bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Stator Clocking on the 3D Aeroelastic Characteristics of Compressor Rotor Blades
Authors: Rza˛dkowski Romuald , Gnesin Vitally , Kolodyazhnaya Luba
Published: August 2009

Presented here are numerical calculations of the 3D transonic flow of an ideal gas through a three-row compressor stage including the clocking effects. The approach is based on the solution of the coupled aerodynamic-structure problem for the 3D flow through the turbine stage in which fluid and dynamic equations are integrated simultaneously in time, thus providing the correct formulation of a coupled problem, as the blades’ oscillations and loads acting on the blades are a part of the solution. An ideal gas flow through the mutually moving stators and rotor blades with periodicity on the entire annulus is described using unsteady Euler conservation equations, integrated using the Godunov-Kolgan explicit monotonous finite-volume difference scheme and a moving hybrid H-H grid. The structure analysis uses the modal approach and a 3D finite element model of a blade. The blade motion is assumed to be constituted as a linear combination of the first natural modes of blade oscillations with the modal coefficients depending on time. A calculation has been performed for the compressor stage with 0.106 m long rotor blades. The aeroelastic characteristics are obtained for different positions of the upstream stator.
Secondary Air System Component Modelling for Engine Performance Simulations
Authors: Alexiou A. , Mathioudakis K.
Published: August 2009

This paper describes the modelling of typical secondary air system elements such as rotating orifices, seals and flow passages with heat and work transfer from the surrounding surfaces. The modelling is carried out in an object-oriented simulation environment that allows the creation of different configurations in a simple and flexible manner. This makes possible to compare the performance between different designs of individual components or complete secondary air systems as well as integrate them directly in whole engine performance models. The modelling is validated against published experimental data and computational results. An example of implementation in an engine model is also presented.
Steady-State and Transient Performance Modeling of Smart UAV Propulsion System Using SIMULINK
Authors: Ki Jayoung , Kong Changduk , Kho Seonghee , Lee Changho
Published: August 2009

Because aircraft gas turbine operates under various flight conditions that changes with altitude, flight velocity and ambient temperature, performance estimation that considers the flight conditions must be known before developing or operating the gas turbine. More so, for the UAV (Unmanned Aerial Vehicle) where the engine is activated by an onboard engine controller in emergency, the precise performance model including the estimated steady-state and transient performance data should be provided to the engine control system and the engine health monitoring system. In this study, a GUI (Graphic User Interface) type steady-state and transient performance simulation model of the PW206C turbo shaft engine that was adopted for use on the Smart UAV was developed using SIMULINK for performance analysis. For the simulation model, firstly the component maps including compressor, gas generator turbine and power turbine were inversely generated from manufacturer’s limited performance deck data by Hybrid Method. For the work and mass flow matching between components of the steady-state simulation, the state-flow library of SIMULINK was applied. The proposed steady-state performance model can simulate off-design point performance at various flight conditions and part loads, and in order to evaluate the steady-state performance model their simulation results were compared with manufacturer’s performance deck data. According to comparison results, it was confirm that the steady-state model well agreed with the deck data within 3% in all flight envelop. In the transient performance simulation model, the CMF (Continuity of Mass Flow) method was used and the rotational speed change was calculated by integrating the excess torque due to the transient fuel flow change using Runge-Kutta method. In this transient performance simulation, the turbine overshoot was predicted.
Multidisciplinary Optimization of Airfoil Cooling Structure
Authors: Nowak Grzegorz
Published: August 2009

This paper discusses the problem of cooling system optimization within a gas turbine airfoil regarding to thermo-mechanical behavior of the component, as well as some economical aspects of turbine operation. The main goal of this paper is to show the possibilities of evolutionary approach application to the cooling system optimization. This method, despite its relatively high computational cost, seems to be a valuable tool to such technical problems. The analysis involves the optimization of location and size of internal cooling passages within an airfoil. Initially cooling is provided with circular passages and heat is transported by convection. During the optimization the number of channels can vary. The task is approached in 3D configuration. Each passage is fed with cooling air of constant parameters at the inlet. Also a constant pressure drop is assumed along the passage length. The thermal boundary conditions in passages vary with diameter and local vane temperature (passage wall temperature). The analysis is performed by means of the genetic algorithm for the optimization task and FEM for the heat transfer predictions within the component. In the present study the airfoil profile is taken as aerodynamically optimal and the objective of the search procedure is to find cooling structure variant that at given external conditions provides lower stresses, material temperature and indirectly coolant usage.
Numerical Investigation of Relation Between Unsteady Behavior of Tip Leakage Vortex and Rotating Disturbance in a Transonic Axial Compressor Rotor
Authors: Yamada K. , Funazaki K. , Sasaki H.
Published: August 2009

