bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative Study of Vaneless and Vaned Diffusers in a Transonic Centrifugal Compressor With Real Gas
Authors: Cui Michael M.
Published: August 2014

Vaneless and vaned diffusers in a transonic centrifugal compressor with the refrigerant HFC-134a were studied experimentally and numerically. The compressor was tested on a closed-loop stand instrumented to obtain both overall performance data and local flow field quantities. In numerical studies, the thermodynamic and transport properties of the refrigerant gas were modeled by the Martin-Hou equation of state and power laws, respectively. To include the interaction of the compressor components in these analyses, a unified three-dimensional numerical model was built for the complete compressor stage. The flow field was calculated with a Navier-Stokes solver using the k-ε turbulent model. The impact of the different diffusers on both local flow field and overall performance is analyzed comparatively for each component. The experimental and numerical results agree well. The correlation between the overall compressor performance and local flow field quantities is defined. The methodology developed and data obtained in these studies can be applied to centrifugal compressor design and optimization.
Effects of Blade Number on the Efficiency of Centrifugal Compressor Impellers
Authors: Rodgers Colin
Published: August 2014

The results of a study directed towards identifying optimum blade numbers for aviation and turbocharger type centrifugal compressor impellers is presented. The study focused upon a simplified one dimensional frictional model supported by impeller test data over a wide specific speed range, plus limited correlation with computational fluid dynamic models.

The study results indicated that optimum blade numbers were a function of specific speed, blade backsweep angle, and DeLaval number. With a backsweep angle of 45 degrees and DeLaval number of unity the optimum blade numbers were ≈ 30 and ≈ 15 at low and high specific speeds respectively. It was shown that efficiency decreased with low blade number primarily due to low momentum exchange i.e., low slip factor.

In order to condense the analysis only the impeller component of the compressor stage was studied, wherein the geometry and operating conditions were characterized in terms of five parameters, with particular emphasis on specific speed.
Mixed Flow Turbines: Inlet and Exit Flow Under Steady and Pulsating Conditions
Authors: Karamanis N. , Martinez-Botas R. F. , Su C. C.
Published: August 2014

The performance and detailed flow characteristics of a high pressure ratio mixed flow turbine has been investigated under steady and pulsating flow conditions. The rotor has been designed to have a nominal constant incidence (based on free vortex flow in the volute) and it is for use in an automotive high speed diesel turbocharger. The results indicated a departure from the quasi-steady analysis commonly used in turbocharger turbine design. The pulsations from the engine have been followed through the inlet pipe and around the volute; the pulse has been shown to propagate close to the speed of sound and not according to the bulk flow velocity as stated by some researchers.

The flow entering and exiting the blades has been quantified by a laser Doppler velocimetry system. The measurements were performed at a plane 3.0 mm ahead of the rotor leading edge and 9.5 mm behind the rotor trailing edge. The turbine test conditions corresponded to the peak efficiency point at 29,400 and 41,300 rpm. The results were resolved in a blade-to-blade sense to examine in greater detail the nature of the flow at turbocharger representative conditions. A correlation between the combined effects of incidence and exit flow angle with the isentropic efficiency has been shown.

The unsteady flow characteristics have been investigated at two flow pulse frequencies, corresponding to internal combustion engine speeds of 1600 and 2400 rpm. Four measurement planes have been investigated: one in the pipe feeding the volute, two in the volute (40° and 130° downstream of the tongue) and one at the exit of the turbine. The pulse propagation at these planes has been investigated; the effect of the different planes on the evaluation of the unsteady isentropic efficiency is shown to be significant. Overall, the unsteady performance efficiency results indicated a significant departure from the corresponding steady performance, in accordance with the inlet and exit flow measurements.
Design of Low-Speed Cascades for Investigating Viscous Effects in High-Speed Axial Turbines
Authors: Zavitz K. , Sjolander S. A.
Published: August 2014

For turbine flow phenomena which are dominated by viscous effects, many valuable insights into the flow physics can be gained through low-speed cascade measurements. For example, for low-pressure turbines unsteady wake-blade interactions can be investigated in cascade provided that the Reynolds number, freestream turbulence conditions and the pressure coefficient distributions are the same in the cascade as in the high-speed counterpart.

This paper describes an iterative procedure for inversely designing low-speed linear cascades with prescribed blade pressure-coefficient distributions. The inverse-design problem is treated as an optimization problem. The optimization strategy features the use of a genetic algorithm and a gradient-type algorithm. At the end of each global iteration of the design procedure a Navier-Stokes analysis is used to see if the final cascade geometry gives the specified pressure-coefficient distribution to the desired degree of accuracy.

