bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Loading Level and Distribution on LPT Losses
Authors: Prakash C. , Cherry D. G. , Shin H. W. , Machnaim J. , Dailey L. , Beacock R. , Halstead D. , Wadia A. R. , Guillot S. , Ng W. F.
Published: August 2009

This paper reports the results of an experimental and analytical study dealing with the effect of loading level and distribution on low-pressure turbine (LPT) blade performance. Only a single blade row is considered here, and the study is conducted in a stationary linear cascade that simulates the aero characteristics of a modern LPT design. The loading level and distribution are systematically varied by changing the number of blades (solidity), the stagger angle, and the unguided turning angle. The exit Mach number for this high-speed test is set at 0.64. The Zweifel number ranges from ∼ 1 (nominal lift) to ∼ 1.27 (high lift). The Reynolds number (based on chord and exit velocity) is varied from ∼70,000 to ∼350,000, a range that is broad enough to cover typical cruise and take-off conditions. While some data is taken near the end-walls, the primary focus of this study is on measurements at the mid-span. In addition to the profile loss, measurements include static pressure distribution on the blade surface (loading) and flow visualization. Data demonstrates increased suction side separation and consequent high losses as the loading level increases, the loading is moved aft, or the Reynolds number decreases. Three-dimensional CFD simulations, in conjunction with a turbulence transition model, corroborate these findings.
Static Performance Characteristics and Rotordynamic Coefficients for a Four-Pad Ball-in-Socket Tilting Pad Journal Bearing
Authors: Harris Joel , Childs Dara
Published: August 2009

Static performance characteristics and rotordynamic coefficients were experimentally determined for a four-pad, spherical-seat, tilting-pad journal bearing in load-between-pad configuration. Measured static characteristics include journal static equilibrium position, estimated power loss, and trailing-edge pad temperatures. Rotordynamic coefficients were determined from curve fits of measured complex dynamic-stiffness coefficients as a functions of the excitation frequency. A frequency-independent [M]-[C]-[K] model did a good job of fitting the measurements. Test conditions included speeds from 4 to 12 krpm and unit loads from 0 to 1896 kPa (0 to 275 psi). The bearing uses cool inlet oil to decrease the pad operating temperatures and increase the bearing’s load and speed capacity. The bearing has a nominal diameter of 101.78 mm (4.0070 in). Measurements indicated significant bearing crush with a radial bearing clearance of 99.63 μm (3.92 mils) in the axis 45° counterclockwise from the loaded axis and 54.60 μm (2.15 mils) in the axis 45° clockwise from the loaded axis. The pad length is 101.60 mm (4.00 in), giving L/D = 1.00. The pad arc angle is 73°, and the pivot offset ratio is 65%. Testing was performed using a test rig described by Kaul [1], and rotordynamic coefficients were extracted using a procedure adapted from Childs and Hale [2]. A bulk-flow Navier-Stokes model was used for predictions, using adiabatic conditions for the fluid in the bearings. However, the model assumes constant nominal clearances at all pads, and an average clearance was used based on measured clearances. Measured static eccentricities and attitude angles were significantly lower than predicted. Attitude angles varied from 6° to 39° and decreased with load. Power loss was well-predicted, with a maximum value of 25 kW (34 hp). The maximum detected pad temperature was 71°C (160°C) while the temperature rise from inlet to exit was over-predicted by 8°C (14°F). Direct stiffness and damping coefficients were significantly over-predicted, but the addition of a simple pivot-stiffness in series with the measured stiffness and damping values vastly improved the agreement between theory and experiment. Direct added masses were negative to a higher degree for Myy (y load direction) at low speeds and increased with speed. With the exception of Myy at zero load, they became positive before reaching 8,000 rpm. Although significant cross-coupled stiffness terms were present, they always had the same sign, producing a whirl frequency ratio of zero and netting unconditional stability over all test conditions.
Improved Performance of a Radial Turbine Through the Implementation of Back Swept Blading
Authors: Barr Liam , Spence Stephen W. T. , Eynon Paul
Published: August 2009

This report details the numerical investigation of the performance characteristics and internal flow fields of an 86 mm radial turbine for a turbocharger application. A new blade was subsequently designed for the 86 mm rotor which departed from the conventional radial inlet blade angle to incorporate a 25° inlet blade angle. A comparative analysis between the two geometries is presented. Results show that the 25° back swept blade offers significant increases in efficiency while operating at lower than optimum velocity ratios (U/C). This enhanced efficiency at off-design conditions would significantly improve turbocharger performance where the turbine typically experiences lower than optimum velocity ratios while accelerating during engine transients. A commercial CFD code was used to construct single passage steady state numerical models. The numerical predictions show off-design performance gains of 2% can be achieved, while maintaining design point efficiency. Primary and secondary flow patterns are examined at various planes within the turbine blade passage and reasons for the increase in performance are discussed. A finite element analysis has been conducted to assess the stress implications of introducing a non-radial angle at turbine rotor inlet. A modal analysis was also carried out in order to identify the natural frequencies of the turbine geometry, thus calculating the critical speeds corresponding to the induction of the excitational frequencies from the stator vanes. Although the new blade design has resulted in stress increases in some regions, the numerical study has shown that it is feasible from both an aerodynamic and structural point of view to increase the performance characteristic of a radial turbine through the implementation of back swept blading.
Static and Dynamic Performance of Pressure Dam Bearings With Dam Steps That Are (I) Square and (II) Filleted
Authors: Childs Dara , Schaible Andrew , Al Jughaiman Bader
Published: August 2009