The purpose of this study is to have a better understanding of the unsteady behavior of tip clearance flow at near-stall condition from a multi-passage simulation and to clarify the relation between such unsteadiness and rotating disturbance. This study is motivated by the following concern. A single passage simulation has revealed the occurrence of the tip leakage vortex breakdown at near-stall condition in a transonic axial compressor rotor, leading to the unsteadiness of the tip clearance flow field in the rotor passage. These unsteady flow phenomena were similar to those in the rotating instability, which is classified in one of the rotating disturbances. In other words it is possible that the tip leakage vortex breakdown produces a rotating disturbance such as the rotating instability. Three-dimensional unsteady RANS calculation was conducted to simulate the rotating disturbance in a transonic axial compressor rotor (NASA Rotor 37). The four-passage simulation was performed so as to capture a short length scale disturbance like the rotating instability and the spike-type stall inception. The simulation demonstrated that the unsteadiness of tip leakage vortex, which was derived from the vortex breakdown at near-stall condition, invoked the rotating disturbance in the rotor, which is similar to the rotating instability.
Optimal Mission Analysis Accounting for Engine Aging and Emissions
Authors: Kelaidis M. , Aretakis N. , Tsalavoutas A. , Mathioudakis K.
Published: August 2009

This paper describes an aircraft mission analysis procedure, comprising a flight simulation module, an engine model and an optimization method. The incorporation of engine deterioration modeling extends this procedure’s ability to estimate the on board performance of a given engine as it ages through time and use. Additionally, in order to investigate the environmental impact, pollutant emissions semi-empirical correlations have been introduced, after being adapted to available emissions data. The proposed procedure allows the optimization of a flight scenario for a variety of aircrafts, missions, and engine condition combinations, using an optimization method. The values of mission profile characteristics (e.g. cruise, altitude, and speed) that provide the optimum overall performance, regarding fuel conservation, time related costs, or pollutants production, are studied.
Recovery of Automobile Engine Exhaust Energy
Authors: Jansen Willem , Heitmann Arnold M. , Hanawa Masanori
Published: August 2009

This paper describes a method for converting car engine exhaust heat into useable electric energy that can be used either to improve fuel efficiency by as much as 10 percent, or for powering an air-cycle type Air Conditioning (A/C) system. The concept is based on designs that are currently used to construct air-cycle A/C systems.
Low CO2 Combustion System Retrofits for Existing Heavy Duty Gas Turbines
Authors: Stuttaford Peter J. , Oumejjoud Khalid
Published: August 2009

CO2 emissions generated by power plants make up a significant portion of global carbon emissions. Although there has been a great deal of focus on new power sources incorporating state of the art environmental protection systems, there has been little focus on addressing the issues of existing power plants. The purpose of this work is to address the options available to existing gas turbine based power plants to retrofit CO2 reduction measures cost effectively at the source of emissions, the combustor. Pre-combustion decarbonization is a highly efficient method of carbon removal, as only a small fraction of the gas turbine system flow needs to be addressed. This results in the requirement to burn a hydrogen based fuel, which presents challenges due to its highly reactive nature. The properties of hydrogen/syngas combustion are reviewed with emphasis on solutions for premixed combustion systems. Premixed combustion as opposed to diffusion combustion systems are key to retrofit solutions for existing gas turbines. Premixed systems provide the life cycle cost benefit, and heat rate benefit of not requiring the addition of diluent to the cycle to control emissions. Fuel flexibility is critical for retrofit systems, allowing operators to run on high hydrogen fuels as well as back-up standard natural gas to maximize power plant availability. Pre-combustion decarbonization may occur remote from the power plant at a centralized fuel processing facility, or it may be integrated into the combined cycle gas turbine power plant. Existing combined cycle power plants operating on natural gas could be modified to incorporate fuel decarbonization into the cycle, minimizing the parasitic loss of such a system while capturing carbon credits which are likely to become of increasing monetary value. An example cycle to address such integrated systems is presented. The focus of this work is to present a cycle to provide decarbonized fuel, cost effectively, from existing natural gas systems, as well as centralized coal/petcoke based fuel processing facilities. An additional focus is on the combustion system design requirements to burn such fuels, which are retrofitable to existing heavy duty gas turbine based power plants.
A Study Into the Auto-Ignition Characteristics of Hydrocarbon Fuels With Application to Gas Turbines
Authors: Sims G. J. , Mistry S. L. , Wood J. P. , Bowen P. , Crayford A.
Published: August 2009

The design of a premix duct is heavily reliant upon knowledge of the auto-ignition delay time for a given fuel-air mixture and operating range. An experimental investigation into the auto-ignition characteristics of alternative gaseous and liquid fuels has been carried out and the results compared against those for the conventional fuels. Gaseous fuels derived from sources such as bio-gas and refinery wastes were successfully compared against datum fuels of natural gas and methane — whilst among the liquid fuels — 100% biodiesel (consistent with BS EN 14214) and grade 2 diesel were tested and compared. The experimental results were obtained using a flow rig equipped with a generic premix duct and operated at GT-relevant conditions. For the gaseous fuels no ignition events were detected within the maximum test section residence time of 130ms. Therefore, a kinetic scheme previously validated at GT relevant conditions was used to evaluate effects of temperature, pressure and equivalence ratios for the gaseous fuels under investigation. In general gaseous fuels were found to have long auto-ignition delay times at temperatures < 900K and no differences were found between grade 2 diesel and 100% biodiesel. Therefore, the results under this study would be useful to the operators and designers of DLE systems when evaluating potential replacements for the current traditional fuels.
Unsteady Performance of a Double Entry Turbocharger Turbine With a Comparison to Steady Flow Conditions
Authors: Copeland Colin D. , Martinez-Botas Ricardo , Seiler Martin
Published: August 2009

