bluuebunny/crossref_metadata_2025 huggingface dataset:
Cirrhosis but not neutropenia is associated with the development of infection in patients with chronic hepatitis C undergoing treatment with pegylated interferon‐alpha and ribavirin
Authors: Striki A. , Manolakopoulos S. , Deutsch M. , Mela M. , Kalafateli M. , Schini M. , Anagnostou O. , Triantos C. , Andreadis I. , Ketikoglou I. , Papatheodoridis G. , Pectasides D.
Published: November 2013

Peginterferon‐alpha (PegIFNa) frequently causes neutropenia, mainly due to bone marrow suppression. The aim of this study was to explore factors that are associated with infections during antiviral treatment. We analysed data from 275 chronic hepatitis C (CHC) patients with compensated liver disease who underwent 318 courses of PegIFNa and ribavirin. Neutropenia was defined as neutrophils <1000 cells/μL. Mean leucocytes count significantly decreased from baseline to treatment nadir (7081 ± 2182 vs 3293 ± 1331 cells/μL, P < 0.001), while neutropenia was observed in 32% during treatment. Thirty‐one infections were observed. The incidence rate for infection was assessed at 1.46 infections per 100 person‐months of therapy. The hazard rate for infection did not correlate with the neutrophils' nadir or the decrease in white blood cells. In multivariate Cox's regression analysis, cirrhosis was the only factor that was significantly associated with the occurrence of infection. Our data show that the development of bacterial infections during treatment with PegIFNa and ribavirin in patients with compensated CHC is not associated with reduction or the nadir of white cells or neutrophil counts. Baseline cirrhosis is the only factor related with infection during treatment. The common practice of dose adjustment or discontinuation of interferon should be revised; careful assessment of liver damage before therapy and close monitoring during therapy are essential in all patients receiving interferon‐based regimes, to minimize the detrimental consequences of infections.
Predictors of early treatment discontinuation in a cohort of patients treated with boceprevir‐based therapy for hepatitis C infection
Authors: Majid A. , McAninch J. , Morgan D. J. , El Kamary S. S. , Zhan M. , Kapelusznik L. , Talwani R.
Published: November 2013

In this real‐world cohort, 49% of patients stopped boceprevir‐based hepatitis C therapy early, with only 20% stopping due to treatment futility. Having more comorbidities was significantly associated with early discontinuation. Tolerability of boceprevir‐based regimens may be substantially worse than reported in clinical trials, particularly for patients with comorbidities.
An essential enzyme for phospholipid synthesis associates with the Bacillus subtilis divisome
Authors: Takada Hiraku , Fukushima‐Tanaka Sanae , Morita Masato , Kasahara Yasuhiro , Watanabe Satoru , Chibazakura Taku , Hara Hiroshi , Matsumoto Kouji , Yoshikawa Hirofumi
Published: November 2013

The mechanism by which the membrane synthetic machinery might be co‐organized with the cell‐division architecture during the bacterial cell cycle remains to be investigated. We characterized a key enzyme of phospholipid and fatty acid synthesis in Bacillus subtilis, the acyl–acyl carrier protein phosphate acyltransferase (PlsX), and identified it as a component of the cell‐division machinery. Comprehensive interaction analysis revealed that PlsX interacts with FtsA, the FtsZ‐anchoring protein. PlsX mainly localized at the potential division site independent of FtsA and FtsZ and then colocalized with FtsA. By multidirectional approaches, we revealed that the Z‐ring stabilizes the association of PlsX at the septum and pole. The localization of PlsX is also affected by the progression of DNA replication. PlsX is needed for cell division and its inactivation leads to aberrant Z‐ring formation. We propose that PlsX localization is prior to Z‐ring formation in the hierarchy of septum formation events and that PlsX is important for co‐ordinating membrane synthesis with cell division in order to properly complete septum formation.
The thinking ape: the enigma of human consciousness
Authors: Paulson Steve , Chalmers David , Kahneman Daniel , Santos Laurie , Schiff Nicholas
Published: November 2013

What is the origin and nature of consciousness? If consciousness is common to humans and animals alike, what are the defining traits of human consciousness? Moderated by Steve Paulson, executive producer and host of To the Best of Our Knowledge, Nobel laureate psychologist Daniel Kahneman, philosopher David Chalmers, expert in primate cognition Laurie Santos, and physician‐scientist Nicholas Schiff discuss what it means to be conscious and examine the human capacities displayed in cognitive, aesthetic, and ethical behaviors, with a focus on the place and function of the mind within nature. The following is an edited transcript of the discussion that occurred October 10, 2012, 7:00–8:15 PM, at the New York Academy of Sciences in New York City.
Narrowband Ultraviolet B Light in Langerhans Cell Histiocytosis: A Case Report
Authors: Ness Molly J. , Lowe Garrett C. , Davis Dawn M. R. , Hand Jennifer L.
Published: November 2013

