bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Investigation on a Stator Vane Bypass Transition Over a Separation Bubble Using v′2-f and LCL-Models
Authors: Heidecke Axel , Stoffel Bernd
Published: September 2008

With this paper, results of a numerical investigation of the influence of the inlet condition variation on a stator vane suction side boundary layer and its separation tendencies are presented. The profile used for the examination is a so called high-lift-profile and designed for a laminar-turbulent transition over a steady separation bubble in a 1.5-stage low pressure turbine. Hence, the turbulence model must be capable for these effects. Especially, the stream line curvature has to be kept properly which leads to higher level turbulence models. The calculations were conducted with a two-dimensional Navier-Stokes solver using a finite volume discretisation scheme. The turbulence models used are the v′2-f and the LCL turbulence model which are both of higher order. In the first part of the paper, wake free averaged inflow conditions were used. Through this, the influence of the mean flow on the bubble could be examined.
Portable Optical System for In-Situ Thermal Barrier Assessment of Service Operated Blades
Authors: De Maria Letizia , Rinaldi Claudia , Lupetin Piero , Sergo Valter
Published: September 2008

Thermally Grown Oxide (TGO) layer develops and grows subjected to very high compressive residual stresses at the interface between metallic bond coat and EB-PVD thermal barrier coating. A significant decrease of such stress level is a useful indicator of incipient local detachment of the TBC. Photo-Stimulated Luminescence Piezo Spectroscopy (PLPS) provides information on the TGO stress state. In this paper a new portable PLPS instrument is described, developed to allow the in shop detection of PLPS signals on service operated blades with TBCs, to detect incipient failure. The instrument capability was verified comparing its results with the measurements performed with a commercial instrument on both TBC coated specimens aged in laboratory conditions and on new and operated components. The results confirm the system capability of prematurely detect and localise initial damage processes, before spallation of the TBC. A miniaturised probe was shaped to perform the PLPS measurement also at the leading edge. Finally the first in-shop application of the prototype is discussed starting from the results of the damage level assessment performed on operated first stage blades of a V94.3A2 gas turbine.
Modeling of Combustion Noise in Turbulent, Premixed Flames
Authors: Kok Jim B. W. , de Jager Bram
Published: September 2008

In regular operation all gas turbine combustors have a significant noise level induced by the turbulent high power flame. This noise is characteristic for the operation as it is the result of the interaction between turbulence and combustion. Pressure fluctuations may also be generated by thermoacoustic instabilities induced by amplification by the flame of the acoustic field in the combustor. This paper focuses on prediction of the former process of the noise generation in a premixed natural gas combustor. In order to predict noise generated by turbulent combustion, a model is proposed to calculate the power spectrum of combustion noise in a turbulent premixed natural gas flame on the basis of a steady state RaNS CFD analysis. The instantaneous propagation of acoustic pressure fluctuations is described by the Lighthill wave equation, with the combustion heat release acting as a monopole source term. For a semi infinite tube the solution can be written as a volume integral over the acoustic domain using a Green’s function. The source term is written as a function of a reaction progress variable for combustion. Finite chemical kinetics is taken into account by using the TFC model, and turbulence is described by the k-ε model. Subsequently the volume integral for the noise field is evaluated for the turbulent situation on basis of the calculated steady state combustion solution and presumed shape probability density function weighting. The k- ε model provides the parameters for the presumed spectrum shape. Experiments have been performed in a 100 kW preheated premixed natural gas combustor. Comparison of predicted sound spectra with experimental results shows that the model is capable of prediction of the Sound Pressure Level. The modeled spectrum agrees well with the trends observed in the measured spectra.
Design for Service: Harmonising Product Design With a Services Strategy
Authors: Harrison Andrew
Published: September 2008

Over the last 10 years, the airline industry has come under increasing pressure to reduce operating costs and provide an improved service in an environment of declining revenues. As a result, operators expect engine suppliers to provide more efficient and reliable products and services, with lower and more predictable operating costs. In particular, the creation of long term service agreement offerings such as Rolls-Royce TotalCare™ align the goals of the Original Equipment Manufacturer (OEM) and the operator in ensuring that engines keep flying with minimal disruption at minimised cost. Whilst great strides can be made to optimise cost of ownership around existing products the real potential for quantum reductions comes when the product and service are designed in harmony. This requires a cultural shift from ‘offering a Service around an existing Product’ to ‘designing a Service and the Product that supports it’. In 2002 a programme was launched within Rolls-Royce plc to create and deploy an improved process for ensuring our new products are truly ‘Designed for Service’. This has encompassed a cultural change programme, working practice and process changes, enhanced tools and technique development and embodiment of control systems within the design change process gates. The Trent 1000 engine for the Boeing 787 is the first Rolls-Royce new product to have fully deployed ‘Design for Service’ from its earliest stages of preliminary design. The process has already driven both architectural and detailed design change. This attention to detail from the earliest stages of design is fully expected to ensure that the Trent 1000 is the lowest cost of ownership solution for the Boeing 787 aircraft. This paper discusses the elements of the process, including some of the problems and successes experienced during this initial application.
Reduced Kinetic Mechanism for Reactive Flow Simulation of Syngas/Methane Combustion at Gas Turbine Conditions
Authors: Gokulakrishnan P. , Kwon S. , Hamer A. J. , Klassen M. S. , Roby R. J.
Published: September 2008