Circumferentially divided, double-entry turbocharger turbines are designed with a dividing wall parallel to the machine axis such that each entry feeds a separate 180° section of the nozzle circumference prior to entry into the rotor. This allows the exhaust pulses originating from the internal combustion exhaust to be preserved. Since the turbine is fed by two separate unsteady flows, the phase difference between the exhaust pulses entering the turbine rotor will produce a momentary imbalance in the flow conditions around the periphery of the turbine rotor. This research seeks to provide new insight into the impact of unsteadiness on turbine performance. The discrepancy between the pulsed flow behaviour and that predicted by a typical steady flow performance map is a central issue considered in this work. In order to assess the performance deficit attributable to unequal admission, the steady flow conditions introduced in one inlet were varied with respect to the other. The results from these tests were then compared to unsteady, in-phase and out-of-phase pulsed flow most representative of the actual engine operating condition.
On the Use of Actively Controlled Auxiliary Bearings in Magnetic Bearing Systems
Authors: Cade Iain S. , Sahinkaya M. Necip , Burrows Clifford R. , Keogh Patrick S.
Published: August 2009

Auxiliary bearings are used to prevent rotor/stator contact in active magnetic bearing systems. They are sacrificial components providing a physical limit on the rotor displacement. During rotor/auxiliary bearing contact significant forces normal to the contact zone may occur. Furthermore, rotor slip and rub can lead to localized frictional heating. Linear control strategies may also become ineffective or induce instability due to changes in rotordynamic characteristics during contact periods. This work considers the concept of using actively controlled auxiliary bearings in magnetic bearing systems. Auxiliary bearing controller design is focused on attenuating bearing vibration resulting from contact and reducing the contact forces. Controller optimization is based on the H∞ norm with appropriate weighting functions applied to the error and control signals. The controller is assessed using a simulated rotor/magnetic bearing system. Comparison of the performance of an actively controlled auxiliary bearing is made with that of a resiliently mounted auxiliary bearing. Rotor drop tests, repeated contact tests, and sudden rotor unbalance resulting in trapped contact modes, are considered.
Review of Metrics and Assignment of Confidence Intervals for Health Management of Gas Turbine Engines
Authors: Davison Craig R. , Bird Jeff W.
Published: August 2009

The development and evaluation of new diagnostic systems requires statistically-based methods to measure performance. Various metrics are in use by developers and users of diagnostic systems. Current metrics practices are reviewed, including receiver operating characteristics, confusion matrices, Kappa coefficients and various entropy techniques. A set of metrics is then proposed for assessment of diverse gas path diagnostic systems. The use of bootstrap statistics to compare metric results is developed, and demonstrated for a set of hypothetical data sets with a range of relevant characteristics. The bootstrap technique allows the expected range of the metric to be assessed without assuming a probability distribution. A method is proposed to develop confidence intervals for the calculated metrics. The application of a confidence interval could prevent a good diagnostic technique being discarded because of a lower value metric in one test instance. The strengths and weaknesses of the various metrics with derived confidence intervals are discussed. Recommendations are made for further work.
Micro Mixing Fuel Injectors for Low Emissions Hydrogen Combustion
Authors: Hernandez Steven R. , Wang Qing , McDonell Vincent , Mansour Adel , Steinthorsson Erlendur , Hollon Brian
Published: August 2009

The consideration of hydrogen as a fuel for next generation low emissions gas turbines raises a number of challenges and potential benefits relative to the combustion system. The present work examines the use of a micro-mixing injection strategy for hydrogen as a means to achieve rapid mixing and inherent flexibility for accommodating various staging, dilution, and dual fuel requirements for future gas turbine engines. The work presented includes numerical and experimental results associated with the fuel-air mixing process in a representative injector configuration. Measured NOx emissions and fuel/air ratios at the exit of the mixer are shown along with visualization of the reactions generated. Detailed computational fluid dynamics (CFD) is used in parallel to elucidate the behavior of the flow inside and downstream of the injectors. Results are also presented for natural gas to provide a point of reference. The results illustrate a number of interesting features and characteristics of the hydrogen/air mixtures which are in dramatic contrast to the behavior of natural gas/air mixtures. Comparison of the measured and modeled mixing behavior illustrates a number of challenges associated with the selection of a robust modeling approach for hydrogen/air combustion. The results demonstrate that the use of micro-mixing fuel injection to achieve ultra low NOx emissions is very promising.
On the Teaching of Performance Evaluation and Assessment of a Combined Cycle Cogeneration System
Authors: Arnas A. O¨zer , Boettner Daisie D. , Norberg Seth A. , Tamm Gunnar , Whipple Jason R.
Published: August 2009

