bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Impact of Pad Flexibility on the Rotordynamic Coefficients of Tilting-Pad Journal Bearings
Authors: Gaines Jennifer E. , Childs Dara W. 
Published: August 2015

Static and dynamic load tests were performed on a three-pad, rocker-pivot, tilting-pad journal bearing (TPJB) with three interchangeable pad configurations, each with measurably different pad flexibilities. Measured dynamic-stiffness data for the bearing were readily fitted by a frequency-independent, constant-coefficient [K][C][M] model.
The test bearing had a 101 .74 mm diameter with L/D = 0.6 Tests were conducted over the speed range of 6 to 12 krpm, with unit loads varying from .172 to 1.724 MPa. An ISO VG 46 lubricant was used as the test fluid.
Pad flexibility was characterized as the change in the pad’s bending stiffness or the change in pad thickness. A finite-element model was created to predict the structural bending stiffness of each pad configuration, showing a significant pad-flexibility increase as pad thickness decreased.
To examine the effect of pad flexibility on the rotordynamic coefficients, the measured results were compared across pad configurations and showed that the pad-flexibility increase reduced the direct damping coefficients by 12–20%. As pad flexibility increased, the direct stiffness coefficients could increase or decrease, depending on the unit load. They varied from an increase of 12% at low unit loads to a decrease of 3% at high unit loads.
Results show that the pad’s structural bending stiffness or flexibility is important when predicting the bearing’s dynamic performance. Damping is consistently over-predicted when neglecting pad flexibility.
A non-dimensional pad flexibility parameter αflex was developed. It related the average deflection across the pad surface to the pad’s arc length and was to relate the pad flexibility of multiple bearings of different sizes.
A bearing code was used to predict the percent change in direct damping coefficients for rigid-pad/flexible-pivot and flexible-pad/flexible-pivot models for a surface speed of 54 m/s and a unit load of 783 kPa for the three pad configurations tested here plus five additional tested bearings from the literature. For the minimum-pad-thickness configuration tested here, the code predicted a 20% drop in predicted Cxx (off-load-axis direct damping) when comparing a model that included pad flexibility with a model that neglected pad flexibility. In terms of αflex, the two thinnest pad configurations tested here are quite flexible compared to both TPJB’s pads used in industry and previously-tested TPJB pads.
Regression-Based Modelling of a Fleet of Gas Turbine Engines for Performance Trending
Authors: Borguet S. , Léonard O. , Dewallef P. 
Published: August 2015

Module performance analysis is a well-established framework to assess changes in the health condition of the components of the engine gas-path. The primary material of the technique is the so-called vector of residuals, which are built as the difference between actual measurement taken in the gas-path and values predicted by means of an engine model. Obviously, the quality of the assessment of the engine condition depends strongly on the accuracy of the engine model.
The present paper proposes a new approach for data-driven modelling of a fleet of engines of a given type. Such black-box models can be designed by operators such as airlines and third-party companies. The fleet-wide modelling process is formulated as a regression problem that provides a dedicated model for each engine in the fleet, while recognising that all engines are of the same type. The methodology is applied to a virtual fleet of engines generated within the ProDiMES environment. The set of models is assessed quantitatively through the coefficient of determination and is further used to perform anomaly detection.
Numerical Investigation of Inlet Distortion for Different Rear Mounted Engine Installations at Taking-Off Conditions
Authors: Xie Hairun , Wu Yadong , Wang Anjenq , Ouyang Hua 
Published: August 2015

