Showing papers in "Journal of Engineering for Gas Turbines and Power-transactions of The Asme in 2006"

Fuel Flexibility Influences on Premixed Combustor Blowout, Flashback, Autoignition, and Stability

Abstract: This paper addresses the impact of fuel composition on the operability of lean premixed gas turbine combustors. This is an issue of current importance due to variability in the composition of natural gas fuel supplies and interest in the use of syngas fuels. Of particular concern is the effect of fuel composition on combustor blowout, flashback, dynamic stability, and autoignition. This paper reviews available results and current understanding of the effects of fuel composition on the operability of lean premixed combustors. It summarizes the underlying processes that must be considered when evaluating how a given combustor’s operability will be affected as fuel composition is varied.Copyright © 2006 by ASME

A Modular Code for Real Time Dynamic Simulation of Gas Turbines in Simulink

Abstract: A high-fidelity real-time simulation code based on a lumped, nonlinear representation of gas turbine components is presented. The code is a general-purpose simulation software environment useful for setting up and testing control equipments. The mathematical model and the numerical procedure are specially developed in order to efficiently solve the set of algebraic and ordinary differential equations that describe the dynamic behavior of gas turbine engines. For high-fidelity purposes, the mathematical model takes into account the actual composition of the working gases and the variation of the specific heats with the temperature, including a stage-by-stage model of the air-cooled expansion. The paper presents the model and the adopted solver procedure. The code, developed in Matlab-Simulink using an object-oriented approach, is flexible and can be easily adapted to any kind of plant configuration. Simulation tests of the transients after load rejection have been carried out for a single-shaft heavy-duty gas turbine and a double-shaft aero-derivative industrial engine. Time plots of the main variables that describe the gas turbine dynamic behavior are shown and the results regarding the computational time per time step are discussed.

A Review of Wave Rotor Technology and Its Applications

Abstract: The objective of this paper is to provide a succinct review of past and current research in developing wave rotor technology. This technology has shown unique capabilities to enhance the performance and operating characteristics of a variety of engines and machinery utilizing thermodynamic cycles. Although there have been a variety of applications in the past, this technology is not yet widely used and is barely known to engineers. Here, an attempt is made to summarize both the previously reported work in the literature and ongoing efforts around the world. The paper covers a wide range of wave rotor applications including the early attempts to use wave rotors, its successful commercialization as superchargers for car engines, research on gas turbine topping, and other developments. The review also pays close attention to more recent efforts: utilization of such devices in pressure-gain combustors, ultra-micro gas turbines, and water refrigeration systems, highlighting possible further efforts on this topic. Observations and lessons learnt from experimental studies, numerical simulations, analytical approaches, and other design and analysis tools are presented.

Study on Biomass Pyrolysis Kinetics

Abstract: Pyrolysis is the most fundamental process in thermal chemical conversion of biomass, and pyrolysis kinetic analysis is valuable for the in-depth exploration of process mechanisms. On the basis of thermal gravity analysis of different kinds of biomass feedstock, thermal kinetics analysis was performed to analyze the pyrolysis behavior of biomass. With the apparent kinetic parameters derived, a kinetic model was proposed for the main reaction section of biomass pyrolysis process. The pyrolysis characteristics of three kinds of biomass material were compared in view of corresponding biochemical constitution. Through model simulation of different pyrolysis processes, the diversity in pyrolysis behavior of different kinds of biomass feedstock was analyzed and pyrolysis mechanism discussed. The results derived are useful for the development and optimization of biomass thermal chemical conversion technology.

Bayesian Network Approach for Gas Path Fault Diagnosis

Abstract: A method for solving the gas path analysis problem of jet engine diagnostics based on a probabilistic approach is presented. The method is materialized through the use of a Bayesian Belief Network (BBN). Building a BBN for gas turbine performance fault diagnosis requires information of a stochastic nature expressing the probability of whether a series of events occurred or not. This information can be extracted by a deterministic model and does not depend on hard to find flight data of different faulty operations of the engine. The diagnostic problem and the overall diagnostic procedure are first described. A detailed description of the way the diagnostic procedure is set-up, with focus on building the BBN from an engine performance model, follows. The case of a turbofan engine is used to evaluate the effectiveness of the method. Several simulated and benchmark fault case scenarios have been considered for this reason. The examined cases demonstrate that the proposed BBN-based diagnostic method composes a powerful tool. This work also shows that building a diagnostic tool, based on information provided by an engine performance model, is feasible and can be efficient as well.

