bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of the LM6000 for Power Generation and Cogeneration
Authors: Casper R. L.
Published: February 2015

Since its inception in 1989, the LM6000 gas turbine has undergone a series of successful factory tests and several turbines have begun commercial operation. Derived from the CF6-80C2, the LM6000 has been widely accepted for industrial cogeneration and peaking electrical power applications due to its high output power and high simple cycle thermal efficiency. The successful application of GE’s other LM series gas turbines, such as the LM1600, LM2500, and LM5000, for cogeneration use was factored into the development of the LM6000.

This paper provides an update of the LM6000 performance and operating characteristics based upon data recorded in factory tests completed in 1992. In addition, it discusses how the LM6000 can be adapted to meet power generation and cogeneration needs, both today and beyond the year 2000, including conversion to Dry Low NOx combustion technology.
Fan Noise Reduction From a Supersonic Inlet During Simulated Aircraft Approach
Authors: Nuckolls W. E. , Ng W. F.
Published: February 2015

A series of experiments was conducted to investigate the radiation of fan noise from a supersonic inlet during a simulated aircraft approach. A scaled-down model of an axisymmetric, mixed-compression, supersonic inlet (P-inlet) was used in conjunction with a 10.4 cm (4.1 in) diameter turbofan engine simulator as the noise source. The tests were conducted at an outdoor facility under static conditions. The main goal of the experiment was to reduce the forward radiating fan noise by modifying the auxiliary inlet doors. The modified doors are designed to reduce the inlet distortion to the fan face. In addition, the new door design also uses a converging flow passage in order to take advantage of the noise attenuation due to the choking effect at the auxiliary door. The simulator was tested at 60% design speed in an attempt to match the simulator noise source to that of a real aircraft engine on approach. Both aerodynamic and acoustic measurements were taken in the experiments. The results show that when compared to the original design, the modified auxiliary inlet doors reduced the circumferential inlet distortion to the fan face by a factor of two. The key result is that the blade passing frequency tone has been decreased by an average of 6 dB in the forward sector for the modified door design. Results from the closed auxiliary inlet door case are also presented to provide additional comparisons.
Flow Between Contra-Rotating Discs
Authors: Gan Xiaopeng , Kilic Muhsin , Owen J. Michael
Published: February 2015

The paper describes a combined experimental and computational study of laminar and turbulent flow between contra-rotating discs. Laminar computations produce Batchelor-type flow: radial outflow occurs in boundary layers on the discs and inflow is confined to a thin shear layer in the mid-plane; between the boundary layers and the shear layer, two contra-rotating cores of fluid are formed. Turbulent computations (using a low-Reynolds-number k-ε turbulence model) and LDA measurements provide no evidence for Batchelor-type flow, even for rotational Reynolds numbers as low as 2.2 × 104. Whilst separate boundary layers are formed on the discs, radial inflow occurs in a single interior core that extends between the two boundary layers; in the core, rotational effects are weak. Although the flow in the core was always found to be turbulent, the flow in the boundary layers could remain laminar for rotational Reynolds numbers up to 1.2 × 105. For the case of a superposed outflow, there is a source region in which the radial component of velocity is everywhere positive; radially outward of this region, the flow is similar to that described above. Although the turbulence model exhibited premature transition from laminar to turbulent flow in the boundary layers, agreement between the computed and measured radial and tangential components of velocity was mainly good over a wide range of nondimensional flow rates and rotational Reynolds numbers.
Development of an Aeroderivative Gas Turbine Dry Low Emissions Combustion System
Authors: Leonard Gary , Stegmaier James
Published: February 2015

This paper gives the development status of GE’s new aeroderivative premixed combustion system. This system consists of a new fuel staged annular combustor, compressor rear frame, first stage turbine nozzle, electronic staging controller, and fuel delivery system. Component test results along with a description of the combustion system are presented. This new system will reduce NOx emissions by 90% relative to the original aircraft engine combustion system while maintaining low emissions of CO and UHCs. Tests of a LM6000 gas turbine equipped with the new system are planned for early 1994.
Spanwise Transport in Axial-Flow Turbines: Part 2 — Throughflow Calculations Including Spanwise Transport
Authors: Lewis K. L.
Published: February 2015

In Part 1 of this paper, a repeating stage condition was shown to occur in two low aspect ratio turbines, after typically two stages. Both turbulent diffusion and convective mechanisms were responsible for spanwise transport. In this part, two scaling expressions are determined that account for the influence of these mechanisms in effecting spanwise transport. These are incorporated into a throughflow model using a diffusive term. The inclusion of spanwise transport allows the use of more realistic loss distributions by the designer as input to the throughflow model and therefore focuses attention on areas where losses are generated. In addition, modelling of spanwise transport is shown to be crucial in predicting the attenuation of a temperature profile through a turbine.
Magnetic Bearing Control of Flexible Shaft Vibrations Based on Multiaccess Velocity-Displacement Feedback
Authors: Petela G. , Botros K. K.
Published: February 2015

A model of the forced vibrations of a flexible, asymmetric and unbalanced shaft, supported by two magnetic bearings is derived to simulate the effect of different schemes of active control on shaft dynamic behaviour.

