bluuebunny/crossref_metadata_2025 huggingface dataset:
Anisotropic Eddy Viscosity in the Secondary Flow of a Low-Speed Linear Turbine Cascade
Authors: MacIsaac G. D. , Sjolander S. A.
Published: May 2012

The final losses within a turbulent flow are realized when eddies completely dissipate to internal energy through viscous interactions. The accurate prediction of the turbulence dissipation, and therefore the losses, requires turbulence models which represent, as accurately as possible, the true flow physics. Eddy viscosity turbulence models, commonly used for design level computations, are based on the Boussinesq approximation and inherently assume the eddy viscosity field is isotropic. The current paper compares the computational predictions of the flow downstream of a low-speed linear turbine cascade to the experimentally measured results. Steady-state computational simulations were performed using ANSYS CFX v12.0 and employed the shear stress transport (SST) turbulence model with the γ-Reθ transition model. The experimental data includes measurements of the mean and turbulent flow quantities. Steady pressure measurements were collected using a seven-hole pressure probe and the turbulent flow quantities were measured using a rotatable x-type hotwire probe. Data is presented for two axial locations: 120% and 140% of the axial chord (Cx) downstream of the leading edge. The computed loss distribution and total bladerow losses are compared to the experimental measurements. Differences are noted and a discussion of the flow structures provides insights into the origin of the differences. Contours of the shear eddy viscosity are presented for each axial plane. The secondary flow appears highly anisotropic, demonstrating a fundamental difference between the computed and measured results. This raises questions as to the validity of using two-equation turbulence models, which are based on the Boussinesq approximation, for secondary flow predictions.
New Locking Arrangement for Radial Entry Turbine Blades
Authors: Golinkin Samuel L. , Lipski Michael J. , Loudon John S. , DiOrio Gennaro J. , Ewer Timothy
Published: May 2012

Turbine blades with radial fasteners (T-shank, radial fir-tree, etc.) are commonly used in current steam turbomachinery, especially in power generation applications. However, this reliable and cost-effective design is limited by the strength of the axial pins which lock the closing part in the radial entry slot in the disc. In applications with high speed rotors or heavy blades, the centrifugal force of the blade exceeds the pin strength. In those applications, the airfoil portion of the closing blade is cut off leaving only the bottom portion which is located in the radial entry slot. Some original equipment manufactures (OEMs) also remove the airfoil of the blade 180 degrees opposite for better balancing. The absence of two airfoils is detrimental to efficiency and reliability of the entire row. Siemens Demag Delaval Turbomachinery, Inc. (SDDTI) developed a new locking arrangement which eliminates the above described shortcoming associated with standard radial entry blades. This paper presents the design of the new patented locking arrangement and mechanical stress calculations (FEA) of its major components. In order to verify the validity of the design and calculations, a full-scale row of modernized radial entry blades for an existing US Navy turbine with the new locking arrangement was tested. The testing was done over the full range of operating speeds in a vacuum bunker. The paper also describes the special test rotor, instrumentation used, and the test results which were compared with the stress calculations. The tests confirmed all the advantages of the new locking arrangement and showed acceptable correlation with the stress calculations. The patented design will expand applications for radial entry blades, modernize radial entry blades with missing blade airfoils, and provide a cost-effective method to repair localized cracks in the fastener area of the turbine discs.
Increasing the Passive Scalar Mixing Quality of Jets in Crossflow With Fluidics Actuators
Authors: Lacarelle Arnaud , Paschereit Christian O.
Published: May 2012

Jets in crossflow are widely used in the industry for homogenization or cooling tasks. Recently, pulsating jets have been investigated as a mean to increase the scalar mixing efficiency of such configurations, whether for a single jet or for an array of jets. To avoid the disadvantages of mechanically actuated flows (costs, maintenance), a new injector based on a fluidics oscillator has been designed. Four injectors have been implemented in a generical jet in crossflow configuration and the mixing efficiency of the setup was compared with the one of the same setup equiped with standard non oscillating jets. With help of high-speed concentration measurement technique, the scalar mixing quality of both setups was measured at three positions downstream of the injection plane. In all the cases tested, the fluidics injectors present a better temporal homogenization, characterized with the Danckwerts unmixedness criterion, than the standard jets. For a defined mixing quality, a decrease of the mixing length by approximately 50% can be achieved with the fluidics injectors. Furthermore, the new injectors exhibit a mixing quality which is less sensitive to variations of the jet to crossflow momentum. The flapping motion of the fluidics injectors induces a wider azimuthal spreading of the fluidics jets immediately downstream of the injection location. This increases the macro- and micromixing phenomea which lead then to the high gains in mixing quality. It is thus demonstrated that fluidics oscillators present a strong potential to improve the passive scalar homogenization of jet in crossflow configurations.
Effects of Using Hydrogen-Rich Syngas in Industrial Gas Turbines While Maintaining Fuel Flexibility on Compressor Design
Authors: Nucara Pascal , Sayma Abdulnaser
Published: May 2012

