bluuebunny/crossref_metadata_2025 huggingface dataset:
Ignition Characteristics of a Fischer-Tropsch Synthetic Jet Fuel
Authors: Gokulakrishnan P. , Klassen M. S. , Roby R. J.
Published: August 2009

Ignition delay times of a “real” synthetic jet fuel (S8) were measured using an atmospheric pressure flow reactor facility. Experiments were performed between 900 K and 1200 K at equivalence ratios from 0.5 to 1.5. Ignition delay time measurements were also performed with JP8 fuel for comparison. Liquid fuel was prevaporized to gaseous form in a preheated nitrogen environment before mixing with air in the premixing section, located at the entrance to the test section of the flow reactor. The experimental data show shorter ignition delay times for S8 fuel than for JP8 due to the absence of aromatic components in S8 fuel. However, the ignition delay time measurements indicate higher overall activation energy for S8 fuel than for JP8. A detailed surrogate kinetic model for S8 was developed by validating against the ignition delay times obtained in the present work. The chemical composition of S8 used in the experiments consisted of 99.7 vol% paraffins of which approximately 80 vol% was iso-paraffins and 20% n-paraffins. The detailed kinetic mechanism developed in the current work included n-decane and iso-octane as the surrogate components to model ignition characteristics of synthetic jet fuels. The detailed surrogate kinetic model has approximately 700 species and 2000 reactions. This kinetic mechanism represents a five-component surrogate mixture to model generic kerosene-type jets fuels, namely, n-decane (for n-paraffins), iso-octane (for iso-paraffins), n-propylcyclohexane (for naphthenes), n-propylbenzene (for aromatics) and decene (for olefins). The sensitivity of iso-paraffins on jet fuel ignition delay times was investigated using the detailed kinetic model. The amount of iso-paraffins present in the jet fuel has little effect on the ignition delay times in the high temperature oxidation regime. However, the presence of iso-paraffins in synthetic jet fuels can increase the ignition delay times by two orders of magnitude in the negative temperature (NTC) region between 700 K and 900 K, typical gas turbine conditions. This feature can have a favorable impact on preventing flashback caused by the premature autoignition of liquid fuels in lean premixed prevaporized (LPP) combustion systems.
Thermo-Mechanical Transient Analysis and Conceptual Optimization of a First Stage Bucket
Authors: Campos-Amezcua A. , Mazur Z. , Gallegos-Mun˜oz A.
Published: August 2009

This paper presents a thermo-mechanical analysis of a first stage bucket during a gas turbine start-up. This analysis uses two simulation techniques, Computational Fluid Dynamics (CFD) for the conjugate heat transfer and flow analysis, and Finite Element Analysis (FEA) for the thermo-structural analysis. Computational three dimensional models were developed using two commercial codes, including all elements of the real bucket, to avoid geometric simplifications. An interface was developed to transfer the three-dimensional behavior of bucket temperatures during turbine start-up from CFD analysis to subsequent FEA analysis, imposing them as a thermal load. This interface virtually integrates the computational models, although they have different grids. The results of this analysis include temperature evolution and related stresses, as well as the thermo-mechanical stresses and zones where they are present. These stresses are dominated by thermal mechanisms, so a new temperature start-up curve is proposed where the maximum calculated stress decline around 100 MPa, and almost all stresses are lower throughout the transient analysis. The results are compared to experimental data reported in the literature obtaining acceptable approximation.
Investigation of Loss Generation in an Embedded Transonic Fan Stage at Several Gaps Using High Fidelity, Time-Accurate CFD
Authors: List Michael G. , Gorrell Steven E. , Turner Mark G.
Published: August 2009

The Blade-Row Interaction (BRI) rig at the Air Force Research Laboratory (AFRL), Compressor Aero Research Laboratory (CARL), has been simulated at three axial gaps between the highly loaded upstream stator row and the downstream transonic rotor using TURBO. Previous work with the Stage Matching Investigation (SMI) demonstrated a strong dependence of mass flow rate, efficiency, and pressure ratio on the axial spacing between an upstream wake generator and the downstream rotor through the variation of the axial gap. Several loss producing mechanisms were discovered and related to the spacings, referred to as close, mid, and far. In the SMI work, far spacing had the best performance. The BRI experiments were a continuation of the SMI work with the wake generator replaced by a swirler row to turn the flow and a deswirler row to create a wake by diffusion. Results of the BRI experiments showed a performance degradation between mid and far spacing which was not observed in SMI. This trend is seen in the numerical work as well, and the time-averaged data shows that the majority of this performance change occurred in the rotor. An unsteady separation bubble periodically forms and collapses as shocks reflect through the stator passage, creating additional aerodynamic blockage. The shed vortices induced by the unsteady loading and unloading of the stator trailing edge are chopped, with a frequency related to the spacing, by the rotor leading edge and ingested by the rotor. Once ingested the vortices interact in varying degrees with the rotor boundary layer. A treatment of the loss production in the BRI rig is given based on the time-accurate and time-averaged, high-fidelity TURBO results.
Parametric Analysis and Optimization of a High Temperature Fuel Cell: Supercritical CO2 Turbine Hybrid System
Authors: Sa´nchez D. , Chacartegui R. , Mun˜oz A. , Sa´nchez T.
Published: August 2009

