bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship of Influence Coefficients Between Static-Couple and Multi-Plane Methods on Two-Plane Balancing
Authors: Yu John J.
Published: August 2009

This paper demonstrates analytical relationship of influence coefficients between static-couple and multi-plane methods on two-plane balancing as well as its application. For the static-couple approach, cross effects are defined between static weights and couple response as well as between couple weights and static response, thus making it possible to offset both static and couple vibration vectors effectively with appropriate combination of static and couple weights. Relationship of influence coefficients between static/couple and individual probe due to static/couple weights is also given. Static, couple, or individual probe influence coefficients due to static or couple weights can be obtained directly without having to place static or couple trial weights if influence coefficients used in the multi-plane approach are known. From static and couple influence data as well as cross effects, influence data for the multi-plane approach can be obtained directly as well without having to place any trial weights at either plane. The above findings and conversion equations are obtained analytically, and verified by experimental results. Conversion of influence coefficients from multi-plane to static-couple format can determine whether static or couple weights are more effective as well as running vibration modes, while conversion from static-couple to multi-plane format can determine which balance plane is more effective.
Improving Efficiency of a High Work Turbine Using Non-Axisymmetric Endwalls: Part II—Time-Resolved Flow Physics
Authors: Schuepbach P. , Abhari R. S. , Rose M. G. , Germain T. , Raab I. , Gier J.
Published: August 2009

This paper is the second part of a two part paper that reports on the improvement of efficiency of a one-and-half stage high work axial flow turbine. The first part covered the design of the endwall profiling as well as a comparison with steady probe data, this part covers the analysis of the time-resolved flow physics. The focus is on the time-resolved flow physics that lead to a total-to-total stage efficiency improvement of Δηtt = 1.0% ± 0.4%. The investigated geometry is a model of a high work (Δh/U2 = 2.36), axial shroudless HP turbine. The time-resolved measurements have been acquired upstream and downstream of the rotor using a Fast Response Aerodynamic Probe (FRAP). The paper contains a detailed analysis of the secondary flow field that is changed between the axisymmetric and the non-axisymmetric endwall profiling cases. The flowfield at exit of the first stator is improved considerably due to non-axisymmetric endwall profiling and results in reduced secondary flow and a reduction of loss at both hub and tip, as well as a reduced trailing shed vorticity. The rotor has reduced losses and a reduction of secondary flows mainly at the hub. At the rotor exit the flow field with non-axisymmetric endwalls is more homogenous due to the reduction of secondary flows in the two rows upstream of the measurement plane. This confirms that non-axisymmetric endwall profiling is an effective tool for reducing secondary losses in axial turbines. Using a frozen flow assumption the time-resolved data is used to estimate the axial velocity gradients, which are then used to evaluate the streamwise vorticity and dissipation. The non-axisymmetric endwall profiling of the first nozzle guide vane show reductions of dissipation and streamwise vorticity due to reduced trailing shed vorticity. This smaller vorticity explains the reduction of loss at mid-span, which is shown in the first part of the two part paper. This leads to the conclusion that non-axisymmetric endwall profiling also has the potential of reducing trailing shed vorticity.
Letterbox Trailing Edge Heat Transfer: Effects of Blowing Rate, Reynolds Number, and External Turbulence on Heat Transfer and Film Cooling Effectiveness
Authors: Fiala N. J. , Jaswal I. , Ames F. E.
Published: August 2009

Heat transfer and film cooling distributions have been acquired for a vane trailing edge with letterbox partitions. Additionally, pressure drop data have been experimentally determined across a pin fin array and a trailing edge slot with letterbox partitions. The pressure drop across the array and letterbox trailing edge arrangement was measurably higher than for the gill slot geometry. Experimental data for the partitions and the inner suction surface region downstream from the slot have been acquired over a four to one range in vane exit condition Reynolds number (500,000, 1,000,000 and 2,000,000), with low (0.7%), grid (8.5%), and aero-combustor (13.5%) turbulence conditions. At these conditions, both heat transfer and adiabatic film cooling distributions have been documented over a range of blowing ratios (0.47 ≤ M ≤ 1.9). Heat transfer distributions on the inner suction surface downstream from the slot ejection were found to be dependent on both ejection flow rate and external conditions. Heat transfer on the partition side surfaces correlated on both exit Reynolds number and blowing ratio. Heat transfer on partition top surfaces largely correlated on exit Reynolds number but blowing ratio had a small effect at higher values. Generally, adiabatic film cooling levels on the inner suction surface are high but decrease near the trailing edge and provide some protection for the trailing edge. Adiabatic effectiveness levels on the partitions correlate with blowing ratio. On the partition sides adiabatic effectiveness is highest at low blowing ratios and decreases with increasing flow rate. On the partition tops adiabatic effectiveness increases with increasing blowing ratio but never exceeds the level on the sides. The present paper, together with a companion paper which documents letterbox trailing edge aerodynamics, is intended to provide engineers with the heat transfer and aerodynamic loss information needed to develop and compare competing trailing edge designs.
An Experimental Investigation of Airfoil Performance in Wet Gas Flow
Authors: Gru¨ner Trond G. , Bakken Lars E. , Brenne Lars , Bjo̸rge Tor
Published: August 2009

