bluuebunny/crossref_metadata_2025 huggingface dataset:
Advanced Multi-Cup Fuel Injector Technology for Environmentally Responsible Aviation Gas Turbine Engines
Authors: Steinthorsson Erlendur , Mansour Adel , Hollon Brian , Teter Michael , Chang Clarence
Published: August 2015

Participating in NASA’s Environmentally Responsible Aviation (ERA) Project, Parker Hannifin built and tested multipoint Lean Direct Injection (LDI) fuel injectors designed for NASA’s N+2 55:1 Overall Pressure-Ratio (OPR) gas turbine engine cycles. The injectors are based on Parker’s earlier three-zone injector (3ZI) which was conceived to enable practical implementation of multipoint LDI schemes in conventional aviation gas turbine engines. The new injectors offer significant aerodynamic design flexibility, excellent thermal performance, and scalability to various engine sizes.

The injectors built for this project contain 15 injection points and incorporate staging to enable operation at low power conditions. Ignition and flame stability were demonstrated at ambient conditions with ignition air pressure drop as low as 0.3% and fuel-to-air ratio (FAR) as low as 0.011. Lean Blowout (LBO) occurred at FAR as low as 0.005 with air at 460 K and atmospheric pressure. A high pressure combustion testing campaign was conducted in the CE-5 test facility at NASA Glenn Research Center at pressures up to 250 psi and combustor exit temperatures up to 2,033 K (3,200 °F). The tests demonstrated estimated LTO cycle emissions that are about 30% of CAEP/6 for a reference 60,000 lbf thrust, 54.8-OPR engine. This paper presents some details of the injector design along with results from ignition, LBO and emissions testing.
Methodology to Correct the Magnetic Field Effect on Thin Film Measurements
Authors: Cuadrado D. G. , Lavagnoli S. , Paniagua G.
Published: August 2015

Machined ferrous metal components may carry a magnetic field, which in rotation disturb the output of electrical sensors. To minimize the effect on the electrical instrumentation, the rotating components are usually demagnetized. However, even after the demagnetization process, a residual magnetism unavoidably remains. This paper presents a methodology to predict the effects of a rotating magnetic field induced on thin-film measurements. In addition to the prediction of the magnetic effects, a procedure to correct the spurious variation in the readings of thin film gauges has been developed to enhance the fidelity of the measurements. An analytical model was developed to reproduce the bias on the electrical signal from sensors exposed to rotor airfoils with magnets. The model is based on the Biot-Savart law to generate the magnetic field, and the Faraday’s law to calculate the electromotive force induced along the measurement circuit. The model was assessed by means of controlled experiments varying the rotor tip clearance and rotational speed. The presented methodologies allowed the correction of the magnetic field effects. The raw signal of the thin film sensors, in the absence of any correction, is prone to deliver errors in the heat flux amounting to about 8% of the mean overall value. Thanks to the developed corrective approach, the residual magnetic effect contribution to the heat flux error would be 2% at most.
Evaluation of Two Measurement Techniques to Quantify Fuel-Air Mixing of a Gas Turbine Pre-Mixer at Atmospheric Conditions
Authors: Estefanos Wessam , Bhayaraju Umesh , Hamza Mahmoud , Jeng San-Mou
Published: August 2015

In the present study, two measurement techniques are adopted to evaluate the fuel-air mixing under atmospheric conditions using an industrial fuel-air pre-mixer. These techniques are CO2 mixing and Planar Laser Induced Fluorescence (PLIF) in water. In these techniques, CO2 and fluorescent dye are injected as fuel simulants. CO2 measurements are used to validate PLIF in water. In the CO2 technique, CO2 concentrations are converted to fuel mass fractions whereas, in the PLIF technique, a modified post processing method is used to convert the LIF signal into fuel mass fraction. The experiments are conducted at the same Reynolds number and momentum flux ratio for two injection strategies. To study the effect of the flow aerodynamics on the mixing results, high speed PIV measurements are conducted in water at the same Reynolds number. A comparison of fuel concentrations measured with the CO2 and PLIF techniques shows good quantitative agreement at all momentum flux ratios. However, deviations between the two techniques are observed at high fuel concentration gradients. The unsteady mixing is evaluated using PLIF technique with high temporal resolution. Analysis of PIV and PLIF data shows that unsteady mixing is lower at regions of high fluctuations in velocity. Moreover, it is found that there is high unsteady mixing at locations where there is high concentration gradient.
Field and Laboratory Evaluations of Commercial and Next Generation Alumina-Forming Austenitic Foil for Advanced Recuperators
Authors: Pint Bruce A. , Dryepondt Sebastien , Brady Michael P. , Yamamoto Yukinori , Ruan Bo , McKeirnan Robert D.
Published: August 2015

