bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect on Combustor Diffuser Performance of Structural OGV/Pre-Diffuser Systems
Authors: Barker A. G. , Carrotte J. F. , Frodsham C. W.
Published: December 2014

An experimental investigation has been carried out to assess the aerodynamic effects of locating radial struts within the pre-diffuser of a modern combustor dump diffuser system. Engine representative inlet conditions were generated by a single stage rotor, with the diffuser system incorporating various compressor outlet guide vane (OGV)/pre-diffuser assemblies and an annular flame tube with representative porosity. Stagnation and static pressure measurements were obtained at numerous locations and included assessment of the upstream pressure field, associated with the struts, which impacts on the rotor and OGV aerodynamics. Measurements were also obtained within the feed annuli, surrounding the flame tube, with attempts also being made to assess the stagnation pressure distributions presented to a simulated flame tube burner. Initial tests were performed with an OGV row attached to a conventional 1.45 area ratio pre-diffuser, this providing the datum to which all other systems were assessed. These included systems with thin or thick struts with the strut blockage, at pre-diffuser exit, being 5% and 11% of the gas passage area respectively. For the geometries tested it was shown that the method of adjusting each pre-diffuser passage area, to account for the strut blockage, was successful in providing similar levels of reduced kinetic energy at pre-diffuser exit. Despite this, however, the presence of strut wakes and their effect on the dump cavity flow produced increases in stagnation pressure loss. These loss variations were evaluated for both the feed annuli and burner flows, with the magnitudes depending on whether the struts were aligned or midway between burners. Also assessed was the impact of the increased circumferential flow non-uniformity that was observed for the flow within the inner feed annulus. A beneficial effect produced by the struts was the significant reductions in flow swirl, within the diffuser system, relative to the datum. This improved axial alignment of the flow, provided a more uniform pressure distribution to the burners and a more stable feed to the various flame tube features.
CFD Modeling of Combustion Instability in Premixed Axisymmetric Combustors
Authors: Smith Clifford E. , Leonard Andy D.
Published: December 2014

Time-accurate CFD analysis is used to model combustion instability in a premixed axisymmetric combustor typical of industrial gas turbine engines. The experiment of Richards and Janus (1997) is modeled; the hardware consists of a fuel injector similar to industrial premix fuel nozzles, a water-cooled can combustor, an uncooled refractory plug that reduces flow area, and a long exhaust duct. The CFD calculation domain extends from the air swirler within the fuel nozzle to the exhaust duct exit. Two cases are modeled using 2D time-accurate axisymmetric CFD analysis: a low nozzle air velocity (u = 30 m/s) case that exhibits combustion instability and a high nozzle air velocity (u = 60 m/s) case that does not. The CFD analysis agrees well with the experimental measurements, including peak-to-peak pressure variation and instability frequency for the unstable case. For the unstable case, the airflow through the swirler actually flows upstream part of the time, and hot combustion products are forced into the premix annulus. The potential of using a time-accurate CFD approach for modeling combustion instability in complex 3D combustors is discussed.
A Comparison of the Influence of Fuel/Air Unmixedness on NOx Emissions in Lean Premixed, Non-Catalytic and Catalytically Stabilized Combustion
Authors: Schlegel A. , Streichsbier M. , Mongia R. , Dibble R.
Published: December 2014

Experimental results on the influence of temporal unmixedness on NOx emissions are presented for both non-catalytic and catalytically stabilized, lean premixed combustion. The test rig used for the experiments consists of a fuel/air mixing section which allows variation of the degree of temporal unmixedness while maintaining a uniform “average over time” concentration profile over the cross section at the inlet to the combustion chamber. The unmixedness is measured as “rms fluctuations in fuel concentration” by an optical probe using laser absorption at 3.39μm over a 9mm gap. “Average over time” measurements are taken with “conventional” suction probe analyzers. The combustion chamber is an insulated, tubular reactor (i.d. 26.4mm). At the inlet to the combustion chamber a honeycomb monolith section is inserted. This monolith is either catalytically active or inactive for catalytically stabilized or non-catalytic combustion respectively. For both modes, the exact same inlet conditions are applied. In catalytically stabilized combustion a fraction of the fuel is consumed within the catalyst and the remaining fuel is burnt in the subsequent homogeneous combustion zone.

