| 1. |
- Wang, Wujun
(författare)
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Development of an Impinging Receiver for Solar Dish-Brayton Systems
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A new receiver concept utilizing impinging jet cooling technology has been developed for a small scale solar dish-Brayton system. In a typical impinging receiver design, the jet nozzles are distributed evenly around the cylindrical absorber wall above the solar peak flux region for managing the temperature at an acceptable level. The absorbed solar irradiation is partially lost to the ambient by radiation and natural convection heat transfer, the major part is conducted through the wall and taken away by the impingement jets to drive a gas turbine. Since the thermal power requirement of a 5 kWe Compower® micro gas turbine (MGT) perfectly matches with the power collected by the EuroDish when the design Direct Normal Irradiance (DNI) input is 800 W/m2, the boundary conditions for the impinging receiver design in this work are based on the combination of the Compower®MGT and the EuroDish system.In order to quickly find feasible receiver geometries and impinging jet nozzle arrangements for achieving acceptable temperature level and temperature distributions on the absorber cavity wall, a novel inverse design method (IDM) has been developed based on a combination of a ray-tracing model and a heat transfer analytical model. In this design method, a heat transfer model of the absorber wall is used for analyzing the main heat transfer process between the cavity wall outer surface, the inner surface and the working fluid. A ray-tracing model is utilized for obtaining the solar radiative boundary conditions for the heat transfer model. Furthermore, the minimum stagnation heat transfer coefficient, the jet pitch and the maximum pressure drop governing equations are used for narrowing down the possible nozzle arrangements. Finally, the curves for the required total heat transfer coefficient distribution are obtained and compared with different selected impinging arrangements on the working fluid side, and candidate design configurations are obtained.Furthermore, a numerical conjugate heat transfer model combined with a ray-tracing model was developed validating the inverse design method and for studying the thermal performance of an impinging receiver in detail. With the help of the modified inverse design method and the numerical conjugate heat transfer model, two impinging receivers based on sintered α-SiC (SSiC) and stainless steel 253 MA material have been successfully designed. The detailed analyses show that for the 253 MA impinging receiver, the average air temperature at the outlet and the thermal efficiency can reach 1071.5 K and 82.7% at a DNI level of 800 W/m2 matching the system requirements well. Furthermore, the local temperature differences on the absorber can be reduced to 130 K and 149 K for two different DNI levels, which is a significant reduction and improvement compared with earlier published cavity receiver designs. The inverse design method has also been verified to be an efficient way in reducing the calculation costs during the design procedure.For the validation and demonstration of the receiver designs, a unique experimental facility was designed and constructed. The facility is a novel high flux solar simulator utilizing for the first time Fresnel lenses to concentrate the light of 12 commercial high power Xenon-arc lamps. Finally, a prototype of a 253 MA based impinging was experimentally studied with the help of the 84 kWe Fresnel lens based high flux solar simulator in KTH.
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| 2. |
- Zhang, Xiaoxiang, 1984-
(författare)
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Numerical Study on Combustion Features of Gasified Biomass Gas
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is a great interest to develop biomass combustion systems for industrial and utility applications. Improved biomass energy conversion systems are designed to provide better combustion efficiencies and environmental friendly conditions, as well as the fuel flexibility options in various applications. The gas derived from the gasification process of biomass is considered as one of the potential candidates to substitute traditional fuels in a combustion process. However, the gascomposition from the gasification process may have a wide range of variation depending on the methods and fuel sources. The better understanding of the combustion features for the Gasified Biomass Gas(GBG) is essential for the development of combustion devices to be operated efficiently and safely at the user-end.The objective of the current study is therefore aiming to achieve data associated with the combustion features of GBG fuel for improving the efficiency and stability of combustion process. The numerical result is achieved from the kinetic models of premixed combustion with a wide range of operating ranges and variety of gas compositions. The numerical result is compared with experimental data to provide a better understanding of the combustion process for GBG fuel.In this thesis the laminar flame speed and ignition delay time of the GBG fuel are analyzed, using 1-D premixed flame model and constant volume model respectively. The result from different kinetics are evaluated and compared with experimental data. The influences of initial temperature, pressure and equivalence ratio are considered, as well as the variation of gas compositions. While the general agreement is reached between the numerical result and experimental data for laminarflame speed prediction, deviations are discovered at fuel-rich region and increased initial temperature. For the ignition delay time, deviations are found in the low-temperature and low pressure regime. The empirical equations considering the influence of initial temperature,pressure and equivalence ratio are developed for laminar flame speed and ignition delay times. The influence of major compositions such as CO, H2 and hydrocarbons are discussed in details in the thesis. Furthermore, a simplified kinetic model is developed and optimized based on the evaluation of existing kinetics for GBG fuel combustion. The simplified kinetic model is expected to be used for simulating the complexc ombustion process of GBG fuel in future studies.