Performance evaluation and assessment of combined cycle cogeneration systems are not taught well in academia. One reason is these parameters are scattered in the literature with each publication starting and ending at different stages. In many institutions professors do not discuss or even mention these topics, particularly from a second law perspective. When teaching combined cycle cogeneration systems to undergraduates, the professor should introduce pertinent parameters in a systematic fashion and discuss the usefulness and limitations of each parameter. Ultimately for a given situation, the student should be able to determine which parameters form the most appropriate basis for comparison when considering alternative designs. This paper provides two approaches, one based on energy (the First Law of Thermodynamics) and the other based on exergy (the Second Law of Thermodynamics). These approaches are discussed with emphasis on the “precise” teaching of the subject matter to undergraduates. The intent is to make coverage of the combined cycle cogeneration systems manageable so that professors can appropriately incorporate the topic into the curricula with relative ease.
Non-Linear Modal Analysis for Bladed Disks With Friction Contact Interfaces
Authors: Laxalde Denis , Salles Loi¨c , Blanc Laurent , Thouverez Fabrice
Published: August 2009

A method for non-linear modal analysis of mechanical systems with contact and friction interfaces is proposed. It is based on a frequency domain formulation of the dynamical system’s equations of motion. The dissipative aspects of these non-linearities result in complex eigensolutions and the modal parameters (natural frequency and modal damping) can be obtained without any assumptions on the external excitation. The generality of this approach makes it possible to address any kind of periodic regimes, in free and forced response. In particular, stability analysis in flutter applications can be performed. Applications for the design of friction ring dampers for blisks and for the dynamical simulation of bladed disk with dovetail attachment are proposed. Finally, we propose a study of dynamical behaviour coupling with the calculation of fretting-wear at the interfaces based on non-linear modal characterization.
Experimental and Numerical Investigations of Friction Rings Damping of Blisks
Authors: Laxalde Denis , Gibert Claude , Thouverez Fabrice
Published: August 2009

The use of friction ring dampers for integrally bladed disks (blisks) is investigated numerically and experimentally in this paper. A test rig was developed and consists in an industrial HP compressor blisk rotating inside a vacuum chamber. Excitation is produced through piezoelectric actuators and measured data are obtained from strain gauges. Non-linear resonance curves obtained by stepped sine tests are studied. Interesting phenomena on the behaviour of this damping technology are obtained experimentally. Parametric studies on the influence of the rotation speed or of the excitation level are also presented. A non-linear modal identification method is used in order to extract the modal parameters from the resonance curves. Then a comparison of these experimental results to the results of numerical simulations is proposed. The numerical methods is based on a frequency domain formulation of the system’s dynamics; a non-linear modal approach is used. The correlation between the experiments and the predicted results are in quite good agreement given the complexity and the variability of the system and phenomena.
The Application of Flow Control to an Aft-Loaded Low Pressure Turbine Cascade With Unsteady Wakes
Authors: Bons Jeffrey P. , Pluim Jon , Gompertz Kyle , Bloxham Matthew , Clark John P.
Published: August 2009

The synchronous application of flow control in the presence of unsteady wakes was studied on a highly-loaded low pressure turbine blade. The L1A blade has a design Zweifel coefficient of 1.34 and a suction peak at 58% axial chord, making it an aft-loaded pressure distribution. Velocity and pressure data were acquired at Rec = 20,000 with 3% incoming freestream turbulence. Unsteady wakes from an upstream vane row are simulated with a moving row of bars at a flow coefficient of 0.76. At this Reynolds number, the blade exhibits a non-reattaching separation bubble beginning at 57% axial chord under steady flow conditions without upstream wakes. The separation zone is modified substantially by the presence of unsteady wakes, producing a smaller separation zone and reducing the area-averaged wake total pressure loss by more than 50%. The wake disturbance accelerates transition in the separated shear layer but stops short of reattaching the flow. Rather, a new time-averaged equilibrium location is established for the separated shear layer, further downstream than without wakes. The focus of this study was the application of pulsed flow control using two spanwise rows of discrete vortex generator jets (VGJs). The VGJs were located at 59% Cx, approximately the peak cp location, and at 72% Cx. The most effective separation control was achieved at the 59% Cx location. Wake total pressure loss decreased 60% from the wake only level and the cp distribution fully recovered its high Reynolds number (attached flow) performance. The VGJ disturbance dominates the dynamics of the separated shear layer, with the wake disturbance assuming a secondary role only. When the pulsed jet actuation (30% duty cycle) was initiated at the 72% Cx location, synchronization with the wake passing frequency (10.6Hz) was key to producing the most effective separation control. A 25% improvement in effectiveness was obtained by aligning the jet actuation between wake events. Evidence suggests that flow control using VGJs will be effective in the highly unsteady LPT environment of an operating gas turbine, provided the VGJ location and amplitude are adapted for the specific blade profile.
Unsteady Blade and Disk Resonant Stress Analysis Due to Supersonic Inlet Guide Vane Wakes
Authors: Nordwall G. , Leduc M. , Demeulenaere A.
Published: August 2009

