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Repowering means addition of gas turbine unit(s) to a steam power plant in order to make use of the exhaust gas heat and to increase efficiency of the new combined cycle. There are two groups of repowering methods: partial repowering and full repowering. Full repowering is more common and is used in power plants with nearly ended useful lifetime. In this case the capital investment is considerably reduced compared with the case of making a similar combined cycle. Objective functions are per kWh electricity cost and exergy efficiency. These functions are based on important independent variables of heat recovery boiler, steam turbines, gas turbine. Finally, considering the introduced objective functions, it is tried to achieve the most optimized techno-economic characteristics for Be'sat power plant repowering cycle, using genetic algorithm optimization method with two scenarios of single and multiobjective.

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Thermal power plants consume near to 50 billion cubic meters of natural gas each year. So, optimization of power plants in terms of fuel consumption has become an important issue because of economic values and environmental effects. More than 50 percent of electricity is produced by CCGT and SCGT. In addition, CCGT efficiency is much higher than that of SCGT. So, in this paper these technologies are compared. The outcomes show benefits over costs ratio is affected by fuel price and utilization time. In subsidy prices (before energy price reform), B/C ratio of this substitution is less than one. If fuel price increases more than 500 Rials per cubic meter, using CCGT is more economical than SCGT for mid load power plants. If fuel prices are more than 1300 Rials per cubic meter, B/C ratio will be greater than one in any utilization time.  But this ratio is not greater than one for all cases. If all SCCTs are substituted with CCGTs, yearly natural gas consumption will reduce near to 3.5 billion cubic meters. These are 7% and 2.5% of yearly fuel consumption in power plants and total yearly natural gas consumption respectively. 

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This paper has proposed‎ ‎a gain-scheduled controller‎ with stability proof and guaranteed cost for a turboshaft driving a variable pitch propeller‎‎. ‎In order to overcome the complexity of the nonlinear model‎, a linear parameter varying (LPV) model is proposed for the first time which is in affine form.‎ Proposed model is established based on a family of local linear models and is suitable for LPV gain scheduling methods‎. Thus a gain scheduled design procedure is proposed which considers parameter dependent Lyapunov matrices to ensure stability and a quadratic cost function for guaranteed performance of the closed loop system‎‎. Proposed procedure also has the advantage of considering an upper bound for change rate of the scheduling signal which decreases conservativeness. ‎Controller design problem and calculating its gain matrices is formulated in a set of Linear Matrix Inequalities‎ which easily can be solved using LMILAB toolbox. Simulation results showed the effectiveness and practicality of the proposed procedure.    

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The performance of turbine section of a gas turbine deteriorates over operation because of working in high temperature conditions and characteristics of the entry gas. On the other hand, due to complexity of the flow field within the turbine, three-dimensional analysis is required. This paper presents a numerical study of roughness effects on turbine flow field and performance. In this paper, effects of blade surface roughness caused by operation conditions on turbine performance were numerically calculated. Numerical calculations were carried out for the fourth stage of an axial turbine which was experimentally tested in the technical university of Hannover, using ANSYS software. Calculated results were verified with the measured data and showed a good agreement. To find out the effects of blade surface roughness on turbine stage performance and flow field, Two equivalent sand-grain roughness heights of 106㎛ (transitionally rough regime) and 400㎛ (fully rough regime) in four different mass flow rates were considered. Results showed that summation of efficiency reductions of the rough stator and rough rotor approximately equals to that of the totally rough stage for each roughness height and effect of stator roughness on efficiency reduction is same as the effect of rotor roughness on stage efficiency.

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Single shaft gas turbine and the cycles based on it are sensitive to frequency drops and sudden change loads or large frequency dips might affect their stability. This phenomenon is related to reduction of air mass flow rate through the gas turbine during frequency dips, which might lead to interaction between the governor and temperature control loop. This interaction will prevent the gas turbine from being loaded further and might affect its stability. In this paper, the performance of the two well-known power generation cycles based on the gas turbine -combined cycle and steam injected gas turbine (STIG cycle)- are investigated during frequency dips and transient maneuvers. For this purpose, two similar units are developed based on these cycles and their performance are studied and compared in different scenarios. The simulation results show that the steam injected gas turbine has a better performance during frequency drops and it can handle larger step change loads. This superior performance of the steam injected gas turbine unit is almost twice as good as the similar combined cycle unit in some of the operating conditions.

