bluuebunny/crossref_metadata_2025 huggingface dataset:
A Viscoplastic Constitutive Theory for Monolithic Ceramics — II
Authors: Janosik Lesley A. , Duffy Stephen F.
Published: December 2014

This paper, which is the second of two in a series, exercises the viscoplastic constitutive model developed by the authors in the previous article (Janosik and Duffy, 1998). The model accounts for time-dependent phenomena (e.g., creep, rate sensitivity, and stress relaxation) in monolithic ceramics. Additionally, the formulation exhibits a sensitivity to hydrostatic stress, and allows different behavior in tension and compression. Here, the constitutive equations formulated for the flow law (i.e., the Strain rate) and the evolutionary law have been incorporated into computer algorithms for predicting the multiaxial inelastic (creep) response of a given homogeneous state of stress. Numerically simulated examples illustrate the model’s ability to capture the time-dependent phenomena suggested above. For each imposed service (load) history considered, creep curves and viscoplastic flow surfaces are examined to demonstrate the model’s ability to capture the inelastic creep deformation response. No attempt is made here to assess the accuracy of the model in comparison to experiment. A quantitative assessment is reserved for a later date, after the material constants have been suitably characterized for a specific ceramic material.
Iron-Aluminide Filters for Hot-Gas Cleanup
Authors: Tortorelli Peter F. , McKamey Claudette G. , Lara-Curzio Edgar , Judkins Roddie R.
Published: December 2014

Iron aluminides have shown good to excellent high-temperature corrosion resistance in sulfur-bearing environments and thus have potential for use as the material of construction for metallic filters used to clean fossil-fuel-derived gases prior to their introduction into gas turbine systems. Consequently, a background for consideration of such alloys for filter applications is given in terms of a brief summary of the physical metallurgy and relevant high-temperature corrosion behavior of iron aluminides. In addition, preliminary characterization results on iron-aluminide filter elements exposed in test beds that simulate environments associated with advanced coal-fired energy production are presented. Although good corrosion resistance was found, there were minor to moderate strength reductions that did not necessarily scale with time. Little degradation in ductility was observed.
Blade Life — A Comparison by Cumulative Damage Theories
Authors: Rao J. S. , Pathak A. , Chawla A.
Published: December 2014

A turbine blade is modeled as a rotating pretwisted beam and subjected to aerodynamic excitation from the flow path interference. The resonant stresses are determined using a modal analysis. With the help of steady steam bending and centrifugal stresses and the dynamic stresses, life estimates are made using the linear and nonlinear cumulative damage theories and a comparison of the results is presented. Based on these results, recommendations are made on the usefulness of different theories for practical application.
Low NOx LPP Combustion Test Facility With Four Transparent Windows for Non Intrusive Flow Diagnostics
Authors: Alfaro J. A. , Rodríguez P. A. , Lecuona A. , Calle R. , Lázaro B.
Published: December 2014

A high-pressure facility capable for testing Lean Premixed Pre-vaporized (LPP) combustor geometries is reported. The proposed design enables the use of both single-point and whole-field non-intrusive measuring techniques when the combustor operates under conditions representative of gas turbines or jet engines operation, thereby enabling the complete characterization of the turbulent flow field that develops inside LPP combustors. The individual control of the air and fuel supplies, provided, respectively, by a number of industrial compressors and a specific LPG supply facility, allows the investigation of a wide range of operating conditions. In this paper, the facility specifications are explained and adequately justified. Preliminary results are presented, showing the suitability of the design.
CFD Liquid Spray Combustion Analysis of a Single Annular Gas Turbine Combustor
Authors: Smiljanovski Vanco , Brehm Norbert
Published: December 2014

In this paper CFD analysis of the steady two-phase turbulent combusting flow in a single annular low-NOx combustor is presented. For this purpose the commercial code CFD-ACE (1998) was used, where Eulerian equations are solved for the gas phase and the liquid spray fuel droplets are treated in a Lagrangian frame of reference allowing for evaporation of droplets and providing source terms for the gas phase. The standard k-ε model was used for turbulence and an assumed shape probability density function was used for the instantaneous chemistry in the conserved scalar combustion model. Thermal NOx is assumed to be the only source of NOx production and is decoupled from the gas phase reacting flow and calculated in a postprocessing step. The calculation is done on a block structured multi-domain computational grid. Particular attention has be paid to the detailed modeling of the fuel injector having multiple air swirler passages starting from the trailing edge of the air swirler vanes and utilizing up to 400000 computational grid cells for the entire model.

The model represents the single annular low-NOx combustor for the BR700 aircraft engine family, which is based on a Rich Burn - Quick Quench - Lean Burn (RQL) concept. CFD analysis is done for high power reduced take off conditions and is compared with full annular rig test results for the temperature traverse and the integral EINOx. The results imply satisfactory prediction capability for the EINOx and the average radial temperature distribution. The prediction of the details of the temperature traverse is not satisfactory and will remain a challenge for the future.
Real-Time Monitoring of Bearing Condition
Authors: Taylor Barry
Published: December 2014

Magnetic chip detectors, vibration monitoring devices, and spectrographic oil analysis typically do not detect bearing distress until the bearing is in the latter stages of failure. Now, through the innovation of digital signal processing technology and a breakthrough in inductive sensors, it is possible to provide several months of advance notice on a bearing failure.

