bluuebunny/crossref_metadata_2025 huggingface dataset:
Status of the European Gas Turbine Program — AGATA
Authors: Gabrielsson Rolf , Lundberg Robert , Avran Patrick
Published: December 2014

The European Gas Turbine Program “AGATA” which started in 1993 now has reached its verification phase. The objective of the program is to develop three critical ceramic components aimed at a 60 kW turbogenerator in a hybrid electric vehicle — a catalytic combustor, a radial turbine wheel and a static heat exchanger. The AGATA partners represent car manufacturers as well as companies and research institutes in the turbine, catalyst and ceramic material fields in both France and Sweden. Each of the three ceramic components is validated separately during steady state and transient conditions in separate test rigs at ONERA, France, where the high pressure/temperature conditions can be achieved. A separate test rig for laser measurements downstream of the catalytic combustor is set up at Volvo Aero Turbines, Sweden.

The catalytic combustor design which includes preheater, premix duct and catalytic section operates at temperatures up to 1623 K. Due to this high temperature, the catalyst initially has undergone pilot tests including ageing, activity and strength tests. The premix duct flow field also has been evaluated by LDV measurements. The full scale combustion tests are ongoing.

The turbine wheel design is completed and the first wheels have been manufactured. FEM calculations have indicated that stress levels are below 300 MPa. The material used is a silicon nitride manufactured by AC Cerama (Grade CSN 101). Cold spin tests with complete wheels have started. Hot spin tests at TTT 1623 K will be performed in a modified turbo charger rig and are expected to start in February 1998.

The heat exchanger is of a high efficiency plate recuperator design using Cordierite material. Hot side inlet temperature is 1286 K. Therefore initial tests with test samples have been run to evaluate the thermomechanical properties at high temperatures. Tests are now proceeding with a 1/4 scale recuperator prototype to evaluate performance at steady state conditions. Manufacturing of the full scale heat exchanger is now in progress.
Short Bearing Model for the Evaluation of Journal’s Dynamic Angular Misalignment Effects on Rotor Vibrations
Authors: Zachariadis Demetrio C.
Published: December 2014

The influence of journal’s dynamic angular misalignment effects on single span flexible rotor vibrations is analysed in a simple system. It comprises a cylindrical plain bearing with two narrow lands separated by an annular groove and a Jeffcott based rotor model. Analytical expressions are presented for all 32 dynamic coefficients of the complete linear bearing model, together with simulation results that provide guidelines for early design stage identification of rotor systems sensitive to angular misalignment.
Comparison of ω-Based Turbulence Models for Simulating Separated Flows in Transonic Compressor Cascades
Authors: Currie Tom C.
Published: December 2014

Separated flows in the DLR transonic compressor cascades TSG-91-8K and TSG-89-5 are simulated with a quasi-3D Navier-Stokes code using the zonal k-ω/k-ϵ “Shear Stress Transport” two-equation turbulence model of Menter and the multiscale Reynolds stress model of Wilcox. Both of these models use the specific turbulent dissipation rate ω as the length scale variable. The models are also used to simulate the low speed, separated flow, adverse pressure gradient test case of Driver. While both models predict results which are in good agreement with experiment for the latter test case, they yield relatively poor results, particularly for losses, for the cascade test cases, especially TSG-89-5 where separation occurs from both the suction and pressure surfaces. It is known from the cascade test results that the separations are laminar, so some improvement in agreement is achieved by suppressing transition to the separation points in the simulations. The poor accuracy of the models is believed to be related to severe non-equilibrium of turbulence production and dissipation predicted after the shock-induced separations.
Strut Influences Within a Diffusing Annular S-Shaped Duct
Authors: Norris G. , Dominy R. G. , Smith A. D.
Published: December 2014

Inter-turbine diffusers which provide flow continuity between the H.P. and L.P. turbines, are increasingly important within modern aero gas turbines, as the fan and hence L.P. turbine diameters increase with thrust. These gas turbines rely on struts within the inter-turbine diffuser to serve both as load bearing supports for inner spools and as passages to supply the engine with vital services such as cooling air and lubrication oil.

Experimental measurements have been made on a representative test rig in order to investigate the affect of a ring of struts on both the local and general flow phenomena as well as investigating their effect on overall duct performance. More realistic flow conditions are made available by the use of inlet wakes representative of those created by an upstream turbine row.