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| 3. |
- Binti Munajat, Nur Farizan
(författare)
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Combustion of gasified biomass: : Experimental investigation on laminar flame speed, lean blowoff limit and emission levels
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biomass is among the primary alternative energy sources that supplements the fossil fuels to meet today’s energy demand. Gasification is an efficient and environmental friendly technology for converting the energy content in the biomass into a combustible gas mixture, which can be used in various applications. The composition of this gas mixture varies greatly depending on the gasification agent, gasifier design and its operation parameters and can be classified as low and medium LHV gasified biomass. The wide range of possible gas composition between each of these classes and even within each class itself can be a challenge in the combustion for heat and/or power production. The difficulty is primarily associated with the range in the combustion properties that may affect the stability and the emission levels. Therefore, this thesis is intended to provide data of combustion properties for improving the operation or design of atmospheric combustion devices operated with such gas mixtures.The first part of this thesis presents a series of experimental work on combustion of low LHV gasified biomass (a simulated gas mixture of CO/H2/CH4/CO2/N2) with variation in the content of H2O and tar compound (simulated by C6H6). The laminar flame speed, lean blowoff limit and emission levels of low LHV gasified biomass based on the premixed combustion concept are reported in paper I and III. The results show that the presence of H2O and C6H6 in gasified biomass can give positive effects on these combustion parameters (laminar flame speed, lean blowoff limit and emission levels), but also that there are limits for these effects. Addition of a low percentage of H2O in the gasified biomass resulted in almost constant laminar flame speed and combustion temperature of the gas mixture, while its NOx emission and blowoff temperature were decreased. The opposite condition was found when H2O content was further increased. The blowoff limit was shifted to richer fuel equivalence ratio as H2O increased. A temperature limit was observed where CO emission could be maintained at low concentration. With C6H6 addition, the laminar flame speed first decreased, achieved a minimum value, and then increased with further addition of C6H6. The combustion temperature and NOx emission were increased, CO emission was reduced, and blowoff occurs at slightly higher equivalence ratio and temperature when C6H6 content is increased. The comparison with natural gas (simulated by CH4) is also made as can be found in paper I and II. Lower laminar flame speed, combustion temperature, slightly higher CO emission, lower NOx emission and leaner blowoff limit were obtained for low LHV gas mixture in comparison to natural gas.In the second part of the thesis, the focus is put on the combustion of a wide range of gasified biomass types, ranging from low to medium LHV gas mixture (paper IV). The correlation between laminar flame speed or lean blowoff limit and the composition of various gas mixtures was investigated (paper IV). It was found that H2 and content of diluents have higher influence on the laminar flame speed of the gas mixture compared to its CO and hydrocarbon contents. For lean blowoff limit, the diluents have the greatest impact followed by H2 and CO. The mathematical correlations derived from the study can be used to for models of these two combustion parameters for a wide range of gasified biomass fuel compositions.