Development of wet gas compressors is challenging due to the liquid phase impact on performance. Experimental investigation of airfoil behavior in wet condition contributes to a revised compressor design and increased understanding of multiphase flow mechanisms. The performance of an airfoil was investigated in wet gas flow. An air-water mixture was used as the experimental fluid. The influence of wet gas flow on airfoil performance was investigated at different angles of incidence and gas volume fractions. A qualitative description of the complex physical process observed when liquid is introduced into the flow field is given. Airfoil performance was degraded at increased liquid mass flow rate owing to premature boundary layer separation. The initiation of separation was observed as a local film thickening, followed by increased liquid film fluctuations. A continuity wave was observed surrounding the airfoil, forming a U shape of increased liquid concentration. The wave was initiated by deposited droplets and the formation of secondary droplets. The investigation reveals that compressor operating range, surge and stall margins are affected by the wet gas fluid. Reviewed literature and experiments confirm a reduced stall and surge margin when a compressor is exposed to wet gas. Further investigation will involve sub-scale impeller tests to determine the effects on the performance and stability ranges.
Active and Passive Flow Control of an Incompressible Axisymmetric Jet
Authors: Depuru Mohan Nagendra Karthik , Greenblatt David , Nayeri Christian Navid , Paschereit Christian Oliver , Nagangudy Ramamurthi Panchapakesan
Published: August 2009

An experimental investigation was carried out to compare active and passive flow control of an incompressible axisymmetric jet. For active flow control, the lip of the circular jet was equipped with a single small flap deflected away from the jet stream at an angle of 30°. The flap incorporated a flow control slot through which steady suction and oscillatory suction were implemented. For passive flow control, the lip of the circular jet was equipped with a single small triangular tab deflected into the jet stream at an angle of 30°. Both the flap and triangular tab chord lengths were one sixth of the jet diameter. The momentum of jet increased in the case of active flow control by entraining ambient fluid, whereas momentum decreased in the case of passive flow control. The effect of steady suction saturated for volumetric suction coefficient values greater than approximately 0.82%. The strength of the streamwise vortices generated by active flow control flaps were greater than those generated by the passive triangular tab. Steady suction produced positive pressures just downstream of the flow control slot in the central portion of the flap and negative pressures at the flap edges. Oscillatory suction was highly dependent on dimensionless frequency (F+) based on flap-length; the pressures on the central portion of the flap increased for F+≤0.11 and then decreased for greater F+; finally attaining negative pressures at F+ = 0.44. The increase in jet momentum, combined with the generation of strong streamwise vortices makes a strong case for improvements in propulsion efficiency and jet noise reduction.
Effect of Roughness and Unsteadiness on the Performance of a New LPT Blade at Low Reynolds Numbers
Authors: Montomoli Francesco , Hodson Howard , Haselbach Frank
Published: August 2009

This paper presents a study of the performance of a high lift profile for low pressure turbines at Reynolds numbers lower than in previous investigations. The separate and combined effects of roughness and wake passing are compared. The effect of incidence on cascade losses is also evaluated. The experimental investigation was carried out in the high speed wind tunnel of Whittle Laboratory, University of Cambridge. This is a closed circuit, continuous wind tunnel where the Reynolds number and Mach number can be fixed independently. The unsteadiness caused by wake passing in front of the blades is reproduced using a wake generator with rotating bars. The results obtained confirm that the beneficial effect of unsteadiness on losses is also present at the lowest Reynolds number examined (Re3 = 0.2×105). Roughening the surface also had a beneficial effect on the losses but this effect vanishes at the lower Reynolds numbers, i.e. (Re3 ≤ 0.3×105), where the surface becomes hydraulically smooth. The present study suggests that a blade with as-cast surface roughness has a lower loss than a polished one.
A Semi-Analytical Method for the Solution of Entrance Flow Effects in Inherently Restricted Aerostatic Bearings
Authors: Waumans Tobias , Al-Bender Farid , Reynaerts Dominiek
Published: August 2009

The behaviour of aerostatic bearings is strongly influenced by the entrance flow effects nearby feeding sources. A basic understanding of these flow phenomena and accurate prediction of their relevant parameters are therefore essential in the design and optimisation process of any aerostatic bearing application. The subject matter of this paper has for long been the topic of extensive research. An overview of the different approaches found in literature shows mostly methods based on empirical formulas with a validity limited to the experimental conditions that produced them. The proposed solution method uses the technique of separation of variables to convert the boundary-layer equations describing the laminar channel flow into an initial value problem. This allows the exact calculation of the pressure profile from gap entrance up to the attainment of viscous flow. Knowledge of the pressure distribution near the gap entrance together with the mass flow rate leads to the determination of an expedient coefficient of discharge, allowing a more practical lumped parameter formulation. The results are compared with experimental data from various sources and the agreement is found to be remarkably good, indicating that a laminar flow model is adequate in characterising the entrance flow over a wide range of working parameters.
Research of a Supersonic Axial Vaneless Rotor-Rotor Turbine
Authors: Fang Xiang-Jun , Zhang Wei-Jun , Liu Si-Yong , Wang Ping , Lv Shui-Yan
Published: August 2009