A high specific-power radial inflow turbine is currently being designed for installation in the fall of 2008. This turbine will generate 7,000–18,500 HP (5–14 MW) of electrical power. Operating with a relatively high pressure ratio and high molecular weight (58), which is common in geothermal power generation applications, the process has the ability to produce a very strong wake structure. Such wakes have caused catastrophic impeller fatigue failures in similar applications. To prevent a failure, the current design is based on a study of the interaction between the wake structure and the impeller. The SAFE and Campbell diagram are used for screening purposes, but the final design is analyzed using an unsteady CFD analysis coupled with time-dependent Finite Element Stress analysis. This pairing of CFD and FEA analysis allows the alternating torque to be determined both under resonant and non-resonant conditions. With this analysis, it is possible to approximate the stress resulting from higher order resonant frequencies which cannot be avoided in blade tuning. The analysis has shown that a high order harmonic of the vane passing frequency will not lead to unacceptable alternating stress levels. To facilitate future analysis, the 360° unsteady solution was compared to a harmonic analysis with two harmonic frequencies. The harmonic solution has shown good agreement with the full 360° solution.
Spray Characterization at Jet Engine Thrust Augmentor Flow Conditions
Authors: Lubarsky Eugene , Cutright John T. , Zinn Ben T. , McAmis Robert
Published: August 2009

This paper describes experimental characterization of the spray formed by fuel jet injection in cross-flow under simulated modern augmentor operating conditions. Such data is needed to obtain a better understanding of the fundamental processes that control the performance of aircraft engine augmentors and to support the development of CFD based design tools. The study employed a single flame holder augmentor (SFA) model of a modern jet engine thrust augmentor with a cross-section of 76.2×152.4 mm (3×6 inches) located in a test setup with full optical access to the spray and flame zones provided by a 914.4 mm (36 inches) long transparent quartz section. Tests were performed under conditions simulating those encountered with modern jet engines: Mach number varying between 0.25 and 0.40, temperature ranging from 760°C to 900°C (1860 R to 2111 R), and vitiated air with oxygen content ranging from 12% to 15% by volume. The flame was maintained by a bluff-body flame holder with fuel injector orifice diameter d = 0.711 mm (0.028 inch). Flow rate of the Jet-A fuel varied in the range of 23 ± 0.4 g/s, resulting in a fuel to air momentum flux ratio of Q = 10.5 and an aerodynamic Weber number We = 970. The nature of the fuel spray atomization, both with and without afterburning, was determined using a two dimensional Phase Doppler Particle Analyzer (PDPA) system. The PDPA system simultaneously measured droplet diameters and velocities. The results were used to generate profiles of the droplet diameter distributions and velocities in the center plane and cross-section planes at two locations downstream of the injection point. Measurements with combustion were limited to outside the recirculation zone behind the flame holder due to the evaporation of the droplets there from the heat of combustion. The results showed that the presence of combustion reduces the level of incoming air flow inclination approximately by a factor of 2 and increased the turbulence intensity level by 60% to 70%. The presence of combustion increases the Sauter mean droplet diameters from the range 44 to 68 microns without flame to the range 47 to 79 microns and reduces mean droplet velocities by approximately 10% in the core of the spray and up to 25% near the peripheries of the spray.
Characteristics of Several Steam and Nitrogen Diluted Methods on Hydrogen-Riched Medium Heating Value Syngas Fuel Diffusion Flame
Authors: Xu Gang , Fang Aibin , Liu Quan , Yu Bin , Nie Chaoqun , Zhang Yan
Published: August 2009

For the diffusion syngas flames, inert gases dilution is one of the effective techniques to reduce NOx emissions. In this paper, five methods of steam or nitrogen dilution have been investigated on an atmospheric-pressure downscaled test rig: Air dilution with steam; Fuel dilution with steam; Fuel dilution with N2; Direct dilution with steam; Direct dilution with N2. The experimental results indicate that each method could suppress the NOx emissions less than 10 ppm@15%O2 with proper steam or nitrogen addition while CO emission below 50 ppm@15%O2. However, the optimum steam or nitrogen consumption rate of each method is very different from other methods. For example, the air dilution with steam method needs more steam consumption than fuel dilution with stream and direct dilution with steam. The temperature distribution and species (i.e. CO, NOx, CO2 and O2) concentration distribution of the model combustor have been investigated by a high response thermocouple (type B) and a water-cooled stainless steel sample probe, respectively. The lean blowout (LBO) limits of five methods are obtained at fixed air flowrate condition. The LBO safety margin of direct dilution methods shows much broader than that of those fuel dilution methods. Furthermore, fuel dilution reaches the LBO limit at constant DOD (the flowrate ratio of dilution to syngas) for different equivalence ratio.
Research on Circumferential Fluid Pressure Distribution and Whirl Stability of Rotor-Bearing System
Authors: Chen Ce , Yang JinFu , Nie ChaoQun , Cui Ying , Yu DaRen , Yang ShengBo , Yang Kun , Fu ZhongGuang
Published: August 2009

