bluuebunny/crossref_metadata_2025 huggingface dataset:
Catalytic Partial Oxidation of Natural Gas in Gas Turbine Applications
Authors: Manrique Carrera Arturo , Jayasuriya Jeevan , Fransson Torsten
Published: November 2013

The demands of emissions, combustion efficiency over a wider operational range, and fuel flexibility for industrial gas turbine applications are expected to increase in the coming years. Currently, it is common the use of a stabilizing piloting diffusion flame during part load operation, this flame is accountable for an important part of the thermal NOx emissions on partial load, and in some cases also at full load operation. On the other hand Catalytic Partial Oxidation (CPO) of natural gas is a technique used in petrochemical industry for the Fischer-Tropsch process and for H2 production, and is based in the production of Syn-Gas rich in H2 and CO.

The present work explores the possibility to use the CPO of natural gas in industrial gas turbine applications, it is based in experiments performed between 5 and 13 bar using an arrangement of Rh based catalyst and CH4. The experiments were done at the Catalytic Combustion High Pressure Test Facility, at the Royal Institute of Technology (KTH) in Sweden. The gas produced leaves the CPO reactor between 700 and 850 °C and it is rich in H2 and CO. It was found that the most important parameter after reaching the light off temperature in the CPO reactor is the equivalence ratio Φ, which evidences the kinetically controlled regime in the Rh catalyst that depends on O2 availability. The H2/CO ratio is close to the theoretical value of 2 and the selectivity towards H2 and CO are 90% and 95% respectively while the CH4 conversion reached approximately 55%.

Pressure on the other hand had a small negative influence in the tested pressure range and it is more relevant at richer fuel conditions (high equivalence ratios). The CPO process had shown that it is relatively easy to control the operation temperature of the catalyst. This temperature is kept below the maximum allowed by reducing the O2 availability.

The high temperature Syn-Gas gas produced through CPO process could be burnt in the downstream of the catalysts steadily at flame temperatures below the thermal-NOx threshold. The CPO reactor could provide the flame stabilization function at a wide range of operational conditions, and replace the diffusion piloting flame. This approach could cope with NOx and CO emissions in a wider operational range and offers the possibility of using different fuels as the reaction controlling factor is O2 availability. Furthermore, an initial design of a possible combustion strategy downstream of the CPO reactor is also presented.
Dynamics of a Transversely Excited Swirling, Lifted Flame: Part I — Experiments and Data Analysis
Authors: Malanoski Michael , Aguilar Michael , Acharya Vishal , Lieuwen Tim
Published: November 2013

This paper is the first of two parts, and describes measurements of the response of a transversely forced, single nozzle, swirling flame. This study is motivated by combustion instabilities coupling with azimuthal combustor modes. Two different forcing configurations are applied, where the flame/nozzle are located at a pressure node and anti-node, respectively. High speed velocimetry and chemiluminescence measurements were made of the forced and unforced flow in multiple orthogonal planes, revealing both the axial and azimuthal development of the unsteady flow. Spectra and azimuthal mode decompositions of these data show the dominance of the m = 1 helical mode in the unforced flow. Depending upon the nature of the forcing, the flow response at the forcing frequency can be dominated by the axisymmetric, m = 0 mode, or the m = 1 mode. These results clearly show that the dominant fluid mechanic structures exciting flames during transverse instabilities varies from nozzle to nozzle, depending upon the phase characteristics of the acoustic excitation field. Part II of this paper uses these time averaged and fluctuating measurements as inputs to a flame response model of the unsteady global heat release fluctuations.
Aerodynamic Effects of Non-Uniform Surface Roughness on a Turbine Blade
Authors: Hohenstein Sebastian , Aschenbruck Jens , Seume Joerg
Published: November 2013

The effect on non-uniform surface roughness on the aerodynamics of a turbine blade is investigated. Surface roughness on airfoils has a significant impact on total energy loss due to skin friction and typically leads to an increased thermal loading. In the present research project, investigations are supposed to be carried out experimentally. For this a blade must be designed, which accommodates the contradictory requirements of aerodynamics and manufacturing the sections of surface roughness. A fully automatic design process based on a genetic algorithm is developed and results are shown. The designed blade sufficiently fulfills the given requirements.

A numerical study, using a low-Reynolds approach, is performed to investigate the influence of non-uniform roughness applied to different positions on the suction side of a high pressure turbine blade. It is shown that roughness applied at the leading and trailing edge does not significantly influence the flow whereas roughness at 20% cord length and at midchord induce transition. Especially surface roughness at 20% chord length shows a strong correlation to the change of total pressure loss.
Development of GT24 and GT26 (Upgrades 2011) Reheat Combustors, Achieving Reduced Emissions and Increased Fuel Flexibility
Authors: Düsing K. Michael , Ciani Andrea , Benz Urs , Eroglu Adnan , Knapp Klaus
Published: November 2013

The recent development of the Alstom’s sequential combustion system for the GT24 (60Hz) and GT26 (50Hz) upgrades 2011 is a perfect example of evolutionary design optimizations. Better overall performance is achieved through improved SEV burner aerodynamics and fuel injection, while keeping the main features of the sequential burner technology. In particular this results in further reduced NOx and CO emissions over widest possible load range and allows operation with fuel gases with up to 18% of higher hydrocarbons (C2+) or a low Wobbe index.

