bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced TF40B Gas Turbine Engine Design Changes to Improve Resistance to the Landing Craft Air Cushion (LCAC) Operational Environment
Authors: Yee Roger , Myers Lee
Published: February 2009

The United States Navy Landing Craft Air Cushion (LCAC) vehicles, under the Service Life Extension Program (SLEP), use the Enhanced TF40B (ETF40B) gas turbine engines for main propulsion and lift. These engines provide the additional engine horsepower needed under high ambient temperature conditions, have an increase in operation reliability, and use modern digital engine control equipment. During craft operations, ETF40B engines are exposed to harsh saltwater and sand environments that will cause severe engine corrosion problems if corrosion resistant design features are not utilized. Proper material selection and utilization of anti-corrosion coatings are extremely important to ensure reliability of ETF40B engines on LCAC. This paper will document and outline the Navy’s efforts to improve the ETF40B engine’s resistance to the LCAC operating environment with a focus on the following components/features: • Carbon and Graphite Free Bushing and Washer Materials for Compressor Guide Vanes; • Coatings between the Compressor Casing and Compressor Guide Vane Bushings; • Use of a Silicone Rubber Abradable Material in the First 4 Stages of the Compressor; • Use of Anti-Corrosion Coatings on all Compressor Guide Vanes and Stems.
A 3D Unsteady Analysis of a Wells Turbine in a Sea-Wave Energy Conversion Device
Authors: Camporeale S. M. , Torresi M. , Pascazio G. , Fortunato B.
Published: February 2009

A Wells turbine designed for power generation in an innovative OWC (Oscillating Water Column) device for sea-wave energy conversion is investigated. This work aims to predict the turbine performance under a continuously variable reciprocating flow due to the action of the sea waves. When the amplitude of the oscillating flow reaches high values, stall occurs around the blades with a drop in the turbine performance. CFD simulation has been carried out aiming to provide an insight of flow behavior over the blades approaching these large amplitude flow conditions. Three test cases, preliminarily examined in order to assess the capability of the numerical methods, are presented and discussed: the first test-case concerns the 2D unsteady turbulent flow past a symmetrical airfoil undergoing oscillating pitching motion; the second test case concerns the 3D analysis of a high solidity Wells turbine in presence of different constant axial fluxes; the third test case concerns the 3D analysis of a high solidity Wells turbine in presence of an oscillating axial flux. Finally the flow past the low solidity Wells turbine rotor is simulated. The analysis has been performed by considering the flow to be unsteady, incompressible and viscous, while turbulence was modeled using the one-equation Spalart Allmaras model or the two-equations k-ω model.
Jet Engine Compressor Blade Refurbishment by Application of the Advanced Re-Contouring Process
Authors: Hoenen Herwart T. , Ellenberger Karsten
Published: February 2009

In modern jet propulsion Systems the core engine has an essential influence on the total engine performance. Especially the high pressure compressor plays an important role in this scheme. Substantial factors here are losses due to tip clearance effects and aerodynamic airfoil quality. During flight Operation the airfoils are subject to wear and tear on the leading edge. These effects cause a shortening of the chord length and the leading edge profiles become deformed. This results in a deterioration of the engine efficiency performance level and a reduced stall margin. The paper deals with the re-contouring of the leading edges of compressor airfoils. Lufthansa Technik AG in cooperation with the Institute of Jet Propulsion and Turbomachinery (RWTH Aachen University) developed a new method for the profile definition for the blade refurbishment. The common procedure of smoothing out the leading edges manually on a wheel grinding machine can not provide a defined contour nor a reproducible result of the overhaul process. In order to achieve optimized flow conditions in the compressor blade rows, suitable leading edge contours have to be defined for the worn airfoils. In an iterative process the flow behavior of these redesigned profiles is checked by numerical flow simulations and the shape of the profiles is improved. The following machining of the new defined leading edge contours is achieved on a grinding station handled by an appropriately programmed robot. Within this Advanced Re-contouring Process (ARP) the worn blades are precision-measured and then provided with an aerodynamically optimized leading edge profile numerically newly developed under computer control. The application of this process enhances the performance and lowers the fuel consumption while prolonging the blades’ service life by 25%. The performance achievable with ARP has been confirmed both through a long term analysis and by a back-to-back comparison test on the engine test stand. For this purpose the stages 3 through 14 of a CF6-50 high pressure compressor were on the one hand fitted with conventionally overhauled blades and on the other with ARP-optimized blades of the same basic geometry. By installing the optimized blades the EGT margin could be increased by 3° to 4° C. This results in an prolongation of the on-wing time by more than 1000 hours.
Interaction of Labyrinth Seal Leakage Flow and Main Flow in an Axial Turbine
Authors: Giboni A. , Menter J. R. , Peters P. , Wolter K. , Pfost H. , Breisig V.
Published: February 2009