Unlike magnetic chip detectors, this technology has the capability to track the shedding of both magnetic and nonmagnetic debris from the bearing. It is a true prognostic sensor that detects the first indications of a bearing spall and continues to track, in real-time, the quantities of wear debris being generated by the bearing. The data collected from the sensor can be changed into information such that with a particle trend graph it can clearly be seen when the bearing should be taken out of service prior to a turbine failure and the possibility of expensive secondary damage.
Optical Fibre Aerodynamic Probes for Total Pressure and Total Temperature Measurement in Turbomachinery
Authors: Barton J. S. , Kilpatrick J. M. , MacPherson W. N. , Jones J. D. C. , Chana K. S. , Anderson J. S. , Buttsworth D. R. , Jones T. V.
Published: December 2014

Optical fibre sensors offer the prospect of miniature aerodynamic probes for highly localised flow measurements in aerospace wind tunnels and turbomachines. We discuss the design and construction of optical fibre sensors for temperature and pressure. The temperature sensors consist of multilayer coatings deposited on the fibre end face from which the reflected intensity is temperature-dependent. Two sensors were incorporated in a dual heated probe to measure total temperature. The pressure sensors are miniature diaphragms in which pressure-induced deflection is measured interferometrically in reflection. We present results from initial trials made in unsteady flow in a single stage research turbine, in which total temperature data with harmonic components up to 30 kHz and total pressure signals up to 230 kHz were recorded.
Development of the WR-21 Gas Turbine Recuperator
Authors: Sanders Robert C. , Louie George C.
Published: December 2014

WR-21 is an intercooled and recuperated (ICR) gas turbine engine being developed by the U. S. Navy (USN) with contributions from the Royal Navy and the French Navy. A key component of the WR-21 engine is the recuperator used to recover waste heat from engine exhaust gas. The recuperator is being designed and fabricated by AlliedSignal Aerospace Company under subcontract to Northrop Grumman Marine Services, the prime contractor for the WR-21 gas turbine engine. One of the most challenging developmental items for the WR-21 engine has proven to be the recuperator. This paper discusses the development of the recuperator, including the advanced development (AD) recuperator which failed after a few hours of operation, the limited operating unit (LOU) recuperator which has supported much of the WR-21 engine development testing and the engineering development model (EDM) recuperator which will be used for a 3000 hour engine endurance test. Included is an overview of USN technical requirements for the recuperator and a review of operating experience with the AD and LOU recuperators. Failure modes that have been experienced are discussed in detail, including root cause evaluations and design modifications. Steps taken to extend the life of the LOU recuperator are discussed. In addition, testing (both single core and full size recuperator) and analytical models that have been used to improve the design and reliability of the recuperator are addressed.
Status of the CERAMIC/ERICA Probabilistic Life Prediction Codes Development for Structural Ceramic Applications
Authors: Schenk Bjoern , Brehm Peggy J. , Menon M. N. , Peralta Alonso D. , Tucker William T.
Published: December 2014

Statistical methods for design of ceramic components for fast fracture and time-dependent failure modes have been advanced to significantly enhance component reliability and reduce baseline data generation costs. The statistical methods are incorporated in AlliedSignal Engines CERAMIC and ERICA computer codes. Use of the codes facilitates generation of material strength and fatigue parameters by pooling data from specimens that are of varying sizes, stressed by dissimilar loading conditions, or tested at a variety of temperatures, and by including specimens that have been proof tested. The codes include approaches to calculate confidence bounds for Weibull and fatigue parameters of censored data as well as for predicted reliability of ceramic components. Rather than presenting highly detailed, previously published theoretical derivations (Cuccio, et al., 1994, Schenk, et al., 1998, Schenk, et al., 1999), this paper presents a summary of general methodology and a synopsis of code features and capabilities. The work was sponsored by the Department of Energy/Oak Ridge National Laboratory (DoE/ORNL) under Contract DE-AC05-84OR21400.
A New Probabilistic Approach for Accurate Fatigue Data Analysis of Ceramic Materials
Authors: Schenk Bjoern , Brehm Peggy J. , Menon M. N. , Tucker William T. , Peralta Alonso D.
Published: December 2014

Statistical methods for the design of ceramic components for time-dependent failure modes have been developed which can significantly enhance component reliability, reduce baseline data generation costs, and lead to more accurate estimates of slow crack growth (SCG) parameters. These methods are incorporated into the AlliedSignal Engines CERAMIC and ERICA computer codes. Use of the codes facilitates generation of material strength parameters and SCG parameters simultaneously, by pooling fast fracture data from specimens that are of different sizes, or stressed by different loading conditions, with data derived from static fatigue experiments. The codes also include approaches to calculation of confidence bounds for the Weibull and SCG parameters of censored data and for the predicted reliability of ceramic components.