Measured rotordynamic force coefficients (stiffness, damping, and added-mass) and static characteristics (eccentricity and attitude angle) are presented for two nearly identical pressure-dam bearings. One bearing has a square step at the dam; the other has a filleted step. Because of reduced manufacturing costs, the filleted-step design is used widely. The bearings’ groove dimensions are close to the optimum predictions of Nicholas and Allaire [2] and are consistent with current field applications. The bearings have a diameter of 117.1 mm (4.61 in), a length-to-diameter ratio of 0.655, and a nominal radial clearance of 0.133 mm (5.25 mils). The bottom pad has a deep, centered relief track over 25% of the pad’s axial length. The upper pad for both bearings has a step located at 130° from the horizontal and a 0.620 mm (15.75 mils) deep dam. The dam on the upper pad of one bearing has a square step; the other bearing has a filleted step. Test conditions include four shaft speeds (4000, 6000, 8000 and 10000 rpm) and bearing unit loads from 0 to 1034 kPa (150 psi). Laminar flow was produced for all test conditions within the bearing lands. For the same operating conditions, the filleted step bearing operates at a lower eccentricity ratio (has a larger minimum film thickness). The filleted step design has higher direct stiffness coefficients. Both cross-coupled stiffness coefficients are positive (favorable for stability) for both designs but the filleted design produces higher values. In regard to direct damping, the filleted-step design has higher damping in the load direction and comparable values in the unloaded direction. Hence, for the same operating conditions, a filleted step design should produce reduced amplitudes at or near a critical speed. With respect to stability as defined by WFR, the filleted design is consistently better (lower value) than the square step design, resulting in an elevated onset speed of instability for the filleted-step design.
Heat Transfer in an Impingement Cooling System for Turbine Airfoils With a Sparse Distribution of Holes
Authors: Alvarez Jose Javier , de la Calzada Pedro , Kohler S. T.
Published: August 2009

An experimental investigation of an engine representative Inter-Turbine Duct (ITD) vane with a very sparse distribution of impingement holes along the aerofoil surfaces was conducted using a transient liquid crystal technique. The low jet Reynolds numbers tested drove long crystal phase change times, which required special care when taking measured temperatures for processing the data to obtain accurate local heat transfer coefficients (HTC). Three jet Reynolds numbers (Re) around the design case were measured so that its local influence could be found. HTC results in terms of surface distribution and surface averaged values are presented and compared with some available literature correlations. Finally, an assessment is made of the extension of the local areas of influence where either impingement or duct flow prevails. The correlations which should be used in each of these influence areas are also identified and used to bound experimental results wihtin those limits.
Considerations of a Double-Wall Cooling Design to Reduce Sand Blockage
Authors: Land Camron C. , Thole Karen A. , Joe Chris
Published: August 2009

Gas turbine engines use innovative cooling techniques to keep metal temperatures down while pushing the main gas temperature as high as possible. Cooling technologies such as film-cooling and impingement cooling are generally used to reduce metal temperatures of the various components in the combustor and turbine sections. As cooling passages become more complicated, ingested particles can block these passages and greatly reduce the life of hot section components. This study investigates a double-walled cooling geometry with impingement and film-cooling. A number of parameters were simulated to investigate the success of using impingement jets to reduce the size of particles in the cooling passages. Pressure ratios typically ranged between those used for combustor liner cooling and for blade outer air seal cooling whereby both these locations typically use double-walled liners. The results obtained in this study are applicable to more intricate geometries where the need to promote particle breakup exists. Results indicated that ingested sand had a large distribution of particle sizes where particles greater than 150 μm are primarily responsible for blocking the cooling passages. Results also showed that the blockage from these large particles was significantly influenced and can be significantly reduced by controlling the spacing between the film-cooling and impingement cooling plates.
Ten Years of Experience With a Small Jet Engine as a Support for Education
Authors: Le´onard O. , Thomas J. P. , Borguet S.
Published: August 2009

