bluuebunny/crossref_metadata_2025 huggingface dataset:
Predicting Transition in Turbomachinery: Part I — A Review and New Model Development
Authors: Praisner T. J. , Clark J. P.
Published: November 2008

Here we report on an effort to include an empirically based transition modeling capability in a RANS solver. Testing of well-known empirical models from literature for both attached- and separated-flow transition against cascade data revealed that the models did not provide enough fidelity for implementation in an airfoil design system. Consequently, a program was launched to develop models that would provide sufficient accuracy for use in an airfoil design system. As a first step in the effort, accurate modeling of freestream turbulence development was identified as a need for any form of transition modeling capability. Additionally, capturing the effects of freestream turbulence on pre-transitional boundary layers was found to have a significant effect on the accuracy of transition modeling. A CFD-supplemented database of experimental cascade cases (57 with attached-flow transition and 47 with separation and turbulent reattachment) was constructed to explore the development of new correlations. Dimensional analyses were performed to guide the work and appropriate non-dimensional parameters were then extracted from CFD predictions of the laminar boundary layers existing on the airfoil surfaces prior to either transition onset or incipient separation. For attached-flow transition, exploration of the database revealed a distinct correlation between local levels of freestream turbulence intensity, turbulence length scale, and momentum-thickness Reynolds number at transition onset. It was found that the correlation could be recast as a ratio of the boundary-layer diffusion time to a time-scale associated with the energy-bearing turbulent eddies. In the case of separated-flow transition, it was found that the length of a separation bubble prior to turbulent re-attachment was a simple function of the local momentum thickness at separation and the overall surface length traversed by a fluid element prior to separation. Both the attached- and separated-flow transition models were implemented into the design system as point-like trips.
Cheope: A Tool for the Optimal Design of Compact Recuperators
Authors: Traverso Alberto , Zanzarsi Federico , Massardo Aristide
Published: November 2008

This paper presents the organization, theoretical background and application of a new software tool for the optimization of the technical and economical design of microturbine recuperators. The code called CHEOPE (Compact Heat Exchanger Optimization and Performance Evaluation) considered two types of recuperator concept, which proved to be the most promising for microturbine applications: the furnace-brazed plate-fin type and the welded primary surface type. The general design rules for performance evaluation of gas-gas heat exchangers are summarized and specifically applied to these two types of recuperator. Moreover, the cost equation, employed to estimate the capital cost of these types of heat exchanger, is discussed. CHEOPE can be used both for solving the sizing problem and the rating problem. With regard to the former, the code is capable of a special optimization of the recuperator matrix, which takes into account the compactness, the pressure drops and the expected cost of the device. The objective function can be customized according to the designer’s priorities. The tests performed for the validation are presented, and three case studies are illustrated for three different microturbine sizes, for a 50kW, a 100kW and a 500kW machine.
WIDGET-TEMP: A Novel Web-Based Approach for Thermoeconomic Analysis and Optimization of Conventional and Innovative Cycles
Authors: Traverso Alberto , Massardo Aristide F. , Cazzola Walter , Lagorio Giovanni
Published: November 2008

In a deregulated energy market the adoption of multipurpose and flexible software tools for the optimal design and sizing of energy systems is becoming mandatory. For these reasons, we have developed WIDGET-TEMP (Web-based Interface and Distributed Graphical Environment for TEMP, ThermoEconomic Modular Program), a tool which is the result of an interdisciplinary research which applied recent IT innovations such as XML and web-based approaches to the analysis and optimization of energy plant layouts on a thermoeconomic basis. WIDGET provides an interface for remotely accessing the internal thermoeconomic analysis, the full life-cycle cost and investment assessment, which includes the economic impact of environmental costs due to pollutant emissions. This approach reduces the requirements for the local machine in terms of processor time and memory, and allows users to exploit the tool just when needed. An initial functional productive diagram of the plant is now automatically drawn and is available to the user on a visual basis. We present a general description of the tool organization and outline the approach for modeling the technical performance and cost of the component. Then, we describe the latest upgrades of TEMP, and report the new gas turbine cost equations. Finally, the tool is applied to a conventional simple and combined cycle, showing both the usability of the new tool and the reliability of the results.
Linear Stability Analysis of LPT Rotor Packets: Part II — Three-Dimensional Results and Mistuning Effects
Authors: Corral Roque , Gallardo Juan Manuel , Vasco Carlos
Published: November 2008