Langerhans cell histiocytosis (LCH) (previously called eosinophilic granuloma, Hand–Schüller–Christian syndrome, Letterer–Siwe disease, and Hashimoto–Pritzker disease) is a rare, heterogeneous disorder with highly variable presentation. LCH commonly affects the skin, as well as internal organs. Because the skin lesions appear benign, and LCH is unfamiliar to most physicians, diagnosis is often delayed. Treatment is controversial, with further clinical study needed. For persons with extensive, skin‐limited disease, the existing topical therapies are impractical. We present a child with cutaneous LCH lesions that responded to ultraviolet light phototherapy with minimal adverse effects or patient discomfort.
Human Papilloma Virus is not Prevalent in Nevus Sebaceus
Authors: Kim David , Benjamin Latanya T. , Sahoo Malaya K. , Kim Jinah , Pinsky Benjamin A.
Published: November 2013

Nevus sebaceus (NS) is a common congenital cutaneous hamartoma that typically presents on the scalp and face at birth or in early childhood. Occasionally NS can be associated with the Schimmelpenning–Feuerstein–Mims syndrome, which presents with concomitant severe neurologic, skeletal, cardiovascular, ophthalmic, and genitourologic disorders. In a previous study, maternal transmission of the human papillomavirus (HPV) and infection of ectodermal stem cells by HPV was postulated to result in the development of NS. In this study we aimed to determine the incidence of HPV infection in pediatric NS samples to further clarify the potential link between HPV and the pathogenesis of NS. NS tissue samples (N = 16) were analyzed for HPV DNA using type‐specific, real‐time polymerase chain reaction (PCR) targeting HPV 6, 11, 16, and 18 and conventional PCR with modified general primers designed for broad‐range HPV detection. The tissues were also histologically evaluated for evidence of HPV infection. HPV DNA was not detected in any of the NS tissue samples using PCR and HPV‐associated histopathologic changes were absent in all 16 NS tissues. HPV infection is an unlikely etiologic cause of NS.
Risk factors associated with self‐reported symptoms of digital ischemia in elite male volleyball players in the Netherlands
Authors: van de Pol D. , Kuijer P. P. F. M. , Langenhorst T. , Maas M.
Published: November 2013

One in every four elite male volleyball players in the Netherlands reported blue or pale digits in the dominant hand. Little is known about risk factors. To assess whether personal‐, sports‐, and work‐related risk factors are associated with these symptoms in these volleyball players, a survey was performed among elite male volleyball players in the Dutch national top league and in the Dutch beach volleyball team. The questionnaire assessed the presence of symptoms and risk factors. Binary logistic regression was performed to calculate odds ratios (ORs). A total of 99 of the 107 athletes participated – a response rate of 93%. Two sports‐related risk factors were associated with symptoms of blue or pale digits: 18–30 years playing volleyball [OR = 6.70; 95% confidence interval (CI) 1.12–29.54] and often/always performing weight training to increase dominant limb strength (OR = 2.70; 95% CI 1.05–6.92). No significant other sports‐, personal‐, or work‐related risk factors were found. Playing volleyball for more than 17 years and often/always performing weight training to increase dominant limb strength were independently associated with an increased risk on ischemia‐related complaints of the dominant hand in elite male volleyball players.
New Stability Criteria for Stochastic Takagi–Sugeno Fuzzy Systems With Time-Varying Delays
Authors: Mathiyalagan K. , Sakthivel R. , Marshal Anthoni S.
Published: November 2013

This paper is concerned with the asymptotic stability issue for a class of stochastic Takagi–Sugeno (TS) fuzzy systems with time-varying delays. Then, by utilizing a delay-fractioning method, the stochastic analysis theory combined with the matrix inequality technique, a new set of sufficient condition in terms of linear matrix inequalities is presented which ensures the asymptotic stability of the stochastic TS fuzzy systems with time-delays. The results obtained in this paper are delay-dependent in the sense that they depend on not only the lower bound but also the upper bound of the time-varying delay. Numerical examples are given to illustrate the effectiveness and less conservativeness of the obtained results.
Equilibrium Based Curve Fitting Method for Test Data With Nonuniform Variance
Authors: Wei Zhigang , Maleki Shervin , Nikbin Kamran
Published: November 2013

A recently developed equilibrium based curve/surface fitting method is extended to linear function with heteroscedastic data (variable variance). The concept of equilibrium weighted “force” and “moment” is proposed to derive curve fitting formulae, which are exactly the same as that obtained with the traditional weighted least squares (LS) method for a linear function. Furthermore, a system of four equations, i.e., a “force” equilibrium equation, a “moment” equilibrium equation, an “equivalency” equation, and a “moment balance” equation have been established to solve both mean curve and the standard deviation simultaneously. Finally, the application of these methods to data of fatigue and creep lives is presented.
Offset Turbulent Jets in Low-Aspect Ratio Cavities
Authors: Nath C. , Voropayev S. I. , Lord D. , Fernando H. J. S.
Published: November 2013

