bluuebunny/crossref_metadata_2025 huggingface dataset:
System Integration Issues for a Direct Sodium Borohydride Fuel Cell (DNBFC)
Authors: Kim Kyu-Jung , Miley George , Luo Nie , Ved Ankeeth
Published: February 2010

A fuel cell for air independent mobile applications using Direct Sodium Borohydride/Hydrogen Peroxide fuels in a low temperature PEM configuration is under development [1, 2]. As part of the development of this unique all liquid fuel cell, we have been studying methods for system integration, including methods for water management, stacking issues involving fluid conductivity control, and the design of a composite catalysis-diffusion layers. [3, 4] The goal is to find optimal conditions (minimum activation, ohmic and transport losses plus maximum run time per fuel loading) in this unique all liquid fuel cell. In contrast to conventional H2/O2 cells, the high electron and ion conductivity of the aqueous solution based fuels introduces special design considerations. For example, in stack design, the path length of flow channels connecting cells must be lengthened to increase the electric resistance which would otherwise introduce serious electrical shorting. With the catalyst coated throughout the diffusion layer, increasing ion conductivity from reaction sites to the PEM region also becomes a key design consideration, involving the porosity and entanglement of catalyst materials. Water management in this type of cell involves unique issues beyond humidification of the PEM which is automatically wetted by the liquid fuels. Here the issue is recirculation of product water from the cathode side back to the borohydride side to prevent reaction product NaBO2 from exceeding its solubility limit. These system integration issues are studied by a coordinated experimental approach which will be described in the presentation.
Effect of Distributed Generation on Voltage Levels in a Radial Distribution Network Without Communication
Authors: Auld Allie E. , Brouwer Jack , Samuelsen Scott , Smedley Keyue M.
Published: February 2010

The challenges associated with incorporating a large amount of distributed generation (DG), including fuel cells, into a radial distribution feeder are examined using a Matlab/Simulink™ model. Two generic distribution feeder models are used to investigate possible scenarios where voltage problems may occur. Modern inverter topologies make ancillary features, such as on-demand reactive power generation/consumption economical to include, which expands the design space across which DG can function in the distribution system. The simulation platform enables testing of the following local control goals: DG connected with unity power factor, DG and load connected with unity power factor, DG connected with local voltage regulation (LVR), and DG connected with real power curtailment. Both the LVR and curtailment strategies can regulate the voltage of the simplest circuit case, but the circuit utilizing a substation with load drop compensation has no universal solution. Even DG with a penetration level around 10% of rated circuit power can cause overvoltage problems with load drop compensation. This implies that some degree of communication will be needed to reliably install a large amount of DG on a distribution circuit.
A Distributed Real-Time Control System for PEM Fuel Cell Engine
Authors: Li Jianqiu , Xu Liangfei , Hua Jianfeng , Ouyang Minggao
Published: February 2010

A real time distributed control system for a 100Kw PEM fuel cell engine will be presented in this paper. The fuel cell engine is successful applied to a demonstration city bus in Beijing city for the Olympic Games. The framework of the control system, which is based on the Time Trigger Controller Area Network (TTCAN), will be presented in this paper. The control task schedule and optimize of TTCAN are analyzed. The individual and flexible output power control of the FC blocks is discussed and then the improved solution is presented.
High Temperature Sealing Method: Induction Brazing for SOFCs
Authors: Heo Yeon-Hyuk , Lee Seung-Bok , Lim Tak-Hyung , Song Rak-Hyun , Shin Dong-Ryul
Published: February 2010

The nickel based brazing alloys (BN-2, BNi-4) modified by reactive TiH2 have been studied for their gas sealing properties of anode-supported tubular SOFCs to ferritic stainless steel by induction brazing process. BNi-2 and BNi-4 are not wetted in YSZ electrolyte, but the brazing alloy with added TiH2 showed good wettability with YSZ electrolyte due to formation of a TiOX layer. Among the tested brazing alloys (BNi-2, BNi-4, modified BNi-2, modified BNi-4), all except modified BNi-4 did not join with YSZ. The gas tightness of a brazed cell was confirmed by OCV value, and it was stayed nearly the same as the theoretical value for 600h at 750 °C. Based on these experimental results, it is concluded that the BNi-4 modified by TiH2 is suitable as a sealing material in SOFCs operating at 750 °C.
Oxidation Behaviour of Fe-Cr Based Alloys in Simulated Anode Side Gases of a Solid Oxide Fuel Cell
Authors: Shemet V. , Santacreu P. O. , Singheiser L. , Quadakkers W. J.
Published: February 2010