The reduced kinetic mechanism for syngas/methane developed in the present work consists of a global reaction step for fuel decomposition in which the fuel molecule breaks down into CH2O and H2. A detailed CH2O/H2/O2 elementary reaction sub-set is included as the formation of intermediate combustion radicals such as OH, H, O, HO2, and H2O2 is essential for accurate predictions of non-equilibrium phenomena such as ignition and extinction. Since the chemical kinetics of H2 and CH2O are the fundamental building blocks of any hydrocarbon oxidation, the inclusion of detailed kinetic mechanisms for CH2O and H2 oxidation enables the reduced mechanism to predict over a wide range of operating conditions provided the reaction rate parameters of fuel-decomposition reaction is optimized over those conditions. Therefore, the rate coefficients for the fuel-decomposition step are estimated and optimized for the ignition delay time measurements of CH4, H2, CH4/H2, CH4/CO and CO/H2 mixtures available in the literature over a wide range of pressures, temperatures and equivalence ratios that are relevant to gas turbine operating conditions. The optimized reduced mechanism, consisting of 15 species and around 40 reactions, is able to predict the ignition delay time and laminar flame speed measurements of CH4, H2, CH4/H2, CH4/CO and CO/H2 mixtures fairly well over a wide range conditions. The model predictions are also compared with that of GRI3.0 mechanism. The reduced kinetic mechanism predicts the ignition delay time of CH4 and CH4/H2 mixtures far better than GRI mechanism at higher pressures. To demonstrate the predictive capability of the model in reactive flow systems, the reduced mechanism was implemented in Star-CD/KINetics commercial code using a RANS turbulence model to simulate CH4/air premixed combustion in a backward facing step. The CFD model predictions of the stable species in the exhaust gas agree well with the GRI mechanism predictions in a chemical reactor network modeling by approximating the backward facing step with a series of perfectly-stirred reactor and plug-flow reactor.
Heat Transfer Measurements in a First Stage Nozzle Cascade Having Endwall Contouring: Misalignment and Leakage Studies
Authors: Piggush J. D. , Simon T. W.
Published: September 2008

This work supports new gas turbine designs for improved performance by evaluating endwall heat transfer rates in a cascade that is representative of a first stage stator passage and incorporates endwall assembly features and leakage. Assembly features, such as gaps in the endwall and misalignment of those gaps, disrupt the endwall boundary layer, typically leading to enhanced heat transfer rates. Leakage flows through such gaps within the passage can also affect endwall boundary layers and may induce additional secondary flows and vortex structures in the passage near the endwall. The present paper documents leakage flow and misalignment effects on the endwall heat transfer coefficients within a passage which has one axially-contoured and one straight endwall. In particular, features associated with the combustor-to-turbine transition piece and the assembly joint on the vane platform are addressed.
A Simple and Accurate Interferometric Fringe Analysis Tool for Skin Friction Measurements
Authors: Holley Brian M.
Published: September 2008

Oil film interferometry (OFI) is a measurement technique used to evaluate local wall shear stress and limiting streamline direction. It has been applied to aircraft wings in wind tunnel testing and in turbine cascade testing. The accuracy of the technique is largely dependent on the analysis of interferograms. A new technique for interferogram analysis is presented that is simple and particularly well suited to analyzing interferograms characterized by few fringes. For example, limited fringe definition can occur from dust contamination on the pressure surface of turbine airfoils during cascade wind tunnel testing. The new technique is described and illustrated with examples.
A Neural Network Based Adaptive Observer for Turbine Engine Parameter Estimation
Authors: Shankar Praveen , Yedavalli Rama K.
Published: September 2008

Estimation of immeasurable parameters such as thrust and turbine inlet temperatures in turbine engines constitutes a significant challenge for the aircraft community. A solution to this problem is to estimate these parameters from the measured outputs using an observer. Currently existing technologies rely on Kalman and extended Kalman filters to achieve this estimation. This paper presents an adaptive observer that augments the linear Kalman filter with a neural network to compensate for any nonlinearity that is not handled by the linear filter. The neural network implemented is a Radial Basis Function Network that is trained offline using a growing and pruning algorithm. The adaptive observer is used to estimate HPT inlet temperature, thrust and stall margins.
Performance Evaluation of Gas Turbine Cogeneration Plants Using a Design Optimization Tool: OPS-Design
Authors: Yokoyama Ryohei , Ito Koichi
Published: September 2008