Bump-type foil bearing structural stiffness : Experiments and predictions

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

Modeling and Simulation of a Gas Turbine Engine for Power Generation

Abstract: The gas turbine engine is a complex assembly of a variety of components that are designed on the basis of aerothermodynamic laws. The design and operation theories of these individual components are complicated. The complexity of aerothermodynamic analysis makes it impossible to mathematically solve the optimization equations involved in various gas turbine cycles. When gas turbine engines were designed during the last century, the need to evaluate the engines performance at both design point and off design conditions became apparent. Manufacturers and designers of gas turbine engines became aware that some tools were needed to predict the performance of gas turbine engines especially at off design conditions where its performance was significantly affected by the load and the operating conditions. Also it was expected that these tools would help in predicting the performance of individual components, such as compressors, turbines, combustion chambers, etc. At the early stage of gas turbine developments, experimental tests of prototypes of either the whole engine or its main components were the only method available to determine the performance of either the engine or of the components. However, this procedure was not only costly, but also time consuming. Therefore, mathematical modelling using computational techniques were considered to be the most economical solution. The first part of this paper presents a discussion about the gas turbine modeling approach. The second part includes the gas turbine component matching between the compressor and the turbine which can be met by superimposing the turbine performance characteristics on the compressor performance characteristics with suitable transformation of the coordinates. The last part includes the gas turbine computer simulation program and its philosophy. The computer program presented in the current work basically satisfies the matching conditions analytically between the various gas turbine components to produce the equilibrium running line. The computer program used to determine the following: the operating range (envelope) and running line of the matched components, the proximity of the operating points to the compressor surge line, and the proximity of the operating points at the allowable maximum turbine inlet temperature. Most importantly, it can be concluded from the output whether the gas turbine engine is operating in a region of adequate compressor and turbine efficiency. Matching technique proposed in the current work used to develop a computer simulation program, which can be served as a valuable tool for investigating the performance of the gas turbine at off-design conditions. Also, this investigation can help in designing an efficient control system for the gas turbine engine of a particular application including being a part of power generation plant.

Experimental Study on the Role of Entropy Waves in Low-Frequency Oscillations in a RQL Combustor

Abstract: "Rumble'' is a self-excited combustion instability, usually occurring at the start-up of aero-engines with fuel-spray atomizers at sub-idle and idle conditions, and exhibiting low limit frequencies in the range of 50 H z to 150 Hz. Entropy waves at the (nearly) choked combustor outlet are supposed to be the key feedback mechanism for the observed self-excited pressure oscillations. The experimental study presented here aims at clarifying the role of entropy waves in the occurrence of rumble. A generic air-blast atomizer with a design prone to self-excitation has been incorporated into a thermoacoustic combustor test rig with variable outlet conditions. The thermoacoustic response of the flame was characterized by recording the OH* chemiluminescence, the dynamic pressures. the dynamic temperatures, and by applying PIN. The measurements have shown the occurrence of periodic hot spots traveling with the mean flow with considerable dispersion. Measurements have been conducted with an open-ended resonance tube in order to eliminate the impact of entropy waves on the mechanism of self-excitation. The oscillation obtained, comparable in amplitude and frequency, proved that self-excitation primarily depends on convective time delays of the droplets in the primary zone and thus on the atomization characteristics of the nozzle.

Hot Corrosion of Lanthanum Zirconate and Partially Stabilized Zirconia Thermal Barrier Coatings

Abstract: The hot corrosion resistance of lanthanum zirconate and 8 wt. % yttria-stabilized zirconia coatings produced by thermal spraying for use as thermal barriers on industrial gas turbines or in aerospace applications was evaluated. The two ceramic oxide coatings were exposed for various periods of time at temperatures up to 1000°C to vanadium- and sulfur-containing compounds, species often produced during the combustion of typical fuels used in these applications. Changes in the coatings were studied using a scanning electron microscope to observe the microstructure and x-ray diffraction techniques to analyze the phase composition. The results showed different behaviors for the two materials: the zirconia-based coating being rapidly degraded by the vanadium compounds and resistant to attack by the sulfur materials while the lanthanum zirconate was less damaged by exposure to vanadia but severely attacked in the presence of sulfur-containing species.

