bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling Thermal Ageing Embrittlement in Turbine Rotors Using Neural Networks
Authors: Nappini Duccio , Zonfrillo Giovanni
Published: September 2014

An artificial neural network-based algorithm, which adequately captures the complexity of the temper embrittlement phenomenon in NiCrMoV steels has been developed in order to predict the FATT50% value of material as a function of the chemical composition and serviced time. The model, validated using published data, relies for its training on a very large experimental data set of serviced rotors, aged up to 88,000 hours, and it captures the interactions between input parameters using complex non-linear functions.

The results agree with considerations reported in literature and provide analytical relations between evolution of the FATT50% value at various ageing time for a specific alloy compositions, as well as the influence of the main elements in the alloy composition.
Crack Growth Under Cyclic Loading and Plasticity Conditions
Authors: Szwedowicz Jaroslaw , Bednarz Piotr , Meilgen Christoph , Samuelson Jeff
Published: September 2014

The increasing use of renewable energy sources to produce electricity requires additional operational flexibility from fossil-fuel gas and steam turbines. To compensate for renewable energy fluctuations in the electrical grid, a gas turbine (GT) engine needs to be more flexible, operating in peaking and partial loading modes as well as the base-load operation mode. Understanding how these different modes affect the lifetime of turbine components is critical to ensuring favourable RAM (Reliability, Availability, and Maintainability).

Component lifetimes in peaking modes are limited by the number of thermo-mechanical cycles that a component can experience before crack initiation. The useful lifetime of some components can be increased by basing the predicted lifetime on the number of cycles for crack initiation plus the number of cycles for the crack to reach its maximum allowable length based on the fracture toughness K1C criterion for linear elastic fracture mechanics (LEFM). This is usually accomplished by using the Paris law to predict the rate of crack growth. Once cracks are formed, further propagation depends on the states of stress and strain near the cracks. These factors, which drive crack growth, can be quantified by the energy release rate. The Paris law predicts crack growth as a function of the energy release rate under linear elastic conditions, commonly for load controlled tests with load ration R>0. However, large thermal and mechanical loading can result in plastic deformation under cyclic loading conditions.

Most GT components operate under strain controlled conditions generated by thermal loading. In this paper, a novel method is used to characterize crack growth under cyclic strain conditions in regions under plastic strain. The experimental data reveal that the rate of crack growth changes under plastic conditions in comparison with the linear elastic case. Especially compared to very high stress intensities ΔK of load controlled tests, here the allowable displacement limiting strain control matters. Applying experimental data from material tested under cyclic loading and elastic-plastic material response, component lifetime has been reliably predicted. Hereafter the developed method is referred to as elastic plastic fracture mechanics (EPFM) lifetime assessment. The EPFM approach more closely predicts the observed rate of crack growth than linear elastic fracture mechanics. LEFM over-predicts component lifetime for cracks growing in plastic regions under cyclic loading and could lead to catastrophic failure of a component. Therefore, the lifetime of a highly loaded component is more reliably assessed using the EPFM approach, as demonstrated for two alloys in this paper.
Application of the Harmonic Balance Method in Simulating Almost Periodic Turbomachinery Flows
Authors: Du Pengcheng , Ning Fangfei
Published: September 2014

The time-domain harmonic balance method is now popular in simulating unsteady turbomachinery flows. The essence of this method is that the time marching of a periodic or almost-periodic flow problem is substituted by several coupled steady computations at different time instants in the period of interest. The state-of-the-art non-uniform time sampling algorithm is adopted in our time-domain harmonic balance flow solver to simulate multistage turbomachinery unsteady flows. For a specific blade row in a multi-rows configuration, only the interactions from the adjacent blade rows are considered. A typical highly loaded 1.5 stage fan is studied as validation test case. The results showed that the non-uniform time sampling method is robust regardless of the frequencies considered. In this IGV-Rotor-Stator configuration, the interactions between the upstream-traveling rotor shock and IGV blades and the interactions between the rotor wakes and stator blades are all well captured. Thus, the time-averaged performance map obtained by the harmonic balance method with five resolved frequencies matches well with the reference time-accurate computations. The computational time of this five-frequency harmonic balance simulation is affordable, which ensures the code can be used in performing fast unsteady analysis in the design phase. Besides, the single passage unsteady calculation with the shape-correction phase shift method applied is also performed for comparison purpose. A simple interpolation technique is proposed to update the Fourier coefficients of each disturbance as frequently as possible, thus the convergence speed is enhanced. Similar results can be obtained by this shape-correction phase shift method, making it an alternative unsteady calculation module in an in-house CFD package.
The Physics of H-Darrieus Turbine Starting Behaviour
Authors: Worasinchai Supakit , Ingram Grant L. , Dominy Robert G.
Published: September 2014

This paper investigates Darrieus turbine starting behaviour and provides a resolution to the contradictory accounts of whether or not the Darrieus turbine can self-start. The paper builds on previous work proposing an analogy between the aerofoil in Darrieus motion and flapping-wing flow mechanisms. This analogy suggests that unsteadiness could be exploited to generate additional thrust and that this unsteady thrust generation is governed by rotor geometry.