A supersonic vaneless rotor-rotor turbine (abbr.RRT) which only consists of upstream rotor and downstream rotor rotating in opposite direction is presented to investigate its aerodynamic characters and performance in the paper. The methods of both controlled vortexes and controlled meridional contours are adopted in the through-flow design and analysis of RRT. The counter twisted theory, which is usually used in the stationary vanes is employed the upstream rotor of RRT to adjust its exit angular momentum. The stagnation efficiency of RRT was 94.2% which is about higher 3% than the conventional turbine with the same shaft power. The results of 3D simulation of RRT indicated that it is very important to adopt the method of controlled vortexes to design the upstream rotor in order to improve its aerodynamic performance on condition that its vanes are eliminated completely.
Performance Analysis and Optimal Design of Heat Exchangers Used in a High Temperature and High Pressure System
Authors: Choi Byoung Ik , Kim Kui Soon , Ha Man Yeong , Jeong Ji Hwan , Cho Jong Rae , Lindquist Torbjorn , Walsh Philip P.
Published: August 2009

A computational study for the optimal design of heat exchangers used in a high temperature and high pressure system is presented. Two types of air to air heat exchangers are considered in this study. One is a single-pass cross-flow type with straight plain tubes and the other is a two-pass cross-counter flow type with plain U-tubes. These two types of heat exchangers have the staggered arrangement of tubes. The design models are formulated using the number of transfer units (ε-NTU method) and optimized using a genetic algorithm. In order to design compact light weight heat exchangers with the minimum pressure loss and the maximum heat exchange rate, the weight of heat exchanger core is chosen as the object function. Dimensions and tube pitch ratio of a heat exchanger are used as design variables. Demanded performance such as the pressure loss (ΔP) and the temperature drop (ΔP) are used as constraints. The performance of heat exchangers is discussed and their optimal designs are presented with an investigation of the effect of design variables and constraints.
Implementation and Operation of a Cogeneration Plant for Steam Injection in Oil Field
Authors: Borzea Mihai , Fetea Gheorghe , Codoban Radu
Published: August 2009

As part of Europe, Romania now faces increasing natural gas prices, growing dependence on fuel imports and the threat of global warming. One of the modern and long-term solutions, efficient and environmentally friendly to such issues is cogeneration of both electricity and useful heat. The paper deals with the implementation of an experimental cogeneration plant for combined electrical and thermal energy production, necessary for extracting heavy oil. Located in North West of Romania, at Suplacu de Barcau, the cogeneration plant was built with the aim of studying its efficiency in growing oil production with lower costs for the electrical and thermal energy used in oil field. The cogeneration plant was designed to meet the parameters of superheated steam injected in heavy oil field at 19 bars and 300°C, assuming lower costs than market prices. The cogeneration plant consists in two identical cogenerative lines; each line consisting of an electrical turbogenerator powered by one aero derivative ST18 Pratt&Whitney turbine engine, a Heat Recovery Steam Generator (HRSG) with afterburner and linked installations. The cogeneration plant is automatically operated using Programmable Logic Controllers – PLC, which provide 3 operating conditions: combined electrical and thermal energy production, electrical energy only and steam only. Design, installation and commissioning in 2004 were realized by National Research and Development Institute for Gas Turbines – INCDT COMOTI, providing 32,000 hours between overhauls. Operated over 55,000 hours, the 2 lines of cogeneration plant fulfil an efficiency of 85%. Experimental data of 3 years of cogeneration plant operation is also present in the paper.
Effects of Bowed Stators on a Transonic Fan With Distorted Inlet
Authors: Sun Peng , Han Ji’ang , Zhong Jingjun , Tao Liquan , Yang Muxiao , Yu Yang
Published: August 2009