An extensive validation of the new sequential burners for GT24 and GT26 has been conducted, with a wide range of validation tools. This has included high pressure sector rig testing and full-engine tests at the Alstom Power Plant Birr, Switzerland.

This paper presents the development and validation process, in terms of evolutionary design modifications and successful burner scaling, of the GT24 and GT26 (upgrades 2011) reheat combustors from concept phase to engine validation.
Trailing Edge Cooling of a Gas Turbine Blade With Perforated Blockages With Inclined Holes
Authors: Chung Heeyoon , Park Jun Su , Sohn Ho-Seong , Rhee Dong-Ho , Cho Hyung Hee
Published: November 2013

We propose an improved hole array to enhance the cooling performance of a perforated blockage. The internal passage in the trailing region of the blade was modeled as a wide square channel with three parallel blockages. Various configurations of perforated blockages were tested with a fixed Reynolds number. The baseline design had holes positioned along the centerline of the blockage in the lateral direction, and the array pattern, hole size, and hole direction were manipulated to enhance the cooling performance. Experiments were performed to obtain information on heat transfer and pressure loss. A naphthalene sublimation method was adopted to obtain detailed heat transfer distributions on the surfaces, using the correlation between heat and mass transfer. The pressure was measured at several points to evaluate the pressure loss. The proposed inclined hole array showed noticeably improved cooling performance, as much as 50% higher than the conventional configuration.
Evaluation of Global Mechanisms for LES Analysis of SGT-100 DLE Combustion System
Authors: Abou-Taouk Abdallah , Sadasivuni Suresh , Lörstad Daniel , Eriksson Lars-Erik
Published: November 2013

This paper presents the results of Computational Fluid Dynamics (CFD) analyses obtained for the experimental version of the SGT-100 Dry Low Emission (DLE) gas turbine burner provided by Siemens Industrial Turbomachinery Ltd (SIT). A testing and measurement campaign for this burner was previously carried out at the DLR Institute of Combustion Technology, Stuttgart, Germany, for various operating pressure conditions. The present work shows the successful validation of the CFD model in terms of time-averaged temperature and velocity data within measurement errors at an operating pressure of 3 bar.

Several well known global mechanisms are tested in this work, namely the Westbrook Dryer 2-step (WD) scheme, the Jones and Lindstedt 4-step (JL4) scheme, the Meredith et al. 3-step (M3) scheme and a recently developed in-house 4-step scheme (M4) for methane-air mixtures. The M4 scheme is optimized by matching the detailed GRI-Mech 3.0 mechanism in terms of 1D laminar flame speed, using the CHEMKIN software for a wide range of pressures (1 to 6 bar), unburned gas temperatures (295 to 650 K) and equivalence ratios range (0.4 to 1.6).

CFD simulations are performed using the Eddy Dissipation Model (EDM)/Finite Rate Chemistry (FRC) non-premixed turbulence chemistry interaction model. Both steady-state Reynolds Averaged Navier Stokes (RANS) and hybrid Unsteady Reynolds Averaged Navier Stokes /Large Eddy Simulation (URANS/LES) turbulence models are used. The LES Wall Adaptive Large Eddy-Viscosity (WALE) model with finite rate chemistry is also tested for validation.

Velocity profiles, flame temperatures and major species are compared with experiments for different global reaction mechanisms used with different turbulence models. A reasonable agreement is found with the M4 global reaction mechanism in predicting mixing, temperatures and major species.

RANS simulations are observed to underpredict the temperature profiles downstream and overpredict in the upstream region, while the velocity profiles are found to be in close agreement with experiments. The SAS-SST turbulence model predicts the velocity profiles in good agreement with experimental data and slightly better than the RANS model. Both the transient simulations slightly overpredict the temperature profiles. The LES-WALE model gives too high and unrealistic temperatures.
Quantitative Stability Analysis Using Real-Valued Frequency Response Data
Authors: Schmid Martin , Blumenthal Ralf S. , Schulze Moritz , Polifke Wolfgang , Sattelmayer Thomas
Published: November 2013

Models for the analysis of thermoacoustic instabilities are conveniently formulated in the frequency domain. In this case one often faces the difficulty that the response behavior of some elements of the system is only known at real-valued frequencies, although the transfer behavior at complex-valued frequencies is required for the quantification of the growth rates of instabilities. The present paper discusses various methods for extrapolation of frequency response data at real-valued frequencies into the complex plane. Some methods have been used previously in thermoacoustic stability analysis, others are newly proposed. First the pertinent mathematical background is reviewed, then the sensitivity of predicted growth rates on the extrapolation scheme is explored. This is done by applying different methods to a simple thermoacoustic system, i.e. a ducted premixed flame, for which an analytical solution is known. A short analysis determining the region of confidence of the extrapolated transfer function is carried out to link the present study to practical applications. The present study can be seen as a practical guideline for using frequency response data collected for a set of real-valued frequencies in quantitative linear stability analysis.
Mechanical Work Potential
Authors: Miller Robert J.
Published: November 2013