Part II of this paper compares the aerodynamic damping of a modern Low Pressure Turbine (LPT) interlock bladed-disc to the one obtained when the blades are welded in pairs through the lateral face of the shroud. The damping is computed using the linearized Reynolds averaged Navier-Stokes equations on a moving grid. It is concluded that the increase in stability of the welded-pair with respect the cantilever configuration due to the modification of the mode-shapes, is smaller than the one due to the overall raise of the reduced frequencies of a bladed-disc with an interlock design. The modification of the flutter boundaries due to mistuning effects is taken into account using the reduced order model known as the Fundamental Mistuning Model (FMM). It is shown that the modification on the stability limit of a interlock bladed-disc is negligible, while for a welded-pair configuration an increase of 0.15% on the critical damping may be expected. Two realistic welded-pair bladed-discs are analysed in this work. It is shown that both are aerodynamically unstable, which is in agreement with the experimental observations. Critical reduced frequency stability maps accounting for mistuning effects are derived for both, freestanding and welded in pairs airfoils. The airfoils are assumed to be identical and mechanically uncoupled. The stabilizing effect of mistuning is also retained in these maps.
Metrics for Evaluating the Accuracy of Diagnostic Fault Detection Systems
Authors: DePold Hans , Siegel Jason , Hull Jon
Published: November 2008

This paper presents a method for providing metrics to evaluate the accuracy and cost effectiveness of diagnostic decision support systems. One intention of engine health management (EHM) fault detection systems is to have engines identified for removal and refurbishment as soon as there is evidence of an adverse gas generator trend shift. The benefits of EHM diagnostics and prognostics tests are derived from the resulting improved safety, the reduced operating costs, and most importantly, the good will and trust of the customer. The method presented in this paper is a generalized way of evaluating the performance of some of the tests that are used to make inspection, removal, and maintenance decisions [Ref 1,2]. The detection of faults from shifts in classification data is the first step in EHM systems that use diagnostics and prognostics [Ref 3,4,5]. The minimum parameter shift required to trigger a fault indication is called the threshold. Typically, it is a predetermined multiple of the standard deviation of the parameter measurements. Root cause isolation is usually invoked following these detection tests for the gas path parameter shifts. This paper shows how the achievable accuracy of diagnostic and prognostic system tests can be determined from the signal to noise ratio (SNR), and the system’s design (sensitivity and specificity). From these tests we extract two features, true positives (TP) and false positives (FP) that can be used to compare the accuracy of any simple or complex decision support system. This method is conducive to efficiently handling large amounts of data from multiple sensor tests because it avoids explicit correlation among individual diagnostic tests, and focuses instead on the net results. Each piece of classification information is used to reduce ambiguity. In this approach, the individual diagnostic tests and any data fusion weighting factors can be parametrically varied to optimize the accuracy of the decisions. The resulting plot of TP versus FP is then directly compared to the results of simple idealized classifier systems having known SNRs. This paper applies the receiver operating characteristics (ROC) process to evaluate the potential accuracy of EHM decisions. The paper also shows that the actual accuracy depends on how thresholds are set, and on the local shape of the ROC in the regions where it is used. The method presented can be applied to test the relative accuracy of each phase of the EHM decision-making process. The effects of test accuracies, event probabilities, and consequential event costs on the value of the decision support system are also presented.
Low Solidity Vaned Diffusers for Rotating Stall Prevention: Experimental Analysis of Some Design Parameters
Authors: Ferrara Giovanni , Ferrari Lorenzo , Baldassarre Leonardo
Published: November 2008

Rotating stall in centrifugal compressors is an attractive topic both for academic research and industrial applications. Its complex phenomenology requires detailed and advanced analyses to improve the understanding of the physical mechanisms responsible for its development. From such an investigation, benefits can also come for the design of more efficiently performing industrial compressors. In this context, an activity was planned focusing on the comprehension and characterization of rotating stall for a group of industrial centrifugal stages with a low blade-outlet-width-to-impeller-radius ratio for very high pressure applications. These are generally equipped with vaneless diffusers. In order to improve stage stability, the use of low solidity vaned diffusers (LSD) seems to be a very useful approach. Starting from results obtained for a previous set of LSD, new sets of configurations were tested in order to analyze in detail the influence of vane solidity, inlet radius and incidence at design point on performance and design point. Results are compared with those of the vaneless solution highlighting improvements and drawbacks.
Part-Load Versus Downrated Industrial Gas Turbine Performance
Authors: Bringhenti Cleverson , Barbosa Joa˜o R.
Published: November 2008

For distributed power generation, sometimes the available gas turbines cannot match the power demands. It has been usual to uprate an existing gas turbine in the lower power range by increasing the firing temperature and speeding it up. The development costs are high and the time to make it operational is large. In the other hand, de-rating an existing gas turbine in the upper power range may be more convenient since it is expected to cut significantly the time for development and costs. In addition, the experience achieved with this engine may be easily extrapolated to the new engine. This paper deals with the performance analysis of an existing gas turbine, in the range of 25 MW, de-rated to the range of 18 MW, concerning the compressor modifications that could be more easily implemented. Analysis is performed for the base engine, running at part-load of MW. A variable geometry compressor is derived from the existing one. Search for optimized performance is carried out for new firing temperatures. A variable geometry turbine analysis is performed for new NGV settings, aiming at better cycle performance.
Uncertainty Evaluation for Structural Damage Parameters Prediction Methodology
Authors: Suarez Eva L. , Cassenti Brice , Holmes Richard , Scheuren William
Published: November 2008

