bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Intermediate Temperature Combined Cycles With a Carbon Dioxide Topping Cycle
Authors: Chacartegui R. , Sa´nchez D. , Jime´nez-Espadafor F. , Mun˜oz A. , Sa´nchez T.
Published: August 2009

The development of high efficiency solar power plants based on gas turbine technology presents two problems, both of them directly associated with the solar power plant receiver design and the power plant size: lower turbine intake temperature and higher pressure drops in heat exchangers than in a conventional gas turbine. To partially solve these problems, different configurations of combined cycles composed of a closed cycle carbon dioxide gas turbine as topping cycle have been analyzed. The main advantage of the Brayton carbon dioxide cycle is its high net shaft work to expansion work ratio, in the range of 0.7–0.85 at supercritical compressor intake pressures, which is very close to that of the Rankine cycle. This feature will reduce the negative effects of pressure drops and will be also very interesting for cycles with moderate turbine inlet temperature (800–1000 K). Intercooling and reheat options are also considered. Furthermore, different working fluids have been analyzed for the bottoming cycle, seeking the best performance of the combined cycle in the ranges of temperatures considered.
Range of Variability in the Dynamics of Semi-Cylindrical Friction Dampers for Turbine Blades
Authors: Zucca Stefano , Botto Daniele , Gola Muzio M.
Published: August 2009

Under-platform dampers are used to reduce resonant stresses in turbine blades to avoid high cycle fatigue failures. In this paper a model of semi-cylindrical under-platform damper (i.e. with one flat side and one curved side) for turbine blades is described. The damper kinematics is characterized by three degrees of freedom (DOFs): in-plane translations and rotation. Static normal loads acting on the damper sides are computed using the three static balance equations of the damper. Non-uniqueness of normal pre-loads acting on the damper sides is highlighted. Implementation of the model in a numerical code for the forced response calculation of turbine blades with under-platform dampers shows that non-uniqueness of normal pre-loads leads to non-uniqueness of the forced response of the system. A numerical test case is presented to show the capabilities of the model and to analyze the effect of the main system parameters (damper mass, excitation force, coefficient of friction and damper rotation) on the damper behavior and on the system dynamics.
Design Optimization and Validation of a Power Turbine Blade for an Aero-Derivative Gas Turbine Upgrade
Authors: Del Turco Paolo , D’Ercole Michele , Pieroni Nicola , Mariotti Massimiliano , Gamberi Francesco , Zemitis William
Published: August 2009

Major limitations for power turbine blades for oil & gas and industrial applications are Creep and HCF (High Cycle Fatigue). Power Turbine blades, being normally uncooled, are generally not affected by high temperature gradients; therefore LCF (Low Cycle Fatigue) doesn’t constitute their main limiting life factor. If creep is often not a limiting factor for aircraft engines blades, where inspection, maintenance and replacement intervals are more frequent, it becomes one of the key drivers for an industrial gas turbine where required flow path components life is at least one order larger. To avoid HCF failures, it would be desirable to avoid stimuli crossing natural frequencies in the entire operative range. However, due to the wide operative range and high number of stimuli present, the avoidance of potential resonance crossings is often not possible. This is the one of the reasons why a prototype validation campaign is usually performed, where, during the test, vibratory stress levels are compared to HCF endurance limits. This paper describes the processes used in GE Infrastructure Oil&Gas to verify, design, develop and test a PT (Power Turbine) blade for an upgraded 35 MW-class aero-derivative gas turbine. Initial assessment phases, new material selection, concurrent engineering efforts, bench testing characterization and final validation on FETT (First Engine to Test) are described. A particular focus is given to the analytical tools (i.e. modal cyclic symmetry analysis) used during the design phase and validation tests.
Endwall Film Cooling Effects on Secondary Flows in a Contoured Endwall Nozzle Vane
Authors: Barigozzi Giovanna , Franchini Giuseppe , Perdichizzi Antonio , Quattrore Marco
Published: August 2009

The present paper investigates the effects of endwall injection of cooling flow on the aerodynamic performance of a nozzle vane cascade with endwall contouring. Tests have been performed on a 7 vane cascade with a geometry typical of a real gas turbine nozzle vane. The cooling scheme consists of four rows of cylindrical holes. The same cooling scheme, applied to a flat endwall, was already investigated by the authors. Tests have been carried out at low speed (M2is = 0.2) with a low inlet turbulence intensity level (1.0%) and with a coolant to mainstream mass flow ratio varied in the range from zero (solid endwall) to 2.5%. Energy loss coefficient, secondary vorticity and outlet angle distributions were computed from 5-hole probe measured data. Contoured endwall results, with and without film cooling, were compared to planar endwall data. Endwall contouring was responsible for a significant overall loss decrease, thanks to the reduction of both profile and planar side secondary flows losses; a loss increase on the contoured side was instead observed. Like as for the planar endwall, even for contoured endwall coolant injection modifies secondary flows, reducing their intensity, but the relevance of the changes is reduced. Nevertheless for all the tested injection conditions, secondary losses on the contoured side are always higher than in the planar case, while contoured cascade overall losses are lower. A unique minimum overall loss injection condition was found for both tested geometries, corresponding to an injected mass flow rate of about 1.0%.
Turbine Stator Well CFD Studies: Effects of Cavity Cooling Air Flow
Authors: Andreini Antonio , Da Soghe Riccardo , Facchini Bruno , Zecchi Stefano
Published: August 2009