This paper presents a summary of this new fatigue data analysis technique and an example demonstrating the capabilities of the codes with respect to time-dependent failure modes. This work was sponsored by the U.S. Department of Energy Oak Ridge National Laboratory (DoE/ORNL) under Contract No. DE-AC05-84OR21400.
Compressed Air Storage With Humidification: An Economic Analysis
Authors: Cohn Arthur , Ehrlich Shelton , Darguzas Joseph , Giermac Edwin
Published: December 2014

A large, 530 MW, Compressed Air Storage with Humidification (CASH) cycle was configured as an energy-storage plant utilizing as the low pressure expander the turbine of the Siemens-Westinghouse W 501F2 with a firing temperature of about 2400°F (1315C) and a 1600°F (870C) high pressure Dresser turbine. A selling price for electricity was developed for this CASH plant and compared with that for power produced by simple and combined cycle power plants of similar size. At 90°F ambient, where cycling power is most necessary, the specific capital cost of the CASH plant was calculated to be 405 $/kW while the simple and combined cycle were 403 and 489 $/kW respectively. The CASH plant has a much lower incremental cost than does the simple cycle. These factors result in the CASH plant having lower overall costs than the simple cycle for operation of over about 400 hr/yr. and lower than the combined cycle for operation of less than about 4000 hr/yr.
A Simplified Program to Predict the Temperature Distribution in Gas Turbine Components as a Function of the Mission Profile of the Aircraft
Authors: Naudé Alwyn F. , Visser Jan A.
Published: December 2014

One of the main thrusts of the modern aerospace industry is to reduce the operating costs of aircraft. This requires a longer on-wing time for the gas turbines and subsequently reduced maintenance. Such a program can only be effectively implemented if the effects of operating conditions on the aircraft can be evaluated continuously. This paper presents a simplified computer program, operating on a personal computer, to predict the temperature distribution in components as a function of the operating condition of the aircraft. This information is then used to determine the deterioration of the engine under the specified operating conditions. The program consists of a simplified model to calculate the conditions in the different modules of the engine as a function of parameters like throttle position, altitude, speed of the aircraft etc. The detailed heat transfer to components is calculated using simplified analytical formulations accounting for three-dimensional effects. As a test case, the temperature change on a semi-cooled nozzle guide vane (NGV) is shown as the engine accelerates to full load conditions. It can be concluded that this approach produces realistic values for the thermal loading on components that can be used to predict long-term engine deterioration.
Non-Axisymmetric Turbine End Wall Design: Part I — Three-Dimensional Linear Design System
Authors: Harvey Neil W. , Rose Martin G. , Taylor Mark D. , Shahpar Shahrokh , Hartland Jonathan , Gregory-Smith David G.
Published: December 2014

A linear design system, already in use for the forward and inverse design of three-dimensional turbine aerofoils, has been extended for the design of their end walls.

This paper shows how this method has been applied to the design of a non-axisymmetric end wall for a turbine rotor blade in linear cascade. The calculations show that non-axisymmetric end wall profiling is a powerful tool for reducing secondary flows, in particular the secondary kinetic energy and exit angle deviations. Simple end wall profiling is shown to be at least as beneficial aerodynamically as the now standard techniques of differentially skewing aerofoil sections up the span, and (compound) leaning of the aerofoil. A design is presented which combines a number of end wall features aimed at reducing secondary loss and flow deviation. The experimental study of this geometry, aimed at validating the design method, is the subject of the second part of this paper.

The effects of end wall perturbations on the flow field are calculated using a 3-D pressure correction based Reynolds Averaged Navier-Stokes CFD code. These calculations are normally performed overnight on a cluster of work stations. The design system then calculates the relationships between perturbations in the end wall and resulting changes in the flow field. With these available, linear superposition theory is used to enable the designer to investigate quickly the effect on the flow field of many combinations of end wall shapes (a matter of minutes for each shape).
Non-Axisymmetric Turbine End Wall Design: Part II — Experimental Validation
Authors: Hartland J. C. , Gregory-Smith D. G. , Harvey N. W. , Rose M. G.
Published: December 2014

The Durham Linear Cascade has been redesigned with the non-axisymmetric profiled end wall described in the first part of this paper, with the aim of reducing the effects of secondary flow. The design intent was to reduce the passage vortex strength and to produce a more uniform exit flow angle profile in the radial direction with less over turning at the wall. The new end wall has been tested in the linear cascade and a comprehensive set of measurements taken. These include traverses of the flow field at a number of axial planes and surface static pressure distributions on the end wall. Detailed comparisons have been made with the CFD design predictions, and also for the results with a planar end wall. In this way an improved understanding of the effects of end wall profiling has been obtained.

The experimental results generally agree with the design predictions, showing a reduction in the strength of the secondary flow at the exit and a more uniform flow angle profile. In a turbine stage these effects would be expected to improve the performance of any downstream blade row. There is also a reduction in the overall loss, which was not given by the CFD design predictions. Areas where there are discrepancies between the CFD calculations and measurement are likely to be due to the turbulence model used.

