bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Patternation of Gas Turbine Fuel Sprays During Simulated Engine Operating Conditions
Authors: Guy S. R. D. , Allan W. D. E. , LaViolette Marc , Underhill P. R.
Published: February 2010

Fuel atomizer condition can have a significant impact on gas turbine hot section component life. In order to investigate the depth of this influence, an experimental test apparatus was constructed, which allowed for optical access to the primary zone of a Rolls-Royce/Allison T56–A–15 turboprop combustion chamber. Test conditions were matched to simulate altitude cruise conditions of a C–130H Hercules military transport aircraft. T56 fuel nozzles of various conditions were tested in free air and then in the test rig using optical patternation techniques. Results indicated that spray characteristics observed in quiescent ambient air persisted under the representative engine operating conditions both burning and non-burning. The optical patternation tests also revealed the influence of combustion liner airflow patterns on the spray within the region of the primary zone that was observed. Conclusions were drawn such as the persistence of spray features observed in open air testing when nozzles were tested at engine representative conditions and recommendations were made for future experimentation.
Application of Silicon Carbide Photodiode Flame Temperature Sensors in an Active Combustion Pattern Factor Control System
Authors: Palmer Carl A. , Abel Royce L. , Sandvik Peter
Published: February 2010

This paper describes the development and initial application studies for an active combustion pattern factor controller (APFC) for gas turbines. The system is based around use of a novel silicon carbide (SiC) optical ultraviolet (UV) dual diode flame temperature sensor (FTS) developed by General Electric’s Global Research Center and GE Energy. The APFC system determines combustion flame temperatures, validates the values, and integrates an assessment of signal and combustion hardware health to determine how to trim the fuel flow to individual fuel nozzles. Key aspects of the system include: • Determination of each flame’s bulk temperature using the FTS. • Assessment of the reliability of the flame temperature data and physical combustion hardware health through analysis of the high frequency output of the sensor. • Validation of the flame temperature signal using a data-driven approach (model based validation - MBV). • Fusion of sensor ‘health indices’ into the APFC to alter the trim control signal based on the health (or ‘believability’) of each sensor and fuel nozzle/combustor. • Fault-tolerant peak/valley detection and control module that selects individual fuel valves to target for reducing pattern factor, while simultaneously balancing the overall fuel flow. The authors demonstrated feasibility of the approach by performing simulations using a quasi-2D T700 turbine engine model. Tests were run on the simulated platform with no faults, simulated sensor faults, and on a system with underlying combustion hardware issues. The final APFC system would be applicable for aviation, naval and land-based commercial gas turbines, and can be used in closed-loop control or adapted as an open-loop advisory / diagnostic system.
Numerical Characterisation of a Gas Turbine Model Combustor Applying Scale-Adaptive Simulation
Authors: Widenhorn Axel , Noll Berthold , Aigner Manfred
Published: February 2010

In this contribution the three-dimensional reacting turbulent flow field of a swirl-stabilized gas turbine model combustor is analyzed numerically. The investigated partially premixed and lifted CH4/air flame has a thermal power load of Pth = 35kW and a global equivalence ratio of φ = 0.65. To study the reacting flow field the Scale Adaptive Simulation (SAS) turbulence model in combination with the Eddy Dissipation/Finite Rate Chemistry combustion model was applied. The simulations were performed using the commercial CFD software package ANSYS CFX-11.0. The numerically achieved time-averaged values of the velocity components and their appropriate turbulent fluctuations (RMS) are in very good agreement with the experimental values (LDA). The same excellent results were found for other flow quantities like temperature and mixture fraction. Here, the corresponding time-averaged and the appropriate RMS profiles are compared to Raman measurements. Furthermore the instantaneous flow features are discussed. In accordance with the experiment the numerical simulation evidences the existence of a precessing vortex core (PVC). The PVC rotates with a frequency of 1596Hz. Moreover it is shown that in the upper part of the combustion chamber a tornado-like vortical structure is established.
Effect of Radial Location of Nozzles on Heat Transfer in Pre-Swirl Cooling System
Authors: Kakade V. U. , Lock G. D. , Wilson M. , Owen J. M. , Mayhew J. E.
Published: February 2010

This paper investigates heat transfer in a rotating disc system using pre-swirled cooling air from nozzles at high and low radius. The experiments were conducted over a range of rotational speeds, flow rates and pre-swirl ratios. Narrow-band thermochromic liquid crystal (TLC) was specifically calibrated for application to experiments on a disc rotating at ∼ 5000 rpm and subsequently used to measure surface temperature in a transient experiment. The TLC was viewed through the transparent polycarbonate disc using a digital video camera and strobe light synchronised to the disc frequency. The convective heat transfer coefficient, h, was subsequently calculated from the one-dimensional solution of Fourier’s conduction equation for a semi-infinite wall. The analysis accounted for the exponential rise in the air temperature driving the heat transfer, and for experimental uncertainties in the measured values of h. The experimental data was supported by ‘flow visualisation’ determined from CFD. Two heat transfer regimes were revealed for the low-radius pre-swirl system: a viscous regime at relatively low coolant flow rates; and an inertial regime at higher flow rates. Both regimes featured regions of high heat transfer where thin, boundary layers replaced air exiting through receiver holes at high radius on the rotating disc. The heat transfer in the high radius pre-swirl system was shown to be dominated by impingement under the flow conditions tested.
Centrifugal Compressor Working Fluids for Refrigeration Cycle
Authors: Ro¨ytta¨ Pekka , Honkatukia Juha , Turunen-Saaresti Teemu
Published: February 2010

