bluuebunny/crossref_metadata_2025 huggingface dataset:
From Provider to Decider: The Changing Face of Royal Navy Gas Turbine Support
Authors: Timbrell Ian , Startin Howard
Published: March 2009

Marine Propulsion Systems Integrated Project Team (MPSIPT), part of the UK’s Defence Logistics Organisation (DLO), has traditionally provided gas turbine life cycle management to a collaboration of four European navies operating the Rolls Royce Olympus, Tyne and Spey marine gas turbines. With the drive towards the need to deliver greater efficiencies, a shrinking supplier base and in keeping with DLO’s Strategic Plan to transform in-service support arrangements, MPSIPT explored ways by which they could move from a provider to intelligent decider role. This transformation was realised in the form of a Total Care Package (TCP), introduced in April 2005, whereby Rolls Royce has taken responsibility for the support of Olympus and Tyne marine gas turbines. The issues raised should be of interest to Navies and other organisations facing similar challenges in gas turbine support. This paper gives a brief history behind how gas turbine life cycle management has been provided to the Royal Navy in the past, before concentrating on the reasons behind and the practical issues raised by our move to the TCP arrangement. The paper sets out the philosophy behind the DLO’s Strategic Plan, what that means in practical terms, how it has been applied for gas turbine support and the implications for the future. It explains how TCP has been approached in partnership with Rolls Royce, describes the issues that were faced, what the benefits are, what it means for the front line and our partners and how the contract is being managed. It concludes by identifying the lessons from the first year of operation of the TCP contract.
Integrated Computations of an Entire Jet Engine
Authors: Medic Gorazd , You Donghyun , Kalitzin Georgi , Herrmann Marcus , Ham Frank , Pitsch Heinz , van der Weide Edwin , Alonso Juan
Published: March 2009

In this paper, we present a framework that we have developed for integrated computations of an entire jet engine. It is based on a software environment, CHIMPS, that allows a simulation of multi-component effects by executing multiple solvers simultaneously. Each of these solvers computes a portion of a given flow domain and exchanges flow data at the interfaces with its peer solvers. We demonstrated this approach in a simulation of a 20 degree sector of the entire gas turbine jet engine, encompassing the fan, low and high pressure compressor, combustor, high and low pressure turbine and the exit nozzle. We will show that such a simulation can deliver important insight into the physics of interaction between different engine components, within a reasonable turnover time, which is necessary for it to be useful in the design process of an engine.
Turbulent Flow and Heat Transfer in Variable Geometry U-Bend Blade Cooling Passage
Authors: Lucci Jose Martinez , Amano R. S. , Guntur Krishna
Published: March 2009

It has been a common practice that serpentine cooling passages are used in gas turbine blade to enhance the cooling performance. Insufficient cooled blades are subject to oxidation, creep rupture, and even melting of the material. To control and improve temperature of blade; it requires better understanding of a flow behavior and heat transfer inside the curved U-bends. The interactions between secondary flows and separation lead to very complex flow patterns. To accurately simulate these flows and heat transfer, and to improve the cooling performance, both refined turbulence models and higher-order numerical schemes are indispensable tools for turbine designers. Previous studies have shown that the flow and heat transfer characteristics through curved bends, even with a moderate curvature, cannot be accurately simulated. It is the conventional belief and practice that the usage of a proper turbulence model and a reliable numerical scheme achieves accurate computations. The three-dimensional turbulent flows and heat transfer in a square U-bend duct are numerically studied by using a nonlinear low-Reynolds number (low-Re) k-ω, k-ε and RSM models and the cubic terms are included to represent the effects of extra strain-rates such as streamline curvature and three-dimensionality on both turbulence normal and shear stresses. The finite volume method incorporated with a higher-order bounded interpolation scheme has been employed in the present study. The objective of this study is to validate the simulations using RSM, k-ω, and k-ε models with the experimental results. Three different Reynolds numbers, 36,000, 60,000 and 100,000, were used.
Non-Metallic Brush Seal in Heavy Duty GT Units, GE-Made Frame No. 7, Model EA
Authors: Ingistov Steve
Published: March 2009

This Paper describes design, fabrication, installation and operational experience with non-metallic brush seals installed in all four GT Units, GE-made, Frame No 7, Model EA, presently operating at Watson Cogeneration Company, Carson, California, USA. First non-metallic brush seal was installed early 2002 and is currently in operation. Non-metallic brush seal serves in particular application to reduce the leakage of lubrication oil into the axial compressor suction. At the time of installation, it was the first application[1], to author’s knowledge, where the non-metallic bristle brush seal was used in heavy duty industrial gas turbine. Non-metallic brush seal can be successfully used where the local temperatures and pressures allow their safe usage. Compressor bearing number one is close to its suction where the air temperatures are low enough to enable the usage of non-metallic bristles which in turn are the core of the brush seals.
Kinetics of Natural Gas, Natural Gas/Syngas Mixtures Oxidation and Effect of Burnt Gas Recirculation: Experimental and Detailed Modeling
Authors: Le Cong Tanh , Dagaut Philippe
Published: March 2009