Design Concept for Large Output Graz Cycle Gas Turbines

Abstract: The introduction of closed cycle gas turbines with their capability of retaining combustion generated CO 2 can offer a valuable contribution to the Kyoto goal and to future power generation. Therefore research and development work at the Graz University of Technology since the 1990s has led to the Graz Cycle, a zero emission power cycle of highest efficiency. It burns fossil fuels with pure oxygen which enables the cost-effective separation of the combustion CO 2 by condensation. The efforts for the oxygen supply in an air separation plant are partly compensated by cycle efficiencies far higher than for modern combined cycle plants. Upon the basis of the previous work, the authors present the design concept for a large power plant of 400 MW net power output making use of the latest developments in gas turbine technology. The Graz Cycle configuration is changed, insofar as condensation and separation of combustion generated CO 2 takes place at the 1 bar range in order to avoid the problems of condensation of water out of a mixture of steam and incondensable gases at very low pressure. A final economic analysis shows promising CO 2 mitigation costs in the range of $20―30/ton CO 2 avoided. The authors believe that they present here a partial solution regarding thermal power production for the most urgent problem of saving our climate.

Jet Engine Model for Control and Real-Time Simulations

Abstract: The main objective of this paper is development of a simple real-time transient performance model for jet engine control. A jet engine arrives to its most dangerous condition during transient operation that may be triggered by fast changes of the input fuel command signal. Thus, the control system specifications are formulated to specify the maximal variance of the fuel flow command (from idle to maximum power level) during transient maneuver. Linear and piecewise-linear techniques are not always convenient and appropriate for turbine engine controller design. An alternative quasilinear simple/ fast engine model is discussed in this paper. This model has maximum accuracy for maximal variance of the fuel flow input command in accordance to the jet engine control system specifications. The fast model is obtained using the Novel Generalized Describing Function, proposed for investigation of nonlinear control systems. The paper presents the Novel Generalized Describing Function definition and then discusses the application of this technique for the development a fast turbine engine simulation suitable for control and real-time applications. Simulation results are compared between the conventional and fast models and found to provide good agreement.

Numerical-Experimental Study and Solutions to Reduce the Dwell-Time Threshold for Fusion-Free Consecutive Injections in a Multijet Solenoid-Type CR System

Abstract: In ‘Multijet’ Common Rail (C.R.) diesel injection systems, when two consecutive injection current-pulses are approached to each other, the fusion of the two injections can occur. This causes undesired excessive amount of injected fuel, which leads to worsening of particulate emissions and fuel consumption. In order to avoid such a phenomenon, lower limits to the values of dwell time are introduced in the control unit maps, by means of a conservatively overestimated threshold, limiting the flexible management of multiple injections and C.R. system capability to perform a larger number of injection shots. The reason of the injection fusion is mainly due to the time delay between the electrical signal to the solenoid and the needle lift at both valve opening and closure. In particular, the dwell-time range inside of which injection fusion occurs was shown to decrease by reducing the nozzle closure delay. Experimental tests were carried out on a high-performance Moehwald-Bosch MEP2000/CA4000 test bench for determining the functional dependence of nozzle closure and opening delays on solenoid energizing time and nominal rail pressure. Besides, a mathematical relation between the solenoid energizing time and the injection time interval was determined. A Multijet C.R. injection system mathematical model, that was previously developed, including thermodynamics of liquids, fluid dynamics, subsystem mechanics, and electromagnetism equations, was applied to better understand the cause and effect relationships for nozzle opening and closure delays. In particular, numerical results on the time histories of delivery- and control-chamber pressures, pilot- and needle-valve lifts, mass flow rates through Z and A holes, were obtained and analyzed in order to highlight the dependence of nozzle opening and closure delays on electro-injector internal geometric features and on the needle dynamics. For all the considered operating conditions, the model predictions were compared to the experimental injection flow-rate patterns and to the pressure data taken at the injector inlet, for assessment. The nozzle closure delay was shown to strongly depend on the needle dynamics. Parametric tests were carried out with the numerical code by changing needle and control plunger mass, needle spring preload and stiffness, maximum needle stroke, in order to identify configurations useful for minimizing the nozzle closure delay. On the basis of the indications derived from these numerical tests, a modified version of the commercial electro-injector was realized so as to achieve effectively reduced nozzle closure delays and very close sequential injections without any fusion between them.Copyright © 2006 by ASME

An Integrated Fault Diagnostics Model Using Genetic Algorithm and Neural Networks

Abstract: This paper presents the development of an integrated fault diagnostics model for identifying shifts in component performance and sensor faults using the Genetic Algorithm and Artificial Neural Network. The diagnostics model operates in two distinct stages. The first stage uses response surfaces for computing objective functions to increase the exploration potential of the search space while easing the computational burden. The second stage uses the concept of a hybrid diagnostics model in which a nested neural network is used with genetic algorithm to form a hybrid diagnostics model. The nested neural network functions as a pre-processor or filter to reduce the number of fault classes to be explored by the genetic algorithm based diagnostics model. The hybrid model improves the accuracy, reliability, and consistency of the results obtained. In addition significant improvements in the total run time have also been observed. The advanced cycle Intercooled Recuperated WR21 engine has been used as the test engine for implementing the diagnostics model.