Most of the current industrial gas turbine systems are designed to operate with conventional fossil fuels. Recently, the use of Low Calorific Value (LCV) fuels gained interest, particularly, Hydrogen rich Syngas resulting from coal and solid waste gasification. When LCV fuels are used the performance and behavior of the engines could significantly change and modifications may be needed. For instance, due to the relatively low heating value the fuel mass flow rate will be much higher than natural gas, increasing substantially the mass flow through the turbine. This leads to a decrease of demand for air from the compressor, which results in increased back pressure, reduction of stall margin and possible compressor instability. This paper presents a preliminary study to pave the way to the design of a 300 MW industrial gas turbine’s compressor with the objective of operating efficiently with Hydrogen rich syngas, while maintaining the flexibility for a quick switch to natural gas in the event of gasifier failure or breakdown of feedstock supply. NASA Rotor 37 is used as the test vehicle to provide design concepts because of its simplicity in being a single stage compressor and the availability of experimental data for the CFD model validation. Geometric modifications were performed on the rotor to shift the working line towards an estimated lower air mass flow rate working line. Further modifications were investigated in order to maintain the design point compressor efficiency primarily based on sweep and lean of the blade. Once the new working line geometry was obtained, inlet variable guide vane (IGV) effects were explored to allow the compressor to shift to the original working line without further changes to the blade shape.
Direct Numerical Simulation Study of Premixed Flame Response to Fuel-Air Ratio Oscillations
Authors: Hemchandra Santosh
Published: May 2012

The coupling between heat release oscillations produced by equivalence ratio fluctuations with combustor acoustic modes in lean premixed combustion systems, is a serious problem that limits the operation envelope of these devices. Such oscillations are produced by an oscillating pressure drop across air inlets and/or fuel injectors due to the presence of acoustic oscillations. This results in fluctuations in mass flow rates of air and/or fuel entering the combustor, thereby, changing the local equivalence ratio of the mixture at these injector/inlet locations. These perturbations in equivalence ratio are advected by the flow into the flame, causing its heat release to oscillate. Detailed reduced order models for the heat release response of premixed flames to equivalence ratio oscillations, based on this phenomenological picture, have been developed in the past. A key problem in validating these models is the ambiguity of interpretation of chemiluminescence signals when, the length scale of equivalence ratio fluctuations is smaller than the characteristic flame length. As such, the present work performs a DNS of a premixed methane-air flame, subject to unsteady forcing in upstream methane mass fraction. Predictions from prior reduced order modelling approaches are compared with present DNS results. The agreement between modelling and DNS predictions in the characteristics of flame response is good at low excitation frequencies and amplitudes. This agreement, however, degrades as forcing amplitude and frequency increase due to the influence of hydrodynamic coupling between the flow-fields on either side of the flame as well as damping of equivalence ratio perturbations by diffusion, on the dynamics of the flame.
Effect of the Hot Gas Composition on a Highly Thermally Loaded Film Cooling System
Authors: Sun Peng , Wang Wenping , Ren Jing , Jiang Hongde
Published: May 2012

To reduce the CO2 emission, three types of the coal-based power generation system are promising: IGCC, the hydrogen-fired turbine cycle and the oxy-fuel cycle. The thermal characteristics of the turbines are expected to be dependent on the different hot and wet gases. For studying the effect of the hot gas composition on the highly thermally loaded cooling system, both the experimental and the numerical studies are carried out in the present work. Five hot gases are focused in the study, which are corresponding to the combustion products of the liquefied petroleum gas, the natural gas, the syngas, the hydrogen and the oxy-fuel gas. A highly thermally loaded film cooling test rig is built up in Tsinghua University. The Discrete Transfer Model (DTM) and the Weighted Sum of Gray Gases (WSGG) spectral model are employed to solve the radiative heat transfer in the multi-composition field. By comparing the experimental and the numerical data, it is resulted that the implemented thermal conduction/convection/radiation method is valid for the studied cases. The results show that the temperature rise on the plate top surface is about 50∼60 K under the condition of the five hot gas compositions due to the radiative heat transfer. The magnitude of the temperature rise is the reverse of the mole fraction of the radiative gases (CO2+H2O) in the hot gas. Furthermore, the local temperature gradient is weakened in the five hot gas compositions cases. It means that the thermodynamics of the film cooling system in the multi-composition hot gas has its own characteristics. It may play a role in the future coal-based turbine technology.
Robust Gas Turbine Speed Control Using QFT
Authors: Biron Zoleikha Abdollahi , Sedigh Ali Khaki , Biron Roghiyeh Abdollahi
Published: May 2012