The oxidation of methane-based fuels was studied experimentally in a fused silica jet-stirred reactor (JSR) operating at 1–10 atm, over the temperature range 900-1400 K, from fuel-lean to fuel-rich conditions. Similar experiments were performed in presence of carbon dioxide or syngas (CO/H2). A previously proposed kinetic reaction mechanism updated for modeling the oxidation of hydrogen, CO, methane, methanol, formaldehyde, and natural gas over a wide range of conditions including JSR, flame, shock tube, and plug flow reactor was used. A detailed chemical kinetic modeling of the present experiments was performed yielding a good agreement between the data and the modeling. Literature burning velocities and ignition delays were also modeled. Reaction paths analyses were used to delineate the important reactions influencing the kinetic of oxidation of the fuels in presence of variable amounts of CO2. The kinetic reaction scheme proposed helps determining the effect of the additives on the oxidation of methane.
Measurement and Analysis of Aerodynamic and Thermodynamic Losses in Pre-Swirl System Arrangements
Authors: Bricaud C. , Geis T. , Dullenkopf K. , Bauer H.-J.
Published: March 2009

In order to separately describe the dominating loss mechanisms in pre-swirled cooling air delivery systems, discharge, temperature and velocity measurements were performed for numerous designs. Whereas pre-swirl nozzles, as first component, were characterized by their discharge coefficients, total pressure losses occurring at the inlet of the receiver holes were correlated depending on the incident angle of the cooling flow. To quantify losses generated inside the rotor-stator gap, flow velocity data, acquired by means of 3D PIV, were compared to total temperature measurements. In addition the influence of wall friction and mixing losses due to the strong velocity gradients inside the preswirl chamber was discussed by means of a simple loss model. Finally, dimensionless loss coefficients, discharge behaviour and expected cooling temperature can be predicted for a family of realistic pre-swirl systems. Moreover, this detailed description of the losses provides a methodology to quantify the impact of individual loss sources on the global efficiency of the pre-swirl system, thus allowing improved designs.
A Precise Full-Dimensional Design System for Multistage Steam Turbines: Part I — Philosophy and Architecture of the System
Authors: Jiang Hongde , Xu Kepeng , Li Baoqing , Xu Xinzhong , Chen Qing
Published: March 2009

A new, precise full-dimensional (PFD) design system for multistage steam turbine has been developed in the past decades by the present authors. The remarkable features of PFD system different from conventional 3D design methodology are as followings: a). Taking into account of unsteady aerodynamic impact on steam turbine performance, b). Simulating 3D real structure of blade and non-blade components without geometric simplification, c). Coupling of aerodynamic design with FEM structure- mechanical analysis for blade and non-blade components. Three levels of design and optimization at global, regional and local level for steam turbine cycle and flow path design are described. The PFD design system consists of conceptual (0D), 1D, Q3D, F3D/4D aerodynamic design and optimization codes, structure analysis and mechanical design (MD) tools, and pre- and post-processing software. In this part of present paper a detail description of philosophy and architecture of the PFD design system, function of each design tools, principles for design consistency are given. The PFD design system is a new plateau of present author’s long-term effort to bring multistage steam turbine design from a simple, passive, empirical-based situation toward a comprehensive, active, knowledge-based environment.
Tools for Estimating Resonant Stresses in Turbine Blades
Authors: Sipatov A. M. , Gladisheva N. V. , Avgustinovich V. G. , Povishev I. A.
Published: March 2009

The problem of obtaining adequate aerodynamical boundary conditions for an analyzed blade is important to predict resonant stresses. According to this, three different CFD approaches of stator-rotor modeling have been investigated for obtaining gas dynamic loading: 1. 3D averaged and then quasi-3D unsteady calculations. 2. Fully 3D unsteady calculations using commercial CFX solver. 3. Fully 3D unsteady calculations using the in-house solver. To carry out 3D structural analysis the ANSYS software and our subroutines have been applied. The methodology to estimate damper ratio for the different mode shapes and mode numbers has been developed. As a result, the tools to predict the resonant stress have been created where we tried to take into account all main factors affecting resonant stress level. The HPT first stage blade of a modern aircraft engine was chosen as an example of using our tools for prediction of resonant stresses level. A comparison of experimental data and obtained calculation results showed good agreement.
A New Slip Factor Correlation for Centrifugal Impellers in a Wide Range of Flow Coefficients and Peripheral Mach Numbers
Authors: Del Greco Alberto Scotti , Biagi Fernando Roberto , Sassanelli Giuseppe , Michelassi Vittorio
Published: March 2009