A centrifugal high-speed compressor is an effective light weight option to power a refrigeration cycle for air conditioning purposes. Perhaps the most important decision in design is the working fluid selection. Modern high-speed technology makes it possible for the refrigeration compressor to be completely oil free, which considerably broadens the scale of possible working fluids. Furthermore, many traditional fluids have become banned and the industry standard R134a might face the same faith in some European countries because of its relatively high global warming potential. In this study eleven different fluids were studied and compared and R22 was used as a reference. It was found that there are many potential fluids for centrifugal compressors that provide better efficiencies than the most common fluids in use today. The purpose of this study is to initially screen a larger set of candidate fluids for more accurate estimation later on. The fluids are evaluated by the efficiency of the cycle, but also mechanical feasibility and dimensions are considered as light weight of the machinery was an important criterion in design process. The comparison was made with constant evaporation and condensation temperature and fixed cooling power for all the fluids. In selection of the working fluid the safety factors often play a dominant role which was also shortly considered. In our study we found out that for a residential HVAC size cooling cycle there are environmentally friendly fluids with high efficiency leading to feasible mechanical designs with centrifugal compressors.
Large-Eddy Simulation of Interacting Film Cooling Jets
Authors: Renze Peter , Schro¨der Wolfgang , Meinke Matthias
Published: February 2010

In the present paper the flow field of a film cooling configuration with three staggered rows of holes is investigated using large-eddy simulations (LES). The numerical method uses the MILES approach (monotone-integrated large-eddy simulation) and the discretization of the governing equations is based on a mixed central-upwind AUSM (advective upstream splitting method) scheme with low numerical dissipation. The current investigations focus on full-coverage film cooling with finest drilling holes. The film cooling configuration consists of three staggered rows of holes with a lateral hole spacing of p/D = 3 and a streamwise row distance of l/D = 6. The inclination angle of the cooling holes is α = 30° and the flat plate thickness is h/D = 12. The cooling hole exit geometry is fanshaped with lateral and streamwise expansions. The results evidence the different nature of the mixing process between the jets and the crossflow after the first, second, and third row. The turbulent kinetic energy peaks at the interaction region of the undisturbed boundary layer with the first row. The low velocity ratio leads to reduced velocity gradients in the lower boundary layer downstream of the first row. Thus, the turbulence production is reduced at the interaction with the following rows. The adiabatic film cooling effectiveness is substantially improved after the second and third injection and the decay of effectiveness is reduced, respectively. The turbulent heat transfer is investigated and strong variations of the turbulent Prandtl number are evident in the flow field.
Future Research Directions for Ship Propulsion Materials
Authors: Shifler David A.
Published: February 2010

High temperature applications demand materials that have a variety of properties such as high strength, toughness, creep resistance, fatigue resistance, as well as resistance to degradation by their interaction with the environment. All potential metallic materials are unstable in many high temperatures environments without the presence of a protective coating on the component surface. High temperature alloys derive their resistance to degradation by forming and maintaining a continuous protective oxide surface layer that is slow-growing, very stable, and adherent. In aggressive environments, the superalloy oxidation and corrosion resistance needs to be augmented by coatings. Propulsion materials for Naval shipboard gas turbine engines are subjected to the corrosive environment of the sea to differing degrees. Increasing fuel efficiency and platform capabilities require higher operating temperatures that may lead to new degradation modes of coatings and materials. Fuel contaminants or the lack of contaminants from alternative synthetic fuels may also strongly influence coating and/or materials performance which, in turn, can adversely affect the life in these propulsion or auxiliary gas turbine engines. This paper will dwell on some past results of materials testing and offer some views on future directions into materials research in high temperature materials in aggressive environments that will lead to new advanced propulsion materials for shipboard applications.
Computational Investigations of Flow and Heat Transfer on an Effused Concave Surface With a Single Row of Impinging Jets for Different Exit Configurations
Authors: Ashok Kumar M. , Prasad B. V. S. S. S.
Published: February 2010