The flow induced by a round turbulent offset jet in a low-aspect ratio cylinder is investigated experimentally, with applications to degassing of U.S. Strategic Petroleum Reserves (SPR). Particle image velocimetry and flow visualization are used for flow diagnostics. The measurements include the jet penetration (mixing) depth l, jet spreading rate, and the mean velocity/vorticity fields for different offset positions Δ. With the introduction of offset, the flow patterns change drastically. For 0 < Δ/D < 0.2 the jet deflects toward the wall while precessing (as in the axisymmetric case), for 0.2 < Δ/D < 0.4 the jet hugs the wall but with an oscillating tail, and for 0.45 < Δ/D the jet appears as a wall jet. In all cases, the jet is destroyed at a certain distance (mixing or penetration depth) from the origin. This mixing depth takes its lowest value for 0 < Δ/D < 0.2, with l ≈ (3.2–3.6)D, becomes maximum at Δ/D = 0.4 with l ≈ 5.2D, and drops to l ≈ 4.5D when the jet is close to the wall. Recommendations are made for suitable Δ/D values for optimal operation of SPR degassing.
Improving Process Performance of Distributed Set-Based Design Systems by Controlling Wellbeing Indicators of Design Actors
Authors: Canbaz Baris , Yannou Bernard , Yvars Pierre-Alain
Published: November 2013

In new complex product development processes, the design problem is usually distributed to multiple actors from different disciplines. Each design actor has a limited responsibility in the design system. Therefore, each design actor has limited control over design variables and performance variables. However, design actors are not isolated since their design activities are coupled. This can generate design conflicts through inconsistencies among design objectives and working procedures. When the design convergence is not controlled, inconsistencies can distort the satisfaction equilibrium between design actors. This means that if a design actor aims at satisfying only his/her local design objective, other actors having conflicting objectives will be dissatisfied. Thus, individual satisfactions diverge. The intensity of conflicts is measured with the satisfaction divergence. In this paper, we define wellbeing indicators in order to control the convergence of distributed set-based design (SBD) processes. Wellbeing indicators reflect design actors' satisfaction degree of their process desires. We performed a constraint programming Monte Carlo simulation of our SBD framework with a complex design problem. We compared the results of wellbeing indicators with the results of the processes where design actors do not use wellbeing indicators. It is shown that when design actors have some means to control their convergence, the solution space converges to a solution in satisfaction equilibrium while epistemic uncertainty of the design model is reduced. Some conflicts are therefore prevented and the satisfaction divergence is reduced, leading thus to an improved design process performance.
Modeling Fuel Injection in Gas Turbines Using the Meshless Smoothed Particle Hydrodynamics Method
Authors: Braun S. , Höfler C. , Koch R. , Bauer H.-J.
Published: November 2013

For predicting primary atomization a numerical code has been developed based on the Lagrangian Smoothed Particle Hydrodynamics (SPH) method. The advantage of this approach is the inherent interface advection. In contrast to commonly used grid based methods such as the Volume of Fluid (VoF) or Level Set method there is no need for costly and approximative interface tracking or reconstruction techniques which are required to avoid interface diffusion. It has been demonstrated by various test cases that the SPH method is capable to correctly predict single — as well as multiphase flows including the effect of surface tension. The goal of this work is to further develop the methodology with the intention to simulate primary atomization within airblast atomizers of jet engines. The authors present two test cases relevant for the simulation of primary atomization. The shear-driven deformation of a fuel droplet in a gaseous flow has been investigated and compared to data from literature. Moreover, the liquid film disintegration at the trailing edge of a planar prefilming airblast atomizer has been studied. The geometry has been derived from an existing test rig, where extensive experimental data have been acquired. Resulting droplet sizes and shear-off frequencies for different geometrical setups have been analyzed and compared to the experiment. The results reveal the promising performance of this new method for predicting primary atomization.
Impacts of Geometric Parameters of Double-Jet Film Cooling on Anti-Kidney Vortex Structure and Cooling Effectiveness
Authors: Wang Zhan , Liu Jian-Jun , Zhang Chao
Published: November 2013

Pressure sensitive paint (PSP) measurement technique and numerical calculation were used to study the impact of geometric parameters of double jet film cooling (DJFC) on the resultant vortex structure and cooling effectiveness, and the design principle of DJFC according to different blowing ratios was put forward. The results indicate that the formation of effective anti-kidney vortices is the key to enhance the cooling effectiveness of DJFC holes. While the blowing ratio is low, the streamwise or lateral distance between the two holes of DJFC should be increased to widen the lateral coverage of the coolant; while the blowing ratio is high, the streamwise and lateral distance should be decreased to prevent the two cooling streams from separating apart so that the malfunction of the anti-kidney vortices could be avoided. Small compound angle is negative to enhance the cooling effectiveness.
Evaluation of GT Outboard Bleed Air on Overall Engine Efficiency and CO2e Emission in Natural Gas Compressor Stations
Authors: Botros K. K. , Golshan H. , Rogers D. , Sloof B.
Published: November 2013