It is shown that catalytically stabilized combustion yields lower NOx emissions and, more important, that the effect of temporal fuel/air unmixedness on NOx emissions is much smaller than with non-catalytic combustion under identical inlet conditions. Experimental evidence leads to the conclusion, that the catalyst is capable of reducing temporal fluctuations in fuel concentration and/or temperature in the combustion process, thereby preventing excess NOx formation. As a result, the requirements on mixing quality are less stringent when using catalytically stabilized combustion instead of conventional, non-catalytic combustion.
CFD Analysis of Liquid Spray Combustion in a Gas Turbine Combustor
Authors: Lai Mark K.
Published: December 2014

A numerical method is presented for predicting steady, three-dimensional, turbulent, liquid spray combusting flows in a gas turbine combustor. The Eulerian conservation equations for gas flow and the Lagrangian conservation equations for discrete fuel liquid droplets were solved. The trajectory computation of the fuel droplets provided the source terms for all the gas-phase equations. A standard k-ε submodel was used for turbulence. The combustion submodel used was a global local equilibrium model, where chemical species (CxHy, O2, CO2, H2O, CO, H2 and N2) approached local thermodynamic equilibrium with a rate determined by a combination of local turbulent mixing and global chemical kinetics times. The numerical methodology for gas-phase calculations involved a staggered finite-volume formulation with a multi-block curvilinear orthogonal coordinate computational grid, and the PISO algorithm. This numerical code was applied to a model gas turbine combustor similar to that of the Allison 570KF currently in use by the Canadian Navy. The combustor was equipped with an advanced airblast fuel nozzle. The calculations included the analysis of the internal passages of the fuel nozzle. Through the numerical study at full-power and low-cruise operating conditions, a better understanding of the physical processes of flow and temperature fields inside the primary zone was obtained. Predicted hot spots corresponded to locations where deterioration of the combustor liner has been observed in practice.
Computational and Experimental Evaluation of Integral Catalytic Ignitor/Injector for Gas Turbine Applications
Authors: Jackson Greg S. , Etemad Shahrokh , Karim Hasan , Pfefferle William C.
Published: December 2014

The provision of an ignition source in the central region of a liquid-fired combustor reduces the requirement for wide spray angles, rich primary zones, and their associated performance drawbacks such as high levels of soot and NOx formation and high liner wall temperatures. Various ignition devices have been considered for providing centrally located ignition sources. The current paper presents a study of one alternative concept — the integral catalytic torch ignitor/injector — as a means for providing both combustor light-off and enhanced flame stability in the combustor primary zone.

An integral catalytic torch in a fuel injector offers the potential to significantly improve ignition arid flame stability and thus the opportunity to operate combustor primary zones at leaner conditions, which may improve emissions, pattern factor, and combustor liner durability. This paper presents computational and experimental results for a conventional liquid-fired combustor with the addition of a catalytic torch (replacing the pilot pressure atomizer) down the centerline of an air-blast fuel injector. The benefits of a lean primary zone with an integral catalytic torch/injector were investigated both computationally and experimentally by comparing combustor performance with standard and successively leaner primary zones. Pattern factor and emissions are compared with different primary zone jet configurations to observe if the central torch can enhance the operability of leaner primary zones in conventional combustor geometries. The experimental and computational results suggest that the integral catalytic torch can provide more than adequate ignition capabilities with improved combustor emissions when it is combined with a relatively lean operating primary zone.
Low Emissions Combustion System for the Allison ATS Engine
Authors: Smith Duane A. , Frey Steve F. , Stansel David M. , Razdan Mohan K.
Published: December 2014

This paper describes the development of an ultra-low emissions combustion system for Allison’s Advanced Turbine System (ATS) engine, which is being developed in cooperation with the U.S. Department of Energy. The simple cycle engine is designed to have a thermal efficiency that is 15% better than today’s best in class engine, and exhaust emissions of 9 ppm NOx, 20 ppm CO, and 20 ppm UHC. The approach taken to meet the low emissions goals is based on ultra-lean premixed fuel-air combustion supported by a catalyst. The progress toward development and integration of lean premix (LPM), catalytic and post-catalytic stages, and the combustor-to-turbine transition duct into an overall ATS combustion system is presented.

A parametric computational fluid dynamics (CFD) study was conducted on the performance of lean premix modules at ATS conditions. Various lean premix modules were tested extensively under atmospheric conditions to determine airflow capacity, flashback propensity, lean blowout (LBO) fuel-air ratios, and fuel concentration profiles at the module exit. Kinetic modeling using the GRI mechanism has been used to estimate ignition delay times in the post-catalytic zone. Comparison between the modeling results and experimental data at high pressure shows good agreement. A detailed computational analysis was performed to design the combustion-to-turbine transition duct. The results indicate that the scroll duct configuration produces an acceptable mass flow uniformity and swirl angle exiting the duct into the turbine section. High pressure sector rig tests have been performed to evaluate staging interaction issues. The results indicate that the series staged approach can facilitate incorporation of the catalytic combustion system by expanding the operability range. NOx emissions levels of 9 ppm or less can be sustained over a wide range of equivalence ratios.
Instrumentation Systems for a Continuous Flow Turbine Rotor
Authors: Davies Mark R. D. , Byrne Catherine M. , Dillon Paul
Published: December 2014