A computational study is reported on flow and heat transfer from single row of circular air jets impinging on a concave surface with either one or two rows of effusion holes and without effusion holes. The effects of arrangement of jet orifices and effusion holes, spent air exit closure configurations, H/D ratio and jet Reynolds number are investigated. The pressure distribution is higher for the configuration with the air exit only through effusion holes. At higher Reynolds number, three peaks in local Nusselt number are identified and explained. Among the cases tested, the configuration with single row of inline effusion holes shows the least heat transfer and there is a significant local enhancement in heat transfer along the stagnation line for single row of staggered effusion holes. However, the effect of arrangement is negligible for two rows of effusion holes. Among the configuration tested the case of one edge open exit configuration with single row of staggered effusion holes (Case-C1s) shows higher heat transfer among others.
Aircraft Engine Performance Improvement by Active Clearance Control in Low Pressure Turbines
Authors: Knipser Christian , Horn Wolfgang , Staudacher Stephan
Published: February 2010

In order to minimize fuel consumption, resulting in reduced operating costs and lower environmental impact, turbofan engines must be of high overall efficiency. The design of the low pressure turbine (LPT) plays a significant role in the development of such engines. During a flight mission changing operating conditions (spool speeds, temperatures, pressures, etc.) cause altering magnitudes of the LPT tip clearance, leading to a decrease in LPT performance. As minimum clearances usually do not occur in steady state cruise condition — the major flight condition concerning fuel consumption — active measures to minimize radial tip clearance (ACC – active clearance control) must be incorporated to achieve a considerable reduction in fuel consumption over the whole flight mission. Actively minimizing radial tip clearance by manipulating the turbine casing requires energy in terms of cooling air (thermal ACC), electrical or hydraulical power (mechanical ACC). The cooling air or the power respectively must be provided by the engine itself, thus partly compensating the benefit gained through the improved LPT behavior. This paper investigates the potential of ACC systems from a whole engine perspective. The approach uses a performance model of a state-of-the-art high bypass turbofan engine with a thermal LPT-ACC system to assess the different benefits and detriments of an enhanced ACC. The overall benefit in TSFC for the simulated engine is compared to measured data of other engines indicating an increase of ACC effectiveness with increasing bypass ratios. To compensate deterioration losses due to single rub-in events, closed-loop controls are required. A tip clearance sensor allows the ACC to adapt to an individual engine. As thermal ACC systems show an optimum benefit with a corresponding optimum ACC cooling air flow, the additional TSFC benefit by compensating deterioration is limited. The achievable overall performance improvement is evaluated for different control loops. Mechanical ACC systems bear the highest potential of eliminating clearance losses, while only minor improvements can be made for thermal ACC systems.
Effect of Blowing Ratio in the Near-Stagnation Region of a Three-Row Leading Edge Film Cooling Geometry Using Large Eddy Simulations
Authors: Sreedharan Sai Shrinivas , Tafti Danesh K.
Published: February 2010

Computational studies are carried out using Large Eddy Simulations (LES) to investigate the effect of coolant to mainstream blowing ratio in a leading edge region of a film cooled vane. The three row leading edge vane geometry is modeled as a symmetric semi-cylinder with a flat afterbody. One row of coolant holes is located along the stagnation line and the other two rows of coolant holes are located at ±21.3° from the stagnation line. The coolant is injected at 45° to the vane surface with 90° compound angle injection. The coolant to mainstream density ratio is set to unity and the freestream Reynolds number based on leading edge diameter is 32000. Blowing ratios (B.R.) of 0.5, 1.0, 1.5, and 2.0 are investigated. It is found that the stagnation cooling jets penetrate much further into the mainstream, both in the normal and lateral directions, than the off-stagnation jets for all blowing ratios. Jet dilution is characterized by turbulent diffusion and entrainment. The strength of both mechanisms increases with blowing ratio. The adiabatic effectiveness in the stagnation region initially increases with blowing ratio but then generally decreases as the blowing ratio increases further. Immediately downstream of off-stagnation injection, the adiabatic effectiveness is highest at B.R. = 0.5. However, further downstream the larger mass of coolant injected at higher blowing ratios, in spite of the larger jet penetration and dilution, increases the effectiveness with blowing ratio.
Impact of the Pre-Swirl Nozzle Location on the Air Transfer System (ATS) Characteristic
Authors: Granovskiy Andrei , Kostege Valery , Chernyshev Sergey , Vassiliev Vladimir
Published: February 2010

In most industrial turbines the cooling air for rotating turbine blades, is extracted from the compressor and transferred via passageways in the stationary parts and the rotor to the blade roots. These passages form the stator-rotor air transfer system (ATS). In stationary part of the ATS the air is usually pre-swirled in the direction of rotation to reduce the temperature and to minimize the losses in the transition area. This paper presents the investigations of the impact of the pre-swirl nozzle location on the ATS characteristics. Two ATSs have been compared. Both have a similar design, with the main difference related to the position of a pre-swirl nozzle. In the first system the pre-swirl nozzle is located at the inlet, and in the second it is located at the outlet of the stationary part of the ATS. The detailed flow structure and characteristics of both systems have been calculated using commercial CFD code. The 3-D calculations provide better insight into the dominant physical mechanisms in complex, rotating, turbulent flow and allow the calculation of the performance of these systems under various conditions. The CFD calculations have been used for the calibration of the cooling system hydraulic model, and the latter was compared with the available measured data. The study showed that the two ATSs considered have very similar characteristics (i.e. similar reduction of cooling air temperature and similar losses) despite the fact that the flow structure is significantly different. Therefore, this design can be considered as neutral to the pre-swirl nozzle location, and this is a positive feature ensuring flexibility of the system.
The Effect of Annulus Performance Parameters on Rotor-Stator Cavity Sealing Flow
Authors: Mirzamoghadam A. V. , Heitland G. , Hosseini K. M.
Published: February 2010