Gas turbine (GT) engines employed in natural gas compressor stations operate in different modes depending on the power, turbine inlet temperature and shaft speeds. These modes apply different sequencing of bleed valve opening on the air compressor side of the engine. Improper selection of the GT and the driven centrifugal gas compressor operating conditions can lead to larger bleed losses due to wider bleed valve openings. The bleed loss inevitably manifests itself in the form of higher overall heat rate of the GT and greater engine emission. It is therefore imperative to determine and understand the engine and process conditions that drive the GT to operate in these different modes. The ultimate objective is to operate the engine away from the inefficient modes by adjusting the driven gas compressor parameters as well as the overall station operating conditions (i.e. load sharing, control set points, etc.). This paper describes a methodology to couple the operating conditions of the gas compressor to the modes of GT bleed valve opening (and the subsequent air bleed rates) leading to identification of the operating parameters for optimal performance (i.e., best overall efficiency and minimum CO2e emission). A predictive tool is developed to quantify the overall efficiency loss as a result of the different bleed opening modes, and map out the condition on the gas compressor characteristics. One year’s worth of operating data taken from two different compressor stations on TransCanada Pipelines’ Alberta system were used to demonstrate the methodology. The first station employs GE-LM1600 gas turbine driving a Cooper Rolls-RFBB-30 centrifugal compressor. The second station employs GE-LM-2500+ gas turbine driving NP PCL-800/N compressor. The analysis conclusively indicates that there are operating regions on the gas compressor maps where losses due to bleed valves are reduced and hence CO2 emissions are lowered, which presents an opportunity for operation optimization.
Axial Turbine Flow Path Design for an Organic Rankine Cycle Using R-245fa
Authors: Moroz Leonid , Kuo Chi-Ron , Guriev Oleg , Li Yi-Chen , Frolov Boris
Published: November 2013

Limited fossil fuel resources along with the ever-increasing demand for inexpensive and environmentally friendly energy are the driving factors of geothermal and waste heat recovery technologies. In the last two decades, the Organic Rankine Cycle (ORC), has been improved and modified to better adapt the cycle to the various conditions of heat sources and has become a preferred means of exploiting low potential heat resources of various types and been widely used in many applications as an efficient and reliable energy source.

This paper represents results for the 250kW power unit, which utilizes the R-245fa refrigerant for ORC cycle in low temperature range up to 150 deg. C. The detailed design process of an ORC turbine is presented and discussed. The effect of general turbine configurations and component design on turbine efficiency and structural integrity is studied. Cost and weight cut off aspects of turbine construction also discussed. The level of efficiency achieved as a result of turbine optimization, is at the top for this class of small turbines. Final variant represents one stage axial turbine with integrally bladed disk, inlet scroll and outlet tail pipe. Structural optimization has been performed to minimize rotor weight at an acceptable level of stress and frequency safety factors.
Assessment and Characterization of Volcanic Ash Threat to Gas Turbine Engine Performance
Authors: Davison Craig R. , Rutke Tim
Published: November 2013

Multiple volcanoes erupt yearly propelling volcanic ash into the atmosphere and creating an aviation hazard. The plinian eruption type is most likely to create a significant aviation hazard. Plinian eruptions can eject large quantities of fine ash up to an altitude of 50,000 m (164,000 feet). While large airborne particles rapidly fall, smaller particles at reduced concentrations drift for days to weeks as they gradually descend and deposit on the ground. Very small particles, less than 1 μm, can remain aloft for years.

An average of three aircraft encounters with volcanic ash was reported every year between 1973 and 2003. Of these, 8 resulted in some loss of engine power, including a complete shutdown of all four engines on a Boeing 747. However, no crashes have been attributed to volcanic ash. The major forms of engine damage caused by volcanic ash are:

1. Deposition of ash on turbine nozzles and blades due to glassification

2. Erosion of compressor and turbine blades

3. Carbon deposits on fuel nozzles

The combination of these effects can push the engine to surge and flame out. If a flame out occurs, engine restart may be possible.

Less serious engine damage can also occur. In most cases the major damage will require an engine overhaul long before the minor damage becomes an operational issue, but under some conditions no sign of volcanic ash is evident and the turbine cooling system blockage could go unnoticed until an engine inspection is performed.

Several organizations provide aircrew procedures to respond to encounters with a volcanic ash cloud. If a volcanic ash encounter is suspected, then an engine inspection, including borescope, should be performed with particular attention given to the turbine cooling system.
An Innovative Inlet Air Cooling System for IGCC Power Augmentation: Part III — Computational Fluid Dynamic Analysis of Syngas Combustion in Nitrogen-Enriched Air
Authors: Morini Mirko , Pinelli Michele , Spina Pier Ruggero , Vaccari Anna
Published: November 2013

In recent years, an innovative system for power augmentation has been presented by the authors. The system is based on gas turbine inlet air cooling by means of liquid nitrogen sprayers. This system is not characterized by the limits of water evaporative cooling (i.e. lower temperature limited by air saturation) and refrigeration cooling (i.e. effectiveness limited by pressure drop in the heat exchangers), but the injection of a large amount of liquid nitrogen at gas turbine inlet section can be disputable.

In fact, the air composition changes, though not considerably, after nitrogen injection. The oxygen content always seems high enough to allow a regular combustion. In any case, local effects should be further investigated.

