bluuebunny/crossref_metadata_2025 huggingface dataset:
Long-Term Degradation of Ceramics for Gas Turbine Applications
Authors: van Roode Mark , Ferber Mattison K.
Published: March 2009

A study has been conducted to establish the effect of long-term (30,000+ hours) properties of monolithic ceramics (Si3N49 SiC), SiC/SiC and oxide/oxide ceramic matrix composites (CMCs), and protective coatings on component life in gas turbine engines with pressure ratios (PRs) ranging from 5:1 to 30:1. A model has been presented that shows the interaction between two major long-term degradation modes of ceramics, creep and degradation from water vapor attack in the ceramic hot section. Water vapor attack is the most severe mode overshadowing creep for long-term (∼30,000 hours) gas turbine operation, and its impact on component durability becomes more severe as PR increases. Components in the turbine hot section, downstream from the combustor (blades, integral turbine rotors, nozzles), fabricated from Si3N4 without protective coatings, have a temperature limitation of ∼800°C for gas turbines with PR ranging from 5:1 to 30:1. These ceramic components afford little, if any, advantage over metallic components for improving gas turbine performance. The application of a BSAS-type Environmental Barrier Coating (EBC) would improve temperature capability of turbine nozzles and rotating parts to ∼1100–1200°C. For small low-PR (5:1) engines, thick (∼10 mm) uncoated monolithic silicon-based combustor liners can be used up to ∼1360°C and thinner (∼3 mm) SiC/SiC CMCs up to ∼1100°C. These temperatures are reduced for higher-PR engines. The incorporation of a BSAS-type EBC improves temperature capability of silicon-based ceramic combustor liners. Oxide/oxide CMCs with protective coatings have a predicted temperature capability of ∼1220-∼1380°C over the range of PR range studied. They can be used as structural materials for combustor liners and other stationary turbine hot section components. As PR increases the durability of coated oxide/oxide CMCs improves relative to that of silicon-based monolithics and CMCs. As expected, ceramic component durability increases for shorter component design lives, making these materials more acceptable for shorter-term applications, such as automotive transportation (∼3,000 hours/150,000 km).
Aero-Thermal Investigations of Tip Leakage Flow In Axial Flow Turbines: Part II — Effect of Relative Casing Motion
Authors: Krishnababu S. K. , Dawes W. N. , Hodson H. P. , Lock G. D. , Hannis J. , Whitney C.
Published: March 2009

A numerical study has been performed to investigate the effect of casing motion on the tip leakage flow and heat transfer characteristics in unshrouded axial flow turbines. The relative motion between the blade tip and the casing was simulated by moving the casing in a direction from the suction side to the pressure side of the stationary blade. Baseline flat tip geometry and squealer type geometries namely double squealer or cavity and suction side squealer were considered at a clearance gap of 1.6%C. The computations were performed using a single blade with periodic boundary conditions imposed along the boundaries in the pitchwise direction. Turbulence was modelled using the SST k-ω model. The flow conditions correspond to an exit Reynolds number of 2.3×105. The results were compared with those obtained without the relative casing motion reported in part I of this paper. In general, the effect of relative casing motion was to decrease the tip leakage mass flow and the average heat transfer to the tip due to the decrease in leakage flow velocity caused by a drop in driving pressure difference. Compared to the computations with stationary casing, in the case of all the three geometries considered, the average heat transfer to the suction surface of the blade was found to be larger in the case of the computations with relative casing motion. At a larger clearance gap of 2.8%C, in case of flat tip, while the tip leakage mass flow decreased due to relative casing motion only a smaller change in the average heat transfer to the tip and the suction surface of the blade was noticed.
Coatings for High Temperature Foil Bearings
Authors: Heshmat Hooshang , Jahanmir Said , Walton James F.
Published: March 2009

High operating speeds and temperatures required for advanced turbomachinery necessitate the development of bearings capable of continuous operation between 3 to 4 million DN at temperatures up to 820°C. Non-contact oil-free bearings such as compliant foil bearings, active magnetic bearings and hybrid foil and magnetic bearings are alternate solutions to the current liquid-lubricated hydrodynamic and rolling element bearings, which have limited life under these extreme conditions. A critical component in these oil-free bearings is the tribological coating system that must be used on the journal and the foil pads to ensure reliable operation during transient periods and start-stop cycles. The purpose of the present investigation was to assess the reliability of tribological coatings being implemented for a large (150 mm diameter) hybrid foil/magnetic bearing. In order to be suitable for use in large turbine engine type applications, the journal coating must accommodate the thermal and centrifugal growth experienced as well as providing the wear life and friction coefficient. Based upon the limitations identified in PS304, this coating is not yet suitable for demanding high temperature and high-speed applications. On the other hand an alternative nickel-chrome based coating applied to the foils versus a shaft with thin dense chrome or a nickel-chrome based coating a has shown excellent characteristics under conditions up to 820°C.
Strategies for Integration of Advanced Gas and Steam Turbines in Power Generation Applications
Authors: Zachary Justin J.
Published: March 2009