To confirm the hypothesis, this investigation incorporated unsteady effects into a rotor analysis which resolved the differences between experiments and predictions made using a steady-state assumption.

The fundamental physics of starting were also studied and the rotor geometry parameters that govern the generation of unsteady thrust were explored: namely chord-to-diameter ratio and blade aspect ratio. Further simulation showed that the Darrieus rotor is prone to be locked in a deadband where the thrust is not continuous around a blade rotation. This discrete thrust is caused by the large variation of incidence angle during start-up making the Darrieus blade ineffective during part of the rotation.

The results also show that unsteady thrust can be promoted through an appropriate selection of blade aspect ratio and chord-to-diameter ratio and therefore it is possible to design rotors that have an ability to self-start. A new definition of self-starting is proposed based upon this improved understanding.
Test and Simulation of the Effects of Surface Roughness on a Shrouded Centrifugal Impeller
Authors: Cousins William T. , Yu Lei , Garofano Jacquelynn , Botros Barbara , Sishtla Vishnu , Sharma Om
Published: September 2014

Surface roughness is an important parameter in the operational efficiency and loss development of turbomachinery components. Many computational fluid dynamics (CFD) simulations are performed on turbomachinery, but often one of the common assumptions is that the surfaces are hydraulically smooth. In this work, examination of the surfaces of two cast impellers is performed and compared to machined impellers with smoother surfaces. Both impeller sets were run in a two-stage industrial chiller unit using R134a refrigerant. Test results are presented and the impact of surface roughness modeling on the design is reviewed. Also discussed is the theory of the impact of roughness on turbulent boundary layers. Details about providing the CFD simulation with the proper sand grain roughness is discussed when surface finish (R-value) in microinches (μin) is measured.
An Experimental Investigation of the Dynamic Performance of a Vertical-Application Three-Lobe Bearing
Authors: Khatri Rasish , Childs Dara W.
Published: September 2014

Dynamic performance test results are provided for a vertical-application three-lobe bearing, geometrically similar to a three-lobe bearing tested by Leader [1] to stabilize a vertical sulfur pump. The bearing has the following specifications: 100° pad arc angle, 0.64 preload, 100% offset, 101.74 mm bore diameter, 0.116 mm radial pad clearance, 76.3 mm axial length, and 100° static load orientation from the leading edge of the loaded pad. The bearing is tested at 2000 rpm, 4400 rpm, 6750 rpm, and 9000 rpm. This bearing is tested in the no-load condition and with low unit loads of 58 kPa and 117 kPa. The dynamic performance of this bearing is evaluated to determine (1) whether a fully (100%) offset three-lobe bearing configuration is more stable than a standard plain journal bearing (0.5 whirl-frequency ratio), and (2) whether a fully offset three-lobe bearing provides a larger direct stiffness than a standard fixed-arc bearing. Hot and cold clearances are measured for this bearing. Dynamic measurements include frequency-independent stiffness and damping coefficients. Bearing stability characteristics are evaluated using the whirl-frequency ratio (WFR). Test results are compared to numerical predictions obtained from a fixed-arc bearing Reynolds equation solver.

Dynamic tests show that the vertical-application three-lobe bearing does not improve stability over conventional fixed-arc bearings. The measured WFRs for the vertical-application bearing are approximately 0.4–0.5 for nearly all test cases. Predicted WFRs are 0.46 at all test points.

The vertical-application bearing dimensionless direct stiffness coefficients were compared to those for a 70% offset three-lobe bearing. Dimensionless direct stiffness coefficients at 0 kPa are larger for the vertical-application bearing by 45–48% in the loaded direction and larger by 15–26% in the unloaded direction. Thus, the vertical-application bearing does impart a larger centering force to the journal relative to the 70% offset bearing, in the no-load condition.

Predictions using both the measured hot clearance and measured cold clearance as inputs to the code are compared to the measured dynamic data. In general, the predicted direct stiffness coefficients using both the hot and cold clearances as inputs were higher than measured direct stiffnesses. The two sets of predicted cross-coupled stiffness coefficients straddle the measured cross-coupled stiffness coefficients. Predicted direct damping coefficients using both solutions were higher than measured values in most cases, but agreement between predictions and measurements improved significantly at high speeds and when applying light loads.
Multi-Objective and Multi-Disciplinary Optimization of Gas Turbine Blade Profile and Cooling System Using Conjugate Heat Transfer Analysis
Authors: Song Yingjie , Guo Zhendong , Song Liming , Li Jun , Feng Zhenping
Published: September 2014

