bluuebunny/crossref_metadata_2025 huggingface dataset:
Prognostics and Health Management Software for Gas Turbine Engine Bearings
Authors: Roemer Michael J. , Byington Carl S.
Published: March 2009

Based on the results of a successful Phase I and II SBIR program performed by Impact Technologies, a suite of Prognostics and Health Management (PHM) algorithms have been developed for detecting incipient faults in the critical bearings associated with aircraft gas turbine engines. The component-level prognostic approach is presented that utilizes available sensor information from vibration transducers, along with material-level component fatigue models to calculate remaining useful life for the engine’s critical components. Specifically, correlation between the sensed data and fatigue-based damage accumulation models were developed to provide remaining useful life assessments for life limited components. The combination of health monitoring data and model-based techniques provides a unique and knowledge rich capability that can be utilized throughout the bearings’s entire life, using model-based estimates when no diagnostic indicators are present and using the monitored vibration features at later stages when incipient failure indications are detectable, thus reducing the uncertainty in model-based predictions. A description and specific implementation of this prognosis approach with application to high speed bearings is illustrated herein, using gas turbine engine and bearing test rig data as validation for the methods.
Comparisons of Steady and Time-Averaged Unsteady Flow Predictions for Impeller–Diffuser Interactions in a Centrifugal Compressor Stage
Authors: He N. , Tourlidakis A. , Elder R. L.
Published: March 2009

In the present paper a computational analysis of the interactions between a backswept impeller and its downstream vaned diffuser in a high-speed centrifugal compressor is presented. Both steady and unsteady simulations are carried out at the peak efficiency point. Geometry scaling was used in the unsteady simulation in order to deal with the problem of unequal pitch. For the steady simulation, an averaging approach is used at the interface between the impeller and the diffuser. A detailed comparison between the time averaged unsteady results and the steady simulation results is performed and some unsteady phenomena are also discussed in order to advance the understanding of the flow physics involved. One important conclusion is that the unsteady simulation is important since the difference between the time averaged unsteady results and steady simulation results is quite significant especially in the velocity field and the stage efficiency. From the comparisons of the predicted results with available experimental data in terms of velocity vectors and isentropic efficiency, it can be concluded that the geometry scaling method used in the current unsteady simulation is reasonable and successful and the computational model employed for the predictions consists a reliable computational tool. In general, the contours of different flow variables for the averaged unsteady simulation results are more uniform than the steady ones, especially in the vaneless space. In the static pressure field, there are relatively small differences. The main differences occur in the region of the vaneless space and downstream of the throat area, and in general the difference is found to be quite small. In the velocity field, the differences are large compared with the ones occurring in the pressure field. The area with the largest differences extends from the vaneless space into the semi-vaneless and vaned diffuser channel. The unsteadiness also modifies the flow angle and hence the incidence angle at the leading edge of the vaned diffuser, the maximum difference can reach 3 degrees. The difference in the stage isentropic efficiency can reach above 1 per cent, which is considered to be quite high. The results also indicate that the larger differences between the time-averaged unsteady and steady state simulation results usually occurred in the area that flows are highly unsteady or nearly separated. Consequently the steady state simulation is still not very accurate to predict highly unsteady flow and separated flows.
Gas Turbine Fault Detection and Isolation Using MLP Artificial Neural Network
Authors: Matuck Gustavo R. , Barbosa Joa˜o Roberto , Bringhenti Cleverson , Lima Isaias
Published: March 2009

This work deals with a nonlinear model, based on a particular form of artificial neural networks, ANN, for application to gas turbines fault diagnosis. The traditional multi-layer perceptron (MLP) is used, with error back-propagation and different activation functions. The application of the model is illustrated using test data from a gas turbine simulation computer program. A specially developed computer program is used to simulate the engine in operation, generating all needed engine data for both baseline and deteriorated engine. A test case using a turboshaft engine is used to demonstrate the capacity of this ANN to identify faults that may occur during engine operation.
Characterization of Unsteady Impeller-Blade Loading in a Centrifugal Compressor With a Discrete-Passage Diffuser
Authors: Gould Kenneth A. , Tan Choon S. , Macrorie Michael
Published: March 2009

Unsteady numerical simulations in a centrifugal compressor stage consisting of an impeller followed by a discrete passage diffuser are employed to characterize unsteady impeller blade loading. For a stage typical of modern design, peak dynamic loads can be as high as 3.5 times greater that the peak steady-state loads. Unsteady load fluctuations of 0.2 times the tip dynamic pressure are observed in the forward 30% splitter chord, indicating a significant upstream propagation of the unsteady pressure disturbance. There can thus be an upstream manifestation of a downstream stimulus. The upstream manifestation is the considerable unsteady loading in the splitter blade leading edge while the downstream stimulus is the unsteady interaction between the rotating impeller and the stationary downstream diffuser. Increased relative frame diffusion, characterized by the DeHaller number, increases the sensitivity to downstream disturbances and leads to decreased attenuation of the upstream disturbance. Increased relative Mach number decreases the relative frame disturbance wavelength and thus improves the attenuation of the upstream disturbance. The length scale of spatial variation in unsteady loading is set by the relative Mach number, diffuser passing time, and the acoustic speed.
Effects of Surface Roughness and Near Hole Obstructions on Film Cooling Effectiveness
Authors: Somawardhana Ruwan P. , Bogard David G.
Published: March 2009

