bluuebunny/crossref_metadata_2025 huggingface dataset:
Rejuvenation Heat Treatments and Their Role in the Repair of IN738 Turbine Components
Authors: Miglietti Warren M. , Curtis Rich , Helm John
Published: February 2009

The thermal processing of turbine engine components is a critical step in the repair and rejuvenation of turbine section hardware to ensure optimal performance and reliability. In the repair process, the thermal process regime must meet the following requirements; improving the weldability of the alloy prior to the repair process (if necessary), returning the microstructure of the alloy to a solutioned state prior to precipitation hardening the alloy, and an aging cycle in order to achieve optimal mechanical properties for the alloy. This paper will focus on the criticality of each step and discuss the typical mechanical properties seen after engine service and the repair process. We will show the importance of these steps and how they will ultimately effect the repair of the hot section component. For almost three decades, gas turbine original equipment manufacturers (OEM’s) have cast high-pressure turbine blades/buckets from In738 Ni-base superalloys. Although significant turbine experience has been gained in the use of this material, little or no standardization of repair heat treatments has been established in the industry. Currently OEM’s and component repair shops utilize a variety of refurbishment heat treatments, all targeted at achieving maximum restoration of mechanical properties and base metal microstructure. This paper also summarizes the results of stress rupture testing of service-run material both before and after six different rejuvenation heat treatments. Microstructures in the service-run and heat-treated conditions are also characterized.
Volumetric X-Ray Imaging for Ceramic Microturbine Rotors
Authors: Ellingson W. A. , Koehl E. R. , Stainbrook J. , Rivers M.
Published: February 2009

Use of ceramic components in the hot section of gas-fired microturbines would allow higher operating temperatures and thus better operating efficiencies. However, the cost of such ceramic components is an issue for commercial-scale production. Costs can be reduced, in part, through improving fabrication yields. Use of nondestructive evaluation (NDE) methods in early stages of fabrication will support the development process to improve yields and subsequently reduce costs by rejecting flawed components prior to final processing and proof testing. An NDE approach using high-speed 3D X-ray tomographic imaging has been investigated. A large (40 × 40 cm), flat-panel, amorphous silicon X-ray detector, together with fast image processing, has been shown to allow full-volume X-ray imaging with detection of internal features in full-size as-cast parts. Gelcast radial-flow microturbine rotors, ≈23 cm in diameter, have been studied for internal defects with this 3D X-ray imaging method. Internal cracks, voids, and other variations in density within the rotors have been detected. Data acquisition speeds of 3 full frames per second have been achieved with reconstruction times of individual cross-sections of less than 1 second. This paper presents details of the 3D X-ray imaging method and results achieved on full-size microturbine rotors.
Local Mass/Heat Transfer on Turbine Blade Near-Tip Surfaces
Authors: Jin P. , Goldstein R. J.
Published: February 2009

Local mass transfer measurements on a simulated high pressure turbine blade are conducted in a linear cascade with tip clearance, using a naphthalene sublimation technique. The effects of tip clearance (0.86%–6.90% of chord), are investigated at an exit Reynolds number of 5.8 × 105 and a low turbulence intensity of 0.2%. The effects of the exit Reynolds number (4–7 × 105) and the turbulence intensity (0.2% and 12.0%) are also measured for the smallest tip clearance. The effect of tip clearance on the mass transfer on the pressure surface is limited to 10% of the blade height from the tip at smaller tip clearances. At the largest tip clearance high mass transfer rates are induced at 15% of curvilinear distance (Sp/C) by the strong acceleration of the fluid on the pressure side into the clearance. The effect of tip clearance on the mass transfer is not very evident on the suction surface for curvilinear distance of Ss/C < 0.21. However, much higher mass transfer rates are caused downstream of Ss/C ≈ 0.50 by the tip leakage vortex atthe smallest tip clearance, while at the largest tip clearance, the average mass transfer is lower than that with zero tip clearance, probably because the strong leakage vortex pushes the passage vortex away from the suction surface. A high mainstream turbulence level (12.0%) increases the local mass transfer rates on the pressure surface, while a higher mainstream Reynolds number generates higher local mass transfer rates on both near-tip surfaces.
Inlet Fogging of Gas Turbine Engines: Climatic Analysis of Gas Turbine Evaporative Cooling Potential of International Locations
Authors: Chaker Mustapha , Meher-Homji Cyrus B.
Published: February 2009

Inlet fogging of gas turbine engines has attained considerable popularity due to the ease of installation and the relatively low first cost compared to other inlet cooling methods. With increasing demand for power and with shortages envisioned especially during the peak load times during the summers, there is a need to boost gas turbine power. There is a sizable evaporative cooling potential throughout the world when the climatic data is evaluated based on an analysis of coincident wet bulb and dry bulb information. This data is not readily available to plant users. In this paper, a detailed climatic analysis is made of 106 major locations over the world to provide the hours of cooling that can be obtained by direct evaporative cooling. This data will allow gas turbine operators to easily make an assessment of the economics of evaporative fogging. The paper also covers an introduction to direct evaporative cooling and the methodology and data analysis used to derive the cooling potential. Simulation runs have been made for gas turbine simple cycles showing effects of fogging for a GE Frame 7EA and a GE Frame 9FA Gas turbine for 60 and 50 Hz applications.
Parametric Analysis of Existing Gas Turbines With Inlet Evaporative and Overspray Fogging
Authors: Bhargava R. , Meher-Homji C. B.
Published: February 2009