One of the challenges in improving the performance and reducing the costs of solid oxide fuel cells (SOFC’s) is the development of suitable interconnect materials. Recent research has shown that specially developed Fe-Cr based alloys possess the suitable combination of properties required for SOFC interconnect materials. Two commercial ferritic steels Crofer22APU (ThyssenKrupp VDM), F18TNb and F18TNbY (ArcelorMittal) were selected and evaluated in respect to oxidation behaviour under conditions relevant to the anode side of SOFC’s. Additionally, the electrical conductivity of the surface oxide scales at the SOFC service temperature of 800°C was determined. Isothermal and cyclic oxidation tests were carried out in three types of gases simulating compositions prevailing at the anode side of an SOFC. The gases differed in water vapour content as well as additions of CO and CO2. The tests were carried out in the temperature range 800–900°C with exposure times up to 3000 h. The results showed that the minor alloying elements Al and Si exhibited a significant effect on oxide scale adherence and area specific resistance (ASR) of the surface oxide scales. The high chromium contents of the steel resulted in formation of oxide scales with excellent protective properties which resulted in excellent resistance against carburization in the CO/CO2-containing test gas. The high chromium content has, however, as disadvantage that the alloys may be prone to embrittlement by σ-phase formation at lower temperatures. If chromium contents are well above approximately 22%, this σ-phase formation may even occur during 800°C exposure. In general, all tested alloys exhibited acceptable performance for interconnect materials but a substantially decrease in oxidation rate could be achieved with an additionally applied Y2O3 coating.
A Method for Processing Transient Heat Transfer Measurements in the Presence of Nonuniform Initial Wall Temperature
Authors: Liu Cun-liang , Zhu Hui-ren , Bai Jiang-tao
Published: February 2010

This paper presents a method to consider the influence of nonuniform initial temperature that always exists in the transient heat transfer measurements. The core of this technique is an equation derived from one-dimensional unsteady conduction equation with nonuniform initial wall temperature through Laplace transformation. Numerical simulation method is used to compute the conduction process of transient heat transfer measurement of film cooling with imposed heat transfer coefficient (HTC) and film cooling effectiveness (FCE). The comparison between calculated values of (HTC, FCE) and the imposed values shows that when the initial temperature is nonuniform and the measurement duration is short, HTC and FCE calculated by the equation derived from constant initial temperature deviate from the true values significantly. If the nonuniform initial temperature distribution in the region where conduction exercises more influence on the wall surface temperature change than convection is well fitted by power series, accurate heat transfer coefficient and film cooling effectiveness can be calculated by the newly derived equation. When the initial temperature distribution is difficult to obtain and the equation derived from constant initial temperature has to be employed, some methods are suggested to reduce the influence of nonuniform initial temperature, such as using low heat conductivity material as the test plate or/and performing the transient measurements in a high heat transfer coefficient condition and properly increasing the duration of transient heat transfer measurements.
Performance Monitoring of Gas Turbine Components: A Real Case Study Using a Micro Gas Turbine Test Rig
Authors: Cafaro Silvio , Traverso Alberto , Ferrari Mario L. , Massardo Aristide F.
Published: February 2010

Estimating the performance of all the components of a recuperated micro gas turbine cycle plays a determinant role in improving their reliability for distributed power generation and cogeneration. The monitoring and diagnostic activity consists in continuously evaluating the productivity capacity and the efficiency of the plant, using the stream of data coming from the plant’s instrumentation. In this framework a diagnostic tool for the micro gas turbine installed at the TPG test rig (located in Savona, Italy) was developed, with the objective of monitoring the operating parameters of the turbomachine, the performance of the heat exchanger and, in general, the good operation of the plant. Even though the commercial machine is equipped with the essential probes for control (rotational speed, TOT, intake temperature and eating water temperature meters) and diagnostic purposes (vibration sensor, filter differential pressure and other thermocouples), further instruments were introduced in the test rig to measure a larger number of properties and points. As result of this, a wide number of measurements is available and can be effectively used for the development of a diagnostic model. The diagnostic model presented in this paper is written in Matlab-Simulink® environment and, in its first version, provides information about compressor and turbine efficiency and heat exchanger effectiveness. The model was developed starting from the turbomachinery maps and the heat exchanger design performance. A validation of the code was performed using the measurements coming directly from the data acquisition system. Preliminary results coming from the model are presented, showing the different performance of each component of the plant in the various operating conditions.
Bottoming Cycle Performance in Large Size Combined Cycle Power Plants—Part A: Health Monitoring System
Authors: Cafaro Silvio , Traverso Alberto , Massardo Aristide F. , Bittarello Roberto
Published: February 2010

This research is focused on the monitoring and diagnostic of the bottoming cycle (BC) of a large size combined cycle, composed by a three pressure level HRSG (Heat Recovery Steam Generator), a three expansion level steam turbine and auxiliary pumps. An original Matlab software was developed, which is composed by two parts: the first calculates HRSG performance, while the second is focused on the calculation of the steam turbines performance, at different power plant operating conditions. In the first part a complete HRSG performance analysis is carried out: it consists of the calculation of each heat exchanger performance and health. The direct result of this analysis is the definition of Non Dimensional Performance Indexes (NDPI) for each heat exchanger, which define the instant degradation of each component, through the comparison between the “actual” and the “expected” effectiveness. The second part calculates steam turbines performance. Two NDPIs are defined: one referred to the high pressure steam turbine and the other referred to the middle-low pressure steam turbine. The performance indexes are calculated comparing the actual expansion efficiency with the expected one. The NDPI previously defined will be used to monitor plant degradation, to support plant maintenance, and to assist on-line troubleshooting. Each performance parameter is coupled with an accuracy factor, which allows to determine the best parameters to be monitored and to define the related tolerance due to measurement errors. The methodology developed has been successfully applied to historical logged data (2 years) of an existing large size (400 MW) combined cycle, demonstrating the capabilities in estimating the degradation of the BC performance throughout plant life.
Simultaneous Noise and Performance Measurements for High-Speed Jet Noise Reduction Technologies
Authors: Long Dean , Martens Steven
Published: February 2010