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| 4. |
- Cardozo, Evelyn, 1984-
(författare)
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Combustion of agricultural residues : Application for Stirling micro-combined heat and power
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Access to energy services is crucial for the development of countries. Therefore, in developing countries, the access to modern conversion technologies would contribute to reduce the poverty, improve health services and promote the economy especially in rural areas. Around 2.5 billion people in these countries use biomass for cooking. However, major concerns are due to the unsustainable use of biomass and the inefficient conversion technologies employed in rural areas. Therefore, the use of locally available biomass in modern biomass conversion technologies would significantly reduce emissions and improve the energy efficiency. These modern technologies may include residential pellet stoves and boilers which at the moment only are used for heating appliances in industrialized countries. Their combination with a prime mover like a Stirling engine could a very attractive solution to produce combined heat and power (CHP) though still in prototype stage. In this context, this study is mainly focused on the development of an energy system fuelled by locally available biomass to produce heat and electricity based on a Stirling engine. The main objective is to perform experiments to find relevant parameters that characterize the energy system proposed.In the first stage of this work, the suitability of using agricultural residues in a pellet boiler was evaluated in comparison to commercial wood pellets. The agricultural residues used during the tests were: sugar cane bagasse, sunflower husks and Brazil nut shells. The first two residues were pelletized and the last one was reduced to a uniform size. Parameters and energy used during the pelletizing were found. Emission levels and boiler efficiency under steady-state and transient conditions were also presented for the different biomass sorts. In the second stage, the integration of the same pellet burner and the Stirling engine was characterized in terms of losses and efficiency calculations. Finally, the integration of the pelletizing, combustion, and heat and power generation was discussed based on experimental and predicted results.
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| 5. |
- Mayorca, Maria Angelica, 1983-
(författare)
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Numerical Methods for Turbomachinery Aeromechanical Predictions
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In both aviation and power generation, gas turbines are used as key components. An important driver of technological advance in gas turbines is the race towards environmentally friendly machines, decreasing the fuel burn, community noise and NOx emissions. Engine modifications that lead to propulsion efficiency improvements whilst maintaining minimum weight have led to having fewer stages and lower blade counts, reduced distance between blade rows, thinner and lighter components, highly three dimensional blade designs and the introduction of integrally bladed disks (blisks). These changes result in increasing challenges concerning the structural integrity of the engine. In particular for blisks, the absence of friction at the blade to disk connections decreases dramatically the damping sources, resulting in designs that rely mainly on aerodynamic damping. On the other hand, new open rotor concepts result in low blade-to-air mass ratios, increasing the influence of the surrounding flow on the vibration response. This work presents the development and validation of a numerical tool for aeromechanical analysis of turbomachinery (AROMA - Aeroelastic Reduced Order Modeling Analyses), here applied to an industrial transonic compressor blisk. The tool is based on the integration of results from external Computational Fluid Dynamics (CFD) and Finite Element (FE) solvers with mistuning considerations, having as final outputs the stability curve (flutter analysis) and the fatigue risk (forced response analysis). The first part of the study aims at tracking different uncertainties along the numerical aeromechanical prediction chain. The amplitude predictions at two inlet guide vane setups are compared with experimental tip timing data. The analysis considers aerodynamic damping and forcing from 3D unsteady Navier Stokes solvers. Furthermore, in-vacuo mistuning analyses using Reduced Order Modeling (ROM) are performed in order to determine the maximum amplitude magnification expected. Results show that the largest uncertainties are from the unsteady aerodynamics predictions, in which the aerodynamic damping and forcing estimations are most critical. On the other hand, the structural dynamic models seem to capture well the vibration response and mistuning effects. The second part of the study proposes a new method for aerodynamically coupled analysis: the Multimode Least Square (MLS) method. It is based on the generation of distributed aerodynamic matrices that can represent the aeroelastic behavior of different mode-families. The matrices are produced from blade motion unsteady forces at different mode-shapes fitted in terms of least square approximations. In this sense, tuned or mistuned interacting mode families can be represented. In order to reduce the domain size, a static condensation technique is implemented. This type of model permits forced response prediction including the effects of mistuning on both the aerodynamic damping as well as on the structural mode localization. A key feature of the model is that it opens up for considerations of responding mode-shapes different to the in-vacuo ones and allows aeroelastic predictions over a wide frequency range, suitable for new design concepts and parametric studies.