To attain the highest performance of gas turbine cogeneration plants, it is important to rationally determine their structures as well as equipment numbers and capacities in consideration of their operational strategies corresponding to seasonal and hourly variations in energy demands. However, it needs much task and time. In this paper, a design optimization tool named “OPS-Design” is developed to determine the structures as well as equipment numbers and capacities for given super structures of energy supply plants. This tool uses optimization approaches based on the mixed-integer linear programming, and has a user-friendly interface for the functions of data registration, graphical flowsheet editing, automatic programming and optimization calculation, and graphical representation of results. In addition, the performance of a gas turbine cogeneration plant is evaluated using the tool in terms of the annual total cost and primary energy consumption. It is demonstrated that the tool is very effective to evaluate the performance rationally, easily, and flexibly.
Robust Design: Methods and Application to Real World Examples
Authors: Karl A. , May G. , Barcock C. , Webster G. , Bayley N.
Published: September 2008

Recent developments in computer capabilities and software have enabled the application of deterministic optimisation and Robust Design methods in real-world aero-engine development programmes. This paper describes both the methods used and several applications of this technology. Using automated processes, deterministic optimisation, and especially Robust Design methods, an increased product quality and reliability have been achieved, while at the same time producing a considerable decrease in development time and cost. It is the application of Robust Design methods that leads to increased product quality and reliability, as deterministic optimisation methods alone often drive on to constraint boundaries, leading to “cliff-edge” designs.
An Investigation of Lock Plate Flow
Authors: Childs Peter , Pizarro de la Fuente Carlos
Published: September 2008

Lock plates are used on some turbine disc assemblies to secure the location of the blades. The pressure ratio across blade roots and the associated clearances inevitably means that there is some leakage through the abutting mating surfaces of the lock plates. This flow is ejected into the corresponding stator well or rotor-stator disc wheelspace. The aim of this study was to investigate the level of penetration of this flow and therefore its potential impact on and interaction with the wheelspace flow and associated heat transfer. Given the low mass flow associated with this leakage, typically less than one percent of the mainstream annulus flow, generation of the validation data was undertaken using a representative wind tunnel slot array. This paper reports the experimental data and corresponding CFD flow predictions and discusses the resultant insight obtained. For the experiments and associated modeling undertaken it was found that the injected flow did not penetrate the cross flow boundary layer for either normal or inclined injection.
Real-Time Engine Modelling of a Three Shafts Turbofan Engine: From Sub-Idle to Max Power Rate
Authors: Kim Sogkyun , Ellis Sean , Challener Mark
Published: September 2008

Real-Time Engine Models are required for operation with engine electronic control systems and/or aircraft simulators for functional demonstration. The challenge for Rolls-Royce has been to establish the sub-idle speed behaviour of the engine. This paper covers the development steps by the Civil Aerospace Modelling and Simulation team to resolve this limitation in the models. The real-time engine model is now generated using two non-linear thermodynamic engine models. One of the thermodynamic engine models, normal range, covers the idle to max power range and the other is for sub-idle operation. Previously sub-idle operation was established by extrapolation from the normal range model. However, this method limited control system development by simulation for altitude starting adding time to altitude test programmes in high cost facilities. The requirement for the technique is to obtain the partial derivatives and steady-state data for the whole operating range. For the partial derivative estimation in sub-idle region, a variable perturbation size is introduced and changed according to the different shaft speed so that the sensitivity issue of using a fixed perturbation size in this operating range is resolved. Furthermore, the partial derivative of each parameter from the non-linear models is fine tuned by comparing with the steady-state values for each parameter. The summation of the integrated partial derivatives should be same as the steady-state value of each engine parameter. If an error exists then an adjustment of each integrated partial derivative is conducted according to the relative weight of each integrated partial derivatives contribution to the whole. It is highlighted that error sharing between the integrated partial derivative parameters results in less error during the validation process. The real-time engine model is constructed in state-space modular subsystems in SIMULINK, which include an engine shaft block to generate the engine shaft speeds, and fuel block to generate a signal of engine lit, etc. The database generated by the process of partial derivatives is then used in calculation of engine’s shaft speeds, temperatures and pressures. For the test of the real-time engine model obtained in this study, simulation of engine starting from stationary is conducted. Using a starter torque as the input to the engine model, starter-assisted starting can be achieved. In addition, engine relighting in flight is also conducted. The output of the real-time engine model has been compared with flight test data for engine relight and agreement has been demonstrated.
An Investigation of the Use of Wet Compression in Industrial Centrifugal Compressors
Authors: Abdelwahab Ahmed
Published: September 2008