With deregulation in the power generation market and the need for flexibility in terms of power augmentation during periods of high electricity demand, power plant operators all over the world are exploring means to augment power from both existing and new gas turbines. An approach becoming increasingly popular is that of high pressure fogging. In this paper, the results of a comprehensive parametric analysis on the effects of inlet fogging on a wide range of existing gas turbines have been presented. Both evaporative and overspray fogging conditions have been analyzed. The results of this study show that the performance parameters indicative of inlet fogging effects have definitive correlation with the key gas turbine design parameters. In addition, this study indicates that aeroderivative gas turbines, in comparison to the industrial machines, have higher performance improvement due to the inlet fogging effects. Plausible reasons for the observed trends are discussed in this paper. This paper represents the first systematic study on the effects of inlet fogging for a large number (a total of 67) of gas turbine engines available from major gas turbine manufacturers.
Combined Heat and Power Sizing Methodology
Authors: Beyene Asfaw
Published: February 2009

As deregulation of the electric market finds legitimate global acceptance, more efficient alternatives to centralized power production, such as the Combined Heat and Power (CHP), also known as cogeneration, are finding growing reception. Advances in sizing methodologies, selection criteria, and control technologies, as well as development of associated regulatory issues, must accompany this favorable disposition. This paper presents an overview of some important applications of a heat recovery system and discusses a simplified method of sizing a CHP as a part of an early feasibility decision.
Semi-Unstructured Grid Methods for Turbomachinery Applications
Authors: Contreras J. , Corral R. , Fernandez-Castan˜eda J. , Pastor G. , Vasco C.
Published: February 2009

A semi-unstructured grid generation system specially designed for the meshing of blade passages is presented. The method retains most of the flexibility of unstructured hybrid grids but is used in a similar way than the traditional structured methods allowing a smooth transition in the design offices from structured to unstructured technology. The advantages and disadvantages of structured and unstructured methods are briefly revisited.
Performance Prediction of Twin-Entry Turbocharger Turbines
Authors: Ghasemi Shahram , Shirani Ebrahim , Hajilouy-Benisi Ali
Published: February 2009

In this paper, the performance of the twin-entry radial flow turbine under steady state and partial admission conditions is modeled. The method, which is developed here, is based on one-dimensional performance prediction. In one-dimensional modeling, the flow properties are assumed constant on a plane normal to the flow direction. This assumption is in contrast with the flow at the rotor entry of a twin-entry turbine under partial admission condition. In this study the one-dimensional performance prediction method for single-entry turbine is modified to analyze the twin-entry turbine. In particular, the loss coefficients due to friction, clearance and blade loading, which are already developed for single-entry turbines, are modified. Also additional losses in the rotor are considered because of twin-entry rotor inlet conditions and the rotor-mixing losses. Indeed in a single-entry turbine with symmetric volute the flow tends to move toward the shroud. A correlation for the radial velocity profile at the rotor entry for this case is obtained and is considered to be optimum. Then the rotor mixing loss is estimated. Finally a model based on the above mentioned matters is developed. The results obtained from the model are compared with experimental results and good agreements are obtained. In this paper, special behaviors of the flow in the twin-entry turbine are also investigated and some physical interpretations are presented.
The Evaluation of CFCC Liners After Field Testing in a Gas Turbine — III
Authors: Miriyala Narendernath , Kimmel Josh , Price Jeffrey , More Karren , Tortorelli Peter , Eaton Harry , Linsey Gary , Sun Ellen
Published: February 2009

Under the Ceramic Stationary Gas Turbine (CSGT) Program and the Advanced Materials Program, sponsored by the U.S. Department of Energy (DOE), several silicon carbide/silicon carbide (SiC/SiC) combustor liners were field tested in a Solar Turbines Centaur 50S gas turbine, which accumulated approximately 40000 hours by the end of 2001. To date, five field tests were completed at Chevron, Bakersfield, CA, and one test at Malden Mills, Lawrence, MA. The evaluation of SiC/SiC liners with an environmental barrier coating (EBC) after the fifth field test at Bakersfield (13937 hours) and the first field test at Malden Mills (7238 hours) is presented in this paper. The work at Oak Ridge National Laboratory (ORNL) in support of the field tests was supported by DOE’s Continuous Fiber-Reinforced Ceramic Composite (CFCC) Program.
Cold Flow Investigation of Silicon Carbide Cylindrical Filter Element
Authors: Al-Hajeri M. H. , Al-Saleh Raed , Al-Hebeshi Adel , Witry Ali
Published: February 2009