This paper presents the results of an experimental investigation into the flow in a 1.5-stage low-speed axial turbine with a straight labyrinth seal on the rotor shroud. The paper focuses on the interaction between the leakage flow and the main flow. The experimental program consists of measurements of the three-dimensional properties of the main flow downstream of the rotor trailing edge after the re-injection of the leakage flow. The measurements were carried out using pneumatic five-hole probes and three dimensional hot-wire probes at different operating points of the turbine. The measurement plane behind the rotor extends over one pitch from the shroud to the casing, with the complex three-dimensional flow field being mapped in great detail by 1,008 measurement points. As demonstrated in this paper, the entering leakage flow not only introduces mixing losses but also predominates the secondary flow behind the rotor and the second stator. The experimental data show that even at realistic clearance heights the leakage flow gives rise to negative incidence of considerable parts of the downstream stator which causes the flow to separate. Thus, labyrinth seal leakage flow should be taken properly into account in the design or optimisation process of turbomachinery. The high number of measurement points allows detailed analysis of the secondary flow phenomena and of the vortex structures. The time-dependence of the position and the intensity of the vortices is shown and the influence of the turbine’s operating point is presented.
Influence of Clocking and Vane/Blade Spacing on the Unsteady Surface Pressure Loading for a Modern Stage and One-Half Transonic Turbine
Authors: Haldeman C. W. , Krumanaker M. L. , Dunn M. G.
Published: February 2009

This paper describes pressure measurements obtained for a modern one and one-half stage turbine. As part of the experimental effort, the position of the HPT vane was clocked relative to the downstream LPT vane to determine the influence of vane clocking on both the steady and unsteady pressure loadings on the LPT vane and the HPT blade. In addition, the axial location of the HPT vane relative to the HPT blade was changed to investigate the combined influence of vane/blade spacing and clocking on the unsteady pressure loading. Time-averaged and time-accurate surface-pressure results are presented for several spanwise locations on the vanes and blade. Results were obtained at four different HPT vane-clocking positions and at two different vane/blade axial spacings for three (of the four) clocking positions. For time-averaged results, the effect of clocking is small on the HPT blade and vane. The influence of clocking on the transition ducts and the LPT vane is slightly greater (on the order of ±1%). Reduced HPT vane/blade spacing has a larger effect than clocking on the HPT vanes and blades (±3%) depending upon the particular surface. Examining the data at blade passing and the first fundamental frequency, the effect of spacing does not produce a dramatic influence on the relative changes that occur between clocking positions. The results demonstrate that clocking and spacing effects on the surface pressure loading are very complex and may introduce problems if the results of measurements or analysis made at one span or location in the machine are extrapolated to other sections.
Separated Flow Transition in a Low Pressure Turbine Cascade: Mean Flow and Turbulence Spectra
Authors: Volino Ralph J. , Murawski Christopher G.
Published: February 2009

Boundary layer separation, transition and reattachment have been studied experimentally in a low-pressure turbine cascade. Cases with Reynolds numbers (Re) ranging from 50,000 to 200,000 (based on suction surface length and exit velocity) have been considered under low free-stream turbulence conditions. Mean and fluctuating velocity profiles and turbulence spectra are presented for streamwise locations along the suction side of one airfoil and in the wake downstream of the airfoils. Hot film gages on the suction side surface of the airfoil are used to measure the fluctuation level and the spectra of the fluctuations on the surface. Higher Re moves transition upstream. Transition is initiated in the shear layer over the separation bubble and leads to boundary layer reattachment. Peak frequencies in the boundary layer spectra match those found in similar cases in the literature, indicating that the important frequencies may be predictable. Spectra in the wake downstream of the airfoils were similar to the spectra in the boundary layer near the trailing edge of the airfoil. Comparisons to the literature indicate that small but measurable differences in the spectra of the low free-stream turbulence can have a significant effect on boundary layer reattachment.
Passive Flow Control on Low-Pressure Turbine Airfoils
Authors: Volino Ralph J.
Published: February 2009

Two-dimensional rectangular bars have been used in an experimental study to control boundary layer transition and reattachment under low-pressure turbine conditions. Cases with Reynolds numbers (Re) ranging from 25,000 to 300,000 (based on suction surface length and exit velocity) have been considered at low (0.5%) and high (8.5% inlet) free-stream turbulence levels. Three different bars were considered, with heights ranging from 0.2% to 0.7% of suction surface length. Mean and fluctuating velocity and intermittency profiles are presented and compared to results of baseline cases from a previous study. Bar performance depends on the bar height and the location of the bar trailing edge. Bars located near the suction surface velocity maximum are most effective. Large bars trip the boundary layer to turbulent and prevent separation, but create unnecessarily high losses. Somewhat smaller bars had no immediate detectable effect on the boundary layer, but introduced small disturbances which caused transition and reattachment to move upstream from their locations in the corresponding baseline case. The smaller bars were effective under both high and low free-stream turbulence conditions, indicating that the high free-stream turbulence transition is not simply a bypass transition induced by the free-stream. Losses appear to be minimized when a small separation bubble is present, so long as reattachment begins far enough upstream for the boundary layer to recover from the separation. Correlations for determining optimal bar height are presented. The bars appear to provide a simple and effective means of passive flow control. Bars which are large enough to induce reattachment at low Re, however, cause higher losses at the highest Re. Some compromise would, therefore, be needed when choosing a bar height for best overall performance.
Condition Based Maintenance, Life Cycle Management, and Autolog
Authors: Hilferty Edward L.
Published: February 2009