In 1997 the Turbomachinery group of the University of Lie`ge decided to acquire a small jet engine to illustrate the courses in propulsion and to provide the students with the opportunity to get some experience in data measurement, acquisition and interpretation. Among others, the SR-30 engine from Turbine Technology Ltd. was chosen. It consists in a single spool, single flow engine with a centrifugal compressor, a reversed combustion chamber, an axial turbine and a fixed convergent nozzle. This engine was installed on a test bench allowing for manual control and providing fuel and oil to the engine. The original set-up included measurements of inter-component pressure and temperatures, EGT and rotational speed. Since then both the engine and the test bench have been deeply modified. These modifications were led by a triple objective: the improvement and the enrichment of the measurement chain, the widening of the engine’s operational domain and, last but not least, the wish to offer appealing, hands-on projects to the students. All these modifications were performed at University of Lie`ge and were conducted by the students, as part of their Master theses. Several performance models of the engine were developed to support data validation and engine condition diagnostic. This paper summarizes the developments conducted with and by the students, and presents the experience that was gained by using this engine as a support for education.
Mistuning Analyses of a Bladed Disk: Pole-Zero and Modal Approaches
Authors: Sinha Alok
Published: August 2009

This paper examines the fundamental aspects of amplitude amplification due to mistuning in a bladed disk. Both pole-zero and modal approaches are used to understand the effects of changes in mode shapes and the natural frequencies on the minimum and maximum values of peak amplitudes among all blades over all excitation frequencies. The nature of variation of this peak amplitude is studied, and algorithms are discussed to determine the statistics of the peak amplitude, maximum and minimum values of the peak amplitude, and corresponding mistuning patterns.
Investigation of Blade Tip Interaction With Casing Treatment in a Transonic Compressor: Part 2—Numerical Results
Authors: Schnell R. , Voges M. , Mo¨nig R. , Mu¨ller M. W. , Zscherp C.
Published: August 2009

A single-stage transonic axial compressor was equipped with a casing treatment, consisting of 3.5 axial slots per rotor pitch in order to investigate its influence on stall margin characteristics as well as on the rotor near tip flowfield both numerically and experimentally. Contrary to most other studies a generic Casing Treatment was designed to provide optimal optical access in the immediate vicinity of the CT, rather than for maximum benefit in terms of stall margin extension. The second part of this two-part paper deals with the numerical developments, and their validation, carried out in order to efficiently perform time-accurate casing-treatment simulations. The numerical developments focus on the extension of an existing coupling algorithm in order to carry out unsteady calculations with any exterior geometry coupled to the main flow passage (in this case a single slot) having an arbitrary pitch. This extension is done by incorporating frequency domain, phase-lagged boundary conditions into this coupling procedure. Whereas the phaselag approach itself is well established and validated for standard rotor-stator calculations, its application to casing treatment simulations is new. Its capabilities and validation will be demonstrated on the given compressor configuration, making extensive use of the detailed PIV flowfield measurements near the rotor tip. Instantaneous data at all measurement planes will be compared for different rotor positions with respect to the stationary slots in order to evaluate the time-dependent interaction between the rotor and the casing treatment.
Efforts to Improve Aerodynamics of the Large Cooling Tower Fan by Modifications of the Fan Stack
Authors: Ingistov Steve
Published: August 2009

This Paper describes the existing cooling air fan stack modification efforts. The cooling air fan is provided with a typical, standard dimension fan stack. The cooling air fan and its stack are integral parts of a cooling cell. The cooling cell in turn is an integral part of a large cooling water tower. The cooling water tower has seven cells. Each cooling air fan is furnished with a central “sealing plate”. This “sealing plate” rotates together with the fan. The “sealing plate” serves to reduce the discharge air leakage back to the fan suction plane. The fan manufacturer modified the “sealing plates” to further reduce parasitic losses. Only one fan (cell 3) was furnished by the fan manufacturer with an upgraded central “sealing plate” in the form of a dish. This last evolution of the “sealing plate” encouraged the introduction of a stationary, aerodynamically shaped central piece. This central piece would match the outside diameter of the existing rotating dish. The intent is therefore to minimize parasitic losses and simultaneously reduce the turbulence and the swirling of discharged air in the stack.
Effect of Water Vapor on the Kinetics of Combustion of Hydrogen and Natural Gas: Experimental and Detailed Modeling Study
Authors: Le Cong Tanh , Dagaut Philippe
Published: August 2009

