bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimating the Loss Associated With Film Cooling for a Turbine Stage
Authors: Lim Chia Hui , Pullan Graham , Northall John
Published: January 2011

A methodology is presented to allow designers to estimate the penalty for turbine efficiency associated with film cooling. The approach is based on the control volume analysis of Hartsel and the entropy-based formulations of Young and Wilcock. The present work extends these techniques to include flow ejected at compound angles and uses three-dimensional CFD to provide the mainstream flow properties. The method allows the loss contribution from each hole to be identified separately. The proposed method is applied to an aeroengine high-pressure turbine stage. It is found that, if the efficiency definition includes all irreversibilities, the penalty associated with film cooling would be 8.0%. However, if the pragmatic approach is adopted whereby the unavoidable entropy generated due to the equilibration of coolant and mainstream static temperatures is ignored, the efficiency penalty is 0.7%. Finally, a series of case studies is used to quantify the impact of changes to the local mainstream flow direction and coolant ejection angle on the predicted turbine efficiency. It is shown, quantitatively, that reducing the angle between the directions of the coolant and mainstream flows offers the greatest potential for the designer to improve film cooled turbine efficiency.
Dynamic Adaptation of Aerodynamic Flame Stabilization of a Premix Swirl Burner to Fuel Reactivity Using Fuel Momentum
Authors: Sangl J. , Mayer C. , Sattelmayer T.
Published: January 2011

Due to the expected increase in available fuel gas variants in the future and the interest in independence from a specific fuel, fuel flexible combustion systems are required for future gas turbine applications. Changing the fuel used for lean premixed combustion can lead to serious reliability problems in gas turbine engines caused by the different physical and chemical properties of these gases. A new innovative approach to reach efficient, safe and low-emissions operation for fuels like natural gas, syntheses gas and hydrogen with the same burner is presented in this paper. The basic idea is to use the additionally available fuel momentum of highly reactive gases stemming from their lower Wobbe index (lower volumetric heating value and density) compared to lowly reactive fuels. Using fuel momentum opens the opportunity to influence the vortex dynamics of swirl burners designed for lowly reactive gases in a favorable way for proper flame stabilization of highly reactive fuels without changing the hardware geometry. The investigations presented in the paper cover the development of the optimum basic aerodynamics of the burner and the determination of the potential of the fuel momentum in water channel experiments using particle image velocimetry (PIV). The results show that a proper usage of the fuel momentum has enough potential to adjust the flow field to the different fuels and their corresponding flame behavior. As the main challenge is to reach flashback safe fuel flexible burner operation, the main focus of the study lies on avoiding combustion induced vortex breakdown (CIVB). The mixing quality of the resulting injection strategy is determined applying laser induced fluorescence (LIF) in water channel tests. Additional OH* chemiluminescence and flashback measurements in an atmospheric combustion test rig confirm the water channel results for CH4, CH4/H2 mixtures, H2 with N2 dilution and pure H2 combustion. They also indicate a large operating window between flashback and lean blow out and show expected NOx emission levels. In summary, it is shown for a conical four slot swirl generator geometry that the proposed concept of using the fuel momentum for tuning of the vortex dynamics allows aerodynamic flame stabilization for different fuels in the same burner.
Control of Tip-Clearance Flow in a Low Speed Axial Compressor Rotor With Plasma Actuation
Authors: Jothiprasad Giridhar , Murray Robert C. , Essenhigh Katherine , Bennett Grover A. , Saddoughi Seyed , Wadia Aspi , Breeze-Stringfellow Andrew
Published: January 2011

This research investigates different dielectric barrier discharge (DBD) actuator configurations for affecting tip leakage flow and suppressing stall inception. Computational investigations were performed on a low-speed rotor with a highly loaded tip region that was responsible for stall-onset. The actuator was mounted on the casing upstream of the rotor leading edge. Plasma injection had a significant impact on the predicted tip-gap flow and improved stall margin. The effect of changing the actuator forcing direction on stall margin was also studied. The improvement in stall margin was closely correlated with a reduction in loading parameter that quantifies mechanisms responsible for end-wall blockage generation. The actuation reduced end-wall losses by increasing the static pressure of tip-gap flow emerging from blade suction-side. Lastly, an approximate speed scaling developed for the DBD force helped estimate force requirements for stall enhancement of transonic rotors.
N-Heptane: Comparison of Spray Autoignition Experiments and Single Droplet Simulations
Authors: Rickmers Peter , Eigenbrod Christian , Klinkov Konstantin
Published: January 2011