Condition Based Maintenance (CBM) was instituted by the United States Navy in a policy outlined in OPNAV INSTRUCTION 4790.16 dated 6 May 1998. The goal is to move from time-directed preventive maintenance to condition-directed maintenance. It is hoped this will optimize readiness while reducing maintenance and manning requirements. The concept is that use of sensors, algorithms, and automated reasoning and decision making models to monitor equipment operations will provide critical analyses to operators that will help prevent impending failure. Red flags to operators allows maximization of maintenance effort that will focus limited resources to areas most needed to ensure safety and mission readiness while simultaneously minimizing operating costs (O & S), labor, and risk of mission degrading failures (Hedderich [3]). For the U.S. Navy, there is a large chasm to bridge between vision and reality. CBM technology is being slowly tested and integrated. But testing, modifying and back fitting all the Navy’s critical systems with CBM technology will be long term and costly and will be constantly faced with the dilemma of having just integrated one technology as it is being replaced by newer ones. In the mean time, more focus could be paid to possible interim phases that could be more quickly and cheaply integrated and still move the Navy forward in utilizing CBM technology. Autolog is such an effort and is offered here as an application and process to gather more real time data needed for CBM from one source that can be quickly and easily provided to distant engineering support activities for Gas Turbines systems while also easing record keeping and data transmittal requirements for the fleet.
The Effect of Real Turbine Roughness With Pressure Gradient on Heat Transfer
Authors: Bons Jeffrey P. , McClain Stephen T.
Published: February 2009

Experimental measurements of heat transfer (St) are reported for low speed flow over scaled turbine roughness models at three different freestream pressure gradients: adverse, zero (nominally), and favorable. The roughness models were scaled from surface measurements taken on actual, in-service land-based turbine hardware and include samples of fuel deposits, TBC spallation, erosion, and pitting as well as a smooth control surface. All St measurements were made in a developing turbulent boundary layer at the same value of Reynolds number (Rex≅900,000). An integral boundary layer method used to estimate cf for the smooth wall cases allowed the calculation of the Reynolds analogy (2St/cf). Results indicate that for a smooth wall, Reynolds analogy varies appreciably with pressure gradient. Smooth surface heat transfer is considerably less sensitive to pressure gradients than skin friction. For the rough surfaces with adverse pressure gradient, St is less sensitive to roughness than with zero or favorable pressure gradient. Roughness-induced Stanton number increases at zero pressure gradient range from 16–44% (depending on roughness type), while increases with adverse pressure gradient are 7% less on average for the same roughness type. Hot-wire measurements show a corresponding drop in roughness-induced momentum deficit and streamwise turbulent kinetic energy generation in the adverse pressure gradient boundary layer compared with the other pressure gradient conditions. The combined effects of roughness and pressure gradient are different than their individual effects added together. Specifically, for adverse pressure gradient the combined effect on heat transfer is 9% less than that estimated by adding their separate effects. For favorable pressure gradient, the additive estimate is 6% lower than the result with combined effects. Identical measurements on a “simulated” roughness surface composed of cones in an ordered array show a behavior unlike that of the scaled “real” roughness models. St calculations made using a discrete-element roughness model show promising agreement with the experimental data. Predictions and data combine to underline the importance of accounting for pressure gradient and surface roughness effects simultaneously rather than independently for accurate performance calculations in turbines.
Improved Accuracy of Fault Diagnosis of Rotating Machinery Using Wavelet De-Noising and Feature Selection
Authors: Juluri Naresh , Swarnamani S.
Published: February 2009