For a film cooled turbine airfoil, significant degradation of adiabatic effectiveness can be caused by near-hole obstructions formed from deposition of contaminants. Since obstructions are a randomly occurring event, there are many variables to consider, namely shape, width, length, height, and position in relation to a film cooling hole. In addition to this, the level of overall surface roughness also must be considered. An investigation was conducted on obstruction characteristics for a single row of holes on the suction side of a simulated turbine vane. It was found that degradation due to near-hole obstructions only occurred when upstream obstructions were present. When directly upstream, degradation levels around 40% were observed and obstruction height was the dominating characteristic.
Toleranced Designs of Cooled Turbine Blades Through Probabilistic Thermal Analysis of Manufacturing Variability
Authors: Moeckel Curtis W. , Darmofal David L. , Kingston T. Robert , Norton Robert J. G.
Published: March 2009

Manufacturing variability is likely the primary cause of a large scatter in the life of gas turbine hot section components. This paper investigates manufacturing variability and its effect on first-stage turbine blades through the use of a parametric CAD model, automated CAD regeneration software, and a parametric finite element thermal model. The probabilistic approach used is substantiated due to differences that arise when input parameters vary at different levels, for example the engine-to-engine and blade-to-blade level. Schemes are proposed to improve robustness through tolerancing out input parameters in ranges of the distributions that make nonconformances more likely. A frame-work is presented for calculating the potential number of prevented non-conformances and the corresponding cost savings associated with various tolerancing schemes. Blade-to-blade cooling flow variability, especially as a result of film-hole diameter variability in critical locations, is identified as the most likely candidate for parameter tolerancing. More effective is a combined two-factor tolerancing scheme which additionally tolerances gas path temperature.
Controlling Journal Bearing Instability Using Active Magnetic Bearings
Authors: El-Shafei A. , Dimitri A. S.
Published: March 2009

Journal Bearings are excellent bearings due to their large load carrying capacity and favorable damping characteristics. However, Journal bearings are known to be prone to instabilities. The oil whirl and oil whip instabilities limit the rotor maximum rotating speed. In this paper, a novel approach is used to control the Journal bearing (JB) instability. An Active Magnetic Bearing (AMB) is used to overcome the JB instability and to increase its range of operation. The concept is quite simple: rather than using the AMB as a load carrying element, the AMB is used as a controller only, resulting in a much smaller and more efficient AMB. The load carrying is done by the Journal bearings, exploiting their excellent load carrying capabilities, and the JB instability is overcome with the AMB. This results in a combined AMB/JB that exploits the advantages of each device, and eliminates the deficiencies of each bearing. Different controllers for the AMB to control the JB instability are examined and compared theoretically and numerically. The possibility of collocating the JB and the AMB is also examined. The results illustrate the effectiveness of the concept.
Aerodynamic Measurements in a Linear Turbine Blade Passage With Three-Dimensional Endwall Contouring
Authors: Gustafson Ross , Mahmood Gazi , Acharya Sumanta
Published: March 2009

Secondary flows created in the turbine blade passage contribute to greater pressure losses and increase the thermal loading on the endwall. The present paper explores the concept of utilizing a three-dimensional endwall for weakening the secondary flows in a low speed linear turbine blade cascade. The endwall contour is designed to reduce the near-wall cross-passage pressure gradient that drives the crossflow. Measurements undertaken include smoke flow visualization, velocity and turbulence data using a hot wire anemometer, velocity and pressure measurements using a five-hole pressure probe, and surface static pressures measurements. The measured data indicate that the endwall contour reduces the mass averaged pressure losses across the blade passage by over 30%. Endwall contouring also produces a much more uniform exit flow field.
Development of Baseline Performance Values for Turbines in Existing IGCC Applications
Authors: Dennis Richard A. , Shelton Walter W. , Le Patrick
Published: March 2009