To achieve high process efficiency, modern combustion machines, inject liquid hydrocarbon fuels into compressed air at high temperatures and high pressure, resulting in a limited residence time of the fuel in the combustion chamber or a premixing duct before autoignition. The residence time however, is the only available time to provide a well stirred mixture with a lean overall equivalence ratio, near the adiabatic flammability limit, reducing the combustion temperature and in turn the production of thermal nitric oxides (NOx) produced via the Zeldovich mechanism [1]. This paper details new results of experiments conducted in a Ludwieg–tube type wind tunnel, providing high temperature (≤1000K) and pressure (≤ 1.5MPa) flows with moderate flow rates (≤ 100m/s). N-heptane was injected into the flow in a simple unobstructed jet in cross flow (JICF) configuration in the middle of the test section. Single droplet numerical simulations were then conducted with an in-house code, the closed–vessel–simulation (CVS), which allows the simulation of the autoignition of a single droplet in a closed environment with fixed overall mixture ratio, using a reduced n-heptane kinetic with 67 species and 437 reactions [2]. The simulations were compared to the spray experiments, by assuming a Rosin-Rammler distribution for the spray and mapping the CVS results onto this distribution. The results show a promising similarity of the simulations and the experiments with a spray ignition likelihood distribution that has a maximum near the MMD (Mass Median Diameter).
An Assessment of the Impact of Emerging High-Temperature Materials on Engine Cycle Performance
Authors: Tong Michael T.
Published: January 2011

Rising concerns about air quality and climate change have made environmental protection one of the most critical issues in aviation today. To achieve environmental protection that allows sustained long-term aviation growth, NASA Glenn (GRC) has been engaged in the development of advanced high-temperature materials and thermal and environmental barrier coatings under its Fundamental Aeronautics and Environmentally Responsible Aviation Programs, with specific objectives to increase engine operating temperature and efficiency, reduce cooling requirements, reduce engine weight, reduce fuel consumption, and increase engine reliability. A parametric study was performed to assess the impact of these advanced materials and coatings on engine performance, with thrust-specific fuel consumption (TSFC) and LTO (landing-and-takeoff) NOx emissions as the key metrics. An ultra-high bypass ratio (UHB) separate flow turbofan engine for an advanced twin-engine single-aisle transport (B737/A320 class aircraft), with a sea-level static thrust of 107-kN thrust (23,000-pound), was chosen for the study. This paper presents the engine performance benefits from these advanced materials and coatings.
Computational Evaluation of Adhesion and Mechanical Properties of Nanolayered Erosion-Resistant Coatings for Gas Turbines
Authors: Bielawski Mariusz , Chen Kuiying
Published: January 2011

A computational method to evaluate fracture toughness of prospective erosion-resistant coatings using a combination of first-principles density functional theory (DFT) calculations and fracture mechanics is proposed. Elastic coefficients C11, C12 and C44, the ideal work of adhesion Wad, bulk moduls B, shear moduls G, and Young’s moduls E of transition metal nitrides with a cubic structure such as TiN, CrN, ZrN, VN and HfN are calculated. Both the G/B ratio and Cauchy pressure C12-C44 indicate brittle behaviour for TiN, ZrN and HfN and more metallic behaviour for CrN and VN. The fracture toughness KIC and interfacial fracture toughness KICInt for bi-layer combinations of these five nitrides is calculated along the [100] and [110] directions. The largest KIC value is obtained for HfN (2.14 MPa·m1/2) in (100) orientation and for TiN (2.16 MPa·m1/2) in (110) orientation. The lowest fracture toughness, in both orientations, is found for CrN. Among ten coherent interfaces of the five investigated nitrides the largest value of interfacial fracture toughness, KICInt = 3.24 MPa·m1/2, is recorded for the HfN/TiN interface in the (110) orientation.
Influence of Different Shoulder Widths on Film Cooling Characteristics on GE-E3 Blade Tip
Authors: Wang Jin , Zhang D. H. , Zeng M. , Wang Q. W.
Published: January 2011

Three-dimensional simulations of squealer tip on GE-E3 blade with eight film cooling holes were numerically studied. Numerical simulations were performed to predict the leakage flow and the tip heat transfer in the tip-gap region with the κ-ε model. For the squealer tip, the depth of the cavity is 2.42 mm, and the width of the shoulder is 0.77 mm, which forms a narrow rim and a wide cavity, decreasing the coolant momentum and the tip leakage flow velocity. The cavity contributes to the improvement of the cooling effect. In view of the absence of detailed three-dimensional flow measurements in the tip region of the blade and current lack of related literatures, it is necessary to fix attention on the shoulder width. To investigate the leakage flow influenced by the rim width, the paper used the asymmetric structure. The rim width in pressure surface in the tip-gap region is different from the one in suction surface. Numerical simulations were made at three different models, which were 0.77 mm, 1.22 mm and 1.67 mm respectively on the pressure side rim, and which were 0.77 mm, 2.27 mm and 3.77 mm respectively on the suction side rim. The rim width has a significant influence on local tip heat transfer coefficient distribution and the tip leakage flow. The detailed information was obtained under global blowing ratios of M = 0.5, 1.0 and 1.5. In addition, varying rim width models of squealer tip without film cooling holes were compared with those with film cooling holes.
Simulation of Tip-Timing Measurements of a Cracked Bladed Disk Forced Response
Authors: Kharyton Vsevolod , Laine Jean-Pierre , Thouverez Fabrice , Kucher Olexiy
Published: January 2011

