Showing papers in "Journal of Engineering for Gas Turbines and Power-transactions of The Asme in 1999"

The Application of Expert Systems and Neural Networks to Gas Turbine Prognostics and Diagnostics

Abstract: Condition monitoring of engine gas generators plays an essential role in airline fleet management. Adaptive diagnostic systems are becoming available that interpret measured data, furnish diagnosis of problems, provide a prognosis of engine health for planning purposes, and rank engines for scheduled maintenance. More than four hundred operations worldwide currently use versions of the first or second generation diagnostic tools. Development of a third generation system is underway which will provide additional system enhancements and combine the functions of the existing tools. Proposed enhancements include the use of artificial intelligence to automate, improve the quality of the analysis, provide timely alerts, and the use of an Internet link for collaboration. One objective of these enhancements is to have the intelligent system do more of the analysis and decision making, while continuing to support the depth of analysis currently available at experienced operations. This paper presents recent developments in technology and strategies in engine condition monitoring including: (1) application of statistical analysis and artificial neural network filters to improve data quality, (2) neural networks for trend change detection, and classification to diagnose performance change, and (3) expert systems to diagnose, provide alerts and to rank maintenance action recommendations.

Nonlinear heat-release/acoustic model for thermoacoustic instability in lean premixed combustors

Abstract: Lean premixed combustors, such as those used in industrial gas turbines to achieve low emissions, are often susceptible to thermoacoustic combustion instabilities, which manifest themselves as pressure and heat release oscillations in the combustor. These oscillations can result in increased noise and decreased durability due to vibration and flame motion. A physically based nonlinear parametric model has been developed that captures this instability. It describes the coupling of combustor acoustics with the rate of heat release. The model represents this coupling by accounting for the effect of acoustic pressure fluctuations on the varying fuel/air ratio being delivered to the flame, causing a fluctuating heat release due to both fuel air ratio variations and flame front oscillations. If the phasing of the fluctuating heat release and pressure are proper, an instability results that grows into a limit cycle. The nonlinear nature of the model predicts the onset of the instability and additionally captures the resulting limit cycle. Tests of a lean premixed nozzle run at engine scale and engine operating conditions in the UTRC single nozzle rig, conducted under DARPA contract, exhibited instabilities. Parameters from the model were adjusted so that analytical results were consistent with relevant experimental data from this test. The parametric model captures the limit cycle behavior over a range of mean fuel air ratios, showing the instability amplitude (pressure and heat release) to increase and limit cycle frequency to decrease as mean fuel air ratio is reduced.

Shift reactors and physical absorption for Low-CO2 emission IGCCs

Abstract: Integrated gasification combined cycles (IGCC) exhibit conditions particularly favourable to the sequestration of CO 2 . The concept pursued in this paper is the generation of syngas low in carbon, where most of the heating value of the coal fuel is carried by hydrogen. Catalytic shift reactors convert most of the CO in the syngas into CO 2 , which is subsequently removed by physical absorption and then compressed to make it suitable for transport and permanent storage. Energy balances, performance, and cost of electricity are evaluated for two plants based on a Texaco gasifier and a large, heavy-duty gas turbine giving an overall IGCC power output between 350 and 400 MW. In one plant the raw syngas exiting the gasifier is cooled in a high-temperature, radiative cooler ; in the other it is quenched by the injection of liquid water. With respect to conventional Texaco IGCCs, the reduction of specific CO 2 emissions by 90 percent reduces LHV efficiency from 5 to 7 percentage points and increases the cost of electricity of about 40 percent. These penalties can be reduced by accepting lower reductions of CO 2 emissions. Compared to the semiclosed cycle considered by other authors, where CO 2 is the main component of the gas turbine working fluid, the plants analyzed here exhibit higher efficiency over the whole range of specific CO 2 emission.