The preliminary design of new centrifugal stages often relies on one-dimensional codes implementing the concept of slip factor. This parameter plays a primary role in the stage design process since it directly affects the calculation of the impeller work coefficient and hence of the components situated downstream. Classical slip factor correlations may not always provide a satisfactory accuracy and generally they fail while attempting at covering a design space in a wide range of flow coefficients and peripheral Mach numbers. In that case the preliminary design has to be refined with more advanced tools, such as computational fluid dynamics (CFD). Often this process needs to be repeated several times before the design cycle ends. In order to predict more effectively the work coefficient as well as to reduce the number of iterations between 1D/CFD codes during the design activity, a new correlation has been developed, which is based on a large number of historical data from both CFD and experimental results. Accurate statistical analyses have shown that slip factor can be strongly linked to significant flow and geometry parameters by means of the outlet deviation angle. As the available calibration dataset gets more and more populated, the presence of specific constants in the structure of the correlation allows the designer to improve the accuracy of predictions.
Investigation Into the Use of Ceramic-Honeycomb Rotary Regenerators for Solar Brayton Cycles
Authors: Wilson David Gordon , Baker Teresa
Published: March 2009

It is conceptually possible to expose a third section of a rotary regenerator (in a gas turbine working on a heat-exchanger cycle) to a concentrated flux of solar radiation energy and thereby to supplement or even supplant the heat input from fuel (figure 1). Normally a regenerator in such a cycle has two sections: one in which the hot gases exhausting from the turbine section give up heat to the regenerator matrix, and one in which the air leaving the compressor passes through in the contrary direction, picking up heat from the matrix. The study reported here gives answers to concerns about the depth to which the solar energy would penetrate in a typical ceramic matrix, about the possibility of melting the top layers of the matrix if the solar energy is not aimed accurately, and about the amount of back radiation from the matrix to the environment that can be expected. It is concluded that the safe and efficient collection of solar energy in this way should be feasible.
A Survey of Advanced Methods for Analysis and Modeling of Propulsion System Reliability
Authors: Millar Richard C. , Mazzuchi Thomas A. , Sarkani Shahram
Published: March 2009

Electronic controls, propulsion system monitoring and health management and application of information technology to maintenance data capture and storage are enabling users to accumulate large amounts of reliability and related maintenance data. Effective analysis and exploitation of these data bases requires advanced tools to extract meaningful and actionable information. The challenges include “competing” failure modes and periodic hard time maintenance that “censors” information from impending failures, and a high number of failure modes that confound analysis. These factors impede accurate assessment of the impact of corrective action and different maintenance procedures on availability and maintenance costs. They confound understanding of the reliability of complex propulsion & power systems that would enable more representative modeling of system availability and maintenance costs for both existing and future applications. Tools providing more complete and accurate characterization of reliability information for complex systems are being developed for aerospace, nuclear and communications industries. These are surveyed and capability gaps identified with respect to commercial and military propulsion & power systems.
A New Statistical-Based Correlation for the Compressor Tandem Cascade Parameters Effects on the Loss Coefficient
Authors: Nezym Vitaliy Yu. , Polupan Georgiy P.
Published: March 2009

One of the effective methods for improvement of compressor stage operation is a flow control within the compressor passages. An application of boundary layer control on the suction surface of a blade profile may be useful in tandem cascade configuration. Total tandem guide vane consists of a series of two vanes: guide vane (the first segment) and straightening vane (the rear segment). These vanes have a definite shift along the axial and peripheral direction, providing a perfect re-distributing of energy within the blade passages between different flow zones. There are several parameters influencing mainly on loss in a tandem cascade. Experimental results of the parametric test are used for the creation of a statistical model of loss determination of compressor tandem cascade using the Group Method of Data Handling (GMDH). The paper focuses on the statistical-based correlation that encompasses most pertinent parameters featuring tandem configuration and operating condition.
Selection of Gas Turbine With Minimum Flue Gas Emission
Authors: Esna Ashari P. , Nayyeri V. , Sarabchee K.
Published: March 2009

Many factories in industry such as petrochemical plants, oil refineries and power plants need heat and power to support their process. This demand can be provided by a combined heat and power cycle (CHP) in the factory site. Some factories use gas turbine cycle to provide heat and power. Emissions from gas turbines, produced by burning fossil fuels in the combustion chambers, have important effects on air pollution. This is a significant problem in many developed and developing countries. Parameters such as inlet temperature and pressure ratio are the most effective parameters in gas turbine emission. By selecting an appropriate gas turbine, emission could be reduced to some extent. Further studies indicate that there is an optimum pressure ratio, which minimizes emissions.
Blade Tip Clearance Flow and Compressor NSV: The Jet Core Feedback Theory as the Coupling Mechanism
Authors: Thomassin Jean , Vo Huu Duc , Mureithi Njuki W.
Published: March 2009