Structural component life estimated from damage tracking parameters in real-time are a subject of recent studies. The proposed project consists of determining parametric equations for the structural damage variables, metal temperature and stress, as a function of design performance parameters, exercising these equations through material property algorithms generated as a function of material characterization, and evaluating the uncertainty of the damage accumulated from a simulated military mission. Thermal and structural finite element results obtained during the component design phase were used as the dependent response for the stress and metal temperature equations. The independent variables used in the statistical linear regression analysis were mission performance parameters. A time function was implemented to account for the response time characteristic of the component metal temperature during transient conditions. The material property algorithm combined critical metal temperatures and stresses with probabilistic material capability generated from stochastic material characterization. Validation of the methodology was accomplished by the statistical analysis performed between predicted results and expected values from the design analysis. Uncertainty analysis established the confidence bound about the predicted result.
Latticework (Vortex) Cooling Effectiveness: Part 1 — Stationary Channel Experiments
Authors: Bunker Ronald S.
Published: November 2008

The present investigation provides detailed information concerning the heat transfer coefficients and pressures in latticework (vortex) cooling channels. Two test methods are used to determine the local and overall heat transfer coefficients for a vortex channel with crossing angle of 45-degrees. Both liquid crystal and infrared thermography methods are used on acrylic and metallic models to discern the heat transfer coefficients without and with the effects of internal rib fin effectiveness. Tests with insulating ribs determine the heat transfer on the primary surfaces representing the pressure and suction side walls of an airfoil. Tests with integral metal ribs determine the additional impact of the fin effectiveness provided by the ribs. A simple radial vortex channel design is employed throughout with subchannel aspect ratios near unity, and Reynolds numbers from 20,000 to 100,000. Pressure loss variations through typical vortex channels are also measured. The objectives of this research are to show the detailed development of heat transfer in vortex channels leading to an understanding of the two main effects of turning and fin enhancements. Detailed primary surface heat transfer coefficients average about 1.5 over smooth duct behavior, but reach local values of about 3 immediately after each turn. Pressure distributions show high turning losses on the order of those associated with serpentine 180-degree turn circuits. Local heat transfer coefficient distributions are remarkably uniform throughout the channels excepting the turns themselves. Turn enhancements are retained for relatively long distances. Overall vortex channel heat transfer coefficient enhancement levels are shown to be 2.5 to 3. The effects of subchannel internal ribs, which act as fins, are shown to be very important in the overall thermal picture. Test results show that treatment of the ribs as simple fins is appropriate and that each rib surface has about the same heat transfer coefficient on average as that of the primary surface. This first detailed study shows that latticework channels have significant potential and should be further investigated.
Application of Low Order Thermo-Acoustic Network to DLE Staged Combustor
Authors: Macquisten M. A. , Whiteman M. , Moran J. A.
Published: November 2008

Lean premixed combustors have been developed to meet stringent NOx emission legislation. Operating close to the lean limit introduces a susceptibility to combustion oscillations, which have a damaging impact on hardware and affect combustor performance. The RB211 DLE aero derivative gas turbine has to be CO and NOx compliant from 60% power. Therefore the required turndown must be incorporated into the design. This is achieved by the addition of a second combustion stage, which provides the required CO burn out. Combustion instabilities can occur at different primary and secondary combustion temperatures in the form of noise islands. A 1/2 wave mode has been identified at high primary zonal temperatures and occurs over a certain range of secondary zonal temperatures. This observation suggests that the secondary flame can excite or dampen the instability depending on the phase relationship between the associated dynamic pressure and the fluctuating heat release rate. The mechanism is though to be fluctuations in temperature originating from the primary flame and convecting to the secondary flame. A second mode is observed at lower primary combustion temperatures, involving the axial combustor length and the circumference of the whole combustion system. A low order thermoacoustic network has been created by Stow et al [1] for the purpose of analysing eigen modes within aero annular combustors. This low order network is used to model the RB211 DLE combustion system. It uses linear perturbation theory to predict the eigen frequencies in the combustion system. Coupling between the unsteady flow and the fluctuating heat release rate is represented by a simple transfer function in both combustion zones. Results and discussion are given for both acoustic modes encountered on the RB211 DLE combustion system.
High Frequency Surface Heat Flux Imaging of Bypass Transition
Authors: Anthony Richard J. , Jones Terry V. , LaGraff John E.
Published: November 2008

A high-frequency surface heat flux imaging technique was used to investigate bypass transition induced by freestream turbulence. Fundamental experiments were carried out at the University of Oxford using high-density thin film arrays on a flat plate wind tunnel model. Bypass transition was induced by grid-generated turbulence with varying intensities of 2.3%, 4.2%, and 17% with a fixed integral length scale of approximately 12mm. Unique high resolution temporal heat flux images are shown which detail significant differences between unsteady surface heat flux events induced by freestream turbulence and the classical Emmons-type spots which many turbomachinery transition models are based on. The temporal imaging technique presented allows study of unsteady surface heat transfer in detail, and helps elucidate the complex nature of transition in the high-disturbance environment of turbomachinery.
Study of Erosion Effects on an Axial Fan Global Range of Operation
Authors: Ghenaiet A. , Tan S. C. , Elder R. L.
Published: November 2008