Rear mounted engines are widely used in business jet and regional jet applications. It is a “clean wing” design. The engine is mounted behind the wing, so that the inlet/exhaust of nacelle has a minor influence on the flow over the wing. The engine thrust line is close to the fuselage axis. As a result, the asymmetric yaw moment will be smaller when single engine stall occurs.
Field experience and historical data have revealed that engine aerodynamic stability and fan aeromechanics are extremely sensitive to the uniformity and steadiness of inlet flow. Engine inlet flow could be distorted and separated at various operating conditions, such as, high ground crosswind, take off, and other high angle of attack (AOA) maneuvers. As a result, strict regulations and requirements were set by certification agencies to assess: i) aircraft maneuver capability, ii) engine operating characteristics, as well as iii) aerodynamics/aeromechanics behaviors and capability, with respect to flow field surrounding the entire propulsion system.
Due to the nature of complexity of the flow field at air intake, the inlet compatibility of fuselage mounted engines becomes one of the most complicated & challenged item to meet the FAR33 as well as the FAR25 certification requirements. This research paper discusses the inlet compatibility of rear-mounted aircraft engine with respect to AOA and crosswind under various operating conditions. Models of two installed configurations, which set by relative position of engine to fuselage and wing, were created. At each case, the engine inlet flow field was calculated at various AOA and crosswind conditions. Comparisons of total pressure contours at air intake were made to assess the likelihood of flow separation. The radial and circumferential inlet distortion levels were calculated at the assumed inlet AIP location for each operating condition and installed configuration. Assessments are made based on intensive usage of CFD analysis, and substantiated by test results. The flow field information obtained by CFD calculation reveals a close coupling phenomenon exist among engine installation, AOA and inlet capability. Analytical results were also checked, and the results agreed well with that of the compliant flight tests.
Time-Domain Implementation of Higher-Order Non-Reflecting Boundary Conditions for Turbomachinery Applications
Authors: Henninger Stefan , Jeschke Peter , Ashcroft Graham , Kügeler Edmund 
Published: August 2015

The present paper demonstrates the time-domain implementation of arbitrary-order non-reflecting boundary conditions for a 3d non-linear time-accurate RANS solver for turbomachinery applications. The conditions are based on the 2d circumferential mode decomposition of the linearized Euler equations. The exact linearized conditions are non-local since they involve space-time Fourier/Laplace transforms. Time-local conditions of arbitrary order are obtained by approximation of the inverse Laplace transform Bessel function convolution kernel by sums of exponential functions. Likewise, this corresponds to a rational function approximation of the exact non-reflecting boundary kernel in the frequency-domain.
The boundary conditions are validated against two numerical test cases. The first test case mimics Tyler-Sofrin modes present in turbomachinery applications by prescribing 2d acoustic modes in a uniform flow. The second test case is concerned with the potential contamination of blade flutter analyses by spurious reflections on artificial boundaries. For the benchmark problem Standard Configuration 10, blade flutter with non-zero inter-blade phase angle, acoustic resonance generates spinning waves susceptible to reflection. Contrasting the results of non-reflecting boundary conditions of varying order of accuracy shows that low order conditions can fail for challenging cases, which emphasizes the need for an accurate non-reflecting boundary treatment.
On the Influence of Fuel Mixing and Flue Gas Recirculation on the Emissions of a Fuel Flexible Gas Turbine Combustor
Authors: Fischer Stefan , Kluß David , Joos Franz 
Published: August 2015

The main benefits of operating a combustor under flue gas recirculation conditions are the increase in efficiency of the post combustion carbon capture and storage process and the potential to reduce NOX emissions while keeping the thermal load of the gas turbine constant. The latter is primarily caused by the change in thermodynamic properties of the combustive mixture with increasing vitiation. As a result, the dominant NOX formation pathways change with increasing FGR ratio.
In a partially premixed combustor, the formation of NOX emissions can also be influenced by the fuel mixing behavior. Different setups lead to combustive mixtures with different degrees of homogeneity as well as influencing the distribution of the mixture within the combustion chamber.
In this paper the combined effects of the variation of mixture homogeneity and the flue gas recirculation ratio on the NOX emissions and the stability range is experimentally investigated for different fuel gases. The experiments are performed on the atmospheric laboratory test rig, which is equipped with a partially premixed combustor. The burner is equipped with modular fuel gas nozzles allowing for the variation of the fuel mixing behavior. Exhaust gas measurements are performed to evaluate the influence of the parameters on the emissions profile of the combustor and to compare the results to a theoretical study.
The results of this study show that the level of nitric oxide emissions as well as the potential to decrease said emissions with FGR operation is dependent on the mixing behavior of the combustor. Furthermore, the combined effects of fuel gas nozzle and FGR operation lead to a proposal of an operational strategy for the combustor which combines the advantages of low nitric oxide emissions and a broad range of stability.
Unsteady Measurements of Periodic Effects in a Transonic Compressor With Casing Treatments
Authors: Brandstetter Christoph , Wartzek Fabian , Werner Jan , Schiffer Heinz-Peter , Heinichen Frank 
Published: August 2015