Alumina-forming austenitic (AFA) steels represent a new class of corrosion- and creep-resistant austenitic steels designed to enable higher temperature recuperators. Field trials are in progress for commercially rolled foil with widths over 39cm. The first trial completed 3,000h in a microturbine recuperator with an elevated turbine inlet temperature and showed limited degradation. A longer microturbine trial is in progress. A third exposure in a larger turbine has passed 16,000h. To reduce alloy cost and address foil fabrication issues with the initial AFA composition, several new AFA compositions are being evaluated in creep and laboratory oxidation testing at 650°–800°C and the results compared to commercially fabricated AFA foil and conventional recuperator foil performance.
Effects of Crossflow in an Internal-Cooling Channel on Film Cooling of a Flat Plate Through Compound-Angle Holes
Authors: Stratton Zachary T. , Shih Tom I-P. , Laskowski Gregory M. , Barr Brian , Briggs Robert
Published: August 2015

CFD simulations were performed to study the film cooling of a flat plate from one row of compound-angles holes fed by an internal-cooling passage that is perpendicular to the hot-gas flow. Parameters examined include direction of flow in the internal cooling passage and blowing ratios of 0.5, 1.0, and 1.5 with the coolant-to-hot-gas density ratio kept at 1.5. This CFD study is based on steady RANS with the shear-stress transport (SST) and realizable k-ε turbulence models. To understand the effects of unsteadiness in the flow, one case was studied by using large-eddy simulation (LES). Results obtained showed an unsteady vortical structure forms inside the hole, causing a side-to-side shedding of the coolant jet. Values of adiabatic effectiveness predicted by CFD simulations were compared with the experimentally measured values. Steady RANS was found to be inconsistent in its ability to predict adiabatic effectiveness with relative error ranging for 10% to over 100%. LES was able to predict adiabatic effectiveness with reasonable accuracy.
Influence of Geometry and Test Method on Fatigue Crack Propagation Behavior of a Ni-Base Jet Engine Alloy
Authors: Lenets Youri N. , Peralta Alonso , Miller Ross , Neumann James
Published: August 2015

The majority of fatigue crack growth tests worldwide makes use of the compact tension (CT) specimens that are not necessarily representative of cracks developing under service conditions in highly stressed components of a jet engine. Over the years other geometries have been designed to facilitate a study of relatively small, semi- or quarter-elliptically shaped surface flaws subjected to high tensile and compressive stresses. Despite an extensive use by the aerospace community, practical aspects of testing and data analysis relevant to the complex surface- or corner-flawed geometries are not regulated by a commonly accepted set of rules.

Two types of test specimens — CT and surface-crack tension (SCT) — were machined from a forged and heat treated Inconel 718. For both geometries the crack orientation and propagation direction with respect to the original forging were the same.

The CT specimens were tested in accordance with the ASTM Standard E647 as well as using an alternative compression pre-cracking procedure. After correct application of the compression pre-cracking to the CT geometry both approaches had yielded reasonably consistent results. At high ΔK values both studied geometries also produced similar results, however, as the ΔK values decreased, a trend towards slower crack growth rates in the SCT specimens became evident.

In order to address a so-called small-crack effect, several SCT specimens received much smaller crack starter notches produced by the focused ion beam (FIB) technology.

The results of the present study highlight the importance of the appropriate material properties for accurate and reliable service life prediction of the critical aerospace propulsion hardware with particular emphasis on the influence of specimen/crack geometry and test method on the fatigue crack propagation behavior of jet engine alloys.
Numerical Simulation Study on Characteristics of Vertical Gravity Separator in a Kalina Cycle System
Authors: Zheng Ya , Li Saili , Hu Dongshuai , Dai Yiping
Published: August 2015

In various novel thermodynamic cycles which utilize waste heat and geothermal resources, the Kalina cycle is the most significant improvement in thermal power plant design and it has been considered as an ambitious competitor against the Organic Rankine Cycle. However, the kalina cycle faces the complicated separate process and the design of separators still depends on the experience empirical formulae. Therefore, the vertical gravity separator used for separating ammonia-water mixture plays a vital important role in this system. The separator should keep high separation performance and enable the system to operate with stability. In this paper, we propose the initial structure design of a vertical gravity separator according to the separation theories. Based on the initial structure design of separator, conventional separator has been improved by changing the structure and operational parameters, including the ammonia concentration, inlet velocity, diameter, angle and height of inlet, and that has been numerically simulated by the means of CFX in computational fluid dynamics. In-depth estimating the separating performance of vertical gravity separator, different structural and operational parameters of vertical gravity separator are simulated and discussed. The separation performance and the distribution of ammonia-water mixture are estimated including flow field, trajectories of motion of particles, pressure drop, separation efficiency and so on. The results can be expected to be of great technical interest as basis for the design of vertical gravity separators.
A Random Sampling Strategy for Tuning Contact Parameters of Underplatform Dampers
Authors: Gastaldi Chiara , Gola Muzio M.
Published: August 2015

All numerical models of friction damped bladed arrays require knowledge of contact-friction parameters, which are established either through direct frictional measurements, done with the help of a separate single contact test arrangement, or by fine tuning the parameters in the numerical model of the real damping device and comparing the experimental response of a damped blade against its computed response. Recent results from direct measurements on underplatform dampers and the subsequent cross-comparison of experimental and numerical results have put into evidence several features which are usually neglected in FE models of damper-blade systems:

