bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Suction and Injection Purge-Flow on the Secondary Flow Structures of a High-Work Turbine
Authors: Schuepbach P. , Abhari R. S. , Rose M. G. , Germain T. , Raab I. , Gier J.
Published: August 2009

In high-pressure turbines, a small amount of air is ejected at the hub rim seal, to cool and prevent the ingestion of hot gases into the cavity between the stator and the disk. This paper presents an experimental study of the flow mechanisms that are associated with injection through the hub rim seal at the rotor inlet. Two different injection rates are investigated: nominal sucking of −0.1% of the main massflow and nominal blowing of 0.9%. This investigation is executed on a one-and-1/2-stage axial turbine. The results shown here come from unsteady and steady measurements, which have been acquired upstream and downstream of the rotor. The paper gives a detailed analysis of the changing secondary flow field as well as unsteady interactions associated with the injection. The injection of fluid causes a very different and generally more unsteady flow field at the rotor exit near the hub. The injection causes the turbine efficiency to deteriorate by about 0.6%.
Sensitization of the SST Turbulence Model to Rotation and Curvature by Applying the Spalart-Shur Correction Term
Authors: Smirnov Pavel E. , Menter Florian R.
Published: August 2009

A rotation-curvature correction suggested earlier by Spalart and Shur for the one-equation Spalart-Allmaras turbulence model is adapted to the Shear Stress Transport model. This new version of the model (SST-CC) has been extensively tested on a wide range of both wall-bounded and free shear turbulent flows with system rotation and/or streamline curvature. Predictions of the SST-CC model are compared with available experimental and DNS data, on one hand, and with the corresponding results of the original SST model and advanced Reynolds stresses transport model (RSM), on the other hand. It is found, that in terms of accuracy the proposed model significantly improves the original SST model and is quite competitive with the RSM, whereas its computational cost is significantly less than that of the RSM.
Experimental Study on Laser-Induced Ignition of Swirl-Stabilized Kerosene Flames
Authors: Moesl Klaus G. , Vollmer Klaus G. , Sattelmayer Thomas , Eckstein Johannes , Kopecek Herbert
Published: August 2009

Conventional ignition systems of aero-engines are an integral part of the combustion chamber’s structure. Due to this hardware-related constraint, the ignition spark has to be generated in the quench zone of the combustion chamber, which is far from the optimum regarding thermo- and aerodynamics. An improved ignitability of the fuel-air mixture can be found in the central zone of the combustor, where higher local equivalence ratios prevail and where mixing is favorable for a smooth ignition. It would be a major advancement in aero-engine design to position the ignition kernel in these zones. A laser system is able to ignite the fuel-air mixture at almost any location inside of the combustion chamber. Commercial laser systems are under development, which can replace conventional spark plugs in internal combustion engines and gas turbines. This study was conducted to evaluate the applicability of laser ignition in liquid-fueled aero-engines. Ignition tests were performed with premixed natural gas and kerosene to evaluate the different approaches of laser and spark plug ignition. The experiments were carried out on a generic test rig with a well-investigated swirler, allowing sufficient operational flexibility for parametric testing. The possibility of the free choice of the laser’s focal point is the main advantage of laser-induced ignition. Placing the ignition kernel at the spray cone’s shear layer or at favorable locations in the recirculation zone could significantly increase the ignitability of the system. Consequently, the laser ignition of atomized kerosene was successfully tested down to a global equivalence ratio of 0.23. Furthermore, the laser outperformed the spark plug at ignition locations below axial distances of 50 mm from the spray nozzle.
Improving the Accuracy of Multihole Probe Measurements in Velocity Gradients
Authors: Chernoray Valery , Hja¨rne Johan
Published: August 2009

This study describes an implementation and verification of an effective and reliable correction for the finite-size effects of pressure probes. A modified version of correction by Ligrani et al. (Exp. Fluids, vol. 7, 1989, p. 424) was used. It is shown that the correction procedure can be implemented in two steps as in Ligrani et al. or in a single step, either for probe pressures, or for velocity components. The latter correction method is found to have the best performance and studied in very detail. The effect of the correction in application to the highly three-dimensional flow downstream of the outlet guide vanes is scrutinized through detailed side-by-side comparison with corresponding cross hot-wire data. The influence of the correction on all three velocity components, flow streamlines and streamwise vorticity fields is thoroughly examined. Two flow cases with different incoming turbulence intensities are considered. The study demonstrates a very good efficiency and reliability of the correction, which lead to a significant improvement of the corrected velocity data. The improvement in crossflow velocity components has allowed correct description of the flow streamlines, and as a result, the secondary flow field structures were resolved more accurately. The considered correction does not affect the streamwise vorticity component, which is clarified as well. A very important fact is that the correction is not found to over-correct and distort the data, thus can be used safely. A very good performance of the correction for the finite-size effects of pressure probes presented in this study allows us to recommend it as a mandatory step in postprocessing procedures for multihole pressure probes.
Extended Models for Transitional Rough Wall Boundary Layers With Heat Transfer: Part I—Model Formulations
Authors: Stripf M. , Schulz A. , Bauer H.-J. , Wittig S.
Published: August 2009