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| 6. |
- Monaco, Lucio
(författare)
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Remote Laboratories in the Training of Turbomachinery Engineering Students
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- When practicing their profession, engineers use their analytical and creative thinking to develop solutions for problems that require the application of scientific knowledge and experience in a dependable and sustainable way. Laboratory exercises represent an ideal scenario for engineering students to comprehend through the application in actual situations of fundamental concepts and to analyze, synthetize, and make judgments based on evidence. Furthermore, in case of group work, students collaborate on an assignment taking decisions and sharing responsibilities thus training their social skills.The use and development of information technology have in the past few decades increased at a very high pace and have had considerable effects on various domains of society, including education. Although distance learning has existed for a while, it is the widespread access to the Internet and familiarity of the current young generation with information technology that has led to the recent boom of interest in massive open online education (MOOC) as well as in various forms of blended learning.Laboratories in education are traditionally hands-on activities carried out on-campus by students with the assistance of an instructor. New laboratory environments such as virtual and remote laboratories have in the past decades been introduced in several disciplines to improve access to distant students, cut down costs, and reduce obsolescence of hands-on labs. Yet many are the doubts concerning their effectiveness in tackling the development of engineering skills, as well as their technical capability of being 24/7 worldwide accessible professional remote infrastructures. The present thesis work is concerned with the conceiving, implementation and evaluation of a set of remote laboratories to be used in the training of turbomachinery engineering students. The focus is put on three new remote laboratory exercises:a pump laboratory exercise focusing on the assessment of operation of pumpsa turbine cascade laboratory exercise focusing on the measurement of aerodynamic losses anda turbine cascade laboratory exercise focusing on the measurement of aeroelastic properties in a vibrating blade row.The laboratories are developed using state-of-the-art instrumentation and a design that allows for reusability of common hardware and software resources. Different technologies are explored for the remote operation of the equipment while laboratory exercises are constructed that include interactive learning material, online self-assessments, and tools for analysis of the experimental test data.Extensive field-testing within ongoing courses at the department proves an overall good technical performance of the remote laboratories. Accessibility is significantly improved with the use of new web technologies while integration in existing networks of remote laboratories and use of remote experiment management systems is perceived as necessary for future scaling up of the application.The concept of the remote laboratory exercises is critically evaluated and leads to changes in the structure of the exercises that improve development of certain laboratory skills and student’s perception of the remote experience. The same experimental setup is used to address different learning outcomes and, in turns, different target audiences showing the potential of significantly improving the economical sustainability of the labs, especially in the case these are integrated in courses at other universities.The generality of conclusions is partially validated by the involvement of external students, researchers and professional in energy technology in the testing of the remote laboratory exercises as part of collaborative initiatives that raise also the interest for a possible application of remote experimentation in research activity.Keywords: remote laboratory, distant education, engineering education, turbomachinery training
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| 7. |
- Sanz Luengo, Antonio, 1986-
(författare)
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Experimental Investigation of the Influence of Local Flow Features on the Aerodynamic Damping of an Oscillating Blade Row
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The general trend of efficiency increase, weight and noise reduction has derived in the design of more slender, loaded, and 3D shaped blades. This has a significant impact on the stability of fan, and low pressure turbine blades, which are more prone to aeroelastic phenomena such as flutter. The flutter phenomenon is a self-excited, self-sustained unstable vibration produced by the interaction of flow and structure. These working conditions will induce either blade overload, or High Cycle Fatigue (HCF) produced by Limited Cycle Oscillation (LCO).The main objectives of the present work are on the investigation of the aeroelastic properties of a high-lift low-pressure in the light of the local flow features present in such profiles, in nominal and extreme off-design conditions both in high and low subsonic Mach number, for three dif-ferent rigid body modes. In addition, the validity of the linearity assump-tion of the influence coefficient technique has also been investigated, in order to expand the understanding of the physical limits of this assumption.This work has been designed as experimental investigation in the influence coefficient domain focused on a high-lift low-pressure turbine designed by ITP within the framework of the European FP7 project FU-TURE. These experiments have been carried out in the Aeroelastic test rig (AETR), at KTH Stockholm, which consist of an instrumented annular sector cascade with a single oscillating blade. The results acquired have been supported by numerical results provided by a non-propietary commercial software package (ANSYS CFX).The results suggest that the typical three-dimensional effects associated secondary flow features and tip leakage flows have a significant influence on the aeroelastic performance and the cascade stability. However the major influence appears as a consequence of the separation surface on the pressure side which appears at extreme off-design operating conditions. The contribution to stability of this local feature depend on the oscillation mode showing for the axial and torsion mode a neutral stability contribution, which is directly associated with the geometrical properties of the cascade. However, on the circumferential mode this separation surface has a stabilizing effect much more independent of the blade geometry.The study of the linearity assumption of the influence coefficient domain has revealed, that an apparent linear relation between the integrated unsteady response and the vibrational amplitude, does not necessary imply that the local unsteady response is linear with respect to the oscillation amplitude. The results also suggest that the validity of the linearity as-sumption is more sensitive to high oscillation amplitudes at high Mach conditions.