– markedly different friction coefficients at different contact points;

– friction coefficients evolving with time and cycle number towards a stable shape, in a systematic and repeatable manner with dramatic consequences on the shape of the hysteresis cycle and on dissipated energy;

– particular cases where minimal variations in the friction coefficients lead to gross changes of the damper behavior;

Identifying the contact parameters to assure the best match between model and experimental results becomes crucial to guarantee that the validated damper model will produce the correct cyclic forces on the blades during vibrational motion. While the tuning process described in the previous papers was a search based on the progressive refinement whose results depended on the operator’s ability to match different patterns of the model and experimental results, this paper dwells on a more objective and controllable method based on properly chosen indicators. The latter method is based on a sampling technique (Latin Hyper-cube) which produces a large number of solutions (in the present case 5000) on the basis of randomized extractions of contact parameters (in the present case 5) between given boundaries.

An advantage of this method is a systematic exploration of the influence of each input contact parameter on the collection of output indicators, considered acceptable according to predetermined criteria.

The main indicators suited for the purpose are three, i.e., the relative errors on the real and imaginary parts of the HBM complex spring equivalent to the hysteresis cycle and a measure of shape similarity between the experimental and simulated cycle. The paper shows the selection procedure which has been adopted to produce the final set of eligible solutions, which are further reduced by applying a secondary indicator based on the similarity of a kinematical parameter. In this paper this parameter is chosen to be a measure of the shape similarity of the damper rotation during the hysteresis cycle.
Numerical Study on Flow Characteristics and Flow Induced Noise of Flexible NACA0018 Airfoil
Authors: Ma Rui-xian , Zhang Guang-hui , Liu Zhan-sheng , Li Dian-lai
Published: August 2015

A numerical investigation of unsteady flow field and flow induced noise frequency characteristics of a 2-D NACA0018 airfoil taking into account the airfoil’s deformation with different angles of attack is presented. The large eddy simulation (LES) method is employed to compute the unsteady flow field, the dynamic response of structure is simulated with finite element code, and the two different fields are coupled via a two way coupling method with the exchange of pressure and displacement. The far field sound levels and frequency features are calculated using FW-H equation with arbitrary boundary movement involved. The flow field results show that flow separation and wall pressure fluctuation are controlled by the deformation of flexible airfoil significantly, which indicates the effects of attack angle are attenuated. Compared with common quasi-periodic vortex shedding, the vortex shedding at 0 degree is obtained to be a restrict periodic process, and the shedding frequency is about 950Hz, and this phenomenon is confirmed both by wall pressure fluctuation and acoustic spectrum characteristics. In addition, the overall sound pressure levels in chordwise and normal direction are influenced by attack angle in different ways.
Trailing Edge Filings and a Modified Stodola’s Slip Factor for Centrifugal Impeller
Authors: Xi Guang , Zhao Huijing , Wang Zhiheng
Published: August 2015

The paper investigates the effect of trailing edge filing in the impeller on the performances of impeller and compressor stage. The 3D viscous numerical simulations are carried out under different positions, thicknesses and lengths of filing. The results show that, the filing on the trailing edge has an obvious effect on the pressure ratios of impeller and compressor stage. The trailing edge filing has little effect on the impeller efficiency while the filing on the pressure side is favorable to improving the stage efficiency. Then, through correcting the blade angles at the suction and pressure sides, considering the viscosity and 3D characteristics of the flow, a modified slip factor formula is proposed for the centrifugal impeller with a trailing edge filing. The validation to the proposed formula shows that the proposed formula can be used to predict the slip factors of different filing cases with a good accuracy. It can provide a theoretical guidance for the quantitative calculation when using the filing technology to improve the performance of centrifugal impeller as well as the stage.
Resonant Response and Random Response Analysis of Mistuned Bladed Disk Consisting of Directionally Solidified Blade
Authors: Kaneko Yasutomo , Mori Kazushi , Ooyama Hiroharu
Published: August 2015

Recently, DS (Directionally Solidified) and SC (Single Crystal) alloys have been widely applied for gas turbine blades instead of CC (Conventional Casting) alloys, in order to improve the creep rupture strength. The DS blade consists of several columnar grains of SC, where the growing direction of the columnar crystal is set to the direction of the centrifugal force. Because the elastic constants of the DS blade are anisotropic, the mistuning characteristics of the bladed disk consisting of the DS blades seem to be different from those of the CC blade. In this study, the resonant response and random response analysis of mistuned bladed disks consisting of the DS blades are carried out, considering the deviations of the elastic constants and the crystal angle of the DS blade. The FMM (Fundamental Mistuning Model) and the conventional modal analysis method are used to analyze the vibration response of the mistuned bladed disk. The maximum resonant response and random response of the mistuned bladed disk consisting of the DS blades are estimated by the Monte Carlo simulation combining with the response surface method. These calculated results for the DS blades are compared with those of the CC blades. From these results, it is concluded that the maximum response of the mistuned bladed disk consisting of the DS blades is the nearly same as that of the CC blades. However, in the design of the tuned blade, where the blade resonance should be avoided, it is necessary to consider that the range of the resonant frequency of the DS blade becomes wider than that of the CC blade.
Fatigue and Strength Studies of Titanium 6Al-4V Fabricated by Direct Metal Laser Sintering
Authors: Scott-Emuakpor Onome , Holycross Casey , George Tommy , Knapp Kevin , Bruns Jeffery
Published: August 2015