Simulation results were compared for several cases of single and multi-access bearing controls, rigid-body-mode only and rigid with flexible mode control, and linear and non-linear bearing responses. It is shown that the multi-access bearing response calculated from the known equation of the stable ROCL (Reduced Order Closed Loop) and based on the direct velocity-displacement feedback, provided the most precise shift in critical frequencies and also reasonable suppression of shaft vibration amplitudes.

The non-linear bearing design was also briefly discussed. The stability analysis showed that stability limits were influenced by more parameters in this case, but no particular advantages were observed in suppression of the vibration amplitudes as compared to the linear case.
Ceramic Stationary Gas Turbine Development
Authors: van Roode Mark , Brentnall William D. , Norton Paul F. , Pytanowski Gregory P.
Published: February 2015

A program has been initiated under the sponsorship of the Department of Energy (DOE), Office of Industrial Technology, to improve the performance of stationary gas turbines in cogeneration through the selective replacement of metallic hot section parts with uncooled ceramic components. It is envisioned that the successful demonstration of ceramic gas turbine technology, and the systematic incorporation of ceramics in existing and future gas turbines will enable more efficient engine operation, resulting in significant fuel savings, increased output power, and reduced emissions. The program which started in September, 1992, takes an engine of the Solar Centaur family of industrial gas turbines, and modifies the design of the hot section to accept ceramic first stage blades and first stage nozzles, and a ceramic combustor liner. The ceramic materials selected for the blade are silicon nitride, for the nozzle silicon nitride and silicon carbide, and for the combustor liner silicon carbide as well as two continuous fiber reinforced ceramic composites, one with a silicon carbide matrix and another with an oxide matrix.

This paper outlines the approach, conceptual component design, and materials selection for the program.
The Applicability of Electrically Driven Accessories for Turboshaft Engines
Authors: Jarvis M. Simon , Ostergren Warren J. , Smith Bert
Published: February 2015

Improved electrical power generation and actuation systems offer new design approaches for performing the engine control and accessory functions in helicopter propulsion systems. Present helicopter technology utilizes turboshaft engines with mechanically driven accessories. These accessories perform the functions of starting, fuel and lube pumping, variable stator actuation and inlet particle separation. This paper discusses the applicability of replacing the mechanically driven accessories with their electrically driven counterparts. An electric accessory system is defined which includes; a switched reluctance starter/generator and its associated control unit; an electric pumping and actuation system; and the engine mounting for the starter/generator. A comparison between the mechanically and electrically driven accessory systems is performed on the basis of cost, weight and reliability. Experience to date with switched reluctance machines and electrically driven turboshaft accessory systems is summarized. The benefits of electrically driven accessories are shown and recommendations for future activity for this important technology are discussed.
Prediction of Vortex and Linear Cascade Interaction Noise
Authors: Lee Yu-Tai , Feng Jinzhang , Merkle Charles L.
Published: February 2015

This paper is concerned with increasing the understanding of the noise generation mechanism assoicated with the interaction between foils and shed vorticity. An inviscid computational method is developed that predicts the flow interaction unsteadiness and the resultant acoustic pressures due to the acceleration and deceleration of vortices in the proximity to foils. This time-accurate prediction method is used to study the generation of shed vorticity and the interaction between a vortex and a foil or linear cascade of blades in terms of flow interaction phenomena, forces acting on foils, instability of free traveling vortices, and radiated acoustic pressure. The results show that the predicted acoustic pressure is proportional to the closeness of the free vortices to the foil or the cascade blades. The number of acoustic pulses, generated when a free vortex encounters a foil, depends on the inflow angle of attack. When compared to a single foil, a cascade produces effects that suppress the vortex/blade flow interaction. However, the acoustic response depends heavily on the free vortex location in relation to the cascade blades.
A New Constitutive Model for Several Metals Under Arbitrary Temperature and Loading Conditions
Authors: Whaley P. W.
Published: February 2015

A new theory of viscoplasticity is described which models yielding as a random phenomenon. A circle on the deviatoric stress plane represents the intensity of yielding with the radius equal to the random yielding microstress. This random model does not utilize a yield surface; yielding intensity is quantified by expected values defined in the deviatoric stress plane. The circle in the deviatoric stress plane with a random radius is a simple way to model multi-axial loading. Approximations for stress, strain energy density and plastic strain energy density are used to improve the computational efficiency of parameter selection and to quantify the flow criterion. The exact state equations are derived which can be manipulated to describe a wide variety of loading conditions for a broad temperature range. Reversed loading, stress relaxation, creep and nonproportional loading are all natural properties of the model which require little additional elaboration. Material properties were specified for five metals, three at room temperature and two over a wide temperature range.
Processing Methods for High Reliability Silicon Nitride Heat Engine Components
Authors: Pujari Vimal K. , Tracey Dennis M.
Published: February 2015