Although the resulting cascade may be designed to the level of accuracy afforded by the Navier-Stokes analysis, the method takes advantage of the fact that the pressure distribution in the low-speed cascade can be predicted with good accuracy and very rapidly using a panel method solution for the potential flow through the cascade. A panel method flow solver is used to minimize the number of Navier-Stokes evaluations to three or four for a given inverse-design problem. As a result, the present procedure is very efficient.
Aerodynamic Performance Measurements of a Fully-Scaled Turbine in a Short Duration Facility
Authors: Keogh R. C. , Guenette G. R. , Sommer T. P.
Published: August 2014

This paper describes the implementation and results of an experiment to measure the isentropic efficiency of a fully scaled transonic turbine stage in a short-duration blowdown type facility. Short duration test facilities offer the potential for low cost, high accuracy testing of turbomachinery components under fully scaled conditions. The method developed employs the ‘brake’ approach for turbine efficiency measurement. This paper describes newly developed techniques to measure the turbine torque and mass flow in this type of facility.

The isentropic efficiency was measured over a test window of 400 to 500 milliseconds. The estimated measurement uncertainty (U95) is 0.45% for absolute measurements, and 0.25% for relative measurements. Corrected mass flow and isentropic efficiency measurements are presented for a range of corrected speed (97–112%) and compared with CFD predictions. Close agreement was observed both in overall magnitudes and trends between the measured data and predictions.
Shape Optimization of Transonic Compressor Blades Using Quasi-3D Flow Physics
Authors: Chung June , Lee Ki D.
Published: August 2014

A design method for transonic compressor rotor blades is developed based on Navier-Stokes physics. The method is applied to optimize the blade sections at several span stations, and new three-dimensional blades are constructed by interpolating the geometry of the designed blade sections. The method is demonstrated with NASA Rotor 37, producing new rotor blades with improved adiabatic efficiency over a wide range of operating conditions. The results indicate that the developed design process can find improved designs at an affordable computational cost.
Kinematic Analysis of 3-D Swept Shock Surfaces in Axial Flow Compressors
Authors: Shan Peng
Published: August 2014

This paper is Part II of a comprehensive study on the blade leading edge sweep/bend of supersonic and transonic axial compressors. The paper explores and analyses the kinematic characteristic variables of 3-D swept shock surfaces. In the research field called sweep aerodynamics of axial flow compressors and fans, many types of high loading swept blades are under an intensive study. So, in both the direct/inverse design methods and the experimental validations, the accurate grasp of the sweep characteristic of the blade’s 3-D swept shock surface becomes more concerned than before. Associated with relevant blading variables, this paper studied in uniformity the forward and zero and backward sweeps of shock surfaces, defined and resolved every kind of useful sweep angle, obtained dimensionless sweep similarity factors, suggested a kind of method for the quantitative classification of 3-D shock structures, proposed the principle of 3-D shock structure measurements. Two rotor blade leading edge shock surfaces from two high loading single stage fans are analysed and contrasted. This study is the foundation of the kinematic design of swept shock surfaces.
Supersonic Through-Flow Fan Blade Cascade Studies: Part I — Baseline Cascade
Authors: Chesnakas Christopher J. , Ng Wing F.
Published: August 2014

An investigation has been performed of the flow in a supersonic through-flow fan blade cascade. The blade shapes are those of the baseline supersonic through-flow fan (STF) under investigation at the NASA Lewis Research Center. Measurements were made at an inlet Mach number of 2.36 over a 15° range of incidence. Flowfield wave patterns were recorded using spark shadowgraph photography and steady-state instrumentation was used to measure blade surface pressure distributions and downstream flowfield. From these measurements, the integrated loss coefficients are presented as a function of incidence angle along with analysis indicating the source of losses in the STF cascade. The results are compared with calculations made using a two-dimensional, cell-centered, finite-volume, Navier-Stokes code with upwind options. Good general agreement is found at design conditions, with lesser agreement at off-design conditions. Analysis of the leading edge shock shows that the leading edge radius is a major source of losses in STF blades. Losses from the leading edge bluntness are converted downstream into the blade wake, and are difficult to distinguish from viscous losses. Shock losses are estimated to account for 70% to 80% of the losses in the STF cascade.
Tip Clearance Flow Induced Endwall Boundary Layer Separation in a Single–Stage Axial–Flow Low–Speed Compressor
Authors: Saathoff Horst , Stark Udo
Published: August 2014

The paper describes an investigation of the overtip end-wall flow in a single–stage axial–flow low–speed compressor utilizing an oil flow technique and a periodic multisampling pressure measurement technique. Representative oil flow pictures and ensemble averaged casingwall pressure distributions with standard deviations — supplemented by selected endwall oil flow pictures from a corresponding 2D compressor cascade — are shown and carefully analysed. The results enable the key features of the overtip endwall flow to be identified and changes with flow rate — or inlet angle — to be determined.
Reducing Bottlenecks in the CAD-to-Mesh-to-Solution Cycle Time to Allow CFD to Participate in Design
Authors: Dawes W. N. , Dhanasekaran P. C. , Demargne A. A. J. , Kellar W. P. , Savill A. M.
Published: August 2014