In this paper, the effect of the increase in nitrogen molar fraction of combustion air is evaluated. A micro gas turbine combustion chamber geometry (i.e. a reverse flow tubular combustor) is taken into consideration since its model has been widely validated by the authors. The analyses are performed by considering two different fuels: methane (which is the design fuel) and syngas. The results are compared in terms of overall performance (e.g. TIT, pollutant emissions) and local distributions (e.g. flow fields, flame shape and position).
Optimization of Organic Rankine Cycles for Off-Shore Applications
Authors: Pierobon Leonardo , Larsen Ulrik , Nguyen Tuong Van , Haglind Fredrik
Published: November 2013

In off-shore oil and gas platform efficiency, the reliability and fuel flexibility are the major concerns when selecting the gas turbine to support the electrical and mechanical demand on the platform. In order to fulfill these requirements, turbine inlet temperature and pressure ratio are not increased up to the optimal values and one or more redundant gas turbines may be employed. With increasing incentives for reducing the CO2 emissions off-shore, improving the thermal efficiency has become a focus area. Due to the peculiar low turbine outlet temperature and due to space and weight constraints, a steam bottoming cycle is not a convenient solution. On the contrary, organic Rankine cycles (ORCs) present the benefits of high simplicity and compactness. Furthermore, the working fluid can be selected considering the temperature profile at which the heat is supplied; hence the heat transfer process and the thermal efficiency of the cycle can be maximized. This paper is aimed at finding the most optimal ORC tailored for off-shore applications using an optimization procedure based on the genetic algorithm. Numerous working fluids are screened through, considering mainly thermal efficiency, but also other characteristics of the fluids, e.g. stability, environmental and human health impacts, and safety issues. Both supercritical and subcritical ORCs are included in the analysis. The optimization procedure is first applied to a conservative ORC where the maximum pressure is limited to 20 bar. Subsequently the optimal working fluid is identified by removing the restriction on the maximum pressure. Different limits on hazards and global warming potential (GWP) are also set. The study is focused on the SGT-500 gas turbine installed on the Draugen platform in the Norwegian Sea. The simulations suggest that, when a high hazard is accepted, cyclohexane is the best solution. With a turbine inlet pressure limit of 20 bar, the combined gas turbine-ORC system presents an efficiency of 43.7%, corresponding to an improvement of 11.9%-points with respect to the gas turbine efficiency. With no upper pressure boundary, cyclohexane at 55.5 bar is the preferable working fluid with a combined thermal efficiency of 44.3%. The supercritical CO2 cycle with a maximum pressure of 192.9 bar is found to be the best alternative if an extremely low hazard is required.
Experimental Investigation, Modeling and Simulation of a Steam Injected Gas Turbine With Water Recovery
Authors: Hoffmann Karl , Buchheim Guntram , Sander Thomas , Gampe Uwe
Published: November 2013

Combined heat and power (CHP) plants are faced with alternating heat load caused by different seasonal heating needs of users or alternating heat consumption of industrial processes. To an increasing degree these CHP plants are decentralized generation units of smaller capacity, where combined cycles reach their limits of economy. In these cases, the steam injected gas turbine (STIG) cycle is considered as a promising and efficient technology for more flexible cogeneration of electricity and heat. At decreasing or missing heat load, the process enables to feed excessive steam, generated in the heat recovery steam generator (HRSG), into the gas turbine. Therefore, a flexible response to alternating heat load is possible. At constant electricity output of the gas turbine, steam injection results in a considerable reduction of specific heat consumption. The water losses can be minimized by condensing the steam in the exhaust gas duct of the gas turbine and reconditioning to feed water quality.

Process thermodynamic investigations with focus on optimum process scheme have already been conducted for several years by the authors. As a step forward in R&D of the process and its components, a small-capacity STIG plant with water recovery has been commissioned at the Technische Universität Dresden (TUD). It is based on a 600 kW class gas turbine. Investigations are focused both on the process such as performance, process control, water recovery, water reconditioning and on the influence of steam injection on gas turbine and compressor.

First experimental results are presented in the paper. Thereby special attention is paid to the measurement instrumentation. In addition, the authors report about thermodynamic simulation of gas turbine operation with and without steam injection.
Overall Effectiveness of a Blade Endwall With Jet Impingement and Film Cooling
Authors: Mensch Amy , Thole Karen A.
Published: November 2013

Ever increasing thermal loads on gas turbine components require improved cooling schemes to extend component life. Engine designers often rely on multiple thermal protection techniques, including internal cooling and external film cooling. A conjugate heat transfer model for the endwall of a seven blade cascade was developed to examine the impact of both convective cooling and solid conduction through the endwall. Appropriate parameters were scaled to ensure engine relevant temperatures were reported. External film cooling and internal jet impingement cooling were tested separately and together for their combined effects. Experiments with only film cooling showed high effectiveness around film cooling holes due to convective cooling within the holes. Internal impingement cooling provided more uniform effectiveness than film cooling, and impingement effectiveness improved markedly with increasing blowing ratio. Combining internal impingement and external film cooling produced overall effectiveness values as high as 0.4. A simplified one-dimensional heat transfer analysis was used to develop a prediction of the combined overall effectiveness using results from impingement only and film cooling only cases. The analysis resulted in relatively good predictions, which served to reinforce the consistency of the experimental data.
Concept for a Combustion System in Oxyfuel Gas Turbine Combined Cycles
Authors: Sundkvist Sven Gunnar , Dahlquist Adrian , Janczewski Jacek , Sjödin Mats , Bysveen Marie , Ditaranto Mario , Langørgen Øyvind , Seljeskog Morten , Siljan Martin
Published: November 2013

A promising candidate for CO2 neutral power production is Semi-Closed Oxyfuel Combustion Combined Cycles (SCOC CC). Two alternative SCOC-CCs have been investigated both with recirculation of the Working Fluid (CO2 and H2O) but with different H2O content due to different conditions for condensation of water from the Working Fluid. The alternative with low moisture content in the re-circulated Working Fluid has shown highest thermodynamic potential and has been selected for further study.