This paper investigates the role of tip clearance flow in the occurrence of non-synchronous vibrations (NSV) observed in the first axial rotor of a high-speed high-pressure compressor (HPC) in an aero-engine. NSV is an aero-elastic phenomenon where the rotor blades vibrate at non-integral multiples of the shaft rotational frequencies in operating regimes where classical flutter is not known to occur. A physical mechanism to explain the NSV phenomenon is proposed based on the blade tip trailing edge impinging jet like flow, and a novel theory based on the acoustic feedback in the jet potential core. The theory suggests that the critical jet velocity, which brings a jet impinging on a rigid structure to resonance, is reduced to the velocities observed in the blade tip secondary flow when the jet impinges on a flexible structure. The feedback mechanism is then an acoustic wave traveling backward in the jet potential core, and this is experimentally demonstrated. A model is proposed to predict the critical tip speed at which NSV can occur. The model also addresses several unexplained phenomena, or missing links, which are essential to connect tip clearance flow unsteadiness to NSV. These are the pressure level, the pitch-based reduced frequency, and the observed step changes in blade vibration and mode shape. The model is verified using two different rotors that exhibited NSV.
Fundamental Mechanism of Entropy Noise in Aero-Engines: Experimental Investigation
Authors: Bake Friedrich , Michel Ulf , Roehle Ingo
Published: March 2009

Entropy noise caused by combustors increases rapidly with rising Mach number in the nozzle downstream of the combustion chamber. This is experimentally shown with a dedicated test facility, in which entropy waves are generated in a controlled way by unsteady electrical heating of fine platinum wires immersed in the flow. Downstream of the heating module called Entropy Wave Generator (EWG) the pipe flow is accelerated through a convergent-divergent nozzle with a maximum Mach number of 1.2 downstream of the nozzle throat. Parameters like mass flux of the flow, nozzle Mach number, amount of heating energy, excitation mode (periodic, pulsed or continuously), and propagation length between Entropy Wave Generator and nozzle have been varied for the analysis of the generated entropy noise. The results are compared with the results of a one-dimensional theory found in early literature.
Application of MADYN 2000 to Rotordynamic Problems of Industrial Machinery
Authors: Schmied Joachim , Perucchi Marco , Pradetto Jean-Claude
Published: March 2009

The special requirements of rotordynamics engineering are illustrated by means of different examples of turbomachines. The differences between the properties of magnetic bearings and the more common fluid film bearings are pointed out in the examples of two turbocompressors. The importance of the bearing support properties are shown for a turbine generator train. The impact of seal forces are demonstrated for the turbocompressor supported on fluid film bearings. Two of the considered seals are honeycomb seals with frequency dependent characteristics. The consequences of the coupling of lateral and torsional vibrations in gears are illustrated for a gear compressor with three pinions. All examples have a practical background from troubleshooting and engineering work although they do not exactly correspond to real cases.
Numerical Investigation of a Bias-Flow Perforated Liner for Damping of Thermoacoustic Instabilities
Authors: Rehman Syed F. , Eldredge Jeff D.
Published: March 2009

Lean premixed prevaporized (LPP) gas turbine generators are naturally prone to thermoacoustic instabilities. Strategic placement of passive damping devices can provide simple, effective fixes for such unstable behavior. In this work, the thermoacoustic damping characteristics of a perforated liner with mean bias flow are examined. A recently-developed theoretical model, along with accompanying experimental investigation, has demonstrated that a bias-flow liner can very effectively absorb incident acoustic waves. Here, a modular simulation tool is utilized to examine the capability of the liner for stabilizing an unstable ducted flame. The simulation tool represents the acoustic interactions between duct elements in the form of transfer matrices, which can be modularly arranged for exploring a variety of configurations. An unstable thermoacoustic system is produced with a gain-delay flame model in a duct. The frequencies and growth rates of the linear model are examined. It is shown that, by tailoring the liner porosity and the bias flow, unstable modes of the thermoacoustic system can be stabilized. Furthermore, it is found that, for a double liner system, there is an optimal liner porosity for a given choice of bias flow, at which the modal decay rate is maximized.
Shock Characteristics Measured Upstream of Both a Forward-Swept and an Aft-Swept Fan
Authors: Podboy Gary G. , Krupar Martin J. , Sutliff Daniel L. , Horvath Csaba
Published: March 2009

Three different types of diagnostic data — blade surface flow visualization, shroud unsteady pressure, and laser Doppler velocimeter (LDV) — were obtained on two fans, one forward-swept and one aft-swept, in order to learn more about the shocks which propagate upstream of these rotors when they are operated at transonic tip speeds. Flow visualization data are presented for the forward-swept fan operating at 13831 RPMc and for the aft-swept fan operating at 12500 and 13831 RPMc (corresponding to tip rotational Mach numbers of 1.07 and 1.19, respectively). The flow visualization data identify where the shocks occur on the suction side of the rotor blades. These data show that at the takeoff speed, 13831 RPMc, the shocks occurring in the tip region of the forward-swept fan are further downstream in the blade passage than with the aft-swept fan. Shroud unsteady pressure measurements were acquired using a linear array of 15 equally-spaced pressure transducers extending from two tip axial chords upstream to 0.8 tip axial chords downstream of the static position of the tip leading edge of each rotor. Such data are presented for each fan operating at one subsonic and five transonic tip speeds. The unsteady pressure data show relatively strong detached shocks propagating upstream of the aft-swept rotor at the three lowest transonic tip speeds, and weak, oblique pressure disturbances attached to the tip of the aft-swept fan at the two highest transonic tip speeds. The unsteady pressure measurements made with the forward-swept fan do not show strong shocks propagating upstream of that rotor at any of the tested speeds. A comparison of the forward-swept and aft-swept shroud unsteady pressure measurements indicates that at any given transonic speed the pressure disturbance just upstream of the tip of the forward-swept fan is much weaker than that of the aft-swept fan. The LDV data suggest that at 12500 and 13831 RPMc, the forward-swept fan swallowed the passage shocks occurring in the tip region of the blades, whereas the aft-swept fan did not. Due to this difference, the flows just upstream of the two fans were found to be quite different at both of these transonic speeds. Nevertheless, despite distinct differences just upstream of the two rotors, the two fan flows were much more alike about one axial blade chord further upstream. As a result, the LDV data suggest that it is unwise to attempt to determine the effect that the shocks have on far field noise by focusing only on measurements (or CFD predictions) made very near the rotor. Instead, these data suggest that it is important to track the shocks throughout the inlet.
Steady State Off-Design Performance of Humid Air Turbine Cycle
Authors: Wang Bo , Zhang Shijie , Xiao Yunhan
Published: March 2009