As CFD has matured to the point that it is capable of reliable and accurate flow simulation, attention is now firmly fixed on how best to deploy that CFD as part of a process to improve actual products. This “process” consists of capturing and controlling the geometry of a suitable portion of an aeroengine (eg a blade row, or an internal cooling system or a fan-plus-nacelle), building a mesh system, solving the flow and responding to an appropriately visualized flow field by changing or accepting the geometry. This paper looks at that process from the point of view of identifying any bottlenecks and argues that current research should be directed at the CAD-to-mesh-to-solution cycle time rather than, as has been traditional, just looking at the solver itself and in isolation. Work aimed at eliminating some of these bottlenecks is described, with a number of practical examples.
A Comparative Study of Optimisation Methods for Aerodynamic Design of Turbomachinery Blades
Authors: Shahpar Shahrokh
Published: August 2014

A new approach to three-dimensional design of turbomachinery blades is presented. A number of heuristic and gradient based optimisers are used in conjunction with a linear sensitivity analysis tool, FAITH, to re-design a turbine nozzle guide vane. A novel linear approach is used to eliminate the large computational costs usually associated with function evaluations which are essentially solutions to the Navier-Stokes equations. Results are compared with those obtained previously from the inverse design mode of FAITH. With the present approach, it is shown that nonlinear complicated cost functions can be reduced significantly and aerodynamic and geometrical constraints can be handled easily and efficiently.
3D Inverse Method for Turbomachine Blading With Splitter Blades
Authors: Qiu X. , Dang T.
Published: August 2014

The use of a full 3D and viscous inverse method for turbomachine blading with splitter blades is demonstrated by carrying out a design modification of a transonic axial stator blade row with splitter blades. In this design modification study, the goal is to improve the aerodynamics of the full blade and the splitter blade, including weakening of shock wave and control of flow incidence. The improved blade design is “validated” using a well-known 3D Navier-Stokes analysis solver.
Status of Silicon Nitride Material Properties, Component Fabrication, and Applications for Small Gas Turbines
Authors: Newson Danielle D. , Pollinger John P. , Twait Douglas J.
Published: August 2014

Extensive progress has been made in the development of high performance silicon nitride structural ceramics and component fabrication. This has in turn led to a number of successful applications in small turbines, including commercial aircraft production components and a number of successful tests and continuing field tests in aircraft auxiliary power units, air turbine starters, and stationary power generation engines. The current status, capabilities, limitations, and material refinement efforts for silicon nitride at AlliedSignal Ceramic Components (ASCC) will be presented, including environmental durability and environmental barrier coating investigations. Two key issues in the implementation of silicon nitride turbine components have been the ability to fabricate engine quality hardware, and fabrication at low-enough costs to allow commercialization. The current status of production forming processes will be presented and the development of new low cost forming and advanced technologies including gelcasting and solid freeform fabrication will be discussed, both in regards to component fabrication capability and production cost potential. Finally, the status of a number of commercial and development applications such as propulsion turbine engine seals, APU hot section wheels, blades, and nozzles, industrial turbine nozzles, and power generation microturbine components will be discussed.
The New PGT5B/2: A State-of-the-Art 6MW Two-Shaft Gas Turbine
Authors: Bianchi Dino , Noccioni Paolo , Silvestri Catherine J.
Published: August 2014

The new PGT5B is a compact, state-of-the-art, 6 MW industrial gas turbine. The unit is available in two configurations: a single shaft for power generation and a two-shaft for mechanical drive applications. Maximum commonality has been maintained between the single and two shaft models. Both units share a common gas generator, with evident benefits in all the installations where mixed operations are required. The two-shaft engine is simply obtained by removing the second stage turbine from the single shaft unit and adding a two-stage power turbine.

The unit is an evolution of the existing PGT5, building on the experience of the successful PGT10 model. The synergy between GE Aircraft Engines and GE Power System Nuovo Pignone, with the benefit of GE’s Six Sigma Total Quality Methodology, has permitted the application of the most advanced technology in the development of the major components of the engine.

The high efficiency axial compressor is a scaled down version of the successful PGT10B, chosen as the base compressor for the new PGT’s product line. It has been obtained by the combination of advanced fully 3D aero-design, custom airfoil shape and blade stacking optimization.

The annular DLE, dual fuel combustion system, developed according to the proven aircraft engines design, is able to satisfy the most stringent environmental regulations.

The axial turbine, with sophisticated air cooling system, is designed to reach high values of firing temperature consistent with future uprates. The application of advanced CFD analysis using 3D viscous multi-rows codes and unsteady simulation has resulted in a very high efficiency turbine.

The two stage uncooled power turbine capitalizes on Nuovo Pignone’s experience in the mechanical drive market. While the single shaft version is particularly suitable for power generation and cogeneration due to the high exhaust temperature, the two-shaft version, with wide operating speed range, is designed to be a reliable and efficient mechanical drive for compressors and pumps.

The Power Turbine speed for optimum application efficiency (up to 34.%) is 12,500 rpm, with a capability range from 50% to 105% of nominal speed.

The flexibility of the standard package satisfies the different installation requirements of oil and gas market.