The study intends to simulate the process of the blade tip amplitude calculation by the tip-timing method. An attention is focused on tip-timing measurements for detection of a cracked blade from the bladed disk forced response. The cracked blade is considered within frameworks of the bladed disk dynamic model that takes into account mistuning presence. Nonlinear formulation of a crack behavior is done with the harmonic balance method in its combination with the contact analysis that allows simulation of crack breathing. In order to make the cracked blade detection process evident, the crack length and location are set in such a way as to produce the cracked blade frequency localization. Reconstruction of the blade tip amplitudes is attained with the arriving time of measured probes of the blade tips. The results are compared with the blade forced response obtained by the bladed disk dynamic model. A possibility is also considered how to reconstruct time-history of the bladed disk forced response with tip-timing data.
Identification of Numerical Squeeze-Film Damper Models for Efficient Aeroengine Vibration Analysis
Authors: Groves Keir , Bonello Philip
Published: January 2011

The accuracy of the dynamic analysis of rotor systems incorporating squeeze film damper (SFD) bearings is typically limited by a trade-off between the capabilities and the computational cost of the bearing model used. Simplified solutions to the Reynolds equation such as short and long bearing models, and their variants, while providing rapid solution, significantly restrict the general applicability of the solutions. Numerical solutions to the Reynolds equation allow its solution in full form, with a variety of boundary conditions. Solving the Reynolds equation numerically imposes a significant computational cost on the dynamical analysis, rendering it computationally prohibitive for industrial applications. To surmount this problem, the present paper develops the use of Chebyshev polynomial fits to mimic the hydrodynamic relationship obtained through the finite difference (FD) solution of the incompressible Reynolds equation. In order to overcome limitations of previous interpolation approaches, the proposed method has three features: (i) a reduced number of input variables with a clearly defined finite range; (ii) interpolation of the pressure rather than the bearing force; (iii) division of the pressure function into its static and dynamic parts. These manipulations allow for efficient and accurate identification in the presence of cavitation and the presence of the groove, feed-ports and end-plate seals. The ability of Chebyshev polynomials to rapidly reproduce results obtained using FD routines is demonstrated. The advanced bearing models developed are proven to give more accurate results than alternative analytical bearing models when compared to experimental results.
Shape Optimization of a Laidback Fan-Shaped Film-Cooling Hole to Enhance Cooling Performance
Authors: Lee Ki-Don , Kim Kwang-Yong
Published: January 2011

Shape optimization of a laidback fan-shaped film-cooling hole has been performed by surrogate-based optimization techniques using three-dimensional Reynolds-averaged Navier-Stokes analysis. Spatially-averaged film-cooling effectiveness has been maximized for the optimization. The injection angle of the hole, the lateral expansion angle of the diffuser, the forward expansion angle of the hole, and the ratio of the length to the diameter of the hole are chosen as design variables, and thirty-five experimental points within design space are selected by Latin hypercube sampling. Basic surrogate models, such as second-order polynomial response approximation (RSA), Kriging meta-modeling technique, radial basis neural network (RBNN), are constructed using the analysis results, and the PBA model is composed from these basic surrogate models with the weights being calculated for each basic surrogate. The optimal points are searched from the above constructed surrogates by sequential programming (SQP). It is shown that use of multiple surrogates increases the robustness in prediction of better design with minimum computational cost.
Simulation of Particle Trajectories and Erosion Through a Centrifugal Compressor
Authors: Ghenaiet Adel
Published: January 2011

Under particulate environments, turbocompressors suffer from erosion which is of serious concern to both manufacturers and users of these equipments. In this paper, the results of a numerical study of particle laden air flows through a radial compressor ‘Schwitzer’ are presented. Particle trajectories used an updated version of our in-house code based on a stochastic Lagrangian tracking approach, where equations of particle motion are solved separately from the air-stream. This latter considers the effects of turbulence on particles, initial locations of particles and random particle size and rebound. The tracking of particles in different computational cells and theirs corresponding impacts used the finite element method. The number of particles, their sizes and initial positions were specified according to a concentration profile and an AC coarse (0–200 micron) size distribution. The simulations results are depicting that the impeller rotating speed and particle size strongly affect the trajectories, locations of impacts and erosion rates. For a high rotational speed, erosion is spreading over the pressure side of the main blade and splitter. Regions of high erosion rates are seen on the blades leading edges and towards the upper corner at blade exit. However, the main blade is highly eroded than the splitter. The suction side is almost without erosion except near the leading edge. Furthermore, the casing is mainly affected over the inducer and along the tips of blades.
Performance Deterioration of Intake Air Filters for Gas Turbines in Offshore Installations
Authors: Brekke Olaf , Bakken Lars E.
Published: January 2011