The improvement of the aerodynamic efficiency of gas turbine components is becoming more and more difficult to achieve. Nevertheless there are still some devices that could be improved to enhance engine performance. Further investigations on the internal air cooling systems, for instance, may lead to a reduction of cavities cooling air with a direct beneficial effect on engine performance. At the same time, further investigations on heat transfer mechanisms within turbine cavities may help to optimize cooling air flows saving engine life duration. This paper presents some CFD preliminary studies conducted on an two-stage axial turbine rig developed in a research programme on internal air systems funded by EU, named the Main Annulus Gas Path Interactions (MAGPI). Each turbine stage consists of 39 vanes and 78 rotating blades and the modelled domain includes both the main gas path of the two turbine stages and the second stator well. Pre experimental tests CFD computations were planned in order to point out the reliability of numerical models in the description of the flow patterns in the main annulus and in the cavities. Several computational meshes were considered with steady and unsteady approaches in order to assess the sensitivity to computational approach regarding the evaluation of the interactions between main annulus and disk cavities flows. Results were obtained for several cavities cooling air mass-flow rates and data were further analyzed to investigate the influence of the sealing flow inside the main annulus. MAGPI project is a 4 years Specific-Targeted-Research-Project (2007–2011) and its consortium includes six universities and nine gas turbines manufacturing companies. The project is focused on the analysis of interactions between primary and secondary air systems achieving a novel approach as these systems have, up to now, only been considered separately. In particular one of the tasks of the project will focus on heat transfer phenomena and delivering experimental data which will be used to validate the advanced design tools used by industries (CFD codes and correlative formulations).
Enhanced Fault Localization Using Probabilistic Fusion With Gas Path Analysis Algorithms
Authors: Kyriazis A. , Mathioudakis K.
Published: August 2009

A method for gas turbine fault identification from gas path data, in situations with a limited number of measurements, is presented. The method consists of a two stage process: (a) localization of the component or group of components where the fault is located and (b) fault identification, by determining the precise location and magnitude of component performance deviations. The paper focuses on methods that allow improved localization of the faulty components. Gas path analysis algorithms are applied to diagnostic sets comprising different combinations of engine components. The results are used to derive fault probabilities, which are then fused to derive a conclusion as to the location of a fault. Once the set of possible faulty components is determined, a well defined diagnostic problem is formulated and the faulty parameters are determined by means of a suitable algorithm. It is demonstrated that the method has an improved effectiveness when compared to previous GPA based methods.
Design and Optimization of the Internal Cooling Channels of a HP Turbine Blade: Part II—Optimization
Authors: Verstraete Tom , Amaral Sergio , Van den Braembussche Rene´ , Arts Tony
Published: August 2009

This second paper presents the aerothermal optimization of the first stage rotor blade of an axial HP turbine by means of the conjugate heat transfer method (CHT) and lifetime model described in paper 1. The optimization system defines the position and diameter of the cooling channels leading to the maximum lifetime of the blade while limiting the amount of cooling flow. It is driven by the results of a CHT and subsequent stress analysis of each newly designed geometry. Both temperature and stress distributions are the input for the Larson-Miller material model to predict the lifetime of the blade. The optimization procedure makes use of a Genetic Algorithm (GA) and requires the aerothermal analysis of a large number of geometries. Because of the large computational cost of each CHT analysis, this results in a prohibitive computational effort. The latter has been remediated by using a more elaborate optimization system, in which a large part of the CHT analyzes are replaced by approximated predictions by means of a meta-model. Two metamodels, an Artificial Neural Network (ANN) and a Radial Basis Function (RBF) network, have been tested and their merits have been discussed. It is shown how this optimization procedure based on CHT calculations, a GA and a metamodel can lead to a considerable extension of the blade lifetime without increase of the amount of cooling flow or the complexity of the cooling geometry.
Modelling of Variables Gas Properties and Compositions in Turbomachinery Flow Simulations
Authors: Di Mare Luca
Published: August 2009