Silicon carbide cylindrical filter elements have proven to be an effective mean of removing particulates to levels exceeding the new source performance standard. This paper reports a Laser Doppler anemometry (LDA) investigation to study the flow behavior in the vicinity of the cylindrical filter. A single cylindrical filter has based in vertical channel. The flow enters from the bottom of the channel towards the filter element passing through to the outlet at the top of the channel. The particles deposition distribution around the filter element is studied using different face velocities.
Thermodynamic Analyses of Wet Compression Process in the Compressor of Gas Turbine
Authors: Zheng Qun , Sun Yufeng , Li Shuying , Wang Yunhui
Published: February 2009

Thermodynamic model of wet compression process is established in this paper. The topics of ideal wet compression process, actual wet compression process, water droplet evaporative rate, wet compression work, inlet evaporative cooling, concept of wet compression efficiency, aerodynamic breaking of water droplets etc. are investigated and discussed in this paper.
Fail Safe, High Temperature Magnetic Bearings
Authors: Minihan Thomas , Palazzolo Alan , Kim Yeonkyu , Lei Shuliang , Kenny Andrew , Na Uhn Joo , Tucker Randy , Preuss Jason , Hunt Andrew , Carter Bart , Provenza Andy , Montague Gerald , Kascak Albert
Published: February 2009

This paper contributes to the magnetic bearing literature in two distinct areas: high temperature and redundant actuation. Design considerations and test results are given for the first published combined 538°C (1000°F)-high speed rotating test performance of a magnetic bearing. Secondly, a significant extension of the flux isolation based, redundant actuator control algorithm is proposed to eliminate the prior deficiency of changing position stiffness after failure. The benefit of the novel extension was not experimentally demonstrated due to a high active stiffness requirement. In addition, test results are given for actuator failure tests at 399°C (750°F), 12,500rpm. Finally, simulation results are presented confirming the experimental data and validating the redundant control algorithm.
Improving the Aero-Thermal Characteristics of Turbomachinery Cascades
Authors: Manna Marcello , Tuccillo Raffaele
Published: February 2009

The paper presents the application of an optimization procedure to the aero-thermal design of high performance turbomachinery cascades. The blade profiles are parameterized with fourth order Bezier polynomials for the pressure and suction sides, and quadratic functions for the leading and trailing edges, according to the composite curve approach. Evidence is given that fairly complicated blade shapes are well approximated by the present parameterization. The method is applied to an existing nozzle guide vane for which extensive and detailed experimental data are available, with the objective of decreasing in an integral sense the thermal load, maintaining or increasing the blade efficiency and the aerodynamic load. The results demonstrate that despite the excellence of the initial design, there is room for improvements.
Numerical Investigation of Anisotropic Turbulence Effects Around a Film Cooled Turbine Vane
Authors: Bohn Dieter E. , Tu¨mmers Christian
Published: February 2009

In this paper the 3D flow around a turbine vane with showerhead cooling is simulated with the anisotropic cubic-eddy-viscosity k-ε turbulence model of Craft et. al. The results are analyzed in detail and compared to calculations performed with the isotropic algebraic turbulence model by Baldwin & Lomax and the isotropic Low-Reynolds k-ε-model of Launder et. al. for the same test case. The computational domain consists of the coolant supply (plenum), the ejection holes and the main flow region around the vane. Periodic boundary conditions have been used in the radial direction. Thus, endwall effects have been excluded. The numerical investigations focus on the influence of the anisotropic effects in the flow field. The flow conditions are taken from experimental investigations conducted by other authors and the results have been documented as a test case for numerical calculations of ejection flow phenomena. The results show a similar distribution of the predicted total pressure loss in the kidney vortex and downstream the ejection holes for the cubic-eddy viscosity model in comparison to the other turbulence models. Furthermore it is shown, that the influence of the cooling jets on the main flow, predicted by the two-equation models of Launder et. al. and Craft. et al., seems to be slightly higher compared to the algebraic model of Baldwin & Lomax.
Reducing Low-Pressure Turbine Stage Blade Count Using Vortex Generator Jet Separation Control
Authors: Sondergaard Rolf , Bons Jeffrey P. , Sucher Matthew , Rivir Richard B.
Published: February 2009