Active control of combustion instability in a liquid-fueled low-NOx combustor

Abstract: A practical active control system for t nitigation of combustion instability has been designed and demonstrated in a lean, premixed, single-nozzle combustor at realistic engine operating conditions A full-scale engine fuel nozzle was modified to incorporate a simple fuel flow actuator Results indicate that the system was capable of reducing pressure fluctuations by 82 percent (15 dB or 56×) while maintaining or reducing NO x and CO emissions levels

Zero-Emission MATIANT Cycle

Abstract: In this paper, a novel technology based on the zero CO{sub 2} emission MATIANT (contraction of the names of the two designers MAThieu and IANTovski) cycle is presented. This latter is basically a gas cycle and consists of a supercritical CO{sub 2} Rankine-like cycle on top of regenerative CO{sub 2} Brayton cycle. CO{sub 2} is the working fluid and O{sub 2} is the fuel oxidizer in the combustion chambers. The cycle uses the highest temperatures and pressures compatible with the most advanced materials in the steam and gas turbines. In addition, a reheat and a staged compression with intercooling are used. Therefore, the optimized cycle efficiency rises up to around 45% when operating on natural gas. A big asset of the system is its ability to remove the CO{sub 2} produced in the combustion process in liquid state and at high pressure, making it ready for transportation, for reuse or for final storage. The assets of the cycle are mentioned. The technical issues for the predesign of a prototype plant are reviewed.

Reduced Order Modeling and Vibration Analysis of Mistuned Bladed Disk Assemblies With Shrouds

Abstract: This paper presents important improvements and extensions to a computationally efficient reduced order modeling technique for the vibration analysis of mistuned bladed disks. In particular, this work shows how the existing modeling technique is readily extended to turbomachinery rotors with shrouded blades. The modeling technique employs a component mode synthesis approach to systematically generate a reduced order model (ROM) using component modes calculated from a finite element model (FEM) of the rotor. Based on the total number of degrees of freedom, the ROM is typically two or three orders of magnitude smaller than the FEM. This makes it feasible to predict the forced response statistics ofmistuned bladed disks using Monte Carlo simulations. In this work, particular attention is devoted to the introduction of mistuning into the ROM of a shrouded assembly. Mistuning is modeled by projecting the mistuned natural frequencies of a single, cantilever blade with free shrouds onto the harmonic modes of the shrouded blade assembly. Thus, the necessary mistuning information may be measured by testing individual blades.

Compression Ratio Effect on Methane HCCI Combustion

Abstract: The authors have used the HCT (hydrodynamics, chemistry, and transport) chemical kinetics code to simulate HCCI (homogeneous charge compression ignition) combustion of methane-air mixtures. HCT is applied to explore the ignition timing, burn duration, NO{sub X}production, gross indicated efficiency and gross IMEP of a supercharged engine (3 atm. intake pressure) with 14:1, 16:1 and 18:1 compression ratios at 1200 rpm. HCT has been modified to incorporate the effect of heat transfer and to calculate the temperature that results from mixing the recycled exhaust with the fresh mixture. This study uses a single reaction zone that varies as a function of crank angle. The ignition process is controlled by adjusting the intake equivalence ratio and the residual gas trapping (RGT). RGT is internal exhaust gas recirculation, which recycles both thermal energy and combustion product species. Adjustment of equivalence ratio and RGT is accomplished by varying the timing of the exhaust valve closure in either two-stroke or four-stroke engines. Inlet manifold temperature is held constant at 300 K. Results show that, for each compression ratio, there is a range of operational conditions that show promise of achieving the control necessary to vary power output while keeping indicated efficiency above 50 percent andmore » NO{sub X}levels below 100 ppm. HCT results are also compared with a set of recent experimental data for natural gas.« less

Development of a five-step global methane oxidation-NO formation mechanism for lean-premixed gas turbine combustion