Vibratory bending fatigue life behavior of Titanium (Ti) 6Al-4V plate specimens has been assessed. The plates were manufactured via direct metal laser sintering (DMLS), which is a powder bed, laser deposition additive manufacturing process. Motivation for this work is based on unprecedented performance demands for sixth generation gas turbine engine technology. For example, the inclusion of a third stream flow for improving engine performance may add complexity and weight that could offset anticipated thrust and fuel efficiency gains. Therefore, complex, lightweight components with improved functionalities are desired. Novel component design concepts have been cost, schedule, and feasibility limited when using conventional manufacturing methods. Additive manufacturing, however, can extend the thresholds of component concepts. Though additive manufacturing can be a promising addition to the turbine engine community, the manufacturing process controls required to achieve consistency in material properties have not been fully identified. The work presented in this manuscript investigates variability in vibration-based bending fatigue life of DMLS Ti 6Al-4V compared to cold-rolled Ti 6Al-4V. Results show discrepancies between the fatigue life variation of DMLS and cold-rolled data. Along with the support of fusion and post-fusion process parameters, the fatigue results are also supported by tensile property characterization, fractography, and microscopy.
Investigation of an Asymmetric Double Entry Centrifugal Compressor With Different Radial Impellers Matching for a Wide Operating Range
Authors: Jing Lei , Yang Ce , Wu Wangxia , Chen Shan
Published: August 2015

The work presented here investigates the impeller matching characteristics and widens the stable operating range of front and rear impellers for an asymmetric entry double sided centrifugal compressor. A numerical approach is employed to analyze the operating characteristics of front and rear impellers, and a strategy to widen the stable operating range of double sided compressor is presented. Firstly, the performance curves of a double sided centrifugal compressor are obtained by simulating the operation of the whole-stage compressor. The result shows that the compressor operating mode switches from parallel mode to single impeller mode automatically with the decrease of the mass flow. Thus, the stable operating range of the compressor is limited. Second, the simulation of a simplified double sided compressor is conducted to reveal the mechanism of the compressor operating mode conversion. It is found that the essential reason for the conversion of the compressor operating mode is the total pressure difference between the front and rear impeller inlets. A proper increase of the rear impeller radii is helpful for improving the impeller power capability, which enables the front and rear impeller to obtain a superior matching relationship in a wider operating range and widens the stable operating range of the compressor. Furthermore, by analyzing the respective performance characteristic curves in various calculation cases, there is a critical mass flow value between the front and rear impellers for compressors with the same flow capability. When one side impeller mass flow is below the critical value, with further decrease of the flow, the pressure ratio characteristic curve of this side rises and enters the stall zone gradually. Thus, the operating mode is converted from parallel mode to single mode. This result further explains the mechanism for extending the stable operating range of a double sided compressor in a wider scope.
S-Duct Intake Configuration Sensitivity of a Highly Loaded Turboprop by CFD Methods
Authors: Atalayer Çağlar , Friedrichs Jens , Wulff Detlev
Published: August 2015

Highly-loaded turboprop intake was investigated for two different shaft connection types to assess the configuration sensitivity on performance. Turboprop intakes inherently have S-shape to bend around the gearbox, which have significant effects on the flow. Previous geometric sensitivity analysis on uninstalled, isolated single scoop S-ducts with shaft penetration showed higher recovery and lower distortion trends for long intakes with shorter ducts. The major pressure loss was observed over the bore due to the penetrating shaft. It is expected that changing the configuration to wrap-around will overcome the loss introduced by flow around the bore. The two configurations were compared by varying the S-duct curvatures using computational methods. The results showed an increase in recovery with lower total pressure distortion levels for wrap-around configuration of the same sizes. The gain in the recovery by the configuration change was observed to be similar to the gain when the ducts were shortened. However, wrap-around S-duct suffered from higher swirl distortion than shaft penetration of the same size but these were observed to be lower than the shaft penetration type with short ducts. Distortion intensities showed opposite trends for the two configurations, with wrap-around producing low distortion in circumferential whereas high in radial direction. The results will be used as the basis for the turboprop intake design and its over-the-wing integration on the high-lift aircraft.
Numerical Investigations of Tangential Direction Cooling in the Intermediate Pressure Cylinder (IPC)
Authors: Liu Liangliang , Zhou Daiwei , Liu Hao , Zhu Xiaocheng , Du Zhaohui
Published: August 2015