The necessity to use recirculated exhaust gas as the Working Fluid will make the design of the gas turbine quite different from a conventional gas turbine. For a combined cycle using a steam Rankine cycle as a bottoming cycle it is vital that the temperature of the exhaust gas from the Brayton cycle is well suited for steam generation that fits steam turbine live steam conditions. For oxyfuel gas turbines with a combustor outlet temperature of the same magnitude as conventional gas turbines a much higher pressure ratio is required (close to twice the ratio as for a conventional gas turbine) in order to achieve a turbine outlet temperature suitable for combined cycle.

Based on input from the optimized cycle calculations a conceptual combustion system has been developed, where three different combustor feed streams can be controlled independently: the natural gas fuel, the oxidizer consisting mainly of oxygen plus some impurities, and the re-circulated Working Fluid. This gives more flexibility compared to air-based gas turbines, but introduces also some design challenges. A key issue is how to maintain high combustion efficiency over the entire load range using as little oxidizer as possible and with emissions (NOx, CO, UHC) within given constraints. Other important challenges are related to combustion stability, heat transfer and cooling, and material integrity, all of which are much affected when going from air-based to oxygen-based gas turbine combustion.

Matching with existing air-based burner and combustor designs has been done in order to use as much as possible of what is proven technology today. The selected stabilization concept, heat transfer evaluation, burner and combustion chamber layout will be described. As a next step the pilot burner will be tested both at atmospheric and high pressure conditions.
A Novel Method of Coupling the Steam Turbine Exhaust Hood and the Last Stage Blades Using the Non-Linear Harmonic Method
Authors: Burton Zoe , Ingram Grant , Hogg Simon
Published: November 2013

The exhaust hood of a steam turbine is a vital area of turbomachinery research its performance strongly influences the power output of the last stage blades. It is well known that accurate CFD simulations are only achieved when the last stage blades are coupled to the exhaust hood to capture the strong interaction. This however presents challenges as the calculation size grows rapidly when the full annulus is calculated. The size of the simulation means researchers are constantly searching of methods to reduce the computational effort without compromising solution accuracy.

This work uses a novel approach, by coupling the last stage blades and exhaust hood by the Non-Linear Harmonic Method, a technique widely used to reduce calculation size in high pressure turbine blades and axial compressors. This has been benchmarked against the widely adopted Mixing Plane method. The test case used is the Generic Geometry, a representative exhaust hood and last stage blade geometry that is free from confidentiality and IP restrictions and for which first calculations were presented at last year’s conference [1]. The results show that the non-uniform exhaust hood inlet flow can be captured using the non-liner harmonic method, an effect not previously achievable with single passage coupled calculations such as the mixing plane approach. This offers a significant computational saving, estimated to be a quarter of the computation time compared with alternative methods of capturing the asymmetry with full annulus frozen rotor calculations.
Rub Diagnostics Based on Vibration Data
Authors: Yu John J.
Published: November 2013

Vibration excursion in turbomachinery is troublesome, especially when approaching or exceeding a trip level. Understanding of its root-cause is extremely crucial for taking appropriate actions and resolving the issue. Rubs are certainly among the most common malfunctions that cause vibration excursion. This paper discusses how to diagnose rubs that typically occur in turbomachinery based on vibration data. These include rubs occurring in both steady-state and transient conditions. Selection and interpretation of vibration data plots such as trend, polar, Bode, orbit, and waterfall are illustrated that pinpoint rubbing and resulted shaft bow symptoms. All data presented have been obtained from real machines where rubs occurred. Mainly case studies are presented in this paper. The presented cases and concluded diagnostic rules using vibration data plots will help practicing engineers as well as enhance diagnostic tools.
Simulation of a Heat Recovery Steam Generator Operating in a Combined Cycle Plant
Authors: Duarte Raphael , Ferreira Sandro , Barbosa Rafael
Published: November 2013