Abstract: It is known that many of the previously published global methane oxidation mechanisms used in conjunction with computational fluid dynamics (CFD) codes do not accurately predict CH{sub 4} and CO concentrations under typical lean-premixed combustion turbine operating conditions. In an effort to improve the accuracy of the global oxidation mechanism under these conditions, an optimization method for selectively adjusting the reaction rate parameters of the global mechanisms (e.g., pre-exponential factor, activation temperature, and species concentration exponents) using chemical reactor modeling is developed herein. Traditional global mechanisms involve only hydrocarbon oxidation; that is, they do not allow for the prediction of NO directly from the kinetic mechanism. In this work, a two-step global mechanism for NO formation is proposed to be used in combination with a three-step oxidation mechanism. The resulting five-step global mechanism can be used with CFD codes to predict CO, CO{sub 2}, and NO emission directly. Results of the global mechanism optimization method are shown for a pressure of 1 atmosphere and for pressures of interest for gas turbine engines. CFD results showing predicted CO and NO emissions using the five-step global mechanism developed for elevated pressures are presented and compared to measured data.

Mixing of Multiple Jets With a Confined Subsonic Crossflow: Part II—Opposed Rows of Orifices in Rectangular Ducts

Abstract: This paper summarizes experimental and computational results on the mixing of opposed rows of jets with a confined subsonic crossflow in rectangular ducts. The studies from which these results were excerpted investigated flow and geometric variations typical of the complex three-dimensional flowfield in the combustion chambers in gas turbine engines. The principal observation was that the momentum-flux ratio, J, and the orifice spacing, S/H, were the most significant flow and geometric variables. Jet penetration was critical, and penetration decreased as either momentum-flux ratio or orifice spacing decreased. It also appeared that jet penetration remained similar with variations in orifice size, shape, spacing, and momentum-flux ratio when the orifice spacing was inversely proportional to the square-root of the momentum-flux ratio. It was also seen that planar averages must be considered in context with the distributions. Note also that the mass-flow ratios and the orifices investigated were often very large (jet-to-mainstream mass-flow ratio > 1 and the ratio of orifices-area-to-mainstream-cross-sectional-area up to 0.5, respectively), and the axial planes of interest were often just downstream of the orifice trailing edge. Three-dimensional flow was a key part of efficient mixing and was observed for all configurations.

A Numerical Analysis of the Emissions Characteristics of Biodiesel Blended Fuels

Abstract: Computer simulations were conducted to study the combined effects of methyl soyate (biodiesel) blends with no. 2 diesel fuel on diesel engine (D.I.) performance. Diesel engine emissions and heat release rates were some of the parameters studied. The results from the computer simulations were compared against previously published results (Choi et al., 1997) from engine tests conducted on a single cylinder version of the Caterpillar 3400 series heavy duty diesel engine. The experiments and simulations were performed over a range of injection timings allowing particulate versus NO{sub x} trade-off curves to be generated. Phillips 66 certified no. 2 diesel fuel was used as the baseline; mixtures of 20% and 40% by volume of methyl soyate with the baseline no. 2 diesel fuel were used as the biodiesel blends. The multidimensional KIVA-II code (ERC version 2.4) was used to better understand the factors controlling the formation of NO{sub x} and soot. KIVA-II modeled the high load, single injection combustion of the baseline {number_sign}2 diesel fuel and the biodiesel blends. The code was changed to account for different fuel effects and the computational results were then compared against the experimental data. It is concluded that the increased NO{sub x} observed with themore » use of biodiesel fuels (in spite of their lower heats of combustion) is due to increased local temperatures as a result of enhance fuel/air mixing and increased spray penetration. The increased spray penetration results from the higher fuel viscosity of the biodiesel blended fuels which leads to reduced injection durations.« less

Rapid Characterization of Fuel Atomizers Using an Optical Patternator

Abstract: Planar laser scattering (PLS) and planar laser-induced fluorescence (PLIF) techniques are currently being used for rapid characterization of fuel sprays associated with gas turbine atomizers, diesel injectors, and automotive fuel injectors. These techniques can be used for qualitative, quantitative, and rapid measurement of fuel mass, spray geometry, and Sauter mean diameters in various sprays. The spatial distribution of the fuel mass can be inferred directly from the PLIF image, and the Sauter mean diameter can be measured by simultaneously recording the PLIF and PLS images and then rationing the two. A spray characterization system incorporating the PLS and/or PLIF techniques has been loosely termed an optical patternator, and in this study, it has been used to characterize both steady and pulsed sprays. The results obtained with the optical patternator have been directly validated using a phase Doppler particle analyzer (PDPA).