The Humid Air Turbine (HAT) cycle is recognized as a competitive innovative gas turbine cycle with good off-design thermodynamic performance. However, the off-design performance of the HAT cycle has not been sufficiently analyzed. In this paper, a steady state on-design and off-design thermodynamic performance investigation of the HAT cycle was presented by comparing the HAT cycle with other competitive gas turbine cycles. In order to perform energy analysis of various gas turbine cycles, a gas turbine cycle analysis system was developed, where the advanced detailed component models of the investigated cycles were built and integrated. A detailed turbine cooling model including various cooling methods was used to indicate the effects of the turbine cooling on the thermodynamic performance of the gas turbine cycles when the turbine inlet temperature is high. The model can also indicate changes in level of cooling technology. The saturator was simulated as a one-dimensional model which can be used to size the saturator at on-design condition and to investigate the thermodynamic performance of the saturator at off-design condition. The HAT cycle was compared with four different cycles for on-design and off-design thermodynamic performances: 1) simple cycle, 2) recuperated cycle (REC), 3) recuperated water injected (RWI) cycle and 4) steam injection gas turbine (STIG) cycle. The focus of the comparison was put on the thermodynamic off-design performance of the different gas turbine cycles. The effects of ambient temperature and load reduction (part-load at ISO conditions) on the thermodynamic performance of the simple, the recuperated, the RWI, the STIG and the HAT cycle were investigated and compared. The results indicate that the HAT cycle can recover the low grade heat efficiently and when ambient temperature increases, HAT cycle has the most favorable off-design performance. At part-load conditions, the off-design performance of HAT cycle is not so good as STIG cycle and simple cycle, but is better than the RWI cycle and recuperated cycle.
Combustion Characteristics of Methane-CO2 Mixture and a Microturbine Cogeneration System Utilized Sewage Digester Gas
Authors: Kataoka Tadashi , Nakajima Teruyuki , Nakagawa Takahiro , Hamano Nobuhiko , Yuasa Saburo
Published: March 2009

This paper describes an approach to utilize sewage digester gas as a fuel for gas turbines. Sewage digester gas is composed of about 60% methane and 39% carbon dioxide. To apply it as a gas turbine fuel requires optimizing the combustion system to improve the combustion efficiency, flame-holding characteristics, etc. This paper presents an approach whereby a mass-produced microturbine and its peripheral equipment can be converted for such application with a minimum of modification and without the use of extraordinary combustors. The approach is described whereby a recuperative cycle microturbine having rich-burn, quick-mix, lean-burn (RQL) combustor is started up with a high-Btu fuel and the fuel is switched to digester gas when the inlet-air has been preheated to 600K or higher. This approach has proven that reliable starting, stable operation from idling to the rated power output, and efficiency equivalent to that obtained with a high-Btu fuel, can be achieved by the microturbine utilizing sewage digester gas.
A Novel Perturbation-Based Approach for the Accurate Prediction of the Forced Response of Mistuned Bladed Disks
Authors: Han Yun , Mignolet Marc P.
Published: March 2009

This paper focuses on the formulation and validation of a novel perturbation method for the prediction of the forced response of mistuned bladed disks. At the contrary of previous approaches, the proposed one involves the sum of the inverses of the tuned and mistuned impedance matrices through the use of the Sherman-Morrison-Woodbury formula. Then, considering these inverses as diagonal dominant matrices leads to an efficient series representation of the forced response of mistuned bladed disks. A detailed validation effort of this new procedure was next achieved. In particular, it was demonstrated that this approach leads to a convergent series representation over the entire range of blade-disk coupling levels for small mistuning. The dominant parameter affecting the magnitude of the largest mistuning for which convergence occurs is shown to be the system damping with a weaker effect of the blade-disk coupling. Examples of application to a single-degree-of-freedom per blade model and the reduced order model of a blisk demonstrate the potential of this novel approach. Finally, the applicability of this technique for the optimization of intentional mistuning pattern is shown.
Investigation of the Effects of Fuel Injection Nozzle Parameters on Ignition Delay in Diesel Fuels
Authors: Abo El Ella Hamza M. , Gauthier J. E. Donald
Published: March 2009