The dilution of fuels by exhausts gases (mainly CO, CO2 and H2O) affects the kinetics of combustion. This dilution is used in gas turbines and flameless combustor. It helps reducing pollutant emissions, particularly NOx. Therefore, it is useful to study the effect of such compounds on the kinetics of oxidation of fuels such as natural gas and hydrogen. The oxidation of hydrogen and that of methane were studied experimentally in a fused silica jet-stirred reactor (JSR) over the temperature range 800–1500 K, from fuel-lean to fuel-rich conditions. The experiments were repeated in presence of 10% in mole of water vapor. A detailed chemical kinetic modeling of the present experiments and of literature data (flame speed, ignition delays) was performed using a previously proposed kinetic reaction mechanism, showing good agreement between the data and this modeling. Sensitivity and reaction paths analyses were used to delineate the important reactions influencing the kinetic of oxidation of the fuels in presence of water vapor. The kinetic reaction scheme proposed helps understanding the inhibiting effect of water vapor on the oxidation of hydrogen and methane. The effect of water vapor on NOx formation under gas turbine conditions was also investigated numerically using the proposed kinetic scheme.
Turbine Blade Platform Film Cooling With Typical Stator-Rotor Purge Flow and Discrete-Hole Film Cooling
Authors: Gao Zhihong , Narzary Diganta , Han Je-Chin
Published: August 2009

This paper is focused on the effect of film hole configurations on platform film cooling. The platform is cooled by purge flow from a simulated stator-rotor seal combined with discrete-hole film cooling within the blade passage. The cylindrical holes and laidback fan-shaped holes are assessed in terms of film cooling effectiveness and total pressure loss. Lined up with the freestream streamwise direction, the film holes are arranged on the platform with two different layouts. In one layout, the film cooling holes are divided into two rows and more concentrated on the pressure side of the passage. In the other layout, the film cooling holes are divided into four rows and loosely distributed on the platform. Four film cooling hole configurations are investigated totally. Testing was done in a five-blade cascade with medium high Mach number condition (0.27 and 0.44 at the inlet and the exit, respectively). The detailed film cooling effectiveness distributions on the platform was obtained using pressure sensitive paint (PSP) technique. Results show that the combined cooling scheme (slot purge flow cooling combined with discrete hole film cooling) is able to provide full film coverage on the platform. The shaped holes present higher film cooling effectiveness and wider film coverage than the cylindrical holes, particularly at higher blowing ratios. The hole layout affects the local film cooling effectiveness. The shaped holes also show the advantage over the cylindrical holes with lower total pressure loss.
Effect of Rib Spacing on Heat Transfer in a Two-Pass Rectangular Channel (AR=1:4) With a Sharp Entrance at High Rotation Numbers
Authors: Huh Michael , Liu Yao-Hsien , Han Je-Chin , Chopra Sanjay
Published: August 2009

The focus of the current study was to determine the effects of rib spacing on heat transfer in rotating 1:4 AR channels. In the current study, heat transfer experiments were performed in a two-pass, 1:4 aspect ratio channel, with a sharp bend entrance. The channel leading and trailing walls in the first pass and second pass utilized angled rib turbulators (45° to the mainstream flow). The rib height-to-hydraulic diameter ratio (e/Dh) was held constant at 0.078. The channel was oriented 90° to the direction of rotation. Three rib pitch-to-rib height ratios (P/e) were studied: P/e = 2.5, 5, and 10. Each ratio was tested at five Reynolds numbers: 10K, 15K, 20K, 30K and 40K. For each Reynolds number, experiments were conducted at five rotational speeds: 0, 100, 200, 300, and 400 rpm. Results showed that the sharp bend entrance has a significant effect on the first pass heat transfer enhancement. In the second pass, the rib spacing and rotation effect are reduced. The P/e = 10 case had the highest heat transfer enhancement based on total area, whereas the P/e = 2.5 had the highest heat transfer enhancement based on the projected area. The current study has extended the range of the rotation number (Ro) and local buoyancy parameter (Box) for a ribbed 1:4 aspect ratio channel up to 0.65 and 1.5, respectively. Correlations for predicting heat transfer enhancement, due to rotation, in the ribbed (P/e = 2.5, 5, and 10) 1:4 aspect ratio channel, based on the extended range of the rotation number and buoyancy parameter, are presented in the paper.
Numerical Investigation of Entropy Noise and Its Acoustic Sources in Aero-Engines
Authors: Mu¨hlbauer Bernd , Noll Berthold , Aigner Manfred
Published: August 2009

In the present work, the generation and propagation of entropy noise was simulated applying a compressible three dimensional URANS CFD approach. To this end, a test rig, the so-called Entropy Wave Generator (EWG) was modeled. The EWG implies a non-reactive tube flow where entropy modes are induced to the air flow by a heating module. The generated temperature nonuniformities are accelerated in a convergent-divergent nozzle and excite entropy noise. Simulation results of pressure fluctuations and power spectra in the standard configuration as well as simulations of different operating points of the EWG are in very good agreement with measurements. Additionally, entropy noise was deduced for realistic gas turbine conditions with calculated sound pressure level above 160 dB, which evidences the relevance of entropy noise in gas turbines. The numerical investigation is completed by the analysis of the acoustic sources. For this purpose the acoustic sources caused by the acceleration of density inhomogeneities suggested by Dowling [1] were calculated. Thus, for the first time a method is introduced to locate the acoustic sources of entropy noise in the acceleration region.
Microwave Turbine Tip Clearance Measuring System for Gas Turbine Engines
Authors: Maslovskiy Alexandr
Published: August 2009