This paper describes the formulation of computational methods for aerothermodynamic predictions in turbomachinery passages and gas-turbine engine components accounting for changes in fluid properties. The changes accounted for include the change of specific heats with temperature and changes in composition as consequence of the injection of chemical compounds different from those forming the main gas stream, and the reactions between the main gas stream and these compounds. The flow equations for compressible flow with variable properties and compositions are stated, with particular reference to the inviscid flux jacobians and their eigenvalues and eigenvectors. These are used to derive a Roe-like flux difference splitting algorithm. The algorithm derived is applied to the computation of variable property, reacting flow in a transonic nozzle and to the computation of equilibrium flow in a High-Pressure turbine stage.
The Influence of the History of Thermal Expansion on the Axial Turbine Characteristic
Authors: Silivestru Valentin , Vilag Valeriu A. , Petcu Romulus , Popescu Jeni A.
Published: August 2009

The ability to predict the dynamic behaviour of a gas turbine is of great importance, even from the early design stages, as it impacts the designer’s ability to select higher performance operating regimes while maintaining the gas turbine within the required safety margins, inside stable operation envelope. Most of the models used for numerical simulations of the dynamic response of a gas turbine are based on the turbine characteristic curve, determined, in most cases, for the steady operating states of the gas turbine. From a manufacturing standpoint, the geometrical accuracy of the machined blade profiles is a major concern, as it strongly impacts on the actual gas turbine performance. Even relatively small deviations in the shape of the axial turbine blade profile affect the value of the area of the channel between two adjacent turbine blades minimum section, and, thus, impacts significantly upon of the actual gas turbine performance. With this in view, this paper aims at studying the influence of the thermal expansion history on the axial turbine characteristic curve. The thermal expansion that occurs between the temperature defining the idle operating regime and the temperature defining the maximum stable operating regime usually takes about 30 minutes, while the gas turbine acceleration process from idle to the maximum stable operating regime takes between four to eight seconds. Due to the thermal expansion, the minimum area of the channel between two adjacent turbine blades (a.k.a. the throttle area) increases by about 1.5% when the gas turbine moves from idle to the maximum stable operating regime, change that affects significantly the turbine characteristic curve. Hence, the deviation of a turbine characteristic curve due to the thermal expansion history must be taken into account in order to improve the gas turbine dynamic behaviour prediction. To demonstrate this improvement, this paper will present two numerical simulations. In the first case, the simulation reproduces the turbine characteristic for nominal regime. In the second case, the turbine characteristic at dilatation state at idle regime. The results of the numerical simulation are compared against each other in order to highlight the differences in the two turbine characteristics induced by the thermal expansion history.
CFD Investigation on the Circumferential Grooves Casing Treatment of Transonic Compressor
Authors: Huang Xudong , Chen Haixin , Fu Song
Published: August 2009

The performance of NASA Rotor 37 with Circumferential Grooves Casing Treatment (CGCT) is studied with an in-house CFD code NSAWET. Based on the stall mechanism analysis, a number of CGCT configurations have been proposed and numerically tested. The computation results show that the stall mechanisms are strongly related with the width of tip clearance. With a small tip clearance, the stall process is dominated by the trailing edge separation, while the leading edge tip leakage vortex breakdown induced blockage causes stall in a large tip clearance configuration. Circumferential grooves at appropriate axial locations can be beneficial to the stall margin in these two types of stall processes. The effects of the groove width and depth are presented. The mechanisms of CGCT for different tip clearances are also discussed.
Advanced Modeling of Fluid Thermodynamic Properties for Gas Turbine Performance Simulation
Authors: Sethi Vishal , Diara Fulvio , Atabak Sina , Jackson Anthony , Bala Arjun , Pilidis Pericles
Published: August 2009

This paper describes the structure of an advanced fluid thermodynamic model which has been developed for a novel advanced gas turbine simulation environment called PROOSIS. PROOSIS (PRopulsion Object Oriented SImulation Software) is part of the VIVACE-ECP (Value Improvement through a Virtual Aeronautical Collaborative Enterprise - European Cycle Programme) project. The main objective of the paper is to determine a way to achieve an accurate, robust and reliable fluid model. The results obtained demonstrate that accurate modeling of the working fluid is essential to avoid convergence problems of the thermodynamic functions thereby increasing the accuracy of calculated fluid properties. Additionally, the impact of accurately modeling fuel thermodynamic properties, at the point of the injection, is discussed.
Continued Enhancement of SGT-600 Gas Turbine Design and Maintenance
Authors: Navrotsky Vladimir , Blomstedt Mats , Lundin Niklas , Uebel Claes
Published: August 2009

Current power generation and oil & gas markets are dynamic with continuously growing requirements on gas turbines for high reliability and availability and low emissions and life cycle cost. In order to meet these growing requirements on the gas turbines, the OEM should sustain continued product improvement and employment of innovative solutions and technologies in the area of design, operation and maintenance. This paper describes the successful development and operation experiences of SGT-600 Siemens’ medium size gas turbine and in particular the latest achievements in maintenance and life cycle improvements. High reliability and availability of SGT-600 gas turbine were enabled by further improvements and modifications of the combustor, compressor turbine blade 1 and vane 1, power turbine diffuser and control system. The developed modifications enable operators to utilize the opportunity: • to extend the life cycle of the engine beyond 120,000 EOH (Equivalent Operating Hours), up to 180,000 EOH, depending on the previous operation profile and history of the installation; • to extend the maintenance intervals from 20,000 EOH to 30,000 EOH and that to increase the availability of the engine by up to 1%; • to reduce the emission level to the latest SGT-600 standards.
Thermoeconomic Optimization of the Part-Flow Evaporative Gas Turbine Cycles
Authors: Yari Mortaza
Published: August 2009