The design and testing of instrumentation systems for the measurement of steady and unsteady turbine blade surface pressure and boundary layer condition for a turbine stage operating at design Mach and Reynolds numbers is presented. The boundary layer condition is monitored by an array of suction and pressure surface heated thin-film gauges. This paper describes the desigo of a forty channel constant temperature bridge to drive these gauges. The bridge fits into the centre of a sub-shaft driven by the turbine wheel. The amplified bridge output is transferred from the rotor via an array of light emitting diodes. The surface pressure is recorded by unpackaged pressure transducer chips laid into the surface of the blade. This paper also describes the circuitry necessary to drive these transducers. The position of these circuits and the transmission method are the same as those used for the thin film gauges. Both systems have a bandwidth sufficient for the resolution of vane-blade interactions.
Research Into Mechanism of Formation of Alumo-Boron-Nitride Ceramics: A Structural Material for GTE Parts
Authors: Grishaev V. V. , Soudarev A. V. , Okatova G. P.
Published: December 2014

Alumo-boron-nitride-based heat-resistant, thermostable, shrinkage-free structural ceramic material was developed and manufactured by vacuum-compression impregnation technology. Actually, all the high-temperature path parts for 2.5 MW gas-turbine engine were made of this ceramic material [1]. The results of the granulometric, microstructural, phase and other characterization into the material are presented. New conditions of interaction between the boron nitride and aluminium were identified.
Mathematical Model Describing the Coupled Heat Transfer in Effusion Cooled Combustor Walls
Authors: Martiny M. , Schulz A. , Wittig S.
Published: December 2014

A mathematical model to describe the coupled heat transfer in effusion-cooled combustor walls is presented. A heat balance with respect to the heat transfer with film cooling on the hot side, heat transfer on the cold side and heat exchange between the wall and the coolant inside the holes leads to a system of four equations for the unknown temperatures on the hot and cold side of the wall and for the inlet and exit temperature of the coolant. The model is validated with experimentally determined exit temperatures. A parameter study showing the influence of the major dimensionless parameters is performed.
A One Dimensional, Time Dependent Inlet / Engine Numerical Simulation for Aircraft Propulsion Systems
Authors: Garrard Doug , Davis Milt , Wehofer Steve , Cole Gary
Published: December 2014

The NASA Lewis Research Center (LeRC) and the Arnold Engineering Development Center (AEDC) have developed a closely coupled computer simulation system that provides a one dimensional, high frequency inlet / engine numerical simulation for aircraft propulsion systems. The simulation system, operating under the LeRC-developed Application Portable Parallel Library (APPL), closely coupled a supersonic inlet with a gas turbine engine. The supersonic inlet was modeled using the Large Perturbation Inlet (LAPIN) computer code, and the gas turbine engine was modeled using the Aerodynamic Turbine Engine Code (ATEC). Both LAPIN and ATEC provide a one dimensional, compressible, time dependent flow solution by solving the one dimensional Euler equations for the conservation of mass, momentum, and energy. Source terms are used to model features such as bleed flows, turbomachinery component characteristics, and inlet subsonic spillage while unstarted. High frequency events, such as compressor surge and inlet unstart, can be simulated with a high degree of fidelity. The simulation system was exercised using a supersonic inlet with sixty percent of the supersonic area contraction occurring internally, and a GE J85-13 turbojet engine.
Effect of Fuel Composition on NOx Formation in Lean Premixed Prevaporized Combustion
Authors: Capehart Scott A. , Lee John C. Y. , Williams Joseph T. , Malte Philip C.
Published: December 2014

The effect of fuel composition on NOx formation in lean premixed prevaporized (LPP) combustion is examined using an atmospheric pressure jet-stirred reactor fitted with a prevaporizing-premixing chamber and liquid fuel atomizing nozzle. Four liquid fuels are studied, including the pure hydrocarbons n-heptane (C7H16) and n-dodecane (C12H26), No. 2 low sulfur diesel fuel oil (LSDFO#2) with 0.0195% sulfur and 0.0124% nitrogen by weight, and n-dodecane doped with n-ethylethylenediamine (C2H5NHCH2CH2NH2 or C4H12N2) to give 0.0096% nitrogen by weight in the doped fuel. For comparison, propane (C3H6) is burned. The combustion temperature range of the experiments is 1625 to 1925K, and the nominal residence time of the reactor is 3.5ms. The first objective of the work is to determine the effect which increasing fuel carbon number has on the NOx yield of high-intensity LPP combustion. For combustion at 1800K, an increase of 15 to 20% is measured in the NOx yield when the fuel is changed from C3H6 to C12H26. Comparison to earlier work on CH4 and C3H6 combustion in the jet-stirred reactor operating at 1800K shows essentially an identical increase in NOx yield between CH4 and C3H6 as between C3H6 and C12H26. The second objective of the work is to determine the conversion of fuel-nitrogen to NOx for the combustion of low nitrogen content fuels in high-intensity LPP combustion. The measurements indicate a fuel-nitrogen to NOx conversion of 70 to 100%. These conversion values should be regarded as preliminary since only two nitrogen-containing fuels have been examined and only one prevaporizer-premixer system has been used.
Once-Through Heat Recovery Steam Generators Working With Sub- and Supercritical Steam Conditions for Combined Cycles
Authors: Dechamps P. J. , Galopin J.-F.
Published: December 2014

This paper characterizes the performances of once-through heat recovery steam generators in combined cycle applications. Although the concept of once-through boilers has been extensively used for fired boilers, this circulation mode is rather new in combined cycles.