The amount of cooling air assigned to seal high pressure turbine rim cavities is critical for performance as well as component life. Insufficient air leads to excessive hot annulus gas ingestion and its penetration deep into the cavity compromising disk or cover plate life. Excessive purge air, on the other hand, adversely affects performance. This paper is Part-2 of the authors’ work on ingestion reported last year [1]. Whereas, the main focus of that investigation was to qualitatively describe ingestion driven by annulus circumferential pressure asymmetry under constant annulus conditions and rotational speed, in this paper, the research team investigated the variation of annulus circumferential pressure fluctuation and rotational speed on the double overlap platform rim seal cavity reported in Part-1, and mapped out the resulting non-dimensional minimum sealing flow (minimum value of Cw or Cw,min) as it relates to entrained ingestion in the absence of cavity cooling flow (Cw,ent). As was done in Part-1, the runs were made with 3D CFD in setup/run mode option using Fine/Turbo. At two rotational speeds, annulus conditions were varied by reducing turbine inlet pressure (i.e. mass flow) from the baseline operating condition, and the resulting pressure fluctuation was quantified. In addition, a preliminary investigation to assess the aft-located mixing plane steady state solution for this study was performed. The results yielded the linear decrease in Cw,ent at fixed rotational Reynolds number as annulus Reynolds number was decreased. Moreover, the rate of change in entrained flow sharply increases with increase in rotational Reynolds number. As annulus mass flow is reduced to a critical value defined by annulus-to-rotational Reynolds number ratio, the CFD prediction for Cw,ent converges to the turbulent boundary layer entrainment solution for the rotor, and Cw,min reverts to the rotational Reynolds number dominating region. The results from this study were compared to what has been observed by a previous study for a single overlap platform geometry. The resulting design curve allows insight in relating cavity purge flow requirements versus turbine cycle parameters which could lead to better efficiency.
Turbine Blade Tip Heat Transfer in Low Speed and High Speed Flows
Authors: Wheeler Andrew P. S. , Atkins Nicholas R. , He Li
Published: February 2010

In this paper, high and low speed tip flows are investigated for a high-pressure turbine blade. Previous experimental data are used to validate a CFD code, which is then used to study the tip heat transfer in high and low speed cascades. The results show that at engine representative Mach numbers the tip flow is predominantly transonic. Thus, compared to the low speed tip flow, the heat transfer is affected by reductions in both the heat transfer coefficient and the recovery temperature. The high Mach numbers in the tip region (M>1.5) lead to large local variations in recovery temperature. Significant changes in the heat transfer coefficient are also observed. These are due to changes in the structure of the tip flow at high speed. At high speeds, the pressure side corner separation bubble reattachment occurs through supersonic acceleration which halves the length of the bubble when the tip gap exit Mach number is increased from 0.1 to 1.0. In addition, shock/boundary-layer interactions within the tip gap lead to large changes in the tip boundary-layer thickness. These effects give rise to significant differences in the heat-transfer coefficient within the tip region compared to the low-speed tip flow. Compared to the low speed tip flow, the high speed tip flow is much less dominated by turbulent dissipation and is thus less sensitive to the choice of turbulence model. These results clearly demonstrate that blade tip heat transfer is a strong function of Mach number, an important implication when considering the use of low speed experimental testing and associated CFD validation in engine blade tip design.
Simulation of Mist Film Cooling on Rotating Gas Turbine Blades
Authors: Dhanasekaran T. S. , Wang Ting
Published: February 2010

Film cooling technique has been successfully applied to gas turbine blades to prevent it from the hot flue gas. However, a continuous demand of increasing the turbine inlet temperature to raise the efficiency of the turbine requires continuous improvement in film cooling effectiveness. The concept of injecting mist (tiny water droplets) into the cooling fluid has been proven under laboratory conditions to significantly augment adiabatic cooling effectiveness 50–800% in convective heat transfer and impingement cooling. The similar concept of ejecting mist into air film cooling has not been proven in the laboratory, but computational simulation has been performed on stationary turbine blades. As a continuation of previous research, this paper extends the mist film cooling scheme to the rotating turbine blade. For the convenience of understanding the effect of rotation, the simulation is first conducted with a single pair of cooling hole located near the leading edge at either side of the blade. Then a row of multiple-hole film cooling jets are simulated at stationary and rotational condition. Operating condition under both the laboratory (baseline) and elevated gas turbine conditions are simulated and compared. The effects of various parameters including mist concentration, water droplet diameter, droplet wall boundary condition, blowing ratio, and rotational speed are investigated. The results showed the effect of rotation on droplets at lab condition is minimal. The CFD model employed the Discrete Phase Model (DPM) including both wall film and droplet reflect conditions. The results showed that the droplet-wall interaction is stronger on the pressure side than on the suction side resulting in a higher mist cooling enhancement on the pressure side. The average mist cooling enhancement of about 15% and 35% are achieved on the laboratory and elevated conditions, respectively. This translates into a significant blade surface temperature reduction of 100–125 K with 10% mist injection at elevated condition.
Practical Experience With the Development of Superalloy Rejuvenation
Authors: Liburdi Joseph , Lowden Paul , Nagy Douglas , Rusan De Priamus Tiberius , Shaw Stephanie
Published: February 2010