Two extended models for the calculation of rough wall transitional boundary layers with heat transfer are presented. Both models comprise a new transition onset correlation, which accounts for the effects of roughness height and density, turbulence intensity and wall curvature. In the transition region, an intermittency equation suitable for rough wall boundary layers is used to blend between the laminar and fully turbulent state. Finally, two different submodels for the fully turbulent boundary layer complete the two models. In the first model, termed KS-TLK-T in this paper, a sand roughness approach from Durbin et al., which builds upon a two-layer k-ε-turbulence model, is used for this purpose. The second model, the so-called DEM-TLV-T model, makes use of the discrete-element roughness approach, which was recently combined with a two-layer k-ε-turbulence model by the present authors. The discrete element model will be formulated in a new way suitable for randomly rough topographies. Part I of the paper will provide detailed model formulations as well as a description of the database used for developing the new transition onset correlation. Part II contains a comprehensive validation of the two models, using a variety of test cases with transitional and fully turbulent boundary layers. The validation focuses on heat transfer calculations on both, the suction and the pressure side of modern turbine airfoils. Test cases include extensive experimental investigations on a high-pressure turbine vane with varying surface roughness and turbulence intensity, recently published by the current authors as well as new experimental data from a low-pressure turbine vane. In the majority of cases, the predictions from both models are in good agreement with the experimental data.
Design and Flow Analysis of Radial and Mixed Flow Turbine Volutes
Authors: Hamel Mohammed , Hamidou Mohamed K. , Cherif Hichem T. , Abidat Miloud , Litim Sid Ali
Published: August 2009

Radial and mixed flow turbines which are an important component of a turbocharger consist essentially of a volute, a rotor and a diffuser. Vaneless volute turbines, which have reasonable performance and low cost, are the most widely used in turbochargers for automotive engines. Care has to be done in the design of the volute, whose function is to convert a part of the engine exhaust gas energy into kinetic energy and direct the flow towards the rotor inlet at an appropriate flow angle with reduced losses. Turbulent compressible flow analysis and performance prediction using the finite volume method with two turbulence models (RNG k-ε and SST) implemented in the ANSYS-CFX software, are carried out on two different volute types. Four volutes, with different cross section areas used for radial turbines, are studied and the computed results are compared with the available experimental data. The second volute studied is the one used for a mixed flow turbine in the turbocharger test rig at Imperial College. In this part of the study, the interest is focused on the influence of the volute inlet flow conditions on its performance (efficiency, exit flow angle, etc).
Foreign Object Damage in an Oxide/Oxide Composite at Ambient Temperature
Authors: Choi Sung R. , Alexander Donald J. , Kowalik Robert W.
Published: August 2009

Foreign object damage (FOD) behavior of an oxide/oxide (N720/AS) ceramic matrix composite (CMC) was determined at ambient temperature using impact velocities ranging from 100 to 400 m/s by 1.59-mm diameter steel-ball projectiles. Two different support configurations of target specimens were used: fully supported and partially supported. The degree of post-impact strength degradation increased with increasing impact velocity, and was greater in a partially supported configuration than in a fully supported one. For the fully supported configuration, frontal contact stress played a major role in generating composite damage, while for the partially supported case both frontal contact and backside flexure stresses were the combined sources of damage generation. The oxide/oxide composite was able to survive high energy (∼1.3 J) impacts without complete structural failure. The degree of relative post-impact strength degradation of the oxide/oxide composite was similar to that of an advanced SiC/SiC composite observed from a previous study, regardless of the type of specimen support. Like the SiC/SiC composite, impact-damage tolerance was greater in the oxide/oxide than in monolithic silicon nitride ceramics for impact velocities >300 m/s.
The History of the Siemens Gas Turbine
Authors: Diakunchak Ihor , Kiesow Hans Juergen , McQuiggan Gerald
Published: August 2009

Siemens gas turbine history can be traced back to the early years of World War II. The Westinghouse aero jet engine (J 30) and the Junkers JUMO 004 jet engine were the basis for the industrial gas turbines designed and manufactured by Westinghouse and Siemens / Kraftwerk-Union since World War II. KWU was formed in 1969 as a joint venture of AEG and Siemens and became wholly owned by Siemens in 1977. AEG worked with Junkers on the development of the Jumo 004 jet engine during the War. Westinghouse Power Generation was purchased by Siemens in 1998. This paper examines the history of those early gas turbines and traces the evolution of the modern Siemens gas turbine from that time. Details are also given of the latest Siemens gas turbine to enter into operation, the 340MW SGT5-8000H.
Investigation of Multi-Functional Energy System (MES) for CO2 Removal
Authors: Han Wei , Jin Hongguang , Zhang Guoqiang , Lin Hu
Published: August 2009