Once-through circulation is required at very high pressures, including supercritical conditions, for which there is a possible advantage in terms of the plant efficiency. The concept is also certainly the best solution for high subcritical pressures, such as those required by repowering applications.

In addition to cycle performance, this paper describes the advantages and disadvantages of the once-through in heat recovery applications. The operational behaviour of such heat recovery steam generators is discussed, together with the main design implications.

A prototype plant running in supercritical steam conditions is also described, as well as some of its possible applications.
Parametric Study of Fuel Cell and Gas Turbine Combined Cycle Performance
Authors: Stephenson Dawn , Ritchey Ian
Published: December 2014

A number of cycles have been proposed in which a solid oxide fuel cell is used as the topping cycle to a gas turbine, including those recently described by Beve et al. (1996). Such proposals frequently focus on the combination of particular gas turbines with particular fuel cells. In this paper, the development of more general models for a number of alternative cycles is described. These models incorporate variations of component performance with key cycle parameters such as gas turbine pressure ratio, fuel cell operating temperature and air flow. Parametric studies are conducted using these models to produce performance maps, giving overall cycle performance in terms of both gas turbine and fuel cell design point operating conditions. The location of potential gas turbine and fuel cell combinations on these maps is then used to identify which of these combinations are most likely to be appropriate for optimum efficiency and power output. It is well known, for example, that the design point of a gas turbine optimised for simple cycle performance is not generally optimal for combined cycle gas turbine performance. The same phenomenon may be observed in combined fuel cell and gas turbine cycles, where both the fuel cell and the gas turbine are likely to differ from those which would be selected for peak simple cycle efficiency. The implications of this for practical fuel cell and gas turbine combined cycles and for development targets for solid oxide fuel cells are discussed. Finally, a brief comparison of the economics of simple cycle fuel cells, simple cycle gas turbines and fuel cell and gas turbine combined cycles is presented, illustrating the benefits which could result.
Aerodynamic Modeling of Multistage Compressor Flowfields: Part 1 — Analysis of Rotor/Stator/Rotor Aerodynamic Interaction
Authors: Hall Edward J.
Published: December 2014

The primary purpose of this study was to investigate improved numerical techniques for predicting flows through multistage compressors. The vehicle chosen for this study was the Pennsylvania State University Research Compressor (PSRC). The PSRC facility consists of a 3-1/2 stage axial flow compressor which shares design features which are consistent with embedded stages of modern gas turbine engine axial flow compressors. In Part 1 of this two part paper, several Computational Fluid Dynamics (CFD) techniques were applied to predict both steady and unsteady flows through the PSRC facility. Inter-blade row coupling via a circumferentially-averaged mixing plane approach was employed for steady flow analysis. A mesh density sensitivity study was performed to define the minimum mesh requirements necessary to achieve reasonable agreement with the experimental data. Time dependent flow predictions were performed using a time dependent interblade row coupling technique. These calculations evaluated the aerodynamic interactions occurring between the second rotor, second stator, and third rotor for the PSRC rig.
The Effect of Hub Leakage Flow on Two High Speed Axial Flow Compressor Rotors
Authors: Shabbir A. , Celestina M. L. , Adamczyk J. J. , Strazisar A. J.
Published: December 2014

The effect of hub leakage flow on the performance of two high speed transonic rotors is investigated through numerical simulations and experiments. The leakage flow emanates from a small gap between the stationary and rotating parts of the hub flow path upstream of the rotor. Results of both the experiments and CFD simulations show that the introduction of a small leakage flow (0–25% of the main passage flow) can reduce the total pressure rise produced by the rotor across the entire span and generate a significant deficit in the total pressure profile near the hub. Numerical simulations done with a sinusoidal distribution of the leakage flow across the rotor pitch show that this deficit is present even when there is zero net leakage. Particle tracer studies of CFD simulations show that this deficit is due to the flow blockage produced by the radial migration of the low momentum leakage fluid. The performance degradation trends predicted by the simulations are qualitatively confirmed in the experimental investigation.
Foil Air/Gas Bearing Technology — An Overview
Authors: Agrawal Giri L.
Published: December 2014

This paper summarizes the chronological progress of foil air bearings for turbomachinery during the last 25 years. Descriptions of various machines which are in production are provided. The foil bearing air cycle machine on the 747 aircraft has demonstrated an MTBF (mean time between failure) in excess of 100,000 hours. Many advantages of foil air bearings are noted. Various designs of foil air bearings presently in use and their relative merits are described. Analytical methods, their limitations, and their relationships with test results are noted. Descriptions of various machines built and tested in process fluids being gases, other than air, and cryogenic liquids are described. Conclusions are drawn that various high speed turbomachines including high temperature applications can be designed and developed using foil air bearings which will increase efficiency and reduce cost of these machines.
Life Prediction Method Under Creep-Fatigue Loading for Gas Turbine Combustion Transition Piece of Ni-Based Superalloy N263
Authors: Kusumoto J. , Watanabe H. , Kanaya A. , Ichikawa K. , Sakurai S.
Published: December 2014