Model scale tests are conducted to assess the Noise/Performance trade for high speed jet noise reduction technologies. It is demonstrated that measuring the near field acoustic signature with a microphone array can be used to assess the far field noise using a procedure known as acoustic holography. The near field noise measurement is mathematically propagated producing an estimate of the noise level at the new location. Outward propagation produces an estimate of the far field noise. Propagation toward the jet axis produces the source distribution. Tests are conducted on convergent/divergent nozzles with three different area ratios, and several different chevron geometries. Noise is characterized by two independent processes: Shock cell noise radiating in the forward quadrant is produced when the nozzle is operated at non-ideally expanded conditions. Mach wave radiation propagates into the aft quadrant when the exhaust temperature is elevated. These results show good agreement with actual far field measurements from tests in the GE Cell 41 Acoustic Test Facility. Simultaneous performance measurement shows the change in thrust coefficient for different test conditions and configurations. Chevrons attached to the nozzle exit can reduce the noise by several dB at the expense of a minimal thrust loss.
Conjugate Simulation of the Effects of Oxide Formation in Effusion Cooling Holes on Cooling Effectiveness
Authors: Bohn Dieter , Krewinkel Robert
Published: February 2010

Within Collaborative Research Center 561 “Thermally Highly Loaded, Porous and Cooled Multi-Layer Systems for Combined Cycle Power Plants” at RWTH Aachen University an effusion-cooled multi-layer plate configuration with seven staggered effusion cooling holes is investigated numerically by application of a 3-D in-house fluid flow and heat transfer solver, CHTflow. The effusion-cooling is realized by finest drilled holes with a diameter of 0.2 mm that are shaped in the region of the thermal barrier coating. Oxidation studies within SFB 561 have shown that a corrosion layer of several oxides with a thickness of appoximately 20μm grows from the CMSX-4 substrate into the cooling hole. The goal of this work is to investigate the effect this has on the cooling effectiveness, which has to be quantified prior to application of this novel cooling technology in real gas turbines. In order to do this, the influence on the aerodynamics of the flow in the hole, on the hot gas flow and the cooling effectiveness on the surface and in the substrate layer are discussed. The adverse effects of corrosion on the mechanical strength are not a part of this study. A hot gas Mach-number of 0.25 and blowing ratios of approximately 0.28 and 0.48 are considered. The numerical grid contains the coolant supply (plenum), the solid body for the conjugate calculations and the main flow area on the plate. It is shown that the oxidation layer does significantly affect the flow field in the cooling holes and on the plate, but the cooling effectiveness differs only slightly from the reference case. This seems to justify modelling the holes without taking account of the oxidation.
Phase Shift Control of Combustion Instability in a Gas Turbine Matrix Burner Using Acoustic Forcing and Pulsed Fuel Injection
Authors: Bohn Dieter , Willie James F. , Ohlendorf Nils
Published: February 2010

This paper reports the successful attenuation of self-exciting thermoacoustic instabilities inside a gas turbine matrix burner using phase-shift control. The test rig configuration is a matrix burner suitable for simulating the conditions prevailing in stationary gas turbines. The geometry consists of three main parts: 1. a mixing chamber where gaseous fuel is injected into the incoming air stream, 2. a contraction into several small slots which prevents upstream flame propagation, and 3. the combustion chamber. The fuel is first injected upstream before a high incoming velocity air forces it to move downstream. This design enhances fuel/air mixing by increasing the residence time of the mixture in the mixing chamber. But, introducing this time lag will lead to combustion instability in the matrix burner if it is approximately in phase with an integer multiple of the acoustic period. Phase shifting was done using a loudspeaker in one case and a fast response injector in another case to modulate the inlet air and primary fuel streams respectively. The dominant modes in each case were successfully suppressed with that due to the loudspeaker achieving a 45% reduction and the pulsed primary fuel injection achieving a 70% reduction. In both cases, however, secondary peaks were generated due to a coupling of the controller and the dynamics of the test rig. PIV measurements of the cold flow velocity field are first reported and compared with CFD results. This is followed by the determination and the explanation of the stability map of the matrix burner from measurements. Finally the pressure monitored inside the combustor of the matrix burner using unsteady CFD is validated with that obtained from microphone measurements.
Application of the Geared Turbofan With Constant Volume Combustor on Short-Range Aircraft: A Feasibility Study
Authors: Colmenares Quintero Fernando , Brink Rob , Ogaji Stephen , Pilidis Pericles , Colmenares Quintero Juan Carlos , Garci´a Quintero Alexander
Published: February 2010