Efficient inlet air filtration is a key element for limiting fouling, erosion, and corrosion in the compressor section of offshore gas turbine installations. Current filtration systems are normally successful in preventing serious erosion and corrosion problems in the compressor section, but significant performance deterioration caused by compressor fouling still remains a challenge. This performance deterioration increases fuel consumption and emissions and has a particularly severe economic impact when it reduces oil and gas production. Operating experience from different offshore installations has shown that the deterioration rate in gas turbine performance increases when the turbines are operating in wet or humid weather and that the differential pressure loss over the intake system is affected by ambient humidity. An experimental test rig has been built in the laboratory at the Norwegian University of Science and Technology (NTNU) in order to increase understanding of the fundamentals related to gas turbine inlet air filtration. This paper presents the results from an experimental investigation of the performance of gas turbine inlet air filter elements that have been in operation offshore. Performance under both dry and wet conditions is assessed. Different types of filter elements show significantly different changes in differential pressure signature when exposed to moisture, and all of the tested filter elements demonstrate a loss of accumulated contamination after operating in wet conditions. Hence, contaminants originally accumulated by the filter elements are re-entrained into the airstream on the downstream side of the filters when they are exposed to moisture. The change in differential pressure signature as a result of operating in wet conditions demonstrates another weakness of solely applying differential pressure for condition monitoring of the filter system.
CFD Aerodynamic and Reactive Study of an Innovative Lean Combustion System in the Frame of the NEWAC Project
Authors: Marini Alessandro , Bucchieri Lorenzo , Peschiulli Antonio
Published: January 2011

This paper deals with the very last activities carried out by EnginSoft in the frame of the EU funded research programme NEWAC. The work regards the pre-production numerical tests performed on the single annular combustor with the purpose of verify its performance in reactive frame. The core of this study is the innovative lean-burn injection system technology, developed by University of Karlsruhe and AVIO for medium OPR. Such device has been widely investigated in previous activities in order to optimise the combustor layout and the numerical procedure for this work [1].
Modal Stress Efficiency Scaling for Gas Turbine Combustion Systems
Authors: Day W. David , Auerbach Scott
Published: January 2011

Can-annular combustion systems for gas turbines are complex assemblies of relatively thin components made of heat resistant alloys or superalloys. The thermal environment requires minimal structural constraints in order to accommodate deformation due to thermal growth and expansion. As a result, the systems have the potential to be rich in modes within the range of combustion dynamic frequencies. The natural frequencies of the system are extremely sensitive to variations in contact, damping and thickness. Combustion dynamic frequencies vary, to some extent, from can-to-can and engine-to-engine. Frequencies can also change with ambient conditions, engine load and emissions tuning. Tuning the design to avoid resonant frequencies can be extremely difficult or impractical. A method for determining which modes are likely to be responsive to combustion drivers, for obtaining approximate response magnitudes, for identifying limiting locations, and for comparing two design concepts, would be a great aid to combustion system designers. An analytical technique is proposed for scaling modal stresses. This technique, hereafter referred to as modal stress efficiency scaling (or the acronym MOSES), includes the effect of the efficiency with which a traveling sine wave couples with structural modes of differing wavelengths. Excitation is assumed to come from stationary waves impacting exposed surfaces simultaneously as well as waves traveling in all 3 orthogonal directions. Excitation due to base motion in 3 axis is also considered. In order to quickly evaluate multiple sources of excitation, this technique assumes the driver is at resonance. It is assumed that the modes are widely spaced so no modal superposition is considered. As a result of these simplifications, the response is simple rather than complex. No phase relationships are calculated. The result is the mode shape scaled by the calculated efficiency factor. The method was applied to a combustion system component with a history of cracking, and a low emissions redesign expected to eliminate the problem. The technique identified modes most likely to be excited, and predicted substantially lower responses and stresses in the new design. Results were validated through instrumented engine testing conducted with multiple accelerometers and pressure transducers on engines with each design. Acceleration measurements from these tests confirmed MOSES’s identification of the harmful response and demonstrated the robustness of the redesigned component. The MOSES technique is demonstrated to be a useful tool for root cause analysis as well as for design of combustion hardware.
Measurements of Density Pulsations in the Outlet Nozzle of a Combustion Chamber by Rayleigh-Scattering Searching Entropy Waves
Authors: Rausch Anne , Fischer Andre , Konle Holger , Gaertlein Andrea , Nitsch Steffen , Knobloch Karsten , Bake Friedrich , Ro¨hle Ingo
Published: January 2011

The development of measurement techniques which enable temporal and spatial highly resolved density investigations even in harsh environments is essential. Rayleigh-Scattering is a non-invasive optical measurement technique permitting such investigations. A Rayleigh-Scattering measurement system is set up, providing a new insight into fluid mechanical processes in turbo machines. In this paper Rayleigh-Scattering is used for the detection of density oscillations in the optical accessible convergent-divergent outlet nozzle of a small scale combustion test rig at various power consumptions and equivalence ratios. Until now this part of the combustion chamber is sparsely investigated due to the challenging measurement conditions. The temporal density oscillation inside the nozzle can be shown up to 4kHz as well as its spatial distribution. Systematic errors of the setup are investigated. Spectra of pressure and density oscillations are compared. Measurements with non-reacting air flow are conducted to study flow induced density fluctuations. Entropy noise related correlations between density and pressure fluctuations are found. Therewith, the built up Rayleigh-Scattering system enables investigations of the presumed region of indirect noise generation.
A New Analysis Tool Assessment for Rotordynamic Modeling of Gas Foil Bearings
Authors: Howard Samuel A. , San Andre´s Luis
Published: January 2011