The U.S. Department of Energy (DOE) Office of Fossil Energy has established projects to develop highly efficient turbines for coal-based fuels in integrated gasification combined-cycle applications. These fuels include coal-derived synthesis gas and pure hydrogen. The projects, with both General Electric and Siemens, have specific performance goals they must strive to attain. In order to ascertain the actual performance improvements that must be realized in these projects to reach the project goals, existing turbine baseline performance must be established. This paper will present the work conducted to establish the baseline performance parameters, and the values of these parameters. Performance parameters and values reported in the open literature will be presented. Parameters that are not available in the literature are also reported and were obtained by using ASPEN PLUS (Aspen Technology, Inc.) and GT-PRO (Thermoflow, Inc.) simulation software. A survey was conducted to obtain available process conditions and parameters related to Simple-Cycle (SC) and Combined-Cycle (CC) gas turbine performance in integrated gasification combined-cycle (IGCC) applications that use coal as the primary fuel source. Information sources include commercial IGCC plants funded through the Clean Coal Technology (CCT) Demonstration Program, a proposed greenfield IGCC plant, NETL system studies, and other open literature sources. The report results can be employed to assist DOE in establishing a “Baseline IGCC Plant Performance Model” for comparisons with future improvements. The year 2010 IGCC performance goals include 45-50% HHV efficiency, $1,000 / kW total capital costs, and near-zero emissions. Contributions toward this goal are provided by DOE’s Gasification and Advanced Turbines programs. Contributions from the Turbines program are targeted to provide 2-3 percentage points improvement in combined-cycle performance by 2010 for synthesis gas applications, and 3-5 percentage points (total) by 2015 for hydrogen fuels. The results are summarized in a series of tables that highlight the information identified that includes gas turbine type, turbine simple-cycle and combined-cycle efficiencies, turbine temperatures (e.g., firing temperature, exhaust temperature), pressure ratio, diluents, fuel composition, ASU integration, coal analysis, emissions, and the overall plant efficiency. The turbines and plants assessed to determine this baseline performance included the U.S.-based GE 7F frame turbines at the Wabash IGCC, Tampa IGCC, and Ashtabula IGCC (Nordic Energy - proposed 2002, Ashtabula, Ohio), as well as two European IGCC plants based on Siemens-Westinghouse V94.2 / V94.3 frame turbines located at the Buggenum IGCC (Netherlands) and Puertollano IGCC (Spain).
Enhancements to the Load Acceptance and Rejection Capability of a High Pressure Aeroderivative Engine
Authors: Price Brian , Demers Louis , Lebel Jean-Francois , Bonneville Sylvain
Published: March 2009

This paper describes improvements to the control of a high pressure, aeroderivative industrial gas turbine in order to better accommodate rapid load changes. In such circumstances it is important to maintain the speed of the driven equipment within an acceptable range. This can require the gas turbine to quickly adjust to the new load, to minimize the power imbalance, which is the cause of the speed variation. The paper describes the theory behind control schedules required to achieve this, and how they relate to avoiding surge, flameout or instability, while minimizing speed variations of the driven equipment. A whole engine thermodynamic model coupled to the control software was used to simulate the engine response during these rapid transients. The features of this model are described. The model allowed optimization of the control software in advance of the engine test. Results of whole engine tests are presented and compared to the model; and the types of load steps that remain most challenging are highlighted. The resulting capability remains partly determined by the specifics of the application, for example the inertia of the driven equipment, the nominal speed of operation, and the allowable speed variations. The effects of these can be predicted using the model and are discussed.
The Response Statistics, Jump and Bifurcation of Nonlinear Dynamical Systems Subjected to White Noise and Combined Sinusoidal and White Noise Excitation
Authors: Kumar Pankaj , Narayanan S.
Published: March 2009

The prediction of the response of nonlinear systems subjected to stochastic parametric, narrowband and wideband or coloured external excitation is of importance in the field of structural and rotor dynamics. The transitional probability density function (pdf) for the random response of nonlinear systems under white or coloured noise excitation (delta-correlated) is governed by both the forward Fokker-Planck (FP) and backward Kolmogorov equations. This paper presents efficient numerical solution of the FP equation for the pdf of response for general nonlinear systems subjected to external white noise and combined sinusoidal and white noise excitation. The effect of intensity of white noise, frequency and amplitude of sinusoidal excitation and level of system nonlinearity on the non-Gaussian nature of response caused by the system nonlinearity are investigated. Stochastic behaviours like stability, jump, bifurcation are examined as the system parameters change. The finite element (FE) scheme is used to solve the FP equation and obtain the statistics of a two degree-of-freedom linear system representative of the vibration of gas turbine tip-shrouded bladed disk assembly subjected to Gaussian white noise excitation as an illustrative example.
Oil Mist Eliminators Are an Excellent Upgrade to a Gas Turbine Package
Authors: Reed Howard C.
Published: March 2009

The installation of an oil mist eliminator on a gas turbine generating or compression package is a real asset to a newly designed system and a very good enhancement to units that have been operating in the field for several years. The mist eliminator not only helps a facility to comply with environmental regulations by removing the oil mist generated by high-speed rotating equipment, but also returns the coalesced oil that would be lost during the venting process, to the lube oil reservoir, greatly reducing make-up oil costs. Another by-product of the installation of a mist eliminator system is the prevention of oil mist settling on the equipment, floors, handrails, and staircases which not only creates an unpleasant work environment but possibly a dangerously slippery safety hazard. The various mist eliminator systems available will, as designed, or can be adapted to, comply with the individual turbine owner’s specific application and project requirements in solving his emission issues.
Unsteady Loss Production Mechanisms in Low Reynolds Number, High Lift, Low Pressure Turbine Profiles
Authors: Lazaro Benigno J. , Gonzalez Ezequiel , Vazquez Raul
Published: March 2009