The adverse impacts of inlet distortion on fan/compressor have been recognized as an important problem for several decades, and it is still a topic of considerable interest. Many research works indicate that it is possible to improve the performance and stability of a fan in clean and distorted inlet flow by using bowed stator blades. But, how bowed stator influences the flow field and what kind of bow patterns and angles can improve fan performance better are still not clearly studied. Therefore, a 3D analysis in fan flow field with different bowed stator blades is required. In this paper, a time-dependent three-dimensional Reynolds averaged Navier-Stokes equation composed in “Fluent Software Pack” is carried out in a parallel supercomputer. The fan with straight/different bowed stators is simulated with a clean/distorted inlet boundary condition to obtain a better understanding of bowed stators effects in distorted flow field. The analysis of results consists of three aspects. The first is about the effects of straight/bowed stators on the fan characteristics with clean and distorted inlet. Bowed stators can improve the fan performance significantly when inlet is distorted, especially at design point. But, when inlet is clean bowed stators even worsen the fan performance at design point. The effects of bowed stators on the fan performance at design point are analyzed secondly. It is found that different bow angles have different influence on rotor or stator flow field. Small bow angle stator reduces the flow loss in rotor but have no effect on stator flow field. Large bow angle stator can reduce the flow loss in stator markedly, but increases the rotor loss. Finally the patterns of flow loss caused by total pressure distortion with straight and different bowed stators are compared and analyzed in detail. The scale of vortex in stator is weakened by large bow angle blades significantly, which decreased the stator loss.
Nonlinear Identification of Mechanical Parameters in a Squeeze Film Damper With Integral Mechanical Seal
Authors: Delgado Adolfo , San Andre´s Luis
Published: August 2009

End seals in squeeze film dampers (SFDs) aid to increase their damping capability while maintaining low lubricant flow rates and reducing the severity of air ingestion. This paper presents measurements of the forced response in a SFD integrating a contacting end seal and with closed flow ports, i.e. no lubricant thru flow. The system motion is non-linear due to dry friction interaction at the mechanical seal mating surfaces. Single parameter characterization of the test system would yield an equivalent viscous damping coefficient that is both frequency and motion amplitude dependent. Presently, an identification method suited for nonlinear systems allows determining simultaneously the squeeze film damping and inertia force coefficients and the seal dry friction force. The identification procedure shows similar (within 10%) force coefficients than those obtained with a more involved two-step procedure that first requires measurements without any lubricant in the test system. The identified SFD damping and inertia force coefficients agree well with model predictions that account for end flow effects at recirculation grooves. The overall test results demonstrate that the non-rotating end seal effectively eliminates side leakage and avoids air ingestion; thus maintaining a consistent damping performance throughout the test frequency range. The nonlinear identification procedure saves time and resources while producing reliable physical parameter estimations.
Enhanced Blade Row Matching Capabilities via 3D Multistage Inverse Design and Pressure Loading Manager
Authors: van Rooij M. P. C. , Dang T. Q. , Larosiliere L. M.
Published: August 2009

Three-dimensional inverse design has become a reliable and powerful tool for facilitating the refinement of blading designs. Its main strength lies in the direct control offered over local aerodynamics and, when the method is based on pressure loading, net circulation. While the ability to specify pressure loading offers many advantages, it is often not obvious to a designer what loading distribution should be prescribed. Not only should a suitable blade shape be achieved, but also satisfactory performance and design constraints such as mass flow, exit flow angle distributions and compression ratio. This problem is exacerbated when applying inverse design in a multistage environment, where interactions between blade rows affect the design and the resulting flow field in ways that are often intractable. Thus, numerous revisions of the prescribed loading, with a careful examination of how changes to the prescribed loading influence the resulting design, can still be necessary before obtaining a satisfactory design. A pressure loading manager has been developed to alleviate these problems. This loading manager can automatically adjust pressure loading distributions during the inverse design process to achieve greater control over the aerodynamic design intent. In combination with a fully three-dimensional multistage viscous inverse design method, a powerful method for blading revision is obtained that offers enhanced aerodynamic matching capabilities and design point control. Increased aero-design quality and productivity in difficult design situations can be achieved. This is demonstrated with the redesign of a highly loaded 2.5-stage transonic compressor.
Analysis of the Effects of Pulsations on the Operational Stability of Centrifugal Compressors in Mixed Reciprocating and Centrifugal Compressor Stations
Authors: Brun Klaus , Kurz Rainer
Published: August 2009

Mixed operation with both centrifugal and reciprocating compressors in a compression plant poses significant operational challenges as pressure pulsations and machine mismatches lead to centrifugal compressors’ instabilities or poor performance. Arrangements with reciprocating compressors placed in series with centrifugal compressors generally lead to higher suction/discharge pulsations on the centrifugal compressor than conventional parallel operation. This paper demonstrates that by properly analyzing and designing the interconnecting piping between the compressors, utilizing pulsation attenuation devices, and matching the compressors’ volumetric-flow rates, a satisfactory functional compression system design can be achieved for even the worst cases of mixed centrifugal and reciprocating compressor operation. However, even small analysis errors, design deviations, or machine mismatches result in a severely limited (or even inoperable) compression system. Also, pulsation attenuation often leads to a significant pressure loss in the interconnect piping system. Utilizing analysis tools in the design process that can accurately model the transient fluid dynamics of the piping system, the pulsation attenuation devices and the compressor machine behaviors is critical to avoid potentially costly design mistakes and minimize pressured losses. This paper presents the methodology and examples of such an analysis using a 1-D transient Navier-Stokes code for complex compression piping networks. The code development, application, and example results for a set of mixed operational cases are discussed. This code serves as a design tool to avoid critical piping layout and compressor matching mistakes early in the compressor station design process.
Influence of Hot Streak/Airfoil Count Ratios on High Pressure Stage of a Vaneless Counter-Rotating Turbine
Authors: Zhao Qingjun , Wang Huishe , Tang Fei , Zhao Xiaolu , Xu Jianzhong
Published: August 2009