For the last fifteen years various research groups have been trying to develop microwave systems that could be used for gas turbine engine condition monitoring and diagnostics. Such systems possess substantial advantages in comparison to other known systems and make possible to define rotor blades vibration parameters, discover blades rupture or their deformation, passing of foreign objects through air-gas channel, combustion chamber burnout as well as to define rotor rotation frequency and angular position. The article gives several examples of microwave systems use (detection of foreign objects in air-gas channel, dents in rotor blades) and results of experiments carried out by us. At present time we work on industrial microwave systems that will be used for measuring of tip clearance on ground and aircraft turbines. The article offers an analysis of microwave systems operation when performing measurements on shrouded and shroudless blades. It describes design concept of microwave system allowing measuring of tip clearance within the accuracy of 0.05 mm for each turbine blade for the whole rotation frequency range and under impact of high temperature and vibration. The results of measuring tip clearance on laboratory bench and gas generator of civil gas turbine engine are offered for consideration. The results of such tests make possible to consider the possibility of implementing proposed design of microwave turbine tip clearance measuring system in commercial equipment for test rigs that are used for gas turbine engine tests and fine tuning. The implementation of proposed design in aircraft version of the equipment is also considered.
Numerical Investigation of a Cryogenic Liquid Turbine Performance and Flow Behavior
Authors: Zhao Wei , Sun Jinju , Zhu Hezhao , Li Cheng , Cai Guocheng , Ma Guohong
Published: August 2009

A single stage cryogenic liquid turbine is designed for a large-scale internal compression air-separation unit to replace the Joule-Thompson valve and recover energy from the liquefied air during throttling process. It includes a radial vaned nozzle, and 3-dimensional impeller. Numerical investigation using 3-D incompressible Navier-Stokes Equation together with Spalart-Allmaras turbulence model and mixing plane approach at the impeller and stator interface are carried out at design and off-design flow. At design condition, recovered shaft power has amounted to 185.87 kW, and pressure in each component decreases smoothly and reaches to the expected scale at outlet. At small flow rates, flow separation is observed near the middle section of blade suction surface, which may cause local vaporization and even cavitation. To further improve the turbine flow behavior and performance, geometry parametric study is carried out. Influence of radial gap between impeller and nozzle blade rows, and nozzle stagger angle on turbine performance are investigated and clarified. Results arising from the present study provide some guidance for cryogenic liquid turbine optimal design.
Combined Cycle Power Plant Long Term Preservation Program: The Arauca´ria Power Station Study Case
Authors: Ferreira Jean Carlos Nunes , de Freitas Marcos , de Albuquerque Fernando Cavalcanti
Published: August 2009

Arauca´ria Power Station, a 484 MW CCPP, is powered by two NG-fired Siemens 501FD2 Combustion Turbines and one Alstom DKZ2-2N34 Steam Turbine. Located in Southern Brazil, near Curitiba, the capital of the State of Parana´, Arauca´ria PS was tested and accepted in September 2002. Due to commercial issues, the plant remained shut down since its COD until 2006. Along four years, the O&M team developed and implemented a comprehensive plant preservation program aiming to keep the equipment safe from degradation. The purpose of this paper is to describe the program and the activities performed during this period. The OEM recommendations were strictly followed. All the operations, tests and inspections were performed according to the Long Term Standby Procedure. The preventive, predictive and corrective maintenance performed in conformity with the Plant Maintenance Manual. Such activities were controlled by means of the corporative Computer-based Operations Management System and the CMMS and always in compliance of the ES&H regulations. The wooden structured cooling tower was maintained wet, the circulating water system was kept in operation, the demineralised water treatment system was run monthly and water microbiology/chemistry control (including the chemicals dosing and weekly water analysis schedule) was kept in accordance with the program designed by GE Water & Process Technologies. In a totally outdoor plant, corrosion prevention is fundamental. For this reason, a painting program designed by LACTEC, a local institute of technology, was followed. By the Plant Valves Lubrication and Tests schedules, each manual and automatic valve was lubricated and tested. The two Aalborg HRSGs (including condensate and steam piping) were maintained at minimum 0.5 barg dry nitrogen atmosphere. Dehumidifiers and heaters were installed in both HRSGs gas side, so the ambient conditions between the CTGs air inlet and the HRSGs stack inlet were maintained with relative humidity below 40%. Similar system was provided for the Steam Turbine. Both systems were automatically controlled and supervised from the Plant Control Room. When Arauca´ria PS was re-commissioned in mid-2006, this strict program proved its effectiveness once no major problems were found and the plant start-up succeeded in a very short time. The plant was operated since June, 2007 through January, 2008 with an average availability in excess of 98%. The long-term preservation program is presently being reviewed and many improvements shall be implemented in order to achieve faster installation/removal of high performance preservation systems, so they shall be used for short-term shutdown periods as well.
Shrink Fit Effects on Rotordynamic Stability: Theoretical Study
Authors: Jafri Syed Muhammad Mohsin , Vance John M.
Published: August 2009