The heavy duty gas turbines evolution led to higher combined cycle efficiencies. Thus, more complex heat recovery steam generators were developed in order to maximize the use of that energy potential. Therefore, computational models capable to predict the operational conditions of the equipment may be needed in order to analyze the system behavior for different situations. This article describes a computational model able to simulate the off-design behavior of a heat recovery steam generator (HRSG) operating in a combined cycle power plant. The model was developed so that it can be used in both model-based diagnostics systems and performance evaluation systems. Each heat exchanger inside the HRSG was designed individually and arranged according to the analyzed equipment. The computer code’s architecture was built in such a way that it can be easily changed, allowing the analysis of other HRSG’s configurations with simple structural changes, given the program’s modularity. In order to deal with the lack of details of the power plant equipment, which means not enough geometrical information of each heat exchanger, a generic algorithm tool was used to calibrate the heat exchangers models using only the measured data of the power plant SCADA. The developed program was validated against operational data from a real plant and showed satisfactory results, confirming the robustness of this model.
Experimental Investigation on the Effect of Boundary Layer Fluid Injection on the Flashback Propensity of Premixed Hydrogen-Air Flames
Authors: Baumgartner Georg , Sattelmayer Thomas
Published: November 2013

Premixed combustion systems show potential to meet future regulations on nitrogen oxide emissions. However, premixed systems always involve the risk of flame flashback into the premixing section. From a gas turbine manufacturer’s point of view it is desirable to broaden the safe operating range, in particular with respect to flame flashback. It has been reported in the literature that flashback along the wall boundary layer represents the most critical failure mechanism for many burner configurations using hydrogen-rich fuels. This paper focuses on the effect of fluid injection into the wall boundary layer on the flashback propensity of a hydrogen-air jet burner. For this purpose, an experiment with a tube burner was designed, where the flame is anchored in the free atmosphere at the burner exit. Pure air was injected through an annular gap at three streamwise locations upstream of the stable flame position and at two different angles — perpendicular and at 45° to the main flow direction, respectively. The turbulent flashback limits for fully premixed hydrogen-air mixtures at atmospheric conditions were measured for a variety of equivalence ratios and different amounts of air injection. It turned out that there is a significant increase in flashback stability with injection devices close to the burner exit. The main reason for this behavior is the dilution of the mixture in the near-wall region and the resulting reduction of the flame speed. The positive effect diminishes quickly with increasing distance between flame and injection location due to considerable mixing of injected flow and main flow. This has been verified by RANS simulations. The simulations also showed that the momentum generated by the injection into the boundary layer has negligible influence on the flashback limits. It was also found that the fluid injection is not capable of stopping the upstream flame propagation once the flame has entered the tube. A probable explanation for this effect is the change from open flame holding at the burner exit to the confined flame situation inside the tube during flashback. The latter is known to substantially increase the flashback propensity, which cannot be counteracted by air injection.
CO Prediction for Aircraft Gas Turbine Combustors
Authors: Xu F. , Nori V. , Basani J.
Published: November 2013

The predictive capabilities of two candidate approaches for CO predictions were assessed for a series of aircraft gas turbine combustors. The first approach involved constructing a large reduced order reactor network coupled with a detailed, 500 species n-dodecane mechanism to simulate the combustion process. The second approach was the traditional RANS based CFD using two finite rate based combustion models in FLUENT. A four step Jet-A global mechanism was developed in-house and was used in the CFD simulations. The global mechanism was validated against the detailed Jet-A mechanism published by Dagaut in 2006 and was able to reproduce the flame speed and species profiles satisfactorily over the range of relevant operating temperatures and pressures. The calibration combustors comprised seven configurations with identical fuel nozzles but different swirlers, dome effusion, liner and quench jet air flow splits. It was found that the CFD approach was better at capturing the trend of rig data than the reactor network approach and was able to capture most of the variations seen in the measurement. The improvement in prediction was attributed mainly to the more accurate global mechanism which results in more accurate kinetic calculation in CFD.
Steady State Engine Test Demonstration of Performance Improvement With an Advanced Turbocharger
Authors: Sun Harold , Hanna Dave , Hu Liangjun , Curtis Eric , Yi James , Tjong Jimi
Published: November 2013

Heavy EGR required on diesel engines for future emission regulation compliance has posed a big challenge to conventional turbocharger technology for high efficiency and wide operation range.

This study, as part of the U.S. Department of Energy sponsored research program, is focused on advanced turbocharger technologies that can improve turbocharger efficiency on customer driving cycles while extending the operation range significantly, compared to a production turbocharger.

The production turbocharger for a medium-duty truck application was selected as a donor turbo. Design optimizations were focused on the compressor impeller and turbine wheel.

On the compressor side, advanced impeller design with arbitrary surface can improve the efficiency and surge margin at low end while extending the flow capacity, while a so-called active casing treatment can provide additional operation range extension without compromising compressor efficiency.

On the turbine side, mixed flow turbine technology was revisited with renewed interest due to its performance characteristics, i.e. high efficiency at low-speed ratio, relative to the base conventional radial flow turbine, which is relevant to heavy EGR operation for future diesel applications.