This paper proposes a new approach to mitigate CO2 with low energy penalty through integrating the process of CO2 removal and the processes of synthetical use of different fuels. Then an example system for CO2 removal with synthetic use of coal and natural gas (multi-functional energy system, MES) is discussed to reveal the mechanism of the new approach. The thermodynamic and economic performance of the system is investigated. The natural gas and coal are synthetically used by a novel method named as coal-fired methane/steam reforming (CMR), in which coal combustion will provide thermal energy for methane/steam reforming reaction instead of combustion of natural gas. Some important parameters of reforming temperature, steam-to-methane ratio and hydrogen separation ratio are selected to clarify their impacts on the system thermodynamic performances. Comparing with the single systems including hydrogen plant based on natural gas with CO2 removal (NHPR) and coal-fired steam cycle with CO2 removal (CSCR), the MES can generate about 22% more hydrogen or about 70% more power with the same fossil fuel consumption and the same amount of CO2 removal. The economic performances of the MES system and the single systems are also investigated and compared. As a result, the cost of the avoided CO2 emission of the MES is only 17.5 $/tonneCO2, which is about 60% lower than that of the single systems. The results obtained here provide a feasible approach for CO2 removal efficiently and economically.
Heat Transfer in Radially Rotating Pin-Fin Channel at High Rotation Numbers
Authors: Chang S. W. , Yang T. L. , Hong G. F. , Liou Tong-Miin
Published: August 2009

Endwall heat transfer measurements for a radially rotating rectangular pin-fin channel with the width-to-height ratio (aspect ratio) of 8 are performed at the parametric conditions of 5000≤Re≤20000, 0≤Ro≤1.4 and 0.1≤Δρ/ρ≤0.21. Centerline heat transfer levels along the leading and trailing endwalls of the rotating pin-fin channel are respectively raised to 1.77–3.72 and 3.06–5.2 times of the Dittus-Boelter values. No previous attempt has examined the heat transfer performances for the pin-fin channel at such high rotation numbers. A selection of experimental data illustrates the individual and interactive Re, Ro and buoyancy number (Bu) effects on heat transfer. Spanwise heat transfer variations between two adjoining pin rows are detected with the averaged Nusselt numbers (Nu) determined. A set of empirical equations that calculates Nu values over leading and trailing endwalls in the developed flow region is derived to correlate all the heat transfer data generated by this study and permits the evaluation of interactive and individual effects of Re, Ro and Bu on Nu. With the aid of the Nu correlations derived, the operating conditions with the worst heat transfer scenarios for this rotating pin-fin channel are identified.
Volume Dynamics Propulsion System Modeling for Supersonics Vehicle Research
Authors: Kopasakis George , Connolly Joseph W. , Paxson Daniel E. , Ma Peter
Published: August 2009

Under the NASA Fundamental Aeronautics Program the Supersonics Project is working to overcome the obstacles to supersonic commercial flight. The proposed vehicles are long slim body aircraft with pronounced aero-servo-elastic modes. These modes can potentially couple with propulsion system dynamics; leading to performance challenges such as aircraft ride quality and stability. Other disturbances upstream of the engine generated from atmospheric wind gusts, angle of attack, and yaw can have similar effects. In addition, for optimal propulsion system performance, normal inlet-engine operations are required to be closer to compressor stall and inlet unstart. To study these phenomena an integrated model is needed that includes both airframe structural dynamics as well as the propulsion system dynamics. This paper covers the propulsion system component volume dynamics modeling of a turbojet engine that will be used for an integrated vehicle Aero-Propulso-Servo-Elastic model and for propulsion efficiency studies.
Application of the Systematic Sensor Selection Strategy for Turbofan Engine Diagnostics
Authors: Sowers T. Shane , Kopasakis George , Simon Donald L.
Published: August 2009

The data acquired from available system sensors forms the foundation upon which any health management system is based, and the available sensor suite directly impacts the overall diagnostic performance that can be achieved. While additional sensors may provide improved fault diagnostic performance there are other factors that also need to be considered such as instrumentation cost, weight, and reliability. A systematic sensor selection approach is desired to perform sensor selection from a holistic system-level perspective as opposed to performing decisions in an ad hoc or heuristic fashion. The Systematic Sensor Selection Strategy is a methodology that optimally selects a sensor suite from a pool of sensors based on the system fault diagnostic approach, with the ability of taking cost, weight and reliability into consideration. This procedure was applied to a large commercial turbofan engine simulation. In this initial study, sensor suites tailored for improved diagnostic performance are constructed from a prescribed collection of candidate sensors. The diagnostic performance of the best performing sensor suites in terms of fault detection and identification are demonstrated, with a discussion of the results and implications for future research.
Heat Transfer Coefficients of Film Cooling on a Rotating Turbine Blade Model: Part I—Effect of Blowing Ratio
Authors: Tao Zhi , Zhao Zhenming , Ding Shuiting , Xu Guoqiang , Yang Bin , Wu Hongwei
Published: August 2009

