bluuebunny/crossref_metadata_2025 huggingface dataset:
Gas Turbine Power and Propulsion Options for the Modern Warship
Authors: Bricknell David J. , Partridge Richard
Published: March 2009

Modern naval combatants appear to be dividing into three distinct ship types: ocean capable patrol-craft, globally deployable combatants, and the developing new class of fast littoral combatant. Each ship type places different and significant demands on the power and propulsion system. This paper describes the technical and operational issues driving the demands on the power and propulsion system including ship speed, un-refuelled endurance, fuel type, on-board maintenance and the new electric mission-systems. Gas turbine powered mechanical-geared systems, gas turbine alternator powered integrated full-electric systems and hybrid mechanical/electrical systems are all examined and their contribution to the success of the system is discussed.
Aerodynamic Characteristics of a Redesigned Turbine
Authors: Vassiliev Vladimir , Mooslechner Norbert , Kostege Mikhail , Granovskiy Andrei
Published: March 2009

The aero-redesign of a 50 Hz Gas Turbine GT13D3A is presented. The modifications enabling performance improvements are described, and the aero-design process is briefly discussed as well. The aerodynamic characteristics of an upgraded turbine (GT13DM) are compared with the original design (GT13D3A) and with the measurements in the field. The measurements confirmed the expected performance improvement.
Use of Cross Flow Fuel Filtration for Gas Turbine Engines
Authors: Jen Chang-Wei , Rauf Walter V.
Published: March 2009

U.S. Navy surface combatants use pre-filters and filter separators in the fuel oil service system to filter out sediment and water in order to meet the fuel oil cleanliness requirements to operate the gas turbine engines and generators. The ships have reported high usage rates of the pre-filters necessitating the replacement of the pre-filter elements. High replacement rates of the elements obviously increases the burden on ships force but it also increases the operating costs due to the cost of the replacement elements and the storage, handling and disposal of the hazardous material generated. One of the causes of the poor quality fuel oil is the purifier’s inability to remove all sediment and water from the fuel oil when transferring fuel from storage to service. A prototype two-stage self-cleaning cross flow filtration unit was installed in parallel with a fuel oil purifier on a surface combatant. This unit was operated during a deployment cycle and had a through put in excess of one million gallons of fuel. The purpose of this paper is to discuss the background leading to the design of the unit, the installation, operation, data, results and future design changes.
Investigation of the Influence of Trailing Edge Shock Waves on Film Cooling Performance of Gas Turbine Airfoils
Authors: Ochs M. , Schulz A. , Bauer H.-J.
Published: March 2009

Transonic turbine stage flows are strongly influenced by shock waves. The oblique trailing edge shock generated at the pressure side impinges on the suction side of the neighboring airfoil leading to a significant alteration of the Mach number distribution. On film cooled turbine airfoils this shock interacts with the local cooling film. The present study deals with the investigation of this kind of shock wave – film cooling interaction. Experiments are conducted in a high pressure high temperature transonic test rig which allows setting engine realistic Reynolds numbers and Mach numbers, as well as temperature and density ratios. The generic test rig simulates a transonic region of an airfoil passage with the advantage of accessibility for optical measurement techniques. Coolant is ejected from a row of 5 cylindrical and 5 fanshaped holes at different locations relative to the position of shock impingement. Blowing ratios are varied within a range of 0.25<M<1.5. A simulated suction side Mach number distribution is generated with a Mach number Mam = 1.45 upstream and Mam = 1.14 downstream of the shock. Experimental data presented comprise spatially resolved and laterally averaged film cooling effectiveness and heat transfer coefficients within the vicinity of the interaction zone.
Multidisciplinary Optimization of a Radial Compressor for Micro Gas Turbine Applications
Authors: Verstraete T. , Alsalihi Z. , Van den Braembussche R. A.
Published: March 2009

A multidisciplinary optimization system and its application to the design of a small radial compressor impeller are presented. The method uses a genetic algorithm and artificial neural network to find a compromise between the conflicting demands of high efficiency and low centrifugal stresses in the blades. Simultaneous analyses of the aero performance and stress predictions replace the traditional time consuming iterative design approach. The aerodynamic performance, predicted by a 3D Navier-Stokes solver, is maximized while limiting the mechanical stresses to a maximum value. The stesses are calculated by means of a finite element analysis and controlled by modifying the blade camber, lean and thickness at the hub. The results show that it is possible to obtain a significant reduction of the centrifugal stresses in the blades without penalizing the performance.
A Unit Cost Comparison Methodology for Turbofan Engines
Authors: Arago Olivia , Bretschneider Stefan , Staudacher Stephan
Published: March 2009

