bluuebunny/crossref_metadata_2025 huggingface dataset:
Aerodynamic and Heat-Flux Measurements With Predictions on a Modern One and 1/2 Stage High Pressure Transonic Turbine
Authors: Haldeman Charles W. , Dunn Michael G. , Barter John W. , Green Brian R. , Bergholz Robert F.
Published: November 2008

Aerodynamic and heat-transfer measurements were acquired using a modern stage and 1/2 high-pressure turbine operating at design corrected conditions and pressure ratio. These measurements were performed using the Ohio State University Gas Turbine Laboratory Turbine Test Facility (TTF). The research program utilized an uncooled turbine stage for which all three airfoils are heavily instrumented at multiple spans to develop a full database at different Reynolds numbers for code validation and flow-physics modeling. The pressure data, once normalized by the inlet conditions, was insensitive to the Reynolds number. The heat-flux data for the high-pressure stage suggests turbulent flow over most of the operating conditions and is Reynolds number sensitive. However, the heat-flux data does not scale according to flat plat theory for most of the airfoil surfaces. Several different predictions have been done using a variety of design and research codes. In this work, comparisons are made between industrial codes and an older code called UNSFLO-2D initially published in the late 1980’s. The comparisons show that the UNSFLO-2D results at midspan are comparable to the modern codes for the time-resolved and time-averaged pressure data, which is remarkable given the vast differences in the processing required. UNSFLO-2D models the entropy generated around the airfoil surfaces using the full Navier-Stokes equations, but propagates the entropy invisicidly downstream to the next blade row, dramatically reducing the computational power required. The accuracy of UNSFLO-2D suggests that this type of approach may be far more useful in creating time-accurate design tools, than trying to utilize full time-accurate Navier-stokes codes which are often currently used as research codes in the engine community, but have yet to be fully integrated into the design system due to their complexity and significant processor requirements.
A Repair Alternative for Worn Square-Base Compressor Vanes
Authors: Anderson Rodger O. , Willett Fred T.
Published: November 2008

Square base compressor vanes are a simple time-tested design and are in use in hundreds of large industrial gas turbines throughout the world. The square base of the vane fits inside a carrier slot machined into the compressor casing. Over time, the motion of the vane base, during operation and due to start-stop cycles, results in wear of both the vane base and the compressor casing. The classic solution to this wear problem is vane replacement and extensive repair of the casing either by welding or remachining and adding a patch ring. The square base compressor vane design is described, along with exemplary evidence of the wear problem. An alternative to the expensive repair is presented. The alternative approach addresses the root cause of the wear, i.e., the sliding motion at the vane base–casing interface. The vane contact is modeled with and without the solution to show, analytically, the benefit of the alternative approach. Successful field experience is also presented and discussed.
A Probabilistic Assessment of NASA Ultra-Efficient Engine Technologies for a Large Subsonic Transport
Authors: Tong Michael T. , Jones Scott M. , Arcara Philip C. , Haller William J.
Published: November 2008

NASA’s Ultra Efficient Engine Technology (UEET) program features advanced aeropropulsion technologies that include highly loaded turbomachinery, an advanced low-NOx combustor, high-temperature materials, intelligent propulsion controls, aspirated seal technology, and an advanced computational fluid dynamics (CFD) design tool to help reduce airplane drag. A probabilistic system assessment is performed to evaluate the impact of these technologies on aircraft fuel burn and NOx reductions. A 300-passenger aircraft, with two 396-kN thrust (85,000-pound) engines is chosen for the study. The results show that a large subsonic aircraft equipped with the UEET technologies has a very high probability of meeting the UEET Program goals for fuel-burn (or equivalent CO2) reduction (−15% from the baseline) and LTO (landing and takeoff) NOx reductions (−70% relative to the 1996 International Civil Aviation Organization rule). These results are used to provide guidance for developing a robust UEET technology portfolio, and to prioritize the most promising technologies required to achieve UEET program goals for the fuel-burn and NOx reductions.
Rotor Wake Variability in a Transonic Compressor Stage
Authors: Key Nicole L. , Lawless Patrick B. , Fleeter Sanford
Published: November 2008

High Cycle Fatigue (HCF) is a fundamental weakness in the technology base for turbine engines. Modern compressor designs feature closely spaced blade rows of low aspect ratio increasing the strength and complexity of aerodynamic forcing functions. Also, modern manufacturing techniques produce blisks with low levels of mechanical damping. Thus, classic simplified views of the forcing functions may no longer be sufficient to accurately predict blade response. The concept of the “average wake” and the role that deviations from this average, or wake variability, plays as an HCF driver become important. Experiments are performed in the Purdue Transonic Research Compressor where two different but geometrically similar rotor blades from the same blisk are investigated; one that produces a near nominal wake and another that demonstrates significant variability according to thermal anemometry measurements. The Particle Image Velocimetry (PIV) measurements provide both phase-locked and instantaneous views of the wake structure showing variability in the individual wake structure.
A Virtual Gas Turbine Laboratory for an Undergraduate Thermodynamics Course
Authors: Benson Michael J. , Van Poppel Bret P. , Boettner Daisie D. , Arnas A. O¨zer
Published: November 2008