Ignition delay of diesel fuels is a strong function of the chemical composition of the fuel. However, fuel injection nozzle parameters such as internal nozzle geometry, and nozzle spray pattern might also have a substantial effect on ignition delay. In order to understand these effects, ASTM test method D6890 was employed to measure the ignition delay of a single diesel reference fuel using several test nozzles. With the aid of test rigs that were developed, the nozzle parameters evaluated included internal nozzle geometry and nozzle spray pattern. The obtained geometry and spray characteristics of each of the test nozzles were then compared to their corresponding ignition delay values. The results of the investigation showed that nozzle pintle clearance has a strong effect on ignition delay, while nozzle spray pattern does not appear to have any effect on ignition delay as measured per ASTM D6890. Consistently, needle dimensions that drive the nozzle spray pattern did not appear to have any effect on ignition delay.
High Temperature Corrosion of Microturbine Combustor Material
Authors: Yakuwa Hiroshi , Kataoka Tadashi
Published: March 2009

Two particular types of high temperature corrosion in a microturbine Rich-burn, Quick-mix, Lean-burn (RQL) combustor are discussed and reported in this paper. One type occurred in mixing tubes, part of fuel supply into the combustor. Dense concentrations of carbon monoxide and unburned hydrocarbons in a high temperature environment carburized the mixing tube, leaving it vulnerable to corrosion. The Co-based alloy was selected for the advantage of good heat resistance was exchanged for a Ni-Cr based alloy of good carburization resistance and the life of combustor successfully extended. The second type is a pitting corrosion on the inner wall of liner in the rich-burn zone. It is inferred that the corrosion was metal dusting caused from defects of the oxide film on the inner wall surface. As a countermeasure, a preoxidation step was applied to the combustor to maintain a protective oxide film for a longer period of time. This paper discusses the mechanisms and the countermeasures for these types of corrosion, which relate to carbon from the fuel origin activated in the fuel-rich environment in the combustor.
Aero-Thermal Investigation of Tip Leakage Flow in Axial Flow Turbines: Part III — Tip Cooling
Authors: Newton P. J. , Lock G. D. , Krishnababu S. K. , Hodson H. P. , Dawes W. N. , Hannis J. , Whitney C.
Published: March 2009

Contours of heat transfer coefficient and effectiveness have been measured on the tip of a generic cooled turbine blade, using the transient liquid crystal technique. The experiments were conducted at an exit Reynolds number of 2.3 × 105 in a five-blade linear cascade with tip clearances of 1.6% and 2.8% chord and featuring engine-representative cooling geometries. These experiments were supported by oil flow visualisation and pressure measurements on the tip and casing and by flow visualisation calculated using CFX, all of which provided insight into the fluid dynamics within the gap. The data were compared with measurements taken from the uncooled tip gap, where the fluid dynamics is dominated by flow separation at the pressure-side edge. Here the highest levels of heat transfer are located where the flow reattaches on the tip surface downstream of the separation bubble. A quantitative assessment using the Net Heat Flux Reduction (NHFR) revealed a significant benefit of ejecting coolant inside this separation bubble. Engine-representative blowing rates of approximately 0.6 – 0.8 resulted in good film cooling coverage and a reduction in heat flux to the tip when compared to both the flat tip profile and the squealer and cavity tip geometries discussed in Part 1 of this paper. Of the two novel coolant-hole configurations studied, injecting the coolant inside the separation bubble resulted in an improved NHFR when compared to injecting coolant at the location of reattachment.
A Model for the Simulation of Large-Size Single-Shaft Gas Turbine Start-Up Based on Operating Data Fitting
Authors: Morini Mirko , Cataldi Giovanni , Pinelli Michele , Venturini Mauro
Published: March 2009

Start-up is an important aspect of gas turbine operation. In the last years plant operators have shown an ever increasing interest in this critical phase, with particular focus on start-up reliability and start-up time. Several issues should be considered in order to achieve optimal start-up behavior: operability issues (e.g. compressor aerodynamics, combustor light-off and light-around, shaft acceleration), impact of thermal stresses on cyclic life, proper sizing of external starting devices. Models for the simulation of gas turbine behavior during start-up are very useful both for the design of new gas turbines and for the analysis and improvement of engines already in operation. In this paper, a physics-based model for the simulation of the start-up phase of large-size single-shaft gas turbines is presented. The model is based on operating data fitting and covers machine operation from combustor light-off to compressor blow off valve closure. The model makes use of steady-state component characteristics, while dynamics is taken into account through shaft power balance. Special features are also included to properly model the effects of heat soakage, i.e. the dependence of the engine behavior on its thermal status before the start-up. The quality of the model has been proven by application to the gas turbine engine ALSTOM GT13E2 and by comparison between measured and simulated data.
Calculating Stall and Surge Transients
Authors: Longley John P.
Published: March 2009