Measurements include static pressures on the strut and duct surfaces along with velocity and total pressure measurements at various axial locations. From these results calculations of total pressure loss have been made. The experimental results presented in this paper have been used to validate C.F.D. flow predictions on the duct with and without struts. The computational results included, capture the main physical features of the flow but clear limitations are observed and are discussed in this paper.
High Pressure Turbine Vane Annular Cascade Heat Flux and Aerodynamic Measurements With Comparisons to Predictions
Authors: Joe Christopher R. , Montesdeoca Xavier A. , Soechting Friedrich O. , MacArthur Charles D. , Meininger Matthew
Published: December 2014

Experimental tests were performed at the USAF Turbine Research Facility (TRF) to obtain heat transfer and aerodynamic data on a first stage vane of a modern high pressure turbine. This is a transient blowdown facility that provides data from short duration tests. Data for a matrix of test conditions were obtained to document the effect of inlet Reynolds number, the stage pressure ratio across the vane, and the gas-to-wall temperature ratio. The objectives of these tests were to assess the capability of obtaining accurate aerodynamic total pressure loss measurements and airfoil static pressure measurements as well as determine the heat transfer coefficient distributions on the vanes. Results from these tests were compared to analytical predictions and are presented. The unique contribution of the work presented herein is: 1) demonstration of circumferential traversing temperature and pressure data in a short duration facility test, and 2) heat loss closure during a short duration test using heat flux gauges and the measured temperature loss. The transient heat loss during a short duration test is a fundamental requirement to determine turbine efficiency when work extraction is determined from the temperature drop across the turbine stage.

Heat transfer data were acquired from heat flux gauges that were fabricated using thin-film sputtering techniques and placed on the airfoil surfaces. The surface temperature of the gauge was measured and heat flux was determined from a closed form transient semi-infinite solution that included the resistance of the heat flux gauge and the underlying metal substrate.

Circumferentially, pressure measurements were obtained on the airfoil surfaces and on traversing rakes at the inlet and exit of the vane test section. Total and differential pressure rake instrumentation was required to obtain accurate aerodynamic loss measurements over a range of gas-to-wall temperature ratios.
NOx Dependency on Residence Time and Inlet Temperature for Lean-Premixed Combustion in Jet-Stirred Reactors
Authors: Rutar Teodora , Horning David C. , Lee John C. Y. , Malte Philip C.
Published: December 2014

The effect of the residence time variation on NOx formation in high-intensity, lean-premixed (LP) methane combustion is explored through experiments conducted in a high-pressure jet-stirred reactor (HP-JSR) operated at 6.5 atm pressure. The residence time is varied between 0.5 ms and 4 ms, holding the measured reactor recirculation zone temperature constant at 1803 K. Air preheat is not used. The results indicate a minimum NOx level of 3.5 ppmvd (15% O2) for reactor mean residence times between 2 and 2.5 ms. As the residence time is reduced from 2.0 ms to 0.5 ms, the NOx increases, consistent with a spreading of super-equilibrium concentrations of free-radicals throughout the reactor. For the shortest residence times examined, PSR modeling agrees with the NOx measurements. At long residence times, (i.e., above 2.5 ms), the measured CO behavior indicates the super-equilibrium free radicals, and thus the rapid NOx production, are confined mainly to the jet zone of the reactor. For the long residence time range, the measured NOx increases with increasing residence time, and is significantly less than the PSR predictions. A simple two-zone model of the HP-JSR is used to interpret and evaluate the NOx formation.

Experiments exploring the effect of inlet temperature on NOx are conducted in an atmospheric pressure, methane-fired, jet-stirred reactor (A-JSR). The reactor temperature is held constant at 1788 K, and the inlet mixture temperature is varied between the no-preheat case and 623 K. These experiments show that increasing the inlet air temperature over the full range tested decreases the NOx by about 30%. Several explanations are offered for the behavior. For both reactors, i.e., the HP-JSR and A-JSR, single inlet jet nozzles are used. The results lead to a practical conclusion that very low NOx levels can be achieved for combustion in strongly back-mixed reaction cavities adjusted to optimal residence time and inlet temperature.
Computations of Discrete-Hole Film Cooling Over Flat and Convex Surfaces
Authors: Lin Y.-L. , Shih T. I-P.
Published: December 2014

Computations were performed to investigate the three-dimensional flow and heat transfer about a flat surface and a convex surface cooled by jets, injected from a plenum through one row of film-cooling holes inclined at 35° with a density ratio of 1.6 and mass flux ratios of 0.5 and 1.0. The focus is on understanding how the mainflow distorts the jets issuing from the film-cooling holes and how the resulting interactions affect film cooling effectiveness and temperature distribution. Results are presented for the surface adiabatic effectiveness, normalized temperature, velocity vector field, and contours of the vorticity magnitude. The computed results for the surface effectiveness on a flat plate were compared with experimental data, and reasonably good agreements were obtained.