The integration of high temperature fuel cells — molten carbonate and solid oxide — and gas turbine engines for efficient power generation is not new. Different strategies for integrating both systems have been proposed in the past ten years and there are some field tests being run presently. However, the commercial availability of such power systems seems to be continuously delayed, probably due to cost and reliability problems. The materials used in high temperature fuel cells are expensive and their cost is not decreasing at the expected pace. In fact, it looks as if they had reached stabilization. Therefore, there seems to be agreement that operating at a lower temperature might be the only way to achieve more competitive costs to enter the market, as metallic materials could then be used. From the point of view of conventional hybrid systems, decreasing the operating temperature of the cell would affect the efficiency of the bottoming cycle dramatically, as long as turbine inlet temperature is a critical parameter for the performance of a Brayton cycle. This is the reason why hybrid systems perform better with solid oxide fuel cells operating at 1000 °C than with molten carbonate cells at 650 °C typically. This work presents a hybrid system comprising a high temperature fuel cell, either SOFC or MCFC, and a bottoming Brayton cycle working with supercritical carbon dioxide. A parametric analysis is done where all the parameters affecting the performance of the hybrid system are studied, with emphasis in the bottoming cycle. For the Brayton cycle: pressure ratio, expansion and compression efficiencies, recuperator effectiveness, pressure losses, turbine inlet temperature... For the fuel cell: fuel utilization, current density, operating temperature, etc. From this analysis, optimum operating point and integration scheme are established and, after this, a comparison with conventional hybrid systems using similar fuel cells is done. Results show that, although the fuel cell is not pressurized in the CO2 based system, its performance is similar to the best conventional cycle. Furthermore, if lower operating temperatures are considered for the fuel cell, the new system performs better than any of the conventional.
A Multi-Step Optimization Approach to Distributed Cogeneration Systems With Heat Storage
Authors: Campanari Stefano , Manzolini Giampaolo , Silva Paolo
Published: August 2009

Distributed cogeneration systems typically face variable electrical and heating demands, especially when applied to civil loads (e.g. residential, tertiary and commercial loads), often showing significant variations during the day of the heat to electricity load ratio. In these cases, application of heat storage gives the possibility of significantly improving the energetic and economic performance of the system. This paper discusses the development and testing of an optimization model for the selection of the best operating strategy and component sizing for cogeneration systems with heat storage, based on the code DCOGEN already presented in a previous work. The model employs a multiple-step optimization approach, discussed in detail in the paper, aiming to select the best hourly operating schedule on a daily basis. Optimization allows to (i) minimize or eliminate the waste of useful heat of the cogeneration prime mover (e.g. a microturbine or a reciprocating engine) and (ii) maximize the economic benefit of running the prime mover at high load, selling excess electricity to the grid when convenient. Results show that an optimized system with heat storage can reduce the thermal power produced by the auxiliary boiler and substantially increases the primary energy savings of the cogeneration unit. The model is tested towards a real application, with time-variable loads and several day-types profiles. The discussion compares different size cogeneration systems, based on micro gas turbine and internal combustion engines. Test case specifications also include tariffs, regulatory and climate data, provided that performance of the main components are corrected as a function of load and ambient conditions. Detailed results are presented, in terms of annual energy balances, energy savings and economic analysis.
A Contact Model for Nonlinear Forced Response Prediction of Turbine Blades: Calculation Techniques and Experimental Comparison
Authors: Firrone Christian M. , Allara Marco , Gola Muzio M.
Published: August 2009

Dry friction damping produced by sliding surfaces is commonly used to reduce vibration amplitude of blade arrays in turbo-machinery. The dynamic behavior of turbine components is significantly affected by the forces acting at their contact interfaces. In order to perform accurate dynamic analysis of these components, contact models must be included in the numerical solvers. This paper presents a novel approach to compute the contact stiffness of cylindrical contacts, analytical and based on the continuous contact mechanics. This is done in order to overcome the known difficulties in simultaneously adjusting the values of both tangential and normal contact stiffness experimentally. Monotonic loading curves and hysteresis cycles of contact forces vs. relative displacement are evaluated as a function of the main contact parameters (i.e. the contact geometry, the material properties and the contact normal load). The new contact model is compared with other contact models already presented in literature in order to show advantages and limitations. The contact model is integrated in a numerical solver, based on the Harmonic Balance Method (HBM), for the calculation of the forced response of turbine components with friction contacts, in particular underplatform dampers. Results from the nonlinear numerical simulations are compared with those from validation experiments.
Instability and Transition in a Separation Bubble Under a Three-Dimensional Freestream Pressure Distribution
Authors: Yaras M. I.
Published: August 2009