Recently a considerable effort was made to understand the gas- and thermodynamics of wave rotor combustion technology. Pressure-gain combustors potentially have superior performance over conventional combustors due to their unsteady flow behaviour. Wave rotor combustion provides semi-constant volume combustion and could be integrated in the steady-flow gas turbine. However, a feasibility study to assess the economical and environmental aspects of this concept has not been conducted for short-range missions. Preliminary Multidisciplinary Design Framework was developed to assess novel and radical engine cycles. The tool comprises modules to evaluate noise, emissions and environmental impact. Uncertainty can be accounted for with Monte Carlo simulation. The geared turbofan with constant volume combustor is simulated and benchmarked against a baseline geared turbofan engine. Results indicate that the former complies with CAEP/6 and FAR Part 36 regulations for noise and emissions. Furthermore, acquisition cost of the engine is higher, but engine direct operating cost decreases by 25.2%. The technology requires further development to meet future noise and emissions requirements.
Prediction of Ingestion Through Turbine Rim Seals—Part 2: Externally-Induced and Combined Ingress
Authors: Owen J. Michael
Published: February 2010

Ingress of hot gas through the rim seals of gas turbines can be modelled theoretically using the so-called orifice equations. In Part 1 (ASME GT 2009-59121) of this two-part paper, the orifice equations were derived for compressible and incompressible swirling flow, and the incompressible equations were solved for axisymmetric rotationally-induced (RI) ingress. In Part 2, the incompressible equations are solved for non-axisymmetric externally-induced (EI) ingress and for combined EI and RI ingress. The solutions show how the nondimensional ingress and egress flow rates vary with Θ0, the ratio of the flow rate of sealing air to the flow rate necessary to prevent ingress. For EI ingress, a ‘saw-tooth model’ is used for the circumferential variation of pressure in the external annulus, and it is shown that ε, the sealing effectiveness, depends principally on Θ0; the theoretical variation of ε with Θ0 is similar to that found in Part 1 for RI ingress. For combined ingress, the solution of the orifice equations shows the transition from RI to EI ingress as the amplitude of the circumferential variation of pressure increases. The predicted values of ε for EI ingress are in good agreement with available experimental data, but there are insufficient published data to validate the theory for combined ingress.
Study of Combustion Instabilities Imposed by Inlet Velocity Disturbance in Combustor Using LES
Authors: Sato Kenji , Knudsen Ed , Pitsch Heinz
Published: February 2010

Stable combustion is one of the most important requirements for the development of heavy duty gas turbine engines that comply with stringent environmental regulations at high firing temperatures. In this research, one of the typical combustion instabilities which is caused by an acoustically forced velocity disturbance is investigated using variable density LES simulations. The G-equation approach for LES is used as the combustion model [1], and an experiment by Balachandran et al. [2, 3] is selected for case study. The velocity profiles in the experimental combustion chamber are compared with experimentally measured data at non-reacting conditions and it is confirmed that these are in good agreement. At the reacting conditions, predicted flame shapes are compared with OH PLIF measurements. The transfer function of the heat release due to inlet velocity forcing at 40 Hz and 160 Hz frequencies is also compared with the experimental data. These are in good agreement, including the nonlinear response of heat release. The transfer function is highly related to the flow field. The non-linearity of the transfer function can be traced to the interaction of the flow field in the combustion chamber with the combustion process itself.
Unsteady Conjugate Heat Transfer Modelling
Authors: He L. , Oldfield M. L. G.
Published: February 2010

For high pressure turbine heat transfer designs, a primary requirement is to predict blade metal temperature. There has been considerable recent effort in developing coupled fluid convection and solid conduction (conjugate) heat transfer prediction methods. They are so far, however, confined to steady flows. In the present work, a new approach to conjugate analysis for periodic unsteady flows of practical interest is proposed and demonstrated. This paper starts with a simple model analysis to quantify the huge disparity in time scale between convection and conduction and the implications of this for steady and unsteady conjugate solutions. To realign the greatly mismatched time scales, a hybrid approach of coupling between time-domain fluid solution and frequency-domain solid conduction is adopted in conjunction with a continuously updated Fourier transform at the interface. A novel semi-analytical harmonic interface condition is introduced, initially for reducing the truncation error in Finite-difference discretization. More interestingly, the semianalytical interface condition enables the unsteady conjugate coupling to be achieved without simultaneously solving the unsteady temperature field. This unique feature leads to a very efficient and accurate unsteady conjugate solution approach. The fluid and solid solutions are validated against analytical solutions and experimental data. The implemented unsteady conjugate method has been demonstrated for a turbine cascade subject to inlet unsteady hot streaks.
A Quick Search Strategy for Multiple Fault Diagnosis of Turbomachinery
Authors: Yang Tachung , Hsu Ming-Wei
Published: February 2010