This paper presents a multi-objective and multi-disciplinary design optimization and data mining of gas turbine blade profile and cooling system by using conjugate heat transfer analysis. A 3D multi-disciplinary aerothermal optimization and data mining is proposed and developed by integrating the global optimization method of self-adaptive multi-objective differential evolution (SMODE) algorithm based on constraint-handling method, the CHT method for aerothermal performance evaluation of gas turbine blade, the 3D blade parameterization method and the self-organization map (SOM) based data mining technique. Using CHT, a numerical investigation was carried out to evaluate the aerothermal performance of C3X model, which consists of the blade passage, the blade solid domain and the internal coolant flow passages. The results calculated by the CHT method were validated by the experimental results. A new parameterization method for modeling the blade profile and cooling system has been developed. The optimization is intended to minimize the maximum blade temperature and the temperature gradient with constraints on the coolant mass flow rate, total mass flow rate and total pressure recovery coefficient of the blade. 27 Pareto solutions are obtained after the multidisciplinary design optimization for the gas turbine blade. Detailed aerothermal analysis shows that the thermal performance of the blade is significantly improved without deteriorating the related aerodynamic performance, thereby the correctness and effectiveness of our proposed optimization method are demonstrated. The SOM-based data mining on optimization design space is also applied to explore the trade-off relations between objective functions and correlations among design variables and objective function.
Aerodynamic Analysis and Multi-Objective Optimization Design of a High Pressure Ratio Centrifugal Impeller
Authors: Guo Zhendong , Zhou Zhiming , Song Liming , Li Jun , Feng Zhenping
Published: September 2014

The design of high pressure ratio impellers is a challenging task. SRV2-O, a typical high pressure ratio centrifugal impeller is selected for the research. A good understanding of flow characteristics in the passage of SRV2-O is obtained by using 3D Reynolds-Averaged Navier-Stokes (RANS) solutions upon numerical validation. It confirms that tip leakage flow and shock wave boundary layer interactions produce the primary energy loss in this transonic impeller.

A 3D multi-objective aerodynamic optimization and data mining method named BMOE is presented and programmed by integrating a self-adaptive multi-objective differential evolution algorithm SMODE, 3D blade parameterization method based on non-uniformed B-Spline, RANS solver technique and self-organization map (SOM) based data mining technique. Using BMOE, multi-objective aerodynamic design optimization and data mining is performed for SRV2-O. 14 Pareto solutions are obtained for maximizing isentropic efficiency and total pressure ratio of the impeller. Three typical Pareto solutions, Design A with the highest efficiency, Design B with the higher efficiency and larger pressure ratio and Design C with the maximum pressure ratio, are analyzed. Detailed analysis indicates that the aerodynamic performance of optimized designs is greatly improved. Furthermore, by SOM-based data mining on optimization results, trade-off relation between objective functions and parameter influence mechanism on impeller aerodynamic performance are visualized and explored.
Nonreflecting Boundary Conditions for Aeroelastic Analysis in Time and Frequency Domain 3D RANS Solvers
Authors: Kersken Hans-Peter , Ashcroft Graham , Frey Christian , Wolfrum Nina , Korte Detlef
Published: September 2014

This paper describes the implementation of a set of nonreflecting boundary conditions of increasing approximation quality for time-accurate and time-linearized 3D RANS solvers in the time and frequency domain. The implementations are based on the computation of eigenfunctions, either analytically or numerically, of the linearized Euler or Navier-Stokes equations for increasingly complex background flows. This results in a hierarchy of nonreflecting boundary conditions based on 1D characteristics, 2D circumferential mode decomposition, and 3D circumferential and radial mode decomposition, including viscous effects in the latter, for the frequency domain solver. By applying a Fourier transform in time at the boundaries the frequency domain implementations can be employed in the time domain solver as well. The limitations of each approximation are discussed and it is shown that increasing the precision of the boundary treatment the nonreflecting property of the boundary conditions is preserved for more complex flows without incurring an excessive increase in computing time.

Results of a flutter analysis of a low pressure turbine blade obtained by time and frequency domain simulations are validated against each other and against reference results obtained with a 3D Euler frequency domain solver. The comparison of the results for different boundary conditions reveals the importance of using high quality boundary conditions.
Erosion Testing of Thermal Barrier Coatings in a High Enthalpy Wind Tunnel
Authors: Kirschner M. , Wobst T. , Rittmeister B. , Mundt Ch.
Published: September 2014

One of the major problems facing the users of aircraft engines and stationary gas turbines in dusty and dirty environments is erosion, causing engine performance deterioration. Thermal barrier coatings (TBCs) are often applied on metal engine components as combustor heat shields or tiles as well as turbine blades allowing enhanced operating temperatures and resulting in increased thermal efficiency of the turbine and also reduced fuel consumption and gaseous emission. Erosive attack by airborne dust or fly ash, coarse particles causes coating degradation resulting in lifing issues of engine components. In the present study an erosion test facility was used to simulate the mechanisms of coating degradation expected in gas turbines in a more realistic way closer to real engine conditions. A loading situation combining thermal gradient cycling and erosive media was used. The experiments has been performed with an arc heated plasma wind tunnel (total enthalpy up to 20 MJ/kg), which is available at the Institute for Thermodynamics at the University of the Federal Armed Forces in Munich, Germany. The experimental setup and the integration of the air jet erosion test rig into the existing plasma wind tunnel will be elucidated. Different plasma sprayed thermal barrier coating materials, including the standard TBC material yttria-stabilised zirconia, were investigated regarding their erosion resistance. For validation and verification, samples of nickel-based Mar-M 247 and INCO 718 alloys have been used.
Validating the Numerical Prediction of the Aerodynamics of an Axial Compressor
Authors: Wolff Torben , Herbst Florian , Freund Oliver , Liu Le , Seume Joerg R.
Published: September 2014