Topics on gas turbine machinery have been successfully integrated into the thermodynamics course at the United States Military Academy (USMA). Because graduating cadets will encounter gas turbines throughout their service in the U.S. Army, it is important for all engineering students, not just mechanical engineering majors, to learn about gas turbines, their operation, and their applications. This is accomplished by four methods, one of which is an experimental analysis of an operational auxiliary power unit (APU) from an Army helicopter. Due to recent building issues, this gas turbine laboratory was improvised and offered as a fully digital virtual laboratory exercise. Since all undergraduate programs do not have the luxury of having a gas turbine laboratory, our experiences with the virtual laboratory are offered as an effective option. By digitally reproducing the laboratory setup, introduction, instrumentation, data collection and analysis, the virtual experience captures the essence of the laboratory. After viewing the web-based laboratory digital media files, students use one of two data sets, recorded from the data display panel in the real laboratory, in order to complete the laboratory report. While the tremendous advantage of actually seeing, testing, and analyzing the real engine cannot be denied, a well-planned and executed virtual laboratory adequately achieves learning objectives and provides students a unique opportunity to apply gas turbine fundamentals. An assessment of the virtual laboratory and results of student feedback are provided.
Micro Gas Turbine With Ceramic Rotor
Authors: Yoshida Hiro , Matsunuma Takayuki , Iki Norihiko , Akimune Yoshio , Hoya Hiroshi
Published: November 2008

A series of operation tests by using a desktop size gas turbine has been successfully carried out. In the first step of the tests, we have concentrated ourselves on the operation at elevated temperatures. Thus the duration of the bench test at each rotation speed was set to be 1 minute. The baseline machine is J-850 (Sophia Precision, Co., Ltd.) originally made for model airplanes. In this study, we replaced an INCONEL 713C alloy turbine rotor with 5.5 cm diameter into a type SN235 ceramic rotor (Kyocera Corporation). Mixture of 70% white kerosene and 30% gasoline was used as the fuel. The running test was made at the rotational speeds up to 140,000 r.p.m. in the atmospheric air. The basic performance of the small gas turbine was found as follows: At 140,000 r.p.m., 1) the turbine inlet temperature was estimated to be higher than 1,200. This estimation was supported by the observation of the partially melted INCONEL alloy nozzle located before the ceramic rotor. But the ceramic rotor revealed no damages. 2) The compression ratio and the thrust of the ceramic rotor turbine attained at 140,000 r.p.m. were 3 and 100 N, respectively. 3) Total energy level of the exhaust gas jet was 240 kW at the same rotation speed. Experiences learned from the present running tests suggest that the small gas turbine system employed in this study could be a useful tool to quicken the cycle of R & D of micro ceramic gas turbines with reasonable costs.
Probabilistic Gas Path Analysis for Gas Turbine Engine and Its Application
Authors: Vodopianov V. E.
Published: November 2008

Assessments of performance deterioration and its prediction are of major importance to the gas turbines operation and maintenance. The task called Gas Path Analysis (GPA) deals mainly with diagnostics of faults in the engine flow path (the efficiency and capacity changes of the modules), malfunctions in the engine control loops, changes in power off-takes and air-escapes. This approach is based on comparison of the measured thermodynamic data (temperatures, pressures, shaft speeds etc.) at present with the accepted reference data with a subsequent application of different mathematical methods meant for explanation of the data differences. These methods make use of gas turbines mathematical models, often linear in the form of so called fault matrices, representing the effect of different faults on measured parameters. The use of standard non-linear steady state performance models for investigation of in-service problems is essentially restricted because of the lack and inaccuracy of measured information. Application of such models requires reliable and sufficient information about measured performance parameters of the considered engine to carry out a good identification of the engine internal state. In practice there is usually no such information. Even the heavily instrumented development engines data list is often insufficient for a proper identification. In mathematical terms the gas turbine performance diagnostics is a badly-posed problem, with a high degree of uncertainty. So the low and insufficiently accurate instrumentation of production engines has resulted in a need for creating special diagnostic tools exhibiting a special approach to the task. In contrast to the other linear methods dealing with the GPA problem (known to the author), the proposed approach is based on the probability analysis of fault matrices and not on the solution of systems of linear algebraic equations. That makes it principally different from the other GPA methods using fault matrics. The new method has shown high level of working capacity. The application of the proposed diagnostic approach shown in this paper embraces main problems that may occur in operation. It is the routine estimate of performance deterioration shown by an example of analysis of the long-run test bed data, then it is the sifting of sensor faults and control loop settings changes and at last the diagnostic results themselves. The data used is the real test bed data of two-shaft engines with a very low by-pass ratio.
Chemical-Looping Combustion for Combined Cycles With CO2 Capture
Authors: Consonni Stefano , Lozza Giovanni , Pelliccia Giampaolo , Rossini Stefano , Saviano Francesco
Published: November 2008