This paper presents a theoretical analysis of the mechanism of oil whirl, oil whip, and hysteresis in oil whip. A qualitative analysis of the interrelation between whirl frequency, natural frequency, and eccentricity ratio versus speed was conducted using the rotor-bearing load balance equation. By analyzing the interrelation among whirl speed, eccentricity ratio versus speed, rotating speed, oil supply pressure and bearing load, and observing the oil-film load circumferential fluid pressure distribution in the three phases of oil-film load attenuation, instability transition, and oil-film load instability, it was found that in the whirl instability transition phase, the amplitude of rotor whirl speed exceeds half the value of rotor rotation speed, which causes the pressure change in the oil convergent wedge to change from positive to negative, and the pressure change in the divergent wedge to change from negative to positive, and the change in oil-film pressure distribution causes the instability of oil whirl; These changes in oil film pressure distribution are the indicator of oil whirl instability. An experimental study on the whirl instability in a pump supported on fluid film bearings is also presented in this paper to validate the theoretical approach.
Effects of the Inlet Boundary Layer Thickness on Rotating Stall in an Axial Compressor
Authors: Choi Minsuk , Oh Seong Hwan , Ko Han Young , Baek Je Hyun
Published: August 2009

A three-dimensional numerical simulation was conducted to study an effect of the inlet boundary layer thickness on the rotating stall in an axial compressor. The inlet boundary layer thickness had significant effects on the hub-corner-separation in the junction of the hub and the suction surface. The hub-corner-separation grew significantly for the thick inlet boundary layer as the load was increased, while it was diminished to be indistinguishable from the rotor wake for the thin inlet boundary layer and a new corner-separation was originated near the casing. The difference in the internal flow at the near stall condition also had a large effect on characteristics of the rotating stall, especially the first asymmetric disturbance and the size of the stall cell. While a pre-stall disturbance arises firstly in the hub-corner-separation for the thick inlet boundary layer, an asymmetric disturbance was initially generated in the tip region because of the corner-separation for the thin inlet boundary layer. This disturbance was transferred to the tip leakage flow and grew to be an attached stall cell. When this attached stall cell reached a critical size, it moved along the blade row and became a short-length-scale rotating stall. The size of the stall cell for the thick inlet boundary layer was larger than that for the thin inlet boundary layer. The difference of the stall cell’s size affected the performance of the single rotor, causing large performance drop for the former case but a continuous performance change for the latter case.
The Effect of Leading Edge Diameter on the Horse Shoe Vortex and Endwall Heat Transfer
Authors: Hada Satoshi , Takeishi Kenichiro , Oda Yutaka , Mori Seijiro , Nuta Yoshihiro
Published: August 2009

The endwall of the first stage vane / blade of modern high temperature gas turbine has been exposed to severe heat transfer environments. Due to the formation of a horse shoe vortex (HV), the flow field of a vane and blade leading edge juncture to endwall is especially complicated and it is difficult to estimate the heat transfer coefficients and the film cooling effectiveness levels in this area. This paper describes the results of experimental and numerical studies on the heat transfer and flow dynamics in the leading edge endwall region of a symmetric airfoil. The effects of inlet velocity, boundary layer thickness and leading edge diameter of a symmetric airfoil were investigated on the endwall heat transfer in a low speed wind tunnel facility. The time averaged local heat transfer coefficients were measured by naphthalene sublimation method and the instantaneous velocity field was obtained by Particle Image Velocimetry (PIV). As the leading edge diameter of symmetric airfoil decreases, the heat transfer coefficients on an endwall increases and is proportional to Re0.71 that is base on the leading edge diameter. However, the boundary layer thickness was found to have a marginal effect on the endwall heat transfer.
Inlet Air Cooling With Overspray Applied to a Two-Stage Centrifugal Compressor
Authors: Shibata Takanori , Takahashi Yasuo , Hatamiya Shigeo
Published: August 2009