Numerical methods have become the basis for the aerodynamic design of turbomachinery in order to reduce the time for development cycles and associated cost. Designing modern axial compressors requires high confidence in the quality of numerical predictions. In terms of the aerodynamics, the loading of the blades as well as the efficiency targets constantly increase. Losses have to be predicted precisely and the impact of three-dimensional secondary flows, separation, and laminar-turbulent transition must be taken into account. In the present paper, the aerodynamic prediction quality of the state-of-the-art turbomachinery design code TRACE is validated against experimental data from a 2.5-stage axial compressor.

The aerodynamic prediction quality is systematically investigated to determine errors and uncertainties regarding the discretization, turbulence and transition models, and importance of considering unsteady effects. Computations are performed for several operating points and the results are validated by means of the compressors integral pressure ratio as well as by means of local pneumatic probe measurements. It is shown that using the empirical γ–ReΘ model improves the prediction quality of the boundary layers and wake flows. Time-resolved computations at the design point of the compressor show that the strength and the losses of a corner separation in both vane rows are reduced to realistic levels when the periodic-unsteady interaction with the upstream wakes is considered. The generally good aerodynamic predictions for both local and integral experimental quantities qualify TRACE for aeroelastic predictions which are planned for the future.
Numerical Investigation of the Solidity Effect on Linear Compressor Cascades
Authors: Sans J. , Resmini M. , Brouckaert J.-F. , Hiernaux S.
Published: September 2014

Solidity in compressors is defined as the ratio of the aerodynamic chord over the peripheral distance between two adjacent blades, the pitch. This parameter is simply the inverse of the pitch-to-chord ratio generally used in turbines. Solidity must be selected at the earliest design phase, i.e. at the level of the meridional design and represents a crucial step in the whole design process. Most of the existing studies on this topic rely on low-speed compressor cascade correlations from Carter or Lieblein. The aim of this work is to update those correlations for state-of-the-art controlled diffusion blades, and extend their application to high Mach number flow regimes more typical of modern compressors. Another objective is also to improve the physical understanding of the solidity effect on compressor performance and stability. A numerical investigation has been performed using the commercial software FINE/Turbo. Two different blade profiles were selected and investigated in the compressible flow regime as an extension to the low-speed data on which the correlations are based. The first cascade uses a standard double circular arc profile, extensively referenced in the literature, while the second configuration uses a state-of-the-art CDB, representative of low pressure compressor stator mid-span profile. Both profiles have been designed with the same inlet and outlet metal angles and the same maximum thickness but the camber and thickness distributions, the stagger angle and the leading edge geometry of the CDB have been optimized. The determination of minimum loss, optimum incidence and deviation is addressed and compared with existing correlations for both configurations and various Mach numbers that have been selected in order to match typical booster stall and choke operating conditions. The emphasis is set on the minimum loss performance at mid-span. The impact of the solidity on the operating range and the stability of the cascade are also studied.
Microstructures of NiCrAlY Coating Applied on CMSX-4 by Cathodic Arc Deposition
Authors: Zhao L. R. , Lupandina O. , Pankov V. V. , McKellar R. C.
Published: September 2014

NiCrAlY overlay coatings were applied on Ni-base single-crystal superalloy CMSX-4 substrates by cathodic arc deposition. The coated specimens were subjected to one- and two-step heat treatments performed under 870°C/20h/AC (AC stands for air cooling) and 1140°C/6h/AC+870°C/20h/AC conditions, respectively. The microstructure of the original NiCrAlY cathodes fabricated by spark plasma sintering and the as-deposited as well as heat-treated coatings were characterized using the scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction techniques. It was observed that the cathodes contained multiple phases uniformly distributed across the cathode volume. The as-deposited coatings exhibited a duplex microstructure consisting of splats and inter-splat regions with the latter showing internal porosity and a significantly lower Al concentration compared to that of the cathodes. The post-deposition heat treatments eliminated the porosity but further reduced the Al content, resulting in a coating microstructure dominated by the solid solution γ-Ni phase. The total thickness of the coating including the interdiffusion zone increased significantly during the two-step heat treatment. The oxide scale formed on the coating surface during heat treatment consisted primarily of α-Al2O3, with Y2O3 pegs underpinning the scale to the coating. The oxide scale was continuous on the smooth sections of the coating surface, but became fragmented at the protruding macroparticles present on the coating surface.
Experimental Analysis of the Unbalance Response of Rigid Rotors Supported on Aerodynamic Foil Bearings
Authors: Balducchi Franck , Arghir Mihai , Gaudillere Sylvain
Published: September 2014

The paper presents the experimental unbalance response of two slightly different rigid rotors supported by two identical aerodynamic foil bearings. Impulse (Pelton) turbines manufactured directly on the outer surface entrain both rotors at rotation speeds comprised between 50 krpm and 100 krpm. The displacements in the two foil bearings are measured during coast down and are depicted as waterfall plots. They show typical non-linear behavior, i.e. subsynchronous vibrations accompanying the synchronous component. The measurements show clearly that the subsynchronous components bifurcate at typical rotation speeds (mostly rational fractions of the rotation speed). The non-linear behavior of the rigid rotor supported on foil bearings is also underlined by varying the added unbalance: with increasing unbalance the vibration spectrum becomes gradually richer as new subsynchronous vibrations appear.