A Comprehensive Model to Predict Simplex Atomizer Performance

Abstract: The pressure swirl atomizer, or simplex atomizer, is widely used in liquid fuel combustion devices in the aerospace and power generation industries. A computational, experimental, and theoretical study was conducted to predict its performance. The Arbitrary-Lagrangian-Eulerian method with a finite-volume scheme is employed in the CFD model. Internal flow characteristics of the simplex atomizer, as well as its performance parameters such as discharge coefficient pray angle and film thicknes are predicted. A temporal linear stability analysis is performed for cylindrical liquid sheets under three-dimensional disturbance The model incorporates the swirling velocity component, finite film thickness and radius that are essential features of conical liquid sheets emanating from simplex atomizers. It is observed that the relative velocity between the liquid and gas phases, densit ratio and surface curvature enhance the interfacial aerodynamic instability. The combination of axial and swirling velocity components is more effective than only the axial component for disintegration of liquid sheet. For both large and small-scale fuel nozzles, mean droplet sizes are predicted based on the linear stability analysis and the proposed breakup model. The predictions agree well with experimental data at both large and small scale.

Performance of a Low Heat Rejection Diesel Engine With Air Gap Insulated Piston

Abstract: A threaded air gap insulated piston provided effective insulation without causing sealing problems. The performance of the diesel engine with the air gap insulated piston was obtained with different piston crown materials, at differing magnitudes of air gap with varying injection timings. The engine using Nimonic for the piston crown with an air gap of 3 mmm at an injection timing of 29.5{degree} bTDC reduced the BSFC by 12 percent at part loads and 4 percent at full loads. The performance in terms of P-{theta} and T-{theta} was predicted employing a zero dimensional multizone combustion model, and the model results have been validated with measured pressures and the exhaust gas temperatures. More appropriate piston surface temperatures were employed in Annand`s equation to improve the computer predictions using finite element modeling of the piston. The measured temperatures of air in the air gap using an L-link mechanism provided excellent validation for the finite element prediction of isotherms in the piston.

Minimization of the Local Rates of Entropy Production in the Design of Air-Cooled Gas Turbine Blades

Abstract: The paper presents the results of a numerical configuration study made on a two-dimensional model of an internally cooled gas turbine vane. The analysis applies to a two-dimensional cascade at medium Reynolds number, subsonic Mach number, and steady state. The full Navier-Stokes equations of motion for turbulent viscous flow, together with the appropriate energy equation, are solved via a standard finite-element code with a {kappa}-{var_epsilon} closure, to obtain complete velocity and temperature fields. These fields are then used to compute the entropy generation rates corresponding to the viscous (s{sub v}) and thermal (s{sub t}) dissipation. The thermo-fluid dynamic efficiency of different versions of the same base configuration is assessed comparing the global (or integral) entropy generation rate in the passage. The procedure is general, can be extended to different configurations and different operational conditions, and provides the designer with a rational and effective tool to assess the actual losses in the fixed and rotating turbomachinery cascades.