An experimental investigation has been conducted into the feasibility of increasing blade spacing (pitch) at constant chord in a linear turbine cascade. Vortex generator jets (VGJs) located on the suction surface of each blade in the cascade are employed to maintain attached boundary layers despite the increasing tendency to separate due to the increased uncovered turning. Tests were performed at low Mach numbers and at blade Reynolds numbers between 25,000 and 75,000 (based on axial chord and inlet velocity). The vortex generator jets (30 degree injection angle and 90 degree skew angle) were operated with steady flow with momentum blowing ratios between zero and five, and from two spanwise rows of holes located at 45% and 63% axial chord. In the absence of control, pitch-averaged wake losses increase up to 600% as the blade pitch is increased from its design value to twice the design value. With the application of VGJs, these losses were driven down to or below the losses at the design pitch. The effectiveness of VGJs was found to increase modestly with increasing Reynolds number up to the highest value tested, Re = 75,000. The fluid phenomenon responsible for this remarkable range of effectiveness is clearly more than a simple boundary layer transition effect, as boundary layer trips installed on the same blades without VGJ blowing had no beneficial effect on blade losses. Also, tests conducted at elevated levels of freestream turbulence (4% at the cascade inlet) where the suction surface boundary layer is generally turbulent, showed wake loss reduction comparable to tests conducted at the nominal 1% freestream turbulence. For all configurations, blowing from the upstream row had the greatest wake influence. These findings open the possibility that future LPT designs could take advantage of active separation control using integrated VGJs to reduce the turbine part count and stage weight without significant increase in pressure losses.
Evaluation of Mechanical Reliability of Silicon Nitride Vanes After Field Tests in an Industrial Gas Turbine
Authors: Lin H.-T. , Ferber M. K. , Westphal W. , Macri F.
Published: February 2009

This paper provides a review of recent studies undertaken to examine the mechanical and thermal stability of silicon nitride ceramic vanes with and without an oxide-based environmental barrier coating (EBC) after field tests in an industrial gas turbine. Two commercially available silicon nitride vanes (i.e., AS800 and SN282) were evaluated, where the AS800 vanes had an EBC and the SN282 vanes did not. The average temperature and pressure of gas impinging upon the vanes were approximately 1066°C and 8.9 atm, respectively. Both silicon nitride vanes were subjected to exposure time up to 1818h. Scanning electron microscopy was used to provide an insight into the changes in the microstructures of silicon nitrides and EBC arising from the environmental effects. The recession of the airfoils resulting from the volatilization of the normally protective silica layer, and /or EBC, was also measured using a coordinate measuring machine. The long-term chemical as well as structural stability of the secondary phases as well as EBC were characterized using x-ray diffraction. The surface strength of exposed airfoils was evaluated using a miniature biaxial test specimen, which was prepared by a diamond core drilling.
Seal and Bearing Upgrade for Eliminating Rotor Instability Vibration in a High Pressure Natural Gas Compressor
Authors: Li Jiming , De Choudhury Pranabesh , Tacques Rogerio
Published: February 2009

Reported in this paper are the field rotor instability and vibration elimination experienced recently on a compressor train installed on an offshore platform for natural gas service. The compressor train consists of a low-pressure compressor and a high-pressure compressor, which is driven by a gas turbine through a gearbox. The compressor train is rated at a maximum continuous speed of 12,054 rpm. During its first commissioning, a high subsynchronous vibration showed up on the high-pressure compressor when it was put on load at full speed. The high-pressure compressor has nine stages, which are arranged back-to-back in two sections. The high-pressure compressor is rated at a discharge pressure of 176.5 bar (2,560 psia). Field vibration data were analyzed and compared to the rotordynamic results from the lateral vibration model of the rotor. The root of the subsynchronous vibration was identified to be the destabilizing aerodynamic excitation generated mainly by the intermediate seal and the impellers. To eliminate the subsynchronous vibration, a gas pocket damper seal was designed specially to replace the existing intermediate labyrinth seal. Meanwhile, the existing tilt-pad bearings were replaced with the deflection pivot bearings to further improve the rotordynamic performance. The compressor was tested with the new center seal and journal bearings at full load, full pressure, and full speed. The subsynchronous vibration was eliminated. Now the compressor train operates smoothly at its design conditions and the vibration readings remain low and stable.
Integrated Micro-Turbine and Rotary-Kiln Pyrolysis System as a Waste to Energy Solution for a Small Town in Central Italy: Cost Positioning and Global Warming Assessment
Authors: Fantozzi Francesco , Di Maria Francesco , Desideri Umberto
Published: February 2009

Solid waste, and bio-residuals in general, are usually disposed of or alternatively converted into energy by means of medium to big scale power plants. For isolated communities, usually in protected natural areas, this turns into high energy and waste management costs because of their intrinsic distance from landfills and power plants. Considering also the electric dependency from the grid, small towns are commonly showing low sustainability. This paper focuses on both problems by evaluating the economic feasibility and the global warming contribution of an innovative micro scale waste to energy system based on a microturbine fuelled by waste pyrolysis gas. The plant reaches high efficiency, considering the scale, because of its high regenerative rate and is tailored to the waste disposal needs of Giano Dell’Umbria a small town in central Italy. The economic analysis was carried out, with the Net Present Value method, to determine the expected capital cost of the plant considering that the innovative technology utilized does not allow a reliable cost evaluation. The global warming contribution was calculated considering CO2 and CH4 avoided emission from landfilling and the better CO2 emission rate of such a technology with respect to the status quo. Results obtained show an acceptable cost positioning for the plant that makes it an interesting solution for distributed waste to energy systems. Executive projecting and construction of the proposed technology was funded and a pilot plant will be built and tested in 2002, in a laboratory facility of the University of Perugia.
Gas Turbine Research in the AGTSR Program
Authors: Wenglarz Richard A. , Golan Lawrence P.
Published: February 2009