This paper considers the effect of heat transfer between fluid streams on the work output of a turbine. To correctly characterize the effect of heat transfer requires a new property, ‘mechanical work potential’, which is a measure of the maximum useful work that can be extracted from a fluid by an isentropic turbine exhausting to a fixed exit static pressure. A balance equation for the property, over a control volume, is developed. The equation shows that entropy creation through thermal mixing has no effect on turbine work. It does, however, show that a second heat transfer term, ‘thermal creation’, does alter turbine work. Thermal creation occurs in regions of the turbine where heat transfer occurs across a finite pressure difference. The term is the non-linear version of the acoustic energy creation term proposed by Lord Rayleigh in his thermo-acoustic criterion. The balance equation is then used to link local regions of thermal creation to changes in stage efficiency. The method is used to show that, in a modern high pressure turbine stage, heat transfer due to thermal mixing in the freestream causes a negligible change in efficiency and therefore can be ignored in the design process. The method is also used to show that heat transfer due to convective cooling results in ∼0.5% rise in stage efficiency. This is a significant and should be accounted for in the design process.
Improvement of Conventional Seals for Stator-Rotor Cavities of Heavy-Duty Gas Turbines by Application of Interstage Brush-Seals
Authors: Mantero Marco , Vinci Alessandro , Bozzi Luca , D’Angelo Enrico
Published: November 2013

In order to achieve significant secondary air savings in heavy duty gas turbines, a remarkable item of improvement is the reduction of seal flows for turbine stator-rotor cavities. The optimization of such flows allows to avoid waste of air, obligatory with standard labyrinth seals, to ensure the minimum sealing flow rate in all operating conditions.

Based on the experience gained in the design of sealing system of stator-rotor cavities with standard seals, the project of installation of inter-stage brush-seals was undertaken incorporating such devices into the vane seal rings of 2nd and 3rd turbine stages of a AE94.3A Gas Turbine (GT).

The paper offers a detailed description of the installation project. The following describes in detail the design flow process and the calculation methodologies used, step by step, to define the geometry of brush-seals in order to ensure mechanical integrity and durability, needed in the commercial operation, without thereby affecting the performance.

The first prototype of brush-seal devices has been installed on a AE94.3A4 unit of the Ansaldo fleet. In order to verify the behavior of stator-rotor sealing system, in particular in terms of temperature and pressure variations, vane seal rings have been equipped with special instrumentation. A series of tests to optimize the set points of bleed control valves was carried out.
Numerical Investigation to Support the Design of a Flat Plate Honeycomb Seal Test Rig
Authors: Bianchini Cosimo , Micio Mirko , Maiuolo Francesco , Facchini Bruno
Published: November 2013

Among the various type of seals used in gas turbine secondary air system to guarantee sufficient confinement of the main gas path, honeycomb seals well perform in terms of enhanced stability and reduced leakage flow. Reliable estimates of the sealing performance of honeycomb packs employed in industrial gas and steam turbines, are however missing in literature, thus, in order to evaluate the complete characteristic curve of the seals in the wide range of working conditions, an experimental campaign is planned. This work reports the findings of the numerical investigation exploited to properly design such test rig. Computations are performed with the steady-state RANS solver implemented in Ansys CFX ® using k-ω SST turbulence model with automatic wall treatment and exploiting symmetry condition when possible. Due to the generally large amount of honeycomb cells typically present in real seals, it would be convenient to treat the sealing effect of the honeycomb pack as an increased distributed friction factor on the plain top surface that is why the simplest configuration, the honeycomb facing a flat plate, is employed in this paper. The geometry of the hexagonal cell and the investigated clearances were chosen to well represent actual honeycomb packs employed in industrial compressors. First the pressure distribution within the seal was analysed verifying that downstream the first 5 rows of cells where entrance effects are predominant, the relative pressure drop is almost constant thus the use of an equivalent friction factor is appropriate to characterize the seal. Furthermore the calculated pressure field was used to assess potential effects of pressure probe positioning. Subsequent analysis focused on the characterization of the friction factor as function of the Reynolds number with the aim of establishing the proper geometrical scaling to achieve flow conditions similar to real turbine most critical ones. The eventual direct influence of both geometrical scaling and operating conditions was investigated as well. Additional CFD computations were used to assess the entrance length effects and the spanwise extension of the honeycomb pack. Finally the different behaviour of the honeycomb sealing depending on the hexagonal cell arrangement was evaluated both in terms of flow structure and friction factor showing an increase of 15% circa with the facing edge arrangement.
On the Combined Effect on Operating Range of Adjustable IGVs and Variable Speed in Process Multistage Centrifugal Compressors
Authors: Del Greco Alberto Scotti , Tapinassi Libero
Published: November 2013

Adjustable inlet guide vanes (IGVs) and variable speed drivers are known as providing process compressors with an effective regulation all throughout the operating envelope of the machine. A large number of works exists in literature reporting the successful control of multistage centrifugal compressors by means of IGVs or speed separately, while a few studies document the combined use of both devices and their effect on compressor performance.