Fault diagnosis is an important research issue in rotordynamics. Unbalance is one of the most frequent faults occurs in turbomachinery. A quick search strategy for model-based diagnosis is proposed in this paper to identify both locations and amounts of multiple unbalances by using the unbalance responses at the bearing locations under one specified rotating speed. Effects of measurement noise are analyzed and robustness of the proposed method is validated by means of numerical results. The reason for quick searching is non-repeatedly counting the found faults, and the computational time is saved. This method is suitable for on-line monitoring the gradual changes of unbalance on rotating machines; especially those required fixedly operating speeds.
Feasibility Study of a Recuperated Turboshaft-Engine Based on a Micro-Gasturbine
Authors: Harr Clemens , Ga¨rtner Ulrich , Paschereit C. Oliver
Published: February 2010

The present paper shows the current state of a feasibility study of the University of Applied Sciences Esslingen. The intention of this study is the conversion of a model-turbine into a turboshaft-engine for variable applications, with as few as possible modifications. The shaft power of the engine is estimated on 20 kW at least. It is intended to use a recuperator to augment its efficiency. After a general introduction possible applications are discussed and the previous design-process is explained: Subsequent to the concept-phase cycle parameters were calculated and the power turbine was designed and manufactured. At present turbine tests are running. The recuperator is of counter flow type. To shorten the flow path it is mounted directly around the combustor. Currently different variations are being designed which will be optimised. The pressure loss within the exhaust manifold between power turbine and recuperator has already been reduced by simulations and tests. This will be minimised through application of a genetic optimisation software.
CFD Simulation for Reduction of Oil Churning Loss and Windage Loss on Aeroengine Transmission Gears
Authors: Arisawa Hidenori , Nishimura Motohiko , Imai Hideyuki , Goi Tatsuhiko
Published: February 2010

In recent years, the demand for power generation capacity has increased considerably due to the electric drive of air conditioners and so on in the engines of civil aircraft. Therefore, it is estimated that power losses may increase in the gearbox because of generators and pumps that in turn augment fuel consumption. To understand the phenomena of losses in the gearbox and to reduce these losses, Computational Fluid Dynamics (CFD) simulation that analyzes oil churning loss and windage loss was developed and improvements were made to the shroud of bevel gears. The CFD agreed with experimental results on a bevel gearbox of a 100-seater aircraft. And, it was shown that the suppression of momentum transfer from the rotating gears to oil clusters is of importance. In addition, it was revealed that the loss was reduced up to 36% compared to non-shrouded gears by shrouding in the experiments. This CFD simulation can be applied to many types of gearboxes that have spur gears, bearings and seals.
A Modeling Approach to Predict Fretting Fatigue on Highly Loaded Blade Roots
Authors: Wackers Patrick , Arrieta Victor , Alquezar-Getan Marcel , Constantinescu Andrei , Maitournam Habibou
Published: February 2010

A lifing technique for predicting fretting fatigue on highly loaded blade-disk attachments has been developed and calibrated. The approach combines extensive testing on nickel and titanium based alloys using a specially devised multiaxial fretting test machine and an analytical lifing procedure based on finite element contact calculations and multiaxial shakedown fatigue models. In order to reproduce realistic operational conditions and standardize testing conditions a special fretting fatigue testing machine with high temperature testing capabilities was developed. The machine was employed to perform systematic testing under prescribed load and displacement conditions at representative temperatures. Making use of FEA the rig test results were calculated to identify relevant parameters such as friction coefficient, slip conditions and machine compliance. The computation procedure involves the calculation of several major loading cycles until a stabilized response of the structure is achieved. The material response is assumed to be elasto-plastic and a nonlinear friction law (space and time) was applied. From the computed mechanical variables, a several life prediction models are benchmarked to establish their capabilities to predict fretting-fatigue life. Finally, a most promising life estimation procedure was applied to predict life in a real compressor blade-disk attachment. Predicted failure location and number of cycles to failure are compared against engine tests results. The experimental-analytical approach has the potential to predict fretting fatigue risk during the design phase on highly loaded joints as well as estimating the preventive overhaul intervals for parts already in service.
Optimization of 200 to 3000 W Gas Turbine MEMS Arrangement
Authors: Sudarev A. V. , Suryaninov A. A. , Bazarov B. A. , Ten V. S. , Lelait L. , Avran P.
Published: February 2010

The persistent increase in demand for compact efficient power generation plants for the decentralized power supply systems applications, pipelines, micro air vehicles, electronics, etc stipulates developments of independent micro sources. Application of the micro gas turbine engine (μGTE) as an electric generator drive allows a sharp increase in the specific energy and operation independence, elimination of ambient temperature effects on the specific power, environmental friendliness improvement. However, GTE miniaturization causes its efficiency decreasing. Hence, there is a need in improvement of the micro engine of 200–3,000W power efficiency. The approach proposed is the ceramic tunnel turbomachine concept for the regenerative μGTE (MEMS-based) application [1, 2, 3] with conventional annular systems of vanes replaced with three-dimensional conic channels. The μGTE turbocompressor unit design is dependent on the conceptual arrangement approach i.e. a manner the gas turbine engine micro turbocompressor (μTC) is joined with the driven micro electric generator (μEG) assumes a great importance. Two conceptually opposite μTC concepts over the turbocompressor unit are considered: - the μTC rotor connected with the μEG rotor by an electromagnet coupling; - appropriate elements of μEG built into the rotor and stator sections of μTC. Examination of the essentially different concepts of the μEG - micro turbocompressor (μTC) arrangement demonstrated that an independent power generation, high temperature, and high speed μGTE reliable operating can be ensured by different arrangements, e.g. with the rotor and stator sections of the electric generator placed between the appropriate turbine and compressor stage devices. In this case it is easier, compared to some other approaches, to evade an unpropitious effect on the μTC rotor strength characteristics (total stress level, critical velocities within the speed operation range, radial and axial deformations, etc) imposed by sizes and mass of the contact-free electromagnet couplings elements. This inference ensues, also, from the studies conducted [4, 5].
Analysis of Flow Parameters Influencing Carry-Over Coefficient of Labyrinth Seals
Authors: Suryanarayanan Saikishan , Morrison Gerald L.
Published: February 2010