The engine dynamometer test shows that the advanced turbocharger technology enables over 3% BSFC improvement at part-load as well as full-load condition, in addition to an increase in rated power. The performance improvement demonstrated on engine dynamometer seems to be more than what would typically be translated from the turbocharger flow bench data, indicating that mixed flow turbine may provide additional performance benefits under pulsed exhaust flow on an internal combustion engine and in the low-speed ratio areas that are typically not covered by steady state flow bench tests.
Efficient Strategy for Low NOx Combustor Design in the Spatial Domain Using Multi-Fidelity Solutions
Authors: Wankhede Moresh J. , Bressloff Neil W. , Keane Andy J.
Published: November 2013

Gas turbine combustor designers now routinely use high-fidelity reactive computational fluid dynamics (CFD) analyses to gain valuable insight into the complex reactive flow-field and pollutant formation process. But, a large number of such computationally expensive CFD analyses are generally required to arrive at an acceptable combustor configuration. Therefore, given the practical limits on available computational resources and time, traditional combustor design methodologies using only high-fidelity CFD analyses need further improvement. To address this, a combustor design strategy using multifidelity co-Kriging response surface model (RSM) is developed and applied for the design of a two-dimensional test combustor problem in the spatial domain using steady-state Reynolds-averaged Navier Stokes (RANS) formulation. The design and optimization problem is set-up for two geometric variables and a single-objective, NOx concentration, as it is of current interest to the combustor design community. The developed multi-fidelity strategy is also assessed for performance against high-fidelity Kriging RSM strategy. This study demonstrates that the multi-fidelity design strategy can obtain good designs with up to ten times less effort than a full grid sampling search plan. However, the multi-fidelity co-Kriging strategy does not outperform the high-fidelity Kriging strategy for the given spatial domain problem.
The Effect of Axisymmetric Profile on Turbine Blade Platform Heat Transfer Distribution
Authors: Zhang Luzeng , Lee Dong H. , Yin Juan , Moon Hee Koo
Published: November 2013

Flow field near the turbine blade platform is very complex due to the secondary flow motions such as horseshoe vortices, passage vortices and endwall cross flows. It is therefore extremely difficult to predict the platform heat transfer distribution. As the secondary flows are largely affected by platform profile/shape, a number of investigators have studied different platform profiles to minimize aerodynamic loss and heat load. Understanding of the platform heat transfer has become especially critical in recent years, because of firing temperature increase and low NOx combustion requirement, as it is directly related to turbine durability. Three different axisymmetric platform profiles were designed and experimentally studied: flat profile, dolphin nose profile and shark nose profile. All of them were based on the existing engine hardware designs. The measurements were conducted in a high-speed linear cascade, which consisted of five blades and six flow passages. The test platforms were made of FR4 material and painted with Thermo-chromic Liquid Crystal (TLC). The test article was kept in the plenum located under the cascade at the pre-test condition. At the start of each test, the test blade/article was inserted into the cascade rapidly and then two CCD cameras recorded the color changes of the TLC on the platform surface. Engine representative Reynolds numbers were studied from 300,000 to 600,000 and the corresponding inlet Mach numbers were ranged from 0.12 to 0.24. The upstream section of the flat profile platform showed a typical flat plate heat transfer pattern with boundary layer development. The shark-nose and dolphin-nose platforms resulted in lower heat transfer coefficients on the upstream region compared to that for the flat profile, and the peak values moved slightly downstream from the leading edge due to possibly different secondary flow patterns. The heat transfer rate increased with increased Reynolds number for all three platform shapes, while the flat profile showed a higher increase rate. Zone averaged heat transfer distributions in addition to local values were also presented to show the effect of platform profile. In general, the flat profile platform resulted in a higher overall heat transfer rate than that for the other two profile platforms, which suggested that a good design of contoured profile platform could reduce the heat load and aerodynamic loss in gas turbine blade.
Experimental and Reactor Network Study of Nitrogen Dilution Effects on NOX Formation for Natural Gas and Syngas at Elevated Pressures
Authors: Sigfrid Ivan R. , Whiddon Ronald , Collin Robert , Klingmann Jens
Published: November 2013

Gas turbines emissions, NOX in particular, have negative impact on the environment. To limit the emissions gas turbine burners are constantly improved. In this work, a fourth generation SIT (Siemens Industrial Turbomachinery) burner is studied to gain information about the formation of NOX emissions. The gas mixtures for the full burner are limited to natural gas with different nitrogen dilutions. The dilutions vary from undiluted to Wobbe index 40 and 30 MJ/m3. In addition to the full burner, the central body (the RPL – Rich/Pilot/Lean) is investigated. Methane is used to characterize standard gas turbine operation, and a non-standard fuel is explored using a generic syngas (67.5 % Hydrogen, 22.5 % Carbon monoxide and 10 % Methane). Both these gases are also investigated after dilution with nitrogen to a Wobbe index of 15 MJ/m3. The experiments are performed in a high-pressure facility. The pressures for the central body burner are 3, 6 and 9 bar. For the full burner the pressures are 3, 4.5 and 6 bar. The combustion air is preheated to 650 K. The emission measurements are sampled with an emission probe at the end of the combustor liner, and analyzed in an emission rack. The results are compared with previous investigations made at atmospheric conditions.

The burner is modeled using a PSR and plug flow network to show which reaction paths are important in the formation of emissions for the burner under the experimental conditions.

The measurement results show that the NOX concentration increases with pressure and flame temperature. With increasing dilution the NOX concentration is decreased. For rich mixtures PSR calculations show that the NOX concentration decreases with pressure.