The comparison of possible turbofan engine architectures is a vital task during the preliminary design phase of such new products. Already at this point of the product life cycle the architectural decisions which are based on a minimum of product information define a major part of the product life cycle cost. For turbofan engines unit cost is a major part of the life cycle cost. It is not sensible to thrive for a detailed cost assessment in such an early design phase, since neither the required information nor the required time would be available for such an exercise. Hence a cost comparison method is required which produces results of adequate accuracy and detail based on a less complex estimation methodology. The cost comparison methodology proposed in this paper is based on the requirements and methods of a detailed cost assessment. The required information and a possible method for a detailed assessment have been analyzed. In a second step a simplification of the detailed assessment has been derived. This simplified approach uses a minimized set of product data and relies on the similarity of product parts and sub-structures. It turns out that intense thoughts regarding the suitable structuring of the end product turbofan engine have been necessary to derive the method. The uncertainties of such an assessment and its limitations have been verified against a subset of parts of a modern aero engine. It is of importance to notice that the method is also based on the assumption that key parameters of the supply chain and the manufacturing and assembly of the Original Equipment Manufacturer (OEM) are constant. On one hand this restricts the method to a cost comparison method between architectures. The cost comparison methodology not only applies to engines which are manufactured using existing materials and manufacturing methods, but the estimation of the required data for the use of new materials and manufacturing methods still requires detailed analysis since the product structure and the detailed design may change significantly.
Laboratory Study of Premixed H2-Air and H2-N2-Air Flames in a Low-Swirl Injector for Ultra-Low Emissions Gas Turbines
Authors: Cheng R. K. , Littlejohn D.
Published: March 2009

The objective of this study is to conduct laboratory experiments on Low-swirl injectors (LSI) to obtain the basic information for adapting LSI to burn H2 and diluted H2 fuels that will be utilized in the gas turbines of the Integrated Gasification Combined Cycle (IGCC) coal power plants. The LSI is a novel ultra-low emission dry-low NOx combustion method that has been developed for gas turbines operating on natural gas. It is being developed for fuel-flexible turbines burning a variety of hydrocarbon fuels, bio-mass gases and refinery gases. Adaptation of the LSI to accept H2 flames is guided by an analytical expression derived from the flowfield characteristics and the turbulent flame speed correlation. Evaluation of the operating regimes of nine LSI configurations for H2 shows an optimum swirl number of 0.51 which is slightly lower than the swirl number of 0.54 for the hydrocarbon LSI. Using Particle Image Velocimetry the flowfields of 32 premixed H2-air and H2-N2-air flames were measured. The turbulent flame speeds deduced from PIV show linear correlation with turbulence intensity. The correlation constant for H2 is 3.1 and is higher than the 2.14 value for hydrocarbons. Analysis of velocity profiles confirms that the nearfield flow features of the H2 flames are self-similar. These results demonstrate that the basic LSI mechanism is not affected by the differences in the properties of H2 and hydrocarbon flames and support the feasibility of the LSI concept for hydrogen fueled gas turbines.
Effects of Particle Size, Gas Temperature and Metal Temperature on High Pressure Turbine Deposition in Land Based Gas Turbines From Various Synfuels
Authors: Crosby Jared M. , Lewis Scott , Bons Jeffrey P. , Ai Weiguo , Fletcher Thomas H.
Published: March 2009

Four series of tests were performed in an accelerated deposition test facility to study the independent effects of particle size, gas temperature, and metal temperature on ash deposits from two candidate power turbine synfuels. The facility matches the gas temperature and velocity of modern first stage high pressure turbine vanes while accelerating the deposition process. This is done by matching the net throughput of particulate out of the combustor with that experienced by a modern power turbine. In the first series of tests, four different size particles were studied by seeding a natural-gas combustor with finely-ground coal ash particulate. The entrained ash particles were accelerated to a combustor exit flow Mach number of 0.25 before impinging on a thermal barrier coated (TBC) target coupon at 1183°C. Particle size was found to have a significant effect on capture efficiency with larger particles causing significant TBC spallation during a 4-hour accelerated test. In the second series of tests, different gas temperatures were studied while the facility maintained a constant exit velocity of 170m/s (Mach = 0.23–0.26). Coal ash with a mass mean diameter of 3 μm was used. Particle deposition rate was found to decrease with decreasing gas temperature. The threshold gas temperature for deposition was approximately 960°C. In the third and fourth test series impingement cooling was applied to the backside of the target coupon to simulate internal vane cooling. Ground coal and petcoke ash particulates were used for the two tests respectively. Capture efficiency was reduced with increasing massflow of coolant air, however at low levels of cooling the deposits attached more tenaciously to the TBC layer. Post exposure analyses of the third test series (scanning electron microscopy and x-ray spectroscopy) show decreasing TBC damage with increased cooling levels. Implications for the power generation goal of fuel flexibility are discussed.
Management of an Industrial Facility Using an Artificial Neural Network Monitoring System
Authors: Hynes Rory , Seyedan Babak
Published: March 2009