In order to develop the life prediction method under creep-fatigue loading for gas turbine combustion transition piece, creep-fatigue tests were carried out on both as-received and aged Ni-based superalloy Nimonic 263. Crack initiation and propagation behaviors for the smooth specimen were observed. An unique relationship was obtained between life fraction and the maximum surface crack length under triangular wave shape loading tests, except the results for the trapezoidal wave loading tests. The latter results were due to the over estimation of the surface crack length at the crack initiation. These were caused from an oxide film break during straining. In the case of removing the oxide film before the measurement of surface crack, the relationship between life fraction and the maximum surface crack length obtained as unique relationship regardless of triangular and trapezoidal strain wave shapes. Using the life prediction method proposed, which is based on maximum surface crack length, the damage of combustion transition piece materials in service was evaluated.
Integrated Control of Rotating Stall and Surge in High-Speed Multi-Stage Compression Systems
Authors: Eveker K. M. , Gysling D. L. , Nett C. N. , Sharma O. P.
Published: December 2014

Aeroengines operate in regimes for which both rotating stall and surge impose low flow operability limits. Thus, active control strategies designed to enhance operability of aeroengines must address both rotating stall and surge as well as their interaction. In this paper, a previously developed nonlinear control strategy that achieves simultaneous active control of rotating stall and surge is applied to a high-speed 3-stage axial flow compression system with operating parameters representative of modern aeroengines. The controller is experimentally validated for 2 compressor builds and its robustness to radial distortion assessed. For actuation, the control strategy utilizes an annulus-averaged bleed valve with bandwidth on the order of the rotor frequency. For sensing, measurements of the circumferential asymmetry and annulus-averaged unsteadiness of the flow through the compressor are used. Experimental validation of simultaneous control of rotating stall and surge in a high-speed environment with minimal sensing and actuation requirements is viewed as another important step towards applying active control to enhance operability of compression systems in modem aeroengines.
Operating Experience of the First Solar® Taurus 70S Mechanical Drive Installation
Authors: Hoshizaki A. James
Published: December 2014

In October 1995, NOVA Gas Transmission Ltd. (NGTL) commissioned the first mechanical drive application of Solar Turbines’ Taurus™ 70S gas turbine. The unit was installed as a part of a turbine/compressor package at a compressor station on NGTL’s natural gas pipeline system. As this first installation was a part of a development test program by Solar Turbines, field evaluation was conducted subsequent to the original commissioning and related testing. This paper presents NGTL’s experiences in commissioning, startup and operation. Field performance test results for the gas turbine are presented and focus on output power, thermal efficiency and exhaust emissions. Some of the findings and observations from the field evaluation tests performed by Solar are also discussed. In addition, a description of the facility in which the turbine/compressor package is installed is provided.
First V84.3A Gas Turbine Installation at Hawthorn Station
Authors: Johnson T. , Becker B. , Seume J. , Termuehlen H.
Published: December 2014

The first V84.3A gas turbine as tested at the full-load test facility of the Siemens gas turbine factory in Berlin, Germany has now been installed at the Kansas City Power & Light (KCP&L) Company’s Hawthorn Power Station. The unit will be started in spring of this year and is scheduled to be available in June for the 1997 summer peak.

In times when active power is not in demand, the generator can be operated as a synchronous condenser. For this mode of operation, a synchronous clutch has been installed between the gas turbine and the generator.

The advanced V84.3A gas turbine has been chosen because of its high simple cycle efficiency based on the measured 38% in the test facility, providing peaking capacity with a minimum on fuel costs. In addition, later conversion to highly efficient combined cycle operation can easily be performed without the need for external air or even steam cooling systems.
High Efficiency-Coal and Gas (HE-C&G): An Advanced Hybrid Power Plant Concept With Sequential Combustion Gas Turbines GT24/GT26
Authors: Fetescu Mircea
Published: December 2014

The High Efficiency-Coal and Gas (HE-C&G) is a hybrid power plant concept integrating Conventional Steam Power Plants (CSPP) and gas turbine / combined cycle plants. The gas turbine exhaust gas energy is recovered in the HRSG providing partial condensate and feedwater preheating and generating steam corresponding to the main boiler live steam conditions (second steam source for the ST).

The concept, exhibiting very high design flexibility, integrates the high performance Sequential Combustion gas turbines GT24/GT26 technology into a wide range of existing or new CSPP.

Although HE-C&G refers to coal as the most abundant fossil fuel resource, oil or natural gas fired steam plants could be also designed or converted following the same principle.