Application of non-axisymmetric Casing Treatments (CTs) can extend the operating range of a transonic compressor significantly. Recent CT designs have proven successful at achieving operating range extension without efficiency loss under design conditions. Two different CT designs were investigated on a high-speed one and a half stage test rig using extensive instrumentation. The stage setup is representative of the front stage of a modern high-pressure compressor.
Results of Particle Image Velocimetry (PIV) measurements taken in the blade tip region underneath the Casing Treatment show a significantly modified flow structure compared to the Smooth Casing reference case. Blockage zone, secondary flow and shock structures are affected by the CT, especially in highly throttled operating conditions.
The stall inception process of the system with Axial Slots shows unexpected behavior, with modal activities that are not observed without CT. These activities are resolved using unsteady wall pressure and Hot Wire measurements.
Experimental Study on Orifice Discharge Coefficients in Impingement Cooling With Confined Cross Flow
Authors: Schellenberg Andre , Kinell Mats , Eriksson Daniel 
Published: August 2015

This work experimentally investigates the effects of confined cross flow and geometrical parameters in impingement flows on the jet discharge coefficient, Cd. Such cooling configurations are common in the gas turbine industry and all properties were chosen to be applicable in real applications.
The effect on Cd was studied for square edged orifices with thickness to diameter ratio l/d = 1 in the range of jet to cross flow mass velocity ratio 0 ≤ Gc/Gj ≤ 6 at a jet Reynolds number of 104. The distance between orifices in the span wise yn/d = 2.5–8 and stream wise xn/d = 2.5–7 directions as well as the spacing to the target plate z/d = 1–3 were investigated.
Generally, the conclusions from previous studies were confirmed. An exception to this was the observed increase of Cd with increasing Gc/Gj for Gc/Gj < 0.5.
A correlation was developed for the discharge coefficient with the new experimental data as function of z/d, yn/d and Gc/Gj. The resemblance to the measured data was excellent with a maximum deviation of 4%.
CFD Investigation of a Lean Premixed Burner Redesign for High Hydrogen Content Syngas Operation
Authors: Bianchini C. , Da Soghe R. , Andreini A. , Anisimov V. , Bulli A. , Dacca’ F. , Rizzo S. 
Published: August 2015

The continuous challenge to develop more efficient and cleaner combustion systems for energy production, promotes the exploitation of traditional fossil fuels in alternative energy cycles capable of abating pollutant emissions. Integrated coal gasification combined cycle (IGCC) technology for instance permits to convert standard coal and other carbon based fuels into hydrogen-rich syngas. These gases are generally used to fuel standard gas turbine engines typically designed for natural gas combustion. Due to the increased propensity to flashback with high hydrogen content, lean premixed burners usually need a specific redesign to ensure adequate flow velocity at the burner exit section so as to extend lean blow out limits.
However design practices for flashback prevention are far from being established especially for these unconventional fuels and it is therefore of interest to rely on CFD analysis to establish flame stabilization process and to predict incipient flashback. The purpose of this work is to assess the accuracy and reliability of a CFD methodology to describe the flame anchoring process and exhaust pollutant emissions in a high hydrogen syngas version of a standard swirled lean premixed burner which has been tested in a tubular test rig.
Considered numerical setup is based on the use of the Flamelet-Generated Manifolds (FGM) method which is a good choice to combine computational efficiency and detailed chemistry modelling. This work aims at providing a first assessment of the FGM model as implemented in Fluent v15 in the framework of RANS turbulence approach. Four different operating conditions at increasing pressure levels are tested and a detailed sensitivity analysis of the combustion model is provided exploring flamelet generation parameters, turbulence-chemistry interaction closures and methods to assign progress variable variance. A specifically developed detailed chemical mechanism for H2 was implemented and used to verify NOx emission predicting capabilities of three alternative methods: lookup table generated integrating with presumed PDF, automatic reactor network model based on CFD aero-thermal solution and Fluent native NOx model. Obtained results are validated against available experimental data.
Blade Resonant Forced Response Excited by Combustor Acoustic Eigenmodes
Authors: Beretta-Müller Arrigo , Szwedowicz Jaroslaw 
Published: August 2015