The simplicity of construction and the modular design concept of both the engine and package facilitate maintenance and reduce downtime and labor during servicing.
Experimental Study of 3D Unsteady Flow Around Oscillating Blade With Part-Span Separation
Authors: Queune O. J. R. , He L.
Published: August 2014

This paper documents an investigation conducted on the aerodynamic response of a turbine blade oscillating in a three-dimensional bending mode under massive tip separation. Flow separation near the tip of the blade was realized by use of a step placed upstream of the blade’s leading edge. Extensive blade surface steady and unsteady pressure measurements were obtained from a test facility with clearly defined boundary conditions for a range of reduced frequency. The experiment is designed to produce detailed and reliable 3D test cases for aeroelastic applications. A complete set of steady and unsteady blade surface pressure measurements is provided for five spanwise sections at 10 %, 30 %, 50 %, 70 % and 90 % of span. In addition, the issue of linearity is addressed. Experimental results demonstrate a predominant linear behaviour of the unsteady pressure response.
Unsteady Flow and Whirl-Inducing Forces in Axial-Flow Compressors: Part I — Experiment
Authors: Storace A. F. , Wisler D. C. , Shin H.-W. , Beacher B. F. , Ehrich F. F. , Spakovszky Z. S. , Martinez-Sanchez M. , Song S. J.
Published: August 2014

An experimental and theoretical investigation has been conducted to evaluate the effects seen in axial-flow compressors when the centerline of the rotor is displaced from the centerline of the static structure of the engine. This creates circumferentially non-uniform rotor-tip clearances, unsteady flow, and potentially increased clearances if the rotating and stationary parts come in contact. The result not only adversely affects compressor stall margin, pressure rise capability and efficiency but also generates an unsteady, destabilizing, aerodynamic force, called the Thomas/Alford force, which contributes significantly to rotor whirl instabilities in turbomachinery. Determining both the direction and magnitude of this force in compressors, relative to those in turbines, is especially important for the design of mechanically-stable turbomachinery components. Part I of this two-part paper addresses these issues experimentally and Part II presents analyses from relevant computational models.

Our results clearly show that the Thomas/Alford force can promote significant backward rotor whirl over much of the operating range of modern compressors, although some regions of zero and forward whirl were found near the design point. This is the first time that definitive measurements, coupled with compelling analyses, have been reported in the literature to resolve the long-standing disparity in findings concerning the direction and magnitude of whirl-inducing forces important in the design of modern axial-flow compressors.
Some Aspects of Modelling Compressor Behavior in Gas Turbine Performance Calculations
Authors: Riegler Claus , Bauer Michael , Kurzke Joachim
Published: August 2014

Performance calculation procedures for gas turbine engines are usually based on the performance characteristics of the engine components, and especially the turbo components are of major interest. In this paper methods of modelling compressors in gas turbine performance calculations are discussed. The basic methodologies based on Mach number similarity are summarized briefly including some second order effects.

Under extreme enginepartload conditions, as for example subidle or windmilling, the operating points in the compressor map are located in a region which is usually not covered by rig tests. In addition the parameters usually used in compressor maps are no longer appropriate. For these operating conditions a method is presented to extrapolate compressor maps towards very low spool speed down to the locked rotor. Instead of the efficiency more appropriate parameters as for example specific work or specific torque are suggested. A compressor map prepared with the proposed methods is presented and discussed.

As another relevant topic the performance modelling of fans for low bypass ratio turbofans is covered. Due to the flow splitter downstream of such a fan the core and bypass stream may be throttled independently during engine operation and bypass ratio becomes a third independent parameter in the map. Because testing a fan on the rig for various bypass ratios is a very costly task, a simplified method has been developed which accounts for the effects of bypass ratio.
Influence of Processing on Microstructure and Performance of EB-PVD Thermal Barrier Coatings
Authors: Schulz U. , Fritscher K. , Leyens C. , Peters M.
Published: August 2014

The paper addresses the effect of processing parameters on microstructure and lifetime of EB-PVD PYSZ coatings deposited onto NiCoCrAlY-coated Ni-base superalloys. In particular, the formation of a thermally grown oxide layer, an equiaxed zone, and various columnar arrangements of the highly textured PYSZ layers are discussed with respect to processing conditions. Three different microstructures were cyclically tested at 1100°C. The intermediate columnar structure was superior with respect to cyclic life times to a fine and to a coarse columnar structure which was mainly attributed to differences in the elastic properties. The effect of PYSZ microstructure on hot corrosion behavior of the TBC system at 950°C is briefly discussed.
A Reduced Order Model for Evaluating the Effect of Rotational Speed on the Natural Frequencies and Mode Shapes of Blades
Authors: Marugabandhu P. , Griffin J. H.
Published: August 2014

A reduced order model has been developed that can be used to accurately and quickly calculate the changes in the natural frequencies and mode shapes of a blade that are caused by centrifugal stiffening. It has been corroborated by comparisons with finite element analyses of a cantilevered tapered plate and with frequencies from a low aspect ratio fan blade.
Oil-Free Turbocharger Demonstration Paves Way to Gas Turbine Engine Applications
Authors: Heshmat Hooshang , Walton James F. , Corte Christopher Della , Valco Mark
Published: August 2014