Conclusions for how the three-dimensional linear design system should be used to define end wall geometries for improved turbine performance are presented.
Power Systems Development Facility: High Temperature, High Pressure Filter System Operations in a Combustion Gas
Authors: Scarborough Patrick T. , Hendrix Howard L. , Davidson Matt. D. , Guan Xiaofeng , Dahlin Robert S. , Landham E. Carl
Published: December 2014

The Power Systems Development Facility (PSDF) is a Department of Energy (DOE) sponsored engineering scale demonstration of two advanced coal-fired power systems. Particulate cleanup is achieved by several High Temperature, High Pressure (HTHP) gas filtration systems. The PSDF was designed at sufficient scale so that advanced power systems and components could be tested in an integrated fashion to provide confidence and data for commercial scale-up. This paper provides an operations summary of a Siemens-Westinghouse Particulate Control Device (PCD) filtering combustion gas from a Kellogg Brown & Root (KBR) transport reactor located at the PSDF.

The transport reactor is an advanced circulating fluidized bed reactor designed to operate as either a combustor or a gasifier. Particulate cleanup is achieved by using one of two PCDs, located downstream of the transport reactor. As of the end of 1998, the transport reactor has operated on coal as a combustor for over 3500 hours. To date, filter elements from 3M, Blasch, Coors, Allied Signal (DuPont), IF&P, McDermott, Pall, Schumacher and Specific Surface have been tested up to 1400°F in the Siemens-Westinghouse PCD.

The PSDF has a unique capability for the collection of samples of suspended dust entering and exiting the PCD with Southern Research Institute’s (SRI) in-situ particulate sampling systems. These systems have operated successfully and have proven to be invaluable assets. Isokinetic samples using a batch sampler, a cascade impactor and a cyclone manifold have provided valuable data to support the operation of the transport reactor and the PCD. Southern Research Institute has also supported the PSDF by conducting filter element material testing.
Intake Engine Interactions of a Modern Large Turbofan Engine
Authors: Freeman Chris , Rowe Arthur L.
Published: December 2014

An engine experiment has been carried out to investigate Fan Stability and response to ambient wind conditions during static high power running of a modern large turbofan engine. This paper describes the experiment and the conclusions.

Intermittently the inlet would separate and drive the fan into stall from which it did not recover when the inlet cleared up: on high working lines one inlet separation could stall the fan; on lower working lines the inlet separation / fan flow / bypass duct pressure would develop a divergent 10Hz oscillation which could eventually stall the fan. The interaction of the stalled fan with the turbine and mixed nozzle would then raise the fan running line above the stall dropout level thus locking the fan into stall even when the inlet cleared up. A one dimensional dynamic model of the engine was created that would exhibit similar behaviour to the engine when a delay was introduced between the inlet loss and fan face loss. The engine never showed steady operation with the inlet separated.
Model Combustor to Assess the Oxidation Behavior of Ceramic Materials Under Real Engine Conditions
Authors: Filsinger D. , Schulz A. , Wittig S. , Taut C. , Klemm H. , Wötting G.
Published: December 2014

A further increase of thermal efficiency and a reduction of the exhaust emissions of ground based gas turbines can be achieved by introducing new high temperature resistant materials. Therfore, ceramics are under international development. They offer excellent strengths at room and elevated temperatures. For gas turbine combustor applications, however, these materials have to maintain their advantageous properties under hostile environment. For the assessment and comparison of the oxidation behavior of different nonoxide ceramic materials a test rig was developed at the Institute for Thermal Turbomachinery (ITS), University of Karlsruhe, Germany.

The test rig was integrated into the high temperature/ high pressure laboratory. A ceramic model combustion chamber was designed which allowed the exposure of standard four-point flexure specimens to the hot combustion gas flow. Gas temperatures and pressures could be varied in a wide range. Additionally, the partial steam pressure could be adjusted to real combustor conditions.

The present paper gives a detailed description of the test rig and presents results of 100 hours endurance tests of ceramic materials at 1400°C. The initial strengths and the strengths after oxidation tests are compared. In addition to this, photographs illustrating the changes of the material’s microstructure are presented.
Pneumatic Fuel Feeding of a Directly Wood Particle Fired Gas Turbine Under Special Consideration of Low Conveying Air Ratio
Authors: Joppich Andreas , Haselbacher Hermann
Published: December 2014

In order to reduce the production of green house gases, the combustion of biomass has been gaining importance in electricity generation. Especially the direct combustion of biomass in gas turbines of a few MW output would offer a very attractive option because of low investment costs and high operational flexibility. Therefore, since 1991 the Institute of Thermal Turbomachines and Powerplants at the Vienna University of Technology has been working on realising a wood particle fired gas turbine with direct combustion. With reference to earlier studies (c.f. Hamrick (1991), Fredriksson and Kallner (1993)), it had been concluded that the design and the operating characteristics of the fuel feed system would strongly influence the combustion and so would be a very important part of the whole facility.