In order to reveal the effects of the hot streak/airfoil count ratio on the heating patterns of high pressure turbine rotor blades in a Vaneless Counter-Rotating Turbine, three-dimensional unsteady Navier-Stokes simulations have been performed. In these simulations, the ratio of the number of hot streaks to the number of the high pressure turbine vanes and rotors is 1:3:3, 1:2:2, 2:3:3 and 1:1:1, respectively. The numerical results show that the migration characteristics of the hot streak in the high pressure turbine rotor are predominated by the combined effects of secondary flow and buoyancy. The combined effects induce the high temperature fluid migrate towards the hub in the high pressure turbine rotor. And the combined effects become more intensified when the hot streak/airfoil count ratio increases. The results also indicate that the peak temperature of the hot streak is dissipated as the hot streak goes through the high pressure turbine vane or the rotor. The dissipated extent of the peak temperature in the high pressure turbine stator and the rotor is increased as the hot streak-to-airfoil ratio increases. And the increase of the hot streak/airfoil count ratio trends to increase the relative Mach number at the high pressure turbine outlet. The relative flow angle from 23% to 73% span at the high pressure turbine outlet decreases as the hot streak-to-airfoil ratio increases. The results also indicate that the isentropic efficiency of the Vaneless Counter-Rotating Turbine is decreased as the hot streak/airfoil count ratio increases.
3D Crack Growth Analysis and Its Correlation With Experiments for Critical Turbine Components Under an International Collaborative Program
Authors: Hou J. , Dubke J. , Barlow K. , Slater S. , Harris L. , Calcuttawala S. , Beres W.
Published: August 2009

Following a reanalysis of the original material data plus supplementary Low Cycle Fatigue (LCF) specimen testing, an Original Equipment Manufacturer (OEM) reduced the low cycle fatigue life limits for a number of turbine components. To ascertain the validity of the new life limits, an international collaborative spin rig test program was initiated to provide more accurate low cycle fatigue life limits. The program covered a broad range of activities including, Finite Element (FE) stress analyses, cyclic spin rig testing, fractographic assessment and fatigue crack growth (FCG) analyses. This paper describes the 2D and 3D crack growth analyses of critical turbine components in a turboprop gas turbine engine, comparison of predicted results obtained using different software and also correlations with spin test results from the program. First, FE stress analyses of selected turbine components were carried out under both engine operating conditions and spin-rig test configurations in order to determine the maximum and minimum operating speeds required to match the stress ranges at the critical location specified by the OEM under engine operating conditions. Second, 2D and 3D crack growth analyses were performed independently by three organisations for a disk bolthole using the state-of-the-art software. Third, the predictions from different software were compared, and the relative technical merits of each software were evaluated. Finally, the predicted results were correlated against the striation counts determined by the OEM from the results of spin rig tests.
Performance Predicting Modeling of Axial-Flow Compressor at Design and Off-Design Conditions
Authors: Madadi Ali , Hajilouy Benisi Ali
Published: August 2009

Axial flow compressor is one of the most important parts of gas turbine units. Therefore, its design and performance prediction are very important. One-dimensional modeling is a simple, fast and accurate method for performance prediction of any type of compressors with different geometries. In this approach, inlet flow conditions and compressor geometry are known and by considering various compressor losses, velocity triangles at rotor, and stator inlets and outlets are determined, and then compressor performance characteristics are predicted. Numerous models have been developed theoretically and experimentally for estimating various types of compressor losses. In present work, performance characteristics of the axial-flow compressor are predicted based on one-dimensional modeling approach. In this work, models of Lieblein, Koch-Smith, Herrig, Johnsen-Bullock, Pollard-Gostelow, Aungier, Hunter-Cumpsty Reneau are implemented to consider compressor losses, incidence angles, deviation angles, stall and surge conditions. The model results are compared with experimental data to validate the model. This model can be used for various types of single stage axial-flow compressors with different geometries, as well as multistage axial-flow compressors.
A Study of Parameter Selection Principle and Internal Flow Mechanism in a Multi-Stage Low-Reaction Axial Flow Compressor
Authors: Wang Songtao , Qiang Xiaoqing , Lin Weichun , Feng Guotai , Wang Zhongqi
Published: August 2009