Accurate prediction of the mass flow rate through labyrinth seals is extremely important especially for rotodynamic analysis of turbomachinery. The integral control volume based rotodynamic coefficient prediction programs are no more accurate than the accuracy of the leakage mass flow rate. A leakage flow equation can be developed by comparing the seal to a series of orifices and cavities. An equation of this type usually contains a discharge coefficient and a carry-over coefficient. The carry-over coefficient represents the effectiveness of each cavity to dissipate the kinetic energy entering the cavity and has an effect upon the value of the discharge coefficient for the constriction following that cavity. Therefore, an effective model for the carry-over coefficient must be developed before a leakage model can be obtained. This paper investigates how flow conditions and geometry variations for a smooth shaft operating in straight though tooth on stator rectangular cavity labyrinth seals affect the value of the carry-over coefficient for incompressible flow. The effect of Reynolds number, pressure ratio, clearance, number of teeth and shaft speed are considered using computational fluid dynamics. It was found that Reynolds number and clearance to pitch ratio have a major influence on the carry-over coefficient. Models for the same were developed for a generic rectangular tooth on stator labyrinth seal. The carry-over coefficient varied from 1.0 at the lowest clearance/pitch ratio and Reynolds numbers to 1.8 for the largest clearance/pitch ratio and Reynolds number considered. Future studies will investigate how the discharge coefficient is dependent upon the same flow and geometry conditions as well as the carry-over coefficient in order to obtain a complete leakage model.
Interaction Between the Acoustic Pressure Fluctuations and the Unsteady Flow Field Through Circular Holes
Authors: Rupp Jochen , Carrotte Jon , Spencer Adrian
Published: February 2010

Gas turbine combustion systems are prone to thermo-acoustic instabilities, and this is particularly the case for new, low emission, lean burn type systems. The presence of such instabilities is basically a function of the unsteady heat release within the system (i.e. both magnitude and phase), and the amount of damping. This paper is concerned with this latter process and the potential damping provided by perforated liners and other circular apertures found within gas turbine combustion systems. In particular the paper outlines experimental measurements that characterise the flow field within the near field region of circular apertures when being subjected to incident acoustic pressure fluctuations. In this way the fundamental process by which acoustic energy is converted into kinetic energy of the velocity field can be investigated. Experimental results are presented for a single orifice located in an isothermal duct at ambient test conditions. Attached to the duct are two loudspeakers that provide pressure fluctuations incident onto the orifice. Unsteady pressure measurements enable the acoustic power absorbed by the orifice to be determined. This was undertaken for a range of excitation amplitudes and mean flows through the orifice. In this way regimes where both linear and non-linear absorption occur along with the transition between these regimes can be investigated. The key to designing efficient passive dampers is to understand the interaction between the unsteady velocity field, generated at the orifice, and the acoustic pressure fluctuations. Hence experimental techniques are also presented that enable such detailed measurements of the flow field to be made using PIV. These measurements were obtained for conditions at which linear and non-linear absorption was observed. Furthermore, Proper Orthogonal Decomposition was used as a novel analysis technique for investigating the unsteady coherent structures responsible for the absorption of energy from the acoustic field.
Advancements in Fast Epitaxial High-Temperature Brazing of Single-Crystalline Nickel-Base Superalloys
Authors: Laux Britta , Piegert Sebastian , Ro¨sler Joachim
Published: February 2010