The evaporative gas turbine cycle is a new high-efficiency power cycle that has reached the pilot plant testing stage. The latest configuration proposed for this cycle is known as part flow evaporative gas turbine cycle (PEvGT) in which humidification is combined with steam injection. Having advantages of both steam injected and humid air cycles, it is regarded as a very desirable plant for future. The aim of this work is to investigate the economic performance of the PEvGT cycles: PEvGT and PEvGT-IC (Intercooled PEvGT cycle), based on the thermoeconomic analysis. The results are presented and the influence of the several parameters is discussed: pressure ratio, part-flow humidification rate and the cycle configuration. Also the thermoeconomic optimization of the cycles have been done and discussed.
An Aerodynamic Optimization Procedure for the Preliminary Design of Centrifugal Compressor Stages
Authors: Elshamy Omar , Ghizawi Nidal , Yon Ce´line , Pazzi Simone , Guenard Denis
Published: August 2009

This paper presents an automated aerodynamic optimization procedure for the preliminary design of centrifugal compressors. The proposed procedure interfaces a well-validated prediction tool with a GE in-house developed optimization code (PEZ). In GE Oil & Gas this tool is used to predict the performance of a single centrifugal compressor stage the outline of which requires more than thirty geometric parameters to be set. In the early phase of a new stage design, the designer manually varies all related parameters in the framework of a trial-and-error approach. The optimization procedure eliminates the inconvenience of a vast amount of manually launched simulations required by variations of the large number of design variables. Additionally, this procedure can perform trade-off studies and sensitivity analysis. In this case the optimization plan consists of a differential evolution (DE) genetic algorithm followed by a simplex-based optimization method (AMOEBA). The procedure was challenged with several existing designs by setting different objective/constraints combinations. The optimizer was often able to improve the predicted performance, as for an old 2D design where it was possible to increase the peak efficiency of approximately 2.6%. Also, the algorithm proved able to maximize the polytropic head (+12% with respect to baseline), while keeping unaltered both surge and choke limits. The computational time was about 40 hours per case on a Windows workstation (3.20 GHz, 3.5 GB RAM).
Wet Gas Performance of a Single Stage Centrifugal Compressor
Authors: Hundseid O̸yvind , Bakken Lars E. , Gru¨ner Trond G. , Brenne Lars , Bjo̸rge Tor
Published: August 2009

This paper evaluates the performance analysis of wet gas compression. It reports the performance of a single stage gas centrifugal compressor tested on wet gas. These tests were performed at design operating range with real hydrocarbon mixtures. The gas volume fraction was varied from 0.97 to 1.00, with alternation in suction pressure. The range is representative for many of the gas/condensate fields encountered in the North Sea. The machine flow rate was varied to cover the entire operating range. The compressor was also tested on a hydrocarbon gas and water mixture to evaluate the impact of liquid properties on performance. No performance and test standards currently exist for wet gas compressors. To ensure nominated flow under varying fluid flow conditions, a complete understanding of compressor performance is essential. This paper gives an evaluation of real hydrocarbon multiphase flow and performance parameters as well as a wet gas performance analysis. The results clearly demonstrate that liquid properties influence compressor performance to a high degree. A shift in compressor characteristics is observed under different liquid level conditions. The results in this paper confirm the need for improved fundamental understanding of liquid impact on wet gas compression. The evaluation demonstrates that dry gas performance parameters are not applicable for wet gas performance analysis. Wet gas performance parameters verified against results from the tested compressor is presented.
Thermodynanic Analysis of a Combined Micro Turbine With a Micro ORC
Authors: Yari Mortaza
Published: August 2009

In the last years, a big effort has been undergone to improve micro turbines thermal efficiency, actually rated at about 30%. A value of 40% is often regarded as a possible target. Such a result could be achieved implementing more complicated thermodynamic cycles, like combined cycles. This paper deals with the hypothesis of bottoming a low pressure ratio, recuperated gas cycle, typically realized in actual micro turbines, with an Organic Rankine Cycle (ORC) with internal heat exchanger (IHE), obtaining a micro-combined-cycle. The results are presented and the influence of the several parameters: Turbine inlet temperature of the micro turbine, compressor pressure ratio, evaporation temperature and evaporator temperature difference are discussed. Both simple ORC and ORC with IHE bottom cycle options are discussed. The dry organic fluids in this study are Isopentane, n-Pentane, n-Heptane, n-Octane, n-Hexane, R113, R123 and Toluene.
Simulation of the Transient Response of a Helicopter Turboshaft Engine to Hot-Gas Ingestion
Authors: Koc¸er Gu¨lru , Uzol Og˘uz , Yavrucuk I˙lkay
Published: August 2009