A Water Atomization Cooling (WAC) system is a kind of inlet fogging technique with overspray, which reduces the compression work due to the intra-cooling effect of over-injected droplet evaporation. The WAC system has been successfully applied to mid- and large-sized gas turbines, but its application to small turbines is rare. Hitachi developed a 3.7 MW Advanced Humid Air Turbine (AHAT) plant as a national project from 2004 to 2006. The plant has a two-stage centrifugal compressor with a total-to-total pressure ratio of 8.3 without the WAC system. We compare theoretical and experimental evaporation behaviors of injected droplets into the compressor and their effect on the compressor characteristics, when the WAC system was applied to the AHAT plant.
Deposition Near Film Cooling Holes on a High Pressure Turbine Vane
Authors: Ai Weiguo , Murray Nathan , Fletcher Thomas H. , Harding Spencer , Lewis Scott , Bons Jeffrey P.
Published: August 2009

Deposition on film-cooled turbine components was studied in an accelerated test facility. The accelerated deposition facility seeds a natural-gas burning combustor with finely-ground coal ash particulate at 1180°C and 180 m/s (M = 0.25). Both cylindrical and shaped holes, with and without TBC coating, were studied over a range of blowing ratios from 0.5 to 4.0. Coolant density ratios were maintained at values from 2.1 to 2.4. Deposition patterns generated with the cylindrical film cooling holes indicated regions of low deposition in the path of the coolant, with heightened deposition between film holes. This distinctive pattern was more accentuated at higher blowing ratios. Optical temperature measurements of the turbine component surface during deposition showed elevated temperatures between coolant paths. This temperature non-uniformity became more accentuated as deposition increased, highlighting a mechanism for deposition growth that has been documented on in-service turbines as well. The shaped-hole components exhibited little or no deposition in the region just downstream of the holes, due to the distributed coolant film. Close cylindrical hole spacing of 2.25d displayed similar behavior to the shaped hole configuration.
High Temperature, Permanent Magnet Biased, Fault Tolerant, Homopolar Magnetic Bearing Development
Authors: Palazzolo Alan , Tucker Randall , Kenny Andrew , Kang Kyung-Dae , Ghandi Varun , Liu Jinfang , Choi Heeju , Provenza Andrew
Published: August 2009

This paper summarizes the development of a magnetic bearing designed to operate at 1,000F. A novel feature of this high temperature magnetic bearing is its homopolar construction which incorporates state of the art high temperature, 1,000F, permanent magnets. A second feature is its fault tolerance capability which provides the desired control forces with over one-half of the coils failed. The construction and design methodology of the bearing is outlined and test results are shown. The agreement between a 3D finite element, magnetic field based prediction for force is shown to be in good agreement with predictions at room and high temperature. A 5 axis test rig will be complete soon to provide a means to test the magnetic bearings at high temperature and speed.
Novel Concepts for the Compression of Large Volumes of Carbon Dioxide
Authors: Moore J. Jeffrey , Nored Marybeth G.
Published: August 2009

In order to reduce the amount of carbon dioxide (CO2) greenhouse gases released into the atmosphere, significant consideration has been given to the sequestration of CO2 from power plants and other major producers of greenhouse gas emissions. Integrated Gasification Combined Cycle (IGCC) power plants offer an alternative to pulverized coal plants because the carbon dioxide may be separated from the process gas stream prior to combustion. The compression of the captured carbon dioxide stream requires a sizeable amount of power, which impacts plant availability, capital expenditures and operational cost. Preliminary analysis has estimated that the CO2 compression process reduces the plant efficiency by 8% to 12% for a typical IGCC plant. The detailed thermodynamic analysis presented here examines methods to minimize the power penalty to the producer through integrated, low-power compression concepts. The goal of the present research is to reduce this penalty through novel compression concepts and integration with existing IGCC processes. The research supports the U.S. Department of Energy (DOE) National Energy Technology Laboratory (NETL) objectives of reducing the energy requirements for carbon capture and sequestration in electrical power production. The primary objective of this study is to boost the pressure of CO2 to pipeline pressures with the minimal amount of energy required. Fundamental thermodynamic analysis methods related to the compression of CO2 are used in the following paper to explore pressure and enthalpy rise in both liquid and gaseous states.
LES and Experimental Study of Flow Features in Humid-Air Combustion Chamber With Non-Premixed Circular-Disc Stabilized Flames
Authors: Guo Peiqing , Zang Shusheng , Ge Bing
Published: August 2009

Sydney/Sandia bluff-body flame series [1] has been world-widely studied based on a simple-geometry bluff-body. This study focuses on a turbulent piloted non-premixed methane jet flame with circular-disc which is used in a humid-air combustion chamber without a swirler. Large eddy simulation has been performed to investigate the flow features. Meanwhile, in order to validate the simulation results, an experimental study is also conducted, where the instantaneous velocity and temperature fields are measured using PIV and high temperature thermocouples, respectively. Compared to Sydney/Sandia flame series, the enlarged simulation area effectively eliminates the boundary effects on flow field. Comparisons with experimental data also show that for high resolution of grids, comparatively good agreement is obtained for the flow field. Unlike Sydney/Sandia flame series, central jet tends to break up early in this case because of the existence of the circular disc. It has also been found that the shear layer between the co-flow and the bluff-body wake is captured by LES as well as by PIV. Because of the difference in geometry between Sydney/Sandia and circular-disc bluff-bodies, it needs to be further studied how to apply the conclusions based on the former to the latter. However, current and future LES and experimental study can help to illustrate the tradeoffs among the degree of swirl and the choice of bluff-body shapes in devices such as industrial burners and gas turbines.
Modeling and Analysis of Power Conversion System for High Temperature Gas Cooled Reactor With Cogeneration
Authors: Afrazeh Ali , Khaledi Hiwa , Ghofrani Mohammad Bagher
Published: August 2009