The experimental results are compared with very simplified theoretical predictions based on the assumption that the air film in the two bearings is infinitely stiff compared to the foil structure. This latter is characterized by a cubic stiffness and a structural damping coefficient. The comparisons show only a rough qualitative agreement and enlighten the actual limits of foil bearings theoretical models.
The Influence of Tabs on Different Area Ratio Short Annular Diffusers
Authors: Cerantola D. J. , Birk A. M.
Published: September 2014

Square tabs were placed on the base of an ellipsoidal centre body in annular diffusers with length to inlet height of 12. Tests were completed with an inlet Reynolds number of 1 × 105, swirl number of 0.71, and inlet flow blockage of 0.02–0.04. Four outer walls were manufactured with area ratios of 1.61, 1.91, 2.73, and 6.18. The tabs with a projected height equivalent to the boundary layer thickness were effective at reducing the outlet distortion but at a pressure penalty for the three smaller diffusers. The largest diffuser improved back pressure coefficient 4.6% with four tabs providing a blockage of 4.7% over its bare diffuser but was 42% lower than that obtained by the AR = 2.73 diffuser with no tabs.
An All-Metal Compliant Seal Versus a Labyrinth Seal: A Comparison of Gas Leakage at High Temperatures
Authors: San Andrés Luis , Anderson Alain
Published: September 2014

Parasitic secondary flows (seals’ leakage) in centrifugal compressors and gas and steam turbines represent a substantial loss in efficiency and power delivery with an increase in specific fuel consumption. Labyrinth seals are the most common and inexpensive means of reducing secondary leakage, albeit wearing out with operation and thereby penalizing performance and even affecting rotordynamic stability. The novel Hydrostatic Advanced Low Leakage (HALO) seal is an all-metal seal with flexibly supported shoes that enable clearance self-control to effectively reduce leakage, in particular for operation with high pressure ratios and at high surface rotor speeds. This paper presents leakage tests with hot air (max. 300°C) conducted in a test rig holding a labyrinth seal and a HALO seal, both of similar diameter, axial length and clearance. The novel seal leaks much less than the labyrinth seal as the supply/discharge pressure ratio (Ps/Pa) increases. The leakage reduction is ∼50% for (Ps/Pa) < 2 and continuously dropping to 70% for (Ps/Pa) > 3.0. Thus, the savings in leakage are maximized for operation with a high pressure differential. Leakage measurements with a rotor spinning to a maximum speed of 2,700 rpm (surface speed ∼ 24 m/s) produce a slight decrease in leakage for both seals. Characterization of seal leakage in terms of a flow factor removes the effect of temperature and supply pressure; the labyrinth seal showing a constant flow factor for (Ps/Pa) > 2. Application of the novel seal technology will aid to increase system efficiency by reducing leakage and will extend maintenance intervals since it eliminates wear of components.
Blockage Effects From Simulated Thermal Barrier Coatings for Cylindrical and Shaped Cooling Holes
Authors: Whitfield Christopher A. , Schroeder Robert P. , Thole Karen A. , Lewis Scott D.
Published: September 2014

Film cooling and sprayed thermal barrier coatings (TBCs) protect gas turbine components from the hot combustion gas temperatures. As gas turbine designers pursue higher turbine inlet temperatures, film cooling and thermal barrier coatings are critical in protecting the durability of turbomachinery hardware. One obstacle to the synergy of these technologies is that TBC coatings can block cooling holes when applied to the components, causing a decrease in the film cooling flow area thereby reducing coolant flow for a given pressure ratio. In this study the effect of TBC blockages was simulated on film cooling holes for widely spaced cylindrical and shaped holes. At low blowing ratios for shaped holes the blockages were found to have very little effect on adiabatic effectiveness. At high blowing ratios, the area-averaged effectiveness of shaped and cylindrical holes decreased as much as 75% from blockage. The decrease in area-averaged effectiveness was found to scale best with the effective momentum flux ratio of the jet exiting the film cooling hole for the shaped holes.
Optimal Turbulent Schmidt Number for RANS Modeling of Trailing Edge Slot Film Cooling
Authors: Ling Julia , Elkins Christopher J. , Eaton John K.
Published: September 2014