The South Carolina Institute for Energy Studies (SCIES), administratively housed at Clemson University, has participated in the advancement of combustion turbine technology for nearly a decade. The Advanced Gas Turbine Systems Research (AGTSR) program has been administered by SCIES for the U. S. DOE. Under the supervision of the DOE National Energy Technology Laboratory (NETL), the AGTSR has brought together the engineering departments at the leading U.S. universities and U.S. combustion turbine developers to assist in providing a solid base of knowledge for the future generations of gas turbines. In the AGTSR program, an Industrial Review Board (IRB) of gas turbine companies and related organizations defines needed gas turbine research. SCIES prepares yearly requests for university proposals that address the research needs identified by the IRB organizations. IRB technical representatives evaluate the university proposals and review progress reports from the awarded university projects. Seventy-five (75) AGTSR university projects have been awarded in the areas of gas turbine combustion, aerodynamics/heat transfer, and materials. An overview of recent AGTSR university projects is given in this paper and research results from several of the projects are described in greater detail.
A Thermodynamic Analysis of Different Options to Break 60% Electric Efficiency in Combined Cycle Power Plants
Authors: Chiesa Paolo , Macchi Ennio
Published: February 2009

All major manufacturers of large size gas turbines are developing new techniques aimed at achieving net electric efficiency higher than 60% in combined cycle applications. An essential factor for this goal is the effective cooling of the hottest rows of the gas turbine. The present work investigates three different approaches to this problem: (i) the most conventional open-loop air cooling; (ii) the closed-loop steam cooling for vanes and rotor blades; (iii) the use of two independent closed-loop circuits: steam for stator vanes and air for rotor blades. Reference is made uniquely to large size, single shaft units and performance is estimated through an updated release of the thermodynamic code GS, developed at the Energy Dept. of Politecnico di Milano. A detailed presentation of the calculation method is given in the paper. Although many aspects (such as reliability, capital cost, environmental issues) which can affect gas turbine design were neglected, thermodynamic analysis showed that efficiency higher than 61% can be achieved in the frame of current, available technology.
Orthogonal Shape Functions and Progressive Optimization for the Design of 2D Transonic Cascades
Authors: Catalano L. A. , Dadone A.
Published: February 2009

This paper describes the main ingredients of a recently-developed very efficient formulation for the inverse design of turbomachinery blades in transonic flow conditions. The flow solution is obtained by means of a highly accurate, basic discretization. A discrete adjoint formulation, using a dissipative auxiliary discretization, is employed for a robust and efficient evaluation of the sensitivities, even in presence of shocks. The progressive optimization relies on the simultaneous convergence of the flow computation, of the adjoint problem and of the optimization process itself, as well as on the use of progressively finer grids; the adjoint equations are always solved at the coarsest level, with a further work reduction. The novel contribution of this paper consists of the development of a method for the generation of a set of orthogonal shape functions for a wide and efficient definition of the blade profile. The proposed approach is tested by generating two sets of ten orthogonal curves for the inverse design of a two-dimensional turbine blade in inviscid transonic flow conditions, with fixed stagger angle and with fixed exit angle. The numerical results demonstrate that the methodology is robust and highly efficient, with a converged design optimization produced in no more than the amount of computational work needed to perform from 3 to 5 converged flow analyses on the finest grid.
Emissions Performance of the Macrolaminate Premixer Tested Under Simulated Engine Conditions
Authors: Mansour Adel , Benjamin Michael A.
Published: February 2009

Single injector, high pressure, rig evaluation of the prototype Parker macrolaminate dual fuel premixer (previously tested at NETL, see Mansour et al., 2001) [1] with pressure swirl macrolaminate atomizers was conducted under simulated engine operating conditions running on No. 2 diesel fuel (DF2). Emissions, oscillations and lean blowout (LBO) performance on liquid fuel at high, part and no load operating points (pressures of 160, 100, 120 psig, and inlet temperatures of 690, 570, 590°F, respectively) and various pressure drops (ΔP/P) and air fuel ratio conditions were investigated. The results indicate that the Parker premixer design has the potential to reduce the DF2 NOX emission to below 15 ppmv, 15% O2. At simulated high load conditions with a nominal flame temperature (TPZ) of 2700°F, the NOX and CO emissions are approximately 10 and 2.5 ppmv at 15% O2, respectively. These results compare extremely favorable to existing commercially available premixer technologies tested under similar rig operating conditions. More importantly, the NOX yield for the Parker Macrolaminate premixer appears to be independent of operating conditions (from high to no load and various pressure drop conditions). Variations in combustor pressure, inlet temperature (T2) and residence time (τ) or pressure drop (ΔP/P) does not seem to have an effect on the formation of NOX. According to Leonard and Stegmaier (1993) [2], insensitivity of NOX formation to operating conditions is a good indication of high degree of premixing. Additionally, the premixer NOX data is only 1 to 2 ppmv higher than the jet stirred reactor (JSR) results (ran at T2 = 661°F, PCD = 14.7 psi and TPZ = 2762°F with similar DF2) of Lee et al., 2001 [3], further confirming the quality of premixing achieved. Combustion driven oscillations was not investigated by tuning the rig so that oscillations would not be a factor.
Exceeding 2000 K at Turbine Inlet: Relative Cooling With Liquid for Gas Turbines — Integrated Systems
Authors: Constantin Sandu , Brasoveanu Dan
Published: February 2009