The objective of this paper is to assess the optimum heat load capacity of a real CHP plant and provide recommendations to improve heat utilization and reduce costs using a computerized system. A simulation model based on component actual behaviour has been developed. The simulation model is capable of plant optimization that could lead to significant economic and energy consumption improvements. The general modular structural of the plant component is described together with a discussion of the results and cost analysis. In the second part, feasibility of the Artificial Neural Network (ANN) approach is evaluated. The data from the simulation model of the plant is used to train such an ANN model. Results from the conventional computer technique are compared with that of the direct method based ANN approach. The results indicate it is feasible to use ANN to predict plant-operating conditions. The ANN gives a good time response and performance prediction capability with change of boundary conditions. Significantly shorter computation time is obtained with the ANN compared to the physical model. The accuracy of the ANN output and its suitability for on-line monitoring of a CHP plant are discussed.
Alternative Fuel Considerations for Gas Turbine Combustion
Authors: Stuttaford Peter J.
Published: March 2009

Gas turbines have the advantage of being able to operate on a wide range of fuels. Given the escalating cost of conventional fuel sources such as natural gas, there is increasing interest in, and implementation of, systems burning lower cost fuel gases. There are significant combustor performance effects when utilizing different fuels. Flame stability, emissions, durability, and combustion dynamics are critical combustion parameters which must be controlled when varying fuel constituents. Significant emphasis continues to be placed on the use of liquefied natural gas (LNG) as well as syngas derived from coal and petroleum coke. The elimination of carbon from gaseous coal based fuels also offers the possibility of burning hydrogen to reduce or eliminate carbon dioxide emissions. Existing stringent emissions permits must be met by power plants utilizing these different fuels. There is also a requirement for the flexible use of these fuels allowing power plants to switch real time between fuel sources using the same combustion hardware, without affecting commercial generating schedules. This highlights the requirement for fuel preparation and control skids, as well as robust combustion systems, for reliable plant operations. The objective of this work is to review fuel properties which affect combustion and consider the methods and tools used to characterize the subsequent combustion characteristics. The work focuses on gaseous fuel premixed combustion. A full scale high pressure combustion test stand was used to evaluate the effects of various gaseous fuels on given gas turbine combustor configurations. Data collected through the testing of natural gas containing heavy hydrocarbons, as might be expected from liquefied LNG or refinery offgas, and hydrogen based syngas fuel blends with natural gas to simulate various coal gas blends, is presented with conclusions drawn based upon the critical combustion parameters mentioned above. A methodology for fuel characterization and combustor qualification for the acceptable operation of gas turbine combustors on various gaseous fuels is discussed. The practical implementation of multi-fuel systems on commercially operating engines is also discussed, with emphasis on diluent free premixed systems.
Effect of Fuel Cell Operating Parameters on the Performance of a Multi-MW Solid Oxide Fuel Cell/Gas Turbine Hybrid System
Authors: Karvountzi Georgia C. , Ferrall Joe , Powers James D.
Published: March 2009

The principal planar solid oxide fuel cell operating parameters are pressure, stack temperature and temperature gradient, cell voltage, fuel utilization, leakage rate and percentage of internal reforming. This paper shows the effects of these parameters on overall fuel cell/gas turbine hybrid system performance. The baseline conceptual system used to investigate these parameters is a 500MW hybrid system. The system performance was simulated using ASPEN Plus and GateCycle™ commercial software platforms and a GE developed FORTRAN code to simulate the fuel cell performance. Parameter choices for the baseline case are: 15atm pressure, 725°C average cell temperature, 150°C stack temperature rise, 0.75V average cell voltage, 80% fuel utilization, 1% leakage rate and 70% internal reforming. At these conditions, the system efficiency is predicted at approximately 65.8%. The addition of a steam turbine bottoming cycle, increases the hybrid system efficiency by 4% to 70%. Increasing the average cell voltage to 0.8V or the percentage of internal reforming to 90% also increases the hybrid system efficiency to nearly 70%. The optimum pressure for maximum efficiency is 8 atm for the hybrid system; the optimum pressure for the hybrid with a steam turbine bottoming cycle is 9 atm. While increasing the SOFC temperature rise, cell voltage, and percentage of internal reforming improve system efficiency, they may adversely affect stack cost and reliability; these competing effects must be traded when designing a practical system.
Combustion Control and Diagnostics Sensor Testing in a Thermal Barrier Coated Combustor
Authors: Chorpening B. T. , Dukes M. G. , Pich P. , Thornton J. D.
Published: March 2009

The combustion control and diagnostics sensor (CCADS) continues to be developed as an in-situ combustion sensor, with immediate application to natural gas fired turbines. In-situ combustion monitoring is also expected to benefit advanced power plants of the future, fueled by coal-derived syngas, liquified natural gas (LNG), hydrogen, or hydrogen blend fuels. The in-situ monitoring that CCADS provides can enable the optimal operation of advanced, fuel-flexible turbines for minimal pollutant emissions and maximum efficiency over the full operating range of an advanced turbine. Previous work has demonstrated CCADS as a useful sensor for in-situ monitoring of natural gas combustion, including detection of important combustion events such as flashback and lean blowoff, in experimental combustors without thermal barrier coatings (TBC). Since typical TBC materials are electrical insulators at room temperature, and CCADS operation requires conduction of electrical current to the walls of the combustor, a TBC on the combustion liner was identified as a potential barrier to CCADS operation in commercial application. This paper reports on CCADS experiments in a turbulent lean premixed combustor with a yttria-stabilized zirconia (YSZ) thermal barrier coating on the combustor wall. The tests were conducted at 0.1 MPa (1 atm), with a 15V excitation voltage on the CCADS electrodes. The results confirm that for a typical thermal barrier coating, CCADS operates properly, and the total measured average resistance is close to that of an uncoated combustor. This result is consistent with previous materials studies that found the electrical resistance of typical TBC materials considerably decreases at combustor operating temperatures.
Combination of Fourier-Domain Optical Coherence Tomography and Photo-Stimulated Luminescence Piezo-Spectroscopy as an NDE Tool for Thermal Barrier Coatings
Authors: Vakhtin Andrei B. , Peterson Kristen A. , Kane Daniel J. , Jordan Eric H. , Hansen Geoffrey , Teicholz Matthew
Published: March 2009

