bluuebunny/crossref_metadata_2025 huggingface dataset:
Aerodynamic Design and Testing of an Axial Flow Compressor With Pressure Ratio of 23.3:1 for the LM2500+ Gas Turbine
Authors: Wadia A. R. , Wolf D. P. , Haaser F. G.
Published: December 2014

The LM2500+ gas turbine, rated between 39,000 to 40,200 shaft horsepower (shp), was introduced for field service in 1998. This growth aero-derivative gas turbine is suitable for a variety of power generation applications, such as co-generation and combined cycle, as well as mechanical drive applications. At the heart of the LM2500+ 25% power increase is an up-rated derivative 17-stage axial compressor. This paper describes the aerodynamic design and development of this high pressure ratio single spool compressor for the LM2500+ gas turbine. The compressor is derived by zero-staging the highly efficient and reliable LM2500 compressor to increase the flow by 23% at a pressure ratio of 23.3:1. The aerodynamic efficiency of the compressor is further improved by using three-dimensional, custom-tailored airfoil designs similar to those used in the CF6-80C2 high pressure compressor. The compressor achieved a peak polytropic efficiency above 91 percent, meeting all its operability objectives. The technical requirements and overall aerodynamic design features of the compressor are presented first. Next, the zero stage match point selection is described and the procedure used to set up the vector diagrams using a through-flow code with secondary flow and mixing is outlined. Detailed design results for the new transonic airfoils in the compressor using three-dimensional viscous analysis are presented. The compressor instrumentation and performance test results are discussed. The performance of the zero stage is separated from that of the baseline compressor with the CF6-80C2 airfoils to show the improvement in efficiency with the new airfoils.
The Secondary Flow Field of a Turbine Cascade With 3D Airfoil Design and Endwall Contouring at Off-Design Incidence
Authors: Duden Arno , Fottner Leonhard
Published: December 2014

A highly loaded turbine cascade with prismatic airfoils and straight endwalls was redesigned with the objective of reducing the secondary flow by applying end wall contouring and 3D airfoil design in the endwall regions. When tested at design conditions the flow field showed distinct improvements. The radial extent of the secondary flows was reduced and a decrease in secondary losses was observed (Duden et al., 1998). As an extension of this investigation, the effects of positive and negative incidence on the performance of the redesigned cascade have been evaluated and compared to the original cascade. The investigations were carried out in a high speed cascade wind tunnel. At negative incidence the redesigned cascade was observed to reduce the radial variation of the circumferential exit flow angle but to increase the magnitude of the secondary losses. At positive incidence, in comparison to the flowfield in the reference cascade, the radial extent of the secondary flows and the magnitude of the secondary losses were greatly reduced. The benefits provided by the 3D airfoil design and endwall contouring were even more obvious at positive incidence than at the design conditions.
Low-Speed Annular Cascade Tests of an Ultra-Highly Loaded Turbine With Tip Clearance: Part 1 — Near Design Incidence
Authors: Yamamoto A. , Outa E.
Published: December 2014

Annular cascade tests were carried out to study the performance of an ultra-highly loaded turbine cascade (UHLTC) with a design turning angle of 160 deg. The UHLTC is for applications to future high-temperature gas turbine engines. This paper describes details of the secondary flows and the associated total pressure losses of the UHLTC obtained at a test incidence of −2.7 deg. The cascade flows were measured with a small five-hole Pitot probe located at 21 traverse measurement planes upstream, inside and downstream of the UHLTC. From the measurements, detailed flow structures and the loss evolution process were analyzed. Flow visualization tests were also carried out to see more details of the flows on the blade surfaces, on the endwalls and in the blade tip gap. Various flow separations and various small vortices associated with the passage and leakage vortices, such as corner vortices and edge vortices, separation bubbles, and the associated reverse flows, were seen. These were clarified from various flow lines showing separation, attachment/reattachment and division of each flow. The results obtained from the flow visualization were compared with those from the traverse measurements. Large total pressure losses occur inside the cascade passage as well as downstream of the cascade. Various strong passage vortices, strong leakage vortex, strong swirling flows upstream and downstream of the cascade and their associated various flow separations, are the main causes of the loss generation. The coefficient of total pressure loss generated inside the cascade was 0.28 at the test near-design incidence. The actual turning angle of the flow from the cascade inlet and the cascade outlet was 146 deg. Some schematic drawings of the flow structures in the present UHLTC were also given. The basic flow structures did not differ significantly from those seen in the conventional cascades with much smaller turning angles, except for stronger passage vortices, larger internal loss and larger downstream mixing loss due to the very high turning angle of the UHLTC.
On the Development of Oxygen Scavenger Additives for Future Jet Fuels
Authors: Beaver B. , Sharief V. , Teng Y. , DeMunshi R. , Guo J. P. , Katondo E.
Published: December 2014

The need for the development of jet fuels that are oxidatively and thermally stable to 480°C (900°F) has been previously detailed (Edwards and Liberio, 1996). Such a fuel is commonly referred to as JP-900. It is our belief that a new class of additives can be developed which, when added to JP-8, will provide both the oxidative and thermal stability requirements of JP-900.