This computational study is based on the ensemble-averaged conservation equations of mass, momentum (compressible Navier-Stokes), and energy closed by a low Reynolds number k-ω/SST turbulence model (i.e., wall functions were not used). Solutions were generated by a cell-centered finite-volume method that uses second-order accurate flux-difference splitting of Roe, multigrid acceleration of a diagonalized ADI scheme with local time stepping, and patched/overlapped structured grids. In the computations, the flow is resolved not just in the cooling-jet/mainflow interaction region, but also inside the film-cooling holes and in the plenum.
A 21st Century Warship With a 21st Century Propulsion System
Authors: Carter Mark , Olsson Magnus , Gustavson Jan-Erik , Ranero Joe
Published: December 2014

The Visby Class Corvette will enjoy the advantages of a Combined Diesel or Gas (CODOG) turbine arrangement in which the diesel engines are used for low-speed mine hunting and ASW missions, while the four turbines can be operated either individually or in pairs to provide cruise or high-speed dash capability. The integration of these features into a single gearbox, the design of the Allied Signal model TF50A turbine engine, and the integration of the CODOG system into the ship is discussed herein. Attention is focused on the unique design features which provide the “stealth” capabilities of this ship.
Performance of Turbulence Models and Near-Wall Treatments in Discrete Jet Film Cooling Simulations
Authors: Ferguson Jeffrey D. , Walters Dibbon K. , Leylek James H.
Published: December 2014

For the first time in the open literature, code validation quality data and a well-tested, highly reliable computational methodology are employed to isolate the true performance of seven turbulence treatments in discrete jet film cooling. The present research examines both computational and high quality experimental data for two length-to-diameter ratios of a row of streamwise injected, cylindrical film holes. These two cases are used to document the performance of the following turbulence treatments: 1) standard k-ε model with generalized wall functions; 2) standard k-ε model with non-equilibrium wall functions: 3) Renormalization Group k-ε (RNG) model with generalized wall functions; 4) RNG model with non-equilibrium wall functions: 51 standard k-ε model with two-layer turbulence wall treatment; 6) Reynolds Stress Model (RSM) with generalized wall functions; and 7) RSM with non-equilibrium wall functions. Overall, the standard k-ε turbulence model with the two-layer near-wall treatment, which resolves the viscous sublayer, produces results that are more consistent with experimental data.
Numerical Simulation of a Film Cooled Nozzle Guide Vane Using an Injection Model
Authors: Dahlander Petter , Abrahamsson Hans , Mårtensson Hans , Håll Ulf
Published: December 2014

Numerical simulations of film cooled nozzle guide vanes (NGV) are difficult since resolving the local flow near each cooling hole requires a very fine computational mesh. In this paper an injection model is used to include the coolant in the main flow by adding the influence of the coolant jets to the source terms in the governing equations.

The present method enables simulations of film cooled turbine stages using rather coarse meshes (i.e. not resolving the cooling holes) and gives the possibility to study, for example, the influence of the secondary flows on the coolant distribution. The disadvantage is that some parameters describing the injection need to be determined.

The development and validation of the injection model is performed using fully resolved 3D simulations and experimental data from single cooling jets. The present injection model is used to simulate the film cooled NGV of the research turbine stage MT1 at DERA, Pyestock, UK. Predictions of the heat transfer using the injection model show promising results.
Effect of Inlet Conditions on Lean Premixed Gas Turbine Combustor Performance
Authors: Vilayanur Suresh R. , Davis Nell T. , Samuelsen Scott
Published: December 2014

To address the complex effect of inlet parameters on combustor performance, a statistically based technique is applied to a model, premixed natural gas fired combustor. In this way, multiple parameters are simultaneously investigated for their contribution to combustion performance. Atmospheric tests are performed at conditions otherwise representative of industrial combustors: 670 K. inlet preheat and an equivalence ratio of 0.47. Experimental results, in combination with CFD modeling, reveal that (1) the statistical approach is an effective tool by which parameters that dominate performance can be identified, (2) the principal statistically significant parameter linked to NOx production is the inlet fuel distribution, (3) the principal statistically significant parameter linked to CO production is swirl solidity, and (4) an inlet fuel distribution that features a concentration peak in line with the shear layer of the recirculation zone yields NOx levels comparable to a well premixed case.
Technology and Cost Options for Capture and Disposal of Carbon Dioxide From Gas Turbines: A System Study for Swedish Conditions
Authors: Ekström Clas , Cavani Adrin , Ericson Sven-Olov , Hinderson Anna , Westermark Mats
Published: December 2014

The current and predicted global massive dependency on fossil fuels calls for the exploration of new options to limit the future carbon dioxide (CO2) emissions. One such option that has been studied within the IEA Greenhouse Gas Implementing Agreement, is the capture and disposal of CO2 from combustion gases. Such options for Sweden have been examined in a system study financed by NUTEK (The Swedish National Board for Industrial and Technical Development).

Aquifers that should be suitable for disposal of CO2, exist in the South of Sweden - Denmark and in the Baltic Sea close to Lithuania.

Based on commercially available technologies, CO2 can be captured from NGCC (natural gas combined cycle) and coal based IGCC (integrated gasification combined cycle) power plants. Most of the energy needed for the CO2 capture could then be recovered as district heating, thus maintaining the total energy efficiencies. At approximately 300 MW power production capacities, the heat quantities produced (55–85 MW heat) are likely to be suitable for a reasonable number of the Swedish district heating networks.

CO2 neutral production and utilisation of methanol as an automative fuel for the transport sector integrated with production of electric power and district heat, could be achieved with biomass combined with natural gas or coal as a raw material. An amount of CO2 corresponding to the carbon in the fossil fuel then has to be captured and disposed. Examples of possible process concepts have been examined.