A combination of two optical methods — Fourier-domain optical coherence tomography (FD-OCT) and photo-stimulated luminescence piezo-spectroscopy (PLPS) is used as a non-destructive evaluation (NDE) tool for thermal barrier coatings (TBC). This research is focused on NDE of electron beam physical vapor deposition (EB-PVD) TBC’s. FD-OCT is an interferometric technique, which uses spectrally broadband visible or infrared light to obtain spectrally resolved interferograms of the light that is back-scattered from subsurface structures and defects (e.g., interfaces, cracks, voids) in optically translucent material. When the Fourier transform is applied to the interferogram, a depth-resolved image of the back-scattering sites is obtained. FD-OCT is shown to be a useful NDE tool that can profile the top coat-metal substrate interface and measure the top coat thickness. Also, it has the potential of assessing microcracking and spallation damage. PLPS provides quantitative information on stress in the thermally grown oxide (TGO) by measuring the spectral shifts in the laser-induced luminescence spectra of the Cr3+ ions present in the TGO. When combined, the PLPS and FD-OCT methods can provide a set of important input parameters for the TBC remaining life predicting model. Ultimately they will collect spatially resolved data on matching spatial domains. The two optical methods are applied to thermally cycled EB-PVD TBC samples. The experimental results are compared to destructive inspection data.
Optimal Configuration Design of Gas Turbine Cogeneration Plants by a MILP Decomposition Approach
Authors: Yokoyama Ryohei
Published: March 2009

To attain the highest economic and energy saving characteristics of gas turbine cogeneration plants, it is necessary to rationally determine capacities and numbers of gas turbines and auxiliary equipment in consideration of their operational strategies corresponding to seasonal and hourly variations in energy demands. Some optimization approaches based on the mixed-integer linear programming (MILP) have been proposed to such configuration design problems of energy supply plants. However, with increases in the numbers of the equipment which must be considered as candidates as well as the periods which must be set for variations in energy demands, the optimal configuration design problems become too large-scale and complex to solve. The author has proposed a MILP decomposition approach to obtain quasi-optimal solutions of the optimal configuration design problems in reasonable computation times. However, this approach has been limited to the optimal configuration design problems where equipment capacities are treated continuously. In this paper, the MILP decomposition approach is extended to the optimal configuration design problems where equipment capacities are treated discretely. The effectiveness of this extended approach is investigated through a numerical study on a gas turbine cogeneration plant.
Automatic Risk Assessment Methodology for Gas Turbine Engines Employing Adaptive Recursive Triangulation
Authors: Moody Jonathan P. , Millwater Harry R. , Enright Michael P.
Published: March 2009

A new automatic methodology for the risk assessment of gas turbine engine rotor disks subject to metallurgical defects is being investigated. This method has the promise of significantly reducing the amount of human time required to discretize the disk material into zones and to manually refine the zones to ensure convergence. The method is based on the concept of adaptive recursive triangulation which requires only limited initial defect locations from the analyst. Regions of refinement are selected based upon several criteria and various subdivision schemes are investigated. A numerical example using a rotor disk model is presented.
Study of Transient Characteristic of a Simple Rigid Rotor Supported on a Squeeze Film Damper With Valvular Metal Rubber Squeeze Film Ring
Authors: Ma Yanhong , Hong Jie , Zhang Dayi , Wang Hong
Published: March 2009

An efficient oil film damper known as a squeeze film damper with valvular metal rubber squeeze film ring (SFD/VMR) was developed for more effective and reliable vibration control, and especially for improving the blade loss dynamics of high-speed rotors based on the conventional squeeze film damper (SFD). The immobile squeeze film ring of the SFD was replaced by the elastic squeeze film ring with the valvular metal rubber subassembly (VMR) of the SFD/VMR. The squeeze film force properties of the SFD/VMR was improved, because it can passively adjust the squeeze film clearance by taking advantage of the elastic deformation of the VMR and can control the squeeze film clearance in a suitable range. The characteristics of squeeze film stiffness and damping coefficients, as well as the steady-state unbalance response of a simple rigid rotor supported on SFD/VMR and SFD, were reported in a previous literature[1]. In this paper, the transient response of the rigid rotor supported on SFD/VMR and SFD subjected to sudden unbalance of blade loss are inverstigated. Time transient simulation and experimental results indicated that SFD/VMR can operate effectively under much greater unbalance compared with SFD, especially under relative large impact loads of blade loss. The SFD/VMR can suppress the occurrence of the nonlinear vibration phenomenon markedly, such as the bistable jump up phenomenon. Furthermore, the effective eccentricities of SFD/VMR with small transfer ratio (T<1.2) extend to two times of SFD, and optimum film stiffness and damping distribution within the whole film clearance can be achieved.
Subgrid Modeling of Soot Formation in Non-Premixed Turbulent Flames
Authors: El-Asrag H. , Menon S.
Published: March 2009