Chemical-Looping Combustion (CLC) is a process where fuel oxidation is carried out through an intermediate agent — a metal oxide — circulated across two fluidized bed reactors: a reduction reactor, where an endothermic reaction reduces the metal oxide and oxidizes the fuel, and an oxidation reactor, where an exothermic reaction oxidizes the metal oxide in air. Overall, the system carries out the same job of a conventional combustor, with the fundamental advantage of segregating the oxidation products (CO2 and H2O) into an output flow free of nitrogen and excess oxygen. The flow exiting the reduction reactor consists of water and CO2, the latter readily available for liquefaction, transport and long-term storage. The hot, vitiated air from the oxidation reactor is the means to produce power through a thermodynamic cycle. This paper reports of a study supported by the ENI group to assess the potential of the integration between CLC and combined gas-steam power cycles. More specifically, we focus on four issues: (i) optimization of plant configuration; (ii) prediction of overall efficiency; (iii) use of commercial gas turbines; (iv) preliminary economic estimates. The CLC system is based on iron oxides which, to maintain their physical characteristics, must operate below 900–1000°C. Given the crucial importance of the temperature of the vitiated air generated by CLC on the performance of the combined cycle, we consider two options: (i) “unfired” systems, where natural gas is fed only to the CLC system, (ii) “fired” systems, where the vitiated air is supplementary fired to reach gas turbine inlet temperatures ranging 1000–1200°C. Results show that unfired configurations with maximum process temperature 850–1050°C and zero emissions reach net LHV plant efficiencies ranging 43–48%. Fired cycles where temperature is raised from 850 to 1200°C by supplementary firing can achieve 52% net LHV efficiency with CO2 emission about one half of those of a state-of-the-art combined cycles. Fired configurations allow significant capital cost and fuel cost savings compared to unfired configurations; however, a carbon tax high enough to make them attractive (close to 50 €/ton) would undermine these advantages.
Analysis of the Spectral Properties of Premixed, Diffusion, and Hybrid Natural Gas Flames
Authors: Cipriano A. , Gasperetti S. , Mariotti G. , Paganini E.
Published: November 2008

The spontaneous emission of light by pure premixed flames due to chemiluminescence phenomenon has been widely investigated in order to develop monitoring and diagnostic systems of the combustion process and ultimately to control it. In most cases attention has been concentrated on the lines corresponding to the emissions by OH*, CH* and C2* radicals, which are usually well identified in laboratory scale flames. The present work extends the study to industrial premixed flames, with diffusion pilot flame, at atmospheric and full pressure. The experiments show that for the selected configuration there is a threshold value of the diffusion flame (about 8% over the total amount of the fuel injected in the combustor) under which the diffusion flame has a very low influence in the emission light. The OH* emission is well correlated to the NOx emission while the correlation with the equivalence ratio depends on the combustion condition.
Numerical Simulation of Natural Convection in Stationary and Rotating Cavities
Authors: Sun Zixiang , Kifoil Alistair , Chew John W. , Hills Nicholas J.
Published: November 2008

In compressor inter-disc cavities with a central axial throughflow it is known that the flow and heat transfer is strongly affected by buoyancy in the centrifugal force field. As a step towards developing CFD methods for such flows, buoyancy-driven flows under gravity in a closed cube and under centrifugal force in a sealed rotating annulus have been studied. Numerical simulations are compared with the experimental results of Kirkpatrick and Bohn (1986) and Bohn et al (1993). Two different CFD codes have been used and are shown to agree for the stationary cube problem. Unsteady simulations for the stationary cube show good agreement with measurements of heat transfer, temperature fluctuations, and velocity fluctuations for Rayleigh numbers up to 2 × 1010. Similar simulations for the rotating annulus also show good agreement with measured heat transfer rates. The CFD results confirm Bohn et al’s results, showing reduced heat transfer and a different Rayleigh number dependency compared to gravity-driven flow. Large scale flow structures are found to occur, at all Rayleigh numbers considered.
Heat Transfer Characteristic Inside Two-Pass Variable Cross-Section Channels With Ribs and Bleed Holes
Authors: Liu Xiangyun , Ding Shuiting , Tao Zhi , Xu Guoqiang
Published: November 2008

Heat transfer characteristics were experimentally studied for two-pass channels with variable cross-section with and without ribs. Rectangular ribs were placed symmetrically on two opposite walls with attack angles of 90° and 60° to the main flow. The bleed holes were only distributed on the rib roughened surface along the second pass. The cross-section area of the channel varied in the way that it increased along the first pass and decreased along the second. The relative roughness heights were 0.092 and 0.123; the relative roughness pitches were 10 and 20. The experiments were carried out at Reynolds numbers from 7100 to 60000. Analysis of the experimental results may lead to the following conclusions: (1) The heat transfer was enhanced by the presence of variable cross section. (2) The 60° ribs was not necessarily the optimistic option as published in the literature, test showed that 90° ribs produced a hither heat transfer for the relative roughness height of 0.092. (3) For up to 30% of bleeding were outlet, the existence of bleed holes enhanced the heat transfer process.
Dynamic Modeling and Self-Tuning Control of a Gas Turbine
Authors: Zawia Mohamed S. , Al-Khodari Mohamed S. B.
Published: November 2008