The resulting estimated total costs for capture, transport and disposal of CO2, are in the same order of magnitude as the current Swedish carbon dioxide tax (365 SEK/ton CO2). Plant owners have to be credited for the captured and disposed CO2 in order to make this option economically justifiable and interesting for them.

It will be important for the total economy to find favourable combinations of energy conversion, CO2 capture and recovery, transport and disposal. There is also a need to reduce todays uncertainties in the available basis for estimation of costs for large scale transport, injection and disposal of CO2 into aquifers.
Injector Geometry Effect on Plain Jet Airblast Atomisation
Authors: O’Shaughnessy Paul J. , Bideau Richard J. , Zheng Qing-ping
Published: December 2014

Airblast atomisation drop size is a function of the liquid and gas flow conditions. It is also subject to the atomisation geometry, or more specifically the jet breakup mechanism. Plain jet atomisation featuring coaxial air and fuel flows has been investigated to assess the injector geometry effect on the spray characteristics. Results from various flow conditions and atomiser configurations suggest that a prompt atomisation correlation that was evaluated for prefilming injectors can be applied to plain jet airblast atomisation, in a slightly modified form. Changes in the velocity term are necessary to fit the measured data. A scaling factor has been established to compensate for the velocity term change. This factor may also imply the underlying difference between flat sheet and round jet atomisation. The liquid atomisation mode is dependent not only on the manner of geometrical air-liquid contact but also on flow conditions. In this study, the combined air-fuel velocity ratio VR and Weber number (WeVR) is found to be a criteria that determines the air flow pattern influence on atomisation. Data from this experiment show that a small change in the axial distance between the liquid jet and air orifice entrance results in marked difference in spray drop mean size under low air momentum flow conditions.
Hybrid Vehicle Turbine Engine Technology Support (HVTE-TS) Program 1997–98 Progress
Authors: Berenyi Steven G. , Sinnet George T. , French J. Mark
Published: December 2014

The purpose of this program has been the development of advanced gas turbine engine technologies in support of U.S. Department of Energy (DoE) programs for use in generator sets for hybrid-electric automotive propulsion systems.

Initially the objective of this program had been the development of four key technologies to be applied 10 advanced turbogenerators:

• structural ceramic materials and processes

• low emissions combustion systems

• regenerator and seal systems

• insulation systems and processes.

Of these four, the lack of full program funding has limited 1997 activities to two technologies, i.e.: continued development of ceramics applications and continued regenerator and seal system development.

In late 1997, DoE Office of Transportation Technologies discontinued active sponsorship of this effort, and therefore, the potential application to automotive systems now appears to be delayed. However, the application to stationary engines is very relevant and will proceed.
Separated-Flow Transition: Part 3 — Primary Modes and Vortex Dynamics
Authors: Hatman Anca , Wang Ting
Published: December 2014

This paper clearly identifies the possible modes of transition in the separated boundary layers and their specific characteristics. This study distinguishes between the short and long bubbles primarily based on the separated flow structure. A hypothetical description of the vortex structure and evolution for each separated-flow transition mode is provided.

The present approach in analyzing separated-flow transition is based on the assumption that the transition to turbulence in separated boundary layers is a result of the superposition of the effects of two different types of instability. The first type of instability is the Kelvin-Helmholtz (KH) instability. It occurs and develops in the shear layer at a specific location downstream of the separation point. The concentration of spanwise vorticity grows in time and remains in place through the vortex sheet roll-up mechanism. The roll-up vortex interacts with the wall and induces periodic ejection of near-wall fluid into the separated shear layer. The ejection process takes place at a location identifiable by the maximum displacement of shear layer, xMD.

The second type of instability is the (convective) Tollmien-Schlichting (TS) instability. It originates in the boundary layer prior to the separation point and continues to evolve in the separated shear layer. The mechanism for the TS instability also leads to roll-ups, but it involves viscous tuning of the instability waves. Thus, the separated-flow transition is the result of spatially developing, often competing instabilities. The ejection induces the onset of transition for laminar short and long bubble modes of transition and controls the mid-transition point of transitional separation mode. The ejection may be accompanied by vortex shedding. Shedding occurs in the laminar separation - short bubble mode and occasionally in the transitional separation mode; however, it is not present in the laminar separation - long bubble mode of transition.
Cyclic Oxidation Behavior of Aluminide, Platinum Modified Aluminide, and MCrAlY Coatings on GTD-111
Authors: Cheruvu N. S. , Chan K. S. , Leverant G. R.
Published: December 2014