This paper presents measurements of the instability and transition processes in separation bubbles under a three-dimensional freestream pressure distribution. Measurements are performed on a flat plate upon which a pressure distribution is imposed by a contoured surface facing the flat test surface. The three-dimensional pressure distribution that is established on the test surface approximates the pressure distributions encountered on swept blades. This type of pressure field produces crossflows in the laminar boundary layer upstream of separation and within the separation bubble. The effects of these crossflows on the instability of the upstream boundary layer and on the instability, transition onset and transition rate within the separated shear layer are examined. The measurements are performed at two flow Reynolds numbers and relatively low level of freestream turbulence. The results of this experimental study show that the three-dimensional freestream pressure field and the corresponding redistribution of the freestream flow cause significant spanwise variation of the separation-bubble structure. It is demonstrated that the instability and transition processes in the modified separation bubble develop on the basis of the same fundamentals as in two-dimensional separation bubbles, and can be predicted with the same level of accuracy using models that have been developed for two-dimensional separation bubbles.
Modelling Unsteady Transition Effects in an Axial Compressor
Authors: Beevers Adam D. , Amaral-Teixeira Joao , Wells Roger
Published: August 2009

Wake induced transition is simulated at mid-span on a C4 stator blade in a 1.5 stage low speed axial compressor using the CFX γ – θ transition model. IGV and rotor wake inputs were created from a succession of Fourier series produced from experimental data. The purpose of the study was to understand the effectiveness of the γ – θ model implemented in a commercial code to predict the unsteady effects of wake induced transition. The γ – θ transition model was found to predict wake-induced transition and the subsequent calmed region caused by the passing wakes. The wake velocity defect creates conditions within the boundary layer such that the high disturbance energy, which is diffused into the boundary layer at the leading edge from the wake, initiates the transition process. This high disturbance energy travels through the boundary layer directly behind the wake.
NOx Reduction Strategy in GE10 Hydrogen-Fuelled Heavy Duty Gas Turbine
Authors: Benovsky Peter , Brunetti Iarno , Sigali Stefano , Leroy Christine , Gheri Paolo , Cocchi Stefano
Published: August 2009

In December 2006 Enel promoted a project oriented towards Environment and Innovation including the development of zero emission plants. The hydrogen project foresees the construction of a 11 MWe hydrogen-fed gas turbine able to couple high efficiency (fuel utilization) with low nitrogen-oxide emissions. The project (partly funded by Regione Veneto, a local authority in the North-East of Italy), will be built at Enel’s coal-fired Fusina Power Plant [1]. The aim of a first demonstrative phase is to verify the correct operation of the gas turbine supplied by pure hydrogen and to acquire know-how of hydrogen combustion, safety aspects and control technologies in gas turbine cycles. In the second phase, the goal will be to optimize the combustion technology, paying particular attention to NOx emissions. To make hydrogen suitable for the electricity generation in an environmentally compatible manner, Enel is developing the Fusina’s experimental power plant project. Since currently no commercial hydrogen burners are suitable for gas turbine power plants, both Enel and Nuovo Pignone are investigating feasible solutions for a hydrogen-fuelled low-NOx diffusion burner design. In this context, this paper presents the results from a CFD analysis showing the NOx reduction based on steam injection and burner minor modifications. An initial model with a coarse mesh and simple aerodynamic treatment was used to evaluate the NOx emissions with varying amount of steam injected into the combustion chamber. In the view of the following experimental campaign, some solutions have been selected after an initial tuning of the CFD model. Furthermore, a second CFD model based on a finer mesh and a detailed geometry discretization will enable a more precise investigation of the fluidynamic field. Results of the numerical model, which simulates a GE10 gas turbine combustor fuelled with pure hydrogen, are presented and compared with experimental tests at full scale and full pressure conditions.
High Efficiency Gas Turbine Based Power Cycles—A Study of the Most Promising Solutions: Part 1—A Review of the Technology
Authors: Bhargava Rakesh K. , Bianchi Michele , Campanari Stefano , De Pascale Andrea , Negri di Montenegro Giorgio , Peretto Antonio
Published: August 2009

Commercially available gas turbines have been mostly designed based on the simple Brayton cycle and despite the enormous advancements made in their components design, materials technology, blade cooling methods, etc., thermodynamic performance achievable for this simple cycle is limited. Numerous variants to the basic Brayton cycle viz., Recuperated (REC), Inter-Cooled (IC), Re-Heat (RH), steam injected (STIG) and their combinations have been proposed, extensively discussed in the literature since the early stages of gas turbine development and few of them have been successfully implemented. New variants not yet implemented in commercial engines and still in various stages of the development with potential for additional performance improvement are: advanced Steam Injected cycle and its variants (such as Inter-cooled Steam Injected, (ISTIG)), Recuperated Water Injection cycle (RWI), Humidified Air Turbine (HAT) cycle and Cascaded Humidified Advanced Turbine (CHAT) cycle, Brayton cycle with high temperature fuel cells (Molten Carbonate Fuel Cells (MCFC) and Solid Oxide Fuel Cells (SOFC)) and their combinations with the available modified Brayton cycles. The main objective of this paper (Part 1 of the two-part paper) is to provide a comprehensive review of high performance (with most promising solutions) complex gas turbine cycles, describing their main characteristics, benefits and drawbacks in comparison with the simple Brayton cycle. Detailed parametric thermodynamic cycle analyses for the selected high efficiency cycles under development are presented in Part 2 of this paper.
Three-Dimensional Modeling of Creep Damage in Airfoils for Advanced Turbine Systems
Authors: Karaivanov Ventzislav G. , Mazzotta Danny W. , Chyu Minking K. , Slaughter William S. , Alvin Mary Anne
Published: August 2009