Hot-Gas Ingestion (HGI) to the engines can potentially occur when a rotorcraft or a VTOL/STOVL fixed-wing aircraft is operating in close proximity to the ground. Especially for helicopters, due to the rotor downwash hot exhaust gases get recirculated into the engine inlet. Similar conditions may also occur due to the ingestion of hot exhaust gases from rocket launchers or gun fire. In this study, we present the results of a simulation of the transient response of a helicopter turboshaft engine to HGI. Specifically for this study we will present the results for the T800-LHT-800 turboshaft engine. The simulations are performed using an in-house generic simulation code based on an aerothermal model, which consists of the governing equations representing the aero-thermodynamic process of each engine component. The algorithm is composed of a set of differential equations and a set of non-linear algebraic equations which are solved numerically in a sequence. A simple proportional control algorithm is also incorporated into the simulation code, which acts as a simple speed governor. Simulation results show that the code has the potential to correctly capture the transient behaviour of a turboshaft engine under various HGI conditions, such as the reduction in the gas generator speed and the power levels as well as the decrease in the compressor surge margin. The code can also be used for developing engine control algorithms as well as health monitoring systems.
Open Counter-Rotation Fan Blades Optimization Based on 3D Inverse Problem Navier-Stokes Solution Method With the Aim of Tonal Noise Reduction
Authors: Mileshin Victor I. , Nyukhtikov Michael A. , Orekhov Igor K. , Pankov Sergey V. , Shchipin Sergey K.
Published: August 2009

When developing counter-rotating fans for advanced new-generation aeroengines with unducted blades it is very important to provide high acoustic and aerodynamic characteristics [1]. This paper presents some results of gasdynamic and aeroacoustic optimization of unducted CRF blade profile by using 3D viscous inverse problem. Flow in unducted CRF on the basis of unsteady 3D Navier-Stokes equations is modeled at the 1st stage of designing in order to find the key tonal noise sources. Based on these results, it is found that one of the key tonal noise sources is Rotor 1 - Rotor 2 tip vortices interaction and potential rotor interaction. Then, using 3D solver of the viscous inverse problem, aerodynamic loads are redistributed along R1 and R2 blade height aiming at a decrease in tip vortex intensity and potential rotor interaction with a probable increase in the CRF thrust. To verify the aerodynamic characteristics of the modified CRF, steady flow calculations are carried out with the help of 3D Navier-Stokes equations and “mixing plane” interfaces. To verify the acoustic characteristics of the modified CRF, tonal noise modeling is carried out for original and modified CRFs using aeroacoustic CIAM’s 3DAS solver for solution of unsteady inviscid equations for disturbances. Ffowcs–Williams, Howkings approach is used for acoustic calculations in the far field. The near acoustic field and directivity diagrams in the far field are found. Using 3D inverse problem, the fan tonal noise is decreased by 4 dB for take-0ff and landing with no thrust and efficiency losses.
Hot Spots in Turboexpander Bearings: Case History, Stability Analysis, Measurements and Operational Experience
Authors: Schmied Joachim , Pozivil Josef , Walch Joseph
Published: August 2009

Vibration induced hot spots in radial fluid film bearings can cause spiral vibrations. The phenomenon is known as Morton effect. Various authors have described the phenomenon of spiral vibrations caused by rubbing in general [1 – 4] and specifically by the differential viscous shearing in fluid film bearings [5 – 8]. The history of the case of a turbo-expander for the cryogenic industry is described. The investigated machine has a single relatively stiff rotor with two overhung impellers. The rotor is supported on two tilting pad bearings, as they are commonly used for these applications. It was designed in line with API 617 7th edition [11]. During internal factory testing excessive vibration at high speed suddenly developed, in spite of very high damping and comfortable separation margins of the relevant rotor vibration modes. The vibrations evolution in a polar plot had the appearance of a spiral, as they are typically observed in case of vibration induced hot spots. The tilting pad bearings were suspected as the most likely cause for the hot spots. In parallel to the tests, hot spot stability analyses with a rotor dynamic model of the turbo-expander were carried out. The applied method, introduced by Schmied [5] allows the handling of general rotor systems. The hot spot model is based on the theory of Kellenberger [3] using a thermal equation between the shaft’s thermal deflection and the shaft displacement at the hot spot location. The analytical results gave evidence of the instabilities and confirmed the fluid-film bearings as the source of the hot spot. The model was used to assess changes for the solution of the problem. The following measures were studied: Reduction of the oil viscosity, stiffening of the rotor and reduction of the bearing width. The final successfully implemented solution was a combination of lower bearing width and reduced viscosity. Apart from this thoroughly studied case, an overview of further turbo-expanders regarding their hot spot behavior is given.
Automated Preliminary Structural Rotor Design Using Genetic Algorithms and Neural Networks
Authors: Dominique S. , Tre´panier J.-Y.
Published: August 2009