Operating in sandy environments can cause significant erosion damage to gas turbine installations, particularly in the compressor system. This effect is a result of the ingestion of sand particles and their consequent abrasive impacts on blades. In order to better understand the mechanism of sand ingestion in an axial fan stage and the subsequent effects of erosion over its global range of operation, a methodology was developed and presented in this paper. This includes the computations of particle trajectories through an axial fan stage, erosion and blade profile deterioration, in addition to the aerodynamic performance degradation. The flow field at different operating conditions was solved with the CFD code TASCflow. The particle trajectories were computed using an in-house developed trajectory code, which was based on the lagrangian method. The effects of flow turbulence on particles were simulated using the eddy lifetime concept. The estimation of the aerodynamic performance degradation was based on a mean-line method involving Lieblein and Koch correlations, and an erosion fault model derived from blade profile deterioration. This global procedure was applied successfully to a contra-whirl axial fan, and can be generalized easily to other configurations of axial compressors.
Geometrical Effects and Coolant Injection Impact on the Performance of an HP Transonic Heavy-Duty Turbine Stage
Authors: Boncinelli P. , Maceli N. , Arnone A. , Rossi E.
Published: November 2008

A numerical study of a high pressure transonic axial turbine stage for heavy-duty applications was performed. Attention was focused on assessing the aerodynamic impact of coolant injection and geometrical features, such as slots, fillets and clearances, on stage performance. First, stator and rotor blade rows were separately studied to single out the main modeling factors. Results showed the way each factor affects the performance of the blade. Influence coefficient evaluation was performed with screening techniques, such as DOE (Design Of Experiments) methods. Physical mechanisms responsible for performance decay were investigated by analyzing the secondary flow structure. After the main modeling factors had been selected and included, a 3D steady analysis of the full-stage configuration was carried out at both design and off-design conditions. Results were also compared with experimental data available from GE-Oil & Gas Nuovo Pignone. The performed analysis showed endwall fillets and coolant injection at the trailing edge slot as the most significant factors for efficiency for both stator and rotor blades. Coolant injection at the showerhead and at the suction and pressure side holes, and the geometrical slot turned out to affect blade-row performance to a smaller extent. Comparison with experimental data showed that a substantial improvement in both stage efficiency and loading factor prediction capability was obtained.
Enhanced Impingement Heat Transfer: The Influence of Impingement X/D for Interrupted Rib Obstacles (Rectangular Pin Fins)
Authors: Andrews G. E. , Abdul Hussain R. A. A. , Mkpadi M. C.
Published: November 2008

Impingement flat wall cooling, with 15.2 mm pitch square hole arrays, was investigated in the presence of an array of interrupted rib obstacles. These ribs took the form of rectangular pin-fins with a 50% blockage to the crossflow. One side exit of the air was used and there was no initial crossflow. Three hole diameters were investigated, which allowed the impingement wall pressure loss to be varied at constant coolant mass flow rate. Combustor wall cooling was the main application of the work, where a low wall cooling pressure loss is required if the air is subsequently to be fed to a low NOx combustor. The results showed that the increase in surface average impingement heat transfer, relative to that for a smooth wall, was small and greatest for an X/D of 3.06 at 15%. The main effect of the interrupted ribs was to change the influence of crossflow, which produced a deterioration in the heat transfer with distance compared with a smooth impingement wall. With the interrupted ribs the heat transfer increased with distance. If the heat transfer was compared at the trailing edge of the test section, where the upstream crossflow was at a maximum, then at high coolant flow rates the increase in heat transfer was 21%, 47% and 25% for X/D of 4.66, 3.06 and 1.86 respectively.
A Numerical Investigation of the Effects of Steam Ingestion on Compression System Performance
Authors: Klepper Jason , Hale Alan , Davis Milt , Hurwitz Wayne
Published: November 2008

Steam ingestion into a gas turbine engine compression system can have effects on performance and operability. It is important to be able to quantify these effects. This paper describes a preliminary technique developed to model steam ingestion in a gas turbine engine compression system using a loosely coupled technique of a one-dimensional (1-D) vaporization code and a 1-D meanline compressor performance code. The results are presented for two separate parametric studies: first, the effects of the quantity of steam; and second, the effects of the quality of steam. The analytical results are evaluated against the observed industry standards. These results show that steam ingestion does have an effect on compression system performance and, potentially, operability. The effects can be seen in an increase in incidence from the front to the back blades of the machine, which results in stage rematching. These effects are caused mainly as a result of heat transfer during vaporization of the liquid water present in steam with quality less than 100 percent. The effects of fluid property changes (gas constant and specific heat ratio), caused by the addition of the vaporized water, are secondary.
Application of ANN for Diagnostics of the Geometry Deterioration of the Power System Apparatuses
Authors: Gluch Jerzy , Krzyzanowski Jerzy
Published: November 2008