The loss production mechanisms that occur in modern high lift, low pressure turbine profiles operating at low Reynolds numbers and subjected to periodic incoming wakes generated by an upstream located, moving bars mechanism, have been experimentally investigated. In particular, laser-Doppler and hot-wire anemometry have been used to obtain spatially and temporally resolved characterizations of the suction side boundary layer structure at the profile trailing edge. Phase measurements locked to the motion of the upstream moving bars have been used to analyze the effect of the incoming wakes on the suction side boundary layer response, which accounts for most of the profile loss generation. It is observed that the incoming wakes produce a temporal modulation of the boundary layer momentum thickness. This modulation appears to be connected to shedding of rotational flow from the recirculation bubble that develops in the suction side of high lift, low pressure turbine profiles. Furthermore, the momentum thickness reduction and subsequent increase that occurs after the wake passage appears to be related to the unsteady process leading to the recovery of the suction side recirculation bubble. The effect of the wake passage frequency and back surface adverse pressure gradient on the above described mechanisms is also investigated. Conclusions obtained can help understanding the unsteady response of modern low pressure turbine profiles operating in the low Reynolds number regime.
Flowfield in a Film-Cooled Three-Dimensional Contoured Endwall Passage: Aerodynamic Measurements
Authors: Gustafson Ross , Mahmood Gazi I. , Acharya Sumanta
Published: March 2009

The influence of endwall film cooling on the aerodynamic performance of a linear blade cascade employing an asymmetric contoured endwall is measured. Cylindrical coolant holes are strategically located on the contoured endwall to provide full coverage film cooling. The endwall contour is varied along the pitch direction, and is elevated near the pressure side and depressed near the suction surface. The profile height also varies in the axial direction from the inlet to exit. Measurements of total pressure, vorticity, and velocity components are obtained at different axial locations inside the passage for six inlet blowing ratios ranging from 1.0 to 2.4. The results are compared with the measured data on the contoured endwall without any film cooling flow (uncooled case). All the tests are performed in a low speed cascade facility employing a scaled up two-dimensional blade profile of the GE-E3 turbine rotor section. The Reynolds number based on the cascade inlet velocity and blade actual chord is 2.30×105. The results near the leading edge show that the suction side-leg vortex on the uncooled endwall weakens when the film cooling jets are employed. The axial vorticity and velocity vectors near the exit plane indicate that the passage vortex is located nearer to the mid-pitch location and higher above the endwall for the film-cooled endwall than for the uncooled contoured endwall. While the overall total pressure loss coefficient across the passage decreases at the high blowing ratios compared to the uncooled case, the overall cascade loss increases with the blowing ratio.
Computations of Pulsed Film-Cooling
Authors: Muldoon Frank , Acharya Sumanta
Published: March 2009

Direct Numerical Simulation (DNS) of a pulsed film cooling jet is presented to examine if pulsations of the coolant jet can enhance film cooling effectiveness. Calculations are performed for a cylindrical jet inclined at 30-degrees. The jet pulsation is defined by the duty cycle (DC) and the Strouhal number (St), both of which are varied in the present study. Calculations are done for a baseline steady blowing ratio of 1.5. With a peak blowing ratio (M) of 1.5, pulsing with a St = 0.32 and DC = 0.5 is shown to reduce jet blow-off and improve centerline and spanwise-averaged effectiveness over the steady M = 1.5 case.
Computational Aeroacoustics of the Coaxial Flow Exhaust System of a Gas Turbine Engine
Authors: Mihaˇescu Mihai , Gutmark Ephraim J. , Fuchs Laszlo
Published: March 2009

Jet engine noise is an environmental problem that needs to be addressed. Several methods to reduce the jet noise have been proposed in the last decades. The main issue is to find methods that reduce noise without causing considerable loss of thrust. Experimental and computational tools are mandatory in successfully reducing jet engine noise emissions. One of the challenging issues of computing the jet engine noise is the presence of very large scales (associated with the wave length of the acoustic wave) and at the same time also small scales that are responsible for the acoustical sources. In the field of Computational Aero-Acoustics (CAA) different hybrid approaches have been introduced to handle the different scales using problem specific models and methods. Here, a decomposition of flow variables is used that allows separation of flow and acoustic computations. Large Eddy Simulation approach is employed to compute the flow field and the acoustic sources. An inhomogeneous wave equation is used to perform acoustic computations. The paper investigates numerically the flow and the near-field acoustic data from a coaxial jet case with chevrons on the core nozzle that are compared with those obtained from a baseline coaxial jet, showing the spatial character of the acoustic benefit when chevrons are used on the core nozzle. Comparisons in terms of sound pressure levels with experimental data performed with the same geometry show a good agreement.
Thermo Mechanical Optimization of Cooled Turbine Vane
Authors: Nowak Grzegorz , Wro´blewski Włodzimierz
Published: March 2009