This paper provides a Quantitative Feedback Theory (QFT) robust control design of a gas turbine in the presence of uncertain parameters. Frequency domain analysis, disturbance rejection properties for SISO and MIMO plants, are among the distinctive features of QFT. In this paper, a QFT robust controller satisfying the required performance despite uncertainties and various constraints on the control effort and process is designed. The nonlinear gas turbine simulator employed in this paper is based on the gas turbine thermodynamic characteristics presented within MATLAB-SIMULINK. The accuracy of this simulator has been examined through several tests by real gas turbine responses.
Single and Multi Objective CFD Optimization of Horizontal Axis Wind Turbines
Authors: De Bellis Fabio , Catalano Luciano A.
Published: May 2012

In spite of the enlarging interest in wind turbines development, the design optimization of wind turbine blades has not been studied in the past as gas or steam turbines optimization. Due to its reduced computational cost, Blade Element Momentum (BEM) method has been employed up to now to estimate the power output of the turbine. However, BEM method is not able to predict complex three dimensional flow fields or the performance of profiles for which drag and lift coefficients are not available. Theoretically, Computational Fluid Dynamics (CFD) can be more useful in these cases, but at the price of a much higher overall computational cost. In a past work, the authors developed and validated a simplified CFD process (including meshing) capable to assess the aerodynamic loads acting on a wind turbine with acceptable computational resources. Starting from that, in this work a full 3D CFD optimization of a small wind turbine is presented, both with constrained single- and multi-objective. Twist and chord distributions of a single blade have been varied keeping fixed the aerodynamic profile, and the obtained optimums have been compared with a benchmark case. The results demonstrate that CFD optimization can be effectively employed in a wind turbine optimization. As expected, stalled conditions of the blade are more likely to be improved than those characterized by attached flow. Future works will focus on multi-disciplinary optimization and will include also aerodynamic profile variation.
Experimental Analysis of Soot Formation and Oxidation in a Gas Turbine Model Combustor Using Laser Diagnostics
Authors: Geigle Klaus Peter , Zerbs Jochen , Ko¨hler Markus , Sto¨hr Michael , Meier Wolfgang
Published: May 2012

Sooting ethylene/air flames were investigated experimentally in a dual swirl gas turbine model combustor with good optical access at atmospheric pressure. The goals of the investigations were a detailed characterization of the soot formation and oxidation processes under gas turbine relevant conditions and the establishment of a data base for the validation of numerical combustion simulations. The flow field was measured by stereoscopic particle image velocimetry, the soot volume fractions by laser-induced incandescence, the heat release by OH chemiluminescence imaging and the temperatures by coherent anti-Stokes Raman scattering. Two flames are compared: a fuel-rich partially premixed flame with moderate soot concentrations and a second one with the same parameters but additional injection of secondary air. Instantaneous as well as average distributions of the measured quantities are presented and discussed. The measured soot distributions exhibit a high temporal and spatial dynamic. This behaviour correlates with broad temperature probability density functions. With injection of secondary air downstream of the flame zone the distributions change drastically. The data set, including PDFs of soot concentration, temperature and flow velocity, is unique in combining different laser diagnostics with a combustor exhibiting a more challenging geometry than existing validation experiments.
Lifing Requirement Based Turbine Airfoil Mass Estimation Method in Conceptual Aero-Engine Design
Authors: Bretschneider Stefan , Klingels Hermann , Donus Fabian , Weisser Meinrad
Published: May 2012

The presented paper describes a method developed by MTU Aero Engines to estimate the mass of turbine blades during multi-disciplinary conceptual design studies based on a prescribed airfoil lifetime [1, 2]. For a given material, the target lifetime can be translated into a maximally allowable material temperature and stress level. While the latter has to be maintained by an appropriate mechanical design of the turbine blades, the material temperature needs to be established by sufficient cooling air. The predominant life-limiting effects are taken into account to determine the allowable temperatures and stresses as an accumulation of the varying operating condition over a flight cycle. The applicable stress levels are then used to calculate the necessary radial area distribution of the airfoil and by this a prediction of its mass is possible. Furthermore, the methodology estimates the required amount of cooling air per airfoil cascade from the computed material temperatures. Example calculations are presented and discussed which illustrate design trends and the benefits which are gained from the proposed method.
The Architecture and Application of Preliminary Design Systems
Authors: Donus Fabian , Bretschneider Stefan , Schaber Reinhold , Staudacher Stephan
Published: May 2012