The paper discusses highlights of a silicon nitride processing methodology that has been developed in the course of a major four year DoE funded program in processing for reliability. The program focused on the attainment of high strength and reliability through the identification and subsequent control of strength degrading flaws introduced during processing unit operations. Process control and NDE methods applied to achieve an optimized process with the potential to produce high reliability advanced heat engine components are discussed. Concluding remarks are directed to the extensive tensile strength database that has been generated through testing of over 300 tensile rods produced by the optimized process.
Flex Cycle Combustor Development and Demonstration
Authors: Harris Mark M. , Marsh David N. , Vos Eduard A. , Durkin Edward
Published: February 2015

An innovative, “flex-cycle” combustion system has been developed for the Garrett Model 400-1 Integrated Power Unit (IPU), a 425 shp (317 kW) gas turbine engine designed for use on future fighter aircraft. Demonstration of this system required real-time transient operation of the combustor in a full-scale test rig. The transient testing was unique, having been performed with an electronic control which modulated all combustor operating parameters according to programmed engine component maps, drag curves, fuel schedules, and selected ambient test conditions.

The axially-injected annular combustor is capable of engine starts in two seconds, as well as producing 200 shp (149 kW) for emergency use at all altitudes up to 50,000 ft (15.240 m). The combustion system is capable of switching operation from the emergency power stored energy (SE) mode to the normal-air breathing (NAB) auxiliary power mode without loss of engine power. The flex-cycle combustor supplies emergency power in the SE mode with a temperature rise of 2200F (1222C) and in the NAB mode with a temperature rise of 1600F (889C). Specific features which make the above requirements possible include air-assisted simplex airblast fuel atomizers with integral check valves, and effusion-cooled combustor liner walls.

This paper describes the flex-cycle combustion system design, test methods used, and significant test results. Steady-state performance, in both the SE and NAB operating modes, and real-time transient test results are discussed. The transient testing included rapid starts as well as transitions from the SE to NAB operating regimes.
Computation of Unsteady Viscous Flow Through Turbomachinery Blade Row due to Upstream Rotor Wakes
Authors: Ho Y.-H. , Lakshminarayana B.
Published: February 2015

A time-accurate, two-dimensional, pressure-based, Navier-Stokes solver for incompressible flow is developed and used to carry out the numerical simulation of rotor-stator interaction. A low Reynolds number form of the two-equation turbulence model is used to account for the turbulence effects. In order to improve the accuracy of the numerical scheme, a central differencing plus an artificial dissipation scheme is implemented to provide precise control of numerical dissipation. An inner loop iteration scheme is used at each time step to account for the non-linear effects. The computation of unsteady flow through a flat plate cascade subjected to a transverse gust reveals that the choice of grid spacing and the amount of artificial dissipation is critical for accurate prediction of unsteady phenomena. The rotor-stator interaction problem is simulated by starting the computation upstream of the stator, and the upstream rotor wake is specified from the experimental data. The results show that the stator potential effects have appreciable influence on the upstream rotor wake. The predicted unsteady wake profiles are compared with the available experimental data and the agreement is good. The numerical results are interpreted to draw conclusions on the unsteady wake transport mechanism in the blade passage.
Advanced Transonic Fan Design Procedure Based on a Navier-Stokes Method
Authors: Rhie C. M. , Zacharias R. M. , Hobbs D. E. , Sarathy K. P. , Biederman B. P. , Lejambre C. R. , Spear D. A.
Published: February 2015

A fan performance analysis method based upon 3D steady Navier-Stokes equations is presented in this paper. Its accuracy is established through extensive code validation effort. Validation data comparisons ranging from a 2D compressor cascade to 3D fans are shown in this paper to highlight the accuracy and reliability of the code. The overall fan design procedure using this code is then presented. Typical results of this design process are shown for a current engine fan design.

This new design method introduces a major improvement over the conventional design methods based on inviscid flow and boundary layer concepts. Using the Navier-Stokes design method, fan designers can confidently refine their designs prior to rig testing. This results in reduced rig testing and cost savings as the bulk of the iteration between design and experimental verification is transferred to an iteration between design and computational verification.
A Design Procedure for Effervescent Atomizers
Authors: Chin J. S. , Lefebvre A. H.
Published: February 2015

A methodology for the design of effervescent atomizers is described. The objective is to achieve sprays of minimum mean drop size for any stipulated values of liquid flow rate, air supply pressure, and air/liquid ratio. Application of the method leads to optimum values for all the key atomizer dimensions, including the number and size of the air injection holes, and the diameters of the mixing chamber and discharge orifice. It also enables optimum dimensions to be determined for a convergent-divergent nozzle should such a device be fitted to the nozzle exit to improve atomization performance. Examples are provided to demonstrate the application of the recommended design procedure and to illustrate the relative importance of various flow and geometrical parameters in regard to their effects on atomization quality.
Turbulence Characteristics in a Supersonic Cascade Wake Flow
Authors: Andrew Philip L. , Ng Wing-fai
Published: February 2015