Industrial centrifugal compressors generally comprise a number of low pressure ratio intercooled stages. This is done primarily for the purpose of reducing the compressor power requirements and improving the operating range of the multi-stage compressor. In recent years, however, rapid increases in the per-kilowatt-hour prices both domestically and worldwide has led to renewed research efforts to further reduce the power requirements of this type of compression equipment. Several attempts have been made to use direct water injection as a means to overspray the compressor inlet to further reduce its power requirement. This paper presents an investigation into the use of this technology in industrial centrifugal compressors. A simple numerical method is presented for the computation of wet compression processes. The method is based on both droplet evaporation and compressor mean-line calculations. An assessment, based on the developed model, of the effectiveness of evaporative processes in reducing the compressor power consumption per stage is presented. The impacts on stage efficiency and operating range are also presented.
Numerical Analysis of a Laboratory Centrifugal Pump for the Training of Graduate Engineers
Authors: Cenci G. , Pinelli M.
Published: September 2008

The up-to-date design of turbomachinery involves the use of three dimensional computational fluid dynamic analyses to match the challenge of the ever increasing speed of product development. Recently, the application of these analyses to turbomachinery, which in past years was confined to specialist fields, has become widespread in many industrial applications. Hence, besides the teaching of traditional methods for turbomachinery design, an important part of modern engineering education is to produce graduates with advanced skills in Computational Fluid Dynamics (CFD) techniques applied to turbomachinery design. Moreover, at this time, these skills should either match the needs of research laboratories or be compatible with industrial needs, since three dimensional numerical calculation is also coming to be seen as a feasible tool in ordinary applications. For these reasons, CFD courses for the training of graduate students have been developed. In this paper, the methodology followed and the work carried out by the students of the course in Fluid Dynamic Design of Turbomachinery held at the University of Ferrara is presented. In particular, three levels of investigation are taken into consideration and presented: (i) focus on the fundamentals to achieve a basic knowledge of a design process based on numerical simulation; (ii) extension to higher level of in-depth analyses of the specific models which could be used in every phase of a numerical simulation; (iii) insight into the specificity of the main thermodynamic and fluid dynamic characteristics of turbomachinery. To achieve this, the numerical analysis of a simple but exhaustive geometry of a centrifugal pump has been carried out and the results obtained are analyzed. In particular, special emphasis is devoted to: (i) the comparison among the numerical models which can be chosen throughout the simulations of turbomachinery (type of grid, turbulence models, rotor/stator interface models) and (ii) the analysis of some of the most important fluid dynamic phenomena, such as, in this case, velocity profiles and jet-and-wake structure.
Optical Study of Combustor Reaction Zone
Authors: Levy Y. , Lev M. , Ovcharenko V.
Published: September 2008

Measurements of emitted radiation from the gases within the reaction zone of a combustor were performed. The combustor was a 30% flat (rectangular) model of an annular combustion chamber of a turbojet-engine. Nonpremixed, turbulent combustion was fueled by kerosene. The equivalence ratios were within the range of 0.15–0.75. The combustor had two quartz windows permitting optical observation of the combustion process. In an earlier work, the infrared emission from the efflux gases, the combustion products, just outside of the combustor exit plane, was investigated using an infrared camera, equipped with an interference bandpass filter. In the present study, infrared images of the combustion inside the chamber were obtained. The location of the high temperature recirculation zones can be identified in the infrared images obtained by the camera. In the visible spectral range, the emission of CH* radicals and C2* molecules from within the combustion chamber was investigated through the quartz window. These species exist within the reaction zones and play an important role in the combustion mechanism. Their excitation is mainly due to the chemical reactions and so they can serve for diagnosis of combustion processes in reaction zones. The emission from the combustor, in the visible range, was recorded with the aid of a fiber-optic based spectrometer. Local measurements of the emissions of the Swan bands of C2* molecules at 471 nm, 513 nm, 560 nm, vibronic band of CH* radicals at 431 nm and continuum emission of carbonaceous products of pyrolysis were recorded along the combustor centerline. The intensity is correlated with location of the combustion zones. The distribution of the emission was observed as being dependent on the global equivalence ratio.
Experimental Analysis of Air/Oil Separator Performance
Authors: Willenborg K. , Klingsporn M. , Tebby S. , Ratcliffe T. , Gorse P. , Dullenkopf K. , Wittig S.
Published: September 2008

Within the European research project ATOS (Advanced Transmission and Oil System Concepts) a systematic study of the separation efficiency of a typical aero-engine air/oil separator design was conducted. The main objectives were to obtain a basic understanding of the main separation mechanisms and to identify the relevant parameters affecting the separation efficiency. The results of the study contribute to an optimised separator technology. Nonintrusive optical measurement techniques like laser diffraction and multiple wavelength extinction were applied to analyse the separation efficiency and identify potential optimisation parameters. Oil mist with defined oil droplet size distribution was supplied to the breather. By simultaneously measuring particle size and oil concentration upstream and downstream of the breather the separation mechanism was analysed and the separation efficiency was assessed. In addition, the pressure drop across the separator was measured. The pressure drop is an important design feature and has to be minimised for proper sealing of the engine bearing chambers. The experimental programme covered a variation of airflow, oil flow, shaft speed, and droplet size. The main emphasis of the investigations was on the separation of small droplets with a diameter of up to 10 μm. The following trends on separation efficiency of small droplets were observed: the separation efficiency increases with increasing rotational speed, with increasing particle size and with decreasing air flow rate. In parallel, the pressure drop across the breather increases with increasing speed and increasing airflow.
Thermal Modeling of HRSG Transient Behavior in Combined Cycle Power Plants
Authors: Sanaye Sepehr , Rezazadeh Moein , Oladi Jalaleddin , Sadeghpoor Gholam Hossein , Bashiri Farid , Sahebi Jamshid
Published: September 2008