In accordance with common engineering practice, the main source for forced response and subsequent high cycle fatigue problems in axial turbines is classical rotor-stator interaction. This criterion determines the excitability of a blade row for its relative circumferential motion with respect to upstream and downstream blade rows that generate time dependent pressure fields due to potential and viscous flow phenomena as well as possible shock waves.
This publication focuses on a less common source of blade vibration excitation induced by acoustic eigenmodes of a combustion chamber. The article gives an overview of a historical example where acoustic pulsations had the potential for exciting harmful vibration on the adjacent first rotating turbine blade row.
A 3D acoustic FEM analysis is performed to predict acoustic eigenmodes of the combustion cavity that could potentially excite vibration of the first turbine stage. Acoustic modes in the range of the critical frequencies from the point of view of resonance with structural eigenfrequencies of neighbouring components are identified and compared to engine measurements. The knowledge gained of the critical frequencies allows for mitigation of the excitation sources with Helmholtz dampers. This paper delivers an additional excitability criterion of rotating blades by acoustic pressure fluctuations in the combustor. Turbine blade excitation is currently assessed only by considering the number of burners in the combustor chamber.
Evaluation of Experimental Data From a Highly Loaded Transonic Compressor Stage to Determine Loss Sources
Authors: Lurie David P. , Breeze-Stringfellow Andrew 
Published: August 2015

An advanced GE compressor design with high reaction and stage loading, demonstrated front stage efficiencies significantly lower than predicted by CFD calculations. The source of the efficiency miss has proven difficult to pinpoint with conventional inter-stage instrumentation. A test was performed in the NASA Glenn W7 facility with the compressor operating as both a single stage and a two stage machine allowing for the acquisition of detailed traverses at each station throughout the compressor.
This paper presents the data from this test and the GE interpretation of what the data implies, concentrating particularly on one operating point, the stage one peak efficiency point. Tracking of the calculated fluid entropy between the exit of the rotor and the exit of the stator leads to the conclusion that there is significant entropy increase in the freestream fluid outside the stator wakes and this loss is believed to be attributable to mixing loss in the rotor wakes. The loss due to wake mixing is largest, and may indeed be amplified, where the rotor wakes pile up on the pressure surface of the stator.
Bi-Stable Flame Behaviour of Heavy Duty Gas Turbine Burner: RANS, LES and Experiment Comparison
Authors: Anisimov Vyacheslav V. , Chiarioni Aldo , Rofi Luca , Ozzano Claudia , Hermeth Sebastian , Hannebique Gregory , Staffelbach Gabriel , Poinsot Thierry 
Published: August 2015

VeLoNOx™ series (Very Low NOx) burners have been developed by Ansaldo Energia to satisfy the most restrictive emissions limits required by various countries. For these combustion systems the characterization of the field of stable operating conditions is a key design element. In particular, flame transition is of paramount importance for the stability of these combustion systems. Usually, this phenomenon occurs during load ramps and is characterized by a change of the flame shape, occurring in a well-defined load range. Proper flame shape control is essential to achieve more stable operating conditions up to base load.
At transition, experiments in a full scale pressure test-rig clearly show both a modification of the flame shape, a change of the measured air side burner effective area, and a reduction of the combustion chamber wall temperatures.
LES simulations were conducted using the same boundary conditions as RANS simulations discussed in a previous work [1]. In this paper, we show that both RANS and LES were able to correctly predict flame transition and a RANS-LES-Experiment comparison is performed.
Evaluation of CFD Predictions Using Different Turbulence Models on a Film Cooled Guide Vane Under Experimental Conditions
Authors: Zhang Qingbo , Xu Huazhao , Wang Jianhua , Li Ge , Wang Lei , Wu Xiangyu , Ma Shiyan 
Published: August 2015