The present paper details the off-design behavior of a multistage centrifugal compressor equipped with both types of control. It is shown that classical IGVs advantage in extending the operating envelope of a fixed speed multistage compressor tends to reduce when speed regulation is active too. In this sense, the average level of peripheral Mach numbers inside the compressor may be interpreted as a sort of threshold, since it deeply affects the stage mismatching at off-design conditions.

This consideration is corroborated by a number of applications in a wide range of design peripheral Mach numbers. Based on those cases, the paper reviews the general effectiveness of the combined regulation, thus outlining some general rules of thumb for the choice of the optimal control device for a multistage centrifugal compressor.
Experimental and Numerical Study of Particle Ingestion in Aircraft Engine
Authors: De Giorgi Maria Grazia , Campilongo Stefano , Ficarella Antonio , Coltelli Mauro , Pfister Valerio , Sepe Francesco
Published: November 2013

This study is focused on volcanic ash ingestion in aircraft engines, that can lead to slow but constant deterioration in engine performance and engine failure because of the mechanical damages to the wall surface. In particular the particles that impact on blades surfaces cause erosion damage and permanent losses in engine performance. Aircraft engine fans could be severely damaged by the ash flow.. In order to clarify the erosion phenomenon the fan has been simulated through the general-purpose CFD code and the numerical simulations were performed using the Reynolds–Averaged Navier–Stokes (RANS). After validating the numerical modeling of the flow without erosion by comparisons with experimental data in literature, a surface injection of a discrete phase has been introduced in order to evaluate particle ingestion of volcanic ash. This phenomenon is a typical gas-particle two-phase turbulent flow and a multi-physics problem where the flow field, particle trajectory and wall deformation interact with among others. A wide experimental investigation has been carried out on an ash sample from Etna volcano. In particular a sieve analysis to obtain particles dimensional distribution and an analysis of SEM images to calculate particles shape factor. These data were used to modeling the particle injection in the CFD model. The numerical investigation was aimed to clarify the effects of particle erosion and to evaluate the change of the flow field in the case of eroded blades. By erosion rate patterns, the eroded mass was estimated and it was used to model the eroded geometry, by a user routine implemented in the dynamic mesh module of the code. So the performances of the damaged fan were estimated and compared with the baseline geometry without erosion.
Development of a Tool for Temperature Estimation From Microstructural Condition of a NiCoCrAlY+Re Coating Applied on the Surface of Gas Turbine Hot Components
Authors: Costa Alessio , Vacchieri Erica , Barbareschi Emma , Guarnone Paola , Bonadei Alessandra , Calcagno Claudia
Published: November 2013

The hot gas path components of gas turbines have to withstand to severe conditions in terms of high temperature oxidation, hot corrosion and creep-fatigue phenomena. The evaluation of components residual life is an important matter for gas turbines producers and the estimation of service temperatures is a key tool for this evaluation.

The most diffused methods to estimate service temperatures of gas turbines blades and vanes in Ni based superalloys are related to the microstructural evolution of the dispersed intermetallic phase γ′, Ni3Al. The aim of this work has been the determination of a tool to estimate service temperature on the basis of the microstructural evolutions of a NiCoCrAlY+Re coating. In order to obtain a deep characterisation of the coating after exposure at different durations and temperatures, an extensive experimental test program has been planned.

Samples of Ni based superalloys, covered by the investigated coating, have been aged in chamber furnaces in the temperature range 700°C – 1000°C with durations up to 20000 hours.

The microstructure of this coating is characterised by β phase, NiAl, which is the Al reservoir, embedded in the matrix, that is constituted by γ′ phase at low temperature and by γ phase over 900°C. Moreover, electron back scattered diffraction (EBSD) and X-ray diffraction (XRD) measurements on samples have revealed three classes of secondary phases: the first one has been identified as σ-Cr2Re3, the second one as Cr carbide-Cr23C6 and the third one as α-Cr. σ phase is very abundant at the lower temperatures while it disappears after long exposures at temperatures higher than 900°C. The σ phase composition is different at different temperatures and the Re content in particular increases with the temperature.

Starting from the σ phase composition determined at different temperatures, a tool has been constructed that relates the service temperature to the Re content in the same phase. The new tool has been applied to the analyses of different components.

The results of the new method have been compared to those ones obtained with the method based on γ′ features, developed in the past through huge experimental campaigns. The agreement between the two methods is generally good, they can be used in a complementary way due to the fact that the γ′ one seems to be more suitable for high temperature ranges (T>900°C) where it gives a reliable estimation, while the sigma method is more suitable in the temperature range 700°C – 900°C.
On Key Features of the AEV Burner Engine Implementation for Operational Flexibility
Authors: Bothien Mirko R. , Pennell Douglas A. , Zajadatz Martin , Döbbeling Klaus
Published: November 2013