Our most recent data is presented which explores the potential of 1,2,5-trimethylpyrrole (TMP) as a potential oxygen scavenger.
Deposit Formation and Mitigation in Aircraft Fuels
Authors: Spadaccini Louis J. , Sobel David R. , Huang He
Published: December 2014

The development of a viable strategy for limiting coke deposition involves combining synergistic approaches for suppressing deposit buildup and reducing its impact on performance. Candidate approaches, including selection of favorable operating conditions (viz., pressure, temperature, heat flux, residence time and passage size) and coke-tolerant heat exchanger designs, were investigated to evaluate their effectiveness and provide a basis for combining them into a single design philosophy. These approaches were evaluated through testing of current jet fuels in single-tubes and segments of heat exchanger configurations at temperatures up to 1000 F, pressures up to 1200 psi and liquid hourly space velocities up to 40,000/h.

A key result of this work is the ranking of the importance of heat exchanger operating conditions on carbon deposition, with fuel temperature and those parameters that control species diffusion having the most pronounced impact. Residence time and pressure are of lesser importance. Alternative coke-tolerant heat exchanger designs featuring inter-channel communication were evaluated and ranked, with several of these concepts demonstrating improvement over continuous passages.
Scales of Turbulence During Boundary Layer Transition Under Steady and Unsteady Flow Conditions
Authors: Chakka P. , Schobeiri M. T.
Published: December 2014

Boundary layer hot-wire measurements are analyzed for scales of turbulence during transition. Experimental data from two test sections (one consisting of a curved plate and the other consisting of five blades in a turbine cascade) are used in the current analysis. Unsteady wake flow conditions are simulated using circular rods upstream of the test section and the boundary layer measurements are taken for different wake passing frequencies. Recent developments in wavelet analysis are used to quantify the energy corresponding to different scales of turbulence in the signal. Also, dominant scales having the maximum energy content in the velocity signal are extracted to get the macroscopic picture during boundary layer transition. A continuous increase in scale activity during transition is seen for the steady flow data, whereas for unsteady flow cases the energy is dominant for higher frequencies as the wake passing frequency increases. This scale information is essential for improving transition models and validating CFD codes.
USN Land Based Testing of the WR21 ICR Gas Turbine
Authors: Parry Robin W. , House Edward , Stauffer Matthew , Iacovelli Michael , Higgins William J.
Published: December 2014

Development of the Northrop Grumman / Rolls-Royce WR21 Intercooled Recuperated (ICR) Gas Turbine, begun in 1992, is now well advanced and system testing has been completed on eight engine builds at the Royal Navy’s Admiralty Test House located at the Defence Evaluation and Research Agency, Pyestock in the United Kingdom. Test activity is shortly to move to the US Navy’s Test Site at the Naval Surface Warfare Center, Carderock Division – Ship Systems Engineering Station in Philadelphia, PA, where a new test facility has been built to carry out some final development testing and an endurance test. A previous paper on this subject (94-GT-186) defined a test program leading to a design review and the beginning of Qualification Testing.

The development program has since evolved and it is the aim of this paper to summarize engine testing to date and set out the plan for conclusion of development testing. The paper will describe the development of the Philadelphia Test Site, as a combined site for the US Navy’s Integrated Power System (IPS) and ICR testing. This will include a description of the advanced, high-accuracy Data Acquisition System (DAS). Finally, the test program and the development and endurance test objectives will be outlined.
Application of Perturbation Methodology and Directional Filtering for Early Rotor Crack Detection
Authors: Goldman Paul , Muszynska Agnes , Bently Donald E. , Dayton Kenwood P. , Garcin Mauro
Published: December 2014

This paper documents analytical and experimental research of the lateral and torsional responses of a cracked rotor to different types of excitation. The experimental research has been performed on a rotor rig, which emulate a turbogenerator. It includes driving motor coupled to the main rotor, a lateral nonsynchronous perturbation device, and a generator with an electrical field consisting of a constant component (constant torsional load) and a sinusoidal component, provided by a signal generator. The generator was used as a torsional nonsynchronous perturbation device. The midspan of the rotor was modified so that a section could be changed starting with a circular cross-section (undamaged rotor) to the cross-section with transverse crack. The lateral and torsional responses have been measured at two axial locations. The obtained lateral data was processed using directional filtering into forward and reverse components of the corresponding filtered elliptical orbits. The forward component of the lateral response to nonsynchronous perturbation allows to identify overall stiffness reduction and rotating stiffness asymmetry introduced by the change in midspan rotor cross-section, while the reverse component largly depends on the support asymmetry. The nonsynchronous torsional excitation allows identify of the system torsional dynamic stiffness and it’s reduction due to the crack. The ratio of the filtered to 1× or to the perturbation frequency rotor responses at two axial locations was considered as an indicator of a lateral mode shape change due to the crack. The experimental results are compared with the analytical model of the rotor response, which was obtained by the application of a perturbation method of small parameter to the system of nonlinear equations. The equations describe the rotor system with four lateral (two displacements and two inclination angles) and two torsional degrees of freedom.
Development of a Three-Staged Low Emissions Combustor for Industrial Small-Size Gas Turbines
Authors: Sato Hiroshi , Amano Toshiji , Iiyama Yoshihiro , Mori Masaaki , Nakamura Tsuneaki
Published: December 2014