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With respect to special conditions apply to the gas turbine, its blades are affected by many different factors such as, hot corrosion, oxidation, wear, impact of external particles, and etc. and are destroyed. Due to the reduction of their working life time, the turbine efficiency reduces and ultimately the heavy costs of periodic repairs are needed, and also new replacements of their blades are unavoidable. The aim of this study is investigation of the effects of corrosion and blade damage on flow field and gas turbine performance, by numerical simulation. In this research, a two stage turbine is modeled in the form of three dimensional and the results are validated with experimental data. To analyze of the behavior of entire flow, conservation of mass, momentum, and energy equations are solved. The numerical simulation of the turbine is done with ANSYS CFX software. Then the increased rotors tip clearance effects with decreasing thickness due to corrosion in both nozzles and blade leading edge and trailing edge were separately studied on turbine flow field and its performance in five actual different pressure ratios. The results showed that the most important factor in reducing the efficiency of gas turbine is due to rotor tip clearance increasing. Also corrosion of the blade edge respect to the trailing edge damage is a little more affected on reducing efficiency and increasing loss coefficients.

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Solid oxide fuel cells competence in combination with gas turbine cycle has caused the obtained synthetic system to become as a new power production system in consideration of different researchers. One of the important applications of this type of hybrid systems is to use them in UAV propulsion systems and in airliners as an APU. The main purpose of this research is design of a hybrid APU equipped to solid oxide fuel cell that would be one of the basic requirements for electric power generation in larger aircrafts in the future. Design parameters and decision-making variables in analysis of this system are the compressor pressure ratio, gas temperatures entrance to turbine and the number of selected cells. The results show that the system’s increasing pressure causes decrease in the temperature of outlet gases from the turbine and the cell’s operating temperature; and this problem severely affects the productivity and efficiency of the electrical system. At 1000 ° C for entrance gases to the turbine, electrical efficiency of system is about 49 percent. Also, the maximum electrical efficiency of the system in fuel cell is estimated to be about 55 percent. The obtained result shows that in case of controlling the generated heat in the cell and effective usage of it, the overall system efficiency will be augmentable about 84 percent. On the other hand, increasing the number of cells will cause increasing electrical efficiency and reducing the overall efficiency of the fuel cell hybrid system.

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This paper presents a new scheme based on state estimation to diagnosis an actuator or plant fault in a class of nonlinear systems that represent the nonlinear dynamic model of gas turbine engine. An optimal nonlinear observer is designed for the nonlinear system. By utilizing Lyapunov's direct method, the observer is proved to be optimal with respect to a performance function, including the magnitude of the observer gain and the convergence time. The observer gain is obtained by using approximation of Hamilton -Jacobi -Bellman (HJB) equation. The approximation is determined via an online trained neural network (NN). Using the proposed observer, the system states and the fault signal can be estimated and diagnosed, respectively. The proposed approach is implemented for state estimation and fault detection of a gas turbine model subject to compressor mass flow fault. The simulation results illustrate that the proposed fault detection scheme is a promising tool for the gas turbine diagnostics.

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The purpose of this paper is to find the optimum design of a typical gas turbine exhaust diffuser. In order to access the maximum overall static pressure recovery at the condition of swirling flow, an evolutionary algorithm is used. The optimization process is studied in three independent cases. Firstly, the optimization is done for a single profile of strut cover from hub to shroud. Secondly, two profiles are selected for the strut covers, one in the hub section and the other in the shroud section. Finally, the optimization process is done for the strut cover and diffuser channel geometries simultaneously. In order to produce the strut cover profiles the PARSEC parameterization method is used. The turbulent 3D flow is solved using computational fluid dynamic (CFD). The optimization process starts with the initial sampling of solution domain and subsequently the genetic algorithm (GA) is used to find the global optimum. The swirling flow at the turbine exit with the Reynolds number of 1.7 ×105 based on the hydraulic diameter of the diffuser inlet is optimized. All steps of GA and corresponding processes of model creation, mesh generation by TurboGrid, flow simulation by ANSYS CFX and goal function calculation for all members of each generation are coded in the MATLAB platform. As a result of the optimization, the pressure recovery coefficients increased 1.94%, 3.1% and 7.42% in the first, second and third cases of the optimization process respectively.