Future oxy-fuel and hydrogen-fired turbines promise increased efficiency and low emissions. However, this comes at the expense of increased thermal load from higher inlet temperatures and a change in the working fluid in the gas path, leading to aero-thermal characteristics that are significantly different than those in traditional gas turbines. A computational methodology, based on three-dimensional finite element analysis (FEA) and damage mechanics is presented for predicting the evolution of creep in airfoils in these advanced turbine systems. Information revealed from three-dimensional computational fluid dynamics (CFD) simulations of external heat transfer and thermal loading over a generic airfoil provides detailed local distributions of pressure, surface temperature, and heat flux penetrating through the thermal barrier coated layer. There is an additional mechanical loading due to the centrifugal acceleration of the airfoil. Finite element analysis is then used to predict temperature and stress fields over the domain of the airfoil. The damage mechanics-based creep model uses a scalar damage parameter. This creep model is coupled with finite element analysis to predict the evolution of stress and creep damage over the entire airfoil. Visualization of the creep damage evolution over the airfoil shows the regions that are most susceptible to failure by creep.
An Experimental Study on Droplet Generation in Bearing Chambers Caused by Roller Bearings
Authors: Gorse P. , Dullenkopf K. , Bauer H.-J. , Wittig S.
Published: August 2009

The lifetime of aero-engine roller bearings strongly depends on lubrication and particularly on sufficient cooling provided by the oil system of the engine. During the development of advanced engines the overall oilflow has to be minimized to reduce size and weight of oil pipes and pumps. To support this development a fundamental understanding of the complex air/oilflow in bearing chambers is required. Although numerous efforts to characterize the liquid wall films were performed in recent years, only few investigations were carried out to carefully study the droplet generation in bearing chambers under realistic conditions. Therefore, the current research was initiated. Within the scope of this paper, a comprehensive experimental study on the droplet generation by a cylindrical roller bearing was carried out for a wide range of engine relevant conditions. In a first step, the oilflow near the roller bearing was visualized in a model bearing compartment. The results revealed that the pressure difference across the bearing and the design of the bearing support have strong influence on the generation of droplets. Furthermore, the velocity of the droplets was determined by means of stereoscopic particle image velocimetry. Based on these results a significantly improved understanding of the droplet generation caused by roller bearings was derived and compared to the experiments.
Conjugate Heat Transfer Study of a Biaxial Rig: Application to the Lifing of HP Turbine Disc Firtrees
Authors: Mabilat C. , Alizadeh S. , Jackson D. , Clarson R.
Published: August 2009

A full conjugate heat transfer Computational Fluid Dynamics (CFD) study of a Biaxial rig enclosure used for the lifing of the high pressure turbine disc firtrees of a large turbofan engine has been undertaken. Initial rig tests had demonstrated challenges associated with test repeatability and unexpected thermal gradients in some components. The detailed CFD analysis was used to gain an appropriate understanding of the overall heat balance for the assembly, requiring all three modes of heat transfer as well as the fluid dynamics about the disc-blade components. Moreover the detailed modelling methodology presented for the twin short wave infrared emitters allowed the balance of radiation to convection heat transfer from the heaters, essential to the whole study, to be appropriately captured. It was observed that radiation setup the bulk assembly temperature levels (> 900K). Convection heat transfer very much influenced component temperature gradients (10K for disc front-to-back surfaces and >80K for blade front-to-back surfaces). The gap sizes between the assembly and cooling blocks associated with rig setup had a strong influence on the convection currents and flow structures about the assembly and were an important factor in test repeatability. Strong cooler inflows were entrained under the blades, which in the tests had to be compensated by asymmetric top-to-bottom heater power setting of 1.5–2 folds. Once appropriate thermal operating conditions of the assembly were achieved in the tests, the model was tuned to achieve a satisfactory match against the more reliable test thermocouple temperatures, to about -/+10K for the most important locations. Thereafter the model component thermal field was used for follow-on stress analysis, required in critical component lifing and eventual engine certification. This circumvented the need for separate thermal modelling and provided efficient utilization of man-time resource.
CFD Analysis of the Flow Through Tube Banks of HRSG
Authors: Torresi Marco , Saponaro Alessandro , Camporeale Sergio Mario , Fortunato Bernardo
Published: August 2009