This paper describes the development of an ultra-low emission single-can combustor applicable to 200 kW to 3 MW size natural gas-driven gas turbines for cogeneration systems. The combustor, called a three-staged combustor, was designed by applying the theory of lean premixed staged combustion. The combustor comprises two sets of premixing injector tubes located around the combustor liner downstream of the premixing nozzle equipped with a pilot diffusion nozzle in the center. The combustor controls engine output solely by varying the fuel gas flow without the need for complex variable geometry, such as inlet guide vanes, for combustion airflow control. Reliability, response to load variation and retrofit capability have been greatly improved along with wide low-emission operating range. As the result of the atmospheric rig tests, the three-staged combustor has demonstrated superior performance of 3.5 ppm NOx (O2 = 15%) and 7 ppm CO (O2 = 15%) at full load. Assuming the relationship between NOx emission and pressure and taking into account sequential CO oxidation occurring in the scroll, the performance of the combustor at engine operation is expected to be less than 9 ppm NOx (O2 = 15%) and 50 ppm CO (O2 = 15%) emissions between 25% and 100% engine load. During the development, temperature distribution in the atmospheric combustion was measured in detail to gain comprehensive understanding of the low emissions combustion phenomena. The results of the measurement were compared with the theory of lean premixed staged combustion. Employing the concept of effective mixing ratio, the theory of lean premixed staged combustion has proved to be a powerful method to design a lean premixed staged combustor.
Compressor Exit Conditions and Their Impact on Flame Tube Fuel Injector Flows
Authors: Barker A. G. , Carrotte J. F.
Published: December 2014

Within a gas turbine engine the flow field issuing from the compression system is non-uniform containing, for example, circumferential and radial variations in the flow field due to wakes from the upstream compressor outlet guide vanes (OGVs). In addition, variations can arise due to the presence of radial load bearing struts within the pre-diffuser. This paper is concerned with the characterisation of this non-uniform flow field, prior to the combustion system, and the subsequent effect on the flame tube fuel injector flows and hence combustion processes.

A mainly experimental investigation has been undertaken using a fully annular test facility which incorporates a single stage axial flow compressor, diffuser and flame tube. Measurements have been made of the flow field, and its frequency content, within the dump cavity. Furthermore, the stagnation pressure presented to the core, outer and dome swirler passages of a fuel injector has been obtained for different circumferential positions of the upstream OGV/pre-diffuser assembly. These pressure variations, amounting to as much as 20% of the pressure drop across the fuel injector, also affect the flow field immediately downstream of the injector. In addition, general variations in pressure around the fuel injector have also been observed due to, for example, the fuel injector position relative to pre-diffuser exit and the flame tube cowl.
Ingress Determination by Means of Laser Light Scattering Inside a Rotor-Stator System
Authors: Geis T. , Wiebelt A. , Kim S. , Wittig S.
Published: December 2014

A new method based on laser light scattering was developed to detect a radial inflow of gas inside a rotating-disk system. Ambient air was seeded with small particles that followed the flow. Once entering the wheel space between rotor and stator, these particles crossed a laserbeam emitted by an At+-Laser. The scattered light was detected by a photomultiplier whose electrical output signal was finally processed in a data acquisition system. The signal intensity thereby indicated the strength of ingress.

The measuring technique was adapted to a shrouded rotor-stator system in a quiescent environment and an experimental investigation was conducted to determine the minimum cooling flow rate necessary to just prevent ingress (Cw,min) for several seal clearance ratios and two different rotor disk geometries. The results were correlated to the disk rotational Reynolds number and compared with data yielded by applying a pressure criterion. With the rotating disk being 0.5m in diameter and spinning at max. 10000rpm, rotational Reynolds numbers up to 3.8×106 were achieved. The results show an expected behaviour for the seal clearance variation and an unexpected behaviour for the two disk geometries. Compared to the new technique, the pressure criterion underestimates the minimum purge flow. Additional experiments were conducted for a single seal configuration to demonstrate the new method’s capability to acquire the sealing effectiveness. The results are intriguing but also show that further investigations must be conducted to establish this new technique.
3-D Numerical Simulation of Impinging Jet Cooling With Initial Crossflow
Authors: Haiping Chang , Wanbing Chen , Taiping Huang
Published: December 2014