Fault tolerant magnetic bearings

Abstract: A fault tolerant magnetic bearing system was developed and demonstrated on a large flexible-rotor test rig. The bearing system comprises a high speed, fault tolerant digital controller, three high capacity radial magnetic bearings, one thrust bearing, conventional variable reluctance position sensors, and an array of commercial switching amplifiers. Controller fault tolerance is achieved through a very high speed voting mechanism which implements triple modular redundancy with a powered spare CPU, thereby permitting failure of up to three CPU modules without system failure. Amplifier/cabling/coil fault tolerance is achieved by using a separate power amplifier for each bearing coil and permitting amplifier reconfiguration by the controller upon detection of faults. This allows hot replacement of failed amplifiers without any system degradation and without providing any excess amplifier kVA capacity over the nominal system requirement. Implemented on a large (2440 mm in length) flexible rotor, the system shows excellent rejection of faults including the failure of three CPUs as well as failure of two adjacent amplifiers (or cabling) controlling an entire stator quadrant.

Computational Evaluation of Low NOx Operating Conditions in Arch-Fired Boilers

Abstract: In the present paper, a computational model is used to simulate the aero-dynamic, thermal, and chemical conditions inside an arch-fired coal boiler. The model is based on the Eulerian-Eulerian concept, in which Eulerian conservation equations are solved both for the gas and the particulate phases. A NO{sub x} formation and destruction submodel is used to calculate the local concentration of NO. The model is used to simulate a range of operating conditions in an actual, 350 MW, arch-fired boiler, with the aim of reducing, using primary measures, the emissions of NO{sub x}. The model results shed some light on the relevant NO{sub 2}-formation mechanisms under the several operating conditions. Furthermore, they correlate well quantitatively with the available field measurements at the plant, and reproduce satisfactorily the tendencies observed under the different operating modes.

Experimental Rotordynamic Coefficient Results for (a) a Labyrinth Seal With and Without Shunt Injection and (b) a Honeycomb Seal

Abstract: Centrifugal compressors are increasingly required to operate at higher pressures, speeds, and fluid density. In these conditions, compressors are susceptible to rotordynamic instabilities. To remedy this situation, labyrinth seals have sometimes been modified by using shunt injection. In shunt injection, the gas is taken from the diffuser or discharge volute and injected into an upstream chamber of the balance-piston labyrinth seal. The injection direction can be radial or against rotation. This study contains the first measured rotordynamic data for labyrinth seals with shunt injection. A comparison has been made between conventional labyrinth seals, labyrinth seals with shunt injection (radial and against rotation), and a honeycomb seal. Labyrinth seals with injection against rotation are better able to control rotordynamic instabilities than labyrinth seals with radial injection; however, the leakage is slightly higher. The leakage comparison for all seals demonstrates that the honeycomb seal has the best flow control. Test data are presented for a top rotor surface velocity of 110 m/ sec, a supply pressure of 13.7 bars, and IPr = 0.95 (injection pressure is 1.05 = 1/ 0.95 times the seal inlet pressure). For these conditions, and considering effective damping, the labyrinth seal with injection against rotation is better than the honeycomb seal when the pressure ratio across the seal PR 0.45. The effectiveness of the shunt-injection against rotation in developing effective damping is reduced with increasing rotor surface velocity.

Final Report on the Development of a Hydrogen-Fueled Combustion Turbine Cycle for Power Generation

Abstract: Through its New Energy and Industrial Technology Development Organization (NEDO) the Japanese government is sponsoring the World Energy Network (WE-NET) Program. WE-NET is a 28-year global effort to define and implement technologies needed for hydrogen-based energy systems. A critical part of this effort is the development of a hydrogen-fueled combustion turbine system to efficiently convert the chemical energy stored in hydrogen to electricity when hydrogen is combusted with pure oxygen. A Rankine cycle, with reheat and recuperation, was selected by Westinghouse as the general reference system. Variations of this cycle have been examined to identify a reference system having maximum development feasibility, while meeting the requirement of a minimum of 70, 9 percent low heating value (LHV) efficiency. The strategy applied by Westinghouse was to assess both a near-term and long-term Reference Plant. The near-term plant requires moderate development based on extrapolation of current steam and combustion turbine technology. In contrast, the long-term plant requires more extensive development for an additional high pressure reheat turbine, and is more complex than the near-term plant with closed-loop steam cooling and extractive feedwater heating. Trade-offs between efficiency benefits and development challenges of the near-term and long-term reference plant are identified. Results of this study can be applied to guide the future development activities of hydrogen-fueled combustion turbine systems.