A subgrid model for soot dynamics is developed for large-eddy simulation (LES) using the Method of Moment with Interpolative Closure (MOMIC). The soot model is implemented within a subgrid mixing and combustion model so that reaction-diffusion-MOMIC coupling is possible without requiring ad hoc filtering. The combined model includes the entire process, from the initial phase, when the soot nucleus diameter is much smaller than the mean free path, to the final phase, after coagulation and aggregation, where it can be considered in the continuum regime. The soot diffusion and the effect of the thermophoretic forces are included in the model. A relatively detailed but reduced kinetics for ethylene-air is used to simulate an experimentally studied non-premixed ethylene/air jet diffusion flame. In this formulation, acetylene is used as a soot precursor species. The soot volume fraction order of magnitude, the location of its maxima, and the soot particle size distribution are all captured reasonably. Along the centerline, an initial region dominated by nucleation and surface growth is established followed by an oxidation region. A possible initial log-normal distribution followed by a more gaussian distribution downstream the centerline is observed. Limitations of the current approach and possible solution strategies are also discussed.
Internal and Film Cooling of a Flat Plate With Conjugate Heat Transfer
Authors: Na S. , Williams B. , Dennis R. A. , Bryden K. M. , Shih T. I.-P.
Published: March 2009

Computations were performed to study the internal and film cooling of a flat plate with and without thermal-barrier coating (TBC) that account for the heat transfer in the gas and in the solid. The goal is to understand the effects of the conjugate heat transfer on the temperature distribution in the region about the film-cooling hole and in the region further downstream of a row of film-cooling holes. Results obtained show that when there are no TBC, conduction heat transfer in the plate smears out the adverse effects of hot-gas entrainment by the film-cooling jet. When there is a TBC, the surface temperature and the temperature in the super alloy are greatly reduced because of the low thermal conductivity of the ceramic top coat (CTC), but the temperature gradient, which is nearly aligned with the X-axis further away from the film-cooling hole, turns towards the side of the flat plate with internal cooling, which alters the thermal stress distribution. Reducing the thermal conductivity of the CTC by a factor of 10 was found to increase slightly instead of decrease the surface temperature. This computational study is based on the ensemble average continuity, Navier-Stokes, and energy equations closed by the ideal gas equation of state and the two-equation realizeable k-ε turbulence model for the gas phase and the Fourier equations for conduction in the solid phase.
Momentum-Preserving Shaped Holes for Film Cooling
Authors: Shih T. I.-P. , Na S.
Published: March 2009

Shaped holes increase film-cooling effectiveness by using the Coanda effect to make the cooling jet stay attached to the surface and an expanding flow cross-sectional area about the hole exit to make the cooling jet spread out laterally so that more surface can be cooled. Though shaped holes increase lateral spreading, downstream penetration of the coolant is reduced because the expanding cross-sectional area decreased the momentum of the cooling flow. This paper presents a new shaped-hole design concept to enable increased lateral spreading as well as greater downstream penetration. The new shaped-hole design concept involves a W-shaped cross-sectional area in which the middle part of the W-shape protrudes and widens as the W-shaped hole widens. The goal is to keep the film-cooling flow cross-sectional area nearly constant as the shaped hole widens so that momentum can be preserved to increase both lateral and streamwise coverage of the film-cooling jet. To examine the usefulness of this design concept, CFD analyses were performed for two W-shaped holes. In one design, the W-shaped hole is similar to traditional shaped holes except that the middle part of the shaped hole is protruded to form the W shape. In the other design, the W-shaped hole continues as a shallow trench that is aligned with the main flow direction to minimize the entrainment of hot gases and to reduce pressure drag and aerodynamic interference. Computed results show the W-shaped-hole design concept to be promising in enhancing surface adiabatic effectiveness.
Transition Mechanisms in Separation Bubbles Under Low and Elevated Freestream Turbulence
Authors: McAuliffe B. R. , Yaras M. I.
Published: March 2009