Many aspects of the aerodynamic operation and the mechanical integrity of an aeroengine are determined by the stall and surge transients of the compression system. A, physically based, blockage-mixing method and a novel blockage-transport equation are presented that can be used to estimate blade row operation at severe off-design conditions. The blockage-mixing method is proposed based on an analysis of the large separations that are present within a blade passage during reverse-flow (negative axial velocity) conditions. A time accurate computational simulation has been developed, based on the blockage-mixing method, which solves for the moderate to long lengthscale compressible unsteady flowfield within a compression system. The flow through each blade row is resolved in the axial, circumferential and radial directions. Calculated stall and surge events are compared with experimental data and the ability to calculate an aeroengine transient is demonstrated. The simulation is presented as a computational tool for estimating the aerodynamic loads during compression system instability events.
An Innovative Non-Destructive Method for the In-Service Metal Surface Temperature Estimation of Coated GT Parts
Authors: Schnell A. , Germerdonk K. , Mo¨hlig H. , Fehrmann B. , Lee Preston
Published: March 2009

The exact knowledge of the actual airfoil surface metal temperature of advanced GT parts during engine operation is essential with regard to a reliable part lifetime analysis. Typically, in order to assess the airfoil temperatures of service exposed parts, destructive metallographical methods are used, which interpret the superalloy and coating degradation into respective metal temperatures. This traditional metallographical method is well established, however, it provides only limited information on the metal temperatures from few specific cutting locations. This paper describes the development of an innovative approach for the determination of the metal surface temperatures of ex-service turbine blades & vanes using the non-destructive Frequency Scanning Eddy Current Technique (FSECT). The method is basically based on the fact, that MCrAlY coatings, in comparison to the base superalloy material, change their electromagnetic properties in a describable manner with temperature and time. The coated GT part needs to be FSECT measured in the status “ex-service” and after defined reference heat treatments. The respective FSECT signals are then used in order to calculate the actual metal surface temperature. With this method and using an automated robotic system, it is possible to establish accurate and high resolution mappings of the surface temperature distribution over the entire airfoil and platform areas. The exact location of hot spots on the airfoil, which might not be evident with the naked eye, can easily be identified. This new method supports the prediction of local material degradation and lifetime, the optimization of maintenance intervals, and — as a consequence — the establishment of the appropriate reconditioning processes for the ex-service GT parts.
Unsteady Pressure Field Due to Interactions Among Tip Leakage Vortex, Trailing Edge Vortex, and Vortex Shedding in a Ducted Propeller
Authors: Hah Chunill , Lee Yu-Tai
Published: March 2009

A detailed numerical study was performed to investigate the unsteady flow field near the tip of a ducted propeller blade. The primary objective was to understand the formation of the point of minimum static pressure, where cavitation inception occurs, in a ducted propeller. An experimental study showed that cavitation inception (minimum static pressure) occurs at about 50% blade chord downstream of the rotor trailing edge, while conventional estimation predicts it about 10% blade chord downstream in the tip leakage vortex. Steady flow analysis, which indicates that the minimum static pressure occurs about 15% axial chord downstream in the tip leakage vortex, does not calculate measured cavitation inception correctly. The flow field near the tip section is unsteady due to interactions among the tip leakage vortex, the trailing edge vortex, and vortex shedding in the wake. Because the steady flow analysis does not reproduce the measured minimum static pressure location in the current rotor, it was suspected that the observed phenomenon was due to some unsteady flow phenomenon in the tip region. To capture relevant unsteady flow physics as much as possible, a large eddy simulation (LES) was applied to the current investigation. The present study reveals that periodic interaction between the tip leakage vortex and the trailing edge vortex initially creates a local low pressure point about 15% blade chord downstream. As the tip leakage vortex flows downstream, it is bent and stretched by the interaction between the shed trailing edge vortex and the tip leakage vortex originating from the adjacent blade interaction. This stretching of the tip leakage vortex creates a new lower local pressure core in the tip leakage vortex. The current unsteady flow simulation shows that the minimum pressure point, where cavitation inception occurs, is observed intermittently at about 50% blade chord downstream of the trailing edge, as the measurement shows.
Endwall Heat Transfer Measurements in a Staggered Pin Fin Array With an Adiabatic Pin
Authors: Ames Forrest E. , Nordquist Chad A. , Klennert Lindsay A.
Published: March 2009

Full surface endwall heat transfer distributions have been acquired in a staggered pin fin array with the use of an infrared camera. Values are presented at Reynolds numbers of 3000, 10,000 and 30,000 based on pin diameter and average velocity through adjacent pins. Average endwall Nusselt numbers agree closely with archival values at each Reynolds number. Locally averaged heat transfer levels show a substantial increase from the inlet through the first few rows and finally a nearly streamwise periodic condition in the second half of the eight row geometry. Increasing levels of heat transfer in the inlet region can be attributed to the leading edge vortex system, flow acceleration around pins, and the generation of turbulence. Distributions of turbulence intensity and turbulent scale are shown to help document the turbulent transport conditions through the array. Detailed endwall Nusselt number distributions are presented and compared at the three Reynolds numbers for the first four and last four rows. These detailed heat transfer distributions highlight the influence of the horseshoe vortex system in the entrance region and the wake generated turbulence throughout the pin fin array. Local velocity and turbulence distributions are presented together with local Stanton number and skin friction coefficient data to examine the aggressive nature of the turbulent mixing.
Influence of the Blade Geometry on Flow Instabilities in a Radial Pump Elucidated by Time-Resolved Particle-Image Velocimetry
Authors: Krause Nico , Pap Eleme´r , The´venin Dominique
Published: March 2009