A Generic Approach for Gas Turbine Adaptive Modeling

Abstract: For gas turbine engine performance analysis, a variety of simulation tools is available. In order to minimize model development and software maintenance costs, generic gas turbine system simulation tools are required for new modeling tasks. Many modeling aspects remain engine specific however and still require large implementation efforts. One of those aspects is adaptive modeling. Therefore, an adaptive modeling functionality has been developed that can be implemented in a generic component-based gas turbine environment. A single component in a system modeling environment is able to turn any new or existing model into an adaptive model without extra coding. The concept has been demonstrated in the GSP gas turbine modeling environment. An object-oriented architecture allows automatic addition of the necessary equations for the adaptation to measurement values. Using the adaptive modeling component, the user can preconfigure the adaptive model and quickly optimize gas path diagnostics capability using experimentation with field data. The resulting adaptive model can be used by maintenance engineers for diagnostics. In this paper the integration of the adaptive modeling function into a system modeling environment is described. Results of a case study on a large turbofan engine application are presented.

Inlet Air Cooling Methods for Gas Turbine Based Power Plants

Abstract: Background: Power generation from gas turbines is penalized by a substantial power output loss with increased ambient temperature. By cooling down the gas turbine intake air the power output penalty can be mitigated. Method of Approach: The purpose of this paper is to review the state of the art in applications for reducing the gas turbine intake air temperature and examine the merits from integration of the different air-cooling methods in gas-turbine-based power plants. Three different intake air-cooling, methods (evaporative cooling, refrigeration cooling, and evaporative cooling of precompressed air) have been applied in two combined cycle power plants and two gas turbine plants. The calculations were performed on a yearly basis of operation. taking into account the time-varying climatic conditions. The economics from integration of the different cooling systems were calculated and compared. Results: The results have demonstrated that the highest incremental electricity generation is realized by absorption intake air-cooling. In terms of the economic performance of the investment, the evaporative cooler has the lowest total cost of incremental electricity generation and the lowest payback period (PB). Concerning the cooling method of pre-compressed air the results show a significant gain in capacity, but the total cost of incremental electricity generation in this case is the highest. Conclusions: Because of the much higher capacity gain by an absorption chiller system. the evaporative cooler and the absorption chiller system may both be selected for boosting the performance of gas-turbine-based power plants, depending on the prevailing requirements of the plant operator.

Component Map Generation of a Gas Turbine Using Genetic Algorithms

Abstract: In order to estimate the precise performance of the existing gas turbine engine, the component maps with more realistic performance characteristics are needed. Because the component maps are the engine manufacturer's propriety obtained from very expensive experimental tests, they are not provided to the customers, generally. Therefore, because the engineers, who are working the performance simulation, have been mostly relying on component maps scaled from the similar existing maps, the accuracy of the performance analysis using the scaled maps may be relatively lower than that using the real component maps. Therefore, a component map generation method using experimental data and the genetic algorithms are newly proposed in this study. The engine test unit to be used for map generation has a free power turbine type small turboshaft engine. In order to generate the performance map for compressor of this engine, after obtaining engine performance data through experimental tests, and then the third order equations, which have relationships with the mass flow function, the pressure ratio, and the isentropic efficiency as to the engine rotational speed, were derived by using the genetic algorithms. A steady-state performance analysis was performed with the generated maps of the compressor by the commercial gas turbine performance analysis program GASTURB (Kurzke, 2001). In order to verify the proposed scheme, the experimental data for verification were compared with performance analysis results using traditional scaled component maps and performance analysis results using a generated compressor map by genetic algorithms (GAs). In comparison, it was found that the analysis results using the generated map by GAs were well agreed with experimental data. Therefore, it was confirmed that the component maps can be generated from the experimental data by using GAs and it may be considered that the more realistic component maps can be obtained if more various conditions and accurate sensors would be used.