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| 8. |
- Udomsri, Seksan
(författare)
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Combined Electricity Production and Thermally Driven Cooling from Municipal Solid Waste
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasingly intensive efforts are being made to enhance energy systems via augmented introduction of renewable energy along with improved energy efficiency. Resource constraints and sustained high fossil fuel prices have created a new phenomenon in the world market. Enhanced energy security and renewable energy development are currently high on public agenda worldwide for achieving a high standard of welfare for future generations. Biomass and municipal solid waste (MSW) have widely been accepted as important locally-available renewable energy sources offering low carbon dioxide (CO2) emissions. Concerning solid waste management, it has become a critical issue in Southeast Asia since the most popular form for waste disposal still employs open dumping and landfilling. While the need for a complete sustainable energy solution is apparent, solid waste management is also an essential objective, so it makes sense to explore ways in which the two can be joined. Electricity production in combination with energy recovery from flue gases in thermal treatment plants is an integral part of MSW management for many industrialized nations. In Sweden, MSW is considered as an important fuel resource for partially meeting EU environmental targets within cogeneration. However it is normally difficult to justify traditional cogeneration in tropical locations since there is little need for the heat produced. Similarly, MSW-fired cogeneration usually operates with low capacity during non-heating season in Sweden. Therefore, it is very important to find new alternatives for energy applications from waste, such as the implementation of thermally driven cooling processes via absorption cooling in addition to electricity production. The work presented herein concentrates first on an investigation of electricity generation from MSW power plants and various energy applications from waste in tropical urban areas. The potential for various types of absorption chillers driven by MSW power plants for providing both electricity and cooling is of particular interest. Additionally a demonstration and analysis of decentralized thermally driven cooling in district heating network supplied by low temperature heat from a cogeneration of MSW have been conducted. This study aims at developing the best system configuration as well as finding improved system design and control for a combination of district heating and distributed thermally driven cooling. Results show that MSW incineration has the ability to lessen environmental impacts associated with waste disposal, and it can contribute positively towards expanding biomass-based energy production in Southeast Asia. For electricity production, the proposed hybrid dual-fuel (MSW/natural gas) cycles feature attractive electrical efficiency improvements, leading to greenhouse gas emissions reduction. Cogeneration coupled with thermally driven cooling is a solution that holds promise for uniting enhanced sustainability with economic advantages. The system offers great opportunity for primary energy saving, increasing electrical yield and can significantly reduce CO2 emissions per unit of cooling as compared to compression chiller. The demonstration and simulation have also revealed that there is a potential with some modifications and improvements to employ decentralized thermally driven cooling in district heating networks even in temperate regions like Sweden. Thus, expanding cogeneration towards trigeneration can augment the energy supply for summer months in Europe and for year-round cooling in tropical locations.
