| 1. |
- Topel, Monika, 1988-
(författare)
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Steam Turbine Thermal Modeling for Improved Transient Operation
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The growing shares of renewable energy sources in the market and solar thermal power applications have set higher requirements on steam turbine operation.These requirements are related to flexibility during transients. A key aspect sought of such flexibility is the capability for fast starts. Due to the varying temperature gradients during start-up, the speed at which the turbine can start is constrained by thermal stresses and differential expansion. These phenomena either consume component lifetime or may result in machine failure if not carefully controlled. In order to accomplish faster starts while ensuring that lifing requirements are preserved, it is important to analyze the thermal behavior of the machine. For this, a transient thermal model was developed with a focus on adaptability to different turbine sizes and geometries. The model allows for simple and fast prediction of thermo-mechanical properties within the turbine metal, more importantly, of the temperature distribution and the associated thermal expansion. The next step of this work was to validate the assumptions and simplifications of the model. This was done through the study and comparison of two turbines against measured operational data from their respective power plants. Furthermore,validation studies also included comparisons concerning the geometric detail level of the model. Overall, comparison results showed a large degree of agreement with respect to the measured data and between the geometric detail levels. The validated model was then implemented in studies related to reducing start-up times and peak differential expansion. For this, the potential effects of turbine temperature maintaining modifications were investigated and quantified.The modifications studied included: increasing gland steam pressure, increasing back pressure and increasing barring speed. Results yielded significant improvements starting from 9.5% in the start-up times and 7% in the differential expansion.
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| 2. |
- Kyprianidis, Konstantinos G.
(författare)
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Multi-Disciplinary Conceptual Design of Future Jet Engine Systems
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes various aspects of the development of a multi-disciplinary aero engine conceptual design tool, TERA2020 (Techno-economic, Environmental and Risk Assessment for 2020), based on an explicit algorithm that considers: engine performance, engine aerodynamic and mechanical design, aircraft design and performance, emissions prediction and environmental impact, engine and airframe noise, and production, maintenance and direct operating costs.As part of this research effort, a newly-derived semi-empirical NOx correlation for modern rich-burn single-annular combustors is proposed. The development of a numerical methods library is also presented, including an improved gradient-based algorithm for solving non-linear equation systems. Common assumptions made in thermo-fluid modelling for gas turbines and their effect on caloric properties are investigated, while the impact of uncertainties on performance calculations and emissions predictions at aircraft system level is assessed. Furthermore, accuracy limitations in assessing novel engine core concepts as imposed by current practice in thermo-fluid modelling are identified.The TERA2020 tool is used for quantifying the potential benefits from novel technologies for three low pressure spool turbofan architectures. The impact of failing to deliver specific component technologies is quantified, in terms of power plant noise and CO2 emissions. To address the need for higher engine thermal efficiency, TERA2020 is again utilised; benefits from the potential introduction of heat-exchanged cores in future aero engine designs are explored and a discussion on the main drivers that could support such initiatives is presented. Finally, an intercooled core and conventional core turbofan engine optimisation procedure using TERA2020 is presented. A back-to-back comparison between the two engine configurations is performed and fuel optimal designs for 2020 are proposed.Whilst the detailed publications and the work carried out by the author, in a collaborative effort with other project partners, is presented in the main body of this thesis, it is important to note that this work is supported by 20 conference and journal papers.
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| 3. |
- Noor, Hina
(författare)
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Preliminary Design Investigations for the Selection of Optimum Reaction Degree for 1st Stage of a High Pressure Gas Turbine
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- One-dimensional (1D) turbine design calculation phase requires a handful of input data and choice of design parameters to provide the blade flow path geometry along with the flow kinematics and thermodynamics properties at the blade mid-span. The choice of important aerodynamics design parameters namely reaction degree, nozzle guide vane NGV exit flow angle or flow coefficient and stage loading defines the mid-span flow velocity triangles. Despite being a very initial turbine design phase the implication of 1D calculation are such that the design choices made based on the design parameters at this design phase cannot be altered as the design proceeds towards detailed three-dimensional (3D) flow field analysis. Thus an optimum choice of the design parameters is essential for maximum turbine performance. There exist certain design recommendations for the selection of reaction degree, stage loading and flow coefficient for uncooled turbines. The rationale and underlying flow physics is straight forward for an uncooled case but a highly cooled case can benefit from a lower relative flow velocity. The aerodynamic design parameters have their own implications on the design of a cooled turbine, where the choice of reaction degree and flow coefficient has a strong impact on the stage design for a given stage loading. For a design of a cooled turbine, selection of a lower flow coefficient and lower reaction degree seems opportune from the heat transfer and the performance point of view. The flow coefficient has traditionally, in some cases, been set to a higher value on basis of the Smith charts which were originally devised for uncooled turbines. The reaction degree sets the relative rotor inlet temperature (hence cooling requirements) and should be carefully chosen for a high performance. However, presently there do not exist recommendations for the selection of optimum reaction degree for cooled turbine for given stage loading and NGV exit flow angle.This thesis work aims to contribute in developing the recommendations for the choice of optimum reaction degree for a cooled turbine. The goal is to determine the range of optimum values for reaction degree for given stage loading and NGV exit flow angles. A parametric study has been formulated to perform this goal. 1D meanline design tool (LUAXT) is used to implement different loss models. These models are validated using experimental results. The validation showed that Craig & Cox is the most accurate when tested against the test data obtained from two different stage geometries. A discussion on flow physics as represented in different loss models is presented to develop further understanding of loss physics. Craig & Cox loss model is further considered for the parametric design investigations using LUAXT 1D design tool to develop design recommendations for optimum reaction degree values.The performed design investigations indicated that a choice of low reaction value along with a low stage loading and a low flow coefficient reduces the overall stage coolant consumption and results in overall increased stage performance. Since for a HPT 1st stage, the interest lies in a high stage loading, a range of reaction degree has been recommended to be between 0.20 to 0.37 to provide the optimum stage design when chosen for stage loading in between 1.40 to 1.80 and the stator exit flow angle in range of 74o to 78o. A two-dimensional (2D) blade profiling and blade to blade flow field analysis is carried out for one of the recommended cases to verify the velocity triangles as obtained from meanline design. Small differences in the flow velocities were found mainly due to the difference in fluid properties and differences in throat calculations which can be resolved with 1D-2D design iterations. The profiling and the blade to blade flow field analysis for one of the recommended design justified it to have a reasonable cascade. The recommendations on optimum reaction degree for cooled turbine as obtained from the performed calculations can be used for future 1D design investigations of a high pressure cooled turbines.Keywords: 1D design, aerodynamic design parameters, flow kinematic, thermodynamics, rotor inlet temperature, cooled turbine, reaction degree, flow coefficient, stage loading
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