An Adaptation Approach for Gas Turbine Design-Point Performance Simulation

Abstract: Accurate simulation and understanding of gas turbine performance is very useful for gas turbine users. Such a simulation and performance analysis must start from a design point. When some of the engine component parameters for an existing engine are not available, they must be estimated in order that the performance analysis can be carried out. However, the initially simulated design-point performance of the engine using estimated engine component parameters may give a result that is different from the actual measured performance. This difference may be reduced with better estimation of these unknown component parameters. However, this can become a difficult task for performance engineers, let alone those without enough engine performance knowledge and experience, when the number of design-point component parameters and the number of measurable/target performance parameters become large. In this paper, a gas turbine design-point performance adaptation approach has been developed to best estimate the unknown design-point component parameters and match the available design-point engine measurable/target performance. In the approach, the initially unknown component parameters may be compressor pressure ratios and efficiencies, turbine entry temperature, turbine efficiencies, air mass flow rate, cooling flows, bypass ratio, etc. The engine target (measurable) performance parameters may be thrust and specific fuel consumption for aero engines, shaft power and thermal efficiency for industrial engines, gas path pressures and temperatures, etc. To select, initially, the design point component parameters, a bar chart has been used to analyze the sensitivity of the engine target performance parameters to the design-point component parameters. The developed adaptation approach has been applied to a design-point performance matching problem of an industrial gas turbine engine GE LM2500+ operating in Manx Electricity Authority (MEA), UK. The application shows that the adaptation approach is very effective and fast to produce a set of design-point component parameters of a model engine that matches the actual engine performance very well. Theoretically, the developed techniques can be applied to other gas turbine engines.

Optimal Design of Gas Turbine Cogeneration Plants in Consideration of Discreteness of Equipment Capabilities

Abstract: To attain the highest economic and energy-saving characteristics of gas turbine cogeneration plants, it is necessary to rationally determine capacities and numbers of gas turbines and auxiliary equipment in consideration of their operational strategies corresponding to seasonal and hourly variations in energy demands. Some optimization approaches based on the mixed-integer linear programing have been proposed to this design problem. However, equipment capacities have been treated as continuous variables, and correspondingly, performance characteristics and capital costs of equipment have been assumed to be continuous functions with respect to their capacities. This is because if equipment capacities are treated discretely, the number of integer variables increases drastically and the problem becomes too difficult to solve. As a result, the treatment of equipment capacities as continuous variables causes discrepancies between existing and optimized values of capacities and expresses the dependence of performance characteristics and capital costs on capacities with worse approximations. In this paper, an optimal design method is proposed in consideration of discreteness of equipment capacities. A formulation for keeping the number of integer variables as small as possible is presented to solve the optimal design problem easily. This method is applied to the design of a gas turbine cogeneration plant, and its validity and effectiveness are clarified.

Towards Modeling Lean Blow Out in Gas Turbine Flameholder Applications

Abstract: The objective of this study was to assess the accuracy of the large-eddy simulation (LES) methodology, with a simple combustion closure based on equilibrium chemistry, for simulating turbulent reacting flows behind a bluff body flameholder. Specifically, the variation in recirculation zone length with change in equivalence ratio was calculated and compared to experimental measurements. It was found that the present LES modeling approach can reproduce this variation accurately. However, it understated the recirculation zone length at the stoichiometric condition. The approach was assessed at the lean blow out condition to evaluate its behavior at the lean limit and to analyze the physics of combustion instability.

A Comparative Study of Different Methods of Using Animal Fat as a Fuel in a Compression Ignition Engine

Abstract: This work explores a comparative study of different methods of using animal fat as afuel in a compression ignition engine. A single-cylinder air-cooled, direct-injection diesel engine is used to test the fuels at 100% and 60% of the maximum engine power output conditions. Initially, animal fat is tested as fuel at normal temperature. Then, it is preheated to 70 degrees C and used as fuel. Finally, animal fat is converted into methanol and ethanol emulsions using water and tested as fuel. A drop in cylinder peak pressure, longer ignition delay, and a lower premixed combustion rate are observed with neat animal fat as compared to neat diesel. With fat preheating and emulsions, there is an improvement in cylinder peak pressure and maximum rate of pressure rise. Ignition delay becomes longer with both the emulsions as compared to neat fats. However preheating shows shorter ignition delay. Improvement in heat release rates is achieved with all the methods as compared to neat fats. At normal temperature, neat animal fat results in higher specific energy consumption and exhaust gas temperature as compared to neat diesel at both power outputs. Preheating and emulsions of animal fat show improvement in performance as compared to neat fat. Smoke is lower with neat fat as compared to neat diesel. It reduces further with all the methods. At peak power output, the smoke level is found as 0.89 m(-1) with methanol, 0.28 m(-1) with ethanol emulsions, and 1.7 m(-1) with fat preheating, whereas it is 3.7 m(-1) with neat fat and 6.3 m(-1) with neat diesel. Methanol and ethanol emulsions significantly reduce NO emissions due to the vaporization of water and alcohols. However NO increases with fat preheating due to high in-cylinder temperature. Higher unburned hydrocarbon and carbon monoxide emissions are found with neat fat as compared to neat diesel at both power outputs. However these emissions are considerably reduced with all the methods. It is finally concluded that adopting emulsification with the animal fat can lead to a reduction in emissions and an improvement in combustion characteristics of a diesel engine.