Following an overview of the planned gas turbine test facility including the combustion chamber and the recently installed pneumatic fuel feed system, the paper will deal with three basic requirements of fuel feeding in the case of a directly fired gas turbine: feeding against back pressure, continuous fuel flow rate and a low conveying air ratio, which is the ratio of fuel conveying air to total combustion air of the combustion chamber. While the first two requirements, i.e. feeding against back pressure and continuous feeding, are briefly considered, the minimisation of the conveying air ratio is discussed in detail. For instance, important parameters affecting the conveying air ratio are fuel moisture, combustion air ratio and, in particular, techniques. Following theoretical estimation of the conveying air ratio, results of fuel feeding measurements are presented and conclusions drawn with respect to system integration.
Solid Oxide Fuel Cell Power System Cycles
Authors: Veyo Stephen E. , Lundberg Wayne L.
Published: December 2014

Reviewed are power system concepts employing the solid oxide fuel cell (SOFC) at atmospheric pressure in simple cycle; in an atmospheric pressure hybrid cycle with a gas turbine (SOFC/GT); and in a pressurized SOFC/GT hybrid (PSOFC/GT). Estimates of power system performance are presented and discussed. Simple atmospheric pressure SOFC systems designed for combined heat and power (CHP) application can approach 50% electric generation efficiency (net AC/LHV) and 80% fuel effectiveness [(net AC + useful heat)/LHV]. Pressurized SOFC systems with intercooled, recuperated, and SOFC-reheated GT cycles can approach 70% electric generation efficiency, while the atmospheric pressure SOFC/GT hybrid cycle and a simple pressurized SOFC/GT cycle can approach 55% and 60% generation efficiency, respectively. These high levels of efficiency are extraordinary in that they are achievable at the MW capacity level.
The Influence of Technical Surface Roughness on the Flow Around a Highly Loaded Compressor Cascade
Authors: Leipold Robert , Boese Matthias , Fottner Leonhard
Published: December 2014

A highly loaded compressor cascade which features a chord length that is ten times larger than in real turbomachinary is used to perform an investigation of the influence of technical surface roughness. The surface structure of a precision forged blade was engraved in two 0.3mm thick sheets of copper with the above mentioned enlarging factor (Leipold and Fottner, 1998). To avoid additional effects due to thickening of the blade contour the sheets of copper are applied as inlay’s to the pressure and suction side. At the high speed cascade wind tunnel the profile pressure distribution and the total pressure distribution at the exit measurement plane were measured for the rough and the smooth blade for a variation of inlet flow angle and inlet Reynolds number. For some interesting flow conditions the boundary layer development was investigated with the laser-two-focus anemometry and the one-dimensional hot-wire anemometry. At low Reynolds numbers and small inlet angles a separation bubble is only slightly reduced due to surface roughness. The positive effect of a reduced separation bubble is overcompensated by a negative influence of surface roughness on the turbulent boundary layer downstream of the separation bubble. At high Reynolds numbers the flow over the rough blade shows a turbulent separation leading to high total pressure loss coefficients. The laser-two-focus measurements indicate a velocity deficit close to the trailing edge even at flow conditions where positive effects due to a reduction of the suction side separation have been expected. The turbulence intensity is reduced close downstream of the separation bubble but increased further downstream due to surface roughness. Thus not the front part but the rear part of the blade reacts sensitively on surface roughness.
The Potential of Fuel Reforming and Water Evaporation in Gas Turbine Cycles
Authors: Bram Svend , Minsart Olivier , De Ruyck Jacques
Published: December 2014

A general 2-step approach for advanced gas turbine cycle design and finding optimal layouts is used to study chemically recuperated and evaporative gas turbine cycles. The analysis assumes compression with intercooling, the possibility of reheat in the turbine and no bottoming cycle. In a first step, different cycle layouts are first optimized for pressure ratio by considering a general black box heat recovery system while its exergy destruction is monitored. In a second step, after cycle optimization, corresponding heat recovery systems are designed using insights provided by a composite curve analysis. All cycle simulations are performed with ASPEN+, enhanced with in-house exergy subroutines, composite curve tools and a general gas turbine cooling model. Comparative results from this analysis are presented and the important role of pressure ratio is discussed.
Turbine Blade Unsteady Heat Transfer Change due to Stator Indexing
Authors: Johnston David A. , Fleeter Sanford
Published: December 2014

Stator indexing to alter and/or control the unsteady heat transfer of closely spaced airfoil rows in turbomachinery was studied experimentally in a two-stage low-speed research turbine. With the second vane row fixed, the inlet vane row was indexed to six positions over one vane-pitch cycle at design and high stage loadings. The aerodynamic forcing functions to the first- and second-stage rotors were measured in the rotating reference frame, with the resulting rotor blade unsteady heat transfer response quantified by an electrically heated rotor blade instrumented with thin platinum-film heat gages. The level of attenuation of unsteady heat transfer coefficient due to stator indexing was found to be both location and blade loading dependent, ranging from 10% to 80% of the maximum. Because of the attenuation’s location dependence, stator indexing is therefore best suited to minimize unsteady heat transfer in local hot spots on the blade.
Boundary Conditions for Ceramic Turbine Components: Analytical Prediction and Test Validation
Authors: Bagheri Hamid , Jimenez Oscar
Published: December 2014

Ceramics allow gas turbine engines to run at higher temperatures to increase power and efficiency. Ceramic component development is therefore required to understand transient thermal behavior and temperature distributions. As a part of contract with US Department of Energy (DOE), a series of finite element analyses were completed and a Solar Turbine (Solar) Centaur 50S engine was tested to characterize this behavior.

To better understand the interaction between the metallic and ceramic components during engine operation, a finite element model was prepared. The boundary conditions for this model were estimated analytically or using existing test data. To verify the boundary conditions in the vicinity of uncooled ceramic components, two engine tests were performed on a metallic engine simulating the ceramic engine configuration.

