bluuebunny/crossref_metadata_2025 huggingface dataset:
Flue Gas Recirculation in Gas Turbine: Investigation of Combustion Reactivity and NOX Emission
Authors: Guethe Felix , de la Cruz Garci´a Marta , Burdet Andre´
Published: February 2010

Flue gas recirculation (FGR) is a promising technology for the optimization of post-combustion CO2 capture in natural gas combined cycle (NGCC) plants. In this work, the impact of FGR on lean gas turbine premix combustion is predicted by analytical and numerical investigations as well as comparison to experiments. In particular the impact of vitiated air condition and moderate increase of CO2 concentration into combustion reactivity and NOx emission is studied. The influence of inlet pressure, temperature and recirculated NOx are taken as parameters of this study. Two different kinetic schemes are used to predict the impact that FGR has on the combustion process: the GRI3.0 and the RDO6_NO, which is a newly compiled mechanism from the DLR Stuttgart. The effects of the FGR on the NOx emissions are predicted using a chemical reactor network including unmixedness as presumed probability density function (PDF) to account for real effects. The magnitude and ratio of prompt to post-flame thermal NOx changes with the FGR-ratio producing less post flame NOx at reduced O2 content. For technical mixtures (i. e. an industrial fuel injector), NOx emission can be expected to be lower with the vitiation of the oxidizer. This is due to several effects: at low O2 concentration, the highest possible adiabatic flame temperatures for stoichiometric conditions decreases resulting in lower NOx when averaged over all mixing fractions. Further effects result from lower post flame NOx production and the role of “reburn” chemistry, actually reducing NOx (recirculated from the exhaust), which might become relevant for the high recirculation ratios, where parts of the flame would operate at rich stoichiometry at given unmixedness. Therefore in general for each combustor technical mixing could decrease NOx with respect to perfect mixing at high FGR-ratio assuming the engine can still be operated. Although the findings are quite general for gas turbines the advantage that reheat engines have in terms of operation are highlighted. For reheat engines this can be understood as an extension of the “reheat concept” and used as the next step in the goal to achieve minimal emissions at increasing power. In addition, NOx emission obtained in FGR combustion reduces even further when the engine pressure ratio increases, making the concept particularly well suited for reheat engines.
Twin Drive Gas Turbines in Single Proplusion Package for Norwegian Fast Patrol Boat
Authors: Davis Larry D. , Soreng Are
Published: February 2010

The Royal Norwegian Navy, along with ship builder Umoe-Mandal, placed a requirement for two twin drive gas turbine packages (left hand/right hand) to fit into its existing Skjold Class fast patrol boat. Approximate output power was 16,000 HP, providing a vessel propulsion speed of over 60 knots. The design featured turbines of two different sizes: one PWC ST18 - 2680 HP and one PWC ST40 - 5365 HP. This combination proved optimal for the desired fighting ability, vessel range and reduced operating economies. The final COGAG (Combined Gas Turbine and Gas Turbine) configuration is the first of its type and may well have the highest horsepower-to-package size of any system designed to date. Many new techniques were developed to allow the propulsion packages to be assembled in place while providing the means for rapid change out of the gas turbines. The primary topics highlighted in this paper are: 1. Overview of key project and system design requirements. 2. Description of the final package design. 3. The concept development phase and review of the analytical tools used for design verification. 4. The integration and special design features required for incorporating twin turbines into a single package with requirements for single or both turbines operating. 5. The in place installation method and system maintenance of the package. 6. Program summary and testing to date.
Experimental Study of a 200 kW Partial Oxidation Gas Turbine (POGT) for Co-Production of Power and Hydrogen-Enriched Fuel Gas
Authors: Rabovitser Joseph , Wohadlo Stan , Pratapas John M. , Nester Serguei , Tartan Mehmet , Palm Steven , Freedman Steve I. , White David
Published: February 2010

Paper presents the results from development and successful testing of a 200 kW POGT prototype. There are two major design features that distinguish POGT from a conventional gas turbine: a POGT utilizes a partial oxidation reactor (POR) in place of a conventional combustor which leads to a much smaller compressor requirement versus comparably rated conventional gas turbine. From a thermodynamic perspective, the working fluid provided by the POR has higher specific heat than lean combustion products enabling the POGT expander to extract more energy per unit mass of fluid. The POGT exhaust is actually a secondary fuel gas that can be combusted in different bottoming cycles or used as synthesis gas for hydrogen or other chemicals production. Conversion steps for modifying a 200 kW radial turbine to POGT duty are described including: utilization of the existing (unmodified) expander; replacement of the combustor with a POR unit; introduction of steam for cooling of the internal turbine structure; and installation of a bypass air port for bleeding excess air from the compressor discharge because of 45% reduction in combustion air requirements. The engine controls that were re-configured for start-up and operation are reviewed including automation of POGT start-up and loading during light-off at lean condition, transition from lean to rich combustion during acceleration, speed control and stabilization under rich operation. Changes were implemented in microprocessor-based controllers. The fully-integrated POGT unit was installed and operated in a dedicated test cell at GTI equipped with extensive process instrumentation and data acquisition systems. Results from a parametric experimental study of POGT operation for co-production of power and H2-enriched synthesis gas are provided.
Heat Transfer in a Confined Oblique Jet Impingement Configuration
Authors: Hoefler Florian , Schueren Simon , von Wolfersdorf Jens , Naik Shailendra
Published: February 2010