The HE-C&G provides very high marginal efficiencies on natural gas, up to and above 60%, very high operating and dispatching flexibility and on-line optimization of fuel and O&M costs at low capital investment.

This paper emphasizes the operating flexibility and resulting benefits, recommending the HE-C&G as one of the most profitable options for generating power especially for conversion of existing CSPP with gas turbines.
Three-Dimensional Computation of Gas Turbine Combustors and the Validation Studies of Turbulence and Combustion Models
Authors: Biswas D. , Kawano K. , Iwasaki H. , Ishizuka M. , Yamanaka S.
Published: December 2014

The main aim or the present work is to explore computational fluid dynamics and related turbulence and combustion models for application to the design, understanding and development of gas turbine combustor. Validation studies were conducted using the Semi-Implicit Method for Pressure Linked Equations (SIMPLE) scheme to solve the relevant steady, elliptical partial differential equations of the conservation of mass, momentum, energy and chemical species in three-dimensional cylindrical co-ordinate system to simulate the gas turbine combustion chamber configurations. A modified version of k-ε turbulence model was used for characterization of local turbulence in gas turbine combustor. Since, in the present study both diffusion and pre-mixed combustion were considered, in addition to familiar bi-molecular Arhenius relation, influence of turbulence on reaction rates was accounted for based on the eddy break up concept of Spalding and was assumed that the local reaction rate was proportional to the rate of dissipation of turbulent eddies. Firstly, the validity of the present approach with the turbulence and reaction models considered is checked by comparing the computed results with the standard experimental data on recirculation zone, mean axial velocity and temperature profiles, etc. for confined, reacting and non-reacting flows with reasonably well defined boundary conditions. Finally, the results of computation for practical gas turbine combustor using combined diffusion and pre-mixed combustion for different combustion conditions are discussed.
High-Temperature Surface Measurements of Turbine Engine Components Using Thermographic Phosphors
Authors: Alaruri Sami , Brewington Andy
Published: December 2014

A laser-based system for single point high-temperature measurements of turbine engine component surfaces coated with thermographic phosphors is described. Decay lifetime calibration measurements obtained for Y2O3:Eu over the temperature range ∼530–1000°C are presented. Further, the results obtained from a coupon placed in the outlet gas flow of an atmospheric-combustor are described.
A Practical Compressor Casing Treatment
Authors: Khalid Syed
Published: December 2014

A three stage compressor test incorporating casing inserts comprised of compound angled honeycomb cells demonstrated up to 10% higher stall margin than circumferential grooves casing treatment. This is attributed to effective tip flow energization resulting from the unsteady flow induced in and out of the cells as the blade tip sweeps by the cell openings. The rationale for selecting the cell inclination angles both relative to the normal and the tangential directions is discussed. The design intent of the cell orientation is to induce a high cell exit velocity as well as to impart a degree of flow alignment to the injected jets. A first order calculation of cell exit velocity variation based on the cell pressure/volume dynamics is indicative of unsteady blowing which is theorized to effectively mix the tip suction side flow and to enhance the tip flow streamwise momentum. This theory is partially substantiated by the presented compressor test results showing improved radial total pressure profiles, stage characteristics, and stall margin. Since a few unhealthy stages of a multi-stage compressor could make it stall prone, casing treatment of those weak stages could dramatically increase stall margin with negligible impact on overall adiabatic efficiency. In addition to the aerodynamic effectiveness, the mechanical suitability of this casing treatment to multistage compressors, based on its demonstrated abradability and packageability, is discussed.
Computation of a Leading–Edge Film Cooling Flow Over an Experimental Geometry
Authors: Thakur Siddharth , Wright Jeffrey , Shyy Wei
Published: December 2014

Computations are performed to simulate a leading edge film cooling flow over an experimental test geometry. An in-house CFD–heat transfer code based on a pressure correction algorithm is used for the computations. The code allows the use of multiple blocks in the domain with discontinuous grid lines while maintaining flux conservation at block interfaces. A second–order TVD–based controlled variation scheme (CVS) is used for discretization, along with k–ε models with options of using wall functions or low–Reynolds number modifications. From the viewpoint of incorporating CFD into the design process with fast turn–around times, the approach taken in this study is to attempt to simulate the key features of the flowfield with a reasonable grid size, preferably consisting of no more than 250,000 grid points. In order to attain the desired accuracy with these constraints, effective combinations of grid distribution, discretization operators and turbulence models are investigated, and the sensitivity of the computed solution to these factors examined. The results agree qualitatively with the experimental data though some notable quantitative differences can be observed. An attempt is made to explain the key features of the flowfield resulting from the interaction of coolant jets with the hot freestream.
Effects of Engine Aging on Aircraft NOx Emissions
Authors: Lukachko Stephen P. , Waitz Ian A.
Published: December 2014

The impact of representative paths of engine degradation on aircraft cruise NOx emissions was investigated. Engine cycles corresponding to older, current, and future subsonic and supersonic technologies were developed and used to determine the sensitivities of combustor conditions to various changes in component efficiencies and flow capacities due to aging. Estimates of relative changes in NOx emissions levels were made using established empirical correlations that relate emissions to combustor flow parameters. The analysis methodology was validated through comparisons to test data where available.