The turbulent character of the supersonic wake of a linear cascade of fan airfoils has been studied using a two–component Laser Doppler Anemometer. The cascade was tested in the Virginia Polytechnic Institute and State University intermittent wind tunnel facility, where the Mach and Reynolds numbers were 2.36 and 4.8 × 106, respectively. In addition to mean flow measurements, Reynolds normal and shear stresses were measured as functions of cascade incidence angle and streamwise locations spanning the near–wake and the far–wake. The extremities of profiles of both the mean and turbulent wake properties were found to be strongly influenced by upstream shock–boundary–layer–interactions, the strength of which varied with cascade incidence. In contrast, the peak levels of turbulence properties within the shear layer were found to be largely independent of incidence, and could be characterized in terms of the streamwise position only. The velocity defect turbulence level was found to be 23%, and the generally–accepted value of the turbulence structural coefficient of 0.30 was found to be valid for this flow. The degree of similarity of the mean flow wake profiles was established, and those profiles demonstrating the most similarity were found to approach a state of equilibrium between the mean and turbulent properties. In general, this wake flow may be described as a classical free shear flow, upon which the influence of upstream shock–boundary–layer–interactions has been superimposed.
A Model for the Dynamic Simulation of a Two-Shaft Industrial Gas Turbine With Dry Low NOx Combustor
Authors: Blotenberg Wilfried
Published: February 2015

A dynamic simulation model for a twin-shaft industrial gas turbine is presented. The model is of modular design. Each component is modelled individually. This allows the model user to modify selected items without having to remodel the complete system. The model allows the simulation of a complete operation cycle from start-up via part load, full load operation and load drop. Simulation results of 14 selected operating points have been compared with measured values from trial test runs. 65 % of the calculated values do not deviate more than 2 % from the referenced values, and over 90 % of all simulated values are located in a tolerance band of less than 5 %. The dynamic response of the model is demonstrated by comparing the measured speed response during a load shedding test with the respective simulation result.
Externally-Fired Combined Cycle Repowering of Existing Steam Plants
Authors: Vandervort Christian L. , Bary Mohammed R. , Stoddard Larry E. , Higgins Steven T.
Published: February 2015

The Externally-Fired Combined Cycle (EFCC) is an attractive emerging technology for powering high efficiency combined gas and steam turbine cycles with coal or other ash bearing fuels. The key near-term market for the EFCC is likely to be repowering of existing coal fueled power generation units. Repowering with an EFCC system offers utilities the ability to improve efficiency of existing plants by 25 to 60 percent, while doubling generating capacity. Repowering can be accomplished at a capital cost half that of a new facility of similar capacity. Furthermore, the EFCC concept does not require complex chemical processes, and is therefore very compatible with existing utility operating experience.

In the EFCC, the heat input to the gas turbine is supplied indirectly through a ceramic heat exchanger. The heat exchanger, coupled with an atmospheric coal combustor and auxiliary components, replaces the conventional gas turbine combustor. Addition of a steam bottoming plant and exhaust cleanup system completes the combined cycle.

A conceptual design has been developed for EFCC repowering of an existing reference plant which operates with a 48 MW steam turbine at a net plant efficiency of 25 percent. The repowered plant design uses a General Electric LM6000 gas turbine package in the EFCC power island. Topping the existing steam plant with the coal fueled EFCC improves efficiency to nearly 40 percent. The capital cost of this upgrade is 1,090/kW. When combined with the high efficiency, the low cost of coal, and low operation and maintenance costs, the resulting cost of electricity is competitive for base load generation.
Italian Compressor Stations for Gas Storage
Authors: Zampieri Giuliano , Damiani Vanni
Published: February 2015

In Italy the gas transmission network, more than 23.000 km long, has 21 compressor stations with a total power of 500 MW. Some of the stations are used only for transmission purposes while others can also be used alternately or at the same time to compress gas into storage fields (Fig.1).

Italy has one of Western Europe’s biggest gas reserves in storage fields: in fact the working gas used at the moment is about 12 Gm3 and the gas in place is about 24 Gm3. The total compression capacity is about 90 Mm3/d with discharge pressures of up to 150 bar.

All the stations are remote controlled with no personnel on site. For this, very reliable station control systems are used to control plant, engines and all the station’s auxiliary equipment.

A compressor unit consists of a centrifugal compressor driven by a gas turbine. The heavy duty gas turbines have an output of between 3.7 and 10.4 MW, while the jet derivative turbines have an output of 20.5 MW. The gas compressors have two separate stages (sections) that can be put in series or in parallel according to the required compression ratio and flow.

The special configuration of the stations gas piping is designed to match operating requirements.