Experimental investigations were performed to measure the local heat transfer coefficient (hg) distributions of film cooling over a flat blade under both stationary and rotating conditions. Film cooling was via a straight circular hole of 4 mm in diameter located in the middle section of the blade angled 30° along the streamwise direction and 90° along the spanwise direction. The Reynolds (ReD) number based on the mainstream velocity and the film hole diameter was fixed to be 3191 and the rotating speeds (ω) were either 0 and 800 rpm; the film cooling blowing ratios ranged from 0.4 to 2.0 and two averaged density ratios of 1.02 and 1.53 were employed with air and carbon dioxide (CO2) as the coolant respectively. Thermochromic liquid crystal (TLC) was used to measure the solid surface temperature distributions. Experimental results showed that (1) in the stationary case, the blowing ratio has a significant influence on the non-dimensional heat transfer coefficient (hg/h0) especially in the near hole region. (2) the film trajectory in rotation had an obvious deflection in the spanwise direction, and the deflection angles on the suction surface are larger than that on the pressure surface. This was attributed to the combined action of the Coriolis force and centrifugal force. (3) in the rotating case, for CO2 injection, the magnitude of heat transfer coefficient on the pressure surface is reduced compared with the stationary case and the blowing ratio has smaller effects on hg/h0 distribution. However, on the suction surface, the heat transfer coefficient at x/D<1.0 is enhanced and then rapidly reduced to be also below the stationary values. For air injection, rotation also depresses the hg/h0 for both the pressure and the suction surface. (4) the density ratio shows a considerable effect on the streamwise heat transfer coefficient distributions especially for the rotating cases.
Heat Transfer Coefficients of Film Cooling on a Rotating Turbine Blade Model: Part II—Effects of Reynolds Number and Rotation Number
Authors: Wu Hongwei , Xu Guoqiang , Yang Bin , Tao Zhi , Ding Shuiting , Zhao Zhenming
Published: August 2009

An experimental study was conducted to investigate the heat transfer characteristics of film cooling on a rotating turbine blade model with a single cylindrical injection hole. As an important supplement to the study of Tao et al. [Z. Tao, Z.M. Zhao, S.T. Ding, G.Q. Xu, B. Yang and H.W. Wu, Experimental investigation of film cooling on a rotating turbine blade model: Part I. Effect of blowing ratio on heat transfer coefficients], the effects of Reynolds number ReD and rotation number Rt on local heat transfer coefficient distributions are presented in this paper. A steady-state thermochromic liquid crystal technique was employed to measure the temperature distribution of test surface on the blade model, and a telemetering data acquisition system was used to collect the signals from the rotating blade model by wireless approach. During the experiments, the Reynolds number based on the mainstream velocity and film hole diameter varies from 1841 to 4296, and the rotation number ranges from 0 to 0.0249. Both the air and CO2 are used as coolant, yielding the averaged density ratio of DR = 1.02 and 1.53, respectively. Experimental results show that the rotational effect has a significant influence on the heat transfer coefficient distributions. The profiles of h/h0, which is the ratio of heat transfer coefficient with film cooling to that without film cooling, will deflect towards the high-radius locations due to the strong centrifugal effect as Rt increases, and the deflective tendency of h/h0 is more apparent on the suction surface. The h/h0 values augment with the incremental ReD on the pressure surface, but decline firstly and then increase again on the suction surface. Furthermore, the averaged values of h/h0 for CO2 injection presents lower magnitudes as compared to the air injection.
Numerical Study of Unsteady Flow Phenomena in a Partial Admission Axial Steam Turbine
Authors: Hushmandi Narmin B. , Hu Jiasen , Fridh Jens , Fransson Torsten H.
Published: August 2009

This paper presents a numerical investigation of unsteady flow phenomena in a two-stage partial admission axial steam turbine. Results from unsteady three-dimensional computations are analyzed and compared with the available experimental data. Partial admission in the present study is introduced into the model by blocking only one segmental arc of the inlet guide vanes. Blocking only one segment (which corresponds to the experimental setup) makes the model unsymmetrical; therefore it is necessary to model the whole annulus of the turbine. The first stage rotor blades experience large static pressure change on their surface while passing the blocked channel. The effect of blockage on the rotor blades’ surface pressure can be seen few passages around the blocked channel. Strong changes of the blades’ surface pressure impose large unsteady forces on the blades of first stage rotor row. The circumferential static pressure plots at different cross sections along the domain indicate how the non-uniformity propagates in the domain. A peak pressure drop is seen at the cross section downstream of the first stage stator row. At further downstream cross sections, the static pressure becomes more evenly distributed. Entropy generation is higher behind the blockage due to the strong mixing and other loss mechanisms involved with partial admission. Analysis of the entropy plots at different cross sections indicates that the peak entropy moves in a tangential direction while traveling to the downstream stages. Comparisons of the unsteady three-dimensional numerical results and the experimental measurement data show good agreement in tendency. However some differences are seen in the absolute values especially behind the blockage.
Properties, Characteristics, and Combustion Performance of Sasol Fully Synthetic Jet Fuel
Authors: Moses Clifford A. , Roets Petrus N. J.
Published: August 2009