This paper discuses the problem of cooling system optimization within a gas turbine vane regarding to thermo-mechanical behaviour of the component. The analysis involves the optimization of location and size of internal cooling passages within the vane. Cooling is provided with ten circular passages and heat is transported by convection. The task is approached in 3D configuration. Each passage is fed with cooling air of constant parameters at the inlet. Also a constant pressure drop is assumed along the passage length. The thermal boundary conditions in passages varied with diameter and local vane temperature (passage wall temperature). The analysis is performed by means of the genetic algorithm for the optimization task and FEM for the heat transfer predictions within the component. In the present study the vane profile is taken as aerodynamically optimal and the objective of the search procedure is to find cooling structure variant that at given external conditions provides possibly low stresses and material temperature.
Effect of Endwall Contouring on Performance of Ultra-Low Aspect Ratio Transonic Turbine Inlet Guide Vanes
Authors: Sonoda Toyotaka , Hasenja¨ger Martina , Arima Toshiyuki , Sendhoff Bernhard
Published: March 2009

In our previous work on ultra-low aspect ratio transonic turbine inlet guide vanes for a small turbofan engine [1], we used numerical stochastic design optimization to propose the new design concept of an extremely aft-loaded airfoil to improve the difficult-to-control aerodynamic loss. At the same time, it is well known that endwall contouring is an effective method for reducing the secondary flow loss. In the literature, both “axisymmetric” and “non-axisymmetric” endwall geometries have been suggested. Almost all of these geometric variations have been based on the expertise of the turbine designer. In our current work, we employed a stochastic optimization method — the evolution strategy (ES) — to optimize and analyze the effect of the axisymmetric endwall contouring on the inlet guide vanes’ performance. In the optimization, the design of the endwall contour was divided into three different approaches: 1) only hub contour, 2) only tip contour, and 3) hub and tip contour together with the possibility to observe the correlation between hub/tip changes with regard to their joint influence on the pressure loss. Furthermore, three dimensional flow mechanisms, related to a secondary flow near the endwall region in the low-aspect ratio transonic turbine IGV, was investigated, based on above optimization results. A design concept and secondary flow characteristics for the low-aspect ratio full annular transonic turbine IGV is discussed in this paper.
Experimental and Numerical Impingement Heat Transfer in an Airfoil Leading-Edge Cooling Channel With Crossflow
Authors: Taslim M. E. , Bethka D.
Published: March 2009

To enhance the internal heat transfer around the airfoil leading-edge area, a combination of rib-roughened cooling channels, film cooling and impingement cooling is often employed. Experimental data for impingement on various leading-edge geometries are reported by these and other investigators. Effects of strong crossflows on the leading-edge impingement heat transfer, however, have not been studied to that extent. This investigation dealt with impingement on the leading-edge of an airfoil in the presence of crossflows beyond the crossflow created by the upstream jets (spent air). Measurements of heat transfer coefficients on the airfoil nose area as well as the pressure and suction side areas are reported. The tests were run for a range of axial to jet mass flow rates (Maxial/Mjet) ranging from 1.14 to 6.4 and and jet Reynolds numbers ranging from 8000 to 48000. Comparisons are also made between the experimental results of impingement with and without the presence of crossflow and between representative numerical and measured heat transfer results. It was concluded that the presence of the external crossflow reduces the impinging jet effectiveness both on the nose and side walls, even for an axial to jet mass flow ratio as high as 5, the convective heat transfer coefficient produced by the axial channel flow was less than that of the impinging jet without the presence of the external crossflow, and the agreement between the numerical and experimental results was reasonable with an average difference ranging from −8% to −20%.
Common Threads for Marine Gas Turbine Engines in U.S. Navy Applications
Authors: Bonafede Americo , Russom Dennis , Driscoll Matthew
Published: March 2009

This paper discusses the common threads that have been gleaned by the Navy in having operated many different gas turbine engines in a marine environment for nearly thirty years. The status of the Navy’s Honeywell TF40B, Rolls Royce 501 and General Electric LM2500 gas turbine engine programs is discussed.
Reliability and Creep/Fatigue Analysis of a CMC Component
Authors: Murthy Pappu L. N. , Mital Subodh K. , Gyekenyesi John Z. , Gyekenyesi John P.
Published: March 2009