An oil-free, 150 Hp turbocharger was successfully operated to 100% speed (95,000 rpm), with turbine inlet temperatures to 650°C on a turbocharger gas test stand. Development of this high speed turbomachine included bearing and lubricant component development tests, rotor-bearing dynamic simulator qualification and gas stand tests of the assembled turbocharger. Self acting, compliant foil hydrodynamic air bearings capable of sustained operation at 650°C and maximum loads to 750 N were used in conjunction with a newly designed shaft and system center housing. Gas stand and simulator test results revealed stable bearing temperatures, low rotor vibrations, good shock tolerance and the ability of the rotor bearing system to sustain overspeed conditions to 121,500 rpm. Bearing component development tests demonstrated 100,000 start stop cycles at 650°C with a newly developed solid film lubricant coating. In a separate demonstration of a 100 mm compliant foil bearing, loads approaching 4,500 N were supported by a compliant foil bearing. This combination of component and integrated rotor-bearing system technology demonstrations addresses many of the issues associated with application of compliant foil bearings to gas turbine engines.
Viscous-Flow 2D-Analysis Including Secondary Flow Effects
Authors: Mönig Reinhard , Mildner Frank , Röper Ralf
Published: August 2014

During the last few decades extremely powerful Quasi-3D codes and fully 3D Navier-Stokes solvers have been developed and successfully utilized in the design process and optimization of multistage axial-flow compressors.

However, most of these methods proved to be difficult in handling and extremely time consuming. Due to these disadvantages, the primary stage design and stage matching as well as the off-design analysis is nowadays still based on fast 2D methods incorporating loss-, deviation- and end wall modeling. Only the detailed 3D optimization is normally performed by means of advanced 3D methods.

In this paper a fast and efficient 2D calculation method is presented, which already in the initial design phase of multistage axial flow compressors considers the influence of hub leakage flows, tip clearance effects and other end wall flow phenomena. The method is generally based on the fundamental approach by Howard and Gallimore (1992). In order to allow a more accurate prediction of skewed and non-developed boundary layers in turbomachines an improved theoretical approach was implemented. Particularly the splitting of the boundary layers into an axial and tangential component proved to be necessary in order to account for the change between rotating and stationary end walls. Additionally, a new approach is used for the prediction of the viscous end wall zones including hub leakage effects and strongly skewed boundary layers. As a result, empirical correlations for secondary flow effects are no longer required.

The results of the improved method are compared with conventional 2D-results including 3D loss- and deviation-models, with, experimental data of a 3-stage research compressor of the Institute for Jet Propulsion and Turbomachinery of the Technical University of Aachen and with 3D Navier-Stokes solutions of the V84.3A compressor and of a multi-stage Siemens research compressor. The results obtained using the new method show a remarkable improvement in comparison with conventional 2D-methods. Due to the high quality and the extremely short computation time the new method allows an overall viscous design of multistage compressors for heavy duty gas turbines and aeroengine applications.
Rejuvenation Heat Treatment and Weld Repairability Studies of HAYNES® 230® Alloy
Authors: Klarstrom Dwaine L. , Hoback Gregory L. , Ishwar Venkat R. , Qureshi Javaid I.
Published: August 2014

A series of studies were undertaken to determine the optimum rejuvenation heat treatment of HAYNES 230 alloy and to examine its weld repairability. To simulate service exposure, samples of plate nominally 4.75 mm (0.187 in.) thick were exposed at temperatures of 760°C (1400°F) and 871°C (1600°F) for a period of 1500 hours. Room temperature tensile properties and stress-rupture properties at 927°C (1700°F)/62 Mpa (9 ksi) were determined and compared to the material in the unexposed condition. Rejuvenation heat treatments of exposed materials were performed at a temperature of 1177°C (2150°F) for times of 30 minutes to 3 hours followed by a rapid air cool. In all cases, the room temperature tensile and the stress-rupture properties were found to be comparable to those for the unexposed condition. Based on these data, a heat treatment time of 30 minutes was judged to be adequate. Plates representing the as-received, exposed, and exposed and rejuvenated conditions were gas tungsten arc welded (GTAW) using 230-W™ filler metal. Transverse tensile samples containing the weldments were tested at room temperature, and face and root weldment samples were bent around an approximate 2T radius. All of the results, including those for the exposed condition, were found to meet the requirements of Section IX of the ASME Boiler and Pressure Vessel Code.
Limitations on Gas Turbine Performance Imposed by Large Turbine Cooling Flows
Authors: Horlock J. H. , Watson D. T. , Jones T. V.
Published: August 2014

Calculations of the performance of modern gas turbines usually include allowance for cooling air flow rate; assumptions are made for the amount of the cooling air bled from the compressor, as a fraction of the mainstream flow, but this fractional figure is often set in relatively arbitrary fashion.

There are two essential effects of turbine blade cooling:

[i] the reduction of the gas stagnation temperature at exit from the combustion chamber [entry to the first nozzle row] to a lower stagnation temperature at entry to the first rotor and

[ii] a pressure loss resulting from mixing the cooling air with the mainstream.

Similar effects occur in the following cooled blade rows.