Cyclic oxidation behavior of aluminide, platinum modified aluminide, and MCrAlY coatings has been investigated at three temperatures. Aluminide and platinum modified coatings were deposited on GTD 111 material using an outward diffusion process. CoCrAlY coating was applied on GTD-111 by Electron Beam Physical Vapor Deposition (EB-PVD). The oxidation behavior of these coatings is characterized by weight change measurements and by the variation of β phase present in the coating. The platinum modified aluminide coating exhibited the highest resistance to oxide scale spallation (weight loss) during cyclic oxidation testing. Metallographic techniques were used to determine the amount of β phase and the aluminum content in a coating as a function of cycles. Cyclic oxidation life of these coatings is discussed in terms of the residual β and aluminum content present in the coating after exposure. These results have been used to calibrate and validate a coating life model (COATLIFE) developed at the Material Center for Combustion Turbines (MCCT).
The Design of an Improved Endwall Film-Cooling Configuration
Authors: Friedrichs S. , Hodson H. P. , Dawes W. N.
Published: December 2014

The endwall film-cooling cooling configuration investigated by Friedrichs et al. (1996, 1997) had in principle sufficient cooling flow for the endwall, but in practice, the redistribution of this coolant by secondary flows left large endwall areas uncooled. This paper describes the attempt to improve upon this datum cooling configuration by redistributing the available coolant to provide a better coolant coverage on the endwall surface, whilst keeping the associated aerodynamic losses small.

The design of the new, improved cooling configuration was based on the understanding of endwall film-cooling described by Friedrichs et al. (1996, 1997). Computational fluid dynamics were used to predict the basic flow and pressure field without coolant ejection. Using this as a basis, the above described understanding was used to place cooling holes so that they would provide the necessary cooling coverage at minimal aerodynamic penalty. The simple analytical modelling developed in Friedrichs et al. (1997) was then used to check that the coolant consumption and the increase in aerodynamic loss lay within the limits of the design goal.

The improved cooling configuration was tested experimentally in a large scale, low speed linear cascade. An analysis of the results shows that the redesign of the cooling configuration has been successful in achieving an improved coolant coverage with lower aerodynamic losses, whilst using the same amount of coolant as in the datum cooling configuration.

The improved cooling configuration has reconfirmed conclusions from Friedrichs et al. (1996, 1997); firstly, coolant ejection downstream of the three-dimensional separation lines on the endwall does not change the secondary flow structures; secondly, placement of holes in regions of high static pressure helps reduce the aerodynamic penalties of platform coolant ejection; finally, taking account of secondary flow can improve the design of endwall film-cooling configurations.
Effect of Fuel Nozzle Configuration on Premix Combustion Dynamics
Authors: Straub Douglas L. , Richards Geo A.
Published: December 2014

Combustion dynamics (or combustion oscillations) have emerged as a significant consideration in the development of low-emission gas turbines. To date, the effect of premix fuel nozzle geometry on combustion dynamics has not been well-documented. This paper presents experimental stability data from several different fuel nozzle geometries (i.e., changing the axial position of fuel injection in the premixer, and considering simultaneous injection from two axial positions). Tests are conducted in a can-style combustor designed specifically to study combustion dynamics. The operating pressure is fixed at 7.5 atmospheres and the inlet air temperature is fixed at 588K (600F). Tests are conducted with a nominal heat input of 1MWth (3MBTUH). Equivalence ratio and nozzle reference velocity are varied over the ranges typical of premix combustor design. The fuel is natural gas. Results show that observed dynamics can be understood from a time-lag model for oscillations, but the presence of multiple acoustic modes in this combustor makes it difficult to achieve stable combustion by simply re-locating the point of fuel injection. In contrast, reduced oscillating pressure amplitude was observed at most test conditions using simultaneous fuel injection from two axial positions.
Visualization and Measurements of Rub-Groove Leakage Effects on Straight-Through Labyrinth Seals
Authors: Rhode David L. , Allen Brian F.
Published: December 2014

For the first time flow visualization images and leakage measurements were obtained and analyzed for an enhanced understanding of the effect of rub-grooves on straight-through labyrinth seal leakage. It was found that leakage resistance decreases sharply with increasing rub-groove axial width. Further, for small tooth clearances with medium- or large-width rub-grooves, the groove gives an approximate 50 percent drop in leakage resistance. At the medium clearance, the presence of medium- or large-width rub-grooves increases and decreases the resistance at low Re and high Re, respectively. At the large clearance, the presence of grooves increases the resistance by some 200 percent and 40 percent for low Re and high Re, respectively. However, large clearance applications generally give very high Re where the 40 percent increase occurs.