In 1999, as the only inland petroleum refinery in South Africa was reaching capacity, Sasol gained approval of a semi-synthetic jet fuel (SSJF) for civil aviation to augment production and meet the growing demand for jet fuel at the airport in Johannesburg. Prior to this, all jet fuel had to be refined from petroleum sources. SSJF consists of up to 50% of an iso-paraffinic kerosene produced from coal using Fischer-Tropsch processes. The production of SSJF remains vulnerable to the production capacity of conventional jet fuel, however. To ensure supply, Sasol has proposed producing a fully synthetic jet fuel (FSJF) using synthetic kerosene streams that contain aromatics and satisfy all the property requirements of international specifications for jet fuel. Being fully synthetic, it was necessary to demonstrate that the fuel is “fit-for-purpose” as jet fuel, i.e., behaves like conventional jet fuel in all aspects of storage and handling as well as air worthiness and flight safety. Four sample blends were developed covering the practical range of production. Extensive tests on chemistry and physical properties and characteristics demonstrated that Sasol FSJF will be typical of conventional jet fuel. As a final demonstration, the engine manufacturers requested a series of engine and combustor tests to evaluate combustion characteristics, emissions, engine durability, and performance. The performance of the synthetic test fuel was typical of conventional jet fuel. This paper identifies the tests and presents the results demonstrating that Sasol fully synthetic jet fuel is fit-for-purpose as jet fuel for civilian aviation. Sasol FSJF is the first fully synthetic jet fuel approved for unrestricted use.
Liquid Fuel Flameless Combustion RANS Simulation
Authors: Le Clercq Patrick , Schlieper Mark , Noll Berthold , Aigner Manfred
Published: August 2009

The numerical simulation of flameless combustion with liquid fuels is presented. Computations follow a RANS approach for turbulence modeling with a global reaction mechanism and the eddy dissipation concept for the combustion. Several approaches were tested for defining spray boundary conditions. A phenomenological analysis of the two-phase mixing and heat transfer that follow the injection enabled us to derive the spray boundary conditions that would eventually lead to our main goal; the simulation of flameless combustion. Computation results are compared to experimental measurements. First the isothermal mean velocity field computation is validated using LDA measurements. Then, temperature and CO2 radial-profiles at different axial positions and CO and NOx concentration levels at the outlet are compared to experimental data. The effect of spray initial conditions, inlet temperature, mixture properties and chemistry are analyzed.
Steady State Off-Design and Transient Behavior of a SOFC/GT Hybrid Power Plant With Additional Firing of the GT Combustor
Authors: Wa¨chter Christian , Joos Franz
Published: August 2009

The purpose of the current work is to analyze and also to verify the operating behavior of a SOFC/GT hybrid system in order to derive necessary requirements for an appropriate control system. The studies are carried out with a control oriented simplified dynamic model of a 25 MWe hybrid system based on a conceptual design previously presented in literature. As specific feature additional firing of the GT combustor is investigated. First the design point is defined. Then the off-design performance is presented in terms of characteristic performance maps. Based on operating map investigations an appropriate part load operating curve is defined with considerations given to constraints (e.g. stack temperature or surge margin), efficiency and operational flexibility. The load range goes from 40% part-load to 105% overload. To investigate the transient behavior five open loop simulations are carried out changing different model inputs, as well as all model inputs applying a 30% load change according to the operating curve. The simulated behavior reveals that the inputs should be changed with specific care to avoid critical situations during load change.
Experiments and Computations on Large Tip Clearance Effects in a Linear Cascade
Authors: Williams Richard , Gregory-Smith David , He Li , Ingram Grant
Published: August 2009

Large tip clearances typically in the region of six percent exist in the high pressure stages of compressors of industrial gas turbines. Due to the relatively short annulus height and significant blockage, the tip clearance flow accounts for the largest proportion of loss in the HP. Therefore increasing the understanding of such flows will allow for improvements in design of such compressors, increasing efficiency, stability and the operating range. Experimental and computational techniques have been used to increase the physical understanding of the tip clearance flows through varying clearances in a linear cascade of controlled-diffusion blades. This paper shows two unexpected results. Firstly the loss does not increase with clearances greater than 4% and secondly there is an increase of blade loading towards the tip above 2% clearance. It appears that the loss production mechanisms of the pressure driven tip clearance jet do not increase as the clearance is increased to large values. The increase in blade force is attributed to the effect of the strong tip clearance vortex which does not move across the blade passage to the pressure surface, as is often observed for high stagger blading. These results may be significant for the design of HP compressors for industrial gas turbines.
Maps of Vibrational Symptoms of Bearing Misalignment Defects in Large Power Turboset
Authors: Rybczynski Jozef
Published: August 2009