High temperature ceramic matrix composites (CMC) are being explored as viable candidate materials for hot section gas turbine components. These advanced composites can potentially lead to reduced weight and enable higher operating temperatures requiring less cooling; thus leading to increased engine efficiencies. There is a need for convenient design tools that can accommodate various loading conditions and material data with their associated uncertainties to estimate the minimum predicted life as well as the failure probabilities of a structural component. A computer code, NASALife, is used to predict the life of a 2-D woven silicon carbide fiber reinforced silicon carbide matrix (SiC/SiC) turbine stator vane due to a mission cycle which induces low cycle fatigue and creep. The output from this program includes damage from creep loading, damage due to cyclic loading and the combined damage due to the given loading cycle. Results indicate that the trends predicted by NASALife are as expected for the loading conditions used for this study. In addition, a combination of woven composite micromechanics, finite element structural analysis and Fast Probability Integration (FPI) techniques has been used to evaluate the maximum stress and its probabilistic distribution in a CMC turbine stator vane. Input variables causing scatter are identified and ranked based upon their sensitivity magnitude. Results indicate that reducing the scatter in proportional limit strength of the vane material has the greatest effect in improving the overall reliability of the CMC vane.
Design and Validation of an Experiment for the Detection and Prediction of Stall and Surge in a PT6/T400 Turboshaft Engine
Authors: Chalmers Jennifer L. Y. , Bird Jeff W. , Gauthier Donald
Published: March 2009

The aerospace industry is aggressively pursuing many avenues of engine health monitoring to improve aircraft safety and reduce operating cost. A PT6/T400 turboshaft engine has been instrumented specifically to determine if measurable compressor aerodynamic behavior can provide a warning of impending stall or surge, especially in a small (< 5kg/s), service-exposed, axi-centrifugal compressor. In accordance with a survey of experience and methods for stall testing and detection methods, the engine was instrumented with nine fast-response pressure transducers (monitored at 25 kHz) divided between the axial compressor first stage leading edge, the axial compressor exit, and the outlet of the centrifugal compressor diffuser. An automatic bleed valve was gradually disabled to induce compressor stall. The engine response to this gradual change corresponded to the predictions of a simple engine surge model. A technique for monitoring blade air-flow regularity was developed and used to prove that aerodynamic changes could be successfully detected before the onset of stall/surge. The new technique compared favorably to conventional time series analysis, fast Fourier transform and wavelet processing techniques. Recommendations are made for further improvements and study of test and analysis methods.
Spatial Correlation Based Stall Inception Analysis
Authors: Cameron Joshua D. , Morris Scott C.
Published: March 2009

Investigations of stall inception and compressor pre-stall behavior have used a variety of techniques to make inferences about the mechanisms of rotating stall inception. Many of these techniques utilized data from arrays of circumferentially spaced hot-wires or high frequency response pressure transducers. This paper presents results from the application of several typical analysis techniques to the interpretation of unsteady casing pressure measurements recorded during two representative stall event in a high-speed axial compressor stage. Results from visual pressure trace inspection, spatial Fourier decomposition, wavelet filtering, and traveling wave energy techniques are presented and compared. The effects of measurement and analysis parameters are also briefly discussed. A new analysis technique based on windowed two-point spatial correlation between adjacent stall inception sensors is described. The method was found to provide both spatial and temporal information about rotating features in the compressor flow and is insensitive to low pass filtering and parameter selection over a wide range of values. It was also found to be valuable for analysis of both pre-stall and stall inception behavior.
Mechanical and Rotordynamic Design, Fabrication and Testing of a High-Speed Miniature Cryocooler Motor
Authors: Acharya Dipjyoti , Zhou Lei , Zheng Liping , Wu Thomas X. , Kapat Jay , Chow Louis , Arakere Nagaraj
Published: March 2009

An attempt has been made in this work to design, fabricate and performance evaluate a 2 kW permanent magnet synchronous motor operating at 200,000 rpm and at the temperature of both room temperature and 77 K. Structural, thermal and rotordynamic aspects were considered and models were developed on an iterative basis. Prototypes were fabricated and models were validated through experimental results. The PMSM motor/generator prototype was fabricated. At this stage, experimental results were obtained for the test set-up operating at 200,000 rpm and air at room temperature. Models developed were validated comparing to experimental results.
Thermodynamic Modeling of Gas Turbine Blade Cooling
Authors: Sanaye Sepehr , Darvishi Mehdi
Published: March 2009

Gas turbines are widely used in various industries and the thermal modeling of this equipment is of primary interest to predict its operating condition. One of reasons for deviation of numerical values obtained for actual gas turbine performance and the results obtained from thermal modeling is the effects of blade cooling. In this paper, three blade-cooling models are studied. The first one is the El-Masri continuous model which later modified by Bolland and De Paepe. The Jordal stage-by-stage model and Walsh & Fletcher model are the second and third blade cooling models studied here. The amounts of cooling air mass flow rates estimated by three models are compared for various values of compressor pressure ratios and turbine inlet temperatures for gas turbines in various ranges of power outputs. Furthermore the deviation of key performance parameters predicted by using the above blade cooling models from the actual (reported) corresponding values, was analyzed. It was found that for all three above blade cooling models the deviation was less than three percent for various classes of gas turbines.
Fundamental Characterization of Turbocharger Turbine Unsteady Flow Behavior
Authors: Costall Aaron , Martinez-Botas Ricardo F.
Published: March 2009