It has been previously demonstrated that Reynolds Averaged Navier Stokes (RANS) simulations do not accurately capture the mixing between the coolant flow and the main flow in trailing edge slot film cooling configurations. Most RANS simulations use a fixed turbulent Schmidt number of either 0.7 or 0.85 to determine the turbulent scalar flux, based on the values for canonical flows. This paper explores the extent to which RANS predictions can be improved by modifying the value of the turbulent Schmidt number. Experimental mean 3D velocity and coolant concentration data obtained using Magnetic Resonance Imaging techniques are used to evaluate the accuracy of RANS simulations. A range of turbulent Schmidt numbers from 0.05 to 1.05 is evaluated and the optimal turbulent Schmidt number for each case is determined using an integral error metric which accounts for the difference between RANS and experiment throughout a 3-dimensional region of interest. The resulting concentration distribution is compared in detail with the experimentally measured coolant concentration distribution to reveal where the fixed turbulent Schmidt number assumption fails. It is shown that the commonly used turbulent Schmidt number of 0.85 over-predicts the surface effectiveness in all cases, particularly when the k-omega SST model is employed, and that a lower value of the turbulent Schmidt number can improve predictions.
Development of Anode Gas Recycle System Using Ejector for 1 KW Solid Oxide Fuel Cell
Authors: Baba Soumei , Kobayashi Nariyoshi , Takahashi Sanyo , Hirano Satoshi
Published: September 2014

An anode gas recycle system using an ejector for 1 kW solid oxide fuel cells (SOFCs) was developed to increase the electrical efficiency of combined power generation. We call this an AGR-SOFC (anode gas recycle-solid oxide fuel cell). The effects of recirculation ratio, externally steam feed rate, and fuel utilization were determined experimentally on the AGR-SOFC performance (i.e., output power, stack temperature and gas composition) using a variable flow ejector and a recirculation ratio of 0.55–0.62, overall fuel utilization of 0.72–0.84, and steam feed rate of 0–1.5 g/min. A quadrupole mass spectrometer was used to identify the recirculation ratio, the gas composition of reformed gas at the AGR-SOFC inlet, and that of the recycle gas at the outlet. Compared to one-path SOFC systems i.e. without an anode gas recycle, the AGR-SOFC was stable and generated about 15 W more electricity when the overall fuel utilization was 0.84 and the recirculation ratio was 0.622 with no steam supply. This improved performance was due to the reduced H2O concentration in the anodic gas. In addition, although the recirculation ratio did not affect the AGR-SOFC performance, a high recirculation ratio can provide steam produced via the electrochemical reaction to the injected fuel for the steam reforming process.
Effects of Design Variables on High Cycle Fatigue in Steam Turbine Stages
Authors: Chen Tie , Rogerson John , Patel Kush , Millington Peter
Published: September 2014

Modern steam turbine designs are exploring wider design space to gain improved performance. At the same time, the mechanical integrity of the steam turbine needs to be maintained. This requires an in-depth understanding of the effects of each design variable on High Cycle Fatigue (HCF) of a steam turbine stage. In a previous paper, effects of both Blade Count Ratio (BCR) and Gap Ratio (GR) were studied in a steam turbine stage. This paper studies the HCF of a new rotor blade with a narrower chord, which shows higher response. Furthermore, the effect of stagger angle of the stator blade is investigated. Their effects on aero forcing, aero damping and frequency shift are also demonstrated. A one-way coupling approach is used in this study due to its high computing efficiency.
Experimental and Numerical Investigations of Low-Swirl Multi-Nozzle Combustion in a Lean Premixed Combustor
Authors: Liu Weijie , Ge Bing , Tian Yinshen , Yuan Yongwen , Zang Shusheng , Weng Shilie , Zhang Dongfang , Cui Yaoxin
Published: September 2014

This paper presents large-eddy simulations (LES) and laser diagnostic experiments of low-swirl lean premixed methane/air flames in a multi-nozzle combustor including five nozzles with the same structure. OH Planar Laser Induced Fluorescence (PLIF) is used to observe flame shapes and identify main reaction zones. NOx and CO emissions are also recorded during the experiment. The flows and flames are studied at different equivalence ratios ranging from 0.5 to 0.8, while the inlet velocity is fixed at 6.2 m/s. Results show that the neighboring swirling flows interact with each other, generating a highly turbulent mixing zone where intensive reactions take place. The flame is stabilized above the nozzle rim and its liftoff height decreases with increasing equivalence ratio. The center flow is confined and distorted by the neighboring flows, resulting in instabilities of the center flame. Mean OH radical images reveals that the center nozzle flame is extinguished when equivalence ratio is equals to 0.5, which is successfully predicted by LES. In addition, NOx emissions show log-linear dependency on the adiabatic flame temperature, while the CO emissions remain lower than 10 ppm. NOx emissions for multi-nozzle flame are less sensitive to the flame temperature than that for single nozzle. These results demonstrate that the low-swirl multi-nozzle concept is a promising solution to achieve stable combustion with ultra-low emissions in gas turbines.
The Influences of Film Hole Size and Coolant Ejection Angle on Overall Cooling Effectiveness of Laminated Cooling
Authors: Zhang Xiao-Dong , Liu Jian-Jun , An Bai-Tao
Published: September 2014