Examples of series/parallel configurations of the compressors and of the gas piping are given with an explanation of the pros and cons.
Modeling of Tip Clearance Flows Through an Improved 3-D Pressure Correction Navier-Stokes Solver
Authors: Lymberopoulos N. , Giannakoglou K. , Nikolaou I. , Papailiou K. D. , Tourlidakis A. , Elder R. L.
Published: February 2015

Mechanical constraints dictate the existence of tip clearances in rotating cascades, resulting to a flow leakage through this clearance which considerably influences the efficiency and range of operation of the machine. Three-dimensional Navier-Stokes solvers are often used for the numerical study of compressor and turbine stages with tip-clearance. The quality of numerical predictions depends strongly on how accurately the blade tip region is modelled; in this respect the accurate modelling of tip region was one of the main goals of this work. In the present paper, a 3-D Navier-Stokes solver is suitably adapted so that the flat tip surface of a blade and its sharp edges could be accurately modelled, in order to improve the precision of the calculation in the tip region. The adapted code solves the fully elliptic, steady, Navier-Stokes equations through a space-marching algorithm and a pressure correction technique; the H-type topology is retained, even in cases with thick leading edges where a special treatment is introduced herein. The analysis is applied to two different cases, a linear cascade and a compressor rotor, and comparisons with experimental data are provided.
The Influence of Primary and Secondary Orientations on the Elastic Response of a Nickel-Base Single-Crystal Superalloy
Authors: Abdul-Aziz Ali , Kalluri Sreeramesh , McGaw Michael A.
Published: February 2015

The influence of primary orientation on the elastic response of a [001]-oriented nickel-base single-crystal superalloy, PWA 1480, was investigated under mechanical, thermal, and combined thermal and mechanical loading conditions using finite element techniques. Elastic stress analyses were performed using the MARC finite element code on a square plate of PWA 1480 material. Primary orientation of the single crystal superalloy was varied in increments of 2°, from 0° to 10°, from the [001] direction. Two secondary orientations (0° and 45°) were considered, with respect to the global coordinate system, as the primary orientation angle was varied. The stresses developed within the single crystal plate were determined for each loading condition. In this paper, the influence of the angular offset between the primary crystal orientation and the loading direction on the elastic stress response of the PWA 1480 plate is presented for different loading conditions. The influence of primary orientation angle, when constrained between the bounds considered, was not found to be as significant as the influence of the secondary orientation angle, which is not typically controlled.
Observations of Wake-Induced Turbulent Spots on an Axial Compressor Blade
Authors: Walker G. J. , Solomon W. J. , Gostelow J. P.
Published: February 2015

Measurements of transitional flow in regions of strong adverse pressure gradient on an axial compressor stator are reported. The range of observations covers separating laminar flow at transition onset, and reattachment of intermittently turbulent periodically separated shear layers.

Transition was characterised by the regular appearance of turbulent spots in association with the rotor blade wake disturbances. However, the initial breakdown did not coincide with the wake passage as has usually been observed by other workers. The spots rather evolved from the growth of instability wave packets which lagged the wake passage.

Data presented from the compressor blade measurements include: mean and ensemble-average velocities and associated integral parameters; distributions of total, periodic and random disturbance components; typical individual velocity fluctuation records; contours of ensemble-average random disturbance level; and boundary layer intermittency distributions.

Measurements of turbulent intermittency showed a significant fall in this quantity near the wall in the reattaching flow. This has significant implications for the interpretation of transition data from surface film gage observations.
Species Concentrations in a Model Gas Turbine Combustor
Authors: Ghaffarpour M. , Chehroudi B.
Published: February 2015

To investigate the combustion characteristics of hollow-cone spray flames somewhat similar to those occurring in the primary zone of gas turbine combustion chambers or within oil burners, a swirl-stabilized combustor was designed. The combustor is circular in cross section, with a swirl plate and fuel nozzle axis coinciding with the axes of the combustor. Separate swirl and dilution air flows are distributed into the combustor that pass through honeycomb flow straighteners and screens. A kerosene spray was generated by a simplex atomizer with a nominal initial-spray-angle of 30 degrees. Swirling air with swirl number of 1.5 was produced from a swirl plate. A Phase Doppler Particle Analyzer (PDPA) was used to measure the drop size, mean and rms values of axial drop velocity with and without combustion. Air and fuel flow rates and other conditions were kept identical for reacting and non-reacting cases to investigate effects of combustion alone on the spray. A thermocouple was used to measure the average uncorrected temperature in this turbulent spray flame. A water-cooled stainless-steel gas sampling probe was designed to be used with a gas chromatograph (GC) to measure the gaseous species concentrations in this combustor.

Results for mean axial drop velocity profiles indicate widening of the spray, with slight increase in the magnitudes of the peak drop velocities due to combustion. No measurements of this type are possible inside the hollow-cone spray due to burning of fuel droplets within the flame zone. Root-Mean-Square (RMS) values of drop velocity fluctuations decrease due to combination of increase in gas kinematic viscosity and elimination of small drops at high temperatures. Sauter Mean Diameter (SMD) radial profiles at all axial locations increase with combustion as compared to the no-combustion case due to preferential burning of small drops. At the initial stages of combustion near the atomizer, the gas species concentration changes due to droplet evaporation, decomposition of fuel, reaction, and mixing with extra air. At the end of the visible flame zone, away from the nozzle, no significant amounts of methane and hydrogen have been observed. The gas concentration profiles at this axial position are flat within the burned gas zone. The species concentration profiles measured in the burned gas zone near the nozzle and along the spray centerline axis are similar to those of turbulent gaseous-fuel diffusion flame.
CFD Study of Nozzle Configurations for Ultra High Bypass Engines
Authors: Zimmermann H. , Gumucio R. , Katheder K. , Jula A.
Published: February 2015

Performance and aerodynamic aspects of ultra-high bypass ratio ducted engines have been investigated with an emphasis on nozzle aerodynamics. The interference with aircraft aerodynamics could not be covered.