Impingement cooling is widely used in cooling configurations for gas turbine components. Relatively high local heat transfer rates and the possibility of jet adjustment to specific geometries are advantageous for internal turbine blade cooling designs. In this paper a confined impingement cooling configuration is investigated. The assembly consists of four non-perpendicular walls of which one holds two rows of staggered inclined jets, each impinging on a different adjacent wall. The flow extraction is realized through two staggered rows of holes opposing the impingement holes wall. Heat transfer experiments were carried out using a transient liquid crystal technique for a series of jet Reynolds numbers between 10,000 and 75,000. The obtained local heat transfer data was evaluated regarding spatially resolved Nusselt numbers as well as line and area averaged values. The results include measurements of the discharge coefficients for the flow through the impingement holes. Numerical simulations of the flow field were carried out, complementary to the experiments. The simulations yield information for a better understanding of the main flow structures. The jets cause high heat transfer in the flow impinging regions with Nusselt numbers up to 180 for Re = 45,000. By contrast, for the same Reynolds number the Nusselt number drops below 20 in flow recirculation regions. For area-averaged Nusselt numbers, the correlation Nu ∝ Rex was found to be valid with slightly modified exponents for each passage wall.
Design Challenges for Combined Cycles With Post-Combustion CO2 Capture
Authors: Zachary Justin
Published: February 2010

In the present climate of uncertainty about CO2 emissions legislation, owners and power plant planners are looking into the possibility of accommodating “add-on” CO2 capture and sequestration (CCS) solutions in their current plant designs. The variety of CCS technologies currently under development makes it a very challenging task. Nevertheless, it is evident that the new generation of combined cycles must address the CO2 capture issue. This discussion concentrates on the more mature post-combustion CCS technologies, such as chemical absorption, and the associated equipment requirements in terms of layout, integration within the generating plant, and auxiliary power consumption. The analysis specifically addresses combined cycle plants, where the capture process must accommodate low CO2 concentration in the exhaust gases (around 3%). Several plant configurations and various operational scenarios are evaluated. The issues related to balance-of-plant systems, including water treatment and availability and redundancy criteria, are also examined. The paper discusses the option to increase CO2 concentration by recirculating some of the exhaust flue gases. The impact of recirculation on the performance and operation of major gas turbine components (compressor combustion, turbo-machinery) is analyzed, as is the effect of the additional auxiliary loads needed to cool the flue gases prior to reinjection in the gas turbine inlet. Since the post-combustion CO2 process requires substantial steam flows, the paper provides several design options for the steam turbine that address the need for large steam extractions. Finally, the paper presents the results of studies conducted by Bechtel in which a neutral but proactive technical approach was applied in evaluating a variety of post-combustion CO2 capture technologies.
The Role of Nonlinear Acoustic Boundary Conditions in Combustion/Acoustic Coupled Instabilities
Authors: Schuller T. , Tran N. , Noiray N. , Durox D. , Ducruix S. , Candel S.
Published: February 2010

Triggering, frequency shifting, mode switching and hysteresis are commonly encountered during self-sustained oscillations in combustors. These mechanisms cannot be anticipated from classical linear stability analysis and the nonlinear flame response to incident flow perturbations is often invoked to interpret these features. However, the flame may not be solely responsible for nonlinearities. Recent studies indicate that interactions with boundaries can be influenced by the perturbation level and that this needs to be considered. The nonlinear response of acoustic boundary conditions to flow perturbations is here exemplified in two configurations which typify practical applications. The first corresponds to a perforated plate backed by a cavity conveying a bias flow and the second corresponds to a set of flames stabilized at a burner outlet. These systems are submitted to acoustic perturbations of increasing amplitudes as can be encountered during unstable operation. It shown that these terminations can be characterized by an impedance featuring an amplitude dependent response. The classical linear impedance Z(ω) is then replaced by its nonlinear counterpart an Impedance Describing Function (IDF), which depends on the perturbation level input Z(ω, |p′| or |u′|). Using this concept, it is shown that the passive perforated plate optimized to damp instabilities of small amplitudes may eventually loose its properties when submitted to large sound pressure levels and that the flame response shifts when the amplitude of incoming flow perturbations is amplified. The influence of these nonlinear elements on the stability of a generic burner is then examined using a methodology which extends a previous analysis based on the Flame Describing Function (FDF) to systems with complex flow interactions at the boundaries.
A Novel Approach for Gas Turbine Condition Monitoring Combining CUSUM Technique and Artificial Neural Network
Authors: Fast Magnus , Palme´ Thomas , Genrup Magnus
Published: February 2010