The cooling protection of the hot end is the key technique for ultra-supercritical steam turbine to cool the hot components. In this paper, the internal flow mechanism and cooling characteristics in the tangential direction cooling channel in the intermediate pressure cylinder (IPC) are investigated using the method of computational fluid dynamics. Various turbulence models and mesh sizes are evaluated (the k-ε model, the k-ω model, the SST model). Also, calculated results of the nonrotating bottom wall are compared with the experimental results in a previous research to show the reliability of the CFD program used. Detailed predictions of the contours of velocity, pressure and temperature are carried out. The focus of this study is to investigate the effects of inlet Mach number, turbulent Prandtl number, rotational wall speed, and inlet turbulence intensity on the cooling effectiveness of the vortex channel. The inlet Mach number, the turbulent Prandtl number, the rotational wall speed and the inlet turbulence intensity varied from 0.315 to 0.512, from 0.71 to 1.0, from 0 to 3000rpm, and from 1% to 10%, respectively. Results show that the parameters have different effects on the cooling effectiveness of the vortex cooling chamber. The cooling effect of the vortex channel increases with increasing inlet Mach number and rotational wall speed, while decreases with the increasing turbulent Prandtl number. As the inlet turbulence intensity increases, the cooling effect increases firstly, and then decreases.
The Use of Methanol as an Alternative Fuel: Droplet Formation and Evaporation
Authors: Levy Y. , Erenburg V. , Sherbaum V. , Ovcharenko V. , Roizman A.
Published: August 2015

Methanol, produced from natural may be considered as an alternative fuel for fossil based liquid fueled gas turbines, especially for land based systems. In the present work, the effect of physical properties of methanol and kerosene on atomization and evaporation are compared. The spray’s liquid flux, droplet sizes and droplet velocities, cone angle were measured using Phase Doppler Particle Analyzer/Laser Doppler Velocimeter (TSI PDPA/LDV) system. Water, kerosene and ethanol (ethanol instead of methanol was used due to the toxicity of methanol) were used and tested at the same input liquid pressures. Analytical analysis of evaporation time for a single droplet of kerosene and methanol showed that the evaporation time is about the same for two fuels with the same droplet diameters. However, due the methanol’s lower calorific value and the fact that its volume flux must be more than twice as much (for similar thermal power), its corresponding evaporation time is longer than for kerosene. The evaporation time for kerosene and methanol, which took into accounts that more methanol should be evaporated, was simulated by CFD. The simulation results showed that methanol spray requires significantly longer distance than kerosene. Thus, the spray of methanol has larger droplet diameter than kerosene and prolonged evaporation time.
Instability Mechanism in a Swirl Flow Combustor: Precession of Vortex Core and Influence of Density Gradient
Authors: Manoharan Kiran , Hansford Samuel , O’ Connor Jacqueline , Hemchandra Santosh
Published: August 2015

Combustion instability is a serious problem limiting the operating envelope of present day gas turbine systems using a lean premixed combustion strategy. Gas turbine combustors employ swirl as a means for achieving fuel-air mixing as well as flame stabilization. However swirl flows are complex flows comprised of multiple shear layers as well as recirculation zones which makes them particularly susceptible to hydrodynamic instability. We perform a local stability analysis on a family of base flow model profiles characteristic of swirling flow that has undergone vortex breakdown as would be the case in a gas turbine combustor. A temporal analysis at azimuthal wavenumbers m = 0 and m = 1 reveals the presence of two unstable modes. A companion spatio-temporal analysis shows that the region in base flow parameter space for constant density density flow, over which m = 1 mode with the lower oscillation frequency is absolutely unstable, is much larger that that for the corresponding m = 0 mode. This suggests that the dominant self-excited unstable behavior in a constant density flow is an asymmetric, m=1 mode. The presence of a density gradient within the inner shear layer of the flow profile causes the absolutely unstable region for the m = 1 to shrink which suggests a possible explanation for the suppression of the precessing vortex core in the presence of a flame.
Ramp Heating in High-Speed Transient Thermal Measurement With Reduced Uncertainty
Authors: Ma H. , Wang Z. , Wang L. , Zhang Q. , Yang Z. , Bao Y.
Published: August 2015

The uncertainty associated with the convective heat transfer coefficient (HTC) obtained in transient thermal measurement is often high, especially in high speed flow. The present study demonstrates that the experimental accuracy could be much improved by an actively controlled ramp heating instead of the conventional step heating approach. A general design guideline for the proposed ramp heating method is derived theoretically and further demonstrated by simulation cases. This paper also presents a detailed experimental study for transonic turbine blade tip heat transfer. Repeatable, high-resolution tip HTC contour was obtained through transient IR measurement with the proposed ramp heating method. Detailed uncertainty analysis shows that the resulting HTC uncertainty level is much lower than the experimental data currently available in the open literature. The ramp heating approach is specially recommended to the high-speed heat transfer experimental research community to improve the accuracy of the transient thermal measurement technique.
Zonal Detached-Eddy Simulation Approach vs. URANS for the Prediction of the Flow Field Through a Low Pressure Vane Located Downstream of a Transonic High Pressure Turbine
Authors: Gougeon Pierre , Ngo Boum Ghislaine
Published: August 2015