Safe Dynamic Operation of a Simple SOFC/GT Hybrid System

Abstract: Safe Dynamic Operation of a simple SOFC/GT Hybrid Cycle[Safe Dynamic Operation of aSimple SOFC/GT Hybrid System]

Performance Enhancement of Microturbine Engines Topped With Wave Rotors

Abstract: Significant performance enhancement of microturbines is predicted by implementing various wave-rotor-topping cycles. Five different advantageous cases are considered for implementation of a four-port wave rotor into two given baseline engines. In these thermodynamic analyses, the compressor and turbine pressure ratios and the turbine inlet temperatures are varied, according to the anticipated design objectives of the cases. Advantages and disadvantages are discussed. Comparison between the theoretic performance of wave-rotor-topped and baseline engines shows a performance enhancement up to 34%. General design maps are generated for the small gas turbines, showing the design space and optima for baseline and topped engines. Also, the impact of ambient temperature on the performance of both baseline and topped engines is investigated. It is shown that the wave-rotor-topped engines are less prone to performance degradation under hot-weather conditions than the baseline engines.

Analysis of the Pollutant Formation in the FLOX® Combustion

Abstract: FLOX® — or flameless combustion is characterized by ultra-low NOx emissions. Therefore the potential for its implementation in gas turbine combustors is investigated in recent research activities. The major concern of the present paper is the numerical simulation of flow and combustion in a FLOX® -combustor [1, 2] at high pressure operating conditions with emphasis on the pollutant formation. FLOX® -combustion is a highly turbulent and high-velocity combustion process, which is strongly dominated by turbulent mixing and chemical non-equilibrium effects. By this means the thermal nitric oxide formation is reduced to a minimum, because even in the non-premixed case the maximum combustion temperature does not or rather slightly exceed the adiabatic flame temperature of the global mixture due to almost perfectly mixed reactants prior to combustion. In a turbulent flow the key aspects of a combustion model are twofold, i) chemistry and ii) turbulence/chemistry interaction. In the FLOX® -combustion we find that both physical mechanisms are of equal importance. Throughout our simulations we use the complex finite rate chemistry scheme GRI3.0 for methane and a simple partially stirred reactor (PaSR) model to account for the turbulence effect on the combustion. The computational results agree well with experimental data obtained in DLR test-facilities. For a pressure level of 20 bar, a burner load of 417 kW and an air to fuel ratio of λ = 2.16 computational results are presented and compared with experimental data.Copyright © 2006 by ASME

A Fully Integrated Approach to Component Zooming Using Computational Fluid Dynamics

Abstract: Background . This study focuses on a simulation strategy that will allow the performance characteristics of an isolated gas turbine engine component, resolved from a detailed, high-fidelity analysis, to be transferred to an engine system analysis carried out at a lower level of resolution. This work will enable component-level, complex physical processes to be captured and analyzed in the context of the whole engine performance, at an affordable computing resource and time. Approach . The technique described in this paper utilizes an object-oriented, zero-dimensional (0D) gas turbine modeling and performance simulation system and a high-fidelity, three-dimensional (3D) computational fluid dynamics (CFD) component model. The work investigates relative changes in the simulated engine performance after coupling the 3D CFD component to the 0D engine analysis system. For the purposes of this preliminary investigation, the high-fidelity component communicates with the lower fidelity cycle via an iterative, semi-manual process for the determination of the correct operating point. This technique has the potential to become fully automated, can be applied to all engine components, and does not involve the generation of a component characteristic map. Results . This paper demonstrates the potentials of the “fully integrated” approach to component zooming by using a 3D CFD intake model of a high bypass ratio turbofan as a case study. The CFD model is based on the geometry of the intake of the CFM56-5B2 engine. The high-fidelity model can fully define the characteristic of the intake at several operating condition and is subsequently used in the 0D cycle analysis to provide a more accurate, physics-based estimate of intake performance (i.e., pressure recovery) and hence, engine performance, replacing the default, empirical values. A detailed comparison between the baseline engine performance (empirical pressure recovery) and the engine performance obtained after using the coupled, high-fidelity component is presented in this paper. The analysis carried out by this study demonstrates relative changes in the simulated engine performance larger than 1%. Conclusions . This investigation proves the value of the simulation strategy followed in this paper and completely justifies (i) the extra computational effort required for a more automatic link between the high-fidelity component and the 0D cycle, and (ii) the extra time and effort that is usually required to create and run a 3D CFD engine component, especially in those cases where more accurate, high-fidelity engine performance simulation is required.