In addition, a vena contracta effect from the throughflow jet penetration into the rub-grooves was found on the flow pattern and on the leakage resistance. When penetration occurs, the trajectory angle of the jet entering the subsequent labyrinth cavity is sometimes dramatically altered, giving less kinetic energy carry-over to the subsequent tooth clearance.
Active Structural Control for Gas Turbine Engines
Authors: Morris Robert J. , Benedict Barry K. , Cowles Bradford A. , Stange William A. , Scheuren William J.
Published: December 2014

High cycle fatigue (HCF) is a widespread technical problem in aircraft gas turbines, and can lead to the premature failure of plumbing, pumps, accessory drives and airfoils. Roughly 35% of the problems associated with newer production engines are the direct result of HCF. This paper discusses three innovative technologies that can assist in the avoidance or elimination of high cycle fatigue failures in aircraft gas turbines. This work was performed under the sponsorship and direction of the Defense Advanced Research Projects Agency (DARPA) and the United States Air Force Research Laboratory.
Microstructure/Composition Evolution and Ductility Variation in Thermally Aged Aluminized CoCrAlY Coatings
Authors: Kameda J. , Bloomer T. E. , Sugita Y. , Ito A. , Sakurai S.
Published: December 2014

The effect of thermal ageing at 870 °C for 8000 h in air on the microstructure/composition and mechanical properties (RT and 870 °C) has been studied in aluminized CoCrAlY coatings consisting of four layered structure (region I-IV) of advanced gas turbine blades. Thermal ageing led to a little oxidation/nitridation and a decrease in the Al content in a near surface region I. In a coating region II, coarse Cr rich σ precipitates formed during the thermal ageing. Thermally aged internal (III) and near interface (IV) coating regions showed extensive dispersion of σ and/or Al/Ni rich β/α eutectic precipitates. Small punch tests at RT and 870 °C in air have shown that the coating regions I and II of imaged and aged blades indicated easier formation of brittle cracks regardless of the composition change. The ductility of the regions III and IV at RT and 870 °C, and the low cycle fatigue life of the region III were reduced by the thermal ageing. The mechanical degradation at elevated temperatures in the aged coating regions III and IV is elucidated by taking into account the microstructure/composition evolution and environmental oxidizing effects.
Digital Measuring Borescope System
Authors: McGarry Eugene T.
Published: December 2014

Past attempts at endoscopic measurement have borne many interesting theories yet yielded only limited degrees of success. More important, however, are the users’ concerns for reliability and repeatability as compared to traditional methods of non-destructive test or, in the worst case, the undesirable resolve to top-case a turbine to perform measurement. The operator’s decision to proceed with a major maintenance expenditure or perhaps remove a power plant from service has been, as a rule, based largely on subjective interpretations of what is viewed and measured through a borescope.
Film Thickness, Droplet Size Measurements and Correlations for Large Pressure-Swirl Atomizers
Authors: Benjamin M. A. , Mansour A. , Samant U. G. , Jha S. , Liao Y. , Harris T. , Jeng S. M.
Published: December 2014

A parametric experimental study has been conducted to measure the discharge coefficient, the flow number, the film thickness, the spray angle, the velocity coefficient and droplet size of a large-scale simplex nozzle using ultrasonic and optical techniques. Seventeen nozzle geometries have been studied for three mass flow rates. The large-scale nozzle provides adequate resolution for measurements of film thickness, spray angle, and droplet size. The experimental data collected have been used to derive new and improved correlations for nozzle flow and breakup parameters. It is found that the atomizer constant (ratio of total inlet area to product of the swirl chamber and orifice diameter) is the primary parameter affecting the atomizer performance. As the atomizer constant increases, the discharge and velocity coefficients increase and the spray angle decreases.
Investigation of a Turbulence Model for Wall Cooling of Combustion Chambers
Authors: Abdon Andreas , Sundén Bengt
Published: December 2014

The trend in gas turbine engine combustor design is to use forced convection cooling with enhanced surfaces instead of film cooling. Therefore there is a need to develop reliable design tools for the combustor cooling channels. This work investigates the ability to predict heat transfer and pressure drop in a wide channel with ribs by using the Low Re k-ε model of Launder and Sharma with Yap correction. Different rib sizes and Reynolds numbers are tested and the results are compared to experiments. The results show a large variation in predictive ability for different rib sizes. Some care is recommended when using this turbulence model in engineering applications.
Heat Pipe Combustor Cooling
Authors: Silverstein Calvin C.
Published: December 2014

The general approach which has been taken toward cooling aircraft turbine combustor liners is to utilize a portion of incoming combustor air for film-cooling. In this paper an alternate cooling method is considered, which is referred to as Heat Pipe Combustor Cooling. The conventional film-cooled combustor liner is replaced by a thin, metallic heat pipe liner. Incident heat is transported upstream, and then into to an adjacent compressor discharge air stream. After first acting as a heat sink to cool the liner, the compressor discharge air stream enters the combustor and serves as a supplementary combustion air supply/combustion gas diluent. This dual-use capability effectively doubles the available air supply for liner cooling, extending the turbine inlet temperature range for which metallic construction of the combustor liner is feasible.
Gas Turbine Rotor Disc Repair-Case History
Authors: Mazur Zdzislaw , Kubiak Janusz
Published: December 2014

The 20.65 MW gas turbine experienced catastrophic damage. The failure occurred at the first stage buckets and resulted in damage of the all buckets of this stage. Five rotor disc grooves were also seriously damaged. Additionally, all second stage buckets, first and second stage nozzles, shroud segments, the No 2 bearing casing (turbine side), compressor moving blades, and other elements were damaged. Due to urgent power generation needs, it was decided to repair a seriously damaged stage 1 rotor disc in-situ, and replace all the other damaged parts.