Numerical methods were used for aerodynamic investigations of geometrically different aft end configurations for bypass ratios between 12 and 18, this is the optimum range for long missions which will be important for future civil engine applications.

Results are presented for a wide range of operating conditions and effects on engine performance are discussed. The limitations for higher bypass ratios than 12 to 18 do not come from nozzle aerodynamics but from installation effects.

It is shown that using CFD and performance calculations an improved aerodynamic design can be achieved. Based on existing correlations, for thrust and mass-flow, or using aerodynamic tailoring by CFD and including performance investigations, it is possible to increase the thrust coefficient up to 1%.
Experimental Investigations of the Influence of Incoming Wakes on the Losses of a Linear Turbine Cascade
Authors: Ladwig M. , Fottner L.
Published: February 2015

The objective of this work is to enhance the understanding of the influence of wake induced non-uniform, steady inlet flow conditions on the profile losses of highly-loaded turbines. For different Reynolds numbers wake and profile pressure distribution measurements were carried out on a linear subsonic turbine cascade as well as measurements with a single sensor hot-film probe. The non-uniform inlet flow were simulated with two different cascades of cylindrical bars.

The measurements with various circumferential positions of the incoming wakes relative to the turbine cascade show at low Reynolds numbers a decrease of the losses compared to uniform inlet conditions, because no separation of the suction side boundary layer occurs. With increasing Reynolds numbers the non-uniform inlet flow conditions cause an increase in the losses compared to uniform inlet conditions, due to the forward shift of transition. Generally, the smallest influence of the non-uniform incoming flow can be observed when the wakes enter the cascade inlet plane between the pressure-side of the profiles and the middle of the blade passage. Incoming wakes have the highest influence when they enter the blade passage near to the suction side of the profiles.
The Design and Fabrication of a Small Highly Instrumented Counterrotating Turbine Rig
Authors: Davidson D. P. , Finke A. K.
Published: February 2015

The paper describes some of the design solutions that were adopted in the realization of a small two shaft, counterrotating turbine rig. The turbine, for a small space engine technology upper stage liquid propellant rocket turbo pump system, was only 100mm tip diameter with a correspondingly small annulus height. Detailed flow measurements were provided by 3 axis actuators at inlet and outlet of the working section. Torque and Power were measured on each shaft using Radio Frequency (R.F.) telemetry torquemeters.

A modular design allowed the rig to be rebuilt rapidly in one and two stage configurations with different blade sets. This enabled the effect of changing turbine configurations to be studied.
The Ceramic Technology Project: Ten Years of Progress
Authors: Johnson D. Ray , Schulz Robert B.
Published: February 2015

The Ceramic Technology Project was initiated in 1983 for the purpose of developing highly reliable structural ceramics for applications in advanced heat engines, such as the automotive gas turbines and advanced heavy duty diesel engines. The reliability problem was determined to be a result of uncontrolled populations of processing flaws in the brittle, flaw-sensitive materials, along with microstructural features, such as grain boundary phases, that contribute to time dependent strength reduction in service at high temperatures. The approach taken to develop high reliability ceramics included the development of tougher materials with greater tolerance to microstructural flaws, the development of advanced processing technology to minimize the size and number of flaws, and the development of mechanical testing methodology and the characterization of time dependent mechanical behavior, leading to a life prediction methodology for structural ceramics.
Computed Effects of Rim Seal Clearance and Cavity Width on Thermal Distributions
Authors: Ko S. H. , Rhode D. L. , Guo Z.
Published: February 2015

Axisymmetric solutions of the Reynolds averaged Navier-Stokes equations were obtained for the complete momentum/thermal interaction at the interface between the turbine hot mainstream and rim seal flow regions. Specifically, the 2-D, axisymmetric, fully elliptic form of the equations was solved in order to obtain detailed insight concerning the effect of the rim seal clearance and cavity width on the disk temperature, gap recirculation zone GRZ and rotational drag. The mainstream and purge flow rates, pressures and temperatures were selected to match those of a typical commercial engine. The details of seven generic geometries, consisting of different seal clearance gaps and different cavity widths, for each of several cooling flow rates are analyzed.

Of particular interest is the result that halving the engine nominal axial clearance of the generic rim seal is not sufficient for preventing the appearance of the GRZ. However, reducing this clearance to 25% of the nominal value does prevent its formation, and in that case the coolant flow continues outward along the disk surface through the rim seal region.