The development of every new aero-engine follows a specific process; a sequence of steps or activities which an enterprise employs to conceive, design and commercialize a product. Typically, it begins with the planning phase, where the technology developments and the market objectives are assessed; the output of the planning phase is the input to the conceptual design phase where the needs of the target market are then identified, and alternative product concepts are generated and evaluated, and one or more concepts are subsequently selected for further development based on the evaluation. For aero-engines, the main goal of this phase is therefore to find the optimum engine cycle for a specific set of boundary conditions. This is typically done by conducting parameter studies where every calculation point within the study characterizes one specific engine design. Initially these engines are represented as pure performance cycles. Subsequently, other disciplines, such as Aerodynamics, Mechanics, Weight, Cost and Noise are accounted for to reflect interdisciplinary dependencies. As there is only very little information known about the future engine at this early phase of development, the physical design algorithms used within the various discipline calculations must, by default, be of a simple nature. However, considering the influences among all disciplines, the prediction of the concept characteristics translates into a very challenging and time intensive exercise for the pre-designer. This is contradictory to the fact that there are time constraints within the conceptual design phase to provide the results. Since the early 1970’s, wide scale efforts have been made to develop tools which address the multidisciplinary design of aero-engines within this phase. These tools aim to automatically account for these interdisciplinary dependencies and to decrease the time used to provide the results. Interfaces which control the input and output between the various subprograms and automated checks of the calculation results decrease the possibility of user errors. However, the demands on the users of such tools are expected to even increase, as such systems can give the impression that the calculations are inherently performed correctly. The presented paper introduces MTU’s preliminary design system Modular Performance and Engine Design System (MOPEDS). The results of simple calculation examples conducted using MOPEDS show the influences of the various disciplines on the overall engine system and are used to explain the architecture of such complex design systems.
High-Dimensional Constrained Multiobjective Optimization of a Fan Stage
Authors: Aulich Marcel , Siller Ulrich
Published: May 2012

A high-dimensional design space, different objectives, many constraints and a time-consuming process chain result in a complex task for any optimization tool. This paper shows methods and strategies used at DLR, Institute of Propulsion Technology, to handle this kind of problem. The present optimization task is a rotor-stator configuration with more than two hundred free design variables, two objective functions (efficiency, stall margin) and mechanical and aerodynamic constraints (mass flow, eigenfrequencies, etc.). The process chain consists of geometry and mesh generation, FEM-and 3D-CFD calculations for different operating points. After defining the setup and explaining the initial already 3-D-preoptimized configuration, the CFD/FEM optimization tool is described. This tool calculates the complete CFD/FEM process chain and creates new designs (also called members) by using an evolutionary algorithms. Parallel to the CFD/FEM optimization a program based on surrogate models is running. By using surrogate models a fast evaluation of new members is enabled. So a database of new members can be created quickly. Based on this database a set of new members is built. This is send to the CFD/FEM optimization tool, where the complete CFD/FEM process chain is applied. After the CFD/FEM evaluation process, these member are used to train the surrogate models again. This procedure repeats until the optimization goals are reached. In the next part of this paper the implemented surrogate models are discussed. Both neural networks and Kriging models have advantages and disadvantages compared to each other. It is important to understand them to choose the right model at the right time of optimization. The main focus of this paper is on the selection criterion for new members. This criterion has two targets: push the performance of the fan stage and enhance the surrogate models. At first sight these targets seem to be contrary, but the surrogate models do not predict a single mean value for an objective. They offer a density distribution of the potential objective values. That allows calculation of the Paretofront enhancement (ParetoEnSet) for a set of new members. ParetoEnSet is the expected area gain of a set of members to the current Paretofront. This criterion based on the already known expected improvement. It is shown, that ParetoEnSet can rise, when the uncertainty of an prediction increases. The uncertainty is estimated by a surrogate model. So new members tend to explore the design space, where the predicted uncertainty is huge. These members are favorable for improving the surrogate models. In addition, it is easy to couple constraints with ParetoEnSet. In the last section the results of the optimization are illustrated. Compared to baseline design the optimized stage accomplishes a notable improvement in efficiency by obtaining the stall margin and fulfilling multi aerodynamical and mechanical constraints.
Transition Modelling for Vortex Generating Jets on Low-Pressure Turbine Profiles
Authors: Herbst Florian , Kozˇulovic´ Dragan , Seume Joerg R.
Published: May 2012

Steady blowing vortex generating jets (VGJ) on highly-loaded low-pressure turbine profiles have shown to be a promising way to decrease total pressure losses at low Reynolds-numbers by reducing laminar separation. In the present paper, the state of the art turbomachinery design code TRACE with RANS turbulence closure and coupled γ-ReΘ transition model is applied to the prediction of typical aerodynamic design parameters of various VGJ configurations in steady simulations. High-speed cascade wind tunnel experiments for a wide range of Reynolds-numbers, two VGJ positions, and three jet blowing ratios are used for validation. Since the original transition model overpredicts separation and losses at Re2is ≤ 100·103 an extra mode for VGJ induced transition is introduced. Whereas the criterion for transition is modelled by a filtered Q vortex criterion the transition development itself is modelled by a reduction of the local transition-onset momentum-thickness Reynolds number. The new model significantly improves the quality of the computational results by capturing the corresponding local transition process in a physically reasonable way. This is shown to yield an improved quantitative prediction of surface pressure distributions and total pressure losses.
Gas Path Analysis on KLM In-Flight Engine Data
Authors: Verbist Michel L. , Visser Wilfried P. J. , van Buijtenen Jos P. , Duivis Rob
Published: May 2012