Radial pumps are used in a variety of applications. In many cases the pump operates under part-load flow conditions and the inflow condition differs from the dimensioning, optimal point, ultimately leading to flow instabilities. In this paper the influence of three different impeller blade designs are presented under stall conditions. All the impeller blades are designed for the same pressure rise over the impeller but using different concepts. The pump characteristic curves clearly show the changes concerning energy transmission and losses. Time-Resolved Particle-Image Velocimetry (TR-PIV) is used to investigate the onset and development of rotating stall within the centrifugal pump under part-load conditions. These measurements lead to detailed instantaneous velocity distributions during rotating stall. Fast-Fourier-Transformation (FFT) is finally carried out on the series of instantaneous measured flow fields to identify characteristic flow frequencies. The onset of rotating stall is observed for different part-load flow-rates for the three impellers under investigation.
Influence of Water Droplet Size and Temperature on Wet Compression
Authors: Bianchi M. , Melino F. , Peretto A. , Spina P. R. , Ingistov S.
Published: March 2009

In the last years, among all different gas turbine inlet air cooling techniques, an increasing attention to fogging approach is dedicated. The various fogging strategies seem to be a good solution to improve gas turbine or combined cycle produced power with low initial investment cost and less installation downtime. In particular, overspray fogging and interstage injection involve two-phase flow consideration and water evaporation during compression process (also known as wet compression). According to the Author’s knowledge, the field of wet compression is not completely studied and understood. In the present paper, all the principal aspects of wet compression and in particular the influence of injected water droplet diameter and surface temperature, and their effect on gas turbine performance and on the behavior of the axial compressor (change in axial compressor performance map due to the water injection, redistribution of stage load, etc.) are analyzed by using a calculation code, named IN.FO.G.T.E. (INterstage FOgging Gas Turbine Evaluation), developed and validated by the Authors.
Modelling and Measuring Experiences to Evaluate the Modal Behaviour of an Industrial Gas Turbine High Pressure Bucket
Authors: Del Turco Paolo , D’Ercole Michele , Gamberi Francesco , De Prosperis Roberto , Pieroni Nicola , Mariotti Massimiliano
Published: March 2009

In gas turbines, High Cycle Fatigue (HCF) bucket failures are mainly prevented by avoiding resonance frequencies in the operative range. Due to the high number of stimuli present, avoiding potential resonance crossings is often not possible. In these cases, failures can be avoided by controlling vibratory stress levels in order not to exceed high cycle fatigue endurance limits. This paper describes the processes used in GE Infrastructure, Oil&Gas to design, develop and test a new high-pressure turbine bucket for a 32 MW-class industrial gas turbine for mechanical drive and power generation applications. Initial design phases, 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 Analysis) used in the design phase and the validation tests (i.e. Ping Test and Laser Doppler Vibration) including the development of a dedicated instrumentation technique, which allowed the unit not to be disassembled (High Temperature Strain Gauge Splicing).
Identification of the Stability Margin Between Safe Operation and the Onset of Blade Flutter
Authors: Rice Tim , Bell David , Singh Gurnam
Published: March 2009

The introduction of longer last stage blading in steam turbine power plant offers significant economic and environmental benefits. The modern trend, adopted by most leading steam turbine manufacturers, is to develop long last stage moving blades (LSMB) that feature a tip shroud. This brings benefits of improved performance due to better leakage control and increased mechanical stiffness. However, the benefits associated with the introduction of a tip shroud are accompanied by an increased risk of blade flutter at high mass flows. The shroud is interlocked during vibration, causing the first axial bending mode to carry an increased, out of phase, torsional component. It is shown that this change in mode shape, compared to a unshrouded LSMB, can lead to destabilising aerodynamic forces during vibration. At a sufficiently high mass flow, the destabilising unsteady aerodynamic work will exceed the damping provided by the mechanical bladed-disk system, and blade flutter will occur. Addressing the potential for flutter during design and development is difficult. Simple tests prove inadequate as they fail to reveal the proximity of flutter unless the catastrophic condition is encountered. A comprehensive product validation programme is presented, with the purpose of identifying the margin for safe operation in respect to blade flutter. Unsteady CFD predictions are utilised to identify the mechanisms responsible for the unstable aerodynamic condition, and the particular modes of vibration that are most at risk. Using this information, a directed experimental technique is applied to measure the combined aerodynamic and mechanical damping under operating conditions. Results are presented which demonstrate the identification of the aeroelastic stability margin for a new LSMB. The stability margin predicted from the measurements demonstrates a significant margin of safety.