High temperature diffusion brazing is a very important technology for filling cracks in components from single-crystalline nickel-base superalloys as used in aircraft engines and stationary gas turbines: alloys, which are similar to the base material, are enhanced by a fast diffusing melting-point depressant (MPD) like boron or silicon, which causes solidification by diffusing into the base material. Generally, epitaxial solidification of single-crystalline materials can be achieved by use of conventional braze alloys, however, very long hold times are necessary to provide a complete diffusion of the MPD out of the braze gap. If the temperature is lowered before diffusion is completed, brittle secondary phases precipitate, which serve as nucleation sites for stray grains and, therefore, lead to deteriorating mechanical properties. It was demonstrated in earlier works that nickel-manganese-based braze alloys are appropriate systems for the braze repair of particularly wide gaps in the range of more than 200 μm, which allow a significant shortening of the required hold times. This is caused by the complete solubility of manganese in nickel: epitaxial solidification can be controlled by cooling in addition to diffusion. In this work, it will be shown that the nickel-manganese-based systems can be enhanced by chromium and aluminium, which is with regard to high-temperature applications a very important aspect. Furthermore, it will be demonstrated that silicon, which could be identified as appropriate secondary MPD in recent works, can be replaced by titanium, as this element has additionally a γ′ stabilizing effect. Several braze alloys containing nickel, manganese, chromium, aluminium and titanium will be presented. Previously, the influence of the above mentioned elements on the nickel-manganese-based systems will be visualized by thermodynamic simulations. Afterwards, different compositions in combination with a heat treatment, which is typical for nickel-base superalloys, will be discussed: a microstructure, which is very similar to that within the base material can be presented.
Alstom GT11N2 M Expansion Turbine Design Modification and Operation Experience
Authors: Vorontsov Sergey , Irmisch Stefan , Karelin Alexey , Rocha Marcelo
Published: February 2010

This paper summarizes the development steps and measures taken for the upgrade of the GT11N2 Turbine. The main targets to be achieved were specified as follows: - GT power increase; - GT gross efficiency increase; - Flexible operation with respect to power output and service interval length. All 4 turbine stages were re-designed in order to optimize their aerodynamic performance and minimize cooling air consumption. Turbine aerodynamic efficiency improvement was achieved by means of: - Turbine stage-to-stage loading optimization; - 3D airfoil profiling; - Replacement of the damping bolt of blade 4 by a full shroud; - Stator/rotor sealing optimization. On top of that, cooling air consumption was reduced by means of cooling system optimization for Vane 1, Blade 1, Vane 2, Blade2 and SHS/A. This allowed an increase of TIT (inlet turbine mixed temperature) keeping the hot gas temperature at the turbine inlet unchanged, which is important for meeting lifetime and emission targets. One of the key requirements for this Turbine Upgrade was to use exclusively validated design approaches and design features as available from existing and proven Alstom Gas Turbines ([1], [2], [3]) in order to minimize development- and implementation risks. Manufacturing of the new turbine parts was completed in an exceptionally short time, thanks to a dedicated R&D Logistic and Manufacturing support/process, an efficient NCR (Non Conformance Report) process, early supplier involvement and a very close/open work with suppliers. The first prototype of this turbine was implemented in a GT11N2 customer engine. Performance validation runs, performed in May 2008 confirmed that the design targets for power and efficiency were fully met. The validation of the turbine parts lifetime is still ongoing.
Impact of Mechanical Chevrons on Supersonic Jet Flow and Noise
Authors: Kailasanath K. , Liu Junhui , Gutmark Ephraim , Munday David , Martens Steven
Published: February 2010

In this paper, we present observations on the impact of mechanical chevrons on modifying the flow field and noise emanated by supersonic jet flows. These observations are derived from both a monotonically integrated large-eddy simulation (MILES) approach to simulate the near fields of supersonic jet flows and laboratory experiments. The nozzle geometries used in this research are representative of practical engine nozzles. A finite-element flow solver using unstructured grids allows us to model the nozzle geometry accurately and the MILES approach directly computes the large-scale turbulent flow structures. The emphasis of the work is on “off-design” or non-ideally expanded flow conditions. LES for several total pressure ratios under non-ideally expanded flow conditions were simulated and compared to experimental data. The agreement between the predictions and the measurements on the flow field and near-field acoustics is good. After this initial step on validating the computational methodology, the impact of mechanical chevrons on modifying the flow field and hence the near-field acoustics is being investigated. This paper presents the results to date and further details will be presented at the meeting.
Autoignition Delay Time Measurements of Methane, Ethane, and Propane Pure Fuels and Methane-Based Fuel Blends
Authors: Holton M. M. , Gokulakrishnan P. , Klassen M. S. , Roby R. J. , Jackson G. S.
Published: February 2010

Autoignition delay experiments in air have been performed in an atmospheric flow reactor using typical natural gas components, namely methane, ethane and propane. Autoignition delay measurements were also made for binary fuel mixtures of methane/ethane and methane/propane and ternary mixtures of methane/ethane/propane. The effect of CO2 addition to the methane-based fuel blends on autoignition delay times was also investigated. Equivalence ratios for the experiments ranged between 0.5 and 1.25 and temperatures ranged from 930 K to 1140 K. Consistent with past studies, increasing equivalence ratio and increasing inlet temperatures over these ranges decreased autoignition delay times. Furthermore, addition of 5–10% ethane or propane decreased autoignition delay time of the binary methane-based fuel by 30–50%. Further addition of either ethane or propane showed less significant reduction of autoignition delays. Addition of 5–10% CO2 slightly decreased the autoignition delay times of methane fuel mixtures. Arrhenius correlations were used to derive activation energies for the ignition of the pure fuels and their mixtures. Results show a reduction in activation energies at the higher temperatures studied, which suggests a change in ignition chemistry at very high temperatures. Measurements show relatively good agreement with predictions from a detailed kinetics mechanism specifically developed to model ignition chemistry of C1-C3 alkanes.
Low-Calorific Fuel Mix in a Large Size Combined Cycle Plant
Authors: Jonshagen Klas , Genrup Magnus , Eriksson Pontus
Published: February 2010