CO2 Emission Abatement in IGCC Power Plants by Semiclosed Cycles: Part A—With Oxygen-Blown Combustion

Abstract: This paper analyzes the fundamentals of IGCC power plants where carbon dioxide produced by syngas combustion can be removed, liquefied and eventually disposed, to limit the environmental problems due to the greenhouse effect. To achieve this goal, a semiclosed-loop gas turbine cycle using an highly-enriched CO{sub 2} mixture as working fluid was adopted. As the oxidizer, the syngas combustion utilizes oxygen produced by an air separation unit. Combustion gases mainly consist of CO{sub 2} and H{sub 2}O: after expansion, heat recovery and water condensation, a part of the exhausts, highly concentrated in CO{sub 2}, can be easily extracted, compressed and liquefied for storage or disposal. A detailed discussion about the configuration and the thermodynamic performance of these plants is the aim of the paper. Proper attention was paid to: (i) the modelization of the gasification section and of its integration with the power cycle, (ii) the optimization of pressure ratio due the change of the cycle working fluid, (iii) the calculation of the power consumption of the auxiliary equipment, including the compression train of the separated CO{sub 2} and the air separation unit. The resulting overall efficiency is in the 38--39% range, with status-of-the-art gas turbine technology, but resorting to more » a substantially higher pressure ratio. The extent of modifications to the gas turbine engine, with respect to commercial units, was therefore discussed. Relevant modifications are needed, but not involving changes in the technology. A second plant scheme will be considered in the second part of the paper, using air for syngas combustion and a physical absorption process to separate CO{sub 2} from nitrogen-rich exhausts. A comparison between the two options will be addressed there. « less

Acoustic Sensitivities of Lean-Premixed Fuel Injectors in a Single Nozzle Rig

Abstract: An experimental and numerical investigation into the attenuation of combustion induced pressure oscillations in a single nozzle rig was undertaken at the United Technologies Research Center. Results from these investigations indicated a high combustor exit Mach number, similar to that used in a gas turbine engine, was required to correctly simulate the combustor dynamics and evaluate acoustic characteristics of lean premixed fuel injectors. Comparisons made between aerodynamically stabilized and bluff-body stabilized nozzles and the use of premixed and diffusion pilots showed that small levels of diffusion piloting behind a bluff-body yielded the best acoustic/emission performance. Their success is due to increased flame stabilization (superior anchoring ability), which reduced flame motion and thermal/acoustic coupling. For cases where diffusion piloting was not present, both designs exhibited similar dynamical behavior. Increases in the combustor exit Mach number and reductions in the inlet air temperature were shown to degrade acoustic performance of both nozzle designs. The bluff-body configuration with small levels of diffusion piloting, however, was found to be less sensitive to these changes when compared to its aerodynamic counterpart.

Mode Localization of a Cracked Blade Disk

Abstract: In this paper, the effect of blade crack on the mode localization of a rotating blade disk is studied. Pretwisted taper beams are used to simulate blades of a blade disk. The crack on the blade can be regarded as a local disorder of this periodically coupled blades system. An application of Hamilton's principle and Galerkin's method is used to formulate the equations of motion of the mistuned system. Effects of pretwisted angle, rotating speed, and crack depth of the blade on the in-plane and off-plane mode localizations of a rotating system are investigated. Numerical results indicate that the increase of rotating speed pretwisted angle, and crack depth coula enhance the localization phenomenon significantly.

Assessment of combustion modes for internal combustion wave rotors

Abstract: Combustion within the channels of a wave rotor is examined as a means of obtaining pressure gain during heat addition in a gas turbine engine. Three modes of combustion are assessed: premixed autoignition (detonation), premixed deflagration, and non-premixed autoignition. The last two will require strong turbulence for completion of combustion in a reasonable time in the wave rotor. The autoignition modes will require inlet temperatures in excess of 800 K for reliable ignition with most hydrocarbon fuels. Examples of combustion mode selection are presented for two engine applications.