The article presents results of research activities oriented on creating a pattern of the dynamic state of a turboset in the presence of a defect consisting in the misalignment of its bearings. The dynamic state of the machine, described by its vibration pattern, is presented on maps showing vibration intensities of selected machine components as a function of misalignment of individual bearings. Similar maps were also created to present changes of static load caused in all bearings by bearing misalignment. The work contains the exemplary set of maps, which illustrate vibration levels of all bearings as a function of displacement of each turboset bearing in any direction in relation to its proper position. The maps are drawn in the possible bearing displacement ranges, between −5mm and +5mm to any direction. Assuming critical values of bearing vibration and bearing loads, the permissible bearing misalignments can be determined basing on bearing vibration and bearing load maps. Graphs of so defined permissible displacement areas were found for all bearings and are included in the paper. The work was done by means of computer simulation of bearing misalignments in the numerical model of 13K215 turboset by means of MESWIR computer code package. The present work is a continuation and extension of author’s earlier research activities in the area of bearing misalignment defect, which results were presented among others on ASME Turbo Expo 2006 Conference. The bearing misalignment is the very frequently observed inefficiency in large machines of this type; therefore results of the investigations may have important practical application. Although the vibrational maps presented in the article have been created for particular machine, value of this work consists in possibility of application of the presented methodology to any similar machine. Obtained this way vibrational maps may be put to use in vibration diagnostics of the turboset.
On the Prediction of Nitrogen Oxides From Gas Turbine Combustion Chambers Using Neural Networks
Authors: LaViolette Marc , Strawson Michael
Published: August 2009

This paper describes a method of predicting the oxides of nitrogen emissions from gas turbine combustion chambers using neural networks. A short review of existing empirical models is undertaken and the reasoning behind the choice of correlation variables and mathematical formulations is presented. This review showed that the mathematical functions obtained from the underlying theory used to develop the semi-empirical model ultimately limit their general applicability. Under these conditions, obtaining a semi-empirical model with a large domain and good accuracy is difficult. An overview of the use of neural networks as a modelling tool is given. Using over 2000 data points, a neural network that can predict NOx emissions with greater accuracy than published correlations was developed. The coefficients of determination of the prediction for the previous published semi-empirical models are 0.8048 and 0.7885. However one tends to grossly overpredict and the other underpredict. The coefficient of determination is 0.8697 for the model using a neural network. Because of the nature of neural networks, this more accurate model does not allow better insight into the physical and chemical phenomena. It is however, a useful tool for the initial design of combustion chambers.
Characterization of Foil Bearing Structure for Increasing Shaft Temperatures: Part I—Static Load Performance
Authors: Kim Tae Ho , Breedlove Anthony W. , San Andre´s Luis
Published: August 2009

Oil-free turbomachinery relies on gas bearing supports for reduced power losses and enhanced rotordynamic stability. Gas foil bearings (GFBs) with bump-strip compliant layers can sustain large loads, static and dynamic, and provide damping to reduce shaft vibrations. The ultimate load capacity of GFBs depends on the material properties and configuration of the underlying bump strips structure. In high temperature applications thermal effects changing operating clearances and material properties can affect considerably the performance of the FB structure. The paper presents experiments conducted to estimate the nonlinear structural stiffness of a test FB for increasing shaft temperatures. A 38.17 mm inner diameter FB is mounted on a non-rotating hollow shaft affixed to a rigid structure. A cartridge heater inserted into the shaft provides a controllable heat source and thermocouples record temperatures on the shaft and FB housing. For increasing shaft temperatures (up to 188°C) a static load (ranging from 0 N to 133 N) is applied to the bearing and the deflection recorded. Load versus deflection tests render the FB static structural stiffness coefficient. In the test configuration, thermal expansion of the FB housing, larger than that of the shaft, nets a significant increase in bearing radial clearance which produces a significant reduction in the foil bearing structural stiffness. A simple physical model assembling individual bump stiffnesses predicts well the measured FB structural stiffness when accounting for variations with temperature of the bump elastic modulus and the actual radial clearance affected by the thermal growth of the shaft and bearing cartridge. Further tests identifying the FB structure dynamic stiffness and its equivalent viscous damping follow in a companion paper (Part II) for a similar range of shaft temperatures.
Characterization of Foil Bearing Structure for Increasing Shaft Temperatures: Part II—Dynamic Force Performance
Authors: Kim Tae Ho , San Andre´s Luis , Breedlove Anthony W.
Published: August 2009

The forced response of a gas foil bearing (GFB), a typical rotor support in oil-free microturbomachinery, relies heavily on its resilient bump-strip layers structure, which also offers dry-friction type damping to ameliorate rotor vibrations. Operation at high temperature not only changes the FB elastic support material properties, but also produces thermal growth of the rotor and bearing components which ultimately affect the bearing structural stiffness and energy dissipation characteristics. The paper presents dynamic shaker load versus foil bearing structural deflection measurements for increasing shaft temperatures, from ambient to 188°C. In the tests, a FB supported on a non-rotating shaft is excited with a shaker at three load amplitudes (13 N, 22 N, and 31 N) and frequencies ranging from 40 to 200 Hz. A mechanical impedance model identifies the frequency dependent FB structural stiffness and equivalent viscous damping coefficient or dry-friction coefficient. Surface plots show trends in test results across increasing dynamic loads, shaft temperatures, and excitation frequencies. The FB stiffness increases by as much as 50% with dynamic loads amplitudes increasing from 13 N to 31 N. The stiffness nearly doubles from low to high frequencies; and most importantly, it decreases by a third as the shaft temperature rises to 188°C. In general, the FB dynamic structural stiffness is lower than its static stiffness, reported in a companion paper, at low excitation frequencies, while it becomes larger with increasing excitation frequency due apparently to a bump slip-stick phenomenon. The bearing viscous damping is inversely proportional to the amplitude of dynamic load, excitation frequency, and shaft temperature. The FB structure dry-friction coefficient decreases with increasing amplitude of applied load and shaft temperature, and increases with increasing excitation frequency. The experimental results demonstrate the paramount effect of operating temperature on the structural parameters of a foil bearing.
Effect of Side Feed Pressurization on the Dynamic Performance of Gas Foil Bearings: A Model Anchored to Test Data
Authors: Kim Tae Ho , San Andre´s Luis
Published: August 2009

