three-dimensional jet flow injected into the turbulent boundary layer over a curved surface. The surface curvature and the blowing... 

Material selection is one of the most important works should be done prior to the designing of any part of the mechanical and/or nonmechanical structures. Various material selection methods, such as digital logic, modified digital logic, z-transformation and fuzzy logic, have been introduced and used in recent years. All these methods have some advantages and disadvantages in selection of appropriate materials. Since, all these methods exhibit some disadvantages, the main objective of thesis is to introduce the new method to reduce or eliminate the other method’s disadvantages with less complexity. The fuzzy logic method which is mostly used in this thesis will result in some problems due to... 

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... 

The rapid development and growth of the offshore turbine industry has led to the construction of offshore wind farms in earthquake-prone areas, and due to the shape of the structural system, which consists of a long cylindrical tube with a heavy mass on top of it, this structure is a sensitive structure. It has a dynamic behavior, and many environmental loads such as wind load, wave load, current load, and earthquake load in seismic areas are dynamic in nature. In this research, it investigates the seismic dynamic behavior of 5MW offshore wind turbine using the ISO-19901-2 standard and the Endurance Time method. In the modeling of this structure, Soil Structure interaction and Fluid... 

In this study, a framework for reliability analysis of offshore wind turbine structures has been presented. The rapid development of these structures in the world due to the increasing need for electrical energy and limited sources of fossil fuels has increased the importance of research on the behavior and condition of these structures. For Iran, despite its fossil fuels resources due to its international voluntary commitments to reduce greenhouse gases such as Paris agreement, the use of renewable energy such as offshore wind energy is important. Also, the offshore wind turbine structure is affected by different forces and environmental conditions in its life cycle, which are associated... 

The use of wind energy due to the clean and unlimited nature of this energy has received more attention and for this purpose, the types of wind turbines that mainly include; monopile turbines and jacket-based turbines; is used In this research project, it has been tried using criteria such as equal weight of structures with different bracing shapes and taking into account the normalized energy and redundancy factors of the platforms; An optimal structure that can achieve a better capacity curve with the same material cost, which includes ultimate stress and greater ductility, and along with all the above factors; The redundancy of the structure has also been considered to minimize the risk...