The Solar Centaur 50S engine normally operates at 1010°C with all metallic components. A Centaur 50S eagine was retrofitted with a ceramic combustor liner and uncooled first stage turbine blades and nozzles. Two tests were conducted at firing temperatures of 1095 and 980°C. Using metallic components saved time, reduced the complexity of working with ceramic components, and eliminated some of the difficulties of attaching instrumentation to ceramic parts. Component temperatures were measured and used in the finite element analyses to help predict blade tip clearances, ceramic component temperatures, stresses and ultimately component lives.

The strategy undertaken and results presented herein provided a reliable and effective approach to ceramic component development and provides critical temperature information in the qualification process for ceramic gas turbines.
Fatigue Failures of Centrifugal Impeller Disks
Authors: Jansen Willem , Fetfatsidis Paul K.
Published: December 2014

An unusual centrifugal impeller disk failure has been encountered in one of the stages of a multistage air compressor. The failure occurred when a triangular piece of metal separated from the disk at the rim of the impeller disk. Stress analyses show that the steady hoop stresses at the rim were very low. Metallurgical observations indicate that the failure was caused by high cycle fatigue in cast 17-4 PH steel. A modal analysis shows that the failure can be explained by a resonance condition. The excitation of the backward rotating tangential nodal pattern by the stationary vaned diffusers just downstream of the impeller rim causes this resonance condition. Avoiding the resonance condition by changing the number of diffuser vanes has eliminated the failures.
Optimization of a Vaned Diffuser Geometry for Radial Compressors: Part II — Optimization of a Diffuser Vane Profile in Low Solidity Diffusers
Authors: Kmecl Tomaz , ter Harkel Rudi , Dalbert Peter
Published: December 2014

In addition to the diffuser parameter study described in part 1 of this paper the influence of diffuser vane profiles on the efficiency and the operating range of a low solidity diffuser has been studied. Ten different diffuser profiles with identical diffuser configuration (12 vanes, σ = 0.7) were numerically compared. Four of them were tested experimentally.

The basic diffuser for this investigation was a simple circular are profile of constant thickness with rounded leading and trailing edges. The simplest improvement of the basic diffuser was made with an elliptical leading edge. The ellipses of different k values (k = 2, 4, 8) were examined. In addition to circular are diffusers with constant thickness, six fully profiled diffusers with non-constant thickness along the camber line were investigated. Four of them are conformably transformed NACA profiles.

The results show that the diffuser vane profile does not influence the choke of a stage significantly. The choke point is predominantly influenced by the diffuser’s effective throat size, which was kept nearly constant for all investigated diffusers. Near surge the flow field is difficult to predict so that the optimization of a diffuser vane profile does not necessarily result in an improvement of the diffuser performance.
Key Durability Issues With Mullite-Based Environmental Barrier Coatings for Si-Based Ceramics
Authors: Lee Kang N.
Published: December 2014

Plasma-sprayed mullite (3Al2O3·2SiO2) and mullite/yttria-stabilized-zirconia (YSZ) dual layer coatings have been developed to protect silicon-based ceramics from environmental attack. Mullite-based coating systems show excellent durability in air. However, in combustion environments, corrosive species such as molten salt or water vapor penetrate through cracks in the coating and attack the Si-based ceramics along the interface. Thus the modification of the coating system for enhanced crack-resistance is necessary for long-term durability in combustion environments. Other key durability issues include interfacial contamination and coating/substrate bonding. Interfacial contamination leads to enhanced oxidation and interfacial pore formation, while a weak coating/substrate bonding leads to rapid attack of the interface by corrosive species, both of which can cause a premature failure of the coating. Interfacial contamination can be minimized by limiting impurities in coating and substrate materials. The interface may be modified to improve the coating/substrate bond.
Enabling Technologies for Advanced Turbine Component Life Extension
Authors: Liburdi J. , Lowden P.
Published: December 2014

The evolution in materials and turbine design has resulted in the parallel development of advanced equipment and processes capable of manufacturing and repairing critical engine components. Modern, vision based automated welding systems are now widely utilized for precise, low heat welding of crack sensitive alloys. Unique powder metallurgy processes such as LPM™ allow repairs to be engineered for higher localized strength or better wear properties for applications such as abrasive tips. Significant changes have also occurred in the stripping and coating processes with the introduction of sophisticated vapour-based technologies. These advanced technologies are extending opportunities for repair and life extension of turbine components, but the availability and costs associated with these enabling technologies, along with the difficulty in obtaining approvals, may restrict sources for advanced component repairs.
Systematic Reduction of Stress Levels for a Thermally High Loaded Ceramic Nozzle Vane With Trailing Edge Ejection
Authors: Dilzer M. , Schulz A. , Wittig S.
Published: December 2014

This paper presents a design concept for thermally high loaded ceramic shell components, that is developed at the Institute for Thermal Turbomachinery (ITS, University of Karlsruhe). The aim is to obtain homogenous temperature distribution in the ceramic structure for the whole operating cycle of the engine.

Based on simple flat wall considerations design guidelines are introduced to reduce the dominant thermally induced stresses in ceramic components. The concept includes a systematic adjustment of the local cooling configuration and the local wall thicknesses according to the local thermal boundary conditions.