It was found that the sensitivity of specific fuel consumption (SFC) and combustor flow parameters to component aging is enhanced by increases in cycle temperatures and pressures. This ultimately results in a higher sensitivity of NOx emissions to engine degradation for cycles representative of more advanced technology. At constant thrust, turbine degradation typically acts to decrease NOx emissions while compressor aging results in an increase in NOx emissions; both occurring at the expense of SFC. Sample degradation scenarios were used to highlight the balance between turbine and compressor aging effects. Changes in NOx emissions in the −1% to +4% range were predicted for typical aging scenarios. The applicability of these results to the formulation of aircraft emissions inventories is considered.
Automatic Genetic Optimization Approach to 2D Blade Profile Design for Steam Turbines
Authors: Trigg M. A. , Tubby G. R. , Sheard A. G.
Published: December 2014

In this paper a systematic approach to the optimization of 2D blade profiles is presented. A genetic optimizer has been developed which modifies the blade profile and calculates its profile loss. This process is automatic, producing profile designs significantly faster and with significantly lower loss than has previously been possible.

The optimizer developed uses a genetic algorithm to optimize a 2D profile, defined using 17 parameters, for minimum loss with a given flow condition. The optimizer works with a “population” of 2D profiles with varied parameters. A CFD mesh is generated for each profile, and the result is analyzed using a 2D blade to blade solver, written for steady viscous compressible flow, to determine profile loss. The loss is used as the measure of a profile’s “fitness”. The optimizer uses this information to select the members of the next population, applying crossovers, mutations, and elitism in the process. Using this method the optimizer tends towards the best values for the parameters defining the profile with minimum loss.
Direct Full Surface Skin Friction Measurement Using Nematic Liquid Crystal Techniques
Authors: Buttsworth D. R. , Elston S. J. , Jones T. V.
Published: December 2014

New techniques for the direct measurement of skin friction using nematic liquid crystal layers are demonstrated. Skin friction measurements can be made using a molecular rotation time technique or an equilibrium orientation technique. A mathematical model describing the molecular dynamics of the nematic liquid crystal layer has been introduced. Theoretical results from the proposed mathematical model are in excellent agreement with the current experimental measurements. It is thus demonstrated that the present model captures the essential physics of the nematic liquid crystal measurement techniques. Estimates based on the variance of the liquid crystal calibration data indicate that skin friction measurements to within ± 4 % should certainly be possible. The techniques offer the considerable advantage of simplicity, without any compromise on the accuracy, relative to other surface shear stress measurement techniques. The full surface measurement capacity of the equilibrium orientation technique is demonstrated by measuring the skin friction distribution around a cylindrical obstruction in a fully developed laminar flow.
Prediction of the Becalmed Region for LP Turbine Profile Design
Authors: Schulte Volker , Hodson Howard P.
Published: December 2014

Recent attention has focused on the so called ‘becalmed region’ that is observed inside the boundary layers of turbomachinery blading and is associated with the process of wake-induced transition. Significant reductions of profile loss have been shown for high lift LP turbine blades at low Reynolds-numbers due the effects of the becalmed region on the diffusing flow at the rear of the suction surface.

In this paper the nature and the significance of the becalmed region are examined using experimental observations and computational studies. It is shown that the becalmed region may be modelled using the unsteady laminar boundary layer equations. Therefore, it is predictable independently of the transition or turbulence models employed. The effect of the becalmed region on the transition process is modelled using a spot-based intermittency transition model. An unsteady differential boundary layer code was used to numerically simulate a deterministic experiment involving an isolated turbulent spot.

The predictability of the becalmed region means that the rate of entropy production can be calculated in that region. It is found to be of the order of that in a laminar boundary layer. It is for this reason and because the becalmed region may be encroached upon by pursuing turbulent flows that for attached boundary layers, wake-induced transition cannot significantly reduce the profile loss. However, the becalmed region is less prone to separation than a conventional laminar boundary layer. Therefore, the becalmed region may be exploited in order to prevent boundary layer separation and the increase in loss that this entails. It is shown that it should now be possible to design efficient high lift LP turbine blades.
Intermittent Flow and Thermal Structures of Accelerating Transitional Boundary Layers: Part 1 — Mean Quantities
Authors: Wang Ting , Keller F. Jeffrey
Published: December 2014

A conditional sampling technique was employed to separate the turbulent and non-turbulent parts of accelerated boundary layers undergoing laminar-turbulent transition on a uniformly heated flat plate. Tests were conducted with zero pressure gradient and two levels of streamwise acceleration parameter: K = 0.07 ×10−6 and 0.16 × 10−6.