Fluid flow in the volute of a turbocharger turbine can be decidedly unsteady due to the pulsating nature of the exhaust gas in the manifolds of an internal combustion engine. Despite this it is conventional to use a quasi-steady or “filling and emptying” technique to model the turbine in one-dimensional turbocharged engine simulations. Depending on the inherent level of unsteadiness, this approach may be insufficient to capture the true turbine operation since neither method is able to resolve unsteady effects due to the presence of any wave action in the flow. Building on previously reported work, this paper aims to establish a measure of unsteadiness that takes account of the attributes of engine exhaust gas flow that give rise to gas dynamic unsteadiness. This characterization is achieved by decomposing the pulse into its constituent frequencies using Fourier analysis. A one-dimensional wave action code, featuring a bespoke boundary condition that permits application of a pressure pulse in Fourier series form, is used to investigate the effect of the contributing variables for some simplified cases. This allows the construction of the correct form of dimensionless parameter. Finally, the new dimensionless measures, the Fourier series Strouhal and acoustic Strouhal numbers (FSt and FaSt respectively), are evaluated at different test conditions to establish criteria for the transition from a filling and emptying mode to gas dynamic operation. The analysis suggests limiting values of FSt≤0.15, and FaSt≤0.02, to be used as an approximate guide for turbine model selection.
Unsteady Effect in a Nozzled Turbocharger Turbine
Authors: Rajoo Srithar , Martinez-Botas R. F.
Published: March 2009

The unsteady behavior of a nozzled turbocharger turbine under pulsating flow conditions has been studied experimentally in a cold flow test facility that replicates engine pulses. The results presented are obtained at a turbine speed of 48000 rpm for pulsating frequencies of 40Hz and 60Hz (which correspond to 1600rpm and 2400rpm in a twin turbocharger six cylinder internal combustion engine). The turbine unsteady behavior is compared for nozzle vane angles ranging between 40° and 70°. A nozzled turbocharger turbine is found to behave differently from a nozzleless turbine under pulsating flow. The existence of a nozzle ring “damps” the unsteady flow leading to a reduced level of flow dynamics affecting the turbine wheel for all vane angles. The bigger volume in the nozzled turbine is also another contributing factor to the observed characteristics. The results are more pronounced in the higher frequency and maximum vane opening condition. Given this “damping” behavior, the concept of unsteady efficiency is questioned. The level of unsteadiness in the flow is characterized by the relevant non-dimensional parameters and the onset of the unsteadiness in the flow and its effect on a nozzled turbocharger turbine is discussed. The onset of the unsteady effect is suggested to be at 40Hz flow condition. However, the nozzled turbine exhibits more of a filling and emptying characteristics for both the frequency conditions, especially at close nozzle position cases. The effect of unsteadiness on the instantaneous efficiency calculation is more pronounce in the nozzled turbine compared to a nozzleless turbine.
Turbomachinery Design Optimization Using Automatic Differentiated Adjoint Code
Authors: Duta Mihai C. , Shahpar Shahrokh , Giles Michael B.
Published: March 2009

The last decade has established the adjoint method as an effective way in Computational Fluid Dynamics of calculating the gradients of an objective functional in a large dimensional design space. This paper addresses the concerns that code developers face when creating a discrete adjoint computer program for design optimization, starting from a nonlinear flow solver and using Automatic Differentiation. Adjoint code development benefits greatly from using Automatic Differentiation but at its current state of maturity, this technology is best applied selectively rather than on entire codes. The paper discusses the practical aspects of using Automatic Differentiation on a large industrial turbomachinery flow solver with the objective of deriving efficient adjoint code. The use of the adjoint gradients is illustrated in an optimization exercise using gradient based methods on the NASA Rotor 37 public testcase.
Thermodynamic Analysis of Semi-Closed Gas Turbine Combined Cycles With High Temperature Diluted Air Combustion
Authors: Camporeale S. M. , Fortunato B.
Published: March 2009