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Roughness of vanes’ outer surface and that of cooling channels’ inner surface have considerable impact on temperature distribution. Using a rougher surface leads to increased turbulence in near-surface flows and increases the rate of heat transfer. In this study, vane of a C3X turbine cooled via 10 cooling channels was simulated -three-dimensionally- by ANSYS-CFX software based on SST turbulence model, and then the effects of roughness of said surfaces were examined. The results showed that increasing the roughness of the blade’s outer surface, which absorbs the heat of the hot fluid, to values below the threshold of fully rough regime ( Reks < 70 ) makes no significant impact on vane’s surface temperature distribution; but increasing the roughness to values higher than this threshold leads to 8% increase in surface temperature. This indicates that outer surface of the blade should always exhibit a transitionally rough regime. Opposite to the outer surface, increasing the roughness of cooling channels’ inner surface, which transfers the heat to the cooling fluid, found to be the very beneficial, as even a slight increase in the roughness of this surface (within the domain of transitionally rough) decreases the blade’s surface temperature by up to 8%, and improves the hydraulic-thermal performance factor by about 250%.

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The design of combustor has long been the most challenging portion in the design process of a gas turbine. This paper focused on the conceptual design methodology for aircraft combustors. The necessity of this work arose from an urgent need for a comprehensive model that can quickly provide data in the initial phases (conceptual design and preliminary design) of the design process. The proposed methodology integrated the performance and the design of combustors. To accomplish this, a computer code has been developed based on the design procedures. The design model could provide the combustor geometry and the combustor performance. Based on the available inputs data in the initial phases of the design process, a chemical reactor network (CRN) approach is selected to model the combustion with a detailed chemistry. In this way, three different chemical mechanisms are studied for Jet-A aviation fuel. Furthermore, the droplet evaporation for liquid fuel and the non-uniformity in the fuel-air mixture are modelled. The results of a developed design tool are compared with data of an annular engine’s combustor. The results have good agreement with the actual geometry and outputs of engine test rig emissions.

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The present study was undertaken to design and analyze three different configurations of SOFC (solid oxide fuel cell) and MGT (micro-gas turbine) hybrid system. The first presented configuration is a hybrid system with one fuel cell which considered as a basic mode. Two other configurations are considered with two fuel cells that mounted upstream of the turbine in series and parallel forms. The aim of the current study was thermodynamic analyze of designed hybrid systems and achieving the optimum fuel consumption factor for fuel cells that used in hybrid systems. Therefore, other performance parameters such as turbine inlet temperature, compressor pressure ratio and the number of cells, which play an important role in implementation of SOFC and gas-turbine, were parametrically analyzed and the obtained optimum values were used in analyzes. In this regard, the parameters associated with electrochemical processes within cells considered as a function of their chemical and thermodynamic conditions, and their modeling code combined with the modeling code of micro gas turbine cycle. The results of this study revealed that fuel utilization factor has direct impact on the SOFC/MGT hybrid system performance. Also we demonstrate that the optimal fuel utilization factor for basic mode hybrid system was 0.85, hybrid system with 2 series fuel cells were obtained 0.7 and 0.8 respectively and hybrid system with two parallel fuel cells were calculated to be 0.85. Moreover, the SOFC/MGT hybrid system with two series fuel cells account for the highest electrical efficiency and was selected as the most efficient configuration.

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In today’s world, using of biogas is increasing due to its methane content, renewability, and low price. Solid oxide fuel cell is one of the best energy conversion technologies, in order to use biogas and it has a high potential to integrate with the gas turbine. In this paper, solid oxide fuel cell-gas turbine hybrid system, which is fed by biogas is modeled with respect to energy and economic aspects. Maximization of electrical energy efficiency and minimization of total investment cost are objective functions, which are considered to find the optimal design variables of the hybrid system. First, each component of the hybrid system is modeled and validated individually. Then, in order to optimize the hybrid system, multi objective optimization via NSGAII is implemented and optimal values of design parameters of the hybrid system were calculated. Optimal point is obtained using Euclidian non-dimensionalization and LINMAP decision making method in Pareto front. So, optimal design values are 66 percent and 175227.4 $, which are electrical energy efficiency and total investment cost, respectively. In optimal point Levelized unit cost is 6.3 cent per kWh. Finally, in order to determine the effect of design parameters on the objective functions, sensitivity of each design parameters were analyzed using Sobol's sensitivity analysis method. Results show that compressor pressure ratio has the maximum effect on electrical energy efficiency. Furthermore, turbine isentropic efficiency and fuel cell current have the maximum effect on the total investment cost.