The present work aims at studying the aerodynamic flow field within the first Low Pressure Vane (LPV) located downstream of a transonic High Pressure Turbine (HPT). A Zonal Detached-Eddy Simulation (ZDES) which is an hybrid URANS (Unsteady Reynolds Averaged Navier-Stokes)-DES approach, appears as a good alternative in terms of computational cost and quality of turbulent phenomena description when it comes to the capture of key parameters of losses generation in a LPV. ZDES is used on the LPV and the unsteady periodic flow field coming from the upstream HPT is modelled through a nonuniform rotating inlet boundary condition. The result is compared to a URANS simulation carried out with the same mesh and numerical parameters: this enables to quantify the differences and to state on the benefit of an advanced turbulent approach. Turbulent mechanisms are assessed with the computation of the power spectral density at different locations in the domain. To complete the analysis, the two numerical predictions are compared to experimental data. Wakes and vortices evolutions are studied in detail making it possible to put them into perspective with the aerodynamic losses generated in the LPV.
Fuel Composition Influence on Gas Turbine Ignition and Combustion Performance
Authors: Mosbach Thomas , Burger Victor , Gunasekaran Barani
Published: August 2015

The influence of different jet fuel compositions on aviation gas turbine combustion performance was investigated. Eight fuels including conventional crude-derived Jet A-1 kerosene, fully synthetic Jet fuel, synthetic paraffinic kerosenes, linear paraffinic solvents, aromatic solvents and pure compounds were tested. The tests were performed in the altitude relight test facility located at the Rolls-Royce Strategic Research Centre in Derby (UK). The combustor employed was a twin-sector representation of an RQL gas turbine combustor. The combustor was operated at sub-atmospheric air pressure of 41 kPa and air temperature of 265 K. The temperature of the fuels was regulated to 288 K. The combustor operating conditions corresponded to a simulated low stratospheric flight altitude near 9,000 metres.

The experimental work at the Rolls-Royce (RR) test-rig consisted of classical relight envelope ignition and extinction tests, and ancillary optical measurements: Simultaneous high-speed imaging of the OH* chemiluminescence and of the soot luminescence was applied to obtain spatial and temporal resolved insight into the ongoing processes. Optical emission spectroscopy was also applied simultaneously to obtain spectral and temporal resolved insight into the flame luminescence.

First results from the analysis of the OH* chemiluminescence and detailed fuel analysis results were presented in previous papers [1, 2]. This article presents further results from the analysis of the soot luminescence imaging and flame spectra.

It was found in general that the combustion performance of all test fuel formulations was comparable to regular Jet A-1 kerosene. Fuel related deviations, if existent, are found to be small.
Forced Response Sensitivity of a Mistuned Rotor From an Embedded Compressor Stage
Authors: Besem Fanny M. , Kielb Robert E. , Key Nicole L.
Published: August 2015

The frequency mistuning that occurs due to manufacturing variations and wear and tear of the blades can have a significant effect on the flutter and forced response behavior of a blade row. Similarly, asymmetries in the aerodynamic or excitation forces can tremendously affect the blade responses. When conducting CFD simulations, all blades are assumed to be tuned (i.e. to have the same natural frequency) and the aerodynamic forces are assumed to be the same on each blade except for a shift in interblade phase angle. The blades are thus predicted to vibrate at the same amplitude. However, when the system is mistuned or when asymmetries are present, some blades can vibrate with a much higher amplitude than the tuned, symmetric system. In this research, we first conduct a deterministic forced response analysis of a mistuned rotor and compare the results to experimental data from a compressor rig. It is shown that tuned CFD results cannot be compared directly with experimental data because of the impact of frequency mistuning on forced response predictions. Moreover, the individual impact of frequency, aerodynamic, and forcing function perturbations on the predictions is assessed, leading to the conclusion that a mistuned system has to be studied probabilistically. Finally, all perturbations are combined and Monte-Carlo simulations are conducted to obtain the range of blade response amplitudes that a designer could expect.
Study on Rebound Characteristics of Fine Spherical Particles Impacting an AISI 403 Steel With High Velocity
Authors: Di Juan , Wang Shun-sen , Cai Liu-xi , Cheng Shang-fang , Wu Chuang
Published: August 2015