Modern gas turbine combustors have to fulfill two major requirements. On the one hand they have to provide reliable operation with low emissions; on the other operational flexibility is of utmost importance. Alstom’s new AEV (Advanced EnVironmental) burner — an evolution of the proven EV burner technology — is one key feature to fulfill both on engine level. It can be operated on fuel gas and oil. In order to achieve low NOx emissions, modern combustors are operated in lean-premixed mode which is prone to thermoacoustic instabilities. This is accounted for by the implementation of multi-volume dampers. These dampers feature high damping performance in a broad low-frequency range thus widely enlarging the operating window. During transient operation, especially when switching from gaseous to liquid fuel and vice versa, the specific switching procedure with sophisticated fuel flow control schemes allows for a very smooth transmission. Another very important aspect is the optimization of leakage and cooling air into the combustion chamber. In order to validate the reduction of both, multiple thermal paint applications for fuel gas and oil operation in the full scale engine were performed at different engine loads up to baseload. In this paper, the AEV burner, broadband acoustic dampers, optimized cooling and leakage schemes, as well as innovative fuel switchover and operation concepts are described. It is shown that the combination of all of them makes the GT13E2 outstanding in fuel and operational flexibility featuring low emissions over the whole operating window.
Identifying Key Technology Areas to Fundamentally Reduce Risk in Engine Performance and Noise for Future Commercial Applications
Authors: Kestner Brian K. , Jimenez Hernando , Perullo Christopher A. , Schutte Jeff S. , Mavris Dimitri N.
Published: November 2013

There have been many studies in the past which have evaluated the potential fuel savings benefits of various engine technologies applied simultaneously to a gas turbine engine. Coupled with the inclusion of new engine technology is almost always a change to the engine cycle design in order to maximize the full benefits of the technology. Current research focuses on the trends in benefits due to potential technologies and cycle design changes and identifies which specific technology areas can be targeted to reduce risk relative to meeting performance goals. The results are used to identify high priority technologies that increase the chances of meeting performance metrics. Such investigations can add value to government and industry entities that are engaging in aviation technology development programs attempting to simultaneously meet reduction goals for noise and fuel burn.

Jet and fan noise are primary sources of noise on current engine architectures. Noise suppression technologies can be applied to current engine designs to suppress sources of noise thereby reducing the noise impact of the engine. Similarly, the engine cycle can be changed to reduce noise and fuel burn. The critical link is that feasible engine cycles are tightly coupled to the subsystem technologies applied to various engine components. This leads to two critical questions. First, what part of the engine cycle is key to simultaneously meeting noise and fuel burn goals? This inevitably leads to one of three areas, the propulsor (BPR), the core (OPR), or the transmission mechanism between the core and propulsor. The other question is: which subsystem technologies are crucial to achieve the necessary core, propulsor, or power transmission improvements?

To answer these questions, this study examines and quantifies the potential benefits in technologies developed for both noise source reduction and thermal / propulsive efficiency increases. Trade studies on the potential impacts of each of the technologies are performed to capture the sensitivity on fuel burn and noise from changes to assumed benefits of the engine cycle and applied subsystem technologies. It will be demonstrated that a geared transmission is the primary enabler to simultaneously meeting performance goals. Should the geared transmission fall short, other areas of improvement simply cannot overcome the shortfall in fuel burn and noise.
Unified Applicable Propulsion System Performance Metrics
Authors: Schmitz Oliver , Hornung Mirko
Published: November 2013

Progress in the development of electrical storage and conversion technology progressively attains focus in aerospace motive power research. Novel propulsion system concepts based on hybrid or even entirely electrical energy sources are seriously considered for aircraft design. To this point, unified figures of merit are required in order to allow for consistent comparative investigations of existing combustion engines and future electrically-based propulsion systems. Firstly, this paper identifies the shortcomings of conventional performance metrics used for non-thermal electrical conversion processes and then approaches exergy-based loss methods as means of metrics extensions. Subsequently, energy source-independent figures of merit based on exergy analysis are derived and embedded into the well-known performance definitions. Finally, the unified metrics are demonstrated through application to a conventional turbofan, a parallel-hybrid turbofan, a novel integrated-hybrid turbofan concept and an entirely electrical fan concept.
Influence of Leading Edge Fillet and Nonaxisymmetric Contoured Endwall on Turbine NGV Exit Flow Structure and Interactions With the Rim Seal Flow
Authors: Turgut Özhan H. , Camcı Cengiz
Published: November 2013

Three different ways are employed in the present paper to reduce the secondary flow related total pressure loss. These are nonaxisymmetric endwall contouring, leading edge (LE) fillet, and the combination of these two approaches. Experimental investigation and computational simulations are applied for the performance assessments. The experiments are carried out in the Axial Flow Turbine Research Facility (AFTRF) having a diameter of 91.66cm. The NGV exit flow structure was examined under the influence of a 29 bladed high pressure turbine rotor assembly operating at 1300 rpm. For the experimental measurement comparison, a reference Flat Insert endwall is installed in the nozzle guide vane (NGV) passage. It has a constant thickness with a cylindrical surface and is manufactured by a stereolithography (SLA) method. Four different LE fillets are designed, and they are attached to both cylindrical Flat Insert and the contoured endwall. Total pressure measurements are taken at rotor inlet plane with Kiel probe. The probe traversing is completed with one vane pitch and from 8% to 38% span. For one of the designs, area averaged loss is reduced by 15.06%. The simulation estimated this reduction as 7.11%. Computational evaluation is performed with the rotating domain and the rim seal flow between the NGV and the rotor blades. The most effective design reduced the mass averaged loss by 1.28% over the whole passage at the NGV exit.
Experimental Investigation of OH* and CH* Chemiluminescence Under Varying Operating Conditions
Authors: Tautschnig G. , Hampel B. , Hirsch C. , Sattelmayer T.
Published: November 2013