Through numerical simulations, this paper examines the nature of instability mechanisms leading to transition in separation bubbles. The results of two direct numerical simulations are presented in which separation of a laminar boundary layer occurs over a flat surface in the presence of an adverse pressure gradient. The primary difference in the flow conditions between the two simulations is the level of freestream turbulence with intensities of 0.1% and 1.45% at separation. In the first part of the paper, transition under a low-disturbance environment is examined, and the development of the Kelvin-Helmholtz instability in the separated shear layer is compared to the well-established instability characteristics of free shear layers. The study examines the role of the velocity-profile shape on the instability characteristics and the nature of the large-scale vortical structures shed downstream of the bubble. The second part of the paper examines transition in a high-disturbance environment, where the above-mentioned mechanism is bypassed as a result of elevated freestream turbulence. Filtering of the freestream turbulence into the laminar boundary layer results in streamwise streaks which provide conditions under which turbulent spots are produced in the separated shear layer, grow, and then merge to form a turbulent boundary layer. The results allow identification of the structure of the instability mechanism and the characteristic structure of the resultant turbulent spots. Recovery of the reattached turbulent boundary layer is then examined for both cases. The large-scale flow structures associated with transition are noted to remain coherent far downstream of reattachment, delaying recovery of the turbulent boundary layer to an equilibrium state.
Observations of Transition Phenomena on a Controlled Diffusion Compressor Stator With a Circular Arc Leading Edge
Authors: Henderson Alan D. , Walker Gregory J.
Published: March 2009

Laminar-turbulent transition behavior is studied near the leading edge of an outlet stator blade in a low-speed 1.5-stage axial-flow research compressor. The stator is a typical controlled diffusion design with a circular arc leading edge profile. Slow response surface pressure distribution measurements are compared with numerical predictions from the quasi two-dimensional flow solver, MISES. These both show a strong flow acceleration around each side of the circular arc, followed by a rapid deceleration near each blend point of the arc to the main surface profile. The relative magnitude of the localized overspeeds varies significantly over the wide range of stator flow incidence investigated. The unsteady boundary layer behavior on the stator is studied using a midspan array of surface-mounted hot-film sensors. On the suction surface, wake-induced transitional and turbulent strips are observed to originate close to the leading edge. The boundary layer approaches separation near the leading edge blend point on the suction surface, but this does not always lead to localized turbulent breakdown or continuous turbulent flow: a significant portion of the flow on the forward part of the surface remains laminar between the wake-induced transitional strips. At high positive incidence the wake-induced transitional strips originate near the leading edge blend point, but their growth is suppressed by the strong flow acceleration. On the pressure surface, a small separation bubble forms near the leading edge blend point resulting in almost continuous turbulent flow over the whole incidence range studied.
Basic Analysis of Tip Leakage Mixing Loss
Authors: Shao Weiwei , Ji Lucheng , Cheng Ronghui
Published: March 2009

A simple model for tip leakage mixing loss of unshrouded blades for compressible flow is presented. The work draws ideas, is based on the theoretical analysis of the loss by Denton. Relationship for computing the loss is derived, in terms of blade surface static pressure, chordwise distribution of tip clearance, discharge coefficient and total pressure loss coefficient in the tip region. Parameter studies reveal average level and chordwise distribution of the above factors’ contribution to the loss. Results clearly indicate the governing variables and mechanisms which drive tip leakage mixing loss. Combined clearance and blade loading study is developed, most excitedly, an important parameter is put forward, which can reflect synthetically the influence of blade loading and tip clearance distribution on the tip leakage mixing loss.
Combustion Characteristics of Small Size Gas Turbine Combustor Fueled by Biomass Gas Employing Flameless Combustion
Authors: Hiramatsu Masato , Nakashima Yoshifumi , Adachi Sadamasa , Yamasaki Yudai , Kaneko Shigehiko
Published: March 2009

One approach to achieving 99% combustion efficiency (C.E.) and 10 ppmV or lower NOx (at 15%O2) in a micro gas turbine (MGT) combustor fueled by biomass gas at a variety of operating conditions is with the use of flameless combustion (FLC). This paper compares experimentally obtained results and CHEMKIN analysis conducted for the developed combustor. As a result, increase the number of stage of FLC combustion enlarges the MGT operation range with low-NOx emissions and high-C.E. The composition of fuel has a small effect on the characteristics of ignition in FLC. In addition, NOx in the engine exhaust is reduced by higher levels of CO2 in the fuel.
Active Combustion Control by Fuel Forcing at Non-Coherent Frequencies
Authors: Umeh Chukwueloka O. , Kammer Leonardo C. , Barbu Corneliu
Published: March 2009

One impediment to substantially further the reductions in NOx emissions for aviation gas turbine engines is thermal-acoustic instabilities, also referred to as combustion dynamics. Dynamics arise due to the coupling of heat and pressure fluctuations in such systems. Numerous passive and semi-active control schemes, including performance de-rating and fuel staging, have been developed for land-based gas turbine engines. However, many of these schemes are not well suited to aviation engines, as a result of their weight and bulk. Observations of several combustors operating on either gaseous or liquid fuels show that the dominant dynamic frequencies have a special relation to specific non-coherent lower frequencies. Experiments show that combinations of two of these non-coherent frequencies form the dominant tones of the combustor. As part of NASA’s intelligent engines program, active combustion control is used to mitigate dynamics, as the combustor’s bulk fuel-air ratio (FAR) is made leaner in an effort to reduce NOx emissions by about 85% below the Committee on Aviation Environmental Protection (CAEP) 6 limit. In the feedback control scheme suggested in this paper, a small percentage of the overall fuel flow is pulsed at a given non-coherent frequency and with varying amplitude. The effectiveness of the dynamics reduction approach has been demonstrated via preliminary open loop control tests on a liquid-fuelled partially premixed high-pressure combustion test rig at GE Aviation in Evendale, Ohio.
Vane-to-Vane and Blade-to-Blade Indexing of a Highly-Loaded Two-Stage Turbine
Authors: Blaszczak Jaroslaw R.
Published: March 2009