In modern high performance gas turbine aeroengines, the cooling of the turbine guide vane and/or blade is very important for the reliability of the component. The impinging jet with initial crossflow is one of the effectual ways for cooling the airfoils of the midchord region of the turbine guide vane and/or blade. For improving the cooling efficiency and analyzing the thermal stresses in these components, it is necessary to know the flow field and the temperature distribution. The three dimensional numerical analyses for the flow field and temperature distribution of the impinging jet cooling with initial crossflow have been presented in this paper. In this study, the non-staggered grid is used and the undulate pressure field can also be avoided. By comparing the different turbulence models, the low Reynolds number k-ε turbulence model developed by K. Abe and T. Kondoh is employed. The flow field of impinging jet with initial crossflow is very much complicated. By the numerical analysis, the form of the twin vortices, the effect of the jet-to-crossflow mass flux ratio on the heat transfer characteristics have been observed.
Influence of Internal Flow on Film Cooling Effectiveness
Authors: Wilfert Günter , Wolff Stefan
Published: December 2014

Film cooling experiments were conducted to investigate the effects of internal flow conditions and plenum geometry on the film cooling effectiveness. The film cooling measurements show a strong influence of the coolant inlet conditions on film cooling performance. The present experiments were carried out on a flat plate with a row of cylindrical holes oriented at 30 degrees with respect to a constant-velocity external flow, systematically varying the plenum geometry and blowing rates (0.5≤M≤1.25). Adiabatic film cooling measurements using the multiple narrow-banded Thermochromic Liquid Crystal-technique (TLC) were carried out simulating a flow parallel to the main stream flow with and without cross flow at the coolant hole entry compared with a standard plenum configuration. An impingement in front of the cooling hole entry with and without cross flow was also investigated. For all parallel flow configurations ribs were installed at the top and bottom coolant channel wall. As the hole length-to-diameter ratio has an influence on the film cooling effectiveness, the wall thickness has also been varied. In order to optimise the benefit of the geometry effects with ribs, a vortex generator was designed and tested.

Results from these experiments show in a region 5≤X/D≤80 downstream of the coolant injection location differences in adiabatic film cooling effectiveness between +5% and +65% compared with a standard plenum configuration.
Transonic Aerodynamic Losses due to Turbine Airfoil, Suction Surface Film Cooling
Authors: Jackson D. J. , Lee K. L. , Ligrani P. M. , Johnson P. D. , Soechting F. O.
Published: December 2014

The effects of suction surface film cooling on aerodynamic losses are investigated using an experimental apparatus designed especially for this purpose. A symmetric airfoil with the same transonic Mach number distribution on both sides is employed. Mach numbers along the airfoil surface range from 0.4 to 1.24 and match values on the suction surface of airfoils from operating aeroengines. Film cooling holes are located on one side of the airfoil near the passage throat where the freestream Mach number is nominally 1.07. Round cylindrical, and conical diffused film cooling hole configurations are investigated with density ratios from 0.8 to 1.3 over a range of blowing ratios, momentum flux ratios, and Mach number ratios. Also included are discharge coefficients, local and integrated total pressure losses, downstream kinetic energy distributions, Mach number profiles, and n correlation for integral aerodynamic losses as they depend upon film cooling parameters. The contributions of mixing and shock waves to total pressure losses are separated and quantified. These results show that losses due to shock waves vary with blowing ratio as shock wave strength changes. Aerodynamic loss magnitudes due to mixing vary significantly with film cooling hole geometry, blowing ratio, Mach number ratio, and (in some situations) density ratio. Integrated mixing losses from round cylindrical boles are three times higher than from conical diffused holes, when compared at the same blowing ratio. Such differences depend upon mixing losses just downstream of the airfoil as well as turbulent diffusion of streamwise momentum normal to the airfoil symmetry plane.
NOX as a Function of Fuel Type: C1-to-C16 Hydrocarbons and Methanol
Authors: Lee John C. Y. , Malte Philip C. , Nicol David G.
Published: December 2014

The response of NOX to fuel type is determined for lean-prevaporized-premixed combustion in on atmospheric pressure jet-stirred reactor (JSR). Pure, straight chain, alkane fuels from C1 (methane) to C16 (hexadecane) and methanol are tested. Testing is conducted under three conditions, each of which is obtained using a particular inlet-jet nozzle for the JSR. For a selected condition, the fuels are burned under nearly identical macroscopic thermal and fluid mechanical fields in the JSR. A constant mixture inlet total temperature is used that provides for complete vaporization of all of the fuels tested without causing pre-flame reactions in the premixer. Two of the nozzles used have single, centered jets and provide a nominal combustion temperature of 1790 K. The third nozzle has eight diverging jets. In this case, the fuel-air equivalence ratio is increased, providing a nominal combustion temperature of 1850 K.

Lowest levels of NOX are measured when methanol is burned. Upon switching to methane, the NOX concentration increases by 62±10%. For the alkane fuels, methane combustion yields the least amount of NOX. Upon switching from methane to ethane, the NOX increases by 22±2%. Further increases in the size of the alkane fuel molecule (from C2 to C16) show small increases (8±5%) in the NOX concentration. Although the JSR-condition selected affects the absolute NOX concentration, the trends in NOX concentration with respect to fuel-type are the same for the three conditions used.