Dynamic simulation is a great design tool in selecting control strategies and studying of the dynamic response of the engine. A model based on physical description of the plant components has been derived for control purposes, it is complex and highly non-linear but able to provide a more detailed description of the power plant. The non-linear dynamic model is developed in order to simulate the dynamic behavior of the gas turbine, to provide a fast and reliable model for the syntheses of the controller. The complete model comprise of seven differential equations obtained by applying mass and energy balance to each of three components of the plant, including one equation for mechanical energy for the rotor shaft. The non-linear model is linearised in order to design a Single-Input, Single-Output (SISO) controller for the turbine, and an adaptive self-tuning pole assignment controller is considered and designed for the turbine. The models are simulated using the MATLAB and SIMULINK software. The results of the dynamic simulation appear reasonable and confirm that the plant and the selected control will result a safe and efficient operation of the plant under steady state and transient conditions. The output of the theoretical model under a step input was compared to experimentally collected data from the gas turbine. The results of the comparison show that the theoretically derived model can satisfactorily represent the system.
On-Line Aircraft Engine Diagnostic Using a Soft-Constrained Kalman Filter
Authors: Dewallef P. , Le´onard O. , Mathioudakis K.
Published: November 2008

The purpose of this contribution is to apply ridge regression to Kalman filtering in order to stabilize a health parameter identification under low or negative redundancy. The resulting algorithm achieves a so-called soft-constrained recursive health parameter identification, i.e. constraints are applied to parameters in a statistical way, contrary to hard-constrained algorithms based on strong equality or inequality constrains. The method is tested on data generated by a steady state turbofan engine model and representing typical component faults. The benefits that can be realized in terms of stability and accuracy are highlighted and some limits of the method are also mentioned.
Combining Classification Techniques With Kalman Filters for Aircraft Engine Diagnostics
Authors: Dewallef P. , Romessis C. , Le´onard O. , Mathioudakis K.
Published: November 2008

A diagnostic method consisting of a combination of Kalman filters and Bayesian Belief Networks (BBN) is presented. A soft-constrained Kalman filter uses a priori information derived by a BBN at each time step, to derive estimations of the unknown health parameters. The resulting algorithm has improved identification capability in comparison to the stand alone Kalman filter. The paper focuses on the way of combining the information produced by the BBN with the Kalman filter. An extensive set of fault cases is used to test the method on a typical civil turbofan layout. The effectiveness of the method is thus demonstrated and its advantages over individual constituent methods are shown.
Preliminary Design and Economic Analysis of a Biomass Fed Micro-Gas Turbine Plant for Decentralised Energy Generation in Tuscany
Authors: Chiaramonti David , Riccio Giovanni , Martelli Francesco
Published: November 2008

Biomass is a significant renewable energy source in Tuscany. A GIS-based software model, jointly developed by the Energetics Department of the University of Florence (DEF), the Agriculture and Forestry Economic Department of the University of Florence (DEEAF) and Energia Trasporti Agricoltura (ETA) in the framework of a LIFE supported project (BIOSIT) has been used to estimate the available resources in the Tuscany region. In this context, a gas turbine cycle based on a dual combustion system has been considered (DCGT, Dual Combustion Gas Turbine). The size of the plant (∼100 kWe) targets small decentralised power generation. The DCGT system aims at achieving a great flexibility through both internal and external firing. In fact, the adoption of an external combustion chamber makes possible to adapt the plant to various types of solid biomass without affecting significantly the thermodynamic cycle and therefore the performances. The technical analysis of available industrial components (gas turbine, heat exchanger, biomass combustor) has been carried out. The computation of the thermodynamic performances was carried out by a dedicate in-house developed software. The economic analysis was performed for the proposed system, and a sensitivity analysis on the critical parameters elaborated. The use of natural gas and bioethanol was also compared in the dual combustion mode.
Numerical Analysis of Crossflow and Single Jet Impinging on a Heated Surface With Shaped Groove
Authors: Zecchi Stefano , Bacci Alessandro
Published: November 2008