The conditionally sampled distribution of the skin friction coefficients revealed that the values for Cf in the non-turbulent and turbulent portions significantly deviated from the respective laminar and turbulent correlations. These deviations increased as acceleration increased. Reconstructing the local average Cf values using the laminar and fully turbulent correlations consistently overestimated the unconditioned Cf values. Using the conditionally sampled data for reconstructing Cf values provided better results, but does not necessarily result in the same unconditioned Cf values.

The mean velocity profiles from the turbulent portions had the appearance of a low-Reynolds-number turbulent boundary layer with a large wake region. In the late transition region, as acceleration increased, the wake region in the turbulent portion was suppressed relative to the unconditioned result. The integral parameters, δ*, θ, and shape factor, H were conditionally sampled and analyzed.
Unsteady Total Temperature Measurements Downstream of a High Pressure Turbine
Authors: Buttsworth D. R. , Jones T. V. , Chana K. S.
Published: December 2014

An experimental technique for the measurement of flow total temperature in a turbine facility is demonstrated. Two thin film heat transfer gauges located at the stagnation point of fused quartz substrates are operated at different temperatures in order to determine the flow total temperature. With this technique, no assumptions regarding the magnitude of the convective heat transfer coefficient are made. Thus, the probe can operate successfully in unsteady compressible flows of arbitrary composition and high free-stream turbulence levels without a heat transfer law calibration. The operation of the total temperature probe is first demonstrated using a small wind tunnel facility. Based on results from the small wind tunnel tests, it appears that the probe total temperature measurements are accurate to within ± 1K. Experiments using the probe downstream of a high pressure turbine stage are then described. Both high and low frequency components of the flow total temperature can be accurately resolved with the present technique. The probe measures a time-averaged flow total temperature that is in good agreement with thermocouple measurements made downstream of the rotor. Frequencies as high as 182 kHz have been detected in the spectral analysis of the heat flux signals from the total temperature probe. Through comparison with fast-response aerodynamic probe measurements, it is demonstrated that at the current measurement location, the total temperature fluctuations arise mainly due to the isentropic extraction of work by the turbine. The present total temperature probe is demonstrated to be an accurate, robust, fast-response device that is suitable for operation in a turbomachinery environment.
Ceramic Coating Edge Failure due to Thermal Expansion Interference
Authors: Nied Herman A.
Published: December 2014

An investigation of thermal barrier coatings on a metal substrate was conducted when the assembly was subjected to both thermal beating and mechanical edge loads generated by interference in adjoining expansion gaps. Both finite element and closed form solution models were developed and compared. The results of the analyses predict that the application of both thermal and mechanical edge loads on the edge of ceramic/metal composites can produce severe local edge spallation in the ceramic coating when an inadequate expansion gap is provided.
One-Dimensional Predictive Emission Monitoring Model for Gas Turbine Combustors
Authors: Botros K. K. , de Boer M. J. , Price G. R. , Kibrya G.
Published: December 2014

Current predictive emission monitoring (PEM) techniques are briefly reviewed and the concept for a general predictive model was favorably evaluated. Utilizing the commercial process simulation software ASPEN PLUS®, a one dimensional model based on fundamental principles of gas turbine thermodynamics and combustion processes was constructed. Employing a set of 22 reactions including the Zeldovich mechanism, the model predicted for thermal NOx formation. It accounted for combustor geometry, dilution air injection along the combustor annulus, convective heat transfer across the liner, flame length, and full-load inlet flows. The combustor was subdivided into slices, each of which was modeled by a plug flow reactor, giving insight into profiles of NOx formation, species concentration and temperature along the combustor’s length, as well as quantifying the residence time in the combustor. The simulation predicted the levels of NOx for a particular gas turbine combustor and determined the effects of various parameters, such as flame length, hydrocarbon conversion ratio and recycle zones.
Design of New Three Stage Low Pressure Turbine for the BMW Rolls-Royce BR715 Turbofan Engine
Authors: Cobley Keith , Coleman Neil , Siden Gunnar , Arndt Norbert
Published: December 2014

In 1990, BMW and Rolls Royce plc (RR) joined to form a new company BWW-Rolls-Royce GmbH (BRR), to develop the BR700 family of engines aimed at the 12K and 25K lbs thrust range, using advanced technology and a modern organisation working in integrated teams to minimise the engine development timescales. After a successful development programme the BR710 engine rated at 14K lbs thrust, will shortly enter service in Gulfstream and Canadair Executive Jets.

The recent launch of the BR715 engine at 21K lbs thrust, builds on the high pressure core developed for the BR710, plus a low pressure system with an increased diameter fan and 2 stage booster driven by a three stage turbine.

This paper will describe, the advanced design technology incorporated, including the latest three dimensional aerodynamic philosophy using advanced high lift aerofoils for reduced parts count, plus the mechanical design issues addressed to optimise the LP turbine module configuration and the simultaneous design/make process employed to achieve the required parts delivery timescales.