Combined Cycle Power Plants (CCPP) are attractive electricity generation systems due to high cycle efficiency and quick response of the system to load change. Heat recovery steam generator (HRSG) is an important part of a CCPP and it is important to predict the HRSG operating conditions in transient and steady state modes. It should be emphasized that the biggest pressure and thermal stresses are imposed on HRSG superheater and evaporator tubes banks during transient periods (cold start up and load change). Due to these effects a software program was developed for analyzing the HRSG transient and steady state operating conditions. The HRSG software included arbitrary number of pressure levels (usually up to three) and any number of elements (superheater, evaporator, economizer, desuperheater and duct burner). In this paper theories and equations (mass/energy balance and heat transfer coefficients) applied for HRSG thermal analysis are described. Also HRSG program software outputs were compared with real data collected from HRSG cold start-up at Tehran CCPP with specified geometry and arrangement of elements. The closeness of two groups of data in this transient and steady state modes was acceptable. The numerical outputs in steady state condition also were found very close to GT MASTER program software outputs.
Thermal and Economic Analysis of Gas Turbine Steam Injection Plant
Authors: Sanaye Sepehr , Mahdikhani Vahid , Karimeddini Ziaeddin Khajeh , Sadri Gholamreza
Published: September 2008

Steam injection into gas turbine combustion chamber increases the power output and lowers the NOx emissions. Steam may be produced in a heat recovery steam generator (HRSG), using gas turbine exhaust gases. Steam which is usually injected with pressure of combustion chamber, increases the mass flow rate flowing through turbine and decreases the combustion temperature, hence, lowering the amount of NOx emissions. This power augmentation method is usually used for gas turbines with power outputs in range of 2–50 MW with one pressure level in HRSG. In this paper the optimum design parameters of the above mentioned system is obtained for the above range of gas turbine power output. For doing this task an objective function is introduced which contains the economic and thermal characteristics of the system. This objective function is minimized when gas turbine exhaust temperature, compressor pressure ratio, isentropic efficiency of compressor and turbine, fuel mass flow rate (natural gas), inlet air mass flow rate, and the amount of injected steam mass flow rate vary.
Fuel Cell/Gas Turbine Hybrid System Control for Daily Load Profile and Ambient Condition Variation
Authors: Roberts Rory A. , Brouwer Jack , Samuelsen G. Scott
Published: September 2008

Fuel Cell/Gas Turbine (FC/GT) hybrid technology is promising, but introduces challenges in system operation and control. For base-load applications, changes in ambient conditions perturb the system and it becomes difficult to maintain constant power production by the FC/GT system. If the FC/GT hybrid system is load-following then the problem becomes even more complex. In the current study, a dynamic model of a FC/GT power plant is developed with system controls. Two cases are evaluated: (1) system controls are developed to maintain constant power and process control within acceptable constraints, (2) the FC/GT power plant is set in power following mode connected in parallel to the grid for a daily load profile scenario. Changing ambient conditions are employed in the dynamic analysis for both cases. With appropriate attention to design of the system itself and the control logic, the challenges for dynamic system operation and control can be addressed.
Simulation of Mist Film Cooling at Gas Turbine Operating Conditions
Authors: Wang Ting , Li Xianchang
Published: September 2008

Air film cooling has been successfully used to cool gas turbine hot sections for the last half century. A promising technology is proposed to enhance air film cooling with water mist injection. Numerical simulations have shown that injecting a small amount of water droplets into the cooling air improves film-cooling performance significantly. However, previous studies were conducted at conditions of low Reynolds number, temperature, and pressure to allow comparisons with experimental data. As a continuous effort to develop a realistic mist film cooling scheme, this paper focuses on simulating mist film cooling under typical gas turbine operating conditions of high temperature and pressure. The mainstream flow is at 15 atm with a temperature of 1561K. Both 2-D and 3-D cases are considered with different hole geometries on a flat surface, including a 2-D slot, a simple round hole, a compound-angle hole, and fan-shaped holes. The results show that 10%–20% mist (based on the coolant mass flow rate) achieves 5%–10% cooling enhancement and provides an additional 30–68K adiabatic wall temperature reduction. Uniform droplets of 5 to 20 μm are used. The droplet trajectories indicate the droplets tend to move away from the wall, which results in a lower cooling enhancement than under low pressure and temperature conditions. The commercial software Fluent (v. 6.2.16) is adopted in this study, and the standard k-ε model with enhanced wall treatment is adopted as the turbulence model.
Damage and Degradation Assessment of Stage 1 Bucket Coatings in a 1,100° C-Class Gas Turbine
Authors: Yoshioka Yomei , Saito Daizo , Okamoto Hiroaki , Ito Shoko , Ishibashi Kazutoshi
Published: September 2008