Gas turbine performance is strongly affected by firing temperature; raising this parameter has always been one of the major development strategies in gas turbine technology. This trend requires enhancements in materials and cooling techniques in order to keep components temperatures within structural limits and to satisfy expected life requirements. Cooling techniques are proven to be very effective, and it justifies tremendous research efforts. Among these techniques, impingement cooling is widely used, especially in vane cooling. Impingement fluid dynamics is quite complex, and its understanding is still incomplete; moreover further improvements in impingement cooling performance are expected. A great amount of experimental investigations are available on the subject and recently more and more numerical analysis has been performed. Due to advances in computational fluid dynamics (CFD) and availability of commercial codes, numerical investigations are often used in industrial design methodologies. Therefore the present study has been carried out using a commercial code with a two equation turbulence model, as common in industry standard analyses. The aim of this work is to investigate a single jet with cross-flow, at several blowing rates, analysing both flow field and heat transfer. The cross-flow passes through a rectangular duct. The jet is injected on the upper surface from a circular pipe perpendicularly to the duct axis and impacts on the lower surface. Firstly, a comparison of results with experimental data available in literature is provided. This permits to characterize the numerical model, particularly with respect to mesh, boundary conditions, and turbulence model. Then the rectangular duct lower flat surface is replaced by a grooved one. A single groove, horse-shoe shaped and located slightly upstream the impinging region, is used to control the flow field near the impact surface. Effects of the groove on impingement cooling are investigated. Both fluid dynamic and heat transfer analyses are performed. Results show the groove to be effective in driving the flow field interaction between cross-flow and impinging jet; heat transfer is also affected by the groove.
Expansion Line Modeling and Strength Diagnostics of Internally Cooled Gas Turbines
Authors: Chmielniak Tadeusz , Kosman Wojciech
Published: November 2008

This paper regards control and optimization of a gas turbine operation with a respect to effectiveness and reliability criteria. The development of diagnostics procedures begins with modeling of the gas expansion line for various loads with regard to an internal blade cooling. Analyzing an expansion line allows to assess the influence of cooling parameters on gas path and turbine operation. Computational models are described here, which respect various cooling aspects, mainly convection and film cooling. Several examples of gas path, blade temperature and thermal barrier coating (TBC) temperature dependencies on cooling parameters are presented. The determination of gas and metal temperatures is utilized to evaluate creep wear rate. The dependency between the strength and durability of turbine components and their temperature might be regarded in several aspects. Firstly: lower temperature decreases the creep rate. Even small temperature drop leads to a significant deceleration of creep processes. Secondly: the change of the temperatures modifies also the distribution of thermal stresses. This change of thermal stresses is usually very small and might be neglected. Presented analysis omits the influence of temperatures alteration of stresses distribution, it regards however the change of the creep characteristics.
Corrugated Flute Filter Media Packaging Reduces Combustion Turbine Intake Air Filter System Size by 40%
Authors: Gahr Thomas C.
Published: November 2008

Gas turbine output and mass flow have increased significantly over the years. The current generation of self cleaning air filter systems are large and complex, occupying a great deal of space, and requiring significant amounts of field assembly. A new filter technology developed for gas turbine intake air systems allows for the same high efficiency self cleaning performance to be achieved with a system that has a 40% smaller three dimensional footprint. This new corrugated flute filter media packaging technology not only reduces the size of the intake filter system, but can also reduce the complexity of the installation, shorten field installation time, and reduce the total cost of shipping by up to 50%. The key to this size reduction is a new way to package the filter media that allows for twice the airflow per filter at the same initial pressure loss and filtration efficiency as the current industry standard self cleaning filter systems. This paper will discuss the benefits of corrugated flute filter media packaging, and highlight the size reduction possible in the self cleaning air intake system. The resulting advantages are documented through laboratory and field experience.
Micro Turbocharger on a Single Silicon Rotor
Authors: Kang P. , Tanaka S. , Esashi M.
Published: November 2008

This paper describes the design, fabrication and preliminary test of a MEMS-based turbocharger. In this device, a compressor and a turbine are formed on the same side of the rotor to escape miss-alignment during bonding process. The rotor is supported by hydrostatic journal and thrust bearings. The device rotated only at low rotation speed up to 2500 rpm, and the rotation speed did not remarkably changed by adjusting air supplies to the hydrostatic bearings. From the test results, we found important issues to be solved for high speed rotation. Concerning to fabrication, flat and smooth bearing surfaces is difficult to fabricate, and bearing/tip clearances are difficult to precisely control due to spikes on etched surfaces and the warp of the devices induced by anodic bonding. We developed special deep RIE recipe to realize spike-free, uniform etching. And, we found that the wafer warp became negligible at a bonding temperature of 320 °C and an applied voltage of 400–600 V, when a 1 mm thick Pyrex glass substrate was used. Even after 5 times anodic bonding to stack 6 wafers, the warp was below 2 μm. The other concern is on bearing design. The journal bearing has a very low L/D number (length divided by diameter). As a result, the journal bearing has a small journal surface, and it is difficult to install orifices on the journal bearing. Additionally, there is interference between the journal and thrust bearing due to air leakage.
Detailed Flow Investigation Using PIV in a Typical Turbine Cooling Geometry With Ribbed Walls
Authors: Elfert M. , Jarius M. P. , Weigand B.
Published: November 2008