It is important for any design process to have a good starting point in order to reduce the cycle time and the number of design iterations required. This paper presents an automated preliminary structural design system for a gas turbine rotor, using only preliminary aerodynamic data and a simplified structural analysis, with the objective of producing a good, feasible starting solution for the blades and the disc. The process starts with a CBR (case-based reasoning) algorithm coupled with a databank of existing solutions. The algorithm uses a neural network to choose from among the closest existing rotor solutions and interpolate between them. These designs, along with the interpolated solution, will constitute the initial set of possible designs. An adaptation algorithm then processes each possible design using simplified analysis to compute the estimated sensitivity of the design function with respect to each parameter in the neighbourhood of these design solutions. The algorithm uses those sensitivities to separate the design parameters into several layers according to their relative importance. In a following phase, these design solutions are used to train a surrogate neural network model for the function, and also as the starting population for a genetic algorithm (GA). The GA is then run, with the objective of minimizing the weight of the rotor while respecting stress and aerodynamics constraints. More parameter sets (beginning with the most important) are gradually added as an input for each GA run. Although this process would not be capable of replacing a detailed design system, as it currently uses only simplified analysis, it can provide a concept designer with a very good starting solution within a relatively short computing time.
Noise Generated by a Lifted Flame in a Vitiated Co-Flow
Authors: Szasz Robert Z. , Duwig Christophe , Fuchs Laszlo
Published: August 2009

The acoustic field generated by a lifted flame is studied by a hybrid approach. First, Large Eddy Simulations (LES) are used to compute the flow and the acoustic sources. Next, an inhomogeneous wave equation is solved to obtain the resulting acoustic field. The flow computations show good agreement with experimental data. The dominant acoustic sources are found to be located in the ignition region and at the tip of the flame. The acoustic computations revealed the presence of low-frequency waves radiated in the far-field. The shape of the most energetic acoustic modes are identified by POD analysis to be axial modes.
Sensor TBCs: Remote In-Situ Condition Monitoring of EB-PVD Coatings at Elevated Temperatures
Authors: Steenbakker Re´my J. L. , Wellman Richard G. , Nicholls John R. , Feist Jo¨rg P.
Published: August 2009

Thermal Barrier Coatings (TBC) are used to reduce the actual working temperature of the high pressure turbine blade metal surface. Knowing the temperature of the surface of the TBC and at the interface between the bondcoat and the thermally grown oxide (TGO) under realistic conditions is highly desirable. As the major life-controlling factors for TBC systems are thermally activated, therefore linked with temperature, this would provide useful data for a better understanding of these phenomena and to assess the remaining lifetime of the TBC. This knowledge could also enable the design of advanced cooling strategies in the most efficient way using a minimum amount of air. The integration of an on-line temperature detection system would enable the full potential of TBCs to be realised due to improved precision in temperature measurement and early warning of degradation. This in turn will increase fuel efficiency and reduce CO2 emissions. The concept of a thermal-sensing TBC was first introduced by Choy, Feist and Heyes in 1998 [1]. The TBC is locally modified so it acts as a thermographic phosphor. Phosphors are an innovative way of remotely measuring temperatures and also other physical properties at different depths in the coating using photo stimulated phosphorescence [2]. In this study the temperature dependence of several rare earth doped EB-PVD coatings will be compared. Details of the measurements, the influence of aging, the composition and the fabrication of the sensing TBC will be discussed in this paper. Temperature detection at ultra-high temperatures above 1300°C is presented using new types of EBPVD TBC ceramic compositions. Multilayer sensing TBCs will be presented, which enable the detection of temperatures below and on the surface of the TBC simultaneously.
An Experimental Investigation of Passive Control Device: Blade Wake Interaction on a Ultra High Lift Turbine Profile
Authors: Simoni Daniele , Ubaldi Marina , Zunino Pietro , Bertini Francesco , Spano Ennio
Published: August 2009

The transition of the boundary layer subjected to unsteady wake-passing in a linear cascade of ultra high lift profiles has been investigated at the Avio Aerodynamics Laboratory. The blade profiles are representative of the turbine nozzle mid section of a long range aeroengine. Measurements were performed at the cruise Reynolds number. A surface hot-film array was adopted to survey the boundary layer nature and the periodic variations related to the passing wakes. A phase-locked ensemble averaging technique was employed in order to separate the random fluctuations from the periodic ones. Results have been represented in space-time plots in order to provide an overall view of the time-dependent phenomena in terms of the quasi wall shear stress statistical moments, that are important parameters for the analysis of the boundary layer transition and separation. Passive control devices may be adopted to suppress boundary layer laminar separation at critical conditions (low Reynolds numbers, ultra high lift profiles). In the present experimental investigation a wavy step device has been mounted on the suction side of the blade. The effects of this boundary layer control device on the transition process and profile losses have been investigated at cruise Reynolds number, with and without incoming wakes.
Filter-Based Time-Domain Impedance Boundary Conditions for CFD Applications
Authors: Huber Andreas , Romann Philipp , Polifke Wolfgang
Published: August 2009