A subsonic multi-stage highly loaded, low-reaction, boundary layer suction axial flow compressor design concept was proposed in this paper and its feasibility was studied from theoretical analysis. This design concept could greatly raise the single stage pressure ratio while keeping the compressor efficiency in a high level. The distribution principle of total pressure ratio and static pressure ratio in a multi-stage low-reaction compressor was studied as well as the selection principle of reaction, diffusion factor and other total parameters. Considering the design feature of this new type of compressor, the internal flow in a large geometry turning angle cascade was studied in order to establish the relation between geometry parameters and surface pressure distribution. The relation between surface pressure distribution and profile loss, trailing edge loss, etc was also studied in this paper. By using this design concept combined with the boundary layer suction method, a certain eleven stages axial compressor’s count was reduced to seven. The numerical simulation was done in the last two stages which had typical flow characteristics. The simulation result proved that the multi-stage low-reaction axial flow compressor design concept was feasible.
Gas Turbine Flexibility With Carbon Constrained Fuels
Authors: Payrhuber Klaus , Jones Robert M. , Scholz Marcus H.
Published: August 2009

Over the next several decades, the power generation sector will face major landscape changes as CO2 management needs and hydrocarbon fuel options become limited. Uncontrolled carbon emissions from coal plants exceed natural gas fired alternatives by more than two to one due in large part to greater fuel carbon content and lower overall energy conversion efficiencies. In a carbon-constrained environment, power production from coal must realize improvements beyond incremental efficiency gains in order to have significant CO2 emissions reduction. Coal gasification and associated fuel gas process treatment units provide the mechanisms inherently needed to effectively separate carbon components on a “pre-combustion” basis, leaving essentially carbon free hydrogen fuel available for combustion within the combined cycle power plant. Gas turbines will play a significant role in meeting this generation challenge, not only from a fuel flexibility perspective, but also in the area of CO2 reduction where gas turbines will likely become the primary hydrogen energy conversion unit for the foreseeable future. Worldwide, GE gas turbines continue to demonstrate their proven, reliable performance on hydrogen bearing fuels, including installations with up to 95% hydrogen by volume. As the focus on pre-combustion carbon capture continues to grow, never has this experience with high hydrogen fuels been more relevant. Furthermore, GE continues to develop combustion designs to extend this experience to advanced gas turbine platforms, including F-class units operating on synthesis gas. The ever-present focus on efficiency improvement and emissions reduction, combined with improved gasification processes, will require future advanced combustion system designs that can achieve low emissions at higher firing temperatures with minimal to no dilution for NOx abatement. This paper discusses the challenge of low CO2 producing fuel for advanced gas turbines, firing hydrogen rich synthesis gas, in terms of gas turbine fuel and accessory system design.
Internal Losses and Flow Behavior of a Turbofan Stage at Windmill
Authors: Prasad Dilip , Lord Wesley K.
Published: August 2009

The flow through a high-bypass ratio fan stage during engine-out conditions is investigated, with the objective of quantifying the internal losses when the rotor is at “windmill”. An analysis of altitude test data at various simulated flight Mach numbers shows that the fan rotational speed scales with the engine mass flow rate. Making use of the known values of the nozzle coefficients, we deduce the stagnation pressure loss of the fan stage, which rises significantly as the mass flow rate increases. In order to better understand this behavior, numerical simulations of the fan stage were carried out. The predicted losses agree well with the test data, and it is found that the bulk of the stagnation pressure loss occurs in the stator. A detailed examination of the flow field reveals that the relative flow leaves the rotor at very nearly the metal angle. Moreover, the rotational speed of the fan is such that the inboard sections of the fan blade add work to the flow, while the outboard sections extract work from it. The overall work is essentially zero so that the absolute swirl angle at the rotor exit is small, causing the stator to operate at a severely negative incidence. A gross separation ensues and the resulting blockage of the stator passage accelerates the flow to high Mach numbers. The highly separated flow in the vane, together with the mixing of the large wakes behind it are responsible for the high losses in the vane. Based on the simulation results for the flow behavior, a simple physical model to estimate the windmill speed of the rotor is developed and is found to be in good agreement with the test data. The utility of this model is that it enables the development of a procedure to predict the internal drag at engine-out conditions, which is discussed.
An Approach to Maintenance Cost Estimation for Aircraft Engines
Authors: Kang Myoungcheol , Ogaji Stephen , Pilidis Pericles , Kong Changduk
Published: August 2009

This study presents a detailed analysis of aircraft engine maintenance cost based on the relationships between engine performance and geometric parameters. Estimating engine maintenance cost is very complicated and depends upon empirical work based on know-how and huge database to develop the industrial cost estimation program. Engine maintenance costs are basically influenced by the shop visit rates (SVR), the workscope of each shop visit, the shop visit pattern and the manhours and materials used in each shop visit. To estimate these values for a specific engine model, there is a need to develop the empirical correlations of engine maintenance. For this study, an engine performance and maintenance database was created. The engine performance data for each major component were simulated by an engine performance code, TURBOMATCH developed at Cranfield University, U.K., at static sea-level condition and geometric data were collected from open literature. Also, engine maintenance cost data for some current engines were collected and used. Some trend line equations based on the database were developed for the estimation of shop-visit interval, work-scope, Man-Hours, material cost and Life Limited Part cost. Comparisons of the results between trend equations and original data were carried out. The results show that this approach can give a more reasonable and detailed estimation of engine maintenance cost than older empirical methods.
Blade Lean and Shroud Leakage Flows in Low Aspect Ratio Turbines
Authors: Rosic Budimir , Xu Liping
Published: August 2009