Investigation of a novel condition monitoring approach, combining artificial neural network (ANN) with a sequential analysis technique, has been reported in this paper. For this purpose operational data from a Siemens SGT600 gas turbine has been employed for the training of an ANN model. This ANN model is subsequently used for the prediction of performance parameters of the gas turbine. Simulated anomalies are introduced on two different sets of operational data, acquired one year apart, whereupon this data is compared with corresponding ANN predictions. The cumulative sum (CUSUM) technique is used to improve and facilitate the detection of such anomalies in the gas turbine’s performance. The results are promising, displaying fast detection of small changes and detection of changes even for a degraded gas turbine.
Diagnozing and Prognozing Gas Turbine Rotor Shaft Faults Using “The MICE”
Authors: Ogbonnaya Ezenwa A.
Published: February 2010

“MICE” is an acronym for Misalignment, Imbalance, Crack and Eccentricity. These form the most catastrophic faults in rotor shafts of gas turbine engines that could lead to downtime. This paper therefore enunciates steps to early detection of these faults and how they could be solved. A method of computer application using Visual-Basic programming language is suggested. A software, MICE, is used for the analysis. Results obtained compare favorably with those of similar works in this area and show that the software can be extended to other rotating equipment when their characteristics are known.
Experimental Study on the Cooling Performance of a Turbine Nozzle With an Innovative Internal Cooling Structure
Authors: Fujimoto Shu , Okita Yoji , Nakamata Chiyuki
Published: February 2010

An innovative cooling structure named multi-slot cooling was invented for high-pressure turbine (HPT) nozzles and blades. This cooling structure has been designed to be simple, inexpensive, and to exhibit good cooling performance. In a previous study (GT2008-50444), the basic design data on the cooling effectiveness and pressure loss coefficients for HPT cooling design were obtained by using simple test pieces. In this study, the cooling performance of the HPT nozzle with a multi-slotted cooling structure in a cascade was reported. First, the HPT nozzle with a multi-slotted cooling structure and its outer profile were selected; its cooling structure was designed by using the data in the previous study and trial-and-error method. Subsequently, ceramic casting cores and casting nozzles were manufactured by way of trial. Furthermore the cooling performance test for the multi-slotted cooling nozzle (TEST #1) in an annular sector cascade test rig was conducted, and the cooling effectiveness fields and pressure loss data were obtained. In addition, the measurement test for determining the heat transfer coefficient on the nozzle (TEST #2) and that for determining the film cooling effectiveness on the nozzle (TEST #3) were conducted. And then, cooling performance of the multi-slotted cooling nozzle was evaluated by using these data. As a result, for the typical configuration, it was confirmed that the basic design data obtained in the previous study are applicable to designing nozzles with multi-slot cooling by introducing a minor modification and the cooling performance of multi-slot cooling is equivalent to that of the conventional cooling under the test condition; consequently, it was confirmed that the multi-slot cooling is well applicable to the cooling of actual HPT airfoils except in the case that its configuration is significantly changed.
Application of Cost Matrices and Cost Curves to Enhance Diagnostic Health Management Metrics for Gas Turbine Engines
Authors: Davison Craig R. , Drummond Chris
Published: February 2010

Statistically based metrics for gas turbine engine diagnostic systems are required to evaluate competing products fairly and to establish a convincing business case. Diagnostic algorithm validation often includes engine testing with implanted faults. The implantation rate is rarely, if ever, representative of the true fault occurrence rate. A technique is presented to convert a confusion matrix with a non-representative fault distribution to one representative of the expected distribution. The small sample size associated with fault implantation studies requires a confidence interval on the results to provide valid comparisons and a method for calculating them is presented. The use of cost matrices to weight confusion matrices, based on the associated cost of each outcome, is demonstrated. The calculation of metrics on the resulting weighted confusion matrix will measure the relative cost of the diagnostic technique, rather than just its accuracy. In this paper, the generation and use of cost matrices is presented and their application to a hypothetical test case is demonstrated. Receiver operating characteristic (ROC) curves evaluate diagnostic system performance across a range of threshold settings. This allows an algorithm’s ability to be assessed over a range of possible usage. Cost curves are analogous to ROC curves but offer several advantages. The techniques for applying cost curves to diagnostic algorithms are presented and their advantages over ROC curves are outlined.
System Analysis of Waste Heat Applications With LNG Regasification
Authors: Gonza´lez-Salazar Miguel Angel , Belloni Clarissa , Finkenrath Matthias , Berti Simone , Gamberi Francesco
Published: February 2010