In a stationary two-pass coolant channel system the fluid flow is investigated experimentally using the PIV (Particle Image Velocimetry). The cooling system consists of a trapezoidal leading edge channel, a 180 deg. bend and an almost rectangular second channel. The cross sections of the channels were adapted to the shape of a typical turbine blade. It has ribbed walls in both channels to enhance heat transfer performance. Ribs are placed at the top and bottom walls of the channels. The system was analyzed at the German Aerospace Center (DLR) with a small scaled model and at the Institute of Aerospace Thermodynamics (ITLR) of the Stuttgart University with a large scaled model to ease near rib flow analysis. Heat transfer results are not the objective of this paper, they are investigation topics of the ITLR which is in close cooperation [SCHUBERT (2003)]. At DLR presently rotation effects are studied. As a first step to understand the existing flow phenomena, the system is analyzed in non-rotating mode. During future work it will rotate about an axis orthogonal to the centreline of the straight passes. The results shown in this paper demonstrate the effect of the 180° bend with isothermal flow condition excluding any buoyancy. Turbulent channel flow with a REYNOLDS number of 40,000, derived with the hydraulic diameter of the second pass, was investigated. Two models either with smooth or ribbed walls were investigated. Some kinds of flow visualizations were conducted such as oil flow visualization technique for obtaining wall streamlines and laser light sheet visualization technique to detect vortex structures and separations. The results presented in this paper clarify the complex flow situation given by the two-pass system with the inherent turn. Especially in the bend area separation regions and vortices with high local turbulence are apparent. The presence of ribs changes the fluid motion by generating additional vortices impinging the leading and trailing wall. This very demanding measuring task represents a benchmark test case for the application of PIV and later of Stereo PIV, respectively.
Gas Turbine and Sensor Fault Diagnosis With Nested Artificial Neural Networks
Authors: Xiradakis N. , Li Y. G.
Published: November 2008

Accurate gas turbine diagnosis relies on accurate measurements from sensors. Unfortunately, sensors are prone to degradation or failure during gas turbine operations. In this paper a stack of decentralised artificial neural networks are introduced and investigated as an approach to approximate the measurement of a failed sensor once it is detected. Such a system is embedded into a nested neural network system for gas turbine diagnosis. The whole neural network diagnostic system consists of a number of feedforward neural networks for engine component diagnosis, sensor fault detection and isolation; and a stack of decentralised neural networks for sensor fault recovery. The application of the decentralised neural networks for the recovery of any failed sensor has the advantage that the configuration of the nested neural network system for engine component diagnosis is relatively simple as the system does not take into account sensor failure. When a sensor fails, the biased measurement of the failed sensor is replaced with a recovered measurement approximated with the measurements of other healthy sensors. The developed approach has been applied to an engine similar to the industrial 2-shaft engine, GE LM2500+, whose performance and training samples are simulated with an aero-thermodynamic modelling tool — Cranfield University’s TURBOMATCH computer program. Analysis shows that the use of the stack of decentralised neural networks for sensor fault recovery can effectively recover the measurement of a failed sensor. Comparison between the performance of the diagnostic system with and without the decentralised neural networks shows that the sensor recovery can improve the performance of the neural network engine diagnostic system significantly when a sensor fault is present.
Computations of Flow Field and Heat Transfer in a Stator Vane Passage Using the v2–f Turbulence Model
Authors: Sveningsson Andreas , Davidson Lars
Published: November 2008

In this study three-dimensional simulations of a stator vane passage flow have been performed using the v2–f turbulence model. Both an in-house code (CALC-BFC) and the commercial software Fluent are used. The main objective is to investigate the v2–f model’s ability to predict the secondary fluid motion in the passage and its influence on the heat transfer to the endwalls between two stator vanes. Results of two versions of the v2–f model are presented and compared with detailed mean flow field, turbulence and heat transfer measurements. The performance of the v2–f model is also compared with other eddy-viscosity based turbulence models, including a version of the v2–f model, available in Fluent. The importance of preventing unphysical growth of turbulence kinetic energy in stator vane flows, here by use of the realizability constraint, is illustrated. It is also shown that the v2–f model predictions of the vane passage flow agree well with experiments and that, amongst the eddy-viscosity closures investigated, the v2–f model in general performs the best. Good agreement between the two different implementations of the v2–f model (CALC-BFC and Fluent) was obtained.
Preparations for Smart Sensor Usage in Aircraft Gas Turbine Testing
Authors: Patterson Grant , Bennett Mike , Nelius Andy , Irby William , Boals Owen
Published: November 2008