The development of a propietary welding technology for the in-situ repair of the five damaged disc grooves without disc disassembly, and of in-situ disc grooves’ mechanized machining is fully described. The repair process included the removal of damaged grooves, method of groove restoration by welding deposition, stress relief and groove machining to recover their original geometry. After rotor disc repair and assembly, the rotor was put back into service. The approach to the repair of the rotor disc damage has been successful. It enabled significant reductions in expenditure on replacement parts and a reduction of outage time to be achived.
Three Dimensional Unsteady Flow for an Oscillating Turbine Blade and the Influence of Tip Leakage
Authors: Bell D. L. , He L.
Published: December 2014

The results of two investigations, conducted on the aerodynamic response of a turbine blade oscillating in a three dimensional bending mode, are presented in this paper.

The first is an experimental and computational study, designed to produce detailed three dimensional test cases for aeroelastic applications and examine the ability of a 3D time-marching Euler method to predict the relevant unsteady aerodynamics. Extensive blade surface unsteady pressure measurements were obtained for a range of reduced frequency, from a test facility with clearly defined boundary conditions, Bell & He (1997). The test data exhibits a significant three dimensional effect, whereby the amplitude of the unsteady pressure response at different spanwise positions is largely insensitive to the local bending amplitude. The inviscid numerical scheme successfully captured this behaviour, and a good qualitative and quantitative agreement with the test data was achieved for the full range of reduced frequency. In addition, the issue of linearity is addressed and both experimental and numerical tests demonstrate a linear behaviour of the unsteady aerodynamics.

The second, an experimental investigation, considers the influence of tip leakage on the unsteady pressure response of an oscillating turbine blade. Results are provided for three tip clearances. The steady flow measurements show marked increases in the size and strength of the tip leakage vortex for the larger tip gaps and deviations in the blade loading towards the tip section. The changes in tip gap also caused distinct trends in the amplitude of the unsteady pressure at 90% span, which were consistent with those observed for steady flow blade loading. It is the authors opinion, that the existence of these trends in unsteady pressure warrants further investigation into the influence of tip leakage upon the local unsteady flow and aerodynamic damping.
The Influence of Tailboards on Unsteady Measurements in a Linear Cascade
Authors: Ott P. , Norryd M. , Bölcs A.
Published: December 2014

The present paper shows the comparison between steady-state and unsteady results from two versions of a flow solver and measurements in a linear cascade at transonic flow conditions for forced vibration of a single blade.

Experiments have been conducted in a linear test facility with a cascade composed of five turbine blades. The center blade was forced to oscillate in a pure bending mode with a frequency of 160 Hz. Tailboards are fixed in this test facility at the trailing edges of the border blades to create a periodic flow at the outlet of the cascade.

A 2D inviscid flow solver for unsteady flows through vibrating blade rows was adapted to simulate the flow conditions in the linear cascade.

The initial adaptation of the flow solver was the limitation to only one vibrating blade. Comparisons with measurements showed discrepancies which were hypothesized to be due to the presence of the tailboards which can create reflections of pressure waves and shocks.

Therefore, as a second modification of the program, the periodic boundaries downstream of the blades were replaced by solid walls.

Based on these computations it can be concluded that for transonic flows the tailboards have a significant influence on both the steady-state and unsteady flow in the outlet region as well as on the blade in the shock region. In particular, the unsteady data measured in a linear cascade has to be analyzed very carefully to estimate the influence of the tailboards.
Internal Reforming Solid Oxide Fuel Cell-Gas Turbine Combined Cycles (IRSOFC-GT): Part A — Cell Model and Cycle Thermodynamic Analysis
Authors: Massardo A. F. , Lubelli F.
Published: December 2014

The aim of this work is to investigate the performance of Internal Reforming Solid Oxide Fuel Cell (IRSOFC) and Gas Turbine (GT) combined cycles.

To study complex systems involving IRSOFC a mathematical model has been developed that simulates the fuel cell steady-state operation. The model, tested with data available in literature, has been used for a complete IRSOFC parametric analysis taking into account the influence of cell operative pressure, cell and stream temperatures, fuel-oxidant flow rates and composition, etc.

The analysis of IRSOFC-GT combined cycles has been carried out by using the ThermoEconomic Modular Program TEMP (Agazzani and Massardo, 1997). The code has been modified to allow IRSOFC, external reformer and flue gas condenser performance to be taken into account. Using as test case the IRSOFC-GT combined plant proposed by Harvey and Richter (1994) the capability of the modified TEMP code has been demonstrated.