The combination of the continuously growing demand of energy in the world, the depletion of oil and its sharp price increase, as well as the urgent need for cleaner and more efficient fuels have boosted the global trade of liquefied natural gas (LNG). Nowadays, there is an increasing interest on the design philosophy of the LNG receiving terminals, due to the fact that the existing technologies either use seawater as heating source or burn part of the fuel for regasifying LNG, thus wasting the cryogenic energy of LNG and causing air pollution or harm to marine life. This investigation addresses the task of developing novel systems able to simultaneously regasify LNG and generate electric power in the most efficient and environmentally friendly way. Existing and proposed technologies for integrated LNG regasification and power generation were identified and simple, efficient, safe and compact alternatives were selected for further analysis. A baseline scenario for integrated LNG regasification and power generation was established and simulated. Various novel configurations using Rankine and Brayton cycles were created, modeled and compared to the baseline scenario in terms of LNG regasification rate, efficiency and power output. A study case with a simple and compact design was selected, preliminarily designed and analyzed. The performance and design characteristics of the study case were then compared to the baseline case. The results show that the study case results in a smaller footprint of the plant, at the same time offering a simple design solution though with lower efficiencies.
Thermal and Fluid Dynamic Analysis of the Gas Turbine Transition Piece
Authors: Alfaro Ayala J. Arturo , Gallegos Mun˜oz Armando , Zaleta Aguilar Alejandro , Campos Amezcua Alfonso , Mazur Zdzislaw
Published: February 2010

This paper presents the thermal and fluid dynamic analysis of the gas turbine transition piece, applying the Finite Volume Method (FVM) through the Computational Fluid Dynamics (CFD). The study is carried out to examine the flow field and distribution of temperatures of the combustion gases along the transition piece and exit mouth, getting profiles and contours of velocity and temperature. This study is important to know the paths of flow and distribution of temperatures of the hot streaks through the transition piece, which impact on cooling system in stator and rotor. Also, these flow field and distribution of temperature have an effect in performance and life of the vanes and blades in the first stage of the turbine, principally by the difference of heat load. The study was carried out in a steady state three-dimensional model to avoid the geometric simplifications, using code FLUENT® version 6.3.26 where the k-ε turbulence model was applied and different boundary conditions in the inlet of the transition piece were considered. To obtain the results, a structured grid about 5.1 millions of cells with second-order upwind scheme and coupled solver was applied. The results show the effect of the velocity and temperature along the transition piece and exit mouth due to the change of the curved section. In the exit mouth of the transition piece is identified a dimensionless peak temperature for about 1.019 in a point near to 68% of the radial edge, while in the circumferential direction the peak temperature is about 1.027 in a point near to 50% of the circumferential edge with symmetry profiles.
Effect of Nozzle Guide Vanes on Flow Parameters at the Exit of a Micro Gas Turbine Combustor
Authors: Jiang Lei-Yong , Carscallen Bill , Okulov Paul , Gallien Rene , Rigaudier Guillaume
Published: February 2010

The combustor and turbine of a gas turbine engine are directly connected, and their flow fields and performance are closely coupled. However, to reduce turn-around time and avoid numerical difficulties in the development of gas turbine engines, numerical simulations of gas turbine combustors are usually performed without turbine components attached. This decoupling approach is investigated numerically in this paper. A micro gas turbine combustor is used as a test model, and the two-phase, turbulent, reacting flow fields of the combustor with and without nozzle guide vanes (NGV) have been simulated. Complex flow phenomena such as cross-jet flows, separations, recirculation zones, conjugate heat transfers, fuel droplet heating, vaporizing and combusting etc. are observed. The flow features of axial and tangential velocities, Mach number, and static pressure at the combustor exit are substantially different between these two cases. The effect of NGV on the combustor flow field decreases as the distance away from the NGV leading edge increases. At the cross-section, one span upstream of the NGV leading edge, the distributions of flow parameters with and without NGV are almost the same. The findings suggest that for the present combustor configuration, simulations of the combustor and turbine components could be decoupled if the interfacing cross-section or combustor exit is located at one span upstream of NGV. The present study is still preliminary and the results could be configuration dependent. Further study on the combustor-turbine decoupling issue for a traditional gas turbine combustor is on the way.
A New Kind of Multifunctional Energy System (MES) Based on Moderate Conversion of Chemical Energy of Fossil Fuels
Authors: Han Wei , Jin Hongguang
Published: February 2010