Impingement on blade surface by fine particles with high velocity is commonly seen in steam turbines, gas turbines and compressors, which affect the service life and reliability of the equipment. Study on particles’ rebound characteristics is of great significance to reduce the blade erosion and to control particle trajectory. Based on the nonlinear explicit dynamics analysis software ANSYS/LS-DYNA, the impacts of fine spherical particles with different diameters (20 to 500μm) on a typical martensitic stainless steel (AISI 403) target with high velocity (50 to 250m/s) have been systematically studied. The influences of incident velocities, impact angles, particles sizes on its rebound characteristics, relative impact depth, and relative dissipated energy have been analyzed. Results show that velocity restitution coefficient e decreased with the impact angle β1, the incident velocity V1, and the particle size dp. However, the role of particle size on the velocity restitution coefficient seemed to be far less than that of the other two factors. Both of particle’s tangential and normal velocity coefficient of restitution declined with the increasing impact angle in most cases. However, when the incident velocity V1 = 200m / s and the impact angle β1 > 45°, the tangential velocity restitution coefficient et of 100 μm and 200 μm particles increased with the increase in the impact angle β1. The reason might be that the relative impact depth drel was located a zone ranged from 0.1515 to 0.1677, where the tangential rebound behavior could be enhanced. Most of the variation of the tangential and normal velocity restitution coefficient along β1 decreased with the increase in the particle diameter. However, when V1 = 200m/s and β1 > 15°, the tangential reflected velocity of the larger particles was enhanced gradually. In addition, the values of the relative impact depth drel increased with the increasing impact angle and incident velocity, and it increased with the increasing particle diameter in most cases. The relative dissipated energy of particles steadily increased with the impact angle and incident velocity, respectively. Particle diameter had little effect on energy dissipation in comparison with the impact angle and incident velocity.
Development of a Blade Parametric Modeling Methodology for Design and Analysis of Computer Experiments
Authors: Leylek Zafer , Neely A. J.
Published: August 2015

This paper will present an enhanced parametric modeling technique for gas turbine stator and rotor blades. The enhanced blade parametric modeling system has been developed as part of a wider research program into global surrogate modeling of compressor and turbine aerodynamic performance using Design and Analysis of Computer Experiments (DACE) based techniques.

The proposed method is based on a hybrid of geometric feature and Non-uniform Rational B-Spline (NURBS) based techniques. A base-line geometry is defined using the physical parameters and represented using NURBS curves and surfaces. A number of constraints are then imposed on the parametric model to ensure that DACE techniques can be effectively utilized. This is accomplished by mapping the geometric feature based parameters from the physical space to an alternative parametric space so that all feasible and numerically stable blade configurations can be represented using a unit hyper-cube. This method ensures a one-to-one mapping between the parametric sub-space and the geometric feature based system. The mapping is geometrically and numerically stable and does not produce ill-conditioned and unrealistic blade geometries.

The development of the blade parametric modeling process allows the application of the complete suit of DACE tools and techniques. The method is valid for all axial blade profiles which include compressor and turbine stator and rotor blades.
A Method for Forecasting the Condition of Several HPT Parts by Using Bayesian Belief Networks
Authors: Giesecke Daniel , Wehking Moritz , Friedrichs Jens , Binner Matthias
Published: August 2015

The competitive ability of jet engine maintenance companies depends mainly on turn around time and overhaul costs. Both airline and maintenance companies need the best possible accuracy regarding the prediction of emerging costs and time of engine maintenance process to secure their operation. Estimating the deterioration status of engine modules prior to disassembling is one of the greatest challenges for the maintenance process. In a pilot project a Bayesian belief network (BBN) has been developed to determine the deterioration condition of the General Electric CF6-80C2 first stage high pressure turbine (HPT) nozzle guide vane (NGV). The aim of this paper is to extend the used BBN techniques to the HPT first and second stage rotor blades and the second stage vanes. Thereby, its objective is to prove the successful application of the developed method for constructing a BBN for component hardware forecast.

The BBN is composed of following parameters: component repair history, region, on-wing cycles, airfoil material, thrust rating, engine wing position and customer segment. Performing statistical data analysis and combining these parameters with expert knowledge result in component specific BBNs. These nets provide a moderate forecast accuracy of 59 percent for the first stage rotor blades, 65 percent for the second stage rotor blades and promising 89 percent for the second stage NGVs.

The paper concludes that a BBN has very good qualities to forecast the hardware condition of HPT components impressively shown by virtue of the nozzles. Therefore, it is worth to transfer the developed method to other modules in order to accurately predict the degradation of the components in an unconventional way.
Investigation on an Oil Aeration Measurement Technique for the Study of Pump Performance in an Aircraft Engine Lubrication System
Authors: Ippoliti Laurent , Steimes Johan , Hendrick Patrick
Published: August 2015

Previous studies on feed pump performance conducted on the ULB-ATM lubrication system test bench showed the dependence of cavitation and volumetric efficiency with inlet pressure, rotational speed and aeration. This paper presents a technique of aeration measurement applied on the test bench. After a description of the device and a theoretical review of the aeration, the paper shows that the method has been tested with success. The paper illustrates it with a series of tests showing the level of aeration obtained in different operating conditions and a comparison with a pump characteristic measured on the bench.
Mechanism of Blockage Generation in Transonic Centrifugal Compressor at Design and Off-Design Conditions
Authors: Kaneko Masanao , Tsujita Hoshio
Published: August 2015

In a transonic centrifugal compressor, the loss generation is intensified by the formation of the shock wave and consequently the blockage is expected to increase. The blockage is considered to influence not only the flow rate and the increase of the static pressure but also the stall inception. However, the detailed mechanism of the blockage generation in the transonic centrifugal compressor has not been fully clarified.