In this study a measurement method is presented to determine the air excess ratio in two dimensions from the OH*/CH* chemiluminescence intensity ratio. For those measurements three bandpass filtered images of OH*, CH* and CO2* need to be taken simultaneously. The original image is tripled by three lenses. After distortion correction those three images can be used to calculate the OH*/CH* ratio. To validate the gained data, the focus lies on fundamental investigations with a spectrometer, done on two combustion processes: a premixed natural gas/air swirl-flame with a preheat temperature of 450K and a sequential combustion process where the second natural gas/vitiated air flame is investigated. Here the inlet temperature of the vitiated air in the second combustion stage is 1,300K. Beside preheat temperature, pressure is varied from one to three bar. Hence reference data is available for the range below and beyond the autoignition temperature of natural gas at various pressures. Thus the impact of a sequential combustion process on the OH*/CH* chemiluminescence intensity ratio is captured too.
Heat Transfer and Pressure Loss Measurements in a Turbulated High Aspect Ratio Channel With Large Reynolds Number Flows
Authors: Mhetras Shantanu , Han Je-Chin , Huth Michael
Published: November 2013

Experiments to investigate heat transfer and pressure loss are performed in a rectangular channel with an aspect ratio of 6 at very high Reynolds numbers under compressible flow conditions. Reynolds numbers up to 1.3 million are tested. The presence of a turbulated wall and the resultant heat transfer enhancement against a smooth surface is investigated. Three dimpled configurations including spherical and cylindrical dimples are studied on one wide wall of the channel. The presence of discrete ribs on the same wide wall is also investigated. A steady state heat transfer measurement method is used to obtain the heat transfer coefficients while pressure taps located at several streamwise locations in the channel walls are used to record the static pressures on the surface. Experiments are performed for a range of Reynolds numbers from 100,000 to 1,300,000 to cover the incompressible as well as compressible flow regimes. Results for low Reynolds numbers are compared to existing heat transfer data available in open literature for similar configurations. Heat transfer enhancement is found to decrease at high Re with the discrete rib configurations providing the best enhancement but highest pressure losses. Local measurements using the steady state, hue-detection based liquid crystal technique are also performed in the fully developed region for case 1 with dimples. Good comparison is obtained between averaged local heat transfer coefficient measurements and from thermocouple measurements.
Development and Validation of a Methodology for Stationary Gas Turbine Performance Prognostic
Authors: Alkmin Freire Ronaldo Lucas , Barbosa João Roberto
Published: November 2013

The gas turbines have been under intense technological development during the past decades. Among the factors that motivate manufacturers to develop differentiated products, it can be cited the rising fossil fuels prices, environmental legislation and increasingly restrictive competition with other alternatives to generate power. Even in the current scenario of global economic crisis, manufacturers and users expect an increase in the number of gas turbines in operation.

In offshore oil & gas exploration, the thermal efficiency of gas turbines has been traditionally at the background compared to the operational continuity. However, nowadays many operators are investing in subsea pipelines to export the associated gas produced in the platforms. In this scenario, the gas, which has been traditionally burned at the flare system, now represents a commercial product.

Performance monitoring of gas turbines for diagnostic of failures has been developed by researchers over the last decades. There are several diagnostic methodologies currently available in the open literature; however, the amount of publications demonstrating successful application in real cases is still reduced. Regarding the application of performance monitoring for prognostic of failures, the scenario is even more premature. Despite of that, both diagnostic and prognostic techniques are seen as very promising from the user point-of-view.

This paper proposes a methodology for performance prognostic based on parameters effectively measured by typical instruments of commercial units. The method makes use of the performance modeling easily found in the literature. The performance parameters measured and also calculated are then corrected to a reference condition in order to eliminate the effects of the variable ambient condition. Future performance parameters are then extrapolated. The methodology was validated through real data of a gas turbine operating in an oil platform. The results showed that the method produces useful information to support the operation and maintenance teams.
Effect of Water Temperature on the Performance of Gas Turbine Inlet Air-Fogging Systems
Authors: Chaker Mustapha A. , Meher-Homji Cyrus B.
Published: November 2013

With more than 1000 fogging systems installed worldwide on a wide range of gas turbines of different types, gas turbine inlet air fogging systems have become a well-established technology used to increase gas turbines power output.

The major benefit of spraying fog droplets in the inlet airflow of the gas turbines is to increase the density of the air entering the gas turbine by evaporative cooling in the inlet air stream. Significant amount of research has been carried out to improve the efficiency of fogging systems. However, the effect of water temperature on the overall efficiency of a fogging system has yet to be addressed. In this paper, a detailed analysis of this effect will be presented, both from an experimental and a theoretical view point.

Due to the small size of the droplets used in this application, the temperature of the droplet converges quickly to the wet bulb temperature, regardless of the initial water temperature. The rapidity at which this convergence occurs depends on the initial droplet size, the water temperature, the air mass flow to mass of injected water ratio, and the ambient psychrometric conditions of the surrounding air.