This paper presents a theoretical model for analytical study of internal friction-induced whirl instability due to shrink fit and interference fit joints in rotating machines. It is the theoretical continuation of an experimental study on the effects of internal friction published in a companion paper. The theoretical study shows that the follower force internal friction model proposed by Gunter in 1965 is a physically incorrect model due to its inconsistency with Newton’s Third Law of Motion. The internal moments model proposed by Lund in 1976 to explain unstable sub-synchronous vibrations due to micro-slip in interference and shrink fit joints is physically consistent with the basic principles of mechanics and can explain rotordynamic instability due to internal friction in rotating machines. Rotordynamic simulations of the experimental single-disk and two-disk rotor based on an internal moments model are carried out using finite element based rotordynamics software. Rotordynamic simulations of the unstable experimental rotors using the linear viscous form of the internal moments model, with selected moment stiffness and damping parameters at the interface, result in correct prediction of the instabilities (negative real part of the damped eigenvalues).
Development and Testing of a 10 kW Diffusive Micromix Combustor for Hydrogen-Fuelled µ-Scale Gas Turbines
Authors: Funke H. H.-W. , Robinson A. E. , Ro¨nna U.
Published: August 2009

There is a growing need for devices with small weight and large power density as a substitute for today’s accumulators widely used for electrical tools or as thrust application in the aerospace industry e.g. for small unmanned aerial vehicles (UAV). Systems burning liquid or gaseous fuels and working after the principle of the Brayton cycle became more and more interesting as a new field of research (powermems devices). This ongoing miniaturization of power devices such as ultra micro gas turbines requires a reliable and safe combustion of fuels. A new test rig for micro scale combustion chambers has been realized and tested with a new hydrogen prototype burner for a 600 W μ-scale gas turbine. By preheating and pressurizing the flow realistic combustion chamber inlet conditions for the design point and for μ-scale gas turbine part load conditions can be realized. Furthermore the quartz glass prototype burner offers visual access to the flame region during operation at atmospheric condition. Detailed investigations on the burning characteristics for different chamber configurations were carried out for an optimization of the burner concept and gas turbine integration. By changing air mass flow and thermal energy the results allow a mapping of the combustion chamber for setting the control laws of the μ-scale gas turbine. The test results prove a very good flame stability and burning efficiency for the micromix principle covering a wide range of power settings including the design point. Even at extreme part load conditions it was possible to handle all the operating points of the proposed μ-scale gas turbine. Based on the prototype burner results a realistic combustion chamber design for μ-scale gas turbine integration will be presented.
Full 3D Conjugate Heat Transfer Simulation and Heat Transfer Coefficient Prediction for the Effusion-Cooled Wall of a Gas Turbine Combustor
Authors: Jeromin Andreas , Eichler Christian , Noll Berthold , Aigner Manfred
Published: August 2009

Numerical predictions of conjugate heat transfer on an effusion cooled flat plate were performed and compared to detailed experimental data. The commercial package CFX® is used as flow solver. The effusion holes in the referenced experiment had an inclination angle of 17 degrees and were distributed in a staggered array of 7 rows. The geometry and boundary conditions in the experiments were derived from modern gas turbine combustors. The computational domain contains a plenum chamber for coolant supply, a solid wall and the main flow duct. Conjugate heat transfer conditions are applied in order to couple the heat fluxes between the fluid region and the solid wall. The fluid domain contains 2.4 million nodes, the solid domain 300,000 nodes. Turbulence modeling is provided by the SST turbulence model which allows the resolution of the laminar sublayer without wall functions. The numerical predictions of velocity and temperature distributions at certain locations show significant differences to the experimental data in velocity and temperature profiles. It is assumed that this behavior is due to inappropriate modeling of turbulence especially in the effusion hole. Nonetheless, the numerically predicted heat transfer coefficients are in good agreement with the experimental data at low blowing ratios.
Material Temperature Limits and Convection Flow Requirements
Authors: LaFleur Ronald S.
Published: August 2009