This paper proposes a new kind of multifunctional energy system (MES) using natural gas and coal to more efficiently and more economically produce methanol and power. Traditional chemical processes pursue high conversion ratios of chemical energy of fuels. The new MES focuses on the moderate conversion of the chemical energy of fuels. To do this, about 50% of the coal is partially gasified with pure oxygen and steam as oxidant, and then the unconverted residuals (char) and natural gas are utilized synthetically by char-fired reforming to generate syngas. The combustion of char drives the methane/steam reforming reaction. Here, the reforming reaction is also moderately converted, and the reforming temperature is decreased 100°C–150°C compared with that of the conventional method. The carbon-rich syngas from the partial gasifier of coal and hydrogen-rich syngas from char-fired reformer are mixed together and converted into methanol at a proper conversion ratio (lower than that of conventional chemical process). Finally, the unconverted syngas is used in a combined cycle as fuel for power generation. As a result, the total exergy efficiency of the new system is 55–60%. Comparing to individual systems, including IGCC and natural gas-based methanol plants (MSN), this new system can generate 10–20% more electricity with the same quantity of fossil fuels input and methanol output. In addition, the possibility of reducing the size of gasifier, reformer, and methanol synthesis reactor may reduce investment costs accordingly. These results may provide a new way to use coal and natural gas more efficiently and economically.
Analysis of Gas Turbine Performance in IGCC Plants Considering Compressor Operating Condition and Turbine Metal Temperature
Authors: Kim Y. S. , Lee J. J. , Cha K. S. , Kim T. S. , Sohn J. L. , Joo Y. J.
Published: February 2010

An IGCC (integrated gasification combined cycle) plant couples a power block to a gasification block. The method of integrating a gas turbine with a gasification process is the major design option. Matching between the gas turbine and the air separation unit is especially important. This study analyzes the influences of IGCC design options on the operability and performance of the gas turbine. Another research focus is given to the estimation of the change of turbine metal temperature in the IGCC operating environment. For this purpose, a full off-design analysis of the gas turbine is used with the turbine blade cooling model. Four different syngas fuels are considered. As the integration degree becomes lower, the gas turbine power and efficiency increase. However, a lower integration degree causes a reduction of the compressor surge margin and overheating of the turbine metal. Only near 100% integration degree designs are almost free of those two problems. The syngas property also affects the gas turbine operation. As the heating value gets lower, the problems of surge margin reduction and metal overheating become more severe. Modifications of the compressor (adding a couple of stages) and the turbine (increasing gas path area) could solve the compressor surge problem. However, the turbine overheating problem still exists. In particular, the turbine modification is predicted to overheat turbine metal considerably.
Development of a Numerical Procedure for Integrated Multidisciplinary Thermal-Fluid-Structural Analysis of an Aeroengine Turbine
Authors: Peschiulli Antonio , Coutandin Daniele , Del Cioppo Marco , Damasio Massimo
Published: February 2010

The aim of the work is to define a methodology and to develop specific tools that allow engineers to investigate and fully characterize the thermal performance of an aero-engine turbine module. The thermal behaviours of a complex system are the result of strong interactions between the fluid-dynamics aspects, the heat balance within each component and the geometric variations mainly due to the thermal and mechanical loads. All these phenomena are strictly connected and cannot be studied separately without introducing approximations and /or errors in the final results. For long time the industrial approach in turbine design has been based on separate analyses of the phenomena with manual iterations between them to allowed acceptable solutions to be reached. The new requirements in reducing the product time-to-market together with the need of higher accuracy in the design, have driven the development of new approaches based on the multi-disciplinary analysis integration. This paper will summarise the AVIO approach to the turbine design procedure upgrade, mainly focused on the thermal analysis and clearances control. A detail of the methodology used will be presented together with a description of the tools developed. A comparison between numerical predictions and experimental data (full engine test) will be reported.
A New Test Facility for Investigating the Interaction Between Swirl Flow and Wall Cooling Films in Combustors
Authors: Wurm B. , Schulz A. , Bauer H.-J.
Published: February 2010

Swirl stabilization of flames is typically used in combustors of aero engines and gas turbines for power generation. In the near wall region of the combustor liner, the swirling flow interacts in a very particular way with wall cooling films. This interaction and its effect on the local wall cooling performance gave reason to design and commission a new atmospheric test rig for detailed aerodynamic and thermal studies. The new test rig includes three burners in a planar arrangement. Special emphasis was placed on the simulation of realistic operating conditions as Reynolds number and temperature ratio. The liner cooling and the formation of a starter cooling film can be independently controlled. The rectangular flow channel is equipped with large windows to allow for laser optical diagnostics like PIV and 3-component LDA. The thermal analyses are based on highly resolved temperature mappings of the cooled surface utilizing infrared thermography. First experimental results are presented in terms of static pressure distributions on the combustor liner and PIV contour plots of the swirl flow. The static pressure pattern corresponds well to the up wash and downwash regions of the swirl flow.
A Thermoeconomic Comparison Between SOFC Hybrid Systems and the Most Worldwide Used Technologies Towards Competitive Innovative Plants
Authors: Franzoni A. , Magistri L. , Tarnowsky O. , Massardo A. F.
Published: February 2010

