Future fossil-fueled power generation systems will require emission control technologies such as carbon capture and sequestration (CCS) to comply with government greenhouse gas regulations. The three prime candidate technologies which permit carbon dioxide (CO2) to be captured and safely stored include pre-combustion, post-combustion capture and oxy-fuel (O-F) combustion. For more than a decade Clean Energy Systems, Inc. (CES) has been designing and demonstrating enabling technologies for oxy-fuel power generation; specifically steam generators, hot gas expanders and reheat combustors. Recently CES has partnered with Florida Turbine Technologies, Inc. (FTT) and Siemens Energy, Inc. to develop and demonstrate turbomachinery systems compatible with the unique characteristics of oxy-fuel working fluids. The team has adopted an aggressive, but economically viable development approach to advance turbine technology towards early product realization. Goals include short-term, incremental advances in power plant efficiency and output while minimizing capital costs and cost of electricity. Phase 2 of this development work has been greatly enhanced by a cooperative agreement with the U.S. Department of Energy (DOE). Under this program the team will design, manufacture and test a commercial-scale intermediate-pressure turbine (IPT) to be used in industrial O-F power plants. These plants will use diverse fuels and be capable of capturing 99% of the produced CO2 at competitive cycle efficiencies and cost of electricity. Initial plants will burn natural gas and generate more than 200MWe with near-zero emissions. To reduce development cost and schedule an existing gas turbine engine will be adapted for use as a high-temperature O-F IPT. The necessary modifications include the replacement of the engine’s air compressor with a thrust balance system and altering the engine’s air-breathing combustion system into a steam reheating system using direct fuel and oxygen injection. Excellent progress has been made to date. FTT has completed the detailed design and issued manufacturing drawings to convert a Siemens SGT-900 to an oxy-fuel turbine (OFT). Siemens has received, disassembled and inspected an SGT-900 B12 and ordered all necessary new components for engine changeover. Meanwhile CES has been working to upgrade an existing test facility to support demonstration of a “simple” oxy-fuel power cycle. Low-power demonstration testing of the newly assembled OFT-900 is expected to commence in late 2012.
End wall contouring has been widely studied during past two decades for secondary loss reduction in turbine passages. Recent non-axisymmetric end wall contouring methods have shown more promise for loss reduction as compared to the axisymmetric end wall contouring methods used in initial studies. The end wall contouring methods have shown definite promise, especially, for the turbine passages at low design exit Mach numbers. A class of methods exists in the literature where the end wall surface is defined by using a combination of two curves. These curves specify surface topology variation in streamwise and pitchwise directions. Another class of methods depends on surface contour optimization, in which the modification of surface contours is achieved by changing the control point locations that define the surface topology. A definitive, passage design parameter based method of contouring is still not available. However, a general guideline for the trend of contour variation, along pitchwise and streamwise direction, can certainly be extrapolated from the existing literature. It is not clear, however, whether such a trend can be fitted to any blade profile to achieve, least of all a nonoptimum but a definite, reduction in losses. Moreover, almost all of the existing studies have focused on end wall contouring of passages with low exit Mach numbers. Some researchers, indeed, have used blades designed for high turning and high exit Mach number. However, such studies were done at Mach number well below the intended design condition. A study of effect of end wall contouring on a high turning blade with high design exit Mach number is not available in open literature. The present study investigates the effect of application of three different types of end wall contouring methods through numerical simulation, on a high turning transonic turbine blade passage. The main contouring method is based on total loss reduction criterion which is described here in detail. The contouring methodology described here avoids the deficiency of current commercial mesh generation software in context of automated meshing and provides a robust end wall optimization methodology. The geometry that gives minimum SKE values is compared with this loss optimized geometry. Additionally, a normalized contoured surface topology was extracted from a previous study that has similar blade design parameters and this surface was fitted to the turbine passage under study in order to investigate the effect of such trend based surface fitting. This contour geometry has also been compared with the other two contour geometries. Aerodynamic response of these geometries has been compared in detail with the baseline case without any end wall contouring. A comparison of shape and location of end wall contours on aerodynamic performance has been provided. The results indicate that end wall contouring for transonic turbine blades may not result in as significant gains at design conditions as those claimed for low speed turbine passages in previous studies.