Systems-Level Performance Estimation of a Pulse Detonation Based Hybrid Engine

Abstract: A key application for a Pulse detonation engine concept is envisioned as a hybrid engine, which replaces the combustor in a conventional gas turbine with a pulse detonation combustor (PDC). A limit-cycle model, based on quasi-unsteady computational fluid dynamics simulations, was developed to estimate the performance of a pressare-rise PDC in a hybrid engine to power a subsonic engine core. The parametric space considered for simulations of the PDC operation includes the mechanical compression or the flight conditions that determine the inlet pressure and the inlet temperature conditions, fill fraction, and purge fraction. The PDC cycle process time scales, including the overall operating frequency, were determined via limit-cycle simulations. The methodology for the estimation of the performance of the PDC considers the unsteady effects of PDC operation. These metrics include a ratio of time-averaged exit total pressure to inlet total pressure and a ratio of mass-averaged exit total enthalpy to inlet total enthalpy. This information can be presented as a performance map for the PDC, which was then integrated into a system-level cycle analysis model, using GATECYCLE, to estimate the propulsive performance of the hybrid engine. Three different analyses were performed. The first was a validation of the model against published data for a specific impulse. The second examined the performance of a PDC versus a traditional Brayton cycle for a fixed combustor exit temperature; the results show an increased efficiency of the PDC relative to the Brayton cycle. The third analysis performed was a detailed parametric study of varying engine conditions to examine the performance of the hybrid engine. The analysis has shown that increasing the purge fraction, which can reduce the overall PDC exit temperature, can simultaneously provide small increases in the overall system efficiency.

Rotordynamic coefficients measurements versus predictions for a high-speed flexure-pivot tilting-pad bearing (load-between-pad configuration)

Abstract: Experimental dynamic force coefficients are presented for a four pad flexure-pivot tilting-pad bearing in load-between-pad configuration for a range of rotor speeds and bearing unit loadings. Measured dynamic coefficients have been compared to theoretical predictions using an isothermal analysis for a bulk-flow Navier-Stokes (NS) model. Predictions from two models-the Reynolds equation and a bulk-flow NS equation models are compared to experimental, complex dynamic stiffness coefficients (direct and cross-coupled) and show the following results: (i) The real part of the direct dynamic-stiffness coefficients is strongly frequency dependent because of pad inertia, support flexibility, and the effect of fluid inertia. This frequency dependency can be accurately modeled for by adding a direct added-mass term to the conventional stiffness/damping matrix model. (ii) Both models underpredict the identified added-mass coefficient (∼32 kg), but the bulk' flow NS equation predictions are modestly closer. (iii) The imaginary part of the direct dynamic-stiffness coefficient (leading to direct damping) is a largely linear function of excitation frequency, leading to a constant (frequency-independent) direct damping model. (iv) The real part of the cross-coupled dynamic-stiffness coefficients shows larger destabilizing forces than predicted by either model. The frequency dependency that is accounted for by the added mass coefficient is predicted by the models and arises (in the models) primarily because of the reduction in degrees of freedom from the initial 12 degrees (four pads times three degrees of freedom) to the two-rotor degrees of freedom. For the bearing and condition tested, pad and fluid inertia are secondary considerations out to running speed. The direct stiffness and damping coefficients increase with load, while increasing and decreasing with rotor speed, respectively. As expected, a small whirl frequency ratio (WFR) was found of about 0.15, and it decreases with increasing load and increases with increasing speed. The two model predictions for WFR are comparable and both underpredict the measured WFR values. Rotors supported by either conventional tilting-pad bearings or flexure-pivot tilting-pad (FPTP) bearings are customarily modeled by frequency-dependent stiffness and damping matrices, necessitating an iterative calculation for rotordynamic stability. For the bearing tested and the load conditions examined, the present results show that adding a constant mass matrix to the FPTP bearing model produces an accurate frequency-independent model that eliminates the need for iterative rotordynamic stability calculations. Different results may be obtained for conventional tilting-pad bearings (or this bearing at higher load conditions).

Influence of Operating Condition and Geometry on the Oil Film Thickness in Aeroengine Bearing Chambers

Abstract: Increasing the efficiency of modem jet engines does not only imply to the mainstream but also to the secondary air and oil system. Within the oil system the bearing chamber is one of the most challenging components. Oil films on the chamber walls are generated from oil droplets, ligaments, or film fragments, which emerge from bearings, seal plates and shafts, and enter the bearing chamber with an angular momentum. Furthermore, shear forces at its surface, gravity forces, and the design of scavenge and vent ports strongly impact the behavior of the liquid film. The present paper focuses on the experimental determination of the film thickness in various geometries of bearing chambers for a wide range of engine relevant conditions. Therefore, each configuration was equipped with five capacitive probes positioned at different circumferential locations. Two analytical approaches are used for a comprehensive discussion of the complex film flow.