Material temperature limits (MTL) influence the convection flow required to cool the surfaces of HPT parts. The goal of designing minimum-cooling-flow parts is pursued by stating two hypotheses. The ‘Minimum Cooling Hypothesis’ is that cooling flow is minimized by operating surface points at the material temperature limits (MTL). The ‘Isothermal Hypothesis’ states that for spatially uniform materials, the cooling flow is minimized if the limiting material interfaces are isothermal. Demand for convection cooling is measured using a new grouping called the convection flow parameter and theory, covering a variety of material design spaces, is presented to show how the film, metal and coating temperatures each contribute to the convection flow through and cooling technology effectivenesses. An example of film decay over turbulent flat plate demonstrates the stated MTL method satisfies the minimum cooling hypothesis and approaches the second hypothesis of isothermal interface surfaces over a large portion of the cooled surface. This condition of isothermal interfaces is a cornerstone of prior studies by the author on the iceformation design method dating back to 1983. With analogous iceformation geometries solved, their implementation in gas turbines depends on the designer’s ability to determine cooling distributions that provide isothermal material interfaces.
Impedance Boundary Conditions for the Numerical Simulation of Gas Turbine Combustion Systems
Authors: Widenhorn Axel , Noll Berthold , Aigner Manfred
Published: August 2009

The design process of modern gas turbine combustion systems relies more and more on CFD methods. To capture unsteady combustion phenomena like combustion instabilities or direct combustion noise both the reacting flow field and the acoustic field have to be modeled precisely. To take into account the accurate simulation of the acoustic wave reflection at a boundary condition time-domain impedance formulations have to be used. These conditions allow specifying the frequency depending impedance quantities for example of the fuel line, air supply system, combustion chamber outlet and walls in the time-domain. In the present paper the theory and the practical implementation of the time-discrete impedance formulation are discussed. Here, the link between the time and frequency domain is established by utilizing both the z-transform and Fourier transform. By means of simple test cases the physical effects of acoustically treated boundary conditions on the flow and acoustic field are worked out. Furthermore, the accuracy is analyzed and the need for such boundary conditions in the framework of gas turbine combustion system research and development is discussed.
Application of the Transient Heater Foil Technique for Heat Transfer and Film Cooling Effectiveness Measurements on a Turbine Vane Endwall
Authors: Jonsson M. , Charbonnier D. , Ott P. , von Wolfersdorf J.
Published: August 2009

The paper presents an application of the transient heater foil measurement technique using thermochromic liquid crystals (TLC) to endwall heat transfer and film cooling investigations in a transonic turbine vane cascade. The film cooling configuration consists of an upstream slot, representing the leakage flow area between the interface of the combustor and the turbine, and several rows of cylindrical and fan-shaped holes within the passage. With the transient method chosen, the heat transfer and adiabatic film cooling effectiveness distributions can be obtained simultaneously together with the local heat release within the heater foil. Therefore, the heat release in the foil is not required to be uniform, and the foil can contain discrete holes in the film cooling configuration. Some new developments are presented, which are directed towards improved application of the transient heater foil method for such a complex configuration. This includes tailoring the foil heat-release distribution towards the expected heat transfer patterns, supported by numerical Finite-Element computations and the use of a double-TLC mixture for improved time-wise TLC indications. Additionally, CFD-simulations were used to evaluate the recovery temperature distribution through the vane cascade without film cooling. The experiments were performed in the linear cascade facility at the EPFL-Lausanne. A compressor provides a continuous air flow at near-ambient temperature regulated with heat exchangers. Carbon dioxide is used as coolant in order to achieve engine-representative density ratio between coolant and main flow. Multiple experiments with the same main and coolant flow settings but varying heat flux levels and coolant injection temperatures have been performed and simultaneously analysed using nonlinear regression analysis. The time required between successive experiments to return to homogenous initial conditions, as required by the transient method, has been analysed using an analytical solution for heat-on-heat-off conditions. This permits the model assumption of one-dimensional conduction within a semi-infinite wall with a heat releasing layer on the top. Example results for cases without cooling, with film cooling from rows of discrete holes and the addition of slot film cooling are used to illustrate the benefit of the new approaches for the investigated vane cascade.
Optimizing Mixing for Maximum Damping of Fuel-Air Ratio Oscillations in Gas Turbine Premixers
Authors: Chishty Wajid A. , Yimer Ibrahim
Published: August 2009

An analytical model based on advection-diffusion volume is analyzed with the objective to investigate the limits of achievable damping in fuel-air ratio oscillations over the range of frequencies at which combustor thermoacoustic instabilities are normally encountered. Results show that there exists an optimum degree of diffusion that will allow maximum damping in fuel-air ratio fluctuations. The upper bound on damping is found to be dependent on a constant value of a new non-dimensional number, defined as a ratio between Peclet Number and Strouhal Number. The analysis presented here is considered useful to evaluate the extent of damping that is inherently obtainable in practical premixers. Also presented are the results of experimental investigations, which were conducted to verify the analytically predicted behavior of premixers. The measurements were performed over a selected range of frequencies using a premixer configuration with square cross section and with fuel jet issuing in a co-flowing bulk air stream. The effects of modulation amplitude and frequency, and pressure drop across the premixer on the damping effectiveness of the premixer were examined. Results show that for the test conditions considered, the modulation amplitude has a profound effect on the premixer performance, whereas pressure drop effects are insignificant.
Site Conversion and Field Performance of an Ultra-Low Emissions Combustion System for the MS7EA Gas Turbine
Authors: Benoit Jeffrey A.
Published: August 2009