The JSR is modeled as a single perfectly stirred reactor (PSR) operating at the experimental residence time and combustion temperature. This modeling shows that the increase in the NOX measured for the alkane fuels may be explained in terms of the increase in O-atom concentration with increasing C/H ratio. In order to explore the effect of Fenimore prompt NOX, a two-PSRs-in-series model is used. The first PSR is assigned a residence time equal to 5% the total residence time of the reactor. The second PSR accounts for the remaining 95% of the reactor residence time. Because of its short lifetime, the CH radical is effectively restricted to the first PSR, and prompt NOX mainly forms in this zone. Mechanisms directly dependent on the O-atom form NOX throughout the reactor. The modeling suggests that prompt NOX is responsible for the greater concentration of NOX found in the methane combustion compared to the methanol combustion.
Large-Eddy Simulation of Combustion Oscillation in Premixed Combustor
Authors: Murota Tomoya , Ohtsuka Masaya
Published: December 2014

To analyze combustion oscillation in the premixed combustor, a large-eddy simulation program for premixed combustion flow was developed. The subgrid scale (SGS) model of eddy viscosity type for compressible turbulence (Speziale et al., 1988) was adopted to treat the SGS fluxes. The fractal flamelet model, which utilizes the fractal properties of the turbulent premixed flame to obtain the reaction rate, was developed.

Premixed combustion without oscillation was analyzed to verify the present method. The computational results showed good accordance with experimental data (Rydén et al., 1993).

The combustion oscillation of an “established buzz” type in the premixed combustor (Langhorne, 1988) was also analyzed. The present method succeeded in capturing the oscillation accurately. The detailed mechanism was investigated. The appearance of the non-heat release region, which is generated because the supply of the unburnt gas into the combustion zone stagnates, and its disappearance play an important role.
The Calculation of Thermodynamic Non Equilibrium Combustion Product Compositions
Authors: Hurley C. D. , Whiteman M. , Wilson C. W.
Published: December 2014

A method is presented by which the product composition and temperature of constant pressure combustion reactions can be calculated for non equilibrium conditions, by constraining the products free energy and entropy. The calculations for a hydrogen/ oxygen system are compared with chemical kinetic predictions. From the calculated compositions the relationship between free energy and extent of reaction are derived and thence how the individual product mole fractions vary with extent of reaction. The application of these techniques to modelling combustion chemistry is discussed.
A Theoretical Tool to Predict the Effects of Chemical Kinetics on Sound Propagation Within High Temperature Hydrocarbon Combustion Products
Authors: Haque Zakirul , Barton John P.
Published: December 2014

This paper involves a theoretical analysis of the propagation of sound within chemically reacting hydrocarbon combustion products. A new procedure for determining the sound speed and absorption coefficient was developed. Using a similar approach can do analyses for other chemically reacting gas mixture. One-dimensional sound propagation was assumed. Molecular diffusion effects, such as viscous stress, heat conduction, and mass diffusion were appropriately neglected along with possible effects due to vibrational non-equilibrium. In this way only the effects of chemical reactions on sound propagation was considered. The expressions for sound speed and absorption coefficient were derived as a function of frequency.
Fast Response Extraction Probe for Measurement of Air-Fuel Ratio Fluctuations in Lean Premixed Combustors
Authors: Mongia Rajiv , Torres John , Dibble Robert , Lee Darren , Anderson Torger , Sowa William
Published: December 2014

The extent of air and fuel mixing prior to combustion in lean premixed combustion has been shown to drastically affect combustor performance, both in terms of emissions and stability. Standard extraction probes are often used for measuring the spatial (average over time) distribution of fuel concentration. However, the temporal fluctuations in fuel mole fraction, which are averaged by conventional extraction probes, have been also shown to drastically affect combustor performance. Several methods have been developed to measure the fluctuations in fuel mole fraction both temporally and spatially. These techniques are often difficult or impossible to apply to an operating combustor at high pressures and temperatures.

In this paper, we describe a Fast Response Extraction Probe (FREP) which is capable of measuring temporal mole fraction fluctuations up to frequencies of 1 kHz. A short, capillary tube is inserted into the premixing passage (which is at high pressure) for sampling the flow. The capillary tube is connected to a small gas cell at atmospheric pressure. Light from a 3.39 μm He-Ne laser is passed through the gas cell. By measuring the absorption of laser light, the concentration of hydrocarbons can be determined. The temporal response of the system is dependent on the geometry of the gas cell and sampling tube and the pressure drop through the sampling tube. A model for predicting the time response of the FREP is presented and compared to a laboratory scale experiment. The FREP was also tested in a high-pressure combustion rig at United Technologies Research Center. It is shown that the FREP is capable of measuring fuel-air fluctuations at gas turbine conditions. It is also shown that, at the conditions studied, there is a relationship between pressure oscillations and fuel mole fraction oscillations.
An Experimental Investigation on the Aerodynamic Performance and Flowfield Structure of a Film-Cooled Turbine Cascade
Authors: Fu Chen , Hong Yang
Published: December 2014