Gas-path-analysis (GPA) based diagnostic techniques enable health estimation of individual gas turbine components without the need for engine disassembly. Currently, the Gas turbine Simulation Program (GSP) gas path analysis tool is used at KLM Engine Services to assess component conditions of the CF6-50, CF6-80 and CFM56-7B engine families during post-overhaul performance acceptance tests. The engine condition can be much more closely followed if on-wing (i.e., in-flight) performance data are analyzed also. By reducing unnecessary maintenance due to incorrect diagnosis, maintenance costs can be reduced, safety improved and engine availability increased. Gas path analysis of on-wing performance data is different in comparison to gas path analysis with test cell data. Generally fewer performance parameters are recorded on-wing and the available data are more affected by measurement uncertainty including sensor noise, sensor bias and varying operating conditions. Consequently, this reduces the potential and validity of the diagnostic results. In collaboration with KLM Engine Services, the feasibility of gas path analysis with on-wing performance data is assessed. In this paper the results of the feasibility study are presented, together with some applications and case studies of preliminary GPA results with on-wing data.
An Impact of Various Shroud Bleed Slot Configurations and Cavity Vanes on Compressor Map Width and the Inducer Flow Field
Authors: Sivagnanasundaram Subenuka , Spence Stephen , Early Juliana , Nikpour Bahram
Published: May 2012

This paper describes an investigation of map width enhancement and a detailed analysis of the inducer flow field due to various bleed slot configurations and vanes in the annular cavity of a turbocharger centrifugal compressor. The compressor under investigation is used in a turbocharger application for a heavy duty diesel engine of approximately 400hp. This investigation has been undertaken using a CFD model of the full compressor stage which includes a manual multi-block structured grid generation method. The influence of the bleed slot flow on the inducer flow field at a range of operating conditions has been analysed, highlighting the improvement in surge and choked flow capability. The impact of the bleed slot geometry variations and the inclusion of cavity vanes on the inlet incidence angle have been studied in detail by considering the swirl component introduced at the leading edge by the recirculating flow through the slot. Further, the overall stage efficiency and the non-uniform flow field at the inducer inlet have been also analysed. The analysis revealed that increasing the slot width has increased the map width by about 17%. However, it has a small impact on the efficiency due to the frictional and mixing losses. Moreover, adding vanes in the cavity improved the pressure ratio and compressor performance noticeably. A detail analysis of the compressor with cavity vanes has also been presented.
Numerical and Experimental Research on Periodic Solution Stability of Inclined Rotor Journal Bearing System
Authors: Qian Dashuai , Liu Zhansheng , Yan Jiajia , Sun Liquan , Wang Yongliang
Published: May 2012

Rotor bearing systems on ships usually work in inclined states when ships are swaying in wave and wind. The inclined status will affect the lubricant condition of journal bearing and bring about changes of the dynamic characteristics of the rotor system. To study the periodic solution stability of inclined rotor journal bearing system, Capone’s short bearing model is employed to describe the journal bearing support properties. Considering the inclination induced change of bearing radial load, the dynamic equation of inclined rotor system is established by using finite element method. The periodic solution stability is discussed based on bifurcation and response analysis. With the increase of rotating speed, instability of period-1 motion happens and oil whirl occurs. The motion then develops into a kind of quasi-periodic motion. Two special cases of inclined rotor system, the horizontal and the vertical cases, are compared and discussed. Both of the numerical and the experimental results show that the periodic solution unstable threshold decreases with the increase of rotor inclination angle. At last, some experimental results about influences of experiments conditions on rotor system stability are given.
Numerical and Experimental Analysis of the Effect of Variable Blade Row Spacing in a Subsonic Axial Turbine
Authors: Restemeier M. , Jeschke P. , Guendogdu Y. , Gier J.
Published: May 2012

Numerical and experimental investigations have been performed to determine the effect of a variation of the inter blade row axial gap on turbine efficiency. The geometry used in this study is the 1.5 stage axial flow turbine rig of the Institute of Jet Propulsion and Turbomachinery at RWTH Aachen University. The influence of the blade row spacing on aerodynamics has been analyzed by conducting steady and unsteady RANS simulations as well as measurements in the cold air turbine test rig of the Institute. Both potential and viscous flow interactions including secondary flow were investigated. The results show an aero-dynamic improvement of efficiency and favorable spatial distribution of secondary kinetic energy by reduction of the axial gap. It is shown that this relation tends to become less pronounced for multistage turbines.
Mechanical Properties of Titania-Doped Yttria Stabilized Zirconia (TiYSZ) for Use as Thermal Barrier Coating (TBC)
Authors: Kibsey M. , Romualdez J. , Huang X. , Kearsey R. , Yang Q.
Published: May 2012