The concept is applied to increase the reliability of a directly cooled Sintered Silicon Carbide first stage nozzle vane with trailing edge ejection for a 70MW stationary gas turbine. Finite element analyses demonstrate that the application of this methodology leads to a rather uniform temperature distribution in the ceramic structure and therefore to low stress levels for steady state and for tripping conditions.

A transformation of the theoretically derived optimum cooling configuration to a technically feasible cooling setup is performed in the purpose of real engine application. It is found that some differences between optimum and technically feasible cooling configuration (mainly located at the trailing edge region) are of minor importance. The results of failure probability calculations (ITS fracture statistics code CERITS) confirm significantly improved reliability of the ceramic nozzle vane.
Wake Vorticity Decay and Blade Response in an Axial Compressor With Varying Axial Gap
Authors: Wo A. M. , Chung M. H. , Chang S. J. , Lee S. F.
Published: December 2014

This paper addresses the decay of rotor wake vorticity for a rotor/stator axial compressor, with the axial gap between blade rows being 10, 20 and 30 percent chord, and at both design and high loading levels. Experiments were conducted in a large-scale, low-speed axial compressor. Navier-Stokes calculations were also executed.

Both data and Navier-Stokes results reveal that the decay of rotor wake vorticity increases substantially as the axial gap decreases; the decay for 10 percent gap is about twice that of 30 percent. Increased time-mean blade loading causes the vorticity decay to also increase, with this effect more pronounced for large axial gap than small. At the stator inlet mid-pitch location, the wake maximum vorticity for 10 and 30 percent chord gap cases being nearly the same (differ by 3.8%) at design loading. The corresponding stator unsteady force agrees within 5.2%. Variation of vorticity decay with axial gap is directly linked to the change in potential disturbance by the downstream stator on the rotor wake due to the change in gap spacing. This suggests that the stator potential disturbance causes the upstream rotor wake to decay at an increased rate which, in turns, results in a lowered level of stator response compared to that without this stator/wake interaction effect. Thus, in this context, blade row interaction is considered beneficial.
Dicer Switch
Authors: VanHook Annalisa M.
Published: December 2014

ERK-mediated phosphorylation alters the localization and activity of Dicer during oogenesis in
Caenorhabditis elegans
.
IKKβ: Commanding the Inflammatory Response
Authors: Gough Nancy R.
Published: December 2014

The kinase IKKβ activates not only the proinflammatory transcription factor NF-κB but also the interferon-inducing transcription factor IRF5.
Development and Validation of an
In Vitro
Pharmacokinetic/Pharmacodynamic Model To Test the Antibacterial Efficacy of Antibiotic Polymer Conjugates
Authors: Azzopardi Ernest A. , Ferguson Elaine L. , Thomas David W.
Published: December 2014

This study describes the use of a novel, two-compartment, static dialysis bag model to study the release, diffusion, and antibacterial activity of a novel, bioresponsive dextrin-colistin polymer conjugate against multidrug resistant (MDR) wild-type
Acinetobacter baumannii
. In this model, colistin sulfate, at its MIC, produced a rapid and extensive drop in viable bacterial counts (<2 log
10
CFU/ml at 4 h); however, a marked recovery was observed thereafter, with regrowth equivalent to that of control by 48 h. In contrast, dextrin-colistin conjugate, at its MIC, suppressed bacterial growth for up to 48 h, with 3 log
10
CFU/ml lower bacterial counts after 48 h than those of controls. Doubling the concentration of dextrin-colistin conjugate (to 2× MIC) led to an initial bacterial killing of 3 log
10
CFU/ml at 8 h, with a similar regrowth profile to 1× MIC treatment thereafter. The addition of colistin sulfate (1× MIC) to dextrin-colistin conjugate (1× MIC) resulted in undetectable bacterial counts after 4 h, followed by suppressed bacterial growth (3.5 log
10
CFU/ml lower than that of control at 48 h). Incubation of dextrin-colistin conjugates with infected wound exudate from a series of burn patients (
n
= 6) revealed an increasing concentration of unmasked colistin in the outer compartment (OC) over time (up to 86.3% of the initial dose at 48 h), confirming that colistin would be liberated from the conjugate by endogenous α-amylase within the wound environment. These studies confirm the utility of this model system to simulate the pharmacokinetics of colistin formation in humans administered dextrin-colistin conjugates and further supports the development of antibiotic polymer conjugates in the treatment of MDR infections.
The Novel Immunotherapeutic Oligodeoxynucleotide IMT504 Protects Neutropenic Animals from Fatal Pseudomonas aeruginosa Bacteremia and Sepsis
Authors: Chahin Abdullah , Opal Steven M. , Zorzopulos Jorge , Jobes David V. , Migdady Yazan , Yamamoto Michelle , Parejo Nicholas , Palardy John E. , Horn David L.
Published: December 2014