According to increasing the inlet temperature of gas turbines, the role of coating is getting more and more important for the bucket life. It is, therefore, very important to understand the actual phenomena of the bucket coatings under the operation. Four different kinds of new and serviced stage 1 bucket coatings for 1,100°C-class gas turbines, such as a platinum-aluminide diffusion coating and overlay-type coatings of CoCrAlY, over-aluminized CoCrAlY and CoNiCrAlY, were selected and evaluated nondestructively and destructively at every inspection times. The platinum-aluminide and over-aluminized CoCrAlY coatings suffered from heavy cracking that propagated from the root of the airfoil to the tip during operations, but the CoCrAlY and CoNiCrAlY coatings did show little or no cracking. The degrees of oxidation and microstructure degradation were also different not only coating by coating, but also the locations of the airfoil surface due to the surface temperature distributions. To understand precisely the actual phenomena, hardness and 3-point bend tests at room and elevated temperatures were conducted by using the new and serviced bucket coatings and figured out there were good correlation between the hardness and the strain to cracking, which imply higher hardness coating at certain temperature has more sensitive to the cracking. The degrees of the coating crack conditions of the serviced buckets were the same as these fundamental test results. The effects of microstructure degradation on the hardness and the strain to cracking were also evaluated to understand why the cracking propagate to the higher temperature and lower centrifugal stress portion of mid-span and tip of the airfoil. The test results showed the microstructure degradation reduced the hardness and also reduced the sensitivity to the cracking, but still enough sensitivity to cause cracking. Formation of oxide layer was also found to enhance the cracking sensitivity by the further microstructure observation of the serviced buckets.
Isothermal and Cyclic Oxidation Behavior of Turbine Blade Alloys
Authors: Cheruvu N. S. , Chiang K. T.
Published: September 2008

Oxidation behavior of two nickel-based turbine blade alloys has been investigated at three temperatures ranging from 950°C to 1066°C. Thermogravimetric analysis (TGA), isothermal exposure and cyclic oxidation tests were conducted on GTD-111 (Ni-14.1Cr-3.7W-9.2Co-1.5Mo-3.1A1-4.9Ti-0.02Cb-2.93Ta-0.11C) and IN-738 (Ni-16.0Cr-2.6W-8.1Co-1.6Mo-3.5A1-3.4Ti-0.7Cb-1.6Ta-0.10C) blade alloys. TGA results showed that the oxidation kinetics of both alloys obey parabolic rate laws. The GTD-111 material exhibited a higher parabolic rate constant than IN 738 at all temperatures investigated. Cyclic oxidation behavior of these alloys was compared by plotting the weight change results as a function of thermal cycles. Consistent with the TGA results, cyclic oxidation test results also showed that GTD-111 was less resistant to high-temperature oxidation as compared to the IN-738 alloy. To characterize the oxide scales, a series of short term isothermal oxidation tests were conducted and the spalled scale after oxidation exposure was collected and analyzed by energy-dispersive x-ray analysis (EDX) as a function of aging time. The composition of the scales varied between the alloys. The variation of oxidation behavior of these alloys is discussed with respect to the composition differences between the two alloys.
Development of a Heavy Duty GT Syngas Burner for IGCC Power Plant in Order to Enlarge the GT Operating Conditions
Authors: Bonzani Federico , Gobbo Paolo
Published: September 2008

In order to increase the fuel flexibility of the current design of the SynGas burner [4,5,6], Ansaldo Energia, since the growing requests of the market, performed a R&D financed project to use the SynGas fuel available as the unique fuel to feed the gas turbine. Therefore the new working condition to be fulfilled by the modified SynGas burner are the following: a) ignition; b) acceleration; c) loading at part load; d) change over from diffusion line to main SynGas line. To fulfill with new requirements, the standard V94.2K burners have been modified in order to operate from ignition up to the change over point with a SynGas mixture provided by the coal gasification process of a typical IGCC plant [7]. After the design phase, a experimental test campaign on the new design burner has been performed at atmospheric pressure. In order to validate the test results carried out at actual engine working conditions a further test campaign has been performed at the high pressure consistent with the test rig technical limitations [2.3]. The paper show the results carried out that are really promising to meet the customer requirements.
Comparative Performance Analysis of Internal and External Reforming of Methanol in SOFC-MGT Hybrid Power Plants
Authors: Cocco Daniele , Tola Vittorio
Published: September 2008