Blade lean, i.e. non-radial blade stacking, has been intensively used over the past in the design process of low aspect ratio gas and steam turbines. Although its influence on turbine efficiency is not completely understood, it has been proved as an effective way of controlling blade loading and secondary flows on blade passage endwalls. Three-dimensional blade designs in modern industrial practice are usually carried out using clean endwalls. The influence of the leakage flows on three-dimensional blade design is traditionally neglected. This paper presents an experimental study where two different stator blades, with different levels of compound lean, were tested in a low speed three-stage model turbine with the shroud leakage flow geometry representative of industrial practice. The experimental measurements were compared with numerical tests, conducted on the same blade geometries. The influence of the compound lean on the stator flow field was analysed in detail. In order to analyse the combined effects of both the stator hub and rotor shroud leakage flow on the blade lean, in the second part of the paper a numerical study on a two stage turbine with both leakage flow paths representative of a real turbine was carried out. Performance of three different stator blade designs (two different levels of compound lean and a straight blade) was investigated. The aim of this study is to understand the mechanism and the consequence of the stator blade lean on stage performance in an environment with leakage flows and associated cavities.
Numerical Simulation of Transonic Fan Flutter With 3D N-S CFD Code
Authors: Aotsuka Mizuho , Tsuchiya Naoki , Horiguchi Yasuo , Nozaki Osamu , Yamamoto Kazuomi
Published: August 2009

This paper describes the calculation of transonic stall flutter of a fan. A new CFD code has been developed and validated. The code is an unsteady 3D multi-block flow solver. The Reynolds-Averaged Navier-Stokes equations are solved using a finite volume method with Spallart-Allmaras 1 equation turbulence model. A grid deforming system is applied, so the new code is capable of simulating an oscillating blade row. This grid deforming system produces less grid distortion and the code has robustness for a blade oscillating calculation. The code has validated on an IHI’s research transonic fan rig test, and the result was in good agreement with the test data in the prediction of the flutter boundary. In the rig test at part-speed condition, stall-side flutter was experienced. In that condition, the inlet relative Mach number in the tip region is about unity. The aerodynamic work by the CFD at the near flutter condition is positive, which means that the flutter characteristic is unstable, while at other conditions the aerodynamic work is negative. The aerodynamic work increases rapidly just before the zero damping point with the increase of the blade loading. From the detailed CFD result, the shock wave on the suction surface contributes to the excitement of the blade oscillation, and the aerodynamic work of the shock wave has large value at the flutter condition.
A Viscoplastic Modeling Approach for MCrAlY Protective Coatings for Gas Turbine Applications
Authors: Mu¨cke Roland
Published: August 2009

MCrAlY coatings are applied in industrial gas turbines and aircraft engines to protect surfaces of hot gas exposed components from oxidation and corrosion at elevated temperature. Apart from oxidation resistance, coatings have to withstand cracking caused by cyclic deformation since coating cracks might propagate into the substrate material and thus limit the lifetime of the parts. In this context, the prediction of the coating maximum stress and strain range during cyclic loading is important for the lifetime analysis of coated components. Analyzing the state of stress in the coating requires the application of viscoplastic material models. A coupled full-scale cyclic analysis of substrate and coating, however, is very expensive because of the different flow characteristics of both materials. Therefore, this paper proposes an uncoupled modeling approach which consists of a full-scale cyclic analysis of the component without coating and a fast post-processing procedure based on a node-by-node integration of the coating constitutive model. This paper presents different aspects of the coating viscoplastic behavior and their computational modeling. The uncoupled analysis is explained in detail and a validation of the procedure is addressed. Finally, the application of the uncoupled modeling approach to a coated turbine blade exposed to a complex engine start-up and shut-down procedure is shown.
Chemical Kinetic Analysis of a Flameless Gas Turbine Combustor
Authors: Rao G. Arvind , Levy Yeshayahou , Gutmark Ephraim J.
Published: August 2009

Flameless combustion (FC) is one of the most promising techniques of reducing harmful emissions from combustion systems. FC is a combustion phenomenon that takes place at low O2 concentration and high inlet reactant temperature. This unique combination results in a distributed combustion regime with a lower adiabatic flame temperature. The paper focuses on investigating the chemical kinetics of an prototype combustion chamber built at the university of Cincinnati with an aim of establishing flameless regime and demonstrating the applicability of FC to gas turbine engines. A Chemical reactor model (CRM) has been built for emulating the reactions within the combustor. The entire combustion chamber has been divided into appropriate number of Perfectly Stirred Reactors (PSRs) and Plug Flow Reactors (PFRs). The interconnections between these reactors and the residence times of these reactors are based on the PIV studies of the combustor flow field. The CRM model has then been used to predict the combustor emission profile for various equivalence ratios. The results obtained from CRM model show that the emission from the combustor are quite less at low equivalence ratios and have been found to be in reasonable agreement with experimental observations. The chemical kinetic analysis gives an insight on the role of vitiated combustion gases in suppressing the formation of pollutants within the combustion process.
Comparison of Numerical Investigations With Measured Heat Transfer Performance of a Film Cooled Turbine Vane
Authors: Charbonnier D. , Ott P. , Jonsson M. , Ko¨bke Th. , Cottier F.
Published: August 2009