The present study was carried out using water temperatures between 1 °C and 60 °C. Results showed that the water temperature has no significant effect on the droplet size. However, within the range of droplet sizes atomized from nozzles installed in the fogging system, using cold water provides a marginal benefit on the cooling efficiency; using hot water, on the other hand, slightly increases the evaporation efficiency.
Flame and Flow Topologies in an Annular Swirling Flow
Authors: Chterev I. , Foley C. W. , Kostka S. , Caswell A. W. , Jiang N. , Seitzman J. M. , Lieuwen T. C.
Published: November 2013

A variety of different flame configurations and heat release distributions, with their associated flow fields, can exist in high swirl, annular flows. Each of these different configurations, in turn, has different thermoacoustic sensitivities and influences on combustor emissions, nozzle life, and liner heating. These different configurations arise because at least three flame stabilization locations are present, associated with the inner and outer shear layers of the annulus, and the stagnation point of the vortex breakdown region.

This paper discusses the flame and flow topologies that exist in these flows. These results illustrate the importance of the sensitivity of flame configurations to geometric (such as centerbody size and shape, combustor diameter, exhaust contraction) and operational (e.g., bulkhead temperature, preheat temperature, fuel air ratio) parameters. We particularly emphasize the centerbody shape as differentiating between two different families of flame shapes. Results are shown illustrating the time averaged and instantaneous flame shape and flow fields, using high speed PIV, OH-PLIF, and luminosity imaging.
Hybrid inorganic–organic superlattice structures with atomic layer deposition/molecular layer deposition
Authors: Tynell Tommi , Yamauchi Hisao , Karppinen Maarit
Published: November 2013

A combination of the atomic layer deposition (ALD) and molecular layer deposition (MLD) techniques is successfully employed to fabricate thin films incorporating superlattice structures that consist of single layers of organic molecules between thicker layers of ZnO. Diethyl zinc and water are used as precursors for the deposition of ZnO by ALD, while three different organic precursors are investigated for the MLD part: hydroquinone, 4-aminophenol and 4,4′-oxydianiline. The successful superlattice formation with all the organic precursors is verified through x-ray reflectivity studies. The effects of the interspersed organic layers/superlattice structure on the electrical and thermoelectric properties of ZnO are investigated through resistivity and Seebeck coefficient measurements at room temperature. The results suggest an increase in carrier concentration for small concentrations of organic layers, while higher concentrations seem to lead to rather large reductions in carrier concentration.
The Consequence of Tree Pests and Diseases for Ecosystem Services
Authors: Boyd I. L. , Freer-Smith P. H. , Gilligan C. A. , Godfray H. C. J.
Published: November 2013

Dead Wood

Trees can be affected by a wide variety of diseases caused by insects, fungi, and other pathogens. Such diseases often make the headlines—particularly when iconic tree species are affected—for example, in the case of the ash dieback currently spreading through Europe, or the chestnut blight that devastated American chestnut trees. But what is the effect of these diseases on ecosystem services performed by trees in natural and managed ecosystems?

Boyd
et al.

(p.
10.1126/science.1235773
) review the spread of tree diseases, as a result of globalization and climate change, and analyze the resulting damage to timber and fruit production, to climate regulation, and to parks and woodlands caused by tree diseases.
Long-Term Dynamics of Adaptation in Asexual Populations
Authors: Wiser Michael J. , Ribeck Noah , Lenski Richard E.
Published: November 2013

The Fit Get Fitter

Advances in modern biology have allowed us to measure evolutionary fitness and estimate the rate of fixation of beneficial mutations. Drawing on the Long-Term Evolution Experiment, studying the evolution of
Escherichia coli
in a constant environment,

Wiser
et al.

(p.
1364
, published online 14 November) demonstrate that even after 50,000 generations over 20 years, gains in fitness show no evidence of leveling off. Instead, fitness is following a power-law relationship that is dependent on epistasis and clonal interference.
Photon-Mediated Interactions Between Distant Artificial Atoms
Authors: van Loo Arjan F. , Fedorov Arkady , Lalumière Kevin , Sanders Barry C. , Blais Alexandre , Wallraff Andreas
Published: November 2013

Artificial Complexity

Quantum optics probes the interactions between light and matter. Building up from a simple, single-atom system, the exchange of virtual photons between systems of several (or many) atoms is expected to give rise to many exotic effects. Because controlling the separation of the atoms on the atomic scale is experimentally challenging, artificial atom systems may provide a more tractable route for systematic study, as described by

van Loo
et al.

(p.
1494
, published online 14 November). Using a system of two separate superconducting qubits in a microwave transmission line, they show how the interaction between the two qubits can be controlled and mediated by electromagnetic modes. The results illustrate a feasible route to probing the complexity of many-body effects that may otherwise be difficult to realize.
mTOR Inhibition Alleviates Mitochondrial Disease in a Mouse Model of Leigh Syndrome
Authors: Johnson Simon C. , Yanos Melana E. , Kayser Ernst-Bernhard , Quintana Albert , Sangesland Maya , Castanza Anthony , Uhde Lauren , Hui Jessica , Wall Valerie Z. , Gagnidze Arni , Oh Kelly , Wasko Brian M. , Ramos Fresnida J. , Palmiter Richard D. , Rabinovitch Peter S. , Morgan Philip G. , Sedensky Margaret M. , Kaeberlein Matt
Published: November 2013

More from mTOR

Leigh syndrome is a rare, untreatable, inherited neurodegenerative disease in children that is caused by functional disruption of mitochondria, the cell's energy-producing organelles.