The laminated cooling or the layered cooling configuration with integrated impingement, rib-roughed and film cooling can result in a high overall cooling effectiveness and is believed to be a promising cooling technology for the next generation of advanced gas turbines. Previous studies found that the relative locations among the film hole, impingement hole and the pin-fin (i.e., cooling element arrangement) have strong impacts on the cooling effectiveness of the laminated configuration. The laminated configurations with staggered arrangement were investigated in the present paper. Two measures were used to enhance the overall cooling effectiveness, including increasing the area ratio of film hole to cooling area and employing angled film hole. Fluid-thermal coupled computations (conjugate heat transfer) were performed for assessing the overall cooling effectiveness and the pressure coefficient, and the computation method was validated by the experimental data. The computational results for the baseline design show that the area-averaged cooling effectiveness is 0.717 at BR = 1.77 and the film cooling needs to be further enhanced. Through enlarging the diameter of the film hole from 0.8mm to 1.2mm, the lift-off of film coolant is restrained and the cooling effectiveness is increased at the downstream of film hole. By employing angled film hole, the area-averaged cooling effectiveness is increased and the coolant flow resistance is also reduced.
An Alternative Experimental Method for Establishing Detailed Internal Heat Transfer Coefficient Distributions of Complex Cooling Geometries Using IR Thermography
Authors: Kinell Mats , Utriainen Esa , Jaksch Peter
Published: September 2014

Experimental methods for obtaining heat transfer coefficients often include building an upscaled, transparent, low conductivity model to which the transient semi-infinite wall method is applied. Hence, each geometry of interest will demand time consuming manufacturing, careful preparation and the heat transfer on the obstacles themselves, e.g. ribs, has to be neglected. This paper introduces an alternative method in which real geometries in an arbitrary material can be used. At the start of the experiment, the test object is at rest with a uniform temperature. By synchronizing internal air flow using a valve with an IR-camera, the thermal response of the outer wall to a sudden change of the inside temperature will be monitored. The temperature variation over time is imported into a conjugate, 1D internal flow and solid 3D FE, transient solver which will calibrate the inner heat transfer coefficient distribution so that the temperatures of the mesh matches the recorded IR-camera temperatures.

The accuracy and reliability of this method will be shown by comparing the results of an impingement cooling case to other published experimental results. A blade or vane trailing edge triple impingement geometry is also investigated. This pose a more complex challenge than the former but which the presented method is still able to handle. This is demonstrated by comparing the evaluated time resolved surface temperatures to the measured ones.
Wind Profile Effect on Small Wind Turbine Noise Generation
Authors: Grönman Aki , Backman Jari , Avramenko Anna
Published: September 2014

Small wind turbines are usually located close to buildings, and therefore, the noise generation can be both annoying and a risk for the health. The number of wind turbine installations is growing, and the request for distributed small scale energy production is one of the future trends in the energy market. The wind behavior is usually non-linear close to the ground surface. Especially, small turbines with low nacelle heights have a relatively declined wind profile at the blades. The chosen modeling approach coupled three-dimensional RANS with the Ffowcs Williams-Hawkings acoustic analogy. A series of numerical simulations was performed to study the reliability of the modeling. Three different grids were used to study the grid independency close to the turbine nominal tip to speed ratio. A reasonable agreement in the noise trends was found between the modeling and the measurements and previous studies. This encouraged us to study three different wind profiles with a down scaled wind turbine model. The results indicate that the aerodynamic noise of small turbines is not markedly affected by the wind profile.
Application of an Advanced Creep-Fatigue Procedure for Flexible Design of Steam Turbine Rotors Based on Fracture Mechanics Methods
Authors: Sheng Shilun , Almstedt Henning
Published: September 2014

The demand for steam turbine components is driven by high efficiency but also by high plant operational flexibility. Steam turbine rotors are therefore exposed to increased temperatures and increased number of stress cycles. These aspects should be considered for life-time prediction. Fracture mechanics methods are usually applied when crack like defects are detected for new rotors but also for rotor components in service. Based on the findings a decision has to be made with respect to acceptability considering high temperature effects as well as the expected future operating regime.

For defect analysis in the high temperature range, crack initiation and crack propagation under combined creep and fatigue loading need to be taken into account. Based on fracture mechanics methods and long-term testing data, an advanced creep-fatigue procedure for the evaluation of crack initiation and crack growth has been developed within the German Creep Group W14 for creep crack growth behavior. Furthermore, recent studies show that the crack size for creep crack initiation depends on material ductility and creep strain in the ligament.