The authors are currently developing a bi-modular thermal diagnostic system for power cycles, [1]. The target of the system is to search for inefficient components of the complex power cycle, [2], to determine the type of its deterioration, [3], and also to recognise geometry degradation of its faulty apparatuses. The recognition of geometry degradation is the novelty of the present approach and the main topic of the paper.
Co-Utilization of Fossil and Renewable Fuel: Biomass Gas/Natural Gas
Authors: Green Alex E. S. , Swanson Gary P. , Najafi Fazil T.
Published: November 2008

Recently natural gas prices have increased very substantially and USA’s imports have reached 19% of consumption. These trends are due, in part, to the growing number of low capital cost natural gas combined cycle (CC) electrical generating systems. A way of alleviating high NG prices would be to convert local biomass into a biomass gas (BG) for co-utilization with NG. Essentially, construct a biomass integrated gasifier (BIG) CC system or co-generator system (CG) to matched the nearby biomass supply to deliver supplementary BG to an existing NGCC system or an old steam plant to be repowered. If the combustion turbine is robust, retrofitting costs of the NGCC should be modest. The BG might also be used as a supplementary fuel for the heat recovery steam generator (HRSG) and provide added electrical capacity. We consider the technological and economic circumstances required for these forms of co-use to benefit all participants and serve as a sensible use of biomass as a CO2 neutral fuel. As an illustrative case we consider an adaptation of the Kelly plant in Gaines ville Florida that has already been partially re-powered with a NGCC system. We conclude that in rural areas with nearby access to good biomass supplies BG-NG-CC or BG-NG-CG can produce cost competitive electricity particularly when NG prices exceed $4/MBU.
Factors for Improving Reliability in Large Industrial Gas Turbines
Authors: Takahashi K. , Akagi K. , Nishimura S. , Fukuizumi Y. , Kallianpur V.
Published: November 2008

The use of aero engine design methods and experience including higher temperature materials and protective coatings have significantly increased thermal efficiency, and output capability of large industrial gas turbines such as the F, G and H class. As a result the gas path components operate at much higher gas temperatures over significantly longer maintenance intervals, as compared to aero engine experience. Therefore, it is essential that the hardware durability can effectively endure longer periods of attack by oxidation, creep and fatigue because of longer operating intervals between scheduled maintenance periods. Another factor that has become increasingly important is the need for greater flexibility in power plant operation. Specifically, the power plants must operate reliably under more frequent cyclic operation, including partial load cycling. This is in addition to the normal dispatch cycle of the power plant (i.e. daily-start-stop, weekly-start-stop, etc). Gas Turbine reliability is directly dependent on hardware performance and durability. Therefore, the gas turbine must have sufficient design margin to sustain the synergistic effect of higher firing temperature, and the operational challenges associated with greater partial load cycling. This paper discusses Mitsubishi’s approach for achieving the above mentioned objectives so that the overarching goals of higher reliability and durability of hot components are achieved in large advanced gas turbines.
Economic and Scenario Analyses of New Gas Turbine Combined Cycles With No Emissions of Carbon Dioxide
Authors: Gabbrielli R. , Singh R.
Published: November 2008

In this paper economic and scenario analyses of new gas turbine combined cycles with no emissions of carbon dioxide (CO2) and nitrogen oxides are described. The cycles, already presented in a recent paper (ASME GT 2002-30117), have water/steam as working fluid, the compression phase both in liquid and vapour phase, the internal combustion between pure oxygen (O2) and chemically heated natural gas-based syngas, and the CO2 capture and sequestration by water condensation from the exhaust gas. The aim of the economic analyses is to estimate the investment per MW and the levelized discounted cost of the electricity (COE) produced by a power plant based on the cycles here proposed in comparison with a standard reference combined cycle power plant (SRCC). To evaluate the equipment costs, several cost functions of the most important operative parameters have been introduced and tuned with actual data. Using the least square regression technique, explicit functions of the COE have been proposed to highlight the cheapest operative conditions with a derivative approach. Moreover, a wide scenario analysis has been carried out, varying the most important investment parameters, as, for example, the discount rate. In particular, some maps of the COE and break-even carbon tax (BECT) behaviour have been constructed to test the importance of the market uncertainty on the economic results obtained. Finally, the possible technological progress effect on the BECT with a cost reduction of some innovative equipment and the O2 production has been investigated in depth with the 2k factorial design scenario analysis. The O2 production has resulted the most important parameter from the economic point of view.
History, Philosophy, Physics, and Future Directions of Aircraft Propulsion System/Inlet Integration
Authors: Cousins William T.
Published: November 2008