Increasingly restrictive emission regulations for gas turbines are driving key technology decisions across the United States and Europe. For example, in Texas, United States, regulations are forcing permit holders in certain non-attainment areas to ratchet down industrial oxides of nitrogen (NOx) emission levels by over 80% by 2008. Improvements today in the technology of lean pre-mix combustion for gas turbines can result in reduction of NOx and carbon monoxide (CO) emissions to ultra-low levels without using Selective Catalytic Reduction (SCR’s) or Oxidation Catalysts (OCAT’s); and often provides the end user with the most cost effective solution to addressing these requirements. This paper describes the demonstrated current field performance of a dry, lean-premixed combustion system developed for direct replacement in MS7E/EA gas turbines previously configured with either the OEM’s DLN-1 combustion system or converted from a standard diffusion combustion system. The LEC-III® combustion system, developed by Power Systems Mfg. LLC (PSM), owned by Alstom, has proven sub-4ppm NOx and single digit CO emissions levels over the entire premix load operating range with natural gas fuel, from full load down to below 55% of full load conditions in customer machines. A recent conversion effort completed by PSM in 2006 & 2007 now has five gas turbines currently operating at a Texas industrial power producer operating at below 4ppm NOx with the LEC-III system. The conversion scope will also be detailed. Dynamic pressure sensing instrumentation was installed on each combustion chamber to measure and record combustion dynamic oscillations or “noise” to optimize fuel splits within each combustor. Rugged construction and performance optimization enable the dynamics to be maintained within acceptable limits to ensure extended service intervals of over 16,000 equivalent fired hours. Detailed field-installed emissions results are provided for this Frame 7E/EA LEC-III site. Finally an overview of PSM’s Combustion Technology Roadmap (CTR) will be discussed, which leverages their high-pressure, high-airflow test rig to evaluate technology improves with the objective of achieving guaranteed LEC-III combustion system NOx emissions below 3ppm NOx with low levels of CO.
Aerodynamics of a Letterbox Trailing Edge: Effects of Blowing Rate, Reynolds Number, and External Turbulence on Aerodynamic Losses and Pressure Distribution
Authors: Fiala N. J. , Johnson J. D. , Ames F. E.
Published: August 2009

A letterbox trailing edge configuration is formed by adding flow partitions to a gill slot or pressure side cutback. Letterbox partitions are a common trailing edge configuration for vanes and blades and the aerodynamics of these configurations are consequently of interest. Exit surveys detailing total pressure loss, turning angle, and secondary velocities have been acquired for a vane with letterbox partitions in a large scale low speed cascade facility. These measurements are compared with exit surveys of both the base (solid) and gill slot vane configurations. Exit surveys have been taken over a four to one range in chord Reynolds numbers (500,000, 1,000,000, and 2,000,000) based on exit conditions and for low (0.7%), grid (8.5%), and aero-combustor (13.5%) turbulence conditions with varying blowing rate (50%, 100%, 150%, and 200% design flow). Exit loss, angle, and secondary velocity measurements were acquired in the facility using a five-hole cone probe at a measuring station representing an axial chord spacing of 0.25 from the vane trailing edge plane. Differences between losses with the base vane, gill slot vane and letterbox vane for a given turbulence condition and Reynolds number are compared providing evidence of coolant ejection losses and losses due to the separation off the exit slot lip and partitions. Additionally, differences in the level of losses, distribution of losses, and secondary flow vectors are presented for the different turbulence conditions at the different Reynolds numbers. The letterbox configuration has been found to have slightly reduced losses at a given flow rate compared with the gill slot. However, the letterbox requires an increased pressure drop for the same ejection flow. The present paper together with a related paper [1], which documents letterbox heat transfer, is intended to provide designers with aerodynamic loss and heat transfer information needed for design evaluation and comparison with competing trailing edge designs.
Method for Sensitivity Analysis of Resonance Forced Response of Bladed Discs With Nonlinear Contact Interfaces
Authors: Petrov E. P.
Published: August 2009

An effective method has been developed to calculate sensitivity of the resonance peak frequency and forced response level to variation of parameters of nonlinear friction contact interfaces and excitation. The method allows determination of the sensitivity characteristics simultaneously with the resonance peak frequency and response level calculated as a function of any parameter of interest and without significant computational expense. Capabilities of the method are demonstrated on examples of analysis of large-scale finite element models of realistic bladed discs with major types of the nonlinear contact interfaces: (i) a blisk with underplatform dampers; (ii) a bladed disc with friction damping at blade fir-tree roots, and (iii) a high pressure bladed disc with shroud contacts. The numerical investigations show high efficiency of the method proposed.