Johnson
et al.

(p.
1524
, published online 14 November; see Perspective by

Vafai and Mootha

) show that rapamycin, a drug used clinically as an immunosuppressant and for treatment of certain cancers, delayed the onset and progression of neurological symptoms in a mouse model of Leigh syndrome and significantly extended survival of the animals. Rapamycin inhibits the so-called “mTOR” signaling pathway, which is currently under intense study because it plays a contributory role in many common diseases.
Initiative Aims to Minister to Mexico's Unique Genetic Heritage
Authors: Wade Lizzie
Published: November 2013

Mexican and U.S. researchers are teaming up to study the Mexican genome, with the hope of developing new diagnostics and drugs targeted to Latin American populations.
Draft Genome Sequence of Lactobacillus fermentum Lf1, an Indian Isolate of Human Gut Origin
Authors: Grover Sunita , Sharma Vineet K. , Mallapa Rashmi H. , Batish Virender K.
Published: November 2013

Lactobacillus fermentum
is a normal inhabitant of the human gastrointestinal tract. Here, we report the draft genome sequence of an Indian isolate of the probiotic strain
L. fermentum
Lf1, isolated from the human gut.
Metagenome Sequencing of Prokaryotic Microbiota from Two Hypersaline Ponds of a Marine Saltern in Santa Pola, Spain
Authors: Fernandez Ana B. , Ghai Rohit , Martin-Cuadrado Ana Belen , Sanchez-Porro Cristina , Rodriguez-Valera Francisco , Ventosa Antonio
Published: November 2013

Marine salterns are composed of several shallow ponds with a salinity gradient, from seawater to salt saturation, with gradually changing microbial populations. Here, we report the metagenome sequencing of the prokaryotic microbiota of two ponds with 13% and 33% salinity from a saltern in Santa Pola, Spain.
Nosocomial Outbreak of Salmonella enterica Serovar Typhimurium Primarily Affecting a Pediatric Ward in South Africa in 2012
Authors: Smith Anthony M. , Mthanti Mnikelwa A. , Haumann Carel , Tyalisi Nomalungisa , Boon Gerald P. G. , Sooka Arvinda , Keddy Karen H.
Published: November 2013

We describe a nosocomial outbreak of diarrheal disease caused by extended-spectrum β-lactamase-producing multidrug-resistant
Salmonella enterica
serovar Typhimurium, focused on a pediatric ward in South Africa. The outbreak peaked between May 2012 and July 2012. Person-to-person transmission was the most likely mechanism of spread of the infection, expedited due to a breakdown in hand-washing and hygiene, suboptimal infection control practices, overcrowding of hospital wards, and an undesirable nurse-to-patient ratio.
Vaccination with a Fusion Protein That Introduces HIV-1 Gag Antigen into a Multitrimer CD40L Construct Results in Enhanced CD8
+
T Cell Responses and Protection from Viral Challenge by Vaccinia-Gag
Authors: Gupta Sachin , Termini James M. , Raffa Francesca N. , Williams Cindi-Ann , Kornbluth Richard S. , Stone Geoffrey W.
Published: November 2013

CD40 ligand (CD40L, CD154) is a membrane protein that is important for the activation of dendritic cells (DCs) and DC-induced CD8
+
T cell responses. To be active, CD40L must cluster CD40 receptors on responding cells. To produce a soluble form of CD40L that clusters CD40 receptors necessitates the use of a multitrimer construct. With this in mind, a tripartite fusion protein was made from surfactant protein D (SPD), HIV-1 Gag as a test antigen, and CD40L, where SPD serves as a scaffold for the multitrimer protein complex. This SPD-Gag-CD40L protein activated CD40-bearing cells and bone marrow-derived DCs
in vitro
. Compared to a plasmid for Gag antigen alone (pGag), DNA vaccination of mice with pSPD-Gag-CD40L induced an increased number of Gag-specific CD8
+
T cells with increased avidity for major histocompatibility complex class I-restricted Gag peptide and improved vaccine-induced protection from challenge by vaccinia-Gag virus. The importance of the multitrimeric nature of the complex was shown using a plasmid lacking the N terminus of SPD that produced a single trimer fusion protein. This plasmid, pTrimer-Gag-CD40L, was only weakly active on CD40-bearing cells and did not elicit strong CD8
+
T cell responses or improve protection from vaccinia-Gag challenge. An adenovirus 5 (Ad5) vaccine incorporating SPD-Gag-CD40L was much stronger than Ad5 expressing Gag alone (Ad5-Gag) and induced complete protection (i.e., sterilizing immunity) from vaccinia-Gag challenge. Overall, these results show the potential of a new vaccine design in which antigen is introduced into a construct that expresses a multitrimer soluble form of CD40L, leading to strongly protective CD8
+
T cell responses.