Material degradation is one of the primary causes of gas-turbine hot section component retirement. This is characterized by microstructural aging and subsequent loss of creep strength. Under the same temperature conditions, the longer components remain in service, the more microstructural degradation occurs. This can be evaluated both through microscopy and stress-rupture tests, quantifying the material strength under high temperature, constant load creep conditions. In an effort to extend component life and reduce replacement part costs, material rejuvenation processes have been developed and implemented over the past few decades. In total over 35 commercial superalloy rejuvenation processes were studied and it was found that many alloys can be successfully rejuvenated but others pose a greater challenge. Issues of grain growth in forged turbine components and recrystallization in single crystal components impose limits on rejuvenation processes and are areas of ongoing development. The feasibility, successes and limitations of material rejuvenation are reviewed in this paper with a particular focus on the following superalloys: GTD111, IN738, and Nimonic 115. Examples of microstructure and stress-rupture life of turbine components in both the service-exposed and rejuvenated condition are presented. Component microstructure is shown to be restored, and the stress-rupture life following rejuvenation is returned to a condition fit for continued service.
Development of the GT-MHR Turbo Machine
Authors: Baxi C. B. , Telengator A. , Razvi J. , Belov S. E. , Kokochigov N. G.
Published: February 2010

The high-temperature gas-cooled reactor technology is the only nuclear technology capable of achieving coolant temperatures as high as 950 °C and at the same time ensuring safe and efficient production of electricity, process steam and hydrogen. GA in USA and OKBM in Russia started an independent research in this area in the 1990s. In 1995, OKBM in cooperation with GA started development of the GT-MHR design which combines a safe modular reactor and a power conversion unit based on the high-efficiency Brayton cycle. The power conversion unit in the GT-MHR design has integral configuration, with vertical arrangement of the turbo machine consisting of an asynchronous generator and a turbo compressor. Active electromagnetic bearings are used as supports. In order to select optimal technical solutions, the effect of the following factors on the design was considered: vertical or horizontal arrangement, submerged or remote generator with oil bearings, and different turbo machine rotor speeds. Application of electromagnetic bearings and diaphragm coupling between the rotors, integral arrangement of the turbo machine inside the power conversion system vessel, and use of helium as a coolant required performance of comprehensive analyses and experiments. For this purpose, the helium turbo machine technology demonstration program was developed and is currently being implemented. This technology demonstration program aims at validating the quantitative and qualitative characteristics of such turbo machine components as electromagnetic and catcher bearings, control system, computer codes, generator, diaphragm coupling, turbo compressor, etc. At the concluding stage of the technology demonstration program, a full-scale turbo compressor model will be tested at a helium test facility.
Flame Front Characteristic and Turbulent Flame Speed of Lean Premixed Syngas Combustion at Gas Turbine Relevant Conditions
Authors: Daniele S. , Jansohn P. , Boulouchos K.
Published: February 2010

This paper focuses on the description of the turbulent flame speed, at gas turbine like conditions, for different syngas mixtures, selected in order to simulate syngas compositions typically derived from gasification of coal, oil, biomass, and used for power generation in integrated gasification combined cycle (IGCC) processes. In this paper the turbulent flame speed is reported as global consumption rate and calculated based on a mass continuity approach applied to the combustor inlet area and the flame front surface, which was detected experimentally. Flame front detection was done by means of planar laser induced fluorescence technique taking OH radicals as seeding dyes. An in-house developed flame front detection software tool has been further improved and utilized in this work in order to better fit ultra-lean H2-rich flames. Experiments were carried out in a High Pressure Test Rig for operating pressures up to 15 bar. Data provided in this paper will focus on a pressure level of 5 bar, adiabatic flame temperatures up to 1900 K, inlet velocities from 40 to 80 m/s, and inlet temperature of 672 and 772 K. As expected, the results highlight the strongly elevated values of turbulent flame speed for high hydrogen containing fuel gas mixtures. Compared with flame speed data for pure CH4 the ratio (STSyn/STCH4) takes up values of 7 to 8. In absolute terms values go up even beyond 10 m/s. With increased H2 content in the mixture the burning velocity raises, due to the faster chemical kinetics characteristic of this compound and due to physical properties of H2 (Le<1) which enhance flame front corrugation (i.e. flame front surface). Inlet velocity and pressure variations showed to have weak effect on the average flame front position whereas this last parameter is strongly affected by the mixture composition, the equivalence ratio and inlet temperature.
Study on Parametric Optimization of IGCC-SOFC Hybrid System
Authors: Duan Liqiang , Wang Xu , Yang Yongping , He Binbin
Published: February 2010