Past literature shows that artificial neural networks (ANN) can be successfully applied for fault diagnosis of rotating machinery but the results reported in the past literature are not satisfying. It is discovered that the main reasons for this poor accuracy are, noise present in the signals and usage of feature set that do not describe the signals accurately. Data obtained in field contains good degree of noise and this noise hurts the performance of the network. Although neural network, as a function estimator removes noise from time series to a certain extent, denoising prior to the modeling can greatly improve its ability to capture valuable information. The features used to describe the vibration signals implicitly define a pattern language. If the language is not expressive enough, it would fail to capture the information that is necessary for classification and hence regardless of the learning algorithm used, the accuracy of the classification function learned would be limited by this lack of information. Signal de-noising and feature selection are therefore highly desirable to improve the classification performance of the network. In this paper de-noising based on wavelet transforms and feature selection process based on genetic algorithms is presented. The implicit assumption made in all the past literature is, multi defects do not occur. But in reality we can find lot of cases with multi defects. So, cases with multi defects are also considered in this paper. GA is also used to select optimum network parameters. A multi layer feed forward neural network (MLFNN) is trained with error back propagation (EBP) learning algorithm. To have a complete understanding of the concepts behind the classification accuracy first the study is started with ideal signals derived by synthesizing different sinusoids composed of possible frequencies and amplitudes of sinusoids normally observed in machine vibrations and faults such as unbalance, misalignment and defects in anti friction bearings. The test results show that the proposed method improves the performance of diagnosis to 99.2% even with 15% random noise in the input signals.
Dr. Max Bentele: Pioneer of the Jet Age
Authors: Meher-Homji Cyrus B. , Prisell Erik
Published: February 2009

This paper will document the pioneering work of Dr. Max Bentele in his long and distinguished career in Germany, the UK and the United States. His early work on turbojets was in conjunction with his life long friend, Dr. Hans von Ohain, at the Heinkel-Hirth Corporation where he was involved in a wide range of turbojet engines culminating with the advanced HeS 011 (2940 lb thrust, 64 lb/sec, Pr Ratio 4.2:1), which he co-developed with Dr. Hans von Ohain. Dr. Bentele’s pioneering work in the area of blade vibration and its control will be documented along with details of his spectacular solution of the turbine blade vibration problem on the Junkers 004B engine which propelled the world’s first operational jet fighter — the Me-262. Also covered will be his important contributions to turbine blade cooling and unique blade manufacturing techniques that he pioneered for air-cooled blades.
Engineering: What You Don’t Necessarily Learn in School
Authors: Wisler David C.
Published: February 2009

As young engineers progress in their careers, they begin to understand that there is far more to being an outstanding engineer than they might have thought during their days as an undergraduate. In fact, some of the things they need to know weren’t necessarily learned in school. And this is understandable, given the relatively short time spent in school and the significant differences between the missions of academe and industry/government. This paper focuses on twelve vital aspects in engineering that are usually learned after graduation but can make the difference between success and failure in one’s engineering career. To succeed, engineers must: learn to be business oriented; expect tough, multi-disciplinary problems; learn to work and network in the new multi-cultural and multi-national environment; understand the differences between academe and industry; learn to differentiate all over again; understand the values and culture of their particular company or organization; be open to ideas from everywhere; have unyielding integrity; make their manager a success; support their university and technical society; have fun; and most importantly, manage their careers. Each of these aspects is discussed in detail.
Aerodynamic Blade Row Interactions in an Axial Compressor: Part II — Unsteady Profile Pressure Distribution and Blade Forces
Authors: Mailach Ronald , Vogeler Konrad
Published: February 2009

This two-part paper presents experimental investigations of unsteady aerodynamic blade row interactions in the first stage of the four-stage Low-Speed Research Compressor of Dresden. Both the unsteady boundary layer development and the unsteady pressure distribution of the stator blades are investigated for several operating points. The measurements were carried out on pressure side and suction side at midspan. In part II of the paper the investigations of the unsteady pressure distribution on the stator blades are presented. The experiments were carried out using piezoresistive miniature pressure sensors, which are embedded into the pressure and suction side surface of a single blade. The unsteady pressure distribution on the blade is analysed for the design point and an operating point near the stability limit. The investigations show that it is strongly influenced by both the incoming wakes and the potential flow field of the downstream rotor blade row. If a disturbance arrives the leading edge or the trailing edge of the blade the pressure changes nearly simultaneously along the blade chord. Thus the unsteady profile pressure distribution is independent of the wake propagation within the blade passage. A phase shift of the reaction on pressure and suction side is observed. The unsteady response of the boundary layer and the profile pressure distribution is compared. Based on the unsteady pressure distribution the unsteady pressure forces of the blades are calculated and discussed.
Effects of Biogas Combustion on the Operation Characteristics and Pollutant Emissions of a Micro Gas Turbine
Authors: Bohn Dieter , Lepers Joachim
Published: February 2009