This work provides a historical perspective of the developments of propulsion system inlet/engine integration. The flow physics of inlet distortion are discussed, along with the stability effects on the engine compression systems. Throughout the document, both commercial and military applications are considered. Developments in analyses from the original works characterizing inlet distortion, the use of distortion descriptors and early modeling concepts, and the modeling and simulation required today are reviewed. The special requirements and testing techniques necessary to adequately describe inlet distortion and the effects on the propulsion system are summarized. The aspects of pressure distortion, temperature distortion, and swirl are addressed and the physics of interaction described. The compression system response to different types of distortion is discussed with the interaction with various compression system components and designs explained. Axial and centrifugal compressors are covered, as the resulting physics of the inlet distortion effects on each has a different characteristic. An overview of the necessary flow physics to consider in the integration of compression systems in both low and high-Mach number applications is presented.
Evaluation of Algebraic Transition Models for Application to Unsteady Flows in Low-Pressure Turbines
Authors: Jiang Nan , Simon Terrence W.
Published: November 2008

Currently, numerical simulation models for design of low-pressure turbines need submodels for determining the onset and path of transition. It is well known that such models must include the effects of passing wakes. In this paper, data taken in an experiment that simulates flow over the suction surface of a low-pressure turbine blade, as affected by passing wakes, are used for testing models from the literature. The base case data set replicates reasonable design conditions. A second case with double the wake spacing of the base case is applied to heighten the effects of between-wake calming. A third case with high background freestream turbulence intensity allows testing models for application to high disturbance level flows. Tested are (1) separated flow transition onset models such as those of Mayle and of Davis et al. and (2) attached flow transition onset models, such as those of Mayle, Abu-Ghannam and Shaw, Suzen and Huang and Drela. The dependent variables of the models, time-resolved locations of transition onset, are compared to time-resolved experimental values for transition onset. The transition onset values from the models are computed by assuming that the correlations can be applied in a quasistatic way using instantaneous values of the input parameters computed from the experimental data. Comparisons of the three cases are made to discuss the robustness of the transition onset models. Previously, the base case was presented. New in this paper are (1) modeling of an increased wake spacing data set, (2) modeling of a data set with a highly turbulent approach flow and (3) the comparison of the two with the base case results.
Bio-Energy Cogeneration Systems With CO2 Separation and Storage
Authors: Hochenauer C. , Hohenwarter U. , Sanz W. , Schlamadinger B.
Published: November 2008

This paper compares three different bio-energy cogeneration power station concepts where CO2 is sequestered and available for permanent storage instead of discharging into the atmosphere. The different bio-energy cogeneration systems are: The pre-combustion capture of CO2 the post-combustion capture of CO2 from the flue gas and the combustion in an atmosphere of pure oxygen (Graz-Cycle). The three schemes, all based on a thermal input of about 150 MWth, are compared on the basis of their technological features, their performance, projected costs of electricity and CO2 mitigation costs. Compared to a conventional bio-energy cogeneration system, CO2 removal reduces net plant efficiency by 11 to 16 percentage points and increases the cost of electricity by approximately 54 to 89%. The scheme applying reforming and shift reaction and physical absorption of the syngas fuel appears the most appealing option for the short-term implementation of CO2 sequestration bio-energy cogeneration systems. The Graz-Cycle where the syngas is burnt in pure oxygen appears the most appealing option for the long-term option for CO2 sequestration.
Regenerative Gas Turbines With Divided Expansion
Authors: Elmegaard Brian , Qvale Bjo̸rn
Published: November 2008

Recuperated gas turbines are currently drawing an increased attention due to the recent commercialization of micro gas turbines with recuperation. This system may reach a high efficiency even for the small units of less than 100kW. In order to improve the economics of the plants, ways to improve their efficiency are always of interest. Recently, two independent studies have proposed recuperated gas turbines to be configured with the turbine expansion divided, in order to obtain higher efficiency. The idea is to operate the system with a gas generator and a power turbine, and use the gas from the gas generator part for recuperation ahead of the expansion in the power turbine. The present study is more complete than the predecessors in that the ranges of the parameters have been extended and the mathematical model is more realistic using an extensive simulation program. It is confirmed that the proposed divided expansion can be advantageous under certain circumstances. But, in order for todays micro gas turbines to be competitive, the thermodynamic efficiencies will have to be rather high. This requires that all component efficiencies including the recuperator effectiveness will have to be high. The advantages of the divided expansion manifest themselves over a rather limited range of the operating parameters, that lies outside the range required to make modern micro turbines economically competitive.
Nusselt Numbers and Flow Structure On and Above a Shallow Dimpled Surface Within a Channel Including Effects of Inlet Turbulence Intensity Level
Authors: Ligrani P. M. , Burgess N. K. , Won S. Y.
Published: November 2008