The thermodynamic analysis of a number of IRSOFC-GT combined cycles is presented and discussed, taking into account the influence of several technological constraints. The results are presented for both atmospheric and pressurised IRSOFC.
Diffusion Bonding of CMSX-4 to Udimet 720 Using PVD-Coated Interfaces and HIP
Authors: Larker Richard , Ockborn Johan , Selling Bengt
Published: December 2014

There is an increasing interest in development of manufacturing methods for Dual Property BLISKs, consisting of creep resistant airfoils and fatigue resistant disks bonded together by a durable joint. Optimum heat treatments are, however, very different for creep resistant single crystal CMSX-4 and fatigue resistant poly-crystalline Udimet 720 selected in this study, but fortunately the first ageing treatment for CMSX-4 (1140°C, 2–6h, AC) is similar to the partial solution treatment of U 720 HS2 (1115°C, 4h, OQ).

Based on this, diffusion bonding was performed by HIP at 1120°C and 200 MPa argon pressure for 4h, followed by cooling to 400°C. Subsequently, a shortened Udimet 720 HS2 two-step ageing treatment was adopted by heating to 650°C for 6h followed by cooling to 400°C, heating to 760°C for 2h, and finally cooling to R.T. under remaining HIP pressure.

Plasma etching followed by thin (80 nm) PVD coating with either nickel or titanium were used to clean and protect the polished surfaces before joining. The selection of coatings was governed by the possibility to reduce oxidized nickel by flushing with hydrogen at 330°C during evacuation of the HIP capsules, and by the large solubility of oxygen in titanium.

Hot tensile testing was performed at 750°C on both joined and reference materials subjected to the modified heat treatment. Initially solution treated Udimet 720 and CMSX-4 comprised the reference materials. The testing showed that joints with Ni-PVD coatings were almost as strong as Udimet 720 (although with very limited elongation), while the joints with Ti-PVD coatings were weaker.
Experimental Analysis and Numerical Simulation of the Flow Field in Turbine Scrolls
Authors: Menter Uwe W. , Klima Thomas , Pfost Heiner
Published: December 2014

A large selection of one- and two-dimensional methods can be used to calculate the scroll geometries. This paper examines the consequences of different scroll geometry parameters under various flow configurations, including the influence of components in the scroll flow field.

A combination of arrangements of the various components was investigated, (scroll/nozzle/rotor, scroll/nozzle/stator, scroll/vane support/rotor, scroll/vane support/stator), to see how the flow varied. In this particular case a frictionless scroll was designed. The turbine operates with a gas fluid. Using a non-invasive laser two-focus technique and wall pressure drillings the flow field was measured over three scroll cross sections and over its extent at φ = 186° up to φ = 211°. The theoretical analysis was performed on a computer using a commercial 3D finite element programme. Using the programme enables the theoretical flow fields of various scroll geometries to be calculated. The validity of the calculations can be assessed by comparing the theoretical calculations with the above mentioned measurements.

The measurements show that by using a rotor the flow field inside the scroll remains uninfluenced by the vane support and nozzle. Measurable differences appear when the rotor is replaced by a stator, these results are confirmed by the computer program. The calculations also show that the scroll geometry has an important effect on the development of the flow field.
Comparison of defects in crystalline oxide semiconductor materials by electron spin resonance
Authors: Matsuda Tokiyoshi , Kimura Mutsumi
Published: December 2014

Defects in crystalline InGaZnO4 (IGZO) induced by plasma were investigated using electron spin resonance (ESR). Thermal stabilities and ɡ factors of two ESR signals (A and B observed at ɡ = 1.939 and 2.003, respectively) in IGZO were different from those of the ESR signals observed in component materials such as Ga2O3 (signal observed at ɡ = 1.969), In2O3 (no signal), and ZnO (signal observed at ɡ = 1.957). Signal A in IGZO increased upon annealing at 300 °C for 1 h, but decreased when annealing was continued for more than 2 h. On the other hand, signal B decreased upon annealing at 300 °C for 1 h. The ESR signal in ZnO decayed in accordance with a second-order decay model with a rate constant of 2.1 × 10−4 s−1; however, this phenomenon was not observed in other materials. This difference might have been due to randomly formed IGZO lattices such as asymmetrical (Ga, Zn)O and In-O layers. Defects in signals A and B in IGZO were formed in trap states (at the deep level) and tail states, respectively.
Electrical properties of ultrathin titanium dioxide films on silicon
Authors: Dutta Shankar , Leeladhar  , Pandey Akhilesh , Thakur Om Prakash , Pal Ramjay
Published: December 2014

Ultrathin (<50 nm) titanium dioxide (TiO2) films are being widely investigated as high-k dielectrics for future metal oxide semiconductor (MOS) technology. In this paper, ultrathin TiO2 films (∼20 nm) were deposited on silicon substrates by sputtering technique and subsequently annealed at 800 °C in oxygen environment for different durations (15–60 min). The annealed films were polycrystalline in nature with rutile phase. The value of dielectric constant was found to be 32–60 at 1 kHz measurement frequency. Threshold voltages of the MOS structures were found to vary from −0.1 to −0.5 V with the duration of annealing. Leakage current density (1 × 10−2–1 × 10−8 A/cm2 at 1 V) and dielectric breakdown fields (8.15–9.8 MV/cm) were observed to improve with annealing time.