Thermal efficiency of gas turbines is critically dependent on temperature of burnt gases at turbine inlet, the higher this temperature the higher the efficiency. Stochiometric combustion would provide maximum efficiency, but in the absence of an internal cooling system, turbine blades cannot tolerate gas temperatures exceeding 1300 K. This temperature yields a low thermal efficiency, about 15% below the level provide by stoicthiometric combustion. Conventional engines rely on air for blade and disk cooling and limit temperature at turbine inlet to about 1500 K. These engines gain about 3% compared to non-cooled designs. Gas turbines with state of the art air-cooling systems reach up to 1700–1750 K, boosting thermal efficiency by another 2–3%. These temperatures are near the limit allowed by air-cooling systems. Cooling systems with air are easier to design, but air has a low heat transfer capacity, and compressor air bleeding lowers the overall efficiency of engines (less air remains available for combustion). In addition, these systems waste most of the heat extracted from turbine for cooling. In principle, gas turbines could be cooled with liquid. Half a century ago, designers tried to place the pump for coolant recirculation on the engine stator. Liquid was allowed to boil inside the turbine. Seals for parts in relative motion cannot prevent loss of superheated vapors, therefore these experiments failed. To circumvent this problem, another design relied on thermal gradients to promote recirculation from blade tip to root. Liquid flow and cooling capacity were minute. Therefore it was assumed that liquid couldn’t be used for gas turbine cooling. This is an unwarranted assumption. The relative motion between engine stator and rotor provides abundant power for pumps placed on the rotor. The heat exchanger needed for cooling the liquid with ambient air could also be embedded in the rotor. In fact, the entire cooling system can be encapsulated within the rotor. In this manner, the sealing problem is circumvented. Compared to state of the art air-cooling methods, such a cooling system would increase thermal efficiency of any gas turbine by 6%–8%, because stoichimoetric fuel-air mixtures would be used (maybe even with hydrogen fuel). In addition, these systems would recuperate most of the heat extracted from turbine for cooling, are expected to be highly reliable and to increase specific power of gas turbines by 400% to 500%.
CFD Determination of Pre-Chamber Flow Pertubation Inlet Boundary Conditions for Seal Rotordynamics Models
Authors: Venkatesan Ganesh , Rhode David L.
Published: February 2009

A new approach has been developed and utilized to determine the flow field perturbations (i.e. disturbances due to rotor whirl) upstream of a non-contacting seal. The results are proposed for use with bulk-flow perturbation and CFD-perturbation seal rotordynamic models, as well as with fully 3-D CFD models, to specify the approximate inlet boundary flow disturbance values at the computational domain inlet. The radially bulk-averaged disturbance quantities were evaluated in the upstream chamber from nearly 40 cases of geometry/operating conditions. The proposed upstream chamber boundary conditions are applicable for liquid as well as gas seals. For each of the measurement test cases considered, improved agreement with measurements was obtained when using the new boundary conditions, even though there was generally little room for improvement when not using the new boundary conditions. Based on the findings in this study it is recommended that the first-order correlations developed here be used to specify approximate boundary conditions at the domain inlet to be located in the upstream chamber.
Probabilistic Analysis of Solid Oxide Fuel Cell Based Hybrid Gas Turbine System
Authors: Gorla Rama S. R. , Pai Shantaram S. , Rusick Jeffrey
Published: February 2009

The emergence of fuel cell systems and hybrid fuel cell systems requires the evolution of analysis strategies for evaluating thermodynamic performance. A gas turbine thermodynamic cycle integrated with a fuel cell was computationally simulated and probabilistically evaluated in view of the several uncertainties in the thermodynamic performance parameters. Cumulative distribution functions and sensitivity factors were computed for the overall thermal efficiency and net specific power output due to the uncertainties in the thermodynamic random variables. These results can be used to quickly identify the most critical design variables in order to optimize the design and make it cost effective. The analysis leads to the selection of criteria for gas turbine performance.
Effect of Bottoming Cycle Alternatives on the Performance of Combined Cycle
Authors: Yadav R.
Published: February 2009