SOFC-MGT hybrid power plants are a very attractive near term option, as they achieve efficiencies of over 60% even for small power outputs (200–400 kW). The SOFC hybrid systems currently developed are fuelled with natural gas, which is reformed inside the same stack at about 800–900 °C. However, the use of alternative fuels with a lower reforming temperature can lead to enhanced performance of the hybrid power plant. This paper reports a comparative performance analysis of SOFC-MGT power plants fuelled by methane and methanol. Since the reforming temperature of methanol (250–300 °C) is significantly lower than that of methane (700–900 °C), for the methanol fuelled plant both internal and external reforming have been examined. The performance analysis has been carried out by considering different values for the most important operating parameters of the fuel cell. The comparative analysis has demonstrated that simply replacing methane with methanol in SOFC-MGT power plants with internal reforming slightly reduces the efficiency. However, the use of methanol in SOFC-MGT power plants with external reforming enhances efficiency significantly (by about 4 percentage points). The use of methanol with external fuel reforming raises efficiency of the stack thanks to the improved heat management and to the higher hydrogen partial pressure at the anode inlet.
Numerical Simulations of Isothermal Flow in a Swirl Burner
Authors: Garci´a-Villalba Manuel , Fro¨hlich Jochen , Rodi Wolfgang
Published: September 2008

In this paper; the non-reacting flow in a swirl burner is studied using Large Eddy Simulation. The configuration consists of two unconfined co-annular jets at a Reynolds number of 81500. The flow is characterized by a Swirl number of 0.93. Two cases are studied in the paper differing with respect to the axial location of the inner pilot jet. It was observed in a companion experiment (Bender and Bu¨chner, 2005) that when the inner jet is retracted the flow oscillations are considerably amplified. This is also found in the present simulations. Large-scale coherent structures rotating at a constant rate are observed when the inner jet is retracted. The rotation of the structures leads to vigorous oscillations in the velocity and pressure time signals recorded at selected points in the flow. In addition, the mean velocities, the turbulent fluctuations and the frequency of the oscillations are in good agreement with the experiments. A conditional averaging procedure is used to perform a detailed analysis of the physics leading to the low-frequency oscillations.
Environmental Impact of Sewage Sludge Co-Gasification With Coal
Authors: Lopes M. Helena , Pinto Filomena , Crujeira A. Teresa , Andre´ Rui , Dias Ma´rio , Gulyurtlu Ibrahim , Cabrita Isabel
Published: September 2008

The aim of this work is to study the minimization of the environmental impact associated with the gasification of sewage sludge. Co-gasification of a poor quality coal with dried sewage sludge was undertaken on a lab-scale gasifier. The presence of sewage sludge in co-gasification with coal led to higher energy conversions and the gas produced had greater hydrocarbons content. Both temperature and air flow rate were increased with the objective of giving rise to higher energy conversion, thus producing more gas, maximizing hydrogen formation and lowering hydrocarbons, char and tar contents. Due to the adverse effects of the presence of N, S and Cl pollutant precursors leading to the presence of highly corrosive compounds in the syngas, their conversion was evaluated. The increase of sewage sludge content in the feedstock was found to enhance the production of NH3, but working at higher temperatures and with greater Equivalence Ratio (ER) promoted the destruction of NH3. Production of H2S was similar for sewage sludge and coal and seemed to have been decreased by the presence of large quantities of ashes containing Ca and Fe. Temperature had no significant influence on H2S, but higher ER lowered H2S in the syngas. HCl was low and did not varied significantly for the conditions studied. The bed char residues were characterized and their leachability behaviour was evaluated. Heavy metals supplied with the fuel were mostly retained in solid residues, Pb and Hg being the most volatiles at 850°C. However, leachability of these metals was found to be below the analytical detection levels and only small quantities of SO42− and Cl− were released. The bed char residues were found to have variable concentrations of residual C, hence they could be used either as fuels to provide energy for gasification reactions or as sorbents to capture volatile heavy metals.
Advanced Doublewall Cooling System Development for Turbine Vanes
Authors: Coutandin Daniele , Taddei Simone , Facchini Bruno
Published: September 2008

The requirements of always higher thermal performances of turbine vanes and blades push all the aeroengine industries to invest in new cooling technologies. AVIO, the italian aerospace propulsion industry, developed during the last three years an innovative cooling systems for stationary components, based on the doublewall technology, that allow to enhance the internal heat exchange optimising the cooling air distribution. The thermal behaviour of the system has been studied numerically using the standard integrated design methodologies. Some components have been then manufactured in real geometries and finally tested at high temperature in the AVIO’s burner rig. Aim of this work is to present the cooling design methodology used, the manufacturing phases, and to compare the measured thermal efficiency with the theoretical ones. The experimental tests of the blade at high temperature burner rig allowed to determine the effectiveness of the cooling system and validate the integrated aero-thermal numerical procedures. Experimental values of effectiveness are reported in relation with the numerical expected data. Therefore a comparison between this new technology and standard ones based on impingements and turbulated channels is taken into account. Overall numerical results have been found in good agreement with the experimental data and indicate that doublewall cooling system can provide heat transfer enhancements and higher thermal performance if compared with conventional cooling methods with potential benefits on cooling reduction and streamwise uniformity in heat transfer coefficients. Further future improvements and developments are here preliminary proposed.
An Approach for Mechanistic Modeling of Ceramic Matrix Composites
Authors: Santhosh Unni , Ahmad Jalees , Miller Robert , Ojard Greg , Gowayed Yasser , John Reji
Published: September 2008