The paper reviews established methods for determining the amount of cooling air required and semi-empirical relations, for film cooled blading with thermal barrier coatings, are derived. Similarly, the pressure losses related to elements of cooling air leaving at various points round the blade surface are integrated over the whole blade. This gives another semi-empirical expression, this time for the complete mixing pressure loss in the blade row, as a function of the total cooling air used.

These two relationships are then used in comprehensive calculations of the performance of a simple open-cycle gas turbine, for varying combustion temperature and pressure ratio. These calculations suggest that for maximum plant efficiency there may be a limiting combustion temperature [below that which would be set by stoichiometric combustion]. For a given combustion temperature, the optimum pressure ratio is reduced by the effect of cooling air.
Metallurgical Considerations for Life Assessment and the Safe Refurbishment and Re-Qualification of Gas Turbine Blades
Authors: Daleo Joseph A. , Ellison Keith A. , Boone Donald H.
Published: August 2014

Metallurgical analysis of rotating blades operating in advanced gas turbine engines is important in establishing actual operating conditions, degradation modes, remaining life, and most importantly, the proper repair and rejuvenation techniques to be used in developing optimum component life strategics.

The elevated firing temperatures used in the latest engine designs result not only in very high metal surface temperatures but also in very high temperature gradients and concomitant thermal strains induced in part by the complex and efficient cooling systems. This has changed the primary function of today’s superalloy-coating systems from one of hot corrosion protection to moderating high temperature oxidation reactions. Furthermore, as a result of the high thermal strains induced by the cooling systems, long term metallurgical structural stability issues now revolve around optimizing both thermal mechanical fatigue (TMF) resistance and creep life. Thus the gradual change to Directionally Solidified (DS) and Single Crystal (SC) alloys throughout the industry.

The use of DS and SC alloys coated with state of the art TBC, platinum modified aluminide and MCrAlY coatings with or without subsequent aluminizing applied by vacuum plasma spray (VPS), high velocity oxygen fuel (HVOF), physical vapor deposition (PVD), air plasma spray (APS) and by chemical vapor deposition (CVD) methods along with the wide spread use of internal aluminide coatings have made today’s rotating components prohibitively expensive to replace after only one cycle of operation. It is therefore, or should now be a high priority for all cost conscience gas turbine users to help develop reliable repair and rejuvenation strategies and techniques to minimize their operating cost.

Traditional metallurgical considerations required for life assessment and the reliable refurbishment and re-qualification of gas turbine blades are reviewed along with some new exciting techniques. Examples of component degradation modes are presented. Appropriate attention to metallurgical issues allows turbine users to more successfully and economically operate their turbines.
The Design of Transient Wall Heating Experiments for the Determination of Convective Heat Transfer Using Liquid Crystal Thermography
Authors: Graham David , Rhine Jeff
Published: August 2014

The use of liquid crystals as surface temperature sensors in transient wall heating experiments, to measure steady-state convective heat transfer coefficients, is becoming increasingly popular. This paper describes a simple graphical method to assist in the design of these experiments. The analysis assumes that the test specimen, perspex in the given example, behaves as a semi-infinite solid.

Given an expected range of convective heat transfer coefficients, the experimenter can determine the optimum combination of liquid crystal colour change temperature, bounding wall thickness and experiment duration. It is also possible to determine the sensitivity of experimental uncertainty to the operating conditions and the physical properties of the bounding wall.

Emphasis is given to the use of liquid crystal thermography but the methodology could be applied when other temperature measurement devices are employed.
Unsteady Flow Behavior due to Breakdown of Tip Leakage Vortex in an Axial Compressor Rotor at Near-Stall Condition
Authors: Furukawa Masato , Saiki Kazuhisa , Yamada Kazutoyo , Inoue Masahiro
Published: August 2014

The unsteady flow nature caused by the breakdown of the tip leakage vortex in an axial compressor rotor at near-stall conditions has been investigated by unsteady three-dimensional Navier-Stokes flow simulations. The simulations show that the spiral-type breakdown of the tip leakage vortex occurs inside the rotor passage at the near-stall conditions. Downstream of the breakdown onset, the tip leakage vortex twists and turns violently with time, thus interacting with the pressure surface of the adjacent blade. The motion of the vortex and its interaction with the pressure surface are cyclic. The vortex breakdown causes significant changes in the nature of the tip leakage vortex, which result in the anomalous phenomena in the time-averaged flow fields near the tip at the near-stall conditions: no rolling-up of the leakage vortex downstream of the rotor, disappearance of the casing wall pressure trough corresponding to the leakage vortex, large spread of the low-energy fluid accumulating on the pressure side, and large pressure fluctuation on the pressure side. As the flow rate is decreased, the movement of the tip leakage vortex due to its breakdown becomes so large that the leakage vortex interacts with the suction surface as well as the pressure one. The interaction with the suction surface gives rise to the three-dimensional separation of the suction surface boundary layer.
A Computational Study of a Novel Turbine Rotor Partial Shroud
Authors: Harvey Neil W. , Ramsden Ken
Published: August 2014

The over tip leakage (OTL) flow that exists between the stationary casing and the rotor tip of a shroudless HP turbine remains a major source of loss of performance for modern aero gas turbines.