This paper studies an Integrated Gasification Combined Cycle-Solid Oxide Fuel Cell (IGCC-SOFC) hybrid power system. Based on the intercrossing of electrochemical process and thermodynamic cycle, this paper has proposed a dual cycle IGCC-SOFC hybrid power system. Based on the Aspen Plus soft, the model of the IGCC-SOFC hybrid power system has been established and the performance of the overall hybrid power system affected by the main operating parameters of SOFC system has been analyzed and optimized. The obtained results show that IGCC system integrated with the high temperature SOFC combined cycle system has a higher thermal efficiency through decreasing the current density; the higher fuel utilization ratio (ηg) also improves the efficiency of hybrid power system; with the increase of the syngas distribution ratio Xfl, both the total power output and system efficiency of the hybrid power system are improved greatly. When Xfl is 1.0, compared with the base IGCC system without integration with SOFC system, the efficiency of hybrid power system increases by 10 percentage points approximately. Above research achievements will provide a valuable guide for further study on IGCC-SOFC hybrid power system.
Development of Flashback Resistant Low-Emission Micro-Mixing Fuel Injector for 100% Hydrogen and Syngas Fuels
Authors: Lee Howard , Hernandez Steve , McDonell Vincent , Steinthorsson Erlendur , Mansour Adel , Hollon Brian
Published: February 2010

The present work extends previous efforts using “micro-mixing” fuel injectors operating on hydrogen fuel to elevated pressure and temperature and includes initial evaluation of a second injector concept. A micro-mixing fuel injector consists of multiple, small and closely spaced mixing cups, within which fuel and air mix rapidly at a small scale. The micro-mixing injection strategy offers inherent flexibility for the accommodation of staging, dilution, and fuel flexibility, and the manufacturing technology employed for building the cups affords great flexibility to address the conflicting demands of superior fuel-air mixing and flash-back avoidance. In the present work, both radial and axial flow micromixing concepts are investigated using experiments and computational fluid dynamics. The hydrogen/air reaction structure is captured using OH* chemiluminescence at 308 nm, recorded using a 16-bit thermoelectrically cooled ICCD with a UV sensitive phosphor. Instantaneous images are used to assess flashback tendencies at pressures up to 8 atm for reaction temperatures approaching 2000 K. Emissions are measured at the exit of the combustor liner using EPA certified methodologies. The results demonstrate that both concepts can produce low NOx emissions while remaining robust relative to flashback and lean blowout. The radial concepts offer superior emissions performance, while the axial concepts offer superior flashback tendencies. Based on the results obtained to date, the micro-mixing approach appears promising relative to achieving flashback free operation with low emissions at pressures up to 8 atm while maximizing scalability and fuel flexibility.
Heat Transfer and Aerodynamics of Over-Shroud Leakage Flows in a High-Pressure Turbine
Authors: Lehmann Knut , Thomas Richard , Hodson Howard , Stefanis Vassilis
Published: February 2010

An experimental study has been conducted to investigate the distribution of the convective heat transfer on the shroud of a high pressure turbine blade in a large scale rotating rig. A continuous thin heater foil technique has been adapted and implemented on the turbine shroud. Thermochromic Liquid Crystals were employed for the surface temperature measurements to derive the experimental heat transfer data. The heat transfer is presented on the shroud top surfaces and the three fins. The experiments were conducted for a variety of Reynolds numbers and flow coefficients. The effects of different inter-shroud gap sizes and reduced fin tip clearance gaps were also investigated. Details of the shroud flow field were obtained using an advanced Ammonia-Diazo surface flow visualisation technique. CFD predictions are compared with the experimental data and used to aid interpretation. Contour maps of the Nusselt number reveal that regions of highest heat transfer are mostly confined to the suction side of the shroud. Peak values exceed the average by as much as 100 percent. It has been found that the interaction between leakage flow through the inter-shroud gaps and the fin tip leakage jets are responsible for this high heat transfer. The inter-shroud gap leakage flow causes a disruption of the boundary layer on the turbine shroud. Furthermore, the development of the large recirculating shroud cavity vortices is severely altered by this leakage flow.
Time Scale Model for the Prediction of the Onset of Flame Flashback Driven by Combustion Induced Vortex Breakdown (CIVB)
Authors: Konle Marco , Sattelmayer Thomas
Published: February 2010