The preparation and planning process for smart sensor usage in aircraft gas turbine testing is described. The smart sensors are planned for usage in a process called Snap-In/Snap-Out (SISO). The current instrumentation setup process for testing in an altitude test cell requires a multitude of aerodynamic pressure lines (up to 600 lines) and electrical cables for instrumentation measurement and excitation (up to 800 cables) be routed through patch panels to pressure scanners, power supply/signal conditioners, analog-to-digital (A/D) systems, and acquisition systems for processing, display, recording, analysis, and transmission of the data. The process is manpower intensive in both setup and configuration control. The SISO process will use smart sensors with calibrations and measurement information on the sensors plus consolidation of all sensor outputs before they exit the engine test stand; this configuration offers the opportunity to reduce the number of connections for measured data to one or at most a few wires. Measurement information stored with the sensor reduces the probability of configuring the instrumentation system incorrectly. The SISO process is presented here along with attendant cost reductions for instrumentation setup time, configuration management, and infrastructure maintenance. The discussion of planning activities includes certifying the smart sensor units for operation in the test cell environment, assessing the uncertainty of the sensor units, the schedule for implementation, and future requirements for smart sensors. Also discussed are the use of state-of-the-art smart sensors and legacy sensors, for several applications (pressure, temperature, position, and voltage) and for both transient and dynamic measurements.
Factors Affecting the Behaviour and Efficiency of a Targeted Jet Delivering Oil to a Bearing Lubrication System
Authors: Lee C. W. , Johnson G. R. , Palma P. C. , Simmons K. , Pickering S. J.
Published: November 2008

In this study oil delivery to an aero-engine bearing via a targeted jet was investigated using a bearing chamber test rig. The rig contains a high-speed rotating shaft of engine representative geometry within a stationary Perspex housing. Oil is collected from feedholes leading from scoops (scallops) on the shaft. The efficiency of this oil delivery system is dependent on jet structure and trajectory as it interacts with the rotating chamber flow. Flow visualization techniques and parametric tests are used to assess the influence of shaft speed and jet flowrate on oil collected through the feedholes. Detailed pictures of the structure of the jet in quiescent air are presented and compared with those from the rig, where there is a gas crossflow. As expected, jet break-up is accentuated in the rig. This influences jet impact behaviour at the scallop, and a consequent variation of oil distribution in the system is observed.
Unsteady Aerodynamics and Interactions Between a High Pressure Turbine Vane and Rotor
Authors: Urbassik Ryan M. , Wolff J. Mitch , Polanka Marc D.
Published: November 2008

A set of experimental data is presented investigating the unsteady aerodynamics associated with a high pressure turbine vane (HPV) and rotor blade (HPB). The data was acquired at the Turbine Research Facility (TRF) of the Air Force Research Laboratory. The TRF is a transient, blowdown facility generating several seconds of experimental data on full scale engine hardware at scaled turbine operating conditions simulating an actual engine environment. The pressure ratio and freestream Reynolds number were varied for this investigation. Surface unsteady pressure measurements on the HPV, total pressure traverse measurements downstream of the vane, and surface unsteady pressure measurements for the rotor blade were obtained. The unsteady content of the HPV surface was generated by the rotor potential field. The first harmonic decayed more rapidly than the second harmonic with a movement upstream causing the second harmonic to be most influential at the vane throat. The blade unsteadiness appears to be caused by a combination of shock, potential field, and vane wake interactions between the vane and rotor blade. The revolution averaged data resulted in higher unsteadiness than a passing ensemble average for both vane and rotor indicating a need to understand each passage for high cycle fatigue (HCF) effects.
Bump-Type Foil Bearing Structural Stiffness: Experiments and Predictions
Authors: Rubio Dario , San Andres Luis
Published: November 2008

Gas foil bearings (FB) satisfy many of the requirements noted for novel oil-free turbomachinery. However, FB design remains largely empirical, in spite of successful commercial applications. The mechanical structural characteristics of foil bearings, namely stiffness and damping, have been largely ignored in the archival literature. Four commercial bump-type foil bearings were acquired to measure their load capacity under conditions of no shaft rotation. The test bearings contain a single Teflon coated foil supported on 25 bumps. The nominal radial clearance is 0.036 mm for a 38 mm journal. A simple test set up was assembled to measure the FB deflections resulting from static loads. The tests were conducted with three shafts of increasing diameter to induce a degree of preload into the FB structure. Static measurements show nonlinear FB deflections, varying with the orientation of the load relative to the foil spot weld. Loading and unloading tests evidence hysteresis. The FB structural stiffness increases as the bumps-foil radial deflection increases (hardening effect). The assembly preload results in notable stiffness changes, in particular for small radial loads. A simple analytical model assembles individual bump stiffnesses and renders predictions for the FB structural stiffness as a function of the bump geometry and material, dry-friction coefficient, load orientation, clearance and preload. The model predicts well the test data, including the hardening effect. The uncertainty in the actual clearance (gap) upon assembly of a shaft into a FB affects most the predictions.
Development of a Solid-Oxide Fuel Cell/Gas Turbine Hybrid System Model for Aerospace Applications
Authors: Freeh Joshua E. , Pratt Joseph W. , Brouwer Jacob
Published: November 2008