Representative samples of Yttria Stabilized Zirconia (7YSZ) co-doped with varying concentrations of TiO2 were fabricated using plasma spraying. Samples were sintered in order to minimize porosity and to simulate the bulk material properties. After sintering, porosity levels of less than 1.25% were achieved. Both as-sprayed and sintered samples with 5, 10 and 15 wt% TiO2 addition levels were microstructurally characterized using SEM, XRD and optical image analysis methods. Vickers hardness, Young’s modulus, and fracture toughness were measured using nano and macroindentation methods. Microstructural analysis revealed that sintering of the TiO2 doped samples was required to achieve a homogeneous composition distribution, with TiO2 predominantly residing in solid solution within the ZrO2 matrix. Sintering for 325 hours at 1200°C resulted in sufficient diffusion of TiO2 into the 7YSZ. The addition of TiO2 stabilized more tetragonal phase as revealed by XRD measurement. Sintering also showed significant improvements in fracture toughness in all co-doped samples. Fracture toughness values calculated using load-independent equations provided a clear trend in fracture toughness improvement with TiO2 addition. Ferroelastic toughening of the tetragonal phase was believed to have played an effect. There was also a reduction in monoclinic phase content with TiO2 addition, which may have limited microcrack formation and consequently increased the fracture toughness. With the addition of 10 wt% TiO2, the fracture toughness was improved by over 50%; however, this improvement started to decline at 15 wt% TiO2 addition. Volumetric porosity measurements also revealed significant improvements in fracture toughness with respect to lowering the porosity content as observed in all sintered samples.
Fatigue-Life Prediction Method Based on Small-Crack Theory in an Engine Material
Authors: Newman James C. , Annigeri Balkrishna S.
Published: May 2012

Plasticity effects and crack-closure modeling of small fatigue cracks were used on a Ti-6Al-4V alloy to calculate fatigue lives under various constant-amplitude loading conditions (negative to positive stress ratios, R) on notched and un-notched specimens. Fatigue test data came from a high-cycle-fatigue study by the U.S. Air Force and a metallic materials properties handbook. A crack-closure model with a cyclic-plastic-zone-corrected effective stress-intensity factor range and equivalent-initial-flaw-sizes (EIFS) were used to calculate fatigue lives using only crack-growth-rate data. For un-notched specimens, EIFS values were 25-μm; while for notched specimens, the EIFS values ranged from 6 to 12 μm for positive stress ratios and 25-μm for R = −1 loading. Calculated fatigue lives under a wide-range of constant-amplitude loading conditions agreed fairly well with the test data from low- to high-cycle fatigue conditions.
Shock Propagation and MPT Noise From a Transonic Rotor in Non-Uniform Flow
Authors: Defoe J. J. , Spakovszky Z. S.
Published: May 2012

One of the major challenges in hig4h-speed fan stages used in compact, embedded propulsion systems is inlet distortion noise. A body-force-based approach for the prediction of multiple-pure-tone (MPT) noise was previously introduced and validated. In this paper, it is employed with the objective of quantifying the effects of non-uniform flow on the generation and propagation of MPT noise. First-of-their-kind back-to-back coupled aero-acoustic computations were carried out using the new approach for conventional and serpentine inlets. Both inlets delivered flow to the same NASA/GE R4 fan rotor at equal corrected mass flow rates. Although the source strength at the fan is increased by 45 dB in sound power level due to the non-uniform inflow, far-field noise for the serpentine inlet duct is increased on average by only 3.1 dBA overall sound pressure level in the forward arc. This is due to the redistribution of acoustic energy to frequencies below 11 times the shaft frequency and the apparent cut-off of tones at higher frequencies including blade-passing tones. The circumferential extent of the inlet swirl distortion at the fan was found to be 2 blade pitches, or 1/11th of the circumference, suggesting a relationship between the circumferential extent of the inlet distortion and the apparent cut-off frequency perceived in the far field. A first-principles-based model of the generation of shock waves from a transonic rotor in non-uniform flow showed that the effects of non-uniform flow on acoustic wave propagation, which cannot be captured by the simplified model, are more dominant than those of inlet flow distortion on source noise. It demonstrated that non-linear, coupled aerodynamic and aero-acoustic computations, such as those presented in this paper, are necessary to assess the propagation through non-uniform mean flow. A parametric study of serpentine inlet designs is underway to quantify these propagation effects.
Passive Tracer Validity for Cooling Effectiveness Through Flow Computation in a Turbine Rim Seal Environment
Authors: Boutet-Blais Guillaume , Lefrancois Julie , Dumas Guy , Julien Steve , Harvey Jean-Francois , Marini Remo , Caron Jean-Francois
Published: May 2012