Co-Pyrolysis of Coal/Biomass and Coal/Sewage Sludge Mixtures

Abstract: Biomass and sewage sludge are attracting increasing interest in power plant technology as a source of carbon-dioxide-neutral fuels. A new way to reduce the consumption of fossil fuels could be the co-combustion or co-gasification of coal and biomass or coal and sell age sludge. In both cases, pyrolysis is the first step in the technical process. In order to obtain derailed information about the pyrolysis of coal/biomass and coal/sewage sludge mixtures as well as unblended fuels, the textquoterighttextquoterightInstitut fur Verfahrenstechnik und Dampkesselwesen (IVD)textquoterighttextquoteright at the University of Stuttgart has carried out investigations using an electrically heated entrained flow reactor. The test runs provided information about fuel conversion efficiency, pyrolysis gas and tar yield.

CFD Modeling of a Gas Turbine Combustor From Compressor Exit to Turbine Inlet

Abstract: Gas turbine combustor CFD modeling has become an important combustor design tool in the past few years, but CFD models are generally limited to the flow field inside the combustor liner or the diffuser/combustor annulus region. Although strongly coupled in reality, the two regions have rarely been coupled in CFD modeling. A CFD calculation for a full model combustor from compressor diffuser exit to turbine inlet is described. The coupled model accomplishes the following two main objectives: (1) implicit description of flow splits and flow conditions for openings into the combustor liner, and (2) prediction of liner wall temperatures. Conjugate heat transfer with non luminous gas radiation (appropriate for lean, low emission combustors) is utilized to predict wall temperatures compared to the conventional approach of predicting only near wall gas temperatures. Remaining difficult issues such as generating the grid, modeling swirler vane passages, and modeling effusion cooling are also discussed.

Nonlinear Model Predictive Control of a Laboratory Gas Turbine Installation

Abstract: The feasibility of model predictive control (MPC) applied to a laboratory gas turbine installation is investigated. MPC explicitly incorporates (input and output) constraints in its optimizations, which explains the choice for this computationally demanding control strategy. Strong nonlinearities, displayed by the gas turbine installation, cannot always be handled adequately by standard linear MPC. Therefore, we resort to nonlinear methods, based on successive linearization and nonlinear prediction as well as the combination of these. We implement these methods, using a nonlinear model of the installation, and compare them to linear MPC. It is shown that controller performance can be improved, without increasing controller execution-time excessively.

Analyses of radially rotating high-temperature heat pipes for turbomachinery applications

Abstract: A set of closed-form solutions for the liquid film distributions in the condenser section of a radially rotating miniature heat pipe and for the vapor temperature drop along the heat pipe length are derived. The heat transfer limitations of the heat pipe are analyzed under turbine blade cooling conditions. Analytical results indicate that the condenser heat transfer limitation normally encountered by low-temperature heat pipes no longer exists for the high-temperature rotating treat pipes that are employed for turbine blade cooling. It is found that the heat pipe diameter, radially rotating speed, and operating temperature are very important to the performance of the heat pipe, Heat transfer limitations may be encountered for an increased heat input and rotating speed, or a decreased hydraulic diameter. Based on the extensive analytical evaluations, it is concluded that the radially rotating miniature heat pipe studied in this paper is feasible for turbine blade cooling applications.

An Assessment of the Performance of Closed Cycles With and Without Heat Rejection at Cryogenic Temperatures

Abstract: This paper presents optimized cycle performance that can be obtained with systems including a closed cycle gas turbine (CCGT). The influence of maximum temperature, minimum temperature, and recuperator effectiveness on cycle performance is illustrated. Several power-plant arrangements are analyzed and compared based on thermodynamic performance (thermal efficiency and specific work); enabling technologies (available at present); and developing technologies (available in the near term of future). The work includes the effects of utilization of high temperature ceramic heat exchangers and of coupling of CCGT systems with plants vaporizing liquid hydrogen (LH{sub 2}) or liquefied natural gas (LNG). Given the versatility of energy addition and rejection sources that can be utilized in closed gas-cycle systems, the thermodynamic performance of power plants shown in this paper indicate the remarkable capabilities and possibilities for closed gas-cycle systems.