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Gas turbine power and thermal efficiency increase with inlet temperature. Considering the temperature limitations for the alloys used in gas turbine components, employment of techniques for reduction of these components temperatures seems to be an essential subject. Based on the research conducted on this subject, among all the proposed methods, rib cooling yields higher heat transfer coefficient and among various types of ribs, V-shaped ribs have higher heat transfer compared to angled rib. The purpose of this feasibility study is to investigate the two proposed ribs for use in gas turbine from heat transfer and fluid flow view and compare their thermal performance. In this work, 3-D numerical simulation has been performed for V-shaped ribs with an angle of 〖60〗^° for the two cases of staggered and inline ribs in two opposite walls in a rectangular channel. Experimental results have been used for validation. The results indicate an enhancement of ~22% in heat transfer if V-shaped ribs with an angle 〖60〗^° and downstream orientation are located in staggering form in two opposite walls of a channel. In this case, an increase of 10% is observed for pressure drop, however, its thermal performance increases 12% which is positive and considerable.

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Gas turbines are among the most important power generation equipment in industries. One of the methods to enhance the performance of this equipment is the aerodynamic performance optimization of its stator and rotor blades. This paper presents an automatic aerothermodynamic optimization platform for the optimization of 3D stator blade geometry in axial-flow gas turbines using open-source software. This platform can be used for 3D aerothermodynamics optimization of 3D blades and includes parametric 3D modeling, mesh generation, CFD simulation, and implementation of optimization algorithm. 3D models are formed from 2D sections defined by Bézier curves and connected by spline stacking curve. Simulation of flow field includes the solution of compressible viscous flow on structured multi-block grid using parallel processing. Genetic algorithm is used as optimization algorithm. 45 optimization variables govern blade thickness variation in five sections and blade lean, sweep, and twist. Total pressure is selected as objective function and the result of optimization shows 5% decrease of total pressure loss coefficient in the blade. The use of open-source software in the optimization platform provides maximum customization capability to the user. The application of this platform for stator blade optimization shows that the platform can be used for aerothermodynamic optimization of turbomachines effectively.

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In recent years, the importance and requirements for high-quality energy and water has been increased significantly, and this trend will strongly continue. One of the promising solution for the water scarcity's problem is desalination of the oceans salt water by thermal methods, and if the required thermal energy is provided by wastes of a thermal power plant it will be competitive with other methods. In this paper, a combined cycle including solid oxide fuel cell (SOFC) and gas turbine is used as thermal resource. Here, combination of these two systems beside of multi effect desalination (MED) system leads to reduce in energy consumption, pollutant emissions, investment and operation and maintenance cost, as well as increase of efficiency in comparison with the conventional individual systems. Exergetic and economic analysis using a computer program in EES software was performed. The results proposed a system with thermal and exergy efficiency of 60 % and 57%, respectively. The system expenditures and revenues were estimated, and the effect of two important design parameters, i.e. operational temperature and current density of fuel cell, on exergy efficiency and levelized cost of electricity were investigated. Consequently, the reliability and availability of the proposed system are calculated as 0.842, using the Markov method. It is seen after reliability analysis and availability calculation the exergy and energy efficiency is reduced and LCOE increased by 8.8%.