The prediction of the performance of HRSG (Heat Recovery Steam Generator) by means of CFD codes is of great interest, since HRSGs are crucial elements in gas turbine combined cycle power plants, and in CHP (combined heat and power) cycles. The determination of the thermo-fluid dynamic pattern in HRSGs is fundamental in order to improve the energy usage and limit the ineffectiveness due to non-homogeneous flow patterns. In order to reduce the complexity of the simulation of the fluid flow within the HRSG, it is useful modeling heat exchangers as porous media zones with properties estimated using pressure drop correlations for tube banks. Usually, air-side thermo-fluid dynamic characteristics of finned tube heat exchangers are determined from experimental data. The aim of this work is to develop a new procedure, capable to define the main porous-medium non-dimensional parameters (e.g., viscous and inertial loss coefficients; porosity; volumetric heat generation rate; etc...) starting from data obtained by means of accurate three-dimensional simulations of the flow through tube banks. Both finned and bare tube banks will be considered and results presented. The analysis is based on a commercial CFD code, Fluent v.6.2.16. In order to validate the proposed procedure, the simulation of an entire fired HRSG of the horizontal type developed by Ansaldo Caldaie for the ERG plant at Priolo (Italy) has been performed and results have been compared with their data.
Multi-Objective Robust Design Optimization and Knowledge Mining of a Centrifugal Fan That Takes Dimensional Uncertainty Into Account
Authors: Sugimura Kazuyuki , Jeong Shinkyu , Obayashi Shigeru , Kimura Takeshi
Published: August 2009

A new design approach named MORDE (multi-objective robust design exploration), in which multi-objective robust optimization techniques and data mining techniques are combined, is proposed in this paper. We first developed a widely applicable design framework for multi-objective robust optimization. In this framework, probabilistic representation of design variables are introduced and Kriging models are used to approximate relations between design variables with uncertainty and multiple design objectives. A multi-objective genetic algorithm optimizes the mean and standard deviation of the responses. We then applied the framework to the real-world design problem of a centrifugal fan used in a washer-dryer. Taking dimensional uncertainty into account, we optimized the means and standard deviations of the resulting distributions of fan efficiency and turbulent noise level. Steady Reynolds-averaged Navier Stokes simulations were used to build Kriging models that approximate these objective functions. With the obtained non-dominated solutions, we demonstrated how to analyze features of solutions and select design candidates. We also attempted to acquire design knowledge by applying several data mining techniques. Self-organizing map was used to visualize and reuse the high dimensional design data. Decision tree analysis and rough set theory were used to extract design rules to improve the product’s performance. We also discussed differences in types of rules, which were extracted by both methods.
Measurements of Secondary Losses in a Turbine Cascade With the Implementation of Non-Axisymmetric Endwall Contouring
Authors: Knezevici D. C. , Sjolander S. A. , Praisner T. J. , Allen-Bradley E. , Grover E. A.
Published: August 2009

An approach to endwall contouring has been developed with the goal of reducing secondary losses in highly loaded axial turbo-machinery. The present paper describes an experimental assessment of the performance of the contouring approach implemented in a low speed linear cascade test facility. The study examines the secondary flows of a cascade composed of Pratt and Whitney PAKB airfoils. This airfoil has been used extensively in low pressure turbine research and the present work adds intra-passage pressure and velocity measurements to the existing database. The cascade was tested at design incidence and at an inlet Reynolds number of 126,000 based on inlet midspan velocity and axial chord. Quantitative results include seven hole pneumatic probe pressure measurements downstream of the cascade to assess blade row losses, and detailed seven hole probe measurements within the blade passage to track the progression of flow structures. Qualitative results take the form of oil surface flow visualization on the endwall and blade suction surface. The application of endwall contouring resulted in lower secondary losses and caused a reduction in secondary kinetic energy associated with pitchwise flow near the endwall and spanwise flow up the suction surface within the blade passage. The mechanism of loss reduction is discussed in regards to the reduction of secondary kinetic energy.
Inverse Modeling Techniques for Application to Engine Transient Performance Data Matching
Authors: Agarwal Harish , Kale Amit , Akkaram Srikanth , Balasubramaniam Mahadevan , Ebacher Susan , Gilleberto Paul
Published: August 2009