This paper will address the effects of mixing low-calorific fuel in to a natural gas fuelled large size combined cycle plant. Three different biofuels are tested namely; air blown gasification gas, indirect gasification gas and digestion gas. Simulations have been performed from 0–100% biofuel–natural gas mixtures. The biofuel impacts on the full cycle performance are discussed. Some more in-depth discussion about turbo-machinery components will be introduced when needed for the discussion. The compressors pressure ratio will increase in order to push the inert ballast of the low calorific fuels trough the turbine. Despite the increased expansion ratio in the gas turbine, the exhaust temperature raises slightly which derives from changed gas properties. The work is based on an in-house advanced off-design model within the software package IPSEPro. Sweden’s newest plant “O¨resundsverket”, which is a combined heat and power (CHP) plant, is used as a basis for the investigation. The plant is based on a GE Frame-9 gas turbine and has a triple-pressure reheat steam cycle.
Effects of Pilot Fuel and Liner Cooling on the Flame Structure in a Full Scale Swirl-Stabilized Combustion Setup
Authors: Fa¨rber Jens , Koch Rainer , Bauer Hans-Jo¨rg , Hase Matthias , Krebs Werner
Published: February 2010

The flame structure and the limits of operation of a lean premixed swirl flame were experimentally investigated under piloted and non-piloted conditions. Flame stabilization and blow out limits are discussed with respect to pilot fuel injection and combustor liner cooling for lean operating conditions. Two distinctly different flow patterns are found to develop depending on piloting and liner cooling parameters. These flow patterns are characterized with respect to flame stability, blow out limits, combustion noise and emissions. The combustion system explored consists of a single burner similar to the burners used in Siemens annular combustion systems. The burner feeds a distinctively non-adiabatic combustion chamber operated with natural gas under atmospheric pressure. Liner cooling is mimicked by purely convective cooling and an additional flow of ‘leakage air’ injected into the combustion chamber. Both, this additional air flow and the pilot fuel ratio were found to have a strong influence on the flow structure and stability of the flame close to the lean blow off limit (LBO). It is shown by Laser Doppler Velocimetry (LDV) that the angle of the swirl cone is strongly affected by pilot fuel injection. Two distinct types of flow patterns are observed close to LBO in this large scale setup: While non-piloted flames exhibit tight cone angles and small inner recirculation zones (IRZ), sufficient piloting results in a wide cone angle and a large IRZ. Only in the latter case, the main flow becomes attached to the combustor liner. Flame structures deduced from flow fields and CH-Chemiluminescence images depend on both the pilot fuel injection and liner cooling.
The Analysis of Heat Transfer in Automotive Turbochargers
Authors: Baines Nick , Wygant Karl D. , Dris Antonis
Published: February 2010

Heat transfers in an automotive turbocharger comprise significant energy flows, but are rarely measured or accounted for in any turbocharger performance assessment. Existing measurements suggest that the difference in turbine efficiency calculated in the conventional way, by means of the fluid temperature change, under adiabatic conditions differs considerably from the usual diabatic test conditions, particularly at low turbine pressure ratio. In the work described in this paper, three commercial turbochargers were extensively instrumented with thermocouples on all accessible external and internal surfaces in order to make comprehensive temperature surveys. The turbochargers were run at ranges of turbine inlet temperature and external ventilation. Adiabatic tests were also carried out to serve as a reference condition. Based on the temperature measurements, the internal heat fluxes from the turbine gas to the turbocharger structure, and from there to the lubricating oil and the compressor, and the external heat fluxes to the environment, were calculated. A one-dimensional heat transfer network model of the turbocharger was demonstrated to be able to simulate the heat fluxes to good accuracy, and that the heat transfer coefficients required were ultimately found to be mostly independent of the turbochargers tested.
Characterization of a Superheated Fuel Jet in a Crossflow
Authors: Corn May , Cohen Jeff , Hautman Don , Thawley Scott , Brown Christopher , McDonell Vincent
Published: February 2010

An experiment was conducted to characterize a superheated fuel jet (Jet-A) injected into an unheated crossflow. The liquid phase of the fuel jet was characterized with high speed imaging and phase Doppler interferometry while the vapor phase of the fuel was measured with infrared scattering and extinction methods. The transition from a shear-atomized to flash-atomized spray at a fuel temperature of 465°F (513K) was observed at an ambient pressure of 1 atm, which is consistent with the bubble and dew point curves predicted for JP-8. The explosive breakup that was seen in the flash-atomized spray produced sub-micron droplets with a high radial and transverse momentum that resulted in an increasing fuel vapor concentration for the same penetration height when compared with the shear-atomized case. This unique behavior makes superheated fuels an attractive design feature for fuel preparation devices that can employ flash boiling to enhance fuel atomization and mixing in a compact volume.