This paper presents a numerical investigation of the conjugate heat transfer (CHT) to calculate the steady state aerodynamic and thermal characteristics of a film cooled gas turbine vane. The commercial code ANSYS FLUENT 15.0 is applied as the numerical tool. The turbine configuration selected from NASA Energy Efficient Engine program consists of 46 vanes with two impingement baffles in forward and aft cavities. The periodic boundary condition is used to reduce the calculation cost while maintaining a reasonable accuracy of the numerical results.
Using the commercial software ANSYS ICEM 15.0, steady simulations are based on a structured grid method with the finite volume technique. In the numerical simulations, two two-equation turbulence models, i.e. the Realizable k-epsilon (k-ε) and Shear Stress Transport k-omega (SST k-ω), and a four-equation turbulence model, i.e. the V2-F model, are used. To estimate the numerical strategy, the calculated results of the Mach number distributions obtained by the three turbulence models are compared with the experimental data of Timko (NASA CR-168289). Then the detailed flow and heat transfer characteristics, including the cooling effectiveness, heat transfer coefficient distributions on the vane’s surfaces, static pressure distributions along three span-wise lines and total pressure distributions in the cascade passage are predicted. Through the comparison of the numerical results obtained under adiabatic and CHT conditions, the influences of heat conduction on vane cooling effect are discussed.
Effect of Slot Injection and Effusion Array on the Liner Heat Transfer Coefficient of a Scaled Lean Burn Combustor With Representative Swirling Flow
Authors: Andreini Antonio , Becchi Riccardo , Facchini Bruno , Picchi Alessio , Turrini Fabio 
Published: August 2015

International standards regarding polluting emissions from civil aircraft engines are becoming gradually even more stringent. Nowadays, the most prominent way to meet the target of reducing NOx emissions in modern aero-engine combustors is represented by lean burn technology. Swirl injectors are usually employed to provide the dominant flame stabilization mechanism coupled to high efficiency fuel atomization solutions. These systems generate very complex flow structures such as recirculations, vortex breakdown and processing vortex core, that affect the distribution and therefore the estimation of heat loads on the gas side of the liner as well as the interaction with the cooling system flows.
The main purpose of the present work is to provide detailed measurements of Heat Transfer Coefficient (HTC) on the gas side of a scaled combustor liner highlighting the impact of the cooling flows injected through a slot system and an effusion array. Furthermore, for a deeper understanding of the interaction phenomena between gas and cooling flows, a standard 2D PIV (Particle Image Velocimetry) technique has been employed to characterize the combustor flow field.
The experimental arrangement has been developed within EU project LEMCOTEC and consists of a non-reactive three sectors planar rig installed in an open loop wind tunnel. Three swirlers, replicating the real geometry of a GE Avio PERM (Partially Evaporated and Rapid Mixing) injector technology, are used to achieve representative swirled flow conditions in the test section. The effusion geometry is composed by a staggered array of 1236 circular holes with an inclination of 30deg, while the slot exit has a constant height of 5mm. The experimental campaign has been carried out using a TLC (Thermochromic Liquid Crystals) steady state technique with a thin Inconel heating foil and imposing several cooling flow conditions in terms of slot coolant consumption and effusion pressure drop. A data reduction procedure has been developed to take into account the non-uniform heat generation and the heat loss across the liner plate.
Results, in terms of 2D maps and averaged distributions of HTC have been supported by flow field measurements with 2D PIV technique focussed on the corner recirculation region.