For flow simulations, proper boundary conditions are essential for realizing a well-posed, physically meaningful and numerically stable problem formulation. This is particularly difficult for compressible flow, where in general boundary conditions have to be imposed both for mean flow and acoustic quantities. For the acoustic variables, boundary conditions can be formulated in terms of the acoustic impedance or alternatively the reflection coefficient, which are general a complex-valued, frequency dependent quantity. The present work presents a novel, efficient and flexible approach to impose time-domain impedance boundary conditions (TDIBC) for computational fluid dynamics (CFD): The acoustic boundary conditions are represented as a discrete filter model with appropriately optimized filter coefficients. Using the z-transformation the filter model is transferred to a time-domain formulation and applied to the CFD environment in form of advanced filter realizations. Validation studies using various acoustic boundary conditions have been carried out with the new formulation. The results demonstrate that the method works in an accurate and robust manner.
Unsteady Numerical Simulation of the Flow in a Direct Transfer Pre-Swirl System
Authors: Ciampoli Fabio , Hills Nicholas J. , Chew John W. , Scanlon Timothy
Published: August 2009

Results of fully unsteady numerical simulations of the flow in a direct transfer pre-swirl system are presented and compared with previously published experimental data from an aero-engine representative rig. The conditions considered include those where strong unsteady effects were observed experimentally. Two different rig builds are considered, with the main difference being in the design of the pre-swirl nozzles. The agreement between calculation and experiment is very good in terms of nozzle and receiver hole discharge coefficients and in identifying significant unsteady effects at certain conditions. Predicted cooling air delivery temperatures are lower than those measured. This may be due to heat transfer and other effects in the rig which have not been modelled. Present unsteady results also show agreement, where appropriate, with earlier steady CFD and an elementary model. Both calculations and measurements show similar performance in terms of delivery temperature for the two different builds studied, despite significant difference in pre-swirl nozzle discharge coefficients for the two builds. The calculations indicate that this is associated with the nozzle velocity coefficient being considerably higher than the discharge coefficient in one case.
Design of an Aggressive Flow-Controlled Turbine Duct
Authors: Wallin Fredrik , Eriksson Lars-Erik
Published: August 2009

Demands on improved efficiency, reduced emissions and noise restrictions result in the need for very high by-pass ratio turbo-fan engines. Large fans and small high-pressure cores require aggressive intermediate transition ducts connecting the low-pressure and high-pressure systems. In the present work the design of an aggressive flow-controlled turbine duct is presented. A number of vortex generators are installed in a turbine duct to control the boundary layer. The objective is to suppress the existing separation and thus minimize overall duct loss. In doing so the turbine duct design space will be extended toward more aggressive configurations. By using response surface methodology, together with design of experiments based on computational fluid dynamics (CFD), an optimum flow control arrangement is determined. A vortex generator model was adopted in order to be able to investigate a large number of different configurations. The vortex generator installation is optimized with respect to vortex generator position, height, length and angle of attack.
ULN System for the New SGT5-8000H Gas Turbine: Design and High Pressure Rig Test Results
Authors: Gruschka U. , Janus B. , Meisl J. , Huth M. , Wasif S.
Published: August 2009

The lean premixed combustion system was scaled from Siemens 60Hz engine application and optimized for implementation in the new SGT5-8000H 50Hz engine. The Siemens H-class engine is air cooled, uses a pressure ratio of 19:1 and is designed to achieve an efficiency of >60% efficiency in combined cycle operation. This improved dry low NOx system is of can annular type and consists of 16 cans in the SGT5-8000H. It was developed and tested in a full scale, high pressure rig test program. The single can high pressure rig simulates closely the flow conditions upstream of the combustor in the SGT5-8000H midframe and downstream of the combustor at the turbine inlet. The combustion system uses 5 fuel stages which allow flexible tuning over the whole range of engine operation conditions (ignition, idling, part- and base load). The system is designed to operate over a wide range of fuel quality and preheat temperatures. The test program is carried out over multiple years and encompasses rig / engine tests. This paper describes the combustion system in more details and the testing methodology. The test rig results showed that the performance targets are fully achieved in terms of emissions and operational requirements. Furthermore, the development / validation program will continue to reduce emissions through extended programs for future engines.
Computational Modelling of Tip Heat Transfer to a Super-Scale Model of an Unshrouded Gas Turbine Blade
Authors: Tang Brian M. T. , Palafox Pepe , Gillespie David R. H. , Oldfield Martin L. G. , Cheong Brian C. Y.
Published: August 2009