Experimental results from a channel with shallow dimples placed on one wall are given for Reynolds numbers based on channel height from 3,700 to 20,000, levels of longitudinal turbulence intensity from 3 to 11 percent (at the entrance of the channel test section), and a ratio of air inlet stagnation temperature to surface temperature of approximately 0.94. The ratio of dimple depth to dimple print diameter δ/D is 0.1, and the ratio of channel height to dimple print diameter H/D is 1.00. The data presented include friction factors, local Nusselt numbers, spatially-averaged Nusselt numbers, a number of time-averaged flow structural characteristics, and spectra of longitudinal velocity fluctuations which, at a Reynolds number of 20,000, show a primary vortex shedding frequency of 8.0 Hz and a dimple edge vortex pair oscillation frequency of approximately 6.5 Hz. Local flow structure shows some qualitative similarity to characteristics measured with deeper dimples (δ/D of 0.2 and 0.3), with smaller quantitative changes from the dimples as δ/D decreases. A similar conclusion is reached regarding qualitative and quantitative variations of local Nusselt number ratio data, which show that the highest local values are present within the downstream portions of dimples, as well as near dimple spanwise and downstream edges. Local and spatially-averaged Nusselt number ratios sometimes change by small amounts as the channel inlet turbulence intensity level is altered, whereas friction factor ratios increase somewhat at the channel inlet turbulence intensity level increases. These changes to local Nusselt number data (with changing turbulence intensity level) are present at the same locations where the vortex pairs appear to originate, and have the greatest influences on local flow and heat transfer behavior.
Supercritical CO2 Cycle for Fast Gas-Cooled Reactors
Authors: Dostal Vaclav , Driscoll Michael J. , Hejzlar Pavel , Wang Yong
Published: November 2008

Brayton cycles are currently being extensively investigated for possible use with nuclear reactors in order to reduce capital cost, shorten construction period and increase nuclear power plant efficiency. The main candidates are the well-known helium Brayton cycle and the less familiar supercritical CO2 cycle, which has been given increased attention in the past several years. The main advantage of the supercritical CO2 cycle is comparable efficiency with the helium Brayton cycle at significantly lower temperature (550°C/823K), but higher pressure (20MPa/200 normal atmospheres). By taking advantage of the abrupt property changes near the critical point of CO2 the compression work can be reduced, which results in a significant efficiency improvement. Among the surveyed compound cycles the recompression cycle offers the highest efficiency, while still retaining simplicity. The turbomachinery is highly compact and achieves efficiencies of more than 90%. Preliminary assessment of the control scheme has been performed as well. It was found that conventional inventory control could not be applied to the supercritical CO2 recompression cycle. The conventional bypass control is applicable. The reference cycle achieves 46% thermal efficiency at the compressor outlet pressure of 20MPa and turbine inlet temperature of 550°C. The sizing of the heat exchangers and turbomachinery has been performed. The recuperator specific volume is 0.39m3/MWe and pre-cooler specific volume 0.08m3/MWe. For the reference 600MWth reactor this translates to ∼ 99m3 heat exchanger core for the recuperator and ∼ 21m3 for the pre-cooler. Overall the cycle offers an attractive alternative to the steam cycle. The supercritical CO2 cycle is well suited to any type of nuclear reactor with core outlet temperature above ∼ 500°C.
IGCC for Brown Coals With Supercritical Steam Turbine
Authors: Stastny M. , Kucera J. , Hrdina Z. , Hanus D.
Published: November 2008

The paper deals with the IGCC for brown coal (BC) with simultaneous improvement of the steam cycle by the usage of supercritical steam parameters. Two gasifiers with a fluidized bed are used with outlet syngas temperature about 900°C. Main part of the paper is focused on the arrangement and optimization of the IGCC with net total electrical output 454.7 MW and with supercritical inlet parameters 260 bar, 580°C/600°C of steam turbine. The energy sources for the steam part of the cycle are HRSGs downstream of two gas turbines at 122.6 MW each and two raw gas coolers downstream of two gasifiers. The thermal efficiency of this IGCC is on LHV basis about 49.0%. Utilization of brown coal (BC) energy in described IGCC is by 4.7% higher than in steam power station with the same parameters. This IGCC enables reduction of CO2 emission by around 44% compared with existing power stations with thermal efficiency 34%.
Low-Order Modelling of Thermoacoustic Limit Cycles
Authors: Stow Simon R. , Dowling Ann P.
Published: November 2008