Recent interest in fuel cell-gas turbine hybrid applications for the aerospace industry has led to the need for accurate computer simulation models to aid in system design and performance evaluation. To meet his requirement, solid oxide fuel cell (SOFC) and fuel processor models have been developed and incorporated into the Numerical Propulsion Systems Simulation (NPSS) software package. The SOFC and reformer models solve systems of equations governing steady-state performance using common theoretical and semi-empirical terms. An example hybrid configuration is presented that demonstrates the new capability as well as the interaction with pre-existing gas turbine and heat exchanger models. Finally, a comparison of calculated SOFC performance with experimental data is presented to demonstrate model validity.
Experimental Investigation of Diffuser Hub Injection to Improve Centrifugal Compressor Stability
Authors: Skoch Gary J.
Published: November 2008

Results from a series of experiments to investigate whether centrifugal compressor stability could be improved by injecting air through the diffuser hub surface are reported. The research was conducted in a 4:1 pressure ratio centrifugal compressor configured with a vane-island diffuser. Injector nozzles were located just upstream of the leading edge of the diffuser vanes. Nozzle orientations were set to produce injected streams angled at −8, 0 and +8 degrees relative to the vane mean camber line. Several injection flow rates were tested using both an external air supply and recirculation from the diffuser exit. Compressor flow range did not improve at any injection flow rate that was tested and generally diminished as injection rate increased. Compressor flow range did improve slightly at zero injection due to the flow resistance created by injector openings on the hub surface. Resistance and flow range both increased as the injector orientation was turned toward radial. Leading edge loading and semi-vaneless space diffusion show trends that are similar to those reported earlier from shroud surface experiments that did improve compressor range. Opposite trends are seen for hub injection cases where compressor flow range decreased. The hub injection data further explain the range improvement provided by shroud-side injection and suggest that stability factors cited in the discussion of shroud surface techniques are valid. The results also suggest that a different application of hub-side techniques may produce a range improvement in centrifugal compressors.
Experimental and Numerical Investigation of the Unsteady Surface Pressure in a Three-Stage Model of an Axial High Pressure Turbine
Authors: Kachel Carmen E. , Denton John D.
Published: November 2008

This paper presents the results of a numerical and experimental investigation of the unsteady pressure field in a three-stage model of a high pressure steam turbine. Unsteady surface pressure measurements were taken on a first and second stage stator blade respectively. The measurements in the blade passage were supplemented by time resolved measurements between the blade rows. The explanation of the origin of the unsteady pressure fluctuations was supported by unsteady three-dimensional computational fluid dynamic calculations of which the most extensive calculation was performed over two stage. The mechanisms affecting the unsteady pressure field were: the potential field frozen to the upstream blade row, the pressure waves originating from changes in the potential pressure field, the convected unsteady velocity field and the passage vortex of the upstream blade row. One-dimensional pressure waves and the unsteady variation of the pitchwise pressure gradient due to the changing velocity field were the dominant mechanisms influencing the magnitude of the surface pressure fluctuations. The magnitude of these effects had not been previously anticipated to be more important than other recognized effects.
Stainless Steels With Improved Oxidation Resistance for Recuperators
Authors: Pint Bruce A. , More Karren L.
Published: November 2008

New materials are being evaluated to replace type 347 stainless steel in microturbine recuperators operating at higher temperatures in order to increase the efficiency of the microturbine. Commercial alloys 120 and 625 are being tested along with potentially lower cost substitutes such as Fe-20Cr-25Ni and Fe-20Cr-20Ni. Long-term testing of these materials at 650°–700°C shows excellent corrosion resistance to a simulated exhaust gas environment. Testing at 800°C has been used to further differentiate the performance of the various materials. The depletion of Cr from foils of these materials is being used to evaluate the rate of attack. While those alloys with the highest Ni and Cr contents have longer lives in this environment, lower alloyed steels may have sufficient protection at a lower cost.
Full-Scale Demonstration of Surface-Stabilized Fuel Injectors for Sub-Three ppm NOx Emissions
Authors: Greenberg Steven J. , McDougald Neil K. , Arellano Leonel O.
Published: November 2008

ALZETA Corporation has developed surface-stabilized fuel injectors for use with lean premixed combustors which provide extended turndown and ultra-low NOx emission performance. These injectors use a patented technique to form interacting high-flow and low-flow flame zones immediately above a selectively-perforated porous metal surface. This allows stable operation at low reaction temperatures. This technology has been given the product name nanoSTAR™. Previous work involved the development of nanoSTAR technology from the proof-of-concept stage to prototype testing. Rig testing of single injectors and of two injectors simulating a sector of an annular combustion liner have been completed for pressure ratios up to 17 and combustion air inlet temperatures up to 700 K (800°F). This paper presents results from the first ever full-scale demonstration of surface-stabilized fuel injectors. An annular combustion liner, fitted with twelve nanoSTAR injectors was successfully tested up to a pressure ratio of 12 and combustion air inlet temperature of 700 K (800°F). NOx emissions were 2 ppm with CO emissions of 3 ppm both corrected to 15% O2. The combustion system exhibited excellent temperature uniformity around the annular combustor outlet with a maximum pattern factor of 0.16 and engine-appropriate radial profiles.