Control of over-tip leakage flow between turbine blade tips and the stationary shroud is one of the major challenges facing gas turbine designers today. The flow imposes large thermal loads on unshrouded high pressure turbine blades and is significantly detrimental to turbine blade life. This paper presents results from a computational study performed to investigate the detailed blade tip heat transfer on a sharp-edged, flat tip HP turbine blade. The tip gap is engine representative at 1.5% of the blade chord. Nusselt number distributions on the blade tip surface have been obtained from steady flow simulations and are compared to experimental data carried out in a super-scale cascade, which allows detailed flow and heat transfer measurements in stationary and engine representative conditions. Fully structured, multiblock hexahedral meshes were used in the simulations, performed in the commercial solver Fluent. Seven industry-standard turbulence models, and a number of different tip gridding strategies are compared, varying in complexity from the one-equation Spalart-Allmaras model to a seven-equation Reynolds Stress model. Of the turbulence models examined, the standard k-ω model gave the closest agreement to the experimental data. The discrepancy in Nusselt number observed was just 5%. However, the size of the separation on the pressure side rim was underpredicted, causing the position of reattachment to occur too close to the edge. Other turbulence models tested typically underpredicted Nusselt numbers by around 35%, although locating the position of peak heat flux correctly. The effect of the blade to casing motion was also simulated successfully, qualitatively producing the same changes in secondary flow features as were previously observed experimentally, with associated changes in heat transfer to the blade tip.
Validation and Analysis of Numerical Results for a Varying Aspect Ratio Two-Pass Internal Cooling Channel
Authors: Shevchuk Igor V. , Jenkins Sean C. , Weigand Bernhard , von Wolfersdorf Jens , Neumann Sven Olaf , Schnieder Martin
Published: August 2009

Numerical results for an internal ribbed cooling channel including a 180° bend with a 2:1 inlet and 1:1 aspect ratio outlet channel were validated against experimental results in terms of spatially resolved heat transfer distributions, pressure losses, and velocity distributions. The numerical domain consisted of one rib segment in the inlet channel and three ribs segments in the outlet channel to reduce the overall numerical effort and allow for an extensive parametric study. The results showed good agreement for both heat transfer magnitudes and spatial distributions and the numerical results captured the predominate flow physics resulting from the 180° bend. The production of Dean vortices and acceleration of the flow in the bend produced strongly increased heat transfer on both the ribbed and unribbed walls in the outlet channel in addition to increases due to the ribs. Numerical simulations were performed for a wide range of divider wall-to-tip wall distances, which influenced the position of the highest heat transfer levels on the outlet walls and changed the shape of the heat transfer distribution on the tip wall. Analysis of section averages of heat transfer in the bend and outlet channel showed a strong influence of the tip wall distance while no effect was seen upstream of the bend. A similarly large effect on pressure losses in the bend was observed with varying tip wall position. Trends in averaged heat transfer varied linearly with tip wall distance while pressure losses followed a non-linear trend, resulting in an optimum tip wall distance with respect to heat transfer efficiency.
Optimal Design of a Heat Exchanger for an Externally-Fired Microturbine in Combined Heat and Power Generation
Authors: Kaikko Juha , Koskelainen Lasse , Backman Jari L. H. , Larjola Jaakko
Published: August 2009

Biofuels have a vital role in emerging distributed energy systems. Special interest is focused on heat engines that can utilize biomass by direct combustion, such as externally-fired microturbines (EFMT). This paper considers a case where a natural gas-fired microturbine is converted into an EFMT. In the application the combustion chamber is replaced by a metallic heat exchanger retrofitted into a large biomass-fueled hot water boiler. The hot air that leaves the microturbine is directed into the furnace as preheated combustion air. In the paper, techno-economical optimization is performed for the selected heat exchanger configuration. The optimization is based on maximizing the net present value of the investment. The optimum depends on the cost of the new components and the resulting effect on the overall plant performance. The results show that the energy prices have only a mild impact on the optimum dimensions, although the feasibility of the investment itself depends strongly on the economy parameters. Using the optimized heat exchanger, the performance of the EFMT is predicted under part-load conditions of the boiler.
Thermoacoustic Models for Evaluating the Sensitivity to Instabilities of Multi-Burner Annular Combustion Chambers
Authors: Benelli G. , Carrai L. , Sigali S. , Brunetti I. , Castellano L.
Published: August 2009

The work described here has been developed in the context of the initiative TACE® (ThemoACoustic Enel Program) which has the aim to implement the use of mathematical models in the routinary control and diagnostics operations on GT systems for the production of electric power. The background of the models chosen to achieve that objective is the frequency domain approach. The engines of interest are of industrial size and have annular combustion chamber equipped with 24 premixed burners. The subject treated in this paper is the influence on the humming by interactions between undesired or, on the contrary, suitably conceived and designed differences in the actual working mode of each single burner. The underlying idea is that in such a type of machine the assembly of the burners behaves like a chorus line that has to be properly tuned.