The increase in efficiency of combined cycle has mainly been caused by the improvements in gas turbine cycle efficiency. With the increase in firing temperature the exhaust temperature is substantially high around 873 K for moderate compressor pressure ratio, which has positive influence on steam cycle efficiency. Minimizing the irreversibility within the heat recovery steam generator HRSG and choosing proper steam cycle configuration with optimized steam parameters improve the steam cycle efficiency and thus in turn the combined cycle efficiency. In this paper, LM9001H gas turbine, a state of art technology turbine with modified compressor pressure ratio has been chosen as a topping cycle. Various bottoming cycles alternatives (sub-critical) coupled with LM9001H topping cycle with and without recuperation such as dual and triple pressure steam cycles with and without reheat have been chosen to predict the performance of combined cycle.
Acoustic Detection of Imminent Blowout in Pilot and Swirl Stabilized Combustors
Authors: Nair Suraj , Lieuwen Tim
Published: February 2009

This paper describes an experimental effort to characterize the acoustic emissions of lean, premixed combustors operating near blowout conditions. Its objective is to use measurements of the flame’s acoustic signature to determine the proximity of the combustor to incipient blowout. The feasibility of the method was performed on two combustors with fundamentally different flame holding methods: externally anchored pilot and swirl-stabilized. Acoustic measurements indicate that the low frequency spectrum exhibits a strong dependence upon the degree of flame stabilization. High speed intensified camera images of the flame were also taken to get a better understanding of the unsteady flame dynamics. In the piloted burner, it became visibly obvious that the flame was approaching blowoff by increased flickering, unsteadiness, and non-symmetric flame attachment. The results from the swirl burner, however, show that the blow-off transient was characterized by short duration, localized extinction and re-ignition events. These events increase in frequency and duration as blowout is approached. Several data analysis approaches using spectral, statistical and wavelet techniques with varying degrees of sensitivity are shown to be capable of detecting precursors to blowout for both burners.
Maisotsenko Open Cycle Used for Gas Turbine Power Generation
Authors: Gillan Leland , Maisotsenko Valeriy
Published: February 2009

The Maisotsenko Open Cycle combines the thermodynamic processes of heat exchange and evaporative cooling in a unique indirect evaporative cooler resulting in product temperatures that approach the dew point temperature, (not the wet bulb temperature) of the working gas. It is an open thermodynamic cycle utilizing several thermodynamic processes that cools a product fluid with a liquid evaporating into a gas, generally water evaporating into air from the atmosphere and returns it to the atmosphere. It is a new cycle as no other cycle can be diagramed in the same way on the psychrometric chart of a gas. In a gas turbine, the gas is air and evaporate is water. An atmospheric pressure heat and mass exchanger operating with the Maisotsenko Cycle can be used to cool compressor inlet air below the wet bulb temperature. In a high-pressure heat and mass exchanger the cycle can create a compressed air saturator using heat from the turbine exhaust gases and also cools water for heat recovery in a compressor inter-cooler. The same saturator will humidify and/or superheat the compressed air before entering a combustor to the amount desired. From a practical stand point the limit of humidification of the compressed air is the amount of heat available at a temperature above its dew point temperature from the exhaust gas and/or intercompressor coolers. The amount of superheating or humidifying of the compressed air is easily controlled and changed during operation allowing added power, or greater efficiency, (60% overall thermal efficiency) quickly and easily. The equipment uses existing shell and tube heat exchanger or plate heat exchangers technologies. There are many other benefits ranging from lower NOx to greatly reduced equipment cost compared to any other power cycle enhancement systems.
Analysis of Electrochemical Performance and Exergy Loss in Solid Oxide Fuel Cell
Authors: Nishida Kousuke , Takagi Toshimi , Kinoshita Shinichi
Published: February 2009

A solid oxide fuel cell (SOFC) is expected to be applied to the distributed energy systems because of its high thermal efficiency and exhaust gas utilization. The exhaust heat from the SOFC can be transferred to the electric power by a gas turbine, and the high efficiency power generation can be achieved by constructing the SOFC and gas turbine hybrid system. In this study, the local processes in the electrodes and electrolyte of unit SOFC are analyzed taking into account the heat conduction, mass diffusion, electrode reactions and the transport of electron and oxygen ion. The temperature and concentration distributions perpendicular to the electrolyte membrane are shown. The effects of the operating conditions on the cell performance are also shown. Furthermore, the entropy generation and exergy loss of each process in the electrodes and electrolyte are analyzed and the reason for generating the exergy loss in the SOFC is clarified. It is noted that two electrode reactions are responsible for the major exergy loss.
Design Optimisation of the Graz Cycle Prototype Plant
Authors: Jericha H. , Go¨ttlich E. , Sanz W. , Heitmeir F.
Published: February 2009