This paper investigates options for highly efficient SOFC hybrid systems of different sizes. For this purpose different models of pressurised SOFC hybrids systems have been developed in the framework of the European Project “LARGE SOFC - Towards a Large SOFC Power Plant”. This project, coordinated by VTT Finland, counts numerous industrial partners such as Wartsila, Topsoe and Rolls-Royce FCS ltd. Starting from the RRFCS Hybrid System [1], considered as the reference case, several plant modifications have been investigated in order to improve the thermodynamic efficiency. The main options considered are (i) the integration of a recuperated micro gas turbine and (ii) the replacement of the cathodic ejector with a blower. The plant layouts are analysed in order to define the optimum solution in terms of operating parameters and thermodynamic performances. The study of a large size power plant (around 110 MWe) fed by coal and incorporated with SOFC hybrid systems is also conducted. The aim of this study is to analyse the sustainability of an Integrated Gasification Hybrid System from the thermodynamic and economic point of view in the frame of future large sized power generation. A complete thermoeconomic analysis of the most promising plants is carried out, taking into account variable and capital costs of the systems. The designed systems are compared from the thermodynamic and the thermoeconomic point of view with some of the common technologies used for distributed generation (gas turbines and reciprocating engines) and large size power generation (combined cycles and IGCC). The tool used for this analysis is WTEMP software, developed by the University of Genoa (DIMSET-TPG) [2], able to carry out a detailed thermodynamic and thermoeconomic analysis of the whole plants.
Flame Transfer Function Measurement and Instability Frequency Prediction Using a Thermoacoustic Model
Authors: Kim Kyu Tae , Lee Hyung Ju , Lee Jong Guen , Quay Bryan D. , Santavicca Domenic
Published: February 2010

The dynamic response of a turbulent premixed flame to an acoustic velocity perturbation was experimentally determined in a lean-premixed, swirl-stabilized, lab-scale gas turbine combustor. Fuel was injected far upstream of a choked inlet to eliminate equivalence ratio oscillations. A siren-type modulation device was used to provide acoustic perturbations at the forcing frequency of 100 ∼ 400 Hz. To measure global heat release rate, OH*, CH*, and CO2* chemiluminescence emissions were used. The two-microphone method was utilized to estimate inlet velocity fluctuations, and it was calibrated by direct measurements using a hot wire anemometer under cold-flow conditions. Gain of the flame transfer function (FTF) shows a low pass filter behavior, and it is well-fitted by a second-order model. Phase difference increases quasi-linearly with the forcing frequency. Using the n-τ formulation, gain and phase of FTF were incorporated into an analytic thermoacoustic model in order to predict instability frequencies and corresponding modal structures. Self-excited flame response measurements were also performed to verify eigenfrequencies predicted by the thermoacoustic model. Instability frequency predicted by the thermoacoustic model is supported by experimental results. Two instability frequency bands were measured in the investigated gas turbine combustor at all operating conditions: f ∼ 220 Hz and f ∼ 350 Hz. Results show that the self-excited instability frequency of f ∼ 220 Hz results from the fact that the flames amplify flow perturbations with f = 150 ∼ 250 Hz. This frequency range was observed in the flame transfer function measurements. The other instability frequency of f ∼ 350 Hz occurs because the whole combustion system has an eigenfrequency corresponding to the 1/4-wave eigenmode of the mixing section. This was analytically and experimentally demonstrated. Results also show that the flame length, LCH*max, plays a critical role in determining self-induced instability frequency.
Characterization of Forced Flame Response of Swirl-Stabilized Turbulent Lean-Premixed Flames in a Gas Turbine Combustor
Authors: Kim Kyu Tae , Lee Jong Guen , Lee Hyung Ju , Quay Bryan D. , Santavicca Domenic
Published: February 2010

Flame transfer function measurements of turbulent premixed flames were made in a model lean premixed, swirl-stabilized, gas turbine combustor. OH*, CH*, and CO2* chemiluminescence emissions were measured to determine heat release oscillation from a whole flame, and the two-microphone technique was used to measure inlet velocity fluctuation. 2-D CH* chemiluminescence imaging was used to characterize the flame shape: the flame length (LCH* max) and flame angle (α). Using H2-natural gas composite fuels, XH2 = 0.00 ∼ 0.60, very short flame was obtained and hydrogen enrichment of natural gas had a significant impact on the flame structure and flame attachment points. For a pure natural gas flame, the flames exhibit a “V” structure, whereas H2-enriched natural gas flames have an “M” structure. Results show that the gain of “M” flames is much smaller than that of “V” flames. Similar to results of analytic and experimental investigations on the flame transfer function of laminar premixed flames, it shows that the dynamics of a turbulent premixed flame is governed by three relevant parameters: the Strouhal number (St = LCH* max / Lconv), the flame length (LCH* max), and the flame angle (α). Two flames with the same flame shape exhibit very similar forced responses, regardless of their inlet flow conditions. This is significant because the forced flame response of a highly turbulent, practical gas turbine combustor can be quantitatively generalized using the non-dimensional parameters which collapse all relevant input conditions into the flame shape and the Strouhal number.
Thermo-Fluid Modelling for Gas Turbines—Part I: Theoretical Foundation and Uncertainty Analysis
Authors: Kyprianidis Konstantinos G. , Sethi Vishal , Ogaji Stephen O. T. , Pilidis Pericles , Singh Riti , Kalfas Anestis I.
Published: February 2010