Flame flashback driven by Combustion Induced Vortex Breakdown (CIVB) represents one of the most severe reliability problems of modern gas turbines with swirl stabilized combustors. Former experimental investigations of this topic with a 500 kW burner delivered a model for the prediction of the CIVB occurrence for moderate to high mass flow rates. This model is based on a time scale comparison. The characteristic time scales were chosen following the idea that quenching at the flame tip is the dominating effect preventing upstream flame propagation in the center of the vortex flow. Additional numerical investigations showed that the relative position of the flame regarding the recirculation zone influences the interaction of flame and flow field. The recent analysis of turbulence and chemical reaction of data acquired with high speed measurement techniques applied during the CIVB driven flame propagation by the authors lead to the extension of the prediction model. As at the flame tip the corrugated flames regime prevails at low to moderate mass flow rates, a more precise prediction in this range of mass flow rates is achieved using a characteristic burnout time τb∼1/Sl for the reactive volume. The paper presents first this new idea, confirms it then with numerical as well as experimental data and extends finally the former model to a prediction tool that can be applied in the full mass flow range of swirl burners.
Prognostics Model for Predicting Aero-Engine Bearing Grade-Life
Authors: Hong Jie , Miao Xuewen , Han Lei , Ma Yanhong
Published: February 2010

Development of practical and verifiable prognostic approaches for service life of gas turbine engine bearings will play a critical role in improving the reliability and safety of aircraft engines. Upgrading current military aeroengine overhaul metrics based strictly on engine flight hours and total accumulated cycles with higher fidelity prognostic models will provide an opportunity to prevent failures caused by accelerated degradation due to operation in unusually harsh conditions, and will help avoid unnecessary maintenance caused by routine check on engines that operate under nominal operating conditions. Grade-life (GL) is used to describe the bearing’s service life, and a comprehensive engine bearing prognostic model comprised of a physics based mathematical model and a prognostic element is presented in this paper. The mathematical model utilizes information from the Sensed Data module to calculate the cumulative damage sustained by the bearing since it was first installed and the Prediction Grade-life (PGL) is captured. The prognostic estimate model is an empirical lifetime model, in which Empirical Grade-life (EGL) is assessed based on vibration signals intelligently. The final Grade-life of bearings is determined by fusion of analytic Grade-life (PGL) and Grade-life assessment value (EGL) based on Fuzzy Logic Inference, which reduces the uncertainty’s affection towards prediction results of the analytic model. Finally, bearing test stand run-to-failure data is used to verify the approach.
Risk Monitoring During Design and Development of Aircraft Engines Using Monte Carlo Simulations and Performance Model
Authors: Abdullahi Hassan , Schmidt Klaus-Juergen
Published: February 2010

The process of engine design and development is very complex since it comprises various disciplines with their own sub-processes. In addition, the requirements the new generation of engines has to meet become more and more ambitious, which calls for the employment of new technologies. But this involves a very high risk with regard to fulfilling specification requirements, and also with regard to adherence to budgets as well as time frames. In this paper, an approach of risk monitoring during the engine design and development phase is presented. The approach uses Monte-Carlo simulations, which are based on an engine performance synthesis model. For the purpose, a helicopter engine is used as an example for demonstration of the method.
Practical Slot Configurations for Turbine Film Cooling Applications
Authors: Bruce-Black Joshua E. , Davidson Frederick T. , Bogard David G. , Johns David R.
Published: February 2010

Turbine component film cooling is most effective when using a continuous slot to introduce coolant to the surface. However, this is not practical due to the structural weakness that would be inherent with a continuous slot. In this study, several slot-like designs are investigated to establish the film cooling effectiveness. These slot configurations extended only a partial distance through the simulated turbine vane wall, and were fed with impinging cylindrical holes. The configurations were studied on the suction side of a scaled-up turbine vane. In this study varying slot widths, discrete and continuous slots, and diffusing the coolant flow within the slot prior to it being emitted onto the surface of the vane were investigated. Rows of discrete round and shaped holes were also tested for comparison with the slots. The study of varying slot geometries showed that decreasing the width of the slots led to a substantial increase in adiabatic effectiveness. An internal coolant diffusion technique showed promise by maintaining performance levels while potentially providing a design configuration that more readily meets structural demands in real world operating conditions. The coolant flow characteristics were also studied through the use of thermal profiles measurements. These thermal profiles showed significant mainstream ingestion on the top surface of the slot prior to the coolant emitting onto the surface of the vane.
Mapping the Density Fluctuations in a Pulsed Air-Methane Flame Using Laser-Vibrometry
Authors: Giuliani Fabrice , Leitgeb Thomas , Lang Andreas , Woisetschla¨ger Jakob
Published: February 2010