To-date the principal approaches to reducing OTL loss have been to minimise the clearance gap and/ or apply a rotating shroud to the rotor. Tip clearance control systems continue to improve, but a practical limit on tip gap remains. A rotating shroud is highly effective but increases the rotor weight forcing it to run more slowly, thus increasing other aerodynamic losses. Additional means of reducing OTL loss are still needed. Partial shrouds (winglets) have been tried but none have entered commercial service to-date.

This paper presents a novel design of partial shroud derived from a review of past research. The (arbitrary) objectives were to halve the OTL loss of a shroudless rotor, at less than half the size of a full shroud. This design has been analysed using a steady flow RANS CFD code to qualitatively determine its benefits. Attention has been paid to its validation and a realistic determination of its capabilities.

The winglet is predicted to significantly improve the efficiency of a highly loaded HP turbine, by 1.2–1.8% at 2% tip gap/ span. A detailed understanding of the flow field shows this to be credible.
Effect of proton irradiation on thermal resistance and breakdown voltage of InAlN/GaN high electron mobility transistors
Authors: Anderson Travis , Koehler Andrew , Hwang Ya-Hsi , Hsieh Yueh-Ling , Li Shun , Ren Fan , Johnson Jerry Wayne , Pearton Stephen J.
Published: August 2014

InAlN/GaN high electron mobility transistors were irradiated from the front side with 340 keV protons to a dose of 5 × 1013 cm−2. Raman thermography showed that the irradiated devices had higher channel temperatures than unirradiated control devices, but only by ∼10% under typical biasing conditions. Accordingly, the irradiated devices have higher thermal resistance (400 °C/W) compared to reference devices (350 °C/W), based on the slope of the power versus channel temperature line. However, increases of 42% in off-state drain breakdown voltage (VBR) and of >92% in critical voltage (Vcri) were observed for the proton irradiated HEMT. This is ascribed to the reduction of the peak electric field at the gate edges by ∼50% through the introduction of negative trap charges created from vacancies generated by the proton irradiation.
Correction of Joint Angles From Kinect for Balance Exercising and Assessment
Authors: De Rosario Helios , Belda-Lois Juan Manuel , Fos Francisco , Medina Enrique , Poveda-Puente Rakel , Kroll Michael
Published: August 2014

The new generation of videogame interfaces such as Microsoft’s Kinect opens the possibility of implementing exercise programs for physical training, and of evaluating and reducing the risks of elderly people falling. However, applications such as these might require measurements of joint kinematics that are more robust and accurate than the standard output given by the available middleware. This article presents a method based on particle filters for calculating joint angles from the positions of the anatomical points detected by PrimeSense’s NITE software. The application of this method to the measurement of lower limb kinematics reduced the error by one order of magnitude, to less than 10°, except for hip axial rotation, and it was advantageous over inverse kinematic analysis, in ensuring a robust and smooth solution without singularities, when the limbs are out-stretched and anatomical landmarks are aligned.
Muscle Contributions to Elbow Joint Rotational Stiffness in Preparation for Sudden External Arm Perturbations
Authors: Holmes Michael W.R. , Keir Peter J.
Published: August 2014

Understanding joint stiffness and stability is beneficial for assessing injury risk. The purpose of this study was to examine joint rotational stiffness for individual muscles contributing to elbow joint stability. Fifteen male participants maintained combinations of three body orientations (standing, supine, sitting) and three hand preloads (no load, solid tube, fluid filled tube) while a device imposed a sudden elbow extension. Elbow angle and activity from nine muscles were inputs to a biomechanical model to determine relative contributions to elbow joint rotational stiffness, reported as percent of total stiffness. A body orientation by preload interaction was evident for most muscles (P < .001). Brachioradialis had the largest change in contribution while standing (no load, 18.5%; solid, 23.8%; fluid, 26.3%). Across trials, the greatest contributions were brachialis (30.4 ± 1.9%) and brachioradialis (21.7 ± 2.2%). Contributions from the forearm muscles and triceps were 5.5 ± 0.6% and 9.2 ± 1.9%, respectively. Contributions increased at time points closer to the perturbation (baseline to anticipatory), indicating increased neuromuscular response to resist rotation. This study quantified muscle contributions that resist elbow perturbations, found that forearm muscles contribute marginally and showed that orientation and preload should be considered when evaluating elbow joint stiffness and safety.
Functional Data Analyses for the Assessment of Joint Power Profiles During Gait of Stroke Subjects
Authors: Andrade André G. P. , Polese Janaine C. , Paolucci Leopoldo A. , Menzel Hans-Joachim K. , Teixeira-Salmela Luci F.
Published: August 2014