Detailed surface measurements of the heat transfer coefficient and the film cooling effectiveness by application of the transient liquid crystal method were carried out on a heavily film cooled nozzle guide vane (NGV) in a linear cascade wind tunnel at the EPFL as part of the European Research Project TATEF2 (Turbine Aero-Thermal External Flows 2). The external cooling setup included a showerhead cooling scheme and suction and pressure side of the airfoil several rows of fan-shaped cooling holes. By testing two different cooling flow rates at a NGV exit Reynolds number of 1.46E+06, detailed aerodynamic and heat transfer measurement data were obtained that can be used for validation of numerical codes and design tools for cooled airfoils. The data include the NGV surface static pressure distribution and wall heat transfer and film cooling effectiveness obtained by application of the transient liquid crystal technique. An engine representative density ratio between the coolant and the external hot gas flow was achieved by using CO2 as coolant gas. For the coupled simulation of internal cooling and external flow the numerical model was composed of the cooling air feeding the internal plenum, the cooling holes, and the outer external flow domain. An unstructured mesh was generated for the simulations by applying two different commercial CFD codes (Fluent and CFX). Identical boundary conditions were chosen in order to allow for a direct comparison of both codes. The computations were carried in two ways, first using a built-in transition model and second by imposing fully turbulent flow starting at the leading edge. For both codes the same built-in turbulence models were applied. The computations were set up to solve for the aerodynamic flow quantities both within and around the test model and for the thermal quantities on the vane surface, i.e. heat transfer coefficient and film cooling effectiveness. The computational results from the two codes are compared and validated against the results from the experiments. The numerical results were able to confirm a suspicion that the cross flow in the feeding plenum causes an observed non-symmetry of the measured film cooling effectiveness at the outlet of some cooling holes.
Investigations at the Over-Tip Casing of a High Pressure Turbine Including Off-Design Conditions and Heat Transfer Correlations
Authors: van Duikeren Bart , Heselhaus Andreas
Published: August 2009

Turbine inlet temperature is reaching values far above acceptable material temperatures. Thus the thermally highly loaded components have to be cooled intensively. One of the most thermally loaded components is the over-tip casing. In recent years research on heat transfer at the over-tip casing received a big boost by availability of faster and more accurate measurement techniques. So far the investigations are limited to design condition, no information is available at off-design conditions. This paper aims to contribute to a better understanding of the major phenomena governing heat transfer in the over-tip casing region, including the influence of different operating conditions. Using an HP-turbine at different flow conditions, extended measurements were performed at DLR’s wind tunnel for Rotating Cascades (RGG), Go¨ttingen, including the flow field in the tip gap and close to the over-tip casing. The Nusselt correlation for a flat plate was investigated for it’s applicability to the over-tip casing. The influence of the incidence angle on the heat transfer levels at the upstream part of the over-tip casing is investigated. Also the influence of the rotational speed on tip-leakage flow and casing heat transfer will be discussed. These results are compared to flat plate heat transfer correlations for design and off-design conditions.
Performance of a Water Compensated Compressed Air Energy Storage System
Authors: Arnulfi Gianmario L. , Marini Martino
Published: August 2009

In a growing energy scenario, electric utility companies have to take into account new managing strategies. The increasing seasonal gap in energy demand, the penetration of stochastic sources (wind and sun) and of combined heat and power plants are making more and more difficult to schedule power production. Energy storage can balance supply and demand over different time scales, with technical and economical benefits. The two options for large size plants are pumped storage hydro and Compressed Air Energy Storage (CAES). In the present paper, a CAES plant both with and without water compensation, is considered. The time window is an entire year as there is a remarkable difference between the seasons. Indeed in winter and summer the price fluctuation amplitude can be profitably exploited while between seasons are less suitable in a storage perspective because of the relative flatness of the daily price pattern. The adopted strategy is based on two price thresholds: below the former, a single charging step is carried out at night, above the latter, one or more steps of electricity production are carried out at peak hours. Finally, amid the thresholds, the plant works as a mere gas turbine or is shut off. Of course the mere GT working is available only if turbo compressor and expander are consistent and this affects the performance of each machine during charge or discharge phases. The shape of the daily price pattern strongly impacts on the cash flow. The proposed model is applied to the present Italian scenario as the energy market, taxes and services are concerned. The water compensated plant attains a storage density nearly twice higher than without compensation.