Lean premixed prevaporised (LPP) combustion can reduce NOx emissions from gas turbines, but often leads to combustion instability. Acoustic waves produce fluctuations in heat release, for instance by perturbing the fuel-air ratio. These heat fluctuations will in turn generate more acoustic waves and in some situations self-sustained oscillations can form. The resulting limit cycles can have large amplitude causing structural damage. Thermoacoustic oscillations will have a low amplitude initially. Thus linear models can give stability predictions. An unstable linear mode will grow in amplitude until nonlinear effects become important and a limit cycle is achieved. While the frequency of the linear mode can provide a good approximation to that of the resulting limit cycle, linear theories give no prediction of its amplitude. A low-order model for thermoacoustic limit cycles in LPP combustors is described. The approach is based on the fact that the main nonlinearity is in the combustion response to flow perturbations. In LPP combustion, fluctuations in the inlet fuel-air ratio have been shown to be the dominant cause of unsteady combustion: these occur because velocity perturbations in the premix ducts cause a time-varying fuel-air ratio, which then convects downstream. If the velocity perturbation becomes comparable to the mean flow, there will be an amplitude-dependent effect on the equivalence ratio fluctuations entering the combustor and hence on the rate of heat release. A simple nonlinear flame model for this dependence is developed and is assumed to be the major non-linear effect on the limit cycle. Since the Mach number is low, the velocity perturbation can be comparable to the mean flow, with even reverse flow occurring, while the disturbances are still acoustically linear in that the pressure perturbation is still much smaller than the mean. Hence elsewhere the perturbations are treated as linear. In this nonlinear flame model, the flame transfer function describing the combustion response to changes in inlet flow is a function of both frequency and amplitude. The nonlinear flame transfer function is incorporated into a linear thermoacoustic network model for plane waves. Frequency, amplitude and modeshape predictions are compared with results from an atmospheric test rig. The approach is extended to circumferential waves in a thin annular geometry, where the nonlinearity leads to modal coupling.
Advanced Materials for Gas Turbine Combustion Systems: Program Summary
Authors: Price Jeffrey
Published: November 2008

Solar Turbines Incorporated, under cooperative agreement number DEFC02-00CH11049, is improving the durability of advanced combustion systems while reducing life cycle costs. This project is part of the Advanced Materials in Advanced Industrial Gas Turbines program in DOE’s Office of Distributed Energy. The targeted development engine is the Mercury 50 gas turbine under development by Solar Turbines Incorporated under the DOE Advanced Turbine Systems (ATS) program (DOE contract number DE-FC21-95MC31173). The ultimate goal of the program is to demonstrate a fully integrated Mercury 50 combustion system, modified with advanced materials technologies, at a host site for 4,000 hours. The program focuses on a dual path development route to define an optimum mix of technologies for the Mercury 50 and future Solar gas turbine products. For linear and injector development, multiple concepts including high thermal resistance thermal barrier coatings (TBC), oxide dispersion strengthened (ODS) alloys, continuous fiber ceramic composites (CFCC), and monolithic ceramics are being evaluated before down selection to the most promising candidate materials for field evaluation. Preliminary component and sub-scale testing is being conducted to determine material properties and demonstrate proof-of-concept. Full-scale rig and engine testing will validate engine performance prior to field evaluation at a host site. Field testing of CFCC combustor liners in Centaur 50 engines at two field test sites is also being conducted under the Advanced Materials Program. This paper is a status review of the program, detailing the current progress.
Screening and Evaluation of Materials for Microturbine Recuperators
Authors: Lara-Curzio Edgar , Trejo R. , More K. L. , Maziasz P. A. , Pint B. A.
Published: November 2008

The effects of stress, temperature and exposure to microturbine exhaust gases on the mechanical properties and corrosion resistance of candidate materials for microturbine recuperators were investigated. Results are presented for 347 stainless steel metallic foils after 500-hr exposure to temperatures between 620°C and 760°C at a tensile stress of 50 MPa. It was found that the material experienced accelerated attack at the highest temperature and that the corrosion products consisted of mixed oxides of iron and chromium. It was also found that exposure at the highest temperatures resulted in significant decrease in both tensile strength and ductility. ORNL’s microturbine recuperator test facility, where the exposures were carried out, is also described.
A Novel Gas Turbine Product Line for Onsite Generation and Combined Heat and Power Between 400 kWe and 1.6 MWe
Authors: Touchton George L. , Belokon Alexandr , Senkevych Mikhail , Belyaev V.
Published: November 2008

In theory gas turbines have inherent advantages for on-site power generation and combined heat and power production in the size range from 50 kWe to 5 MWe. These include low maintenance costs, low vibration, low emissions impact, and ease of remote operation. They also have the potential for high efficiency and low capital costs. In practice they have failed to seriously challenge reciprocating engines dominant market position, despite many recent attempts by established corporations and innovative start-ups. The authors analyze the reasons for this, and discuss the performance goals that gas turbines (or any other new product) must meet in order to challenge and displace the incumbent technology. They then describe a novel gas turbine product line designed specifically to meet this specification in the size range from 400 kW to 1.6 MW. The design is a “clean sheet” of paper approach uniquely fusing industrial gas turbine and aero engine technologies and practices. Fully commercial, cost effective components and technology are applied throughout. The result is a family of machines, which have efficiencies, capital costs, emissions impact, and operating characteristics that make them directly competitive with reciprocating engines across the board. The authors base the features and operating characteristics of the machines on thermodynamic analysis, and component, and system designs prepared by Salut [Appendix A].