This paper reports the first phase of an investigation aiming to determine the validity of using a CO2 marker in cold rig experiments to characterize the thermal performances of turbine rim seals under actual engine operating conditions. For comparison purposes, simulations are carried out for two sets of operating conditions, namely cold rig (with uniform low temperature) and real turbine thermal conditions (high temperature gaspath and cold purge flow). Sealing effectiveness based on the CO2 diagnostic under cold rig operating conditions is compared to sealing effectiveness based on the computed temperature field under real engine temperature conditions. Unsteady RANS simulations with different purge flow rates are performed. Tested geometries include a 180° domain presenting a simplified rim seal geometry with no vanes nor blades in the gaspath, and a 24° sector of a complete turbine stage including 3 vanes and 4 blades. Three-dimensional flow structures known to affect ingestion are found with both geometries but appear to be sensitive to the differences in operating conditions. Indeed, their circumferential number and strength differ between the two scenarios of conditions. Furthermore, it is found that the cold rig predictor tends to slightly overestimate the sealing effectiveness, while providing nonetheless the right trends and reasonably accurate average values in levels of actual sealing. At this stage of the investigation, we conclude that it seems adequate to use a passive tracer in cold rig experiments to compare performances of rim seal designs.
Bunsen Flame Blow-Off: Velocity-Matching Method
Authors: Huang Xia , Huang Yong , Wang Fang , Hu Bin
Published: May 2012

The effect of the incoming velocity on the anchoring point of a Bunsen flame is studied by theoretical analysis and experiments, since the anchoring point is essential to the flame holding. In order to predict the locations of the anchoring point, the velocity-matching (VM) method, which compares the profile of the flow velocity of the cold flow with that of the flame speed near the exit of a Bunsen burner, is employed together with the consideration of the cold wall quenching. The anchoring point is predicted to be located at x=Cx1u0+Cqdq0u01/2+Cx2dq0y=−Cy1SL01/2u0−1+Cy2SL0u0−2+Cy3SL01/2u0−2+Cy4. The experiment on the variation of the anchoring point with the incoming gas velocity is done with a laminar premixed methane-air flame. The equivalence ratios of the pre-mixture are 1.0, 0.9, and 0.8, respectively, and the incoming velocity is less than 2.00 m/s in the experiment. The results show that the anchoring point moves downstream and towards instead of away from the centerline of the jet as estimated by Bernard Lewis with increasing incoming gas velocity. The prediction of the locations of the anchoring point by VM method agrees well with the experiment within the uncertainty of less than ±20%.
Multi-Body Damping of a Vane Cluster
Authors: Hartung Andreas , Retze Ulrich
Published: May 2012

Spring-damper systems are standard for reducing blade vibration amplitude at vane clusters. Spring-dampers can only be used with an altered geometry of the inner shrouds. In most cases a separation of the inner shrouds is inevitable. In this paper an alternative damping system without changes of the outer inner shroud geometry is developed and analyzed. Two analytical models — a simplified Rigid Body Model and a 3D Finite Element Model show, based on similar results, a good comparison. The analytical results were validated by shaker tests. A high level of agreement between simulation and test was achieved.
Advanced Gas Turbine Diagnostics Using Pattern Recognition
Authors: Kumano Shintaro , Mikami Naotaka , Aoyama Kuniaki
Published: May 2012

Power plant owners require their plants’ high reliability, availability and also reduction of the cost in today’s power generation industry. In addition, the power generation industry is faced with a reduction of experienced operators and sophistication of power generation equipment. Remote monitoring service provided by original equipment manufacturers (OEMs) has become increasingly popular due to growing demand for both improvement of plant reliability and solution of experienced operator shortage. Through remote monitoring service, customers can benefit from swift and appropriate operational support based on OEM’s know-how. Before implementation of remote monitoring, the customer and OEM often required repeated interchanges of information about operation and instrumentation data. These interchanges took a lot of time. Data analysis and estimation of deterioration were time-consuming. Remote monitoring has enabled us, OEMs, not only to access to a plant’s real-time information but also to trace the historical operation data, and therefore the required time of data analysis and improvement has been reduced. Mitsubishi Heavy Industries, Ltd. also embarked on around-the-clock remote monitoring service for gas turbine plant over a decade ago and has increased its ability over time. At present, the application of remote monitoring systems have been extended not only into proactive maintenance by making use of diagnostic techniques carried out by expert engineers but also into building a pattern recognition system and an artificial intelligence system using expert’ knowledge. Conventional diagnostics is only determining whether the plant is being operated within the prescribed threshold levels. Pattern recognition is a state-of-the-art technique for diagnosing plant operating conditions. By comparing past and present conditions, small deterioration can be detected before it needs inspection or repair, while all the operating parameter is within their threshold levels. Mahalanobis-Taguchi method (MT method) is a technique for pattern recognition and has the advantage of diagnosing overall GT condition by combining many variables into one indicator called Mahalanobis distance. MHI has applied MT method to the monitoring of gas turbines and verified it to be efficient method of diagnostics. Now, in addition to the MT method, automatic abnormal data discrimination system has been developed based on an artificial intelligence technique. Among a lot of artificial intelligence techniques, Bayesian network mathematical model is used.
The Effects of Improved Starting Capability on Energy Yield for Small HAWTs
Authors: Worasinchai Supakit , Ingram Grant , Dominy Robert
Published: May 2012