A framework demonstrating the application of inverse modeling technology for engine performance data matching is presented. Transient aero-thermodynamic cycle models are used to simulate engine performance and control characteristics over the entire flight envelope. These models are used not only for engine design and certification but also to provide performance guarantees to the customer and for engine diagnostics. Therefore, it is extremely important that these models are able to accurately predict the performance metrics of interest. Accuracy of these models can be improved by fine-tuning model parameters so that the model output best matches the flight test data. The performance of an aircraft engine is fine tuned from several sensor observations, e.g. exhaust gas temperature, fuel flow, and fan speed. These observations vary with parameters like power level, core speed and operating conditions like altitude, inlet conditions (temperature and pressure), and Mach number, and are used in conjunction with a transient performance simulation model to assess engine performance. This is normally achieved through an iterative manual approach that requires a lot of expert judgment. Simulating transient performance characteristics often requires an engineer to estimate model parameters by matching model response to engine sensor data. Such an estimation problem can be posed using inverse modeling technology. One of the main challenges in the application of inverse modeling for parameter estimation is that the problem can be ill-posed that leads to instability and non-uniqueness of the solution. The inverse method employed here for parameter estimation provides a solution for both well-posed and ill-posed problems. Sensitivity analysis can be used to better pose the data-matching problem. Singular value decomposition (SVD) technique is used to address the ill-posed nature of the inverse problem, which is solved as a finite dimensional non-linear optimization problem. Typically, the transient response is highly nonlinear and it may not be possible to match the whole transient simultaneously. This paper extends the framework on transient inverse modeling developed in [1] for engine transient performance applications. Variable weighting mechanism allows providing different weights to different sensors. This helps in better control on data matching, identify drift in parameter values over time, and point towards incorrect modeling assumptions. The application of the inverse methodology is demonstrated on a single spool non-afterburning engine and a commercial aviation engine model.
On Line Fault Detection and Isolation in Gas Turbine Combustion Chambers
Authors: Medina Pablo , Saez Doris , Roman Roberto
Published: August 2009

This work presents the development of a new model for the exhaust gas temperature based on both basis function expansion and the Brayton cycle. This model is a function of the power generated, ambient temperature, compression rate, and the temperature of each combustion chamber. This last temperature is unknown, but could be estimated. The model basis functions also include the spatial distribution of the combustion chamber and exhaust gases swirl angle surface. Thus, based on the gas path in the turbine, each base function of the model is related to a particular combustion chamber. This is the main assumption that allows solving the fault detection and isolation problem in gas turbines at the level of combustion chambers. As a result of the model identification at every instant, there is a group of coefficients, which are associated to each combustion chamber. From these coefficients, it is possible to generate signals that can be analyzed with statistical techniques and also with wavelets to detect abrupt changes in its behavior.
Spectral Analysis of the Flow in an Intermediate Turbine Duct
Authors: Axelsson Lars-Uno , George William K.
Published: August 2009

The meaning of integral length scale is discussed in the context of inlet boundary conditions for an intermediate turbine duct located downstream a high-pressure turbine stage. Contrary to popular belief, the integral scale determined from spectral or correlation data is not the same as that commonly used in turbulence models, even when the periodic components are removed from consideration. In particular, the “pseudo-integral-scale”, Lε = q3/ε, defined from the turbulence intensity and dissipation, can differ by an order of magnitude or more from the true integral scale, no matter how the latter is determined. And even though the ratio may be asymptotically constant with increasing Reynolds number, it depends on the nature of the turbulence present. It is the pseudo-integral scale that is mostly wanted (at least by turbulence modelers), but it is the dissipation that complicates its determination experimentally. This paper outlines a procedure for obtaining the dissipation using the measured one-dimensional energy spectrum, and lays out criteria for when the procedure can be legitimately used. The theoretical arguments, based on the postulated existence of k−5/3 range, are illustrated with spectral measurements immediately downstream a single-stage turbine using the Chalmers large-scale turbine facility. The spectra are obtained from area traverses with a 2-component hot-wire.
Ignition and Flame Speed Kinetics of Two Natural Gas Blends With High Levels of Heavier Hydrocarbons
Authors: Bourque Gilles , Healy Darren , Curran Henry , Zinner Christopher , Kalitan Danielle , de Vries Jaap , Aul Christopher , Petersen Eric
Published: August 2009

High-pressure experiments and chemical kinetics modeling were performed to generate a database and a chemical kinetic model that can characterize the combustion chemistry of methane-based fuel blends containing significant levels of heavy hydrocarbons (up to 37.5% by volume). Ignition delay times were measured in two different shock tubes and in a rapid compression machine at pressures up to 34 atm and temperatures from 740 to 1660 K. Laminar flame speeds were also measured at pressures up to 4 atm using a high-pressure vessel with optical access. Two different fuel blends containing ethane, propane, n-butane, and n-pentane added to methane were studied at equivalence ratios varying from lean (0.3) to rich (2.0). This paper represents the most comprehensive set of experimental ignition and laminar flame speed data available in the open literature for CH4/C2H6/C3H8/C4H10/C5H12 fuel blends with significant levels of C2+ hydrocarbons. Using these data, a detailed chemical kinetics model, based on current and recent work by the authors, was compiled and refined. The predictions of the model are very good over the entire range of ignition delay times, considering the fact that the data set is so thorough. Nonetheless, some improvements to the model can still be made with respect to ignition times at the lowest temperatures and for the laminar flame speeds at pressures above 1 atm and rich conditions.
Investigation of Sand Blocking Within Impingement and Film-Cooling Holes
Authors: Cardwell N. D. , Thole K. A. , Burd S. W.
Published: August 2009