The capability of gas turbines to burn low-BTU biogenic fuels besides natural gas becomes an increasingly important feature for small sized plants. This is particularly the case for micro gas turbines targeting decentralized applications. The energy conversion of biomass to electricity can be improved by integration of a micro gas turbine with the biogas generation process. Such an integrated plant concept is presented in this paper after a general overview of low-BTU fuels suitable for utilization in gas turbines has been given. The advantages are a more efficient biomass conversion and an extension of biomass digestion to biomass with reduced biochemical availability such as mildly lignocellulosic biomass. The effects of biogas utilization on the characteristics of operation of a representatively modeled microturbine are investigated in this paper. Particularly, contributions to the efficiency decrease occuring when biogas is burnt instead of natural gas are analyzed. Further, an overview of the effects of low-BTU fuels on gas turbine materials and pollutant emissions is given. The change of emissions of nitrogen oxide and carbon monoxide is analyzed with a combustion model based on a systematically reduced 6-step reaction mechanism. This study was conducted for an advanced combustor design applying ceramic materials and a transpiration cooling technology.
Design of the Blade Geometry of Swept Transonic Fans by 3D Inverse Design
Authors: Watanabe H. , Zangeneh M.
Published: February 2009

The application of sweep in the design of transonic fans has been shown to be an effective method of controlling the strength and position of the shock wave at the tip of transonic fan rotors, and the control of corner separations in stators. In rotors sweep can extend the range significantly. However, using sweep in conventional design practice can also result in a change in specific work and therefore pressure ratio. As a result, laborious iterations are required in order to recover the correct specific work and pressure ratio. In this paper, the blade geometry of a transonic fan is designed with sweep using a 3D inverse design method in which the blade geometry is computed for a specified distribution of blade loading. By comparing the resulting flow field in the conventionally and inversely designed swept rotors, it is shown that it is possible to apply sweep without the need to iterate to maintain pressure ratio and specific work when using the inverse method.
Inter-Laboratory Dynamic Modeling of a Carbonate Fuel Cell for Hybrid Application
Authors: Roberts Rory A. , Jabbari Faryar , Brouwer Jacob , Gemmen Randall S. , Liese Eric A.
Published: February 2009

A detailed comparison of dynamic models developed for carbonate fuel cells used in hybrid fuel cell gas turbine systems is presented. The two models are nearly similar in that both treat the bulk behavior of the system (e.g., through lumped or one-dimensional solutions of the fundamental equations. However, both models are implemented independently by different research groups using disparate simulation software programs. As a test case for the comparison, a generic molten carbonate hybrid fuel cell gas turbine system is identified. Such comparison-work benefits all parties by ensuring sub-model reliability prior to integration into a complete hybrid system model. Detailed results for the carbonate fuel cell models are presented. For a generic planar design, voltage and current behavior are shown following step changes in load resistance and fuel flow. The time scales for thermal dynamic response are much greater than those required for the initial electrochemical dynamic response as is expected. These results provide understanding of some of the operational characteristics of fuel cells and indicate the complexity of the dynamic response of fuel cell hybrid components. The results from the two models are not identical, but compare sufficiently well to provide confidence in each of the model’s reliability, enabling them to be integrated for hybrid system simulation. Results from the integrated simulations will provide guidance on future hybrid technology development needs.
Design and Testing of a Unique, Compact Gas Turbine Catalytic Combustor Premixer
Authors: Hack R. L. , McDonell V. G. , Samuelsen G. S. , Blust J. , Dutta P. , Smith K. , Yee D.
Published: February 2009

Catalytic combustion systems represent a potentially significant technology development in low-NOx gas turbine technology. The challenges associated with the implementation of catalytic combustion in a gas turbine include the need to present both a uniform fuel/air mixture as well as a uniform approach velocity to the catalyst within a minimal volume. The effort described herein addresses the design of catalytic combustor premixer for use on a small frame industrial (5 MW) stationary gas turbine. The general requirements for the premixer were to provide velocity and fuel air mixture uniformity at the exit plane of ±10% of the mean and ±3% of the mean respectively at nominal idle and full load conditions while maintaining a pressure drop of 4% maximum. The target turbine’s packaging and air-flow path presented an additional challenge requiring the flow to make a 180 degree flow reversal immediately upstream of the combustor. Computational fluid dynamics modeling was utilized to iterate the mixer design. A unique solution was obtained utilizing an involute shaped contraction/throat/expansion scheme. The most promising design was fabricated and tested at atmospheric conditions. As compared to a “baseline” mixer, the final involute design improved upon the flow mixing and velocity uniformity. The novel premixer design also eliminated the use of fuel injection spokes and static mixers, relying upon fuel injection from the wall and a high turbulent kinetic energy (TKE) throat section to provide the mixing, thereby simplify manufacturing. To test both scaling issues in the mixer and to provide an opportunity to test the design at high pressure, a 25% scale (approximate) reduced size mixer was designed and fabricated. Subsequent atmospheric and elevated pressure (11 atm, 1110 kPa) testing confirmed that the mixture uniformity was maintained and the general concept was applicable at both a reduced scale and at elevated pressures. Finally the premixer was integrated with a catalyst and fueled to confirm the overall system performance. The emissions of NOx were <1ppm.
High-Accuracy Matching of Engine Performance Models to Test Data
Authors: Roth Bryce , Doel David L. , Mavris Dimitri , Beeson Don
Published: February 2009