Gas foil bearings offer several advantages over traditional bearing types that make them attractive for use in high-speed turbomachinery. They can operate at very high temperatures, require no lubrication supply (oil pumps, seals, etc), exhibit very long life with no maintenance, and once operating airborne, have very low power loss. The use of gas foil bearings in high-speed turbomachinery has been accelerating in recent years, although the pace has been slow. One of the contributing factors to the slow growth has been a lack of analysis tools, benchmarked to measurements, to predict gas foil bearing behavior in rotating machinery. To address this shortcoming, NASA Glenn Research Center (GRC) has supported the development of analytical tools to predict gas foil bearing performance. One of the codes has the capability to predict rotordynamic coefficients, power loss, film thickness, structural deformation, and more. The current paper presents an assessment of the predictive capability of the code, named XLGFBTH©. A test rig at GRC is used as a simulated case study to compare rotordynamic analysis using output from the code to actual rotor response as measured in the test rig. The test rig rotor is supported on two gas foil journal bearings manufactured at GRC, with all pertinent geometry disclosed. The resulting comparison shows that the rotordynamic coefficients calculated using XLGFBTH© represent the dynamics of the system reasonably well, especially as they pertain to predicting critical speeds.
A High-Efficiency Heat Exchanger for Closed Cycle and Heat Recovery Gas Turbines
Authors: Catalano Luciano Andrea , De Bellis Fabio , Amirante Riccardo , Rignanese Matteo
Published: January 2011

Designing and manufacturing high-efficiency heat exchangers is usually considered a limiting factor in the development of both heat recovery Joule-Brayton cycles and closed-cycle (external combustion) gas turbine plants. In this work, an innovative heat exchanger is proposed, modeled and partially tested to validate the developed numerical model employed for its design. The heat exchanger is based on an intermediate medium (aluminum oxide Al2O3) flowing in counter-current through an hot stream of gas. In this process, heat can be absorbed from the hot gas, temporarily stored and then similarly released in a second pipe, where a cold stream is warmed up. A flow of alumina particles with very small diameter (of the order of hundreds of micron) can be employed to enhance the heat transfer. Experimental tests demonstrate that simple one-dimensional steady equations, also neglecting conduction in the particles, can be effectively employed to simulate the flow in the vertical part of the pipe, namely to compute the pipe length required to achieve a prescribed heat exchange. On the other side, full three-dimensional Computational Fluid Dynamics (CFD) simulations have been performed to demonstrate that a more thorough gas flow and particle displacement analysis is needed to avoid some geometrical details that may cause a bad distribution of alumina particles, and thus to achieve high thermal efficiency.
Unsteady RANS Simulations of a Highly Loaded Low Aspect Ratio Compressor Stator Cascade With Active Flow Control
Authors: Gmelin Christoph , Steger Mathias , Thiele Frank , Huppertz Andre´ , Swoboda Marius
Published: January 2011

A highly loaded compressor cascade is analyzed by means of time-resolved 3D RANS simulations. Due to the low aspect ratio of the cascade, strong three-dimensional effects emerge, such as large corner vortices and trailing edge separation at the midspan. The feasibility of the simulation using a commercial software and the applicability of controlling the separated regions using zero net mass flux synthetic jets is analyzed. The work includes two control concepts that are investigated separately. One aims to affect the secondary flow emerging from the sidewalls via actuation at the cascade casing walls. The other aims to reattach the separated flow to the blade suction side using an actuator on the blade. Beneficial flow control parameters characterizing a synthetic jet are determined for both locations by a systematic variation. Special attention is drawn to the global efficiency of the stator cascade by means of total pressure loss and pressure rise.
Local Measurements of Disc Heat Transfer in Heated Rotating Cavities for Several Flow Regimes
Authors: Gu¨nther Andre´ , Uffrecht Wieland , Odenbach Stefan
Published: January 2011