Introduction of closed cycle gas turbines with their capability of retaining combustion generated CO2 can offer a valuable contribution to the Kyoto goal and to future power generation. The use of well established gas turbine technology enhanced by recent research results enables designers even today to present proposals for prototype plants. Research and development work of TTM Institute of Graz University of Technology since the 90’s has lead to the Graz Cycle, a zero emission power cycle of highest efficiency and with most positive features. In this work the design for a prototype plant based on current technology as well as cutting-edge turbomachinery is presented. The object of such a plant shall be the demonstration of operational capabilities and shall lead to the planning and design of much larger units of highest reliability and thermal efficiency.
The Effect of Turbulator Lean on Heat Transfer and Friction in a Square Channel
Authors: Bunker Ronald S. , Osgood Sarah J.
Published: February 2009

An experimental study has been performed to investigate the convective heat transfer coefficients and friction factors present in square cooling passages with non-normal, or leaned turbulators. The standard form of turbulated channels used in virtually all turbine vanes and blades is that of nearly square turbulators, or rib rougheners, cast in an orthogonal orientation to the channel surface. While turbulators may be oriented at an angle to the bulk flow direction, the projection of the turbulator is still normal to the cast surface. Non-orthogonal lean angle presents an additional variable which may be used to improve or optimize performance, a factor hitherto not investigated. The present study has performed a series of experiments measuring both detailed heat transfer coefficient distributions and friction factors within a square channel with flow Reynolds numbers up to 400,000. Turbulator lean angles of 45, 22.5, 0, −22.5, and −45-degrees to the surface normal have been tested with a turbulator configuration of 45-degree orientation to the bulk flow, pitch-to-height ratio of 10, and height-to-hydraulic diameter ratio of 0.1. Results show up to a 20% reduction in heat transfer capability, and as much as 30% increase in friction factor. The local distributions of heat transfer are also more variable with lean angle. The conclusion is made that normal turbulators provide the best overall performance.
Experimental and Numerical Investigation of Trailing Edge Film Cooling by Circular Coolant Wall Jets Ejected From a Slot With Internal Rib Arrays
Authors: Martini P. , Schulz A. , Wittig S.
Published: February 2009

The present study concentrates on the experimental and computational investigation of a cooled trailing edge in a modern turbine blade. The trailing edge features a pressure side cutback and a slot, stiffened by two rows of evenly spaced ribs in an inline configuration. Cooling air is ejected through the slot and forms a cooling film on the trailing edge cutback region. In the present configuration the lateral spacing of the ribs equals two times their width. The height of the ribs, i.e. the height of the slot equals their width. Since the ribs are provided with fillet radii of half the slot height in size, circular coolant jets are exiting the slot tangentially to the trailing edge cutback. The adiabatic wall temperature mappings on the trailing edge cutback indicate that strong three-dimensional flow interaction between the coolant jets and the hot main flow takes place in such a way that two or more coolant jets coalesce depending on the blowing ratio. Experimental and numerical data to be presented in the present study include adiabatic film cooling effectiveness on the trailing edge cutback, the pressure distribution along the internal ribbed passage as well as slot discharge coefficients for different blowing ratios ranging from M = 0.35 to 1.1.
Development of a Durable Catalyst Axial Restraint Structure
Authors: Barnes John E.
Published: February 2009

A unique structural component known as the thermally free axial support or TFA has been developed to restrain a foil substrate catalyst within a gas turbine combustor. Designing a device for this application has been extremely challenging due to competing requirements. Functionally, this support must restrain a catalyst against significant pressure load at temperatures as high as 940°Celsius (C). Enough contact area with the catalyst must exist to avoid foil deformation while at the same time the device must not overly restrict or disturb combustion fluid flow. The aerodynamic performance of the TFA has been validated in actual turbine operation. The TFA is also expected to survive in base loaded gas turbine operation for at least 8000 hours. Long-term durability, crucial to this component since it is upstream of the turbine has been proven with significant analytical and testing efforts. Manufacturing quality assurance and control has been utilized to achieve a consistent product.
Parametric Analysis of Combined Cycles Equipped With Inlet Fogging
Authors: Bhargava R. , Bianchi M. , Melino F. , Peretto A.
Published: February 2009

In recent years, deregulation in the power generation market worldwide combined with significant variation in fuel prices and a need for flexibility in terms of power augmentation specially during periods of high electricity demand (summer months or noon to 6 PM) has forced electric utilities, cogenerators and independent power producers to explore new power generation enhancement technologies. In the last 5–10 years, inlet fogging approach has shown more promising results to recover lost power output due to increased ambient temperature compared to the other available power enhancement techniques. This paper presents the first systematic study on the effects of both inlet evaporative and overspray fogging on a wide range of combined cycle power plants utilizing gas turbines available from the major gas turbine manufacturers worldwide. A brief discussion on the thermodynamic considerations of inlet and overspray fogging including the effect of droplet dimension is also presented. Based on the analyzed systems, the results show that high pressure inlet fogging influences performance of a combined cycle power plant using an aero-derivative gas turbine differently than with an advanced technology or a traditional gas turbine. Possible reasons for the observed differences are discussed.