In this two-part publication, various aspects of thermo-fluid modelling for gas turbines are described and their impact on performance calculations and emissions predictions at aircraft system level is assessed. Accurate and reliable fluid modelling is essential for any gas turbine performance simulation software as it provides a robust foundation for building advanced multi-disciplinary modelling capabilities. Caloric properties for generic and semi-generic gas turbine performance simulation codes can be calculated at various levels of fidelity; selection of the fidelity level is dependent upon the objectives of the simulation and execution time constraints. However, rigorous fluid modelling may not necessarily improve performance simulation accuracy unless all modelling assumptions and sources of uncertainty are aligned to the same level. Certain modelling aspects such as the introduction of chemical kinetics, and dissociation effects, may reduce computational speed and this is of significant importance for radical space exploration and novel propulsion cycle assessment. This paper describes and compares fluid models, based on different levels of fidelity, which have been developed for an industry standard gas turbine performance simulation code and an environmental assessment tool for novel propulsion cycles. The latter comprises the following modules: engine performance, aircraft performance, emissions prediction, and environmental impact. The work presented aims to fill the current literature gap by: (i) investigating the common assumptions made in thermo-fluid modelling for gas turbines and their effect on caloric properties and (ii) assessing the impact of uncertainties on performance calculations and emissions predictions at aircraft system level. In Part I of this two-part publication, a comprehensive analysis of thermo-fluid modelling for gas turbines is presented and the fluid models developed are discussed in detail. Common technical models, used for calculating caloric properties, are compared while typical assumptions made in fluid modelling, and the uncertainties induced, are examined. Several analyses, which demonstrate the effects of composition, temperature and pressure on caloric properties of working mediums for gas turbines, are presented. The working mediums examined include dry air and combustion products for various fuels and H/C ratios. The errors induced by ignoring dissociation effects are also discussed.
CFD Predictions of Low NOx Radial Swirlers With Central Fuel Injection
Authors: King Phil T. , Al Kabie Hisham S. , Andrews Gordon E. , Pourkashanian Mohamed M. , McIntosh Andy C.
Published: February 2010

A radial swirler was investigated with central fuel injection in the radial outward direction. 8 radial swirl vanes were used with 8 central radial fuel injector holes. The experimental results showed that central radial outward fuel injection aim had improved flame stability relative to vane passage fuel injection without the large NOx penalty associated with conventional fuel injection. The radially outward fuel jets impinged on the radially inward air from the vane passages and relatively good mixing occurred, but with sufficient unmixedness to stabilise the flame. CFD investigations were carried out to investigate this partial premixed and partial diffusion combustion mode which is commonly used for a pilot fuel location in lean low Nox combustion. RANS CFD predictions were undertaken with three combustion models: flamelet, pdf transport and eddy dissipation. The flamelet model was far superior both in the prediction of the measured quantitative values and in their distribution. The eddy dissipation model grossly over predicted the peak temperature and NOx. However, all the RANS models did not predict the measured direction of flame development, which was more in the axial direction on the inside of the shear layers. The RANS models predicted that the flame development would follow the shear layer. In an attempt to better predict the direction of flame development an LES model has been used. This indicates a better prediction of the direction of fuel and air mixing.
Investigation of Film Cooling Effectiveness on Squealer Tip of a Gas Turbine Blade
Authors: Yang Dianliang , Feng Zhenping , Yu Xiaobing
Published: February 2010

The effect of the film cooling holes arrangements and the blowing ratio on the tip film cooling effectiveness in a rotating blade with the squealer tip was investigated by using numerical methods in this paper. The first stage rotor blade with squealer tip of GE-E3 engine high pressure turbine was adopted to perform this study. The tip clearance was specified as 1% of the blade height, and the groove depth was specified as 2% of the blade height. The different turbulence models were checked by Kim’s experiment data [1] in 1995, and the standard k-ε turbulence model was chosen to predict the film cooling effectiveness on the blade tip. The film holes were arranged at the tip camber line, the tip division line, the tip pressure side and the pressure surface near tip, respectively. The effect of the holes position on the tip film cooling effectiveness in the rotating blade was studied. The effect of the blowing ratio was analyzed for the cases that the film holes were placed at the tip division line and the pressure surface near tip. The results show that the area-averaged tip film cooling effectiveness reaches the highest when the film holes are placed along the tip division line, and the tip leakage mass flow rate can be reduced by placing the film holes on the pressure surface near tip.
Assessment of the Role of Fuel Autoignition Delay at the Limits of Gas Turbine Combustion and Ignition
Authors: Burger Victor , Yates Andy , Savage Nicholas , Metcalf Owen
Published: February 2010