Matching of cycle models to test results for gas turbine engines is fundamentally an exercise in optimal robust parameter estimation. The problem is inherently nondeterministic in nature, so it stands to reason that probabilistic information can be used to secure improved match accuracy if properly employed. This paper proposes an approach to status matching that eliminates the need for parameter weightings, gives an intuitive feel for the results in terms of probabilistic parameters, utilizes all available information (probabilistic and deterministic), and yields high-accuracy matches between model prediction and experiment. The method development begins with a typical sum-squared errors approach and subsequently builds on this. A deviation penalty function formulation is introduced to improve solution conditioning and a multi-objective measure of fit based on the Z-score is introduced. Several measures of model fit are compared including summed-squared errors, minimax, and sum absolute error formulations. This approach is first demonstrated for a simple cantilever beam parameter-matching problem, and is later discussed in the context of turbofan engine matching.
An Output-Based Approach to Emissions Standards for Gas Turbine Facilities
Authors: Klein Manfred , Kurz Rainer
Published: February 2009

The trend towards more gas turbine power and thermal efficiency, derived through high firing temperatures and air compression ratios, has been translated into increased uncontrolled emissions of NOx. Most of these can be readily reduced by 70–90% with reliable Dry Low Emissions combustion. However, legal and regulatory pressures are requiring NOx emission reductions in the order of 98% in some regions. A key point in these traditional methods is that engine system efficiency and CO2 emissions, as well as other impacts, are not directly considered. More efficient units with higher pressure ratios have difficulty meeting ultra-low ppm concentration based standards, especially under transient conditions. This paper examines the permitting approach on overall plant emissions prevention versus controls, and engine operating parameters for several types of units. This can establish a relationship between the mass quantity of NOx emissions, the engine airflows, and the system operational power output. The intent is to explore whether a different approach to emissions standards would enhance engine system reliability and emission prevention effectiveness for already clean energy facilities.
A Statistical Assessment of the Damage State in Plasma-Sprayed Thermal Barrier Coating
Authors: Wu X. J. , Patnaik P. C. , Liao M. , Chen W. R.
Published: February 2009

Thermal barrier coatings (TBC), which consist of yttria-partially-stabilized zirconia top coat and metallic bond coat deposited onto superalloy substrate, are favorably used as protective coatings of the hot section parts in advanced gas turbine engines to withstand increased inlet temperatures and thus improve engine performance. However, understanding and modeling the damage evolution in TBC under service exposed conditions still remain to be a challenge. This is due to the failure by the coupled effects of the external load-environment, the thermal expansion mismatch between the bond coat and TBC, microstructure of the coating, and degradation of the bond coat. In this study, the damage state in an air-plasma-sprayed APS) thermal barrier coating system was assessed using metallurgical and statistical methods. The damage evolution in the TBC can thus be described with a high degree of confidence. A mechanistic model, representing the micro-cracking mechanism, is presented and its prediction is also assessed on a statistical basis.
Development of a Mathematical Compressor Model to Predict Surge in a Closed Loop Brayton Cycle
Authors: Botha B. W. , du Toit B. , Rousseau P. G.
Published: February 2009

The accuracy by which the compressor performance is estimated plays a major role in predicting the transient performance of a gas turbine Brayton cycle. Numerical prediction has proven to be a valuable tool to reduce development costs of such cycles. This document subsequently discusses the expansion of the well-known Greitzer prediction model used for unstable transient compressor operation. The expansion allows for compressibility effects in the compressor as well as integrating the compressor with a turbine in an open cycle. After this it addresses the effect of flow feedback to the compressor inlet due to a closed cycle configuration. From the one-dimensional form of the conservation laws, three partial differential equations are derived governing the dynamics of fluid flow through the compressor. The simulation results for a simple open cycle configuration compares favorably with that published by Greitzer. A similar approach was used for the closed cycle resulting in an oscillation in compressor inlet pressure due to the feedback from the turbine outlet. The study presents a first step into investigating the possibility of including a generic surge and rotating stall model into an existing software code capable of solving complex thermodynamic systems including turbo-machine cycles.
Investigation of Numerical and Physical Modelling Effects on the CFD Simulation of the Unsteady Flow in a HPT Stage
Authors: de la Calzada P. , Ferna´ndez-Castan˜eda J.
Published: February 2009