In order to obtain better performances of multistage modern turbomachines, the understanding of an influence of different geometry configurations is essential. The experimental work presented herein was a continuation of earlier studies (starting from 1990’s) on effects of different geometry configurations, especially the stator-to-stator indexing effect (also referred to as a clocking effect). Likewise as in earlier tests, for comparison reasons, a turbine with two identical stages was investigated. This time special attention was drawn to rotor-to-rotor clocking influences on the overall performance of the two-stage low-pressure turbine of a new design and a comparison to the stator-to-stator indexing benefit. The results were compared to the classical design positions of stators and rotors. The measurements presented in this paper were performed at the nominal speed and some off-design rotational speeds of the machine. The rotor-to-rotor indexing turned out to be more advantageous than the stator-to-stator clocking and only a slight change in the rotor position is needed to yield higher efficiency.
Investigation of the Effect of Incomplete Droplet Prevaporisation on NOx Emissions in LDI Combustion Systems
Authors: Beck Christian H. , Koch Rainer , Bauer Hans-Joerg
Published: March 2009

The influence of incomplete liquid fuel prevaporisation on the emissions of nitric oxides in a swirl stabilized model gas turbine combustor is investigated experimentally and numerically. The design of the model combustor enables the variation of the degree of prevaporisation. This is achieved by using two liquid fuel injectors. One injector is located far upstream of the flame and generates a fully prevaporized and premixed air fuel mixture. The second injector is located at the combustor inlet. Consequently, the liquid fuel mass flow split between the two injectors determines the fraction of non-prevaporized fuel present in the reaction zone. The NO/NO2 measurements were performed with a chemo-luminescence analyzer. In accordance to the findings of other workers, our experimental study revealed that the influence of prevaporization on nitric oxide emissions is of significance for practical applications. The experimental studies were accompanied by numerical studies of partially prevaporized lean combustion in an abstracted configuration. Purpose of this study is to gain detailed understanding of the influence of droplet slip on droplet flame position and peak temperature. The droplet slip velocity was found to have a significant impact on the peak temperature of the droplet flame and, therefore, NO formation rates within the droplet flame. The combustion system used for the experimental investigation was characterized regarding droplet slip velocities with an extended LDA technique. The comparison between numerical and experimental results shows that the droplet slip velocities in the macroscopic reaction zone are within the transition range from an envelope to a wake flame. It is concluded that small-scale mixing effects play a significant role in the formation of nitric oxides in spray combustion systems with incomplete prevaporization.
Cyclic Lifetime Validation of Annular Combustor Liner Segments for Heavy Duty Gas Turbines
Authors: Hughes Martin , Riccius Oliver , Moobola Roy , Kuehn Ingo , Schneider Lothar
Published: March 2009

The cyclic lifetime of combustor liner segments for heavy duty gas turbines has been validated by means of full scale high pressure testing. This testing is part of a systematic combustor component validation ensuring top quality designed parts and a proper integration into the advanced GT24 and GT26 gas turbines. The accuracy of lifetime predictions for such components is highly dependent on the quality of the predicted temperature profiles and induced stress-strain distributions. Three-dimensional computer simulations of both hot combustion gas flows and high velocity cooling air provide detailed knowledge of the flow and temperature fields within a combustor. When linked to finite element representations of the mechanical structure, the resulting models can be used to give predictions of interface contact behaviour, coating integrity, creep deformation and fatigue lifetime. Full size component testing under representative engine conditions provides a means to ensure that a component fulfils its design objective. It also provides a substantiation of the design rules and the analytical models used for combustor liner lifetime prediction. The physical size, and the long time period needed to accumulate a representative number of cycles limits the practicality of full cyclic lifetime component testing in heavy duty gas turbine engines. Rig testing of parts provides a means of lifetime testing at reasonable cost and provides additional advantages relating to monitoring, instrumentation, flexibility and speed. An annular combustor sector test rig operating at high pressure in a cyclic mode and cycling between low and high firing temperatures has been used to cyclically test a single-burner sector of the first GT26 combustor, the so called EnVironmental (EV) combustor. The automatic control and monitoring system allowed accurate and consistent cycling conditions to be maintained. Continuous data logging provided an evolving picture of the conditions being experienced by the components. Between test runs, visual examinations and measurements were carried out by boroscope to assess the structural behaviour. Detailed modelling of the temperature field over the liner allowed the local stress-strain response to be predicted using a Robinson unified material model. Fatigue crack development was simulated by finite element analysis incorporating the effects of accumulated residual stresses. Close correspondence has been demonstrated between the measured temperatures and the predicted temperature fields for the testing conditions used. Regular visual examination of the development of damage during the course of the test has confirmed the accuracy of the mechanical integrity analysis process. Knowledge of the relationship between rig testing conditions and normal engine operating conditions has confirmed the ability of the combustor parts to exceed the specified cyclic life even under the severe conditions used in the test.
Environmental Barrier Coatings for Monolithic Silicon Nitride: Bond Coat Development
Authors: Bhatia Tania , Srinivasan G. V. , Tulyani Sonia V. , Barth Robert A. , Vedula Venkat R. , Tredway William K.
Published: March 2009