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| 9. |
- Araoz Ramos, Joseph Adhemar, 1982-
(författare)
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Thermodynamic analysis of Stirling engine systems : Applications for combined heat and power
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasing energy demands and environmental problems require innovative systems for electrical and thermal energy production. In this scenario, the development of small scale energy systems has become an interesting alternative to the conventional large scale centralized plants. Among these alternatives, small scale combined heat and power (CHP) plants based on Stirling Engines (SE) have attracted the interest among research and industry due to the potential advantages that offers. These include low maintenance, low noise during operation, a theoretically high electrical efficiency, and principally the fuel flexibility that the system offers. However, actual engine performances present very low electrical efficiencies and consequently few successful prototypes reached commercial maturity at elevated costs.Considering this situation, this thesis presents a numerical thermodynamic study for micro scale CHP-SE systems. The study is divided in two parts: The first part covers the engine analysis; and the second part studies the thermodynamic performance of the overall CHP-SE system. For the engine analysis a detailed thermodynamic model suitable for the simulation of different engine configurations was developed. The model capability to predict the engine performance was validated with experimental data obtained from two different engines: The GPU-3 Stirling engine studied by Lewis Research Centre; and the Genoa engine studied on the experimental rig built at the Energy Department at the Royal Institute of Technology (KTH). The second part of the research complemented the study with the analysis of the overall CHP-SE system. This included numerical simulations of the different CHP components and the sensitivity analysis for selected design parameters.The complete study permitted to assess the different operational and design configurations for the engine and the CHP components. These improvements could be implemented for test field evaluations and thus foster the development of more efficient SE-CHP systems. In addition, the detailed thermodynamic-design methodology for the SE-CHP systems was established and the numerical tool for the design assessment was developed.
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| 10. |
- Baagherzadeh Hushmandi, Narmin, 1978-
(författare)
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Numerical Analysis of Partial Admission in Axial Turbines
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- HTML clipboard Numerical analysis of partial admission in axial turbines is performed in this work. Geometrical details of an existing two stage turbine facility with low reaction blades is used for this purpose. For validation of the numerical results, experimental measurements of one partial admission configuration at design point was used. The partial admission turbine with single blockage had unsymmetrical shape; therefore the full annulus of the turbine had to be modeled numerically. The numerical grid included the full annulus geometry together with the disc gaps and rotor shrouds. Importance of various parameters in accurate modeling of the unsteady flow field of partial admission turbines was assessed. Two simpler models were selected to study the effect of accurate modeling of radial distribution of flow parameters. In the first numerical model, the computational grid was two dimensional and the radial distribution of flow parameters was neglected. The second case was three-dimensional and full blades’ span height was modeled but the leakage flows at disc cavity and rotor shroud were neglected. Detailed validation of the results from various computational models with the experimental data showed that modeling of the leakage flow at disc cavities and rotor shroud of partial admission turbines has substantial importance in accuracy of numerical computations. Comparison of the results from two computational models with varying inlet extension showed that modeling of the inlet cone has considerable importance in accuracy of results but with increased computational cost. Partial admission turbine with admission degree of ε = 0.524 in one blocked arc and two opposing blocked arcs were tested. Results showed that blocking the inlet annulus in one single arc produce better overall efficiency compared to the two blocked arc model. Effect of varying axial gap distance between the first stage stator and rotor rows was also tested numerically for the partial admission turbine with admission degree of ε = 0.726. Results showed higher efficiency for the reduced axial gap model. Computations showed that the main flow leave the blade path down to the disc cavity and re-enter into the flow channel downstream the blockage, this flow would pass the rotor with very low efficiency. First stage rotor blades are subject to large unsteady forces due to the non-uniform inlet flow. Plotting the unsteady forces of first stage rotor blades for partial admission turbine with single blockage showed that the blades experience large changes in magnitude and direction while traveling along the circumference. Unsteady forces of first stage rotor blades were plotted in frequency domain using Fourier transform. The largest amplitudes caused by partial admission were at first and second multiples of rotational frequency due to the existence of single blockage and change in the force direction. Results obtained from the numerical computations showed that the discs have nonuniform pressure distribution especially in the first stage of partial admission turbines. The axial force of the first rotor wheel was considerably higher when the axial gap distance was reduced between the first stage stator and rotor rows. The commercial codes used in this work are ANSYS ICEM-CFD 11.0 as mesh generator and FLUENT 6.3 as flow solver.
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