This paper discusses experimental results from a two cavity test rig representative for the internal air system of a high pressure compressor. Thermal steady state measurements of the time-averaged local heat fluxes on both sides of the mid disc are presented for three different flow regimes: pure axial throughflow of cooling air and axial throughflow of cooling air in two directions with a superposed radial inflow of hot air in one cavity. Mass flow ratios between 1/40 < mrad/max < 2/1 are measured. Tests were carried out for a wide range of non-dimensional parameters: Re φ up to 107, Rez up to 2 × 105 and Cw up to −2.5 × 104. In all cases the shroud is uniformly heated to approximately 100°C. The local axial heat fluxes are determined separately for both sides of the mid disc from measurements of the surface temperatures with open spot-welded thermocouples. The method of heat flux determination and an analysis approach calculating the uncertainties and the sensitivity are described and discussed. The local heat flux results of the different flow paths are compared and interpreted by assumed flow structures. The time-averaged heat flux results can adequately be interpreted by flow structures of two toroidal vortices for axial throughflow and a source-sink flow for the radial inflow. The measurements show that the axial heat flux can change the direction, i.e. areas exist where the disc is heated and not cooled by the flow. For axial throughflow a local minimum of heat flux exists on the impinged side in the range of x = 0.65 if the axial Reynolds number is low or the rotational Reynolds number is high. On the back side a heating area exists in all tests in the lower half of the disc (x < 0.6) due to recirculated air of higher temperature. This heating area corresponds to the range of the inner vortex and increases with higher axial and rotational Reynolds numbers.
Validation of a Multi-Axial Fatigue Life Prediction Using Maximum Shear Experimental Results
Authors: Scott-Emuakpor Onome , George Tommy , Cross Charles , Wertz John , Shen M.-H. Herman
Published: January 2011

A multi-axial prediction method is used to calculate the fatigue life of components under pure torsion loading. The general life prediction method was developed based on the understanding that the total accumulated strain energy density in a fatigue and monotonic processes is the same. Due to this understanding, the fatigue life prediction method has been used to calculate fatigue cycles of components experiencing either uniaxial, transverse shear, or multi-axial loads. This manuscript extends the capability of the multi-axial prediction method by calculating the fatigue life of components under pure torsion loads. This calculation is possible because the maximum applied shear stress from a pure torsion load can be observed as two normal principal stresses. Based on some unusual results from experimental torsion fatigue, it was assumed that a linear misalignment was present in the experimental setup. With the inclusion of this correction, a comparison between experimental torsion fatigue results and the energy-based prediction method further affirms the capability to determine fatigue life cycles in a multi-axial loading state.
Probabilistic Engine Maintenance Modeling for Varying Environmental and Operating Conditions
Authors: Mu¨ller Matthias , Staudacher Stephan , Friedl Winfried-Hagen , Ko¨hler Rene´ , Weißschuh Matthias
Published: January 2011

The maintenance and reliability of aircraft engines is strongly influenced by the environmental and operating conditions they are subjected to in service. A probabilistic tool has been developed to predict shop visit arisings and respective maintenance workscope that depends on these factors. The tool contains a performance model of the engine and a number of physics-based damage mechanisms (at piece part level). The performance model includes variation of performance relevant parameters due to production scatter and delivers the conditions to determine the deterioration of the individual parts. Shop visit maintenance is modeled as a result of limitations to engine operation, e.g. reaching TGT limit, or mechanical deterioration. The influence of maintenance actions on engine performance is determined on component basis. The maintenance strategy can consist of proactive and reactive maintenance elements. The decision of repair or replacement of any single part is implemented through a sum of different logic rules in the model. The loading capacity scatter depends on the engine type and is operator independent. It is represented via data-driven distribution functions, in which the probabilities of failure, repair and replacement for each part are specified depending on the number of reference flight cycles. The loading variation is considered through a physics-based cycle weighting. The developed tool runs a Monte Carlo simulation in which a fleet of engines is modeled through their respective lifetime of maintenance and performance deterioration. Using an example it is shown that the model can describe the effects of varying environmental and operating conditions on part damage, and therefore engine maintenance cost and reliability.
Blade Thickness Effect on Impeller Slip Factor
Authors: Zhang Donghui , Di Liberti Jean-Luc , Cave Michael
Published: January 2011

A numerical study of the effect of the blade thickness on centrifugal impeller slip factor is presented in this paper. The CFD results show that generally the slip factor decreases as the blade thickness increases. Changing the thickness at different locations has different effects on the slip factor. The shroud side blade thickness has more effect on the impeller slip factor than the hub side blade thickness. In the flow direction, the blade thickness at 50% meridional distance is the major factor affecting the slip factor. The leading edge thickness has little effect on slip factor. There is an optimum thickness at the trailing edge for the maximum slip factor. For this impeller, the hub side thickness ratio of 0.5 between the trailing edge and the middle of the impeller gives the highest value of the slip factor, while the ratio of 0.25 at shroud side gives the highest value of the slip factor. A blockage factor is added into the slip factor model to include the aerodynamic blockage effect on the slip factor. The model explains the phenomena observed in the CFD results and the test data very well.
Characteristics of Tip Leakage Flow of the Turbine Blade With Cutback Squealer and Coolant Injection
Authors: Wang Jianhua , Liu Yalin , Wang Xiaochun , Du Zhineng , Yang Shijie
Published: January 2011