Comprehensive modeling of gas foil bearings (GFBs) anchored to reliable test data will enable the widespread usage of these bearings into novel high speed turbomachinery applications. GFBs often need a forced cooling gas flow, axially fed through one end of the bearing, for adequate thermal management. The paper presents rotordynamic response measurements on a rigid rotor supported on GFBs during rotor speed run-up and coastdown tests with the GFBs supplied with increasing feed gas pressures to 2.8 bar. Rotor speed run-up tests to 35 krpm show that bearing end side feed gas pressurization delays the onset speed of rotor subsynchronous whirl motions. The test data validate closely predictions of the threshold speed of instability and whirl frequency ratio derived from a GFB model that implements the axial evolution of gas circumferential flow velocity as a function of the imposed side feed pressure. Rotor speed coastdown tests from 25 krpm with a low feed pressure of 0.35 bar evidences a nearly linear synchronous rotor response for small and moderately large imbalance mass distributions. A structural FE rotordynamics model integrates linearized synchronous speed GFB force coefficients and predicts synchronous responses, amplitude and phase angle, agreeing with the test data. The analysis and measurements demonstrate the profound effect of end side, feed gas pressurization on the rotordynamic performance of GFBs.
Analysis of Stall Precursors and Determination of Optimum Signal Processing Methods for an LM-2500 Gas Turbine
Authors: Millsaps Knox T. , Dahl Gustave C. , Caguiat Daniel E. , Patterson Jeffrey S.
Published: August 2009

This paper presents an analysis of data taken from several stall initiation events on a GE LM-2500 gas turbine engine. Specifically, the time series of three separate pressure signals located at compressor stages 3, 6, and 15 were analyzed utilizing various signal processing methods to determine the most reliable indicator of incipient stall for this engine. The spectral analyses performed showed that rotating precursor waves traveling around the annulus at approximately half of the rotor speed were the best indicators. Non-linear chaotic time series analyses were also used to predict stall, but it was not as reliable an indicator. Several algorithms were used and it was determined that stall wave perturbations can be reliably identified about 900 revolutions prior to the stall. This work indicates that a single pressure signal located at stage 3 on an LM-2500 gas turbine is sufficient to provide advance warning of more than 2 seconds prior to the fully developed stall event.
Reduction of Multi-Stage Disk Models: Application to an Industrial Rotor
Authors: Sternchu¨ss Arnaud , Balme`s Etienne , Jean Pierrick , Lombard Jean-Pierre
Published: August 2009

The present study deals with the reduction of multi-stage bladed disk assemblies. The guidelines of the proposed method which uses rotor cyclic modeshapes in conjunction with blade-dominated modes to account for the kinematics of each bladed sector of each disk are first recalled. This leads to compact reduced models whose accuracy has been extensively tested on simple but realistic academic models. In the second part of this paper, the proposed methodology is applied to an industrial rotor provided by Snecma to conduct an analysis at a wider scale.
A New Intermittent Aspirated Probe for the Measurement of Stagnation Quantities in High Temperature Gases
Authors: Massini Michela , Miller Robert J. , Hodson Howard P.
Published: August 2009

This paper presents the design, manufacture and testing of a new probe for the measurement of temperature and pressure in engine environments. The probe consists of a choked nozzle located in the flow and a system downstream including a cooler, a flow measuring device and a valve. It operates in two modes: in the first mode the valve is open, the probe is aspirated and the nozzle is choked. The mass flow through the probe is measured using instrumentation placed downstream of the cooler, so that it does not have contact with the hot flow. In the second mode the valve is closed and the stagnation pressure measured using the same instrumentation downstream the cooler. The total temperature is computed as a derived variable from the measurements of stagnation pressure and mass flow rate. There are a number of advantages of the probe over existing methods of temperature measurement. The measurement inaccuracy due to conduction and radiation errors and calibration drift found in thermocouples is significantly reduced; it can measure both stagnation temperature and pressure, halving the instrumentation costs; it has no wiring or transducer in the sensor head; the system can self-calibrate while located within an engine. The paper describes the design of a probe for use in engine environments. The probe prototype is tested up to 900K and shown to have an accuracy of ±6K.
Analysis and Optimization of the Coupled Parameters of the Graz Cycle
Authors: Alexander Brentan R. , Ghoniem Ahmed F.
Published: August 2009