IMT504 is a novel immunomodulatory oligonucleotide that has shown immunotherapeutic properties in early preclinical and clinical studies. IMT504 was tested in a neutropenic rat model of
Pseudomonas aeruginosa
bacteremia and sepsis. This animal system recapitulates many of the pathological processes found in neutropenic patients with Gram-negative, bacterial infections. The research was conducted in the setting of an academic research laboratory. The test subjects were Sprague-Dawley rats. Animals were rendered neutropenic by administration of cyclophosphamide, colonized with
P. aeruginosa
by oral feeding, and then randomized to receive IMT504 over a range of doses and treatment regimens representing early and late therapeutic interventions. IMT504 immunotherapy conferred a significant survival advantage over the 12-day study period compared with the results seen with placebo-treated animals when the therapy was administered at the onset of neutropenia and even in the absence of antibiotics and after the onset of fever and systemic infection. Notably, even late salvage IMT504 monotherapy was highly effective (13/14 surviving rats with IMT504 therapy versus 2/14 controls,
P
= <0.001). Moreover, late salvage IMT504 monotherapy was as effective as antibiotic therapy (13/14 surviving rats versus 21/21 rats,
P
= 0.88). In addition, no antagonism or loss of therapeutic efficacy was noted with combination therapy of IMT504 plus antibiotics. IMT504 immunotherapy provides a remarkable survival advantage in bacteremia and sepsis in neutropenic animals and deserves further study as a new treatment option in patients with, or at risk for, severe Gram-negative bacterial infections and sepsis.
Comparison of the Accuracy and Precision of Pharmacokinetic Equations To Predict Free Meropenem Concentrations in Critically Ill Patients
Authors: Wong Gloria , Farkas Andras , Sussman Rachel , Daroczi Gergely , Hope William W. , Lipman Jeffrey , Roberts Jason A.
Published: December 2014

Population pharmacokinetic analyses can be applied to predict optimized dosages for individual patients. The aim of this study was to compare the prediction performance of the published population pharmacokinetic models for meropenem in critically ill patients. We coded the published population pharmacokinetic models with covariate relationships into dosing software to predict unbound meropenem concentrations measured in a separate cohort of critically ill patients. The agreements between the observed and predicted concentrations were evaluated with Bland-Altman plots. The absolute and relative bias and precision of the models were determined. The clinical implications of the results were evaluated according to whether dose adjustments were required from the predictions to achieve a meropenem concentration of >2 mg/liter throughout the dosing interval. A total of 157 free meropenem concentrations from 56 patients were analyzed. Eight published population pharmacokinetic models were compared. The models showed an absolute bias in predicting the unbound meropenem concentrations from a mean percent difference (95% confidence interval [CI]) of −108.5% (−119.9% to −97.3%) to 19.9% (7.3% to 32.7%), while absolute precision ranged from −249.1% (−263.4% to −234.8%) to 31.9% (17.6% to 46.2%) and −178.9% (−196.9% to −160.9%) to 175.0% (157.0% to 193.0%). A dose change was required in 44% to 64% of the concentration results. Seven of the eight equations evaluated underpredicted free meropenem concentrations. In conclusion, the overall accuracy of these models supports their inclusion in dosing software and application for individualizing meropenem doses in critically ill patients to increase the likelihood of achievement of optimal antibiotic exposures.
Therapeutic Responses of Plasmodium vivax Malaria to Chloroquine and Primaquine Treatment in Northeastern Myanmar
Authors: Yuan Lili , Wang Ying , Parker Daniel M. , Gupta Bhavna , Yang Zhaoqing , Liu Huaie , Fan Qi , Cao Yaming , Xiao Yuping , Lee Ming-chieh , Zhou Guofa , Yan Guiyun , Baird J. Kevin , Cui Liwang
Published: December 2014

Chloroquine-primaquine (CQ-PQ) continues to be the frontline therapy for radical cure of
Plasmodium vivax
malaria. Emergence of CQ-resistant (CQR)
P. vivax
parasites requires a shift to artemisinin combination therapies (ACTs), which imposes a significant financial, logistical, and safety burden. Monitoring the therapeutic efficacy of CQ is thus important. Here, we evaluated the therapeutic efficacy of CQ-PQ for
P. vivax
malaria in northeast Myanmar. We recruited 587 patients with
P. vivax
monoinfection attending local malaria clinics during 2012 to 2013. These patients received three daily doses of CQ at a total dose of 24 mg of base/kg of body weight and an 8-day PQ treatment (0.375 mg/kg/day) commencing at the same time as the first CQ dose. Of the 401 patients who finished the 28-day follow-up, the cumulative incidence of recurrent parasitemia was 5.20% (95% confidence interval [CI], 3.04% to 7.36%). Among 361 (61%) patients finishing a 42-day follow-up, the cumulative incidence of recurrent blood-stage infection reached 7.98% (95% CI, 5.20% to 10.76%). The cumulative risk of gametocyte carriage at days 28 and 42 was 2.21% (95% CI, 0.78% to 3.64%) and 3.93% (95% CI, 1.94% to 5.92%), respectively. Interestingly, for all 15 patients with recurrent gametocytemia, this was associated with concurrent asexual stages. Genotyping of recurrent parasites at the merozoite surface protein 3α gene locus from 12 patients with recurrent parasitemia within 28 days revealed that 10 of these were the same genotype as at day 0, suggesting recrudescence or relapse. Similar studies in 70 patients in the same area in 2007 showed no recurrent parasitemias within 28 days. The sensitivity to chloroquine of
P. vivax
in northeastern Myanmar may be deteriorating.