In the last years many research studies have been focused on the features of MILD (Moderate and Intensive Low oxygen Diluted) or Flameless combustion, that is a stable form of combustion characterized by low flame temperature and, consequently, low Nox emissions. Early studies showed that flameless conditions can be obtained using high temperature air diluted with a large amount of exhaust gas. MILD combustion is presently applied in industrial furnaces where ceramic regenerators provide to raise the temperature of the entering diluted air, the main advantages being high efficiency and low emissions. Attractive features of MILD combustion (low NOx emissions, stable combustion) addressed in the last years towards investigations about new combustors suitable for applications in gas turbines. Although there is an intense activity aiming at better understanding the features of this form of combustion, there is a limited research effort to understand which could be the power cycles that could be better suitable to the application of MILD combustion. MILD combustion allows for increasing the temperature of the entering reactants beyond the self-ignition temperature thus decreasing combustion exergy losses. High temperature of the reactants can be obtained through recuperative heat exchangers. Recirculation, on the other hand, is the origin of new losses that may reduce partially the advantages produced in the combustion process. The oxidizer and flue gas can be mixed at different points influencing the final cycle efficiency. The paper presents a thermodynamic analysis of semi-closed Joule-Brayton cycles with high temperature diluted air and flue gas recirculation at intermediate pressure. This arrangement shows some favorable characteristics: reduction of the combustion exergy losses due to the increase of the temperature of the oxidizer, limited dimensions of the recuperative heat exchanger, efficient part load operation, favorable conditions for CO2 separation. The effects of the main cycle parameters on the plant efficiency are presented in order to outline the best trade-off that can be reached between the advantages given by high temperature of the reactants and the penalties caused by the recirculation of the flue gas. The combination of the semi-closed cycle with a bottoming steam plant is then examined, assuming state-of-the-art technologies. As applications, two plant configurations are considered. The first one, suitable for small plants using low calorific fuels, is characterized by lower combustor outlet temperature and simple air cooling technology for the turbine blades. The second one, suitable for large power plants, is characterized by higher turbine outlet temperature and steam cooling of the turbine blades. Advantages and disadvantages in comparison modern conventional CCGT power plant fueling natural gas are discussed.
Decision Support for Remote Monitoring and Diagnostics of Aircraft Engine Using Influence Diagrams
Authors: Osborn Mark , Yu LiJie
Published: March 2009

FAA regulations require the monitoring of all commercial aircraft engines to ensure airworthiness. In doing so, it provides economic advantages to engine owners to monitor engine performance and resolve identified issues in a timely manner to reduce operational costs or avoid secondary damage. Various remote monitoring and diagnostics service providers exist in the marketplace. However, a common understanding among most of them is that given limited time and information, it is an extremely difficult task to make quick and optimized decisions. Difficulties arise from the fact that an aircraft engine is a complex system and demands considerable expertise to diagnose, but also due to the uncertainty in estimating an engine’s true physical state because of measurement and process noise. Therefore, it is often difficult to decide what action to take in order to achieve the most desirable outcome. In this paper, a cost sensitive engine diagnostic and decision making methodology is described. Diagnostic tool performance at various decision thresholds is estimated over a large set of validated historical cases to evaluate sensitivity, specificity and other quality indices. These quality indices and a set of cost functions are utilized in influence diagrams to derive the optimized decision model in order to minimize costs given the uncertain engine condition and noisy parametric data.
Progress Update for Commercial Plants of Air Blown IGCC
Authors: Hashimoto Takao , Ota Katsuhiro , Fujii Takashi
Published: March 2009

Integrated Coal Gasification Combined Cycle (IGCC) is attracting considerable attention as clean coal technology for several reasons, including rising natural gas price, escalating environmental scrutiny and fuel diversification. Mitsubishi Heavy Industries, Ltd. (MHI) has developed an air-blown two stage entrained bed coal gasifier, which realizes the highest net plant efficiency by using a smaller ASU (Air Separation Unit), dry coal feed, and excellent reliability with a membrane water wall structure. A 250 MW demonstration plant is currently under construction in Japan and scheduled to start operation in 2007. This plant will validate MHI Air Blown technology under dispatching conditions. In the mean time, responding to increasing interest on this technology around the world, MHI is expediting the design of a 500MW IGCC plant to be operated with G class gas turbines. The MHI air blown gasifier concept is particularly attractive to the US market, not only because of the higher efficiency, when compared with oxygen blown designs, but because of its capability to handle a wide variety of coals including PRB. This paper will discuss what kind of IGCC will soon be commercially available and how it will fit practical needs in the US market showing the time schedule of realization of commercial plants and economical evaluation in addition to the technical integrity. MHI believes that IGCC is one of the most important clean coal technologies to contribute to worldwide energy security and environmental needs.
Adaptive Combustion Control to Improve Diesel HCCI Cycle Fuel Efficiency
Authors: Zheng Ming , Reader Graham T. , Tan Yuyu , Wang Meiping
Published: March 2009

Previous work indicates that the lowered combustion temperature in diesel engines is capable of reducing nitrogen oxides and soot simultaneously, which can be implemented by the heavy use of exhaust gas recirculation or the homogeneous charge compression ignition (HCCI) type of combustion. However, the fuel efficiency of the low temperature combustion cycles is commonly compromised with high levels of hydrocarbon and carbon monoxide emissions. Additionally, in cases of diesel HCCI cycles, the combustion process may even occur before the piston completes the compression stroke, which may cause excessive efficiency reduction and combustion roughness. Adaptive control strategies are applied to precisely navigate and stabilize the engine cycles and to better phase and complete the combustion process. The impact of heat release phasing, duration, shaping, and splitting on the thermal efficiency has also been analyzed with zero-dimensional engine cycle simulations. The correlations between the cylinder pressure and the heat release curves have been characterized to facilitate model based control. The empirical set-up and cases of applications are provided.