Gas turbines are not generally designed for operation with a particle laden inlet flow but, in fact, are commonly operated in unclean environments resulting in dirt, sand, and other debris ingestion. In addition to the negative effects within the main gas path, for aeroengines these particles are pulled into the coolant system where they can clog cooling passages and erode internal surfaces. Unlike previous research that focused on deposition and erosion within the main gas path, this study evaluated blocking in a double wall liner whereby both impingement and film-cooling holes were simulated. Double wall liners are commonly used in the combustor and turbine for combined internal and external cooling of metal components. Specifically, sand blockages were evaluated through comparisons of measured flowrates for a particular pressure ratio across the liner. Four liner geometries were tested whereby the coolant hole size and orientation were varied in test coupons. At ambient temperature, blocking was shown to be a function of the impingement flow area. A significant rise in blocking was observed as sand and metal temperatures were increased. The overlap between the impingement and film-cooling holes was also found to have a significant effect.
Combined-Cycle Power Plant Maintenance Costs
Authors: Grace Dale S.
Published: August 2009

This paper describes a methodology to quantify scheduled and unscheduled maintenance costs and a software framework for estimating operations and maintenance (O&M) costs of combined-cycle power plants over their operating life. Scheduled maintenance costs consist primarily of replacement and repair of hot section components of the combustion turbine that occur during planned inspections and overhaul events. Scheduled maintenance costs can be estimated based on anticipated parts life, operating conditions and parts costs. Some degree of uncertainty exists, but the range of costs is fairly well understood. Unscheduled maintenance costs are not as readily defined. Experiential data of unplanned events from a large sampling of plants over time can be used to estimate unscheduled costs. Because of the wide variation in experience from unit to unit, a range of costs are anticipated. This paper includes a description of a study of F-class combined-cycle plant data that provides the basis for defining a cost distribution of unscheduled maintenance costs. In addition, the reliability and availability statistics of these plants are used to estimate lost generation revenue due to unplanned outages, which can be significantly higher than the cost of performing the repairs to return the unit to service.
Improved Film Cooling Effectiveness by Placing a Vortex Generator Downstream of Each Hole
Authors: Rigby David L. , Heidmann James D.
Published: August 2009

Calculations are presented demonstrating the effect of placing a delta vortex generator downstream of a film cooling hole. The effects of blowing ratio, density ratio, and spanwise pitch are included in the study. Flow over a flat plate with film cooling holes oriented at a 30 degree angle was investigated. The Reynolds numbers based on the freestream velocity and the hole diameter was 11,300. The simulation was performed using the Glenn-HT code, a full three-dimensional Navier-Stokes solver using the Wilcox k-ω turbulence model. A structured multi-block grid was used with approximately one million cells, and average y+ values on the order of unity. Local and span averaged effectiveness are presented. Analysis and visualization of the flow are presented as well as a discussion on the mechanisms which contribute to the dramatic improvement in effectiveness. The results demonstrate that the delta vortex generator was able to annihilate the up-wash vortex pair produced by the film hole and produce a down-wash pair downstream.
CBM Integrated Maintenance Scheduler
Authors: Jessop Simon , Valentine Scott , Roemer Michael
Published: August 2009

Condition Based Maintenance (CBM) is a key technology enabling facility maintenance cost reduction. The CBM approach to maintenance replaces rigid time-based maintenance schedules with the “right maintenance at the right time” identified by real-time equipment health monitoring. This approach creates a new requirement for determining the best time to schedule newly identified critical maintenance actions in light of the real world constraints of available labor and resources. One of the major challenges encountered when attempting to optimize a maintenance schedule is related to the resolution of the many and often complex interdependencies or constraints present throughout the maintenance process. This paper presents a CBM decision support software tool that leverages real-time current and future health condition information to optimize maintenance resources, tasking, and planning in order to maximize the system readiness. Over the past year Impact Technologies, under contract by NAVSEA, has been developing technologies that will provide the necessary decision support tools to address this dynamic maintenance environment. The software scheduling tool utilizes an Open Systems Architecture for Condition-Based Maintenance (OSA-CBM) architecture to facilitate implementation into new or legacy systems. The tool employs a generic maintenance model that accounts for equipment reliability attributes, maintenance task material and labor requirements, system dependencies, and subsystems relationships. The focus of the development has been on Naval Ship maintenance, but the model inputs can be adapted to a variety of applications including power generators, aircraft, ships, and production facilities. The core of the decision support tool is a multi-sweep optimization algorithm that is tuned to the maintenance scheduling problem. The algorithm has been designed to achieve the best computational speed. Benefits and risks of maintenance decisions have been quantified in risk, which can be defined in terms of readiness or financial. The probability and consequence of each system failure are considered in light of the complex system interdependencies, such as dependant and redundant systems, to achieve the best overall system readiness. Novel post-processing steps identify the active solution constraints further enhancing the user’s ability to understand the issues that affect system availability.
Adapting Gas Turbines to Zero Emission Oxy-Fuel Power Plants
Authors: Anderson Roger E. , MacAdam Scott , Viteri Fermin , Davies Daniel O. , Downs James P. , Paliszewski Andrew
Published: August 2009