In order to investigate the unsteady flow behaviour in an HPT stage and the effects on the CFD solution of some numerical and physical modelling assumptions usually undertaken by the engineering community, an ITP in-house unsteady CFD code called Mu2s2T is first validated and then run under different configurations. The code is a fully unstructured code which solves the Reynolds averaged Navier-Stokes equations with a k-ω turbulence model. Hybrid meshes are used by having semi-structured meshes along the profile wall and fully unstructured triangular meshes on the inviscid region. The VKI Brite Euram transonic turbine stage experimental test case is used for the investigation. This turbine is representative of a state of the art HPT and presents high potential interaction due to the vane shock waves. After validating the code in this case, the influence of typical engineering assumptions is investigated. First the influence of the rotor stagger angle is analysed, resulting in a high sensitivity of the predicted pressure level at the front part of the blade and a better matching with the experimental data when an opening of 1° is applied. The influence in the solution of applying an integer airfoil count ratio compared with the solution with exact number off computed by means of phase lagged boundary conditions is also investigated. Additional Euler and Navier-Stokes computations are presented and the influence of the viscous effects is discussed. Finally a simulation including vane trailing edge cooling is performed so that conclusions about the influence of the cooling can be drawn.
Geometry Effects on the Flow Field and the Spectral Characteristics of a Triple Annular Swirler
Authors: Li Guoqiang , Gutmark Ephraim J.
Published: February 2009

The dynamics of vortex breakdown are important to the performance of gas turbine combustors where swirling flows are extensively used to stabilize the flame and extend the lean flammability limit (LBO). Due to the strong interaction of vortical structures in the swirling flow with heat release and acoustical modes, vortex breakdown mechanism is essential to understanding the thermoacoustic behavior and to the development of combustion instability control strategy. This paper analyzes the vortex breakdown behavior downstream of a Triple Annular Research Swirler (TARS) based on velocity flow field data from stereoscopic PIV measurement and spectral data from hotwire/film measurements. The vortical structure is highly dependent on the different swirler combinations (swirler geometry) as well as on inlet conditions such as air flow-rate, mixing tube length and downstream conditions such as exhaust nozzle contraction ratio. The scale, location, strength, and formation mechanisms of the large-scale vortices vary for different geometries. The shape of the recirculation bubble changes with the outlet boundary conditions, suggesting that the swirling flow inside the combustion chamber remains subcritical downstream of the vortex breakdown. However, spectral analysis reveals that the dominant frequencies close to the exit of the TARS show only slight change for different outlet boundary conditions. Three ranges of frequencies characterize the spectral domain of TARS: high frequency close to the TARS exit, middle range frequency downstream of this region, and low frequency in most regions further downstream. The sources of instabilities in these three regions could be attributed to the strong shear layer, precessing vortex core and interaction between spanwise and azimuthal instabilities. The outlet boundary conditions affect the middle and low frequency range but have no effect on the high frequency. The inlet conditions have global effect on the entire flow region.
Inlet Fogging of Gas Turbine Engines: Experimental and Analytical Investigations on Impaction Pin Fog Nozzle Behavior
Authors: Chaker Mustapha A. , Meher-Homji Cyrus B. , Mee Thomas
Published: February 2009

The inlet fogging of gas turbine engines for power augmentation has seen increasing application over the past decade. This paper provides the results of extensive experimental and theoretical studies conducted on impaction pin fog nozzles. It covers the important area of the fog plume pattern of impaction pin nozzles and examines fogplume uniformity. The subject of sprinkle (large droplet formation) from the nozzles is also examined in detail and is shown to be nonsignificant. The effect, on evaporation rate, of ambient climatic conditions and the location of the fog nozzle with respect to the gas turbine inlet duct has been analytically and experimentally analyzed. An Analytical model is used to study the evaporation dynamics of fog droplets injected in the inlet ducts the model is validated experimentally in a wind tunnel.
Aerodynamic Performance of a Very High Lift LP Turbine Blade With Emphasis on Separation Prediction
Authors: Houtermans Re´gis , Coton Thomas , Arts Tony
Published: February 2009

The present paper is based on an experimental study of a front loaded very high lift low pressure turbine blade designed at the VKI. The experiments have been carried out in a low speed wind tunnel over a wide operating range of incidence and Reynolds number. The aim of the study is to characterize the flow through the cascade in terms of losses, mean outlet flow angle and secondary flows. At low inlet freestream turbulence intensity, a laminar separation bubble is present, and a prediction model for a separated flow mode of transition has been developed.
First Assessment of Biogas Co-Firing on the GE MS9001FA Gas Turbine Using CFD
Authors: Lycklama a` Nijeholt J. A. , Komen E. M. J. , Verhage A. J. L. , van Beek M. C.
Published: February 2009