The influence of fuel autoignition chemistry is known to be relevant when approaching the limits of lean blowout and lean ignition in a continuous combustion environment. This was investigated by employing four reference fuels having very different autoignition delay profiles but similar boiling points to interrogate various test environments and thereby to assess the relevance of the differences in autoignition chemistry. A combustion bomb apparatus was used to characterize the reference fuels together with a sample of commercial Jet A-1 for comparison. The measurements were cross-checked using a chemical kinetic simulation model. A continuous combustion rig was used to study the threshold ignition and blowout performance of the pre-vaporized reference fuels and a laminar flame speed bomb was used to study the influence of autoignition chemistry on normal, stoichiometric combustion and normal ignition conditions. In all the experiments, the results reflected the distinctive differences of the test fuels in terms of their autoignition delay timescales. The findings were interpreted against the background of the commercial jet fuel autoignition chemistry and the relevance of traditional autoignition delay metrics such as Octane or Cetane rating. Notwithstanding the influence of fuel evaporation and mixing timescales which can exert an overriding influence in a practical, gas turbine application, it was concluded that the fuel’s autoignition delay timescale also plays a very significant role in threshold operational situations.
Thermal Gradients in Discontinuously Rotated Rotary Regenerative Heat Exchangers
Authors: Bennhold Florian , Wilson David Gordon
Published: February 2010

We present a numerical analysis of the thermal behavior of a high-temperature rotary regenerator with a cordierite heat-exchange matrix which is rotated in an indexed fashion. Such an “indexing regenerator” has recently been proposed as a novel high-temperature high-effectiveness heat-exchange solution for microturbines and other heat engines. Our simulations indicate significant differences in the patterns of thermal gradient development between the indexing regenerator and its continuously rotating siblings (e.g. the Ljundstrom air preheater). These features are crucial in understanding the thermal stresses in the regenerator matrix, which in turn will allow designers to increase the longevity and overall reliability of such devices. In addition to the numerical analysis, we have used thermal-imaging techniques to support our simulations and examine in-plane thermal conditions on the inlet and outlet surfaces of the regenerator disk. The principal result of our study is an understanding of the development of thermal gradients in the matrix of an indexed-rotation regenerator. This understanding is fundamental to thermal stress management in the design and operation of indexed regenerators. Analysis indicates that, for the same operating conditions, indexed-rotation regenerators develop lower thermal gradients than continuous rotation regenerators, and thus have the potential for greater reliability. Design recommendations are made from the simulation and experience with a prototype unit.
Data Center Cooling Optimization: Ambient Intelligence Based Load Management (AILM)
Authors: Somani Ankit , Joshi Yogendra K.
Published: February 2010

Early Data centers can consume 25 to 50 times more electric power than a standard office space of the same footprint. In this paper, a simplified computational fluid dynamics/heat transfer (CFD/HT) model for a unit cell of a data center with a hot aisle-cold aisle (HACA) layout is simulated. Inefficiencies dealing with the mixing of hot air present in the room with the cold inlet air, leading to a loss of cooling potential are identified. The need for a thermal aware job-scheduling algorithm which enhances IT productivity, while maintaining the facility within server inlet temperature constraints is established. The inherent non-linearity of such an optimization problem is explained. A novel algorithm called the Ambient Intelligence based Load Management (AILM) is developed which counters the above issues and enhances the net data center heat dissipation capacity for given energy consumption at the facilities end. It gives a scheme to determine how much and where the computer loads should be allocated, based on the differential loss in cooling potential per unit increase in server workload. Enhancements of heat dissipation capacity of over 50% are proved numerically for the representative values considered. An approach to incorporate heterogeneity in data centers, both for lower heat dissipation and liquid cooled racks has been established. Finally, different objective functions are studied and an ideal combination of the IT objectives and thermal constraints is derived.
Thermal Performance of Counter Flow Microchannel Heat Exchangers Subjected to Axial Heat Conduction and External Heat Transfer
Authors: Mathew B. , Hegab H.
Published: February 2010

The thermal model of a balance counter flow microchannel heat exchanger subjected to external heat transfer and axial heat conduction is modeled in this paper. Three governing equations are developed, one for each of the two fluids and the third for the wall separating the fluids. The ends of the wall separating the fluids are assumed to be insulated. The equations are solved numerically using finite difference method. The model developed in this paper is verified using the conventional effectiveness-NTU equations and existing models that consider each of these effects individually. The combined effect of axial heat conduction and external heating always degraded the hot fluid effectiveness for all values of NTU. Irrespective of NTU the cold fluid effectiveness either increased or decreased depending on whether the degradation in heat gain due to axial heat conduction was compensated by external heat transfer.