In addition, the first-order characteristics of: (a) the heat transport in the rim seal region and (b) the disk temperature rise due to thermal transport via the rim seal (gap) recirculation zone and via disk frictional heating were illuminated. Further, it is concluded that smaller seal clearances are desirable for reducing rotational drag as well as purge flow rates.
The Spray Cast Process and its Applications in Gas Turbine Engines
Authors: Dalal Ranes P. , Prichard Paul D. , Tom Thomas
Published: February 2015

The need for advanced material processing to reduce manufacturing cost and cycle times has never been as great as at this time in our nation’s history. Howmet Corporation has licensed and modified the Osprey, or spray forming, process to produce high quality nickel base superalloys for gas turbine engine applications. The modified process, known as the “Spraycast-X™” process, combined vacuum induction melting with high purity argon gas atomization to produce billet and ring shape products. Process parameters were established to produce fine grain size (ASTM 6-8) billet up to 10” (254 mm) in diameter and ring shape preforms up to 33” (838 mm) in diameter. Mechanical properties of HIP’ed Spraycast-X plus isoforged U720 and Spraycast-X and HIP’ed MERL 76 (no Hf) were comparable to their wrought counterparts. Mechanical property data for ring rolled IN718, René 41, and Waspaloy were all above specification limits.
Wave Cycle Design for NOx-Limited Wave Rotor Core Engines for High Speed Propulsion
Authors: Nalim M. Razi , Mocsari Jeffrey C. , Resler Edwin L.
Published: February 2015

Direct work and pressure exchange between gases can be accomplished by cyclic wave processes in the channels of a wave-rotor, circumventing the limitations of turbo-compressors. A wave-rotor cycle is presented for use as the high-pressure core in a high speed aircraft engine with turbine bypass. The products of a “low-NOx” combustor undergo a large immediate wave-expansion to reach a permissible turbine blade temperature. The wave rotor provides a substantial increase in pressure ratio and peak cycle temperature resulting in high specific power and efficiency.

Approximate analytical methods are employed for initial design and optimization of the cycle. The method of characteristics is then used to compute the detailed time evolution of the flow-field in a wave channel.
Subharmonic Oscillations in Squeeze Film Damped Rotor Bearing Systems Without Centralizing Springs
Authors: Chen Peter Y. P. , Hahn E. J. , Wang G. Y.
Published: February 2015

This paper investigates the nonsynchronous motion of a rigid rotor in squeeze film damped systems without spring support subjected to both unbalance and unidirectional loading. Both harmonic balance and 4th order Runge–Kutta integration are used to obtain the unbalance response, the asymptotic stability of the harmonic balance equilibrium solutions being determined by Floquet theory. Depending on the system parameters stable subharmonic orbits with fundamental frequencies of half, one third and one quarter of excitation frequency were obtained. Also, bistable, tristable and quadristable solution possibilities were found. The effect of these subharmonic orbits on maximum transmissibilities is included.
Analysis of High Mach 2DCD and SERN Scale Model Test Data
Authors: Hoff G. E. , Whittaker R. W.
Published: February 2015

This paper presents the results of analysis of scale model cold flow static performance test data for 2DCD and SERN High Mach (4 to 6) nozzle configurations generated under a GE Aircraft Engines Independent Research and Development Program. The testing was conducted at FluiDyne Engineering Corporation in late 1989. For the 2DCD nozzles, throat area, divergent flap length, contour, expansion ratio, and nozzle pressure ratio were parametrically varied and simulated operating conditions from subsonic to Mach 6. SERN nozzle parameters varied included throat area, expansion ramp length, cowl length and cowl divergence angle. Geometrics and nozzle pressure ratios simulated subsonic to Mach 6 operation. Although these tests were conducted statically, i.e., external flow was not simulated, the analysis presented herein addresses design point performance where the internal performance is not expected to be significantly influenced by external flow.

Data from the test program have been examined for comparison with existing GE performance prediction methods. A second objective was to explore generalization of the data for the preparation of prediction methodologies and design guides for future High Mach propulsion system studies. In general, the study results presented in this paper indicate that current GE 2DCD prediction methods do not extrapolate to the High Mach nozzle regime. Also presented are general performance trends as a function of key geometric parameters and potential correlating factors which provide guidelines for the design of future High Mach exhaust systems.
A method for modeling laterally asymmetric proton beamlets resulting from collimation
Authors: Gelover Edgar , Wang Dongxu , Hill Patrick M. , Flynn Ryan T. , Gao Mingcheng , Laub Steve , Pankuch Mark , Hyer Daniel E.
Published: February 2015

Purpose:

To introduce a method to model the 3D dose distribution of laterally asymmetric proton beamlets resulting from collimation. The model enables rapid beamlet calculation for spot scanning (SS) delivery using a novel penumbra‐reducing dynamic collimation system (DCS) with two pairs of trimmers oriented perpendicular to each other.

Methods:

Trimmed beamlet dose distributions in water were simulated with MCNPX and the collimating effects noted in the simulations were validated by experimental measurement. The simulated beamlets were modeled analytically using integral depth dose curves along with an asymmetric Gaussian function to represent fluence in the beam's eye view (BEV). The BEV parameters consisted of Gaussian standard deviations (sigmas) along each primary axis (σx1,σx2,σy1,σy2) together with the spatial location of the maximum dose (μx,μy). Percent depth dose variation with trimmer position was accounted for with a depth‐dependent correction function. Beamlet growth with depth was accounted for by combining the in‐air divergence with Hong's fit of the Highland approximation along each axis in the BEV.