Environmental barrier coatings (EBCs) are being developed for silicon carbide (SiC) based composites and monolithic silicon nitride (Si3N4) to protect against the accelerated oxidation and subsequent silica volatilization in high temperature high-pressure steam environments encountered in gas turbine engines. It has been found that the application of EBCs developed for SiC-based composites (EBCSiC) to monolithic silicon nitride results in a loss of room temperature mechanical strength of the monolithic substrate. In this paper, we discuss the development of a bond coat system tailored for monolithic silicon nitride that helps retain the strength of the substrate. Some of the unique requirements and challenges associated with the processing of non-line-of-sight EBCs for Si3N4 will also be discussed. Preliminary results from coating of airfoils will be presented.
A Microturbine Cogeneration Package for Japanese Market
Authors: Kataoka Tadashi , Nakajima Teruyuki , Sakata Shigeru , Kishikawa Tadahiko
Published: March 2009

This paper presents the specifications, design, verification testing and performance of a microturbine cogeneration package that conforms to Japanese laws, standards and codes. Elliott microturbine engine was adopted to the package, and peripheral equipments such as a low noise enclosure, a recuperator, a power conditioning system (PCS), a fuel gas compressor and heat recovery equipments were developed. Verification tests such as a containment test, an over speed trip test, a drop load test, pressure tests and strength calculations were conducted under the supervision of an inspection agency, and certified to satisfy requirements of the Japanese technical standards of gas turbines for power generation and microturbines. Other verification tests for the PCS and the fuel gas compressor were conducted, and electric power companies and gas companies accepted that the equipments were conformed to each technical standard. This paper also presents numerous novel features of the package such as low noise, low vibration, alternative heat output of hot water or steam, easy engineering, installation and maintenance.
Experimental and Numerical Investigation on Overall Performance of a Radial Inflow Turbine for 100kW Mircoturbine
Authors: Deng Qinghua , Niu Jiufang , Mao Jingru , Feng Zhenping
Published: March 2009

This paper describes a study on overall performance of the radial inflow turbine for a 100kW microturbine by means of experimental and numerical investigations. All tests are performed with a turbine inlet temperature of 773K and an atmospheric exit pressure, and the rotor rotational speed is ranged from 20000 to 50000 rpm. In addition, the overall performance and the energy loss characteristics for each component of the radial inflow turbine are investigated by 3D Reynolds-averaged Navier-Stokes solutions. The volute, the whole passages of nozzle vanes and rotor, and the exhaust diffuser are meshed with multi-block structured grid. The results of numerical simulation agreed well, as a whole, with that of the experiment both for stage mass flow rate and stage total-static efficiency, which achieved the desired requirements of the design. Based on the results of numerical simulation, the losses of components and exit velocity are analyzed respectively at the off-design conditions. At turbine design point, the losses of volute, nozzle, rotor, exit velocity and exhaust diffuser are about 1.5%, 25%, 43%, 19.5%, 11% of the total loss, respectively, and the rotor incidence angle is basically at optimized value of −23.6°. The losses of rotor and exit velocity change significantly when stage expansion ratio or the rotational speed of rotor altered. In addition, the loss of volute is relative small in the nozzled radial inflow turbine, and then the effect of volute can be neglected in the process of thermal aerodynamic design.
Leading Edge Film Cooling and the Influence of Shaped Holes at Design and Off-Design Conditions
Authors: Wagner Guillaume , Ott Peter , Vogel Gregory , Naik Shailendra
Published: March 2009

Transient liquid crystal experiments have been carried out to measure the effectiveness and heat transfer characteristics of leading-edge film cooling for three different film cooling holes configurations at design and off-design incidence angle. The three configurations are based on the same representative leading edge model of a turbine blade, consisting of a symmetrical blunt body with a specific leading edge wedge angle. Film cooling is introduced from two rows of cooling holes, representative of a pressure-side row and a suction-side row. At design incidence, film cooling performances are symmetric. There is a jet lift-off situation and shaped holes significantly improve the film cooling performances because of a better lateral coverage and a reduced coolant momentum at the hole exit. At 5° off-design incidence angle, on the suction side, the situation is similar to that of a 0° incidence but with higher film cooling performances due to a reduced local blowing ratio. At 5° incidence on the pressure side, a beneficial interaction between the jets of the pressure side row appears. For middle and high blowing ratio, the film cooling performances are also better than 0° incidence. At 5° incidence on the pressure side, shaped holes also improve the film cooling performances in comparison to cylindrical holes.