The paper presents detailed measurements of midspan total pressure loss, secondary flow field, static pressure measurements on airfoil surface at midspan, near hub and near the end walls in a transonic turbine airfoil cascade. Numerous low-speed experimental studies have been carried out to investigate the performance of turbine cascades. Profile and secondary loss correlations have been developed and improved over the years to include the induced incidence and leading edge geometry and to reflect recent trends in turbine design. All of the above investigations have resulted in better understanding of flow field in turbine passages. However, there is still insufficient data on the performance of turbine blades with high turning angles operating at varying incidences angles at transonic Mach numbers. In the present study, measurements were made at +10, 0 and -10 degree incidence angles for a high turning turbine airfoil with 127 degree turning. The exit Mach numbers were varied within a range from 0.6 to 1.1. Additionally, the exit span is increased relative to the inlet span resulting in one end wall diverging from inlet to exit at 13 degree angle. This was done in order to obtain a ratio of inlet Mach number to exit Mach number which is representative to that encountered in real engine and simulates the blade and near end wall loading that is seen in an engine. 3D viscous compressible CFD analysis was carried out in order to compare the results with experimentally obtained values and to further investigate the design and off-design flow characteristics of the airfoil under study. All aerodynamic measurements were compared with CFD analysis and a reasonably good match was observed. INTRODUCTIONWith present day stringent norms set by the government for clean and efficient engines and the ever-growing competition in the market, gas turbine manufactures need to optimize every component of the engine. The need for low cost, compact and fuel efficient engines are apparent. Improvements can be made by designing blades such that minimum losses are generated while making sure that the loading on the blade is maximized in order to reduce the number of airfoils in each stage. The designer also needs to ensure that the turbine efficiency is maintained at off-design conditions. Almost a third of the total losses in turbines are due to end wall losses. The thickness of the upstream boundary layer as well as the blade turning angle influences the strength of the secondary flow observed near the end walls. The secondary flow results into stagnation pressure loss which accounts for a considerable portion of the total stagnation pressure loss occurring in a turbine passage.
Profile and secondary loss correlations have been developed and improved over the years to include the induced incidence and leading edge geometry and to reflect recent trends in turbine design. All of these investigations have resulted in better understanding of the flow field in turbine passages. However, there is still insufficient data on the performance of turbine airfoils with high turning angles operating at varying incidence angles at transonic Mach numbers. The paper presents detailed aerodynamic measurements for three different turbine airfoils with similar turning angles but different aerodynamic shapes. Midspan total pressure loss, secondary flow field, and static pressure measurements on the airfoil surface in the cascades are presented and compared for the three different airfoil sets. The airfoils are designed for the same velocity triangles (inlet/exit gas angles and Mach number). Airfoil curvature and true chord are varied to change the loading vs. chord. The objective is to investigate the type of loading distribution and its effect on aerodynamic performance (pressure loss). Measurements are made at +10, 0 and −10 degree incidence angles for high turning turbine airfoils with ∼127 degree turning. The cascade exit Mach numbers were varied within a range from 0.6 to 1.1. In order to attain a ratio of inlet Mach number to exit Mach number that is representative to that encountered in a real engine, the exit span is increased relative to the inlet span. This results in one end wall diverging from inlet to exit at a 13 degree angle, which simulates the required leading edge loading as seen in an engine. 3D viscous compressible CFD analysis was carried out in order to compare the results with experimentally obtained values and to further investigate the flow characteristics of the airfoils under study.
Modern industrial pallet racking systems in use in New Zealand are adaptions of overseas design, using thin walled cold formed sections. These sections are not generally considered suitable for plastic deformations, or resistance to seismically induced loadings. This paper reviews full scale shaking table tests reported by Rack Manufacturers Institute, Pittsburg, (R.M.I.) in 1980, and comments on the applicability of the results to the seismic design philosophy embodied in NZS 4203. Seismic performance criteria (not strictly the same as for building structures) are proposed, and design approaches suggested that will enable the capacity design requirements of NZS 4203 to be considered, while keeping with the cold formed sections traditionally used for pallet rack construction.
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