Experimental and numerical investigations of the tip leakage flow characteristics between turbine blade tip and stator wall (shroud) were conducted by a particle image velocimetry (PIV) system and the commercially available software CFX 11.0. A three-time scaled profile of the GE-E3 blade was used as specimen. Two rows of cylindrical film-cooling holes with 1.5mm diameter were arranged in the blade tip. One row with 5 holes was placed in pressure side just below the groove floor, and the other with 11 holes was equidistantly arranged on the tip along the mid camber line. To exhibit the generation and movement of leakage vortex, and to compare the coolant injection effects from different rows, several typical velocity profiles were captured by the PIV system. The experimental results were used as a data source to validate the turbulence model and numerical program. To better understand the mixing characteristics of the coolant injected from different rows with the leakage flow, the fluid fields of the leakage vortex and coolant flow were simulated, and the leakage mass rates from the blade tip in different coolant injection cases and different gaps were quantitatively estimated by the validated numerical program.
Effect of Evaporation on the Combustion Behaviour of Kerosene Spray Flame
Authors: Ahmadi W. , Chrigui M. , Sadiki A. , Ngoma G. D.
Published: January 2011

The aim of this paper is to investigate numerically the effects of the evaporation rate on combustion of kerosene sprays in a partially premixed pre-vaporized combustion chamber. The simulations are carried out by means of a Eulerian-Lagrangian approach under consideration of a full two-way coupling. Two different evaporation models (equilibrium and non-equilibrium ansatz) based on the uniform temperature assumption were used. The combustion is described by a BML like model modified for partially premixed combustion description as encountered in LPP (Bray-Moss-Libby Modell) configuration. Dodecane, whose chemistry was described by the flamelet model, was used as a surrogate for kerosene. To isolate the effect of evaporation on spray combustion, liquid droplets have been sprayed at different temperature conditions in a partially premixed pre-vaporized combustor as experimentally investigated in [23]. It turned out that the non-equilibrium performs well and allows achieving an overall agreement with experimental data. With this confidence in place, some parameter studies could be carried out and additional informations, that were not experimentally available, could be extracted to gain insights relevant to understanding the effects under study.
Modelling the Labyrinth Seal Discharge Coefficient Using Data Mining Methods
Authors: Pychynski Tim , Dullenkopf Klaus , Bauer Hans-Jo¨rg , Mikut Ralf
Published: January 2011

This paper presents a data-based method to predict the discharge coefficients of labyrinth seals. At first, leakage flow rate data for straight-through and stepped labyrinth seals from various sources was collected and fused in one consistent data base. In total, over 15000 data points have been collected so far covering a 25-dimensional design space. Secondly, this leakage data set was analysed using open-source Data Mining software, which provides several algorithms such as Multiple Linear Regression (MLR) and Artificial Neural Networks (ANN). The suitability of MLR and ANN for modelling labyrinth discharge coefficients and analysing system sensitivity was tested and evaluated. The developed leakage models showed promising prediction qualities within the design space covered by data. Further improvements of model quality may be achieved by continuing data analysis using advanced methods of Data Mining and enlarging the existing data base. The major advantages of the presented method over numerical or analytical models are possible automation of the modelling process, low calculation efforts and high model qualities.
Experimental and LES Investigation of a SGT-800 Burner in a Combustion Rig
Authors: Lo¨rstad Daniel , Lindholm Annika , Alin Niklas , Fureby Christer , Lantz Andreas , Collin Robert , Alde´n Marcus
Published: January 2011

The Siemens gas turbine SGT-800 has an annular combustor and 30 dry low emission burners. In order to further reduce the emission levels and to obtain improved understanding of the flow and associated flame dynamics, single burner rig tests have been performed. The laboratory measurements are complemented by Large Eddy Simulation (LES) to analyze the effect on the flame dynamics due to the transient fuel distribution and mixing process in the burner. The study includes both atmospheric and high pressure conditions. The computational model was developed jointly by Siemens Industrial Turbomachinery AB (SIT) and FOI. It is based on a finite rate chemistry LES model using a Partially Stirred Reactor (PaSR) turbulence chemistry interaction model and a two-step CH4/air mechanism developed by FOI. The results are compared to measurements performed jointly by SIT and Lund Institute of Technology. The experimental data includes wall temperature, pressure fluctuations, light intensity variation and simultaneous Planar Laser Induced Fluorescence of OH and acetone. The study is further complemented by Reynolds Averaged Navier-Stokes (RANS) calculations of the fuel concentration field evaluated to laser measurements in a water rig using the same burner configuration. Different burner fuel distributions are examined and the corresponding influence on the downstream mixing, fuel distribution and flame dynamics are studied. The results indicate that the fuel distribution upstream the flame, the detailed modeling of the fuel supply manifold, including the specification of numerical boundary conditions, and the flow in the fuel and air supply pipes, have significant influence on the flame dynamics. This is proven by the successful combustion LES of an unstable flame that experiences high flame dynamics and that a modification of the boundary conditions alters the dynamics resulting in a more stable flame. This is well in accordance with the experimental data and previous experience at SIT. The modal structures caused by the interaction between the flow, acoustics and flame dynamics are analyzed using the Proper Orthogonal Decomposition (POD) technique. The dominating modes in general originate from the burner mixing tube air-fuel-mass flow-interaction and flame-combustion chamber interaction.
Characterizing the Effects of G-Loading in an Ultra Compact Combustor via Sectional Models
Authors: LeBay Kenneth D. , Drenth Aaron C. , Thomas Levi M. , Polanka Marc D. , Branam Richard D. , Schmidt Jacob B.
Published: January 2011