Experiments have been performed to study the aerodynamic performance and internal flows in a linear turbine cascade with air injection from various locations of the blade surface. Data were obtained by using pneumatic probe, static pressure taps and surface flow visualization techniques. The experimental results showed that the suction side injection would affect the development of the passage vortex significantly. The passage vortex was strengthened and pushed away from the injection surface, a triangular-shaped region uncovered by the injected air always existed on the suction surface due to the existence of the passage vortex. The passage vortex was weakened with air injection from pressure surface, which would cause a smaller amount of low momentum fluids to migrate into the comer region between suction surface and end wall. Although the scale and intensity of kidney-shaped vortices were different when air was injected from various positions, these vortices might always exist near the blade surface, mixing with mainflow in the flow passage and with wakes at the cascade exit while they moved downstream. The energy loss increased near the blade surface from which air was injected due mainly to the mixing process between mainflow and injected air, and to the formation of kidney-shaped vortices. In contrast to the pressure side injection, the changes of blade surface pressure distribution were more sensitive to the amount of injected air and the locations of injection holes for the suction side injection. In the great majority of cases, the surface pressure decreases owing to the existence of low-pressure zone downstream of the injection holes were more significant than the pressure increases caused by mainflow stagnation upstream of the holes.
Detailed Experimental Studies of Flow in Large Scale Brush Seal Model and a Comparison With CFD Predictions
Authors: Chen L. H. , Wood P. E. , Jones T. V. , Chew J. W.
Published: December 2014

A five times scale model of an engine brush seal has been manufactured. The bristle stiffness and pressure were chosen to satisfy close similarity of the relevant non-dimensional parameters, and the choice of parameters is described. The comparison of flow characteristics for the model seal and an engine seal confirmed the non-dimensional similarity.

Detailed pressure measurements were performed within the bristle pack by employing hollow bristles. This novel measurement allowed insight to be obtained into the operation of both clearance and interference seals. In particular, the measured pressure variation in the region of the bristle tips was significant. The deflection of the bristles was determined by comparing the bristle tip pressures with the static pressures along the shaft. Hence the compaction of the pack in this region was found directly.

A numerical modelling of brush seals employing anisotropic flow resistance has been developed. Predictions were compared with the measured pressure distributions within the pack. This enabled sensible selection of the pack resistance distribution to be made. Although uniform anisotropic resistance throughout the pack gave reasonable flow rate characteristics, the pressure distribution was not reproduced. A variation of resistance coefficient consistent with the observed compaction was required to give a solution comparable with the experiments.
Accelerated High Temperature Performance Evaluation of Superalloys for Process Optimization and Remaining Life Assessment
Authors: Woodford David A.
Published: December 2014

Creep strength and fracture resistance are two properties that are critical in the selection and optimization of high temperature materials. These same properties may be progressively impaired by service exposure and are, therefore, key to the assessment of remaining life of high temperature components. In recent years, a methodology based on accelerated measurements of these properties has been developed. The two critical properties are decoupled in this approach which allows a clearer separation of the effects of microstructural evolution, damage development and environmental attack. The evaluation of creep strength is illustrated using extensive data on conventionally cast (IN738), directionally solidified (GTD111) and monocrystalline (CMSX-4) superalloys. It is shown that the properly defined creep strength is not sensitive to section size for any of the alloy classes. The well known effect of section size on rupture life of conventionally cast alloys is thus an effect on fracture resistance rather than creep strength. The comparisons with long term creep rupture test data show good agreement in all cases indicating that the accelerated testing is quite capable of yielding both comparative and design data. With the added advantage of a separate fracture resistance criterion the new methodology should be broadly useful.
Stress Relaxation Testing as a Basis for Creep Analysis and Design of Silicon Nitride
Authors: Woodford David A. , Wereszczak Andrew A. , Bakker Wate T.
Published: December 2014

A new approach to tensile creep testing and analysis based on stress relaxation is described for sintered silicon nitride. Creep rate data covering up to five orders of magnitude were generated in tests lasting less than one day. Tests from various initial stresses at temperatures from 1250C to 1350C were analyzed and compared with creep rates measured during conventional constant load testing. It was shown that at least 40% of the creep strain accumulated under all test conditions was recoverable, and that the deformation could properly be described as viscoelastic/plastic. Tests were conducted to establish the level of repeatability and the effects of various thermomechanical histories. It was shown that none of the prior exposures led to significant impairment in creep strength. The results were used for three different grades to establish the value of the accelerated test to compare creep strengths for acceptance and for optimization. Several useful correlations were obtained between stress and creep rate. The systematic creep rate dependence as a function of loading strain prior to relaxation provided a possible basis for design in terms of a secant modulus analysis.
The Use of Bio-Fuels as Additives and Extenders for Aviation Turbine Fuels
Authors: Kimble-Thom Melanie A. , Stanley David L. , Cholis John T. , Lopp Denver W.
Published: December 2014

The use of biologically derived oils and fuels has received increasing visibility in recent years. A combination of fuel availability, refinery capacity and environmental responsibility has resulted in interest in their use in turbine engine fuels.