High Temperature Proximity Measurement in Aero and Industrial Turbomachinery

Abstract: The measurement of disc and shaft displacement has been performed for many years as part of the development, commissioning and monitoring of all classes of turbomachinery. This measurement has traditionally been performed using sensors that cannot operate above the curie point of rare earth magnets. In this paper a programme of work is described that was undertaken to develop a measurement system that could make a measurement of target proximity in a high temperature environment. The specific objectives were to make possible the measurement of turbine disc axial movement and shaft motion in the engine core, close to the combustion chamber or turbine; and secondly to make possible the measurement of tip clearance over shrouded turbine rotors.

Application of Stress Relaxation Testing in Metallurgical Life Assessment Evaluations of GTD111 Alloy Turbine Buckets

Abstract: Stress relaxation and constant displacement rate tensile tests were performed on polycrystalline GTD111 alloy material removed from General Electric MS6001B first stage combustion turbine buckets. Samples were examined in the standard heat treated condition, thermally exposed at 900°C for 5000 hours and from service run buckets. Creep rates of the material were measured and evaluated directly in terms of temperature capability at 850°C and 900°C. Stress relaxation tests done at 0.8 percent total strain indicated that the creep rate properties in the service exposed airfoil were an order of magnitude higher than the material properties in the standard heat treated condition measured in the root form. In terms of temperature capability, the creep rate properties of the service run airfoil material had decreased by the equivalent of almost 40°C. The Stress relaxation test method was demonstrated to be a very useful tool in quantifying the degradation of creep properties in service run components. Creep data that would require years to gather using conventional creep tests was generated in a few days. This now makes realistic life assessment and repair/replace decisions possible during turbine overhauls. The test method’s unique ability to measure changes in creep rate over a large stress range, enabled the technique to distinguish between changes in creep strength due to (normal) microstructural evolution from the combined effects of microstructural evolution and strain related creep damage. A method for estimating standard constant load creep rupture life from the stress relaxation creep rate data is also presented along with time-temperature parameter correlations. The data sets examined in this study indicate that creep rupture lives can be estimated within a factor of three from the stress relaxation data. The information and analysis techniques described in this paper are directly applicable to metallurgical life assessment evaluations and the requalification of repaired General Electric buckets in Frame 3, 5, 6, 7, and 9 engine models.

Experimentally Determined Rotor Power Losses in Homopolar and Heteropolar Magnetic Bearings

Abstract: The identification of parameters that dictate the magnitude of rotor power losses in radial magnetic bearings is very important for many applications. Low loss performance of magnetic bearings in aerospace equipment such as jet engines and flywheel energy storage systems is especially critical. Two basic magnetic bearing designs are employed in industrial practice today: the homopolar design, where the flux paths are of a mixed radial/axial orientation, and the heteropolar design, where the flux paths are primarily radial in nature. The stator geometry and flux path of a specific bearing can have a significant effect on the rotor losses. This paper describes the detailed measurement of rotor losses for experimentally comparable homopolar and heteropolar designs. The two test bearing configurations are identical except for geometric features that determine the direction of the flux path. Both test bearing designs have the same air gap length, tip clearance ratio, surface area under the poles, and bias flux levels. An experimental test apparatus was used where run down tests were performed on a test rotor with both bearing designs to measure power losses. Numerous test runs where made for each bearing configuration by running multiple levels of flux density. The components of the overall measured power loss, due to hysteresis, eddy currents, and windage, were determined based on theoretical expressions for power loss. It was found that the homopolar bearing had significantly lower power losses than the heteropolar bearing.