The Graz Cycle is a unique power cycle design that has been proposed for the conversion of coal derived syngas or natural gas into mechanical energy while capturing carbon dioxide. The hydrocarbon is burned in pure oxygen, and water is condensed before a portion of the products are recycled back. Previous analyses have shown theoretical efficiencies of 56.12% [1]. Such a high theoretical efficiency, combined with carbon dioxide capture, makes this cycle design highly attractive. Little previous work has gone into optimizing the Graz Cycle design. Optimizing complex power cycles is complicated by the fact that a change in the operating conditions of one component of the cycle can alter temperatures and pressures around the rest of the cycle, impacting the performance of other cycle machinery. This paper addresses this issue through the application of a multivariable optimization algorithm. We have developed a model for the Graz Cycle using simplified equations of state and verified the results against previous studies. This model predicts a cycle efficiency of 56.72%, while the orginal calculation shows a value of 56.12% [1]. These values do not account for efficiency losses in the liquefaction and sequestration of carbon dioxide, or the efficiency penalty associated with coal gasification when syngas is used. A sensitivity analysis was performed on our model in order to identify the impact of key system parameters, including cycle temperatures, pressures, and molar flow rates, on the efficiency. This procedure, which amounts to changing one parameter at a time to maximize efficiency, resulted in an optimized efficiency of 57.84%. A computational optimization algorithm based on a simulated annealing scheme was then devised and used to alter system parameters simultaneously. An overall theoretical efficiency of 60.11% was achieved using this method. Another optimization scheme which accounts for hardware limitations and plant capital costs was also studied. This optimization yielded an efficiency of 58.76% while limiting the system high pressure to 110 bar. The results reveal that complex relationships between plant costs, fuel costs, and overall efficiency can be taken into account in a single unified analysis that minimizes a plant’s lifetime cost per unit of output. We demonstrate that the optimized cycle is actually simpler that the original cycle, without losing efficiency.
Trench Film Cooling: Effect of Trench Downstream Edge and Hole Spacing
Authors: Lu Yiping , Ekkad Srinath V. , Bunker Ronald S.
Published: August 2009

The present study is a continuation of an experimental investigation of film cooling from cylindrical holes embedded in transverse trenches. In this study, focus is on varying the downstream edge of the trench by angling it along the flow. Different edge angles are studied for the same trench depth. Also, the effect of hole spacing is considered for one of the standard trenches from previous studies to understand the effect of trenching on overall coolant usage. Detailed heat transfer coefficient and film effectiveness measurements are obtained simultaneously using a single test transient IR thermography technique. The study is performed at a single mainstream Reynolds number based on free-stream velocity and film hole diameter of 11000 at four different coolant-to-mainstream blowing ratios of 0.5, 1.0, 1.5 and 2.0. The results show that film effectiveness is greatly enhanced by the trenching due to improved two dimensional nature of the film and lateral spreading. The detailed heat transfer coefficient and film effectiveness contours provide a clear understanding of the jet-mainstream interactions for different hole orientations. The effect of edge angling is minimal on the overall cooling effectiveness but may have an impact on jet-mainstream interaction aerodynamic losses.
Numerical Studies of Diffuser Inlet Configurations for Small Flow Rate Radial Compressors
Authors: Qian Zeng
Published: August 2009

A computational fluid dynamics (CFD) study is presented to predict the impact of a number of inlet configuration features to the performance of centrifugal compressors diffusers. These features include impeller-diffuser alignment, diffuser inlet edge radius, impeller tip gap width, flow angle, and tip leakage/injection. In small flow rate centrifugal compressors the distance between hub and shroud at impeller discharge could be so small that due to thermal expansion and component mechanical tolerance stacking accurate alignment between the impeller and the diffuser is difficult to achieve. The impeller tip gap is relatively big and the leakage percentage is high. These are some of the major factors that contribute to the high loss and low efficiency of small flow rate compressors. In order to reduce the sensitivity of diffuser performance to misalignment, the designers often make a round, i.e., a radius of curvature in the meridional plane, on the diffuser entrance edges. The designers also need to properly determine the impeller tip gap width and estimate the impact of tip leakage. In this study the influences of these design features are investigated. Axisymmetric models are used for the flow inside a vaneless diffuser. Groups of cases are calculated with focus on the impact of each individual feature in a multiple configuration variable environment. In the cases calculated the impeller discharge is positioned in incremental axial misalignment relative to the diffuser. Different sizes of impeller tip gap, diffuser inlet rounds, and quantity of leakage or injection through the gap are calculated. The influences of the skewed impeller discharge velocity field on each of these configuration variations are investigated. The results are compared and the optimized configurations with balanced misalignment tolerance and peak performance are discussed. The study found that diffuser inlet round radius φ has a significant impact on the diffuser performance. At the optimum value of φ the diffuser has the highest tolerance to misalignment and the minimum penalty in pressure recovery. For a given impeller/diffuser misalignment there exists an optimum impeller tip gap width. Small quantities of impeller tip gap leakage or injection always has an adverse effect on diffuser performance. When the meridional flow angle offsets from radial direction the optimum impeller/diffuser alignment shifted as well.