Such a soy methyl ester (SME) is being evaluated as a possible extender and/or additive for aviation turbine fuel per ASTM D-1655. Laboratory testing indicates additive levels of up to 2% by volume can be used while still meeting ASTM D-1655. Engine testing performed at 20% blending levels have demonstrated potential fuel consumption improvements as well as reduction in NOx emissions. The final blend levels have not yet been determined.

The use of SME even at low levels could provided performance benefits. Because of the oil nature of SME, a small addition could result in significant increases in lubricity. The use of the higher flashpoint SME could result in an upward shift in flashpoint with little or no effect to other physical properties. With increased visibility to work place considerations, the potential for “odor” abatement is also of interest.
Field Test of a 1.5 MW Industrial Gas Turbine With a Low Emissions Catalytic Combustion System
Authors: Dalla Betta Ralph A. , Nickolas Sarento G. , Weakley Chris K. , Lundberg Kare , Caron Tim J. , Chamberlain John , Greeb Kevin
Published: December 2014

Combustor hardware employing catalytic combustion technology has been developed for a 1.5 MW gas turbine. This system, combined with state of the art catalyst technology, was used to demonstrate ultra-low emissions on the engine. The demonstrator combustor utilizes a two stage lean premix preburner system to obtain the required catalyst inlet temperatures and low NOx over the operating load range. The performance of the preburner system was characterized during engine tests by measuring temperature rise and emissions just downstream of the preburner. A fuel schedule for the primary and secondary stages was selected to give NOx emissions below 2 ppmv at the engine exhaust. Overall engine performance was measured over the full load range. Emissions of NOx < 3 ppmv and CO and UHC < 5 ppmv were obtained at 72% to 100% load. Combustor dynamics were shown to be less than 0.3 psi(rms). This combustor operated for 1000 hours on a dynamometer test facility and showed low emissions performance over this period.
Test Validation of Flamelet Model Predictions of NOx
Authors: Buriko Yu. , Zakharov V. , Belokon A. , Opdyke G.
Published: December 2014

Calculations of NOx emissions were made for the original high pressure combustor and for the original and a modified design of the low pressure combustor used in a Compressed Air Energy Storage (CAES) plant. All were typical diffusion flame combustors. Since a CAES plant has an independent air supply, the relationship between combustor inlet temperature and pressure is not typical for gas turbines, and the pressure level for the HP combustor is unusually high (up to 4.5 MPa). Vitiated air from HP combustor exhaust is used as combustion air in the LP combustor. The NOx emissions prediction method, which was used, for calculations is based on a flamelet model which takes detailed kinetic schemes for fuel oxidation, NOx generation and turbulence/chemistry interaction into account. Site measurements over the entire load curve confirmed the numerical predictions for both the original combustors and the newly developed LP combustor design.
Simultaneous Optical Measurements of Axial and Tangential Steady-State Blade Deflections
Authors: Kurkov Anatole P. , Dhadwal Harbans S.
Published: December 2014

Currently, the majority of fiber-optic blade instrumentation is being designed and manufactured by aircraft-engine companies for their own use. The most commonly employed probe for optical blade deflection measurements is the spot probe. One of its characteristics is that the incident spot on a blade is not fixed relative to the blade, but changes depending on the blade deformation associated with centrifugal and aerodynamic loading. While there are geometrically more complicated optical probe designs in use by different engine companies, this paper offers an alternate solution derived from a probe-mount design feature that allows one to change the probe axial position until the incident spot contacts either a leading or a trailing edge. By tracing the axial position of either blade edge one is essentially extending the deflection measurement to two dimensions, axial and tangential. The blade deflection measurements were obtained during a wind tunnel test of a fan prototype.
Temperature Measurements in a Heavy Duty Gas Turbine Using Radiation Thermometry Technique: Error Evaluation
Authors: De Lucia M. , De Sabato R. , Nava P. , Cioncolini S.
Published: December 2014

This paper describes a technique for the analysis of temperature measurement data obtained by using a radiation thermometer in a heavy duty gas turbine (PGT2 from Nuovo Pignone GE). The main sources of error are shown and analyzed and their influence on measurements and techniques used to correct data read. Success in significant error elimination in acquisition results in a more realistic and correct description of target temperature distribution.
A Study on Fusion Repair Process for a Precipitation Hardened IN738 Ni-Based Superalloy
Authors: Kim Dae-Young , Hwang Jong-Hyun , Kim Kwang-Soo , Youn Joong-Geun
Published: December 2014

Several fusion repair processes such as laser cladding, laser welding and gas tungsten arc welding have been taken into consideration for repairing IN738 precipitation hardened Ni-based superalloy material. Effect of heat input on weld cracking susceptibility has been studied to obtain optimum condition for crack free welds. Variations in cracking susceptibility as a function of welding heat input is discussed with reference to metallurgical characteristics of the welds.
U. S. Navy Marine Gas Turbine Qualification Testing for the 21st Century
Authors: Groghan Dan A. , Hartranft John J.
Published: December 2014

Two primary topics are addressed in this paper:

1. A brief record of the evolution of U. S. Navy (USN) gas turbine qualification and testing requirements that helped produce the successful engines now in service and

2. Examination of these requirements in light of current and projected defense budgets resulting from changes in the world over the past twenty-five years.