Lower extremity kinetic data during walking of 12 people with chronic poststroke were reanalyzed, using functional analysis of variance (FANOVA). To perform the FANOVA, the whole curve is represented by a mathematical function, which spans the whole gait cycle and avoids the need to identify isolated points, as required for traditional parametric analyses of variance (ANOVA). The power variables at the ankle, knee, and hip joints, in the sagittal plane, were compared between two conditions: With and without walking sticks at comfortable and fast speeds. For the ankle joint, FANOVA demonstrated increases in plantar flexion power generation during 60–80% of the gait cycle between fast and comfortable speeds with the use of walking sticks. For the knee joint, the use of walking sticks resulted in increases in the knee extension power generation during 10–30% of the gait cycle. During both speeds, the use of walking sticks resulted in increased power generation by the hip extensors and flexors during 10–30% and 40–70% of the gait cycle, respectively. These findings demonstrated the benefits of applying the FANOVA approach to improve the knowledge regarding the effects of walking sticks on gait biomechanics and encourage its use within other clinical contexts.
Real-space imaging of the atomic-scale magnetic structure of Fe
1+

y

Te
Authors: Enayat Mostafa , Sun Zhixiang , Singh Udai Raj , Aluru Ramakrishna , Schmaus Stefan , Yaresko Alexander , Liu Yong , Lin Chengtian , Tsurkan Vladimir , Loidl Alois , Deisenhofer Joachim , Wahl Peter
Published: August 2014

Seeing magnetism on an atomic level

Electrons tunneling from the magnetized tip of a scanning tunneling microscope into the surface of a material can reveal the material's magnetic structure. Although researchers have used the technique on simple nanostructures, they've had trouble preparing the tip in just the right way to visualize the magnetic order in more exotic materials. Enayat
et al.
used a tip with a magnetic cluster on its apex to reveal patterns of magnetic ordering in the material Fe
1+y
Te, which becomes superconducting by substituting Te with Se atoms. The researchers prepared the tip by simply picking up atoms from the surface of the material.

Science
, this issue p.
653
Complete Coding Region Sequence of a Chikungunya Virus Strain Used for Formulation of CBER/FDA RNA Reference Reagents for Nucleic Acid Testing
Authors: Añez Germán , Heisey Daniel A. , Rios Maria
Published: August 2014

We have sequenced the complete coding region of a chikungunya virus isolate (R91064) used in the formulation of CBER/FDA RNA reference reagents for nucleic acid technology testing.
Genome Sequence of
Streptomyces toyocaensis
NRRL 15009, Producer of the Glycopeptide Antibiotic A47934
Authors: Kwun Min Jung , Hong Hee-Jeon
Published: August 2014

Here we report the draft genome sequence of
Streptomyces toyocaensis
strain NRRL 15009 which is the producer of the glycopeptide antibiotic A47934. The genome sequence is predicted to harbor a total of 26 secondary metabolite biosynthetic gene clusters including the A47934 cluster.
Mucoepidermoid carcinoma
Authors: Devaraju Ramaraju , Gantala Ramlal , Aitha Harisha , Gotoor Srikanth Goud
Published: August 2014

Salivary gland tumours comprise almost 5% of head and neck malignancies. Minor salivary gland tumours account for 10–15% of all salivary gland neoplasms and are usually malignant. The second most common minor salivary gland tumour (12–40% globally) is mucoepidermoid carcinoma. Mucoepidermoid carcinoma is more frequent in females, occurs in the fifth decade of life and is usually found in the parotid gland. However, the palate is a frequent site when it occurs in the minor glands. We report a case of a high-grade variant of mucoepidermoid carcinoma in the right retromolar trigone of a 21-year man which was treated with wide excision of the tumour with a 1.5 cm margin. Reconstruction was done with a buccal fat pad posteriorly with a pedicled lateral tongue flap. Temporal stripping and right coronoidectomy was carried out in case of post-surgical wound contraction. The patient is currently under periodic review.
Maxillary sinusitis with pulmonary tuberculosis
Authors: Upadhyay Rashmi , Prakash Ved , Singh Abhishek Bahadur , Saheer S
Published: August 2014

Tubercular infection of the nasal cavity is an infrequently encountered condition. More so, after the discovery of relevant antibiotics, nasal sinus tuberculosis is not commonly seen. Few cases have reported tuberculosis of the paranasal sinuses, nasopharynx and larynx. With the increasing incidence of HIV, these rare forms of infection have started re-emerging. We present a case of a middle aged man presenting with nasal cavity lesion along with pulmonary tuberculosis, which came to light only after the diagnosis of maxillary sinus tuberculosis.
A woman who lost weight at the cost of her heartbeat
Authors: Shah Rushikesh , Bansal Nidhi , Manocha Divey
Published: August 2014

With increasing prevalence of obesity worldwide, the number of patients undergoing bariatric surgery is also rising. Although the incidence of adverse outcomes associated with bariatric surgery has reduced, the physiological compensatory changes occurring after weight loss can lead to some unavoidable outcomes. One such condition is sinus bradycardia. The pathophysiology behind this is well studied but there is little awareness about this outcome. Sinus bradycardia in this clinical setting is generally asymptomatic and does not require any treatment. Extensive cardiac workup and unnecessary treatment can be avoided by increasing awareness among healthcare providers.