In this study, in order to clarify the mechanisms of loss and blockage generations in the transonic centrifugal compressor which are expected to be strongly influenced by the operating condition, the flows in the compressor at the off-design condition as well as at the design condition were analyzed numerically. The verifications of the computed results were carried out by comparing with available experimental results. The computed result clarified that the loss generation near the impeller inlet at design condition was mainly caused by the interactions of the shock wave with the tip leakage vortex appearing from the leading edge of the main blade as well as the boundary layer on the suction surface of the main blade. Moreover, these interactions were intensified by the decrease of the flow rate, and consequently enhanced the blockage effects by the tip leakage vortex from the leading edge of the main blade and resulted in the increase of the aerodynamic loss especially along the shroud surface in the impeller passage. On the other hand, the decrease of the blockage effects by the tip leakage vortex from the main blade with the increase of the flow rate formed the shock wave on the suction surface of the splitter blade at near-choke condition. This shock wave interacted with the tip leakage vortex from the splitter blade and consequently increased the aerodynamic loss.
Heat Transfer Implications of Acoustic Resonances in HP Turbine Blade Internal Cooling Channels
Authors: Selcan C. , Cukurel B. , Shashank J.
Published: August 2015

In an attempt to investigate the acoustic resonance effect of serpentine passages on internal convection heat transfer, the present work examines a typical high pressure turbine blade internal cooling system, based on the geometry of the NASA E3 engine. In order to identify the associated dominant acoustic characteristics, a numerical FEM simulation (two-step frequency domain analysis) is conducted to solve the Helmholtz equation with and without source terms. Mode shapes of the relevant identified eigenfrequencies (in the 0–20kHz range) are studied with respect to induced standing sound wave patterns and the local node/antinode distributions. It is observed that despite the complexity of engine geometries, as a first order approximation, the predominant resonance behavior can be modeled by a same-ended straight duct.

Therefore, capturing the physics observed in a generic geometry, the heat transfer ramifications are experimentally investigated in a scaled wind tunnel facility at a representative resonance condition. Focusing on the straight cooling channel’s longitudinal eigenmode in the presence of an isolated rib element, the impact of standing sound waves on convective heat transfer and aerodynamic losses are demonstrated by liquid crystal thermometry, local static pressure and sound level measurements. The findings indicate a pronounced heat transfer influence in the rib wake separation region, without a higher pressure drop penalty. This highlights the potential of modulating the aero-thermal performance of the system via acoustic resonance mode excitations.
Experimental Validation of a Mesh Quality Optimized Morphed Geometric Mistuning Model
Authors: Kaszynski Alexander A. , Beck Joseph A. , Brown Jeffrey M.
Published: August 2015

High cycle fatigue due to mode localization caused by geometric and material mistuning is one of the leading failure risks of integrally bladed rotors (IBRs). Due to the computational analysis cost of full wheel models, IBR mistuned response amplifications are often modeled with reduced order models (ROMs). However, many developed ROMs are based on nominal mode assumptions that do not consider mode shape variations that have been shown to impact predicted mistuned response. Geometrically mistuned finite element models (FEMs) do account for mode shape variations but are notoriously difficult to construct and analyze. Recent advancements in optical scanning have enabled the rapid acquisition of highly accurate dense point clouds representative of manufactured hardware. Previous research pioneered a novel method to automatically and robustly construct an FEM directly from tessellated scan data, this research adds new mesh quality verification algorithms and experimentally validates this algorithm using results from traveling wave excitation. Sensitivity to mesh and point cloud density are also assessed to determine a best practice for creation of the as manufactured mistuned rotor model.
Threshold Speed of Instability of a Herringbone-Grooved Rigid Rotor With a Bearing Bush Flexibly Supported by Straight Spring Wires
Authors: Somaya Kei , Okubo Koki , Miyatake Masaaki , Yoshimoto Shigeka
Published: August 2015

In recent years, small-size aerodynamic bearings for turbomachines such as blowers and compressors have attracted considerable attention for increasing rotational speed. These kinds of bearings require excellent stability at high speeds and durability in a high-temperature environment. Foil bearings are one of the most suitable candidates that can satisfy these requirements but their structure is very complicated, and it is difficult to control their manufacturing accuracy. It is well known that flexibly supported herringbone-grooved aerodynamic journal bearings have excellent stability at high speeds and they are relatively easy to manufacture compared with foil bearings. Moreover, their dynamic characteristics can be easily solved numerically. In this paper, a flexibly supported herringbone-grooved aerodynamic journal bearing using straight spring wires made of stainless steel is proposed to provide a simple and reliable support system for a bearing bush. Six straight spring wires were assembled into a hexagonal shape into which the bearing bush was inserted. The threshold speed of instability of the proposed aerodynamic bearing was investigated numerically and experimentally. For this investigation, the nonlinear orbit method was adopted in numerical calculations. This investigation found that straight spring wires could steadily support the bearing bush and provide a simple and reliable support system for the bearing bush and that a 6-mm-diameter rigid rotor with a mass of 4.8 g supported by the proposed aerodynamic journal bearings could stably rotate at speeds of more than 0.7 million rpm.