The paper proposes changes in the current methods the USN employs in qualifying its gas turbines for surface ship applications. The proposed alternate methods consider commercial testing and service experience as well as testing based on MIL-E-17341 requirements. Finally, the marine gas turbine community is invited to begin a dialogue on the feasibility of these alternate methods.
A Case Study of Mixed Gas-Steam Cycle GT: LM6000 Class Aeroderivative Gas Turbine
Authors: Hanawa Kirk
Published: December 2014

Many ideas were proposed to aim the generation thermal efficiency up to 60%, such as “Steam-Cooled H-Tech. Combined Cycle”, “Methanol Conversion Regenerative Gas Turbine”, “Kalina Cycle” etc.

The target thermal efficiency of 60% based upon LHV, could be also attained, when applying mixed gas-steam cycle like ISTIG and/or GAS3D for advanced aeroderivative gas turbines, which comprise of multiple shafts with overall pressure ratio more than 50, and TIT more than 2600 F (1700 K).

It might be meaningful to evaluate existing aeroderivative gas turbines like LM6000 etc. by applying such a improving concept, as the more advanced gas turbines to be derived from GE90, PW4000, and Trent800 are not available to date for land applications.

The intercooled ICAD GT of 77 MW was adopted as a base engine, and it was derived that the water /steam-injected WI/GAS3D GT version could produce 106 MW with 56% thermal efficiency, and it must be emphasized that the power curve in variation with ambient temperature is very flat than conventional GT plants.
Heat Transfer Over Non-Porous and Porous Smooth End Wall of a Linear Guide Vane in the Presence of Freestream Turbulence
Authors: Khalatov Artem A. , Shevtsov Sergey V. , Syred Nick
Published: December 2014

The end wall of a gas turbine guide vane is one of turbine components where cooling is extremely complex due to a three-dimensional fluid flow and heat transfer nature. Most existing end wall heat transfer data were obtained over a non-porous surface with no effect of freestream turbulence. In real situations the typical turbulence level in front of a guide vane varies widely and reaches 25–30 % in some modern gas turbine engines. No doubt, this factor should be taken into account in the design of end wall cooling systems.

New experimental results are presented in this paper describing the effect of freestream turbulence on local heat transfer over non-porous and porous smooth end walls of the same configuration. A linear scaled-up model of a real gas turbine guide vane was employed in the experimental programme. Decay of the axial freestream turbulence in a space between adjacent blades was measured and two simplified versions of the experimental correction functions describing the effect of freestream turbulence on local end wall heat transfer were obtained. The derived correction functions include the axial component of freestream turbulence and should be envisaged as a first attempt to define quantitatively the effect of freestream turbulence over an end wall in different conditions. It was found that both correction functions are virtually identical and agree satisfactorily with the published experimental data, reflecting the effect of freestream turbulence over a flat plate. It confirms the approximately common character of freestream turbulence influence for different boundary conditions. It was concluded that further experimental studies of three-dimensional turbulent structure over an end wall for various boundary conditions are required to develop more exact correlations.
Computational Modeling and Thermal Paint Verification of Film-Cooling Designs for an Unshrouded High-Pressure Turbine Blade
Authors: Gegg Steven G. , Heidegger Nathan J. , Mikkelson Ronald A.
Published: December 2014

High pressure turbine blades are exposed to an extreme high temperature environment due to increasing turbine inlet temperature. High heat fluxes are likely on the blade pressure surface. Other regions, such as the trailing edge and blade tip may be difficult to cool uniformly. Unshrouded blades present an additional challenge due to the pressure driven transport of hot gas across the blade tip. The blade tip region is therefore prone to severe thermal stress, fatigue and oxidation. In order to develop effective cooling methods, designers require detailed flow and heat transfer information.

This paper reports on computational aerodynamics and heat transfer studies for an unshrouded high pressure turbine blade. The emphasis is placed on the application of appropriate 3-D models for the prediction of airfoil surface temperatures. Details of the film cooling model, boundary conditions and data exchange with heat transfer models are described. The analysis approach has been refined for design use to provide timely and accurate results. Film cooling designs are to be tailored for the best coverage of the blade tip region. Designs include near-tip pressure side films and blade tip cooling holes. Hole placement and angle are investigated to achieve the best coolant coverage on the blade tip. Analytical results are compared to a thermal paint test on engine hardware. In addition to film cooling strategies, other aerodynamic/heat transfer design approaches are discussed to address the cooling requirements for an unshrouded blade.