Numerical and Experimental Damping Assessment of a Thin-Walled Friction Damper in the Rotating Setup With High Pressure Turbine Blades

Abstract: Underplatform friction dampers are possible solutions for minimizing vibrations of rotating turbine blades. Solid dampers, characterized by their compact dimensions, are frequently used in real applications and often appear in patents in different forms. A different type of the friction damper is a thin-walled structure, which has larger dimensions and smaller contact stresses on a wider contact area in relation to the solid damper. The damping performance of a thin-walled damper, mounted under the platforms of two rotating, freestanding high pressure turbine blades, is investigated numerically and experimentally in this paper. The tangential and normal contact stiffness that are crucial parameters in optimal design of any friction damper are determined from three-dimensional finite element computations of the contact behavior of the damper on the platform including friction and centrifugal effects. The computed contact stiffness values are applied to nonlinear dynamic simulations of the analyzed blades coupled by the friction damper of a specified mass. These numerical analyses are performed in the modal frequency domain, which is based on the harmonic balance method for the complex linearization of friction forces. The numerical dynamic results are in good agreement with the measured data of the real mistuned system. In the analyzed excitation range, the numerical performance curve of the thin-walled damper is obtained within the scatter band of the experimental results. For the known friction coefficients and available finite element and harmonic balance tools, the described numerical process confirms its usability in the design process of turbine blades with underplatform dampers.

Aerodynamic Instability and Life-Limiting Effects of Inlet and Interstage Water Injection Into Gas Turbines

Abstract: Gas turbine power enhancement technologies, such as inlet fogging, interstage water injection, saturation cooling, inlet chillers, and combustor injection, are being employed by end users without evaluating the potentially negative effects these devices may have on the operational integrity of the gas turbine. Particularly, the effect of these add-on devices, off-design operating conditions, nonstandard fuels, and compressor degradation/ fouling on the gas turbine's axial compressor surge margin and aerodynamic stability is often overlooked. Nonetheless, compressor aerodynamic instabilities caused by these factors can be directly linked to blade high-cycle fatigue and subsequent catastrophic gas turbine failure; i.e., a careful analysis should always proceed the application of power enhancement devices, especially if the gas turbine is operated at extreme conditions, uses older internal parts that are degraded and weakened, or uses nonstandard fuels. This paper discusses a simplified method to evaluate the principal factors that affect the aerodynamic stability of a single-shaft gas turbine's axial compressor. As an example, the method is applied to a frame-type gas turbine and results are presented. These results show that inlet cooling alone will not cause gas turbine aerodynamic instabilities, but that it can be a contributing factor if for other reasons the machine s surge margin is already slim. The approach described herein can be employed to identify high-risk applications and bound the gas turbine operating regions to limit the risk of blade life reducing aerodynamic instability and potential catastrophic failure.

Experimental Analysis of Soot Formation in Sooting Diffusion Flame by Using Laser-Induced Emissions

Abstract: Two-dimensional images of OH fluorescence, polycyclic aromatic hydrocarbons (PAHs) fluorescence, and laser-induced incandescence (LII) from soot were measured in a sooting diffusion flame. To obtain an accurate OH fluorescence image, two images were taken with the laser wavelength tuned to ("on") and away from ("off") the OH absorption line. An accurate OH fluorescence image was obtained by subtracting the off-resonance image from the on-resonance image. For the PAH fluorescence and LII measurements, temporally resolved measurements were used to obtain the individual images; the LII image was obtained by detecting the LII signal after the PAH fluorescence radiation had stopped and the PAH fluorescence image was obtained by subtracting the LII image from the simultaneous image of PAH fluorescence and LII. Based on the obtained images, the relative location of OH, PAH, and soot in the flame was discussed in detail. To investigate the PAH size distribution in a sooting flame using LIE, an estimation strategy for PAH size is proposed. Emission spectra were measured at several heights in the flame using a spectrograph. Since the emission wavelength of PAH fluorescence shifts toward longer wavelengths with increasing PAH size, the main PAH components in the emission spectra could be estimated. The results suggest that PAH grows and the type of PAH changes as the soot inception region was approached. Near the soot inception region, we estimated that the PAHs, which have over 16 carbon atoms, mainly constituted the emission spectrum.