Future power plants will require some type of carbon capture and storage (CCS) system to mitigate carbon dioxide (CO2) emissions. The most promising technologies for CCS are: oxy-fuel (O-F) combustion, pre-combustion capture, and post-combustion capture. This paper discusses the recent work conducted by Siemens Power Generation, Florida Turbine Technologies, Inc. (FTT) and Clean Energy Systems, Inc. (CES) in adapting high temperature gas turbines to use CES’s drive gases in high-efficiency O-F zero emission power plants (ZEPPs). CES’s O-F cycle features high-pressure combustion of fuel with oxygen (O2) in the presence of recycled coolant (water, steam or CO2) to produce drive gases composed predominantly of steam and CO2. This cycle provides the unique capability to capture nearly pure CO2 and trace by-products by simple condensation of the steam. An attractive O-F power cycle uses high, intermediate and low pressure turbines (HPT, IPT and LPT, respectively). The HPT may be based on either current commercial or advanced steam turbine technology. Low pressure steam turbine technology is readily applicable to the LPT. To achieve high efficiencies, an IPT is necessary and efficiency increases with inlet temperature. The high-temperature IPT’s necessitate advanced turbine materials and cooling technology. O-F plants have an abundance of water, cool steam ∼200°C (400°F) and CO2 that can be used as cooling fluids within the combustor and IPT systems. For the “First Generation” ZEPP, a General Electric J79 turbine, minus the compressor, to be driven directly by CES’s 170 MWt high-pressure oxy-fuel combustor (gas generator), has been adapted. A modest inlet gas temperature of 760°C (1400°F) was selected to eliminate the need for turbine cooling. The J79 turbine operating on natural gas delivers 32 MWe and incorporates a single-stage free-turbine that generates an additional 11 MWe. When an HPT and an LPT are added, the net output power (accounting for losses) becomes 60 MWe at 30% efficiency based on lower heating value (LHV), including the parasitic loads for O2 separation and compression and for CO2 capture and compression to 151.5 bar (2200 psia). For an inlet temperature of 927°C (1700°F), the nominal value, the net output power is 70 MWe at 34% efficiency (LHV). FTT and CES are evaluating a “Second Generation” IPT with a gas inlet temperature of 1260°C (2300°F). Predicted performance values for these plants incorporating the HPT, IPT and the LPT are: output power of approximately 100–200 MWe with an efficiency of 40 to 45%. The “Third Generation” IPT for 2015+ power plants will be based on the development of very high temperature turbines having an inlet temperature goal of 1760°C (3200°F). Recent DOE/CES studies project such plants will have LHV efficiencies in the 50% range for natural gas and HHV efficiencies near 40% for gasified coal.
Second Law Efficiency of the Rankine Bottoming Cycle of a Combined Cycle Power Plant
Authors: Gulen S. Can , Smith Raub W.
Published: August 2009

A significant portion of the new electrical generating capacity installed in the past decade has employed heavy-duty gas turbines operating in a combined cycle configuration with a steam turbine bottoming cycle. In these power plants approximately one third of the power is generated by the bottoming cycle. To ensure that the highest possible combined cycle efficiency is realized it is important to develop the combined cycle power plant as a system. Doing so requires a solid understanding of the efficiency entitlement of both, topping and bottoming, cycles separately and as a whole. This paper describes a simple but accurate method to estimate the Rankine bottoming cycle power output directly from the gas turbine exhaust exergy utilizing the second law of thermodynamics. The classical first law approach, i.e. the heat and mass balance method, requires lengthy calculations and complex computer-based modeling tools to evaluate Rankine bottoming cycle performance. In this paper, a rigorous application of the fundamental thermodynamic principles embodied by the second law to the major cycle components clearly demonstrates that the Rankine cycle performance can be accurately represented by several key parameters. The power of the second law approach lies in its ability to highlight the theoretical entitlement and state-of-the-art design performances simultaneously via simple, fundamental relationships. By considering economically and technologically feasible upper limits for the key parameters, the maximum achievable bottoming cycle power output is readily calculable for any given gas turbine from its exhaust exergy.
Nonlinear Modal Analysis and Energy Localization in a Bladed Disk Assembly
Authors: Georgiades F. , Peeters M. , Kerschen G. , Golinval J. C. , Ruzzene M.
Published: August 2009

The objective of this study is to carry out modal analysis of nonlinear periodic structures using nonlinear normal modes (NNMs). The NNMs are computed numerically with a method developed in [18] that is using a combination of two techniques: a shooting procedure and a method for the continuation of periodic motion. The proposed methodology is applied to a simplified model of a perfectly cyclic bladed disk assembly with 30 sectors. The analysis shows that the considered model structure features NNMs characterized by strong energy localization in a few sectors. This feature has no linear counterpart, and its occurrence is associated with the frequency-energy dependence of nonlinear oscillations.