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In this paper, the performance of a new design cogeneration cycle with various working fluids is investigated. Exergoeconomic and exergoenvironmental approach are developed to study the thermodynamic performance of the cycle and to assess the total cost of products. The naval design is based on organic Rankine cycle by using the gas turbine prime mover for fulfilling of the main goals of gas comperessor station of Nar-Kangan zone (South of Iran). These goals as follows: production of electricity and refrigeration power (cooling requirement) and total cost of products. According to recent parametric studies, boiler, turbine and condensation temperature and turbine inlet pressure significantly affect the three goals. The results show that dichlorotrifluoroethane (R-123) and toluene have a better performance in producing electricity (1.612MW) and refrigeration power (6.282MW) among other working fluids, while, the carbon dioxide has a better operation to reduce of products cost (103.5$/MJ). So, when the condensation temperature increases the refrigeration power decreases and boiler inlet temperature increases, the refrigeration power decreases. The results reveal that the refrigeration power decreases as the turbine temperatures and pressure increase and condensation temperature decreases; however, there is an optimum turbine inlet pressure (12MPa) in the carbon dioxide cycle for a minimum cost of products. The combustion chamber and boiler have a maximum destruction exergy rate for irreversibility and temperature difference among of system components

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In axial flow compressor there is a gap between stationary and rotating members since the stator vane is fixed at the casing and the shaft is rotating at the root. Also, the pressure increases when the air flows through the stator vanes. Therefore, due to pressure increase and existence gap under vanes, the leakage is inevitable in the stator tip. This leakage can change the flow pattern near the stator tip, which causes more separation. Therefore the loss has been increased so it adversely effects on performance. In this paper, the effect of stator tip sealing with honeycomb on compressor performance is investigated. For this purpose, the 9th stage of a ten-stage compressor is examined in two cases of solid wall and sealing with honeycomb. The numerical results have good agreements with experimental results. The results show that by reduction of leakage at stator tip, the size and depth of tip corner separation decreased significantly leading to loss reduction. Also the effect of the leakage on flow angles shows that to have more accurate analysis of compressor performance, it is necessary to be considered the stator tip leakage. On the other hand, according to same effect of honeycomb on reducing stator tip leakage than solid wall, here the honeycomb roles as an abradable material to prevent direct contact between rotor and stator. Also in analysis of stage the honeycomb can be replaced with solid wall model.

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Now a days gas turbines are widely used in the transportation and energy industry. According to Combustion of fossil fuels in these engine, environmental concerns have increased due to production of nitrogen oxides and carbon monoxide. Various methods have been offered to reduce the emission of pollutants. One of these methods is adding steam or water to the combustion chamber to reduce the flame temperature. Different methods can be applied to add steam to the combustion chamber, in this study, the steam is added to the diffuser and premixed with air into the combustion chamber. Steam addition influences the combustion process inside the combustion chamber, which should be considered during the combustion chamber design process. Therefore, a model for the conceptual design of the chamber geometry and the effect of adding steam on it will be presented. For this purpose, the data from an actual combustion chamber will be used to compare results of geometry design by using this model and to study the influence of steam on the chamber geometry. To investigate the combustion chamber performance, the chemical reactor network method for combustion modeling will be used. First, with this procedure an annular conventional combustion chamber will be modeled without steam addition and the results of this method will be compared with the actual data of this combustor. Then the effect of adding steam on the performance will be investigated. The study will show adding steam is an effective way to reduce the flame temperature and emission of pollutants.

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In recent years, the use of Gas Turbine-Modular Helium Reactor (GT-MHR) which operates in accordance with closed Brayton cycle with helium fluid as working fluid has attracted researchers’ attention because of its high efficiency, high reactor safety, being economical, and low maintenance costs. In the present study, a combined system, including GT-MHR cycle, Kalina cycle and Ammonia-water absorption cycle is investigated with respect to energy, exergy, and exergoeconomic. As the bottoming cycle, Kalina cycle and absorption cycle are used in order to avoid energy wasted by gas turbine cycle and to increase efficiency of energy conversion. The results of the simulated model show that, in the basic input mode, the overall work is 304462 kW, the overall exergy destruction is 289766kW and the overall exergy efficeincy of cogeneration cycle is 0.689kW. Also reactor, turbine and compressor in helium cycle are the component to which more attention should be paid with respect to exergoeconomic because the highest amount of cost rate is related to these components. At the end, parametric analysis is carried out in order to evaluate the effect of the changing pressure ratio of helium compressor, input temperature of helium compressor, input pressure and temperature of turbine and mass fraction of the base mode of the Kalina cycle on the output parameters.