The Ultra Compact Combustor (UCC) has shown viable merit for significantly improving gas turbine combustor performance. This concept combines a trapped-vortex approach with a circumferential cavity utilizing buoyancy and high g-loading to improve efficiency and reduce combustor size. Models for small engines can provide g-loading up to 4,000 g’s. However, as the scale of the combustor increases, the g-loading will necessarily decrease. Thus, the importance of understanding the effect of g-loading is pivotal to the applicability of this design to larger engine diameters. The Air Force Institute of Technology’s Combustion Optimization and Analysis Laser (COAL) laboratory studied this effect with sectional models of the UCC. By using both straight and curved sections of the radial cavity, the g-loading can be varied from 0–15,000 g’s. Particle Image Velocimetry (PIV) was used for velocity fields and turbulence statistics. Two-line Planar Laser-Induced Fluorescence (PLIF) of the hydroxyl (OH) radical was used for 2-D temperature profiles. Single-line PLIF was also used for flame location where OH concentrations were too low for temperature determination. Several cases were studied with varying both the equivalence ratio and the main/cavity mass flow ratio. Through the synthesis of velocity fields, temperature and flame location PLIF data, the effect of g-loading was accurately characterized. The immense radial acceleration acts to significantly increase the turbulent intensity present in the combusting regions. This increased turbulent intensity resulted in increased mixing and subsequently a significantly increased flame speed causing a reduced chemistry time. Because the chemistry time was reduced, there was less OH present in the main flow for the high g-load cases due to the combustion process being significantly further progressed when the cavity flow mixes with the main flow.
Passive Boundary Layer Control on a Highly Loaded Low Pressure Turbine Cascade
Authors: Martinstetter Markus , Niehuis Reinhard , Franke Matthias
Published: January 2011

The objective of this work is to investigate the performance of a highly loaded Low Pressure Turbine (LPT)-Cascade over a wide range of turbomachinery realistic Reynolds numbers, while maintaining a constant real engine Mach number. Fundamental investigations show a strong increase in total pressure loss at low Reynolds number due to an enlarged separation region on the suction surface. The aim of this paper is to reduce total pressure loss through the application of passive turbulators on the suction surface. Both, steady inflow conditions, as well as effects of rotor-stator-interaction, are considered. To identify the importance of turbulator geometry on loss reduction, three dimensional turbulator elements have been compared to a two dimensional trip. Both passive devices were located on the suction surface and the three dimensional elements performed better at high Reynolds numbers. Based on the experimental investigations, the use of passive boundary layer control can be recommended as a promising approach for loss reduction on highly loaded low pressure turbine profiles.
Rotor Components Life Evaluation Validated by Field Operation Data
Authors: Maccio` Mauro , Rebizzo Adelmo , Traversone Laura , Bordo Luca
Published: January 2011

Since E class gas turbines manufactured by Ansaldo Energia are approaching their typical life limits for their planned life cycle (100.000 EOH or 3000 start up) a detailed approach has been developed and carried out in order to guarantee main components for a life extension. This approach has become very important in order to overcome the adopted conservative design approach developed in the seventies taking into account an “ideal reference engine” and therefore focusing on the real engine featured by its history and its component peculiarity. This paper presents a complete life analysis approach which includes experimental tests, FEM analysis and life prediction for the gas turbine model AE94.2, using the 170MW-class 3000 rpm.
The Effect of Reynolds and Mach Number on End-Wall Profiling Performance
Authors: Va´zquez Rau´l , Jerez Fidalgo Vicente
Published: January 2011

This paper shows an experimental back-to-back comparison carried out between two annular cascades of identical turbine airfoils operating at the same flow conditions; one of them had axysimmetric endwalls and, the other, non-axysimmetric. The annular cascades consisted of 100 high lift, high aspect ratio and high turning blades that are characteristic of modern low pressure (LP) turbines. Upstream and downstream data were obtained with miniature pneumatic probes. The static pressure fields on the airfoil surface and the end-walls were measured with more than 200 sensors. The motivation of this work is to improve the understanding of profiled end-wall performance in the following three aspects: A. Explore the performance of profiled non-axysimmetric end-walls at off design conditions, namely its sensitivity to Reynolds and Mach numbers, analyzing how the turbine characteristics are modified. For that purpose, the experiment was carried out for a wide range of Reynolds numbers, extending from 120k to 315k, and exit Mach numbers, extending from 0.5 to 0.9. B. Determine experimentally the stagnation pressure loss improvement due to profiled non-axysimmetric end-walls in a relevant environment. C. Investigate further the physical mechanisms that govern the variation of stagnation pressure losses of profiled end-walls. CFD results are presented and are compared with experimental results in terms of total pressure loss, helicity and SKEH.