Laser vibrometry (LV) is originally a laser-based, line-of-sight measurement technique dedicated to the analysis of surface vibrations. It was lately adapted at TU Graz for monitoring the stability of an air-methane flame (Giuliani et al., ASME Turbo-Expo 2006, GT 2006-90413). This paper reports on the mapping of density fluctuations measured with LV in a premixed air-methane flame (free-jet; swirl-stabilised) with a forced flow modulation (quarter-wave resonator; amplification with a siren). In order to correlate the density fluctuations with the jet aerodynamics and turbulent flame shape, stereoscopic PIV and high-speed schlieren visualisations were used. The paper addresses issues regarding the estimate of density fluctuations, the transform from line-of-sight to local measurement with tomographic methods, and the potential of the method for detailed description of thermoacoustic couplings. One emphasised application of LV is its ability to perform precise and low-cost benchmark stability tests on a combustor during the design phase (time-resolved measurement; high frequency and phase resolution on the 5 Hz–20kHz range with the present equipment and settings; near-constant spectral sensitivity over a large bandwidth; no seeding required; measurement possible over the whole combustion volume).
Prediction of Heat Transfer in Turbulent Channel Flow With Spanwise Rotation and Suction/Blowing Through Opposite Walls
Authors: Younis B. A. , Weigand B. , Laqua A.
Published: February 2010

This paper is concerned with the prediction of heat transfer rates in fully-developed turbulent flows in straight channels with mass transfer by suction and blowing through opposite walls, and with rotation about the spanwise axis. The predictions are based on the solution of the Reynolds-averaged forms of the governing equations using a second-order accurate finite-volume formulation. The effects of turbulence on momentum transport were accounted for by using turbulence closures based on the solution of modeled differential transport equations for the Reynolds stresses. A number of alternative models were assessed. These included a high turbulence Reynolds-number model in which the computationally-efficient ‘wall-function’ approach was used to bridge the near-wall region. As the effects of stabilizing system rotation can cause flow relaminarization, the wall-function approach becomes unreliable and integration must be carried out through the viscous sub-layer, directly to the walls. The suitability of three alternative low Reynolds-number models was assessed in these flows. Experimental data from flows in stationary channels with Reynolds numbers spanning the range of laminar, transitional and turbulent regimes were also used in this assessment. Excellent predictions of the wall skin-friction coefficient across the entire range were obtained with a low Reynolds-number model in which the effects of a rigid wall on the fluctuating pressure field in its vicinity were accounted for by a method which incorporates the gradients of the turbulence length scale and the invariants of turbulence anisotropy. For the cases of heated flows, two very different models for the turbulent heat fluxes were examined: one involved the solution of a differential transport equation for each component of the heat-flux tensor and another in which the heat fluxes were obtained from an explicit algebraic model derived from tensor representation theory. It was found that the two models yielded results that were essentially similar and in close agreement with results from recent Direct Numerical Simulations.
Heat Transfer in Rotating Channel With Inclined Pin-Fins
Authors: Park Jun Su , Kim Kyung Min , Lee Dong Hyun , Cho Hyung Hee , Chyu Minking
Published: February 2010

This study is to examine experimentally the effects of pin inclination and pin height-to-diameter ratio on the heat/mass transfer characteristics in a pin-fin channel with and without rotation. The test model consists of staggered pin-fin arrays with an inter-pin spacing of 2.5 times of the pin-diameter (S/D = 2.5) in both longitudinal and transverse directions. Detailed local heat/mass transfer coefficients on the two principal surfaces of rotating channel are measured using the naphthalene sublimation technique. The inclined angles (θ) studied are 60° and 90°. The pin height-to-diameter ratio (Hp/Dp) ranges from 2 to 4. The Reynolds number is fixed at 7.0 × 103 with two Rotation numbers (0.0 and 0.2). The measured data show that the overall array heat/mass transfer decreases with the angle of inclination relative to the vertical orientation. The overall array averaged as well as the row-resolved heat/mass transfer increases with an increase in Hp/Dp. Rotation generally results in higher heat/mass transfer than the corresponding stationary case. The non-uniformity or redistribution of heat/mass transfer induced by the Coriolis force generally perceived in a ribbed or smooth channel is less evident in a pin-fin channel.
Introduction of Combined Usage of Overset Grid Method in Conjugate Heat Transfer Simulation
Authors: Yamane Takashi , Yamamoto Kazuomi
Published: February 2010

The conjugate heat transfer simulation is expected to simulate precise temperature distributions of turbine cooling structures and contribute to the reduction of cooling air usage. However, the generation of computational grids for highly complicated cooling structures in turbine blade is a quite difficult work, especially in the conjugate simulation because grids for fluid and solid regions should be generated simultaneously. In this study the combined usage of the overset grid method with the attached multiblock grid method is introduced for the grid generation with less effort. In the original UPACS flow solver, the overset is treated as one type of boundary conditions where the data are interpolated from the background grid blocks. If the interpolations of data are allowed along the solid surface which is the connecting boundary of fluid and solid grid blocks, the heat flux calculation becomes quite complicated and the benefits of longstanding researches on the turbulence models for boundary fitted grids cannot be used, thus the overset treatments have been limited among the same type of calculation blocks, that is, the fluid blocks should be on the background grid of fluid region and the solid blocks should be on the background grid of solid region. The procedure to create grids with the above restriction has also developed. Numerical result using the overset grid method is compared with the conventional multi-block grid result for evaluation. With this method, the grid generation labor for such as parametric simulations of different arrangements of film holes in a turbine blade will be greatly reduced.