The purpose of this study was to investigate the effect of turbine starting capability on overall energy-production capacity. The investigation was performed through the development and validation of MATLAB/Simulink models of turbines. A novel aspect of this paper is that the effects of load types, namely resistive heating, battery charging, and grid connection were also investigated. It was shown that major contributors to improved starting performance are aerodynamic improvements, reduction of inertia, and simply changing the pitch angle of the blades. The first two contributors can be attained from an exploitation of a “mixed-aerofoil” blade. The results indicate that starting ability has a direct effect on the duration that the turbine can operate and consequently its overall energy output. The overall behaviour of the wind turbine system depends on the load type, these impose different torque characteristics for the turbine to overcome and lead to different power production characteristics. When a “mixed-aerofoil” blade is used the annual energy production of the wind systems increases with the exception of resistive heating loads. Net changes in annual energy production were range of −4% to 40% depending on the load types and sites considered. The significant improvement in energy production strongly suggests that both the starting performance and load types should be considered together in the design process.
Numerical Investigation of Exhaust Diffuser Performances in Low Pressure Turbine Casings
Authors: Tanuma Tadashi , Sasao Yasuhiro , Yamamoto Satoru , Takada Shinji , Niizeki Yoshiki , Shibukawa Naoki , Saeki Hiroshi
Published: May 2012

Low pressure (LP) exhaust hoods are an important component of steam turbines. The aerodynamic loss of LP exhaust hoods is almost the same as those of the stator and rotor blading in LP steam turbines. Designing high performance LP exhaust hoods should lead further enhancement of steam turbine efficiency. This paper presents the results of exhaust hood computational fluid dynamics (CFD) analyses using last stage exit velocity distributions measured in a full-scale development steam turbine as the inlet boundary condition to improve the accuracy of the CFD analysis. One of the main difficulties in predicting the aerodynamic performance of the exhaust hoods is the unsteady boundary layer separation of exhaust hood diffusers. A highly accurate unsteady numerical analysis is introduced in order to simulate the diffuser flows in LP exhaust hoods. Compressible Navier-Stokes equations and mathematical models for nonequilibrium condensation are solved using the high-order high-resolution finite-difference method based on the fourth-order compact MUSCL TVD scheme, Roe’s approximate Riemann solver, and the LU-SGS scheme. The SST turbulence model is also solved for evaluating the eddy viscosity. The computational results were validated using the measurement data, and the present CFD method was proven to be suitable as a useful tool for determining optimum three-dimensional designs of LP turbine exhaust diffusers.
Post Combustion CO2 Capture for Combined Cycles Utilizing Hot-Water for Absorbent Regeneration
Authors: Jonshagen Klas , Sammak Majed , Genrup Magnus
Published: May 2012

The partly hot-water driven CO2 capture plant offers a significant potential for improvement in performance when implemented in a combined-cycle power plant (CCPP). It is possible to achieve the same performance with a dual-pressure steam cycle as in a triple-pressure unit. Even a single-pressure plant can attain an efficiency competitive with that achievable with a triple-pressure plant without the hot-water reboiler. The underlying reasons are better heat utilization in the heat recovery unit and less steam extraction to the absorbent regenerating unit(s). In this paper, the design criteria for a combined cycle power plant utilizing hot-water absorbent regeneration will be examined and presented. The results show that the most suitable plant is one with two steam pressure levels. The low-pressure level should be much higher than in a conventional combined cycle in order to increase the amount of heat available in the economizer. The external heat required in the CO2 capture plant is partly supplied by the economizer, allowing temperature optimization in the unit. The maximum value of the low-pressure level is determined by the reboiler, as too great a temperature difference is unfavourable. This work evaluates the benefits of coupling the economizer and the reboiler in a specially designed CCPP. In the CO2 separation plant both monoethanolamine (MEA) and ammonia are evaluated as absorbents. Higher regeneration temperatures can be tolerated in ammonia-based plants than in MEA-based plants. When using a liquid heat carrier the reboiler temperature is not constant on the hot side, which results in greater temperature differences. The temperature difference can be greatly reduced by dividing the regeneration process into two units operating at different pressures. The possibility of extracting more energy from the economizer to replace part of the extracted steam increases the plant efficiency. The results show that very high efficiencies can be achieved without using multiple pressure-levels.