A gas turbine in combination with a nuclear heat source has been subject of study for some years. This paper describes the advantages of a gas turbine combined with an inherently safe and well-proven nuclear heat source. The design of the power conversion system is based on a regenerative, non-intercooled, closed, direct Brayton cycle with high temperature gas-cooled reactor (HTGR), as heat source and helium gas as the working fluid. The plant produces electricity and hot water for district heating (DH). Variation of specific heat, enthalpy and entropy of working fluid with pressure and temperature are included in this model. Advanced blade cooling technology is used in order to allow for a high turbine inlet temperature. The paper starts with an overview of the main characteristics of the nuclear heat source, Then presents a study to determine the specifications of a closed-cycle gas turbine for the HTGR installation. Attention is given to the way such a closed-cycle gas turbine can be modeled. Subsequently the sensitivity of the efficiency to several design choices is investigated. This model is developed in Fortran.
Study on Metal Rubber Material’s Characteristics of Damping and Sound Absorption
Authors: Ma Yanhong , Wang Hong , Li Haoyu , Hong Jie
Published: August 2009

Metal Rubber (MR) is a kind of new-style porous damping material. It is made of wires through choiceness, encircling, wiredrawing, weaving and molding by compression. The special production techniques make its characteristics incomparable, such as high damping, controllable porosity and strong environmental adaptability, besides it is easy to be fabricated into complex shapes. Thus MR can be widely used in many aspects such as damping, sound absorption, seal and thermal protection. The damping and sound-absorbing characteristics of MR material are studied in theory and experiment in the paper, and the applications of MR products are introduced. This paper first presents the characteristics of MR’s stiffness and damping, and the energy dissipating model is used to describe the relative dry friction process of wires. Through static and dynamic experiments, the influencing laws of production techniques and structural parameters on the performance of MR are studied, and the design parameters’ range of different dampers is obtained. The research on the principle of porous acoustic absorption materials is performed. Through measuring the absorption coefficient and acoustic impedance of MR with different structural parameters, the influencing laws of porosity, thickness, cavity size and other factors on sound-absorbing characteristics of MR are obtained.
Control of Short Length-Scale Rotating Stall Inception on a High-Speed Axial Compressor With Plasma Actuation
Authors: Vo Huu Duc , Cameron Joshua D. , Morris Scott C.
Published: August 2009

This paper presents a computational assessment of the use of Single Dielectric Barrier Discharge (SDBD), or plasma, actuators for the suppression of short-length scale (spike) stall inception in a transonic axial compressor. Casing plasma actuation has the potential to provide a robust and effective stall suppression device without compromising compressor performance. The objective of this work is to determine the optimum actuator location and actuation strength needed to suppress spike stall inception at transonic speeds without imposing a penalty on compressor performance. This is done through the implementation of an actuator model in a turbomachinery CFD code for simulations of a transonic research compressor rotor passage to measure the effectiveness of casing plasma actuation in delaying the tip clearance flow criteria that are believed to lead to the formation of spike disturbances. Results show that the casing plasma actuator should be positioned near the rotor leading edge so as to optimize the impact on the interface between the incoming and tip clearance flows as well as for practical consideration. Simulations also indicate that the required actuator strength is higher than that of typical SDBD actuators while still remaining within practical achievable limits. These results will form the basis for experimental validation of the concept in the corresponding research compressor rig in the near future.
Comparison of Discharge Coefficient Measurements and Correlations for Several Orifice Designs With Cross-Flow and Rotation Around Several Axes
Authors: Hu¨ning M.
Published: August 2009

Gas turbines and jet engines consist of a network of connected cavities beside the main gas path, called secondary air system. These cavities, which are often surrounded by stationary and high angular speed rotating walls are exposed to varying pressure and temperature levels of air or oil contaminated air and are connected to each other by orifices or restrictors. It is vital to control the secondary flow, to enable a reliable and efficient engine design, which meets component durability with a minimum of parasitic air consumption. It is essential to understand the flow physics as well as network inter-dependency in order to minimise the flow consumption and yet, meeting engine operating requirements, as well as practical parts component design or manufacturing needs. In this connexion computer network codes containing model conceptions, which can accurately predict orifice flows, are essential. In an effort to provide usable further insight into flows across restrictors such as orifices this publication compares test results, CFD calculations and orifice loss calculation models from the open literature with the aid of transformation laws and contour plots. The influence of different geometric features is incorporated into a model for the calculation of discharge coefficients.