Replacement of fossil fuel by biomass-derived fuel is currently under study in the Netherlands within the context of CO2 -neutral electricity production. In view of this, co-firing biogas in the natural-gas fired Eems gas turbine power plant is being considered. This would entail extension of the power station with a biomass gasification plant for the production of biogas. The main unit of the Electrabel Eemshaven Power Station consists of five GE MS9001FA-gas turbines. A target is to replace up to 13% of natural gas consumption by biogas. The objective of the current project was to determine the impact of co-firing on the flame behavior. Therefore various options for biogas co-firing using combinations of pilot and premix burners have been studied. Computational Fluid Dynamics (CFD) simulations of the combustion process using a geometrical model of the complete combustion chamber have been performed. The flow conditions at the premix burner outlets were determined with a separate, detailed CFD model of the burner, simulating the fuel-air mixing with the required high accuracy. Advanced combustion modeling with help of the detailed GRI 3.0-reaction mechanism was used, as well as simpler models for fast chemical kinetics. A method was devised for calibrating the applied combustion models. Various firing strategies involving the premix and pilot burners were analyzed. Safe ranges for biogas co-firing have been determined in this first feasibility study.
On Forced Vibration of Shrouded Turbine Blades
Authors: Szwedowicz J. , Sextro W. , Visser R. , Masserey P. A.
Published: February 2009

Numerical predictions of the forced vibration of a disc assembly including frictional effects between the shrouds are presented concerning engineering needs for the blade design process. Assuming a tuned disc assembly, numerical static, free and then forced vibration analyses of a shrouded turbine blade measured in the spin pit are performed systematically. For the excitation forces of an air jet evaluated from the fairly linear behavior of the experimental blade resonance peaks, the reliability of the proposed approach is validated through the very close agreement of the computed and measured resonant peaks. These resonant peaks demonstrate either a fairly linear behavior or a non-linear one like the jump effect of blade resonance amplitudes, or elastic impacts between the shrouds. Also, the damping performance for different contact configurations between the shrouds is numerically analyzed. These numerical results indicate that the shrouds generate higher frictional damping for small angles (0–30 deg) between the circumferential direction and the normal vector to the contact surface.
Performance Assessment of a Transient Model for HRSGs in Combined Cycle Power Plants
Authors: Sanaye Sepehr , Moradi Arash , Bashiri Farid , Dashti Amir Saeed , Mehranian Daryoush , Mehrara Mansoor
Published: February 2009

Heat Recovery Steam Generators (HRSGs) are major Componets in Combined Cycle Power Plants (CCPPs) which are particulary subject to severe thermal and flow stresses specially during cold start-up period. Hence it is important to predict the operational parameters of HRSGs such as temperature of steam, water steam, water, tube metal and flue gas at various parts sections during the transient operation as well as steady sate conditions. In this paper, the transient model proposed by Pasha and Jolly et al. [2,3] has been selected and developed as a program (HRSG) to predict the operational conditions of the whole HRSG elements during transient and steady state operations. The program is able to analyze arbitrary number of pressure levels and any number of elements such as superheater, evaporator, economizer, deaerator and desuperheater. To assess the correct performance of the developed model and program, and to predict the capability of the method in predicting variations of temperature with time at various elements, three groups of data verifications were performed. First, the numerical outputs were checked against the same outputs reported by Jolly et al. [3]. Second, the theoretical results were checked with experimental data obtained for HRSG at Tehran CCPP during cold start run. The variations with time of gas, metal, water and steam temperatures at various sections of HRSG were among the studied parameters. Third, the model outputs were checked against the data reported for the HRSG performance test at Neyshaboor CCPP, at base and part loads. In all above cases the theoretical and measured or reported values were compared and satisfactory closeness was found.
Predicting Skin Friction and Heat Transfer for Turbulent Flow Over Real Gas-Turbine Surface Roughness Using the Discrete-Element Method
Authors: McClain Stephen T. , Hodge B. Keith , Bons Jeffrey P.
Published: February 2009

The discrete-element method considers the total aerodynamic drag on a rough surface to be the sum of shear drag on the flat part of the surface and the form drag on the individual roughness elements. The total heat transfer from a rough surface is the sum of convection through the fluid on the flat part of the surface and the convection from each of the roughness elements. The discrete-element method has been widely used and validated for predicting heat transfer and skin friction for rough surfaces composed of sparse, ordered, and deterministic elements. Real gas-turbine surface roughness is different from surfaces with sparse, ordered, and deterministic roughness elements. Modifications made to the discrete-element roughness method to extend the validation to real gas-turbine surface roughness are detailed. Two rough surfaces found on high-hour gas-turbine blades were characterized using a Taylor-Hobson Form Talysurf Series 2 profilometer. Two rough surfaces and two elliptical-analog surfaces were generated for wind-tunnel testing using a three-dimensional printer. The printed surfaces were scaled to maintain similar boundary-layer thickness to roughness height ratio in the wind tunnel as found in gas-turbine operation. The results of the wind tunnel skin friction and Stanton number measurements and the discrete-element method predictions for each of the four surfaces are presented and discussed. The discrete-element predictions made considering the gas-turbine roughness modifications are within 7% of the experimentally-measured skin friction coefficients and are within 16% of the experimentally-measured Stanton numbers.