A mechanistic modeling approach for material characterization and for life prediction of CMC components is described. The approach includes consideration of environment-induced degradation of CMC properties, progressive microcracking of the matrix material and interfacial damage. The mechanistic model has been embedded in a finite element analysis (FEA) framework to enable structural analyses of components and to analyze macro damage, such as cracks and delaminations. This paper describes the modeling approach and its application in the study of substructures. Examples include analyses of simple test specimen coupons, stress concentration at holes and a structural element configuration of a 2D woven SiC/SiC composite. The results include predicted and measured strain field near circular holes and global load-displacement behavior of structural elements. In each case, the model predictions are compared with the experimental measurements.
Quasi-Three-Dimensional Compressor Performance Simulation Using Streamline Curvature and Multi-Parallel Compressor Theory
Authors: Templalexis Ioannis , Pilidis Pericles , Pachidis Vassilios , Kotsiopoulos Petros
Published: September 2008

Engine inlet distortion can severely affect compressor performance by causing the non-dimensional speed lines and surge line to shift. This paper discusses a highly integrated method for modelling engine inlet total pressure distortion and predicting compressor performance under these conditions. This study utilizes a three dimensional (3D), computational fluid dynamics (CFD) tool, based on vortex lattice theory, to simulate the development of distorted flow within the intake and to establish the boundary conditions at the compressor’s inlet face. The derived 3D pressure distributions at the intake outlet are subsequently decomposed into circumferential and radial pressure profiles. Circumferential and radial distortions are examined separately. The influence of the first profile type on compressor performance is assessed with the support of a multi-parallel compressor calculation procedure. The impact of the radial distortion profile is assessed by using a two-dimensional (2D) streamline curvature (SLC) software. Concerning the radial distortion, several distributions are examined along with various profile types. The circumferential total pressure distortion patterns addressed, are varied with respect to the spoiled sector extend and the absolute value in total pressure difference. More precisely, three spoiled sector angles of 60, 120 and 180 degrees are examined. This work demonstrates the applicability of the method by using a generic intake model fitted in front of a single stage compressor, as a case study. All the individual simulation tools, namely the intake flow simulation code, the SLC code and the multi-parallel compressor code, are briefly presented in this paper with more focus on the SLC software, which has not been published before. All simulation tools, used by this study, have been validated individually in the past against experimental data. Their combined operation however, as a unified simulation package, has not been validated yet and hence, numerical results presented in this study should be taken qualitative.
Rotary Kiln Slow Pyrolysis for Syngas and Char Production From Biomass and Waste: Part 2 — Introducing Product Yields in the Energy Balance
Authors: Fantozzi Francesco , Colantoni Simone , Bartocci Pietro , Desideri Umberto
Published: September 2008

A micro scale electrically heated rotary kiln for slow pyrolysis of biomass and waste was designed and built at the University of Perugia. The reactor is connected to a scrubbing section, for tar removal, and to a monitored combustion chamber to evaluate the LHV of the syngas. The system allows the evaluation of gas, tar and char yields for different pyrolysis temperature and residence time. The feeding screw conveyor and the kiln are rigidly connected; therefore a modification of the flow rate implies a modification of the inside solid motion and of residence time. Part I of the paper describes the theoretical and experimental evaluation of the working envelope of the reactor, as a function of feedstock density and humidity content, to obtain pyrolysis conditions inside the kiln. This paper describes the development and resolution of an energy balance of the reactor under pyrolysis conditions. Once the rotational speed n is fixed, the aim of the balance is to obtain the composition of the yields of the pyrolysis of wood biomass, in terms of syngas, tar and char. Results can be used to choose the correct rotational speed before doing the real pyrolysis test.
Operational Performance Analysis of an Externally Fired Gas Turbine
Authors: Schirmeister Ulf , Staudacher Stephan
Published: September 2008

A biomass-fed externally fired gas turbine (EFGT) based on the performance requirements for a small scale heat and power generation plant has been developed at the Institute of Aircraft Propulsion Systems (ILA). This paper presents the results of studies on the operating behaviour of this externally fired gas turbine plant. Simulations of standard steady state and transient operation modes like design point studies or power fluctuations have been examined. Furthermore emergency situations and degradation were simulated. With this simulation a tool has been created not only for studies on technical aspects but also for evaluation of life cycle costs which takes decreasing power outputs and thus required maintenance into consideration.