This paper demonstrates the industrial application of the abovementioned method for steam turbine rotor assessment, which has a focus on crack initiation and crack growth under creep-fatigue conditions. For crack initiation, a simplified approach based on defect size and material ductility is compared to a standard approach — Two-Criteria-Diagram (2CD). For the advanced evaluation concept, the creep crack initiation criterion is combined for analysis with a creep-fatigue crack growth procedure. The benefit of the method especially for ductile material will be highlighted.
A Study on the Effects of Geometric Non Linearities on the Un-Running Transformation of Compressor Blades
Authors: Timon Vicente P. , Corral Roque
Published: September 2014

A manufactured, cold, turbomachinery blade will deform elastically under the design centrifugal, aerodynamic and thermal loads, giving the hot blade geometry. The hot-to-cold transformation or blade unrunning process consist in the calculation of the cold blade geometry which, when subject to the design conditions, will deform to match the given hot blade geometry. This paper will use a simple spring-mass model to show how the selection of geometrically linear or large displacement, geometrically non-linear, structural solvers affect the hot-to-cold transformation for compressor blades. The geometrically linear solver gives good results below a certain value of the rotational speed, which depends on the blade geometry and on the ratio of density to elastic modulus of the blade material. Above that speed, the geometrically linear solver predicts unrealistically high deformations. This model is applied to a realistic compressor blade, showing the same behavior.
NETL Research Efforts on Development and Integration of Advanced Material Systems and Airfoil Cooling Configurations for Future Land-Based Gas Turbine Engines
Authors: Alvin M. A. , Klinger J. , McMordie B. , Chyu M. , Siw S. , Miller N. , Reddy B. V. K. , Gleeson B. , Anderson I. , Heidloff A. , Ekkad S. , Ramesh S. , Kang B.
Published: September 2014

As future land-based gas turbine engines are being designed to operate with inlet temperatures exceeding 1300°C (2370°F), efforts at NETL have been focused on developing advanced materials systems that are integrated with novel airfoil cooling architectures. Recent achievements in the areas of low cost diffusion bond coat systems applied to single- and poly-crystalline nickel-based superalloys, as well as development of thin nickel-based oxide dispersion strengthened layers are presented in this paper. Integration of these material systems with commercially cast, novel, pin-fin internal cooling airfoil arrays, tripod film cooling hole architectures, trailing edge cooling geometries, and near surface micro-channel concepts is also presented.
Experimental Investigation on Droplet Behaviour in a Transonic Compressor Cascade
Authors: Neupert Niklas , Ober Birger , Joos Franz
Published: September 2014

In recent years overspray fogging has become a powerful means for power augmentation of industrial gas turbines. Most of the studies concerning this topic focus on the problem from a thermodynamic point of view as summarized by Eisfeld and Joos [1]. Only a few studies, however, were undertaken to investigate the droplet behavior in the flow channel of a compressor. Eisfeld and Joos [2] and Ober [3] revealed qualitative results showing a large variety of two-phase phenomena present.

In this paper results of experimental investigation of a water laden flow through a compressor cascade are presented. A finely dispersed spray was used in the measurements (D10 < 10μm). Results of the droplet behavior in a transonic compressor cascade are shown in terms of shadowgraphy images and images of the blade surface film pattern. The angle of attack, the incoming velocity and the water load were varied to estimate the influence of these parameters on the flow pattern. The qualitative observations of the flow pattern are related to LDA/PDA data of the flow channel and at the outlet of the cascade. The data represents a base for numerical and mean line models of two phase compressor flow concerning droplet-wall interactions as well as flow induced breakup.
Vortex-Induced Vibration and Frequency Lock-In of an Airfoil at High Angles of Attack
Authors: Besem Fanny M. , Kamrass Joshua D. , Thomas Jeffrey P. , Tang Deman , Kielb Robert E.
Published: September 2014

Vortex-induced vibration is a fluid instability present in many areas, including offshore platforms, wind turbines, and turbomachinery. The vortices due to secondary flows exert an periodic unsteady force on the elastic structure, leading to potentially dangerous vibrations. Under certain circumstances, the shedding frequency can lock into the structure natural frequency and lead to limit cycle oscillations. These high amplitude vibrations can cause material fatigue, and are a common source of structural failure.

This work uses a frequency domain, harmonic balance, CFD code to predict the lock-in of an airfoil at very high angles of attack. The natural shedding frequency is found using a delta phase per iteration method, and the lock-in region is identified by enforcing airfoil motion at different oscillation amplitudes and frequencies. The numerical results are successfully compared to experimental data from wind tunnel testing on a NACA0012 airfoil at deep stall conditions.
Transient Forced Response Analysis of Mistuned Steam Turbine Blades During Start-Up and Coast-Down
Authors: Siewert Christian , Stüer Heinrich
Published: September 2014

It is well-known that the vibrational behavior of a mistuned bladed disk differs strongly from that of a tuned bladed disk. A large number of publications dealing with the dynamics of mistuned bladed disks is available in the literature. The vibrational phenomena analyzed in these publications are either forced vibrations or self-excited flutter vibrations. Nearly all published literature on the forced vibrations of mistuned blades disks considers harmonic, i. e. steady-state, vibrations, whereas the self-excited flutter vibrations are analyzed by the evaluation of the margin against instabilities by means of a modal, or rather than eigenvalue, analysis. The transient forced response of mistuned bladed disk is not analyzed in detail so far. In this paper, a computationally efficient mechanical model of a mistuned bladed disk to compute the transient forced response is presented. This model is based on the well-known Fundamental Model of Mistuning. With this model, the statistics of the transient forced response of a mistuned bladed disk is analyzed and compared to the results of harmonic forced response analysis.