Results:

The beamlet model showed excellent agreement with the Monte Carlo simulation data used as a benchmark. The overall passing rate for a 3D gamma test with 3%/3 mm passing criteria was 96.1% between the analytical model and Monte Carlo data in an example treatment plan.

Conclusions:

The analytical model is capable of accurately representing individual asymmetric beamlets resulting from use of the DCS. This method enables integration of the DCS into a treatment planning system to perform dose computation in patient datasets. The method could be generalized for use with any SS collimation system in which blades, leaves, or trimmers are used to laterally sharpen beamlets.
Diverse anguilliform swimming kinematics in Pacific hagfish (Eptatretusstoutii) and Atlantic hagfish (Myxineglutinosa)
Authors: Lim J.L. , Winegard T.M.
Published: February 2015

Anguilliform mode swimmers pass waves of lateral bending down their elongate bodies to propel forward. Hagfishes (Myxinidae) are classified as anguilliform swimmers, but their unique habits and reduced morphology—including a flexible body lacking a vertebral column—have the potential to translate into unique swimming behaviour within this broad classification. Their roles as active scavengers and hunters can require considerable bouts of swimming, yet quantitative data on hagfish locomotion are limited. Here, we aim to provide a more complete mechanistic understanding of hagfish swimming by quantifying whole-body kinematics of steady swimming in Pacific hagfish (Eptatretus stoutii (Lockington, 1878)) and Atlantic hagfish (Myxine glutinosa L., 1758), species from the two main lineages of Myxinidae. We analyzed high-speed video of hagfishes swimming at voluntary swim speeds and found that both species swim using high-amplitude undulatory waves. Swim speed is generally frequency-modulated, but patterns in wave speed, wavelength, and amplitude along the body and across swim speeds are variable, implying versatile mechanisms for the control of swim speed in these highly flexible fishes. We propose mechanistic explanations for this kinematic variability and compare hagfish with other elongate swimmers, demonstrating that the hagfish’s rich locomotory repertoire adds variety to the already diverse set of locomotory kinematics found in anguilliform swimmers.
INNER PALINDROMIC CLOSURE
Authors: DASSOW JÜRGEN , MANEA FLORIN , MERCAŞ ROBERT , MÜLLER MIKE
Published: February 2015

We introduce the inner palindromic closure as a new operation ♠, which consists in expanding a factor u to the left or right by a non-empty word v such that vu or uv, respectively, is a palindrome of minimal length. We investigate several language theoretic properties of the iterated inner palindromic closure ♠*(w) = Ui≥0 ♠i(w) of a word w.
SOME DECISION QUESTIONS CONCERNING THE TIME COMPLEXITY OF LANGUAGE ACCEPTORS
Authors: IBARRA OSCAR H. , RAVIKUMAR BALA
Published: February 2015

Almost all the decision questions concerning the resource requirements of a computational device are undecidable. Here we want to understand the exact boundary that separates the undecidable from the decidable cases of such problems by considering the time complexity of very simple devices that include NFAs (1-way and 2-way), PDAs and PDAs augmented with counters - and their unambiguous restrictions. We consider several variations - based on whether the bound holds exactly or as an upper-bound and show decidability as well as undecidability results. In the case of decidable problems, we also attempt to determine more precisely the complexity class to which the problem belongs.
Temperature fluctuations in an inhomogeneous diffusive fluid
Authors: Haba Z.
Published: February 2015

We discuss metric perturbations of the relativistic diffusion equation around the homogeneous Jüttner equilibrium of massless particles in a homogenous expanding universe. We describe the perturbations corresponding to the gravitational wave background. We show that the lowest order perturbation can be treated as a variation of temperature. We derive a formula expressing temperature fluctuations in terms of the diffusion and tensor power spectrum. We discuss the multipole expansion of the fluctuations in the presence of diffusion.
Some properties of graded 2-prime submodules
Authors: Al-Zoubi Khaldoun
Published: February 2015

Let G be a group with identity e. Let R be a G-graded commutative ring and M a graded R-module. In this paper, we introduce the concept of graded 2-prime submodule and we give a number of results concerning such modules. Also, we introduce and prove the graded 2-prime avoidance theorem for graded modules.
Lie triple derivations on primitive rings
Authors: Ebrahimi Sepideh
Published: February 2015

In this paper, we show that for each Lie triple derivation L on primitive ring R of characteristic not 2 with nontrivial idempotent, there exists an ordinary derivation D of R into a primitive ring [Formula: see text] containing R and additive mapping λ of R into the center of [Formula: see text] that annihilates commutators such that L(X) = D(X) + λ(X).
(m, p)-isometric and (m, ∞)-isometric operator tuples on normed spaces
Authors: Hoffmann Philipp H. W. , Mackey Michael
Published: February 2015

We generalize the notion of m-isometric operator tuples on Hilbert spaces in a natural way to operator tuples on normed spaces. This is done by defining a tuple analogue of (m, p)-isometric operators, so-called (m, p)-isometric operator tuples. We then extend this definition further by introducing (m, ∞)-isometric operator tuples and study properties of and relations between these objects.