Combined cycle power plants (CCPPs) using fossil fuel generate the cleanest and most efficient form of electrical power. CCPP technologies have evolved significantly in providing better, more cost-effective products: gas turbines (GTs), steam turbines (STs), heat recovery steam generators (HRSGs), heat sinks, pollutant removal technologies, balance of plant (BOP), water treatment and fuel treatment equipment, etc. A major reason for these improvements was the introduction of the G and H technologies for gas turbines, in which an inseparable thermodynamic and physical link was created between the primary and secondary power generation systems by using steam instead of air, in a closed loop to perform most (or all) turbine cooling activities.
Explicit Finite Element Models of Friction Dampers in Forced Response Analysis of Bladed Discs
Authors: Petrov E. P.
Published: March 2009

A generic method for analysis of nonlinear forced response for bladed discs with friction dampers of different design has been developed. The method uses explicit finite element modelling of dampers, which allows accurate description of flexibility and, for the first time, dynamic properties of dampers of different design in multiharmonic analysis of bladed discs. Large-scale finite element damper and bladed disc models containing 104–106 DOFs can be used. These models, together with detailed description of contact interactions over contact interface areas, allow for any level of refinement required for modelling of elastic damper bodies and for modelling of friction contact interactions. Numerical studies of realistic bladed discs have been performed with three different types of underplatform dampers: (i) a ‘cottage-roof’ (called also ‘wedge’) damper; (ii) seal wire damper; and (iii) a strip damper. Effects of contact interface parameters and excitation levels on damping properties of the dampers and forced response are extensively explored.
Experimental and Computational Analysis of a Gas Compressor Windback Seal
Authors: Morrison G. L. , Al-Ghasem Adnan
Published: March 2009

A gas windback seals is similar to a labyrinth seal except the cavity is one continuous channel which winds around the shaft like a screw thread. One application is in gas compressors to isolate lubrication oil from the gas flow paths. A CFD based study of clearance, pressure ratio, and shaft speed has been performed. One seal geometry was experimentally studied to provide verification of the CFD accuracy. An empirical model for the leakage rate has been developed which fits the data with a standard deviation of 0.8%. The effects of pressure ratio and shaft speed upon the leakage rate are independent of each other. Analysis of the CFD results indicate that the kinetic energy carry over coefficient is substantially less for the windback seal operating at low differential pressures and gas densities than for a labyrinth seal operating under typical conditions.
Film Effectiveness Performance for Coolant Holes Imbedded in Various Shallow Trench and Crater Depressions
Authors: Dorrington John R. , Bogard David G. , Bunker Ronald S.
Published: March 2009

Film cooling adiabatic effectiveness was investigated for various configurations of coolant holes embedded in shallow transverse trenches or circular and elliptical shaped depressions. As a basis of comparison, a shaped hole configuration was also tested. Tests were conducted on the suction side of a simulated vane at a downstream location where pressure gradient and curvature effects were small. For the transverse trench, effects of the trench width with varying depths, the trench wall angle, and the pitch between holes within the trench were investigated with trench depths that ranged from 0.5d to 1d. The crater depressions were tested at a depth of 0.5d. The film effectiveness for the crater depressions was not as good as the best performing trench configuration at that depth, but they all performed better than the baseline configuration of cylindrical holes. The trench configurations were found to have an optimum depth of 0.75d, with little improvement in performance for trench depths greater than this. Comparison of the trench performance with a typical shaped hole configuration showed that film effectiveness for the trench was similar to that of the shaped holes.
A Steady-State Method for the Determination of Casing Convective Heat Transfer Coefficient and Reference Free-Stream Temperature in an Axial Flow Turbine
Authors: Gumusel B. , Camci C.
Published: March 2009

The present study explains a steady-state method of measuring convective heat transfer coefficient on the casing of an axial flow turbine. The goal is to develop an accurate steady-state heat transfer method for the comparison of various casing surface and tip designs used for turbine performance improvements. The free-stream reference temperature, especially in the tip gap region of the casing varies monotonically from the rotor inlet to rotor exit due to work extraction in the stage. In a heat transfer problem of this nature, the definition of the free-stream temperature is not as straight forward as constant free-stream temperature type problems. The accurate determination of the convective heat transfer coefficient depends on the magnitude of the local free-stream reference temperature varying in axial direction, from the rotor inlet to exit. The current study explains a strategy for the simultaneous determination of the steady-state heat transfer coefficient and free-stream reference temperature on the smooth casing of a single stage rotating turbine facility. The heat transfer approach is also applicable to casing surfaces that have surface treatments for tip leakage control. The overall uncertainty of the method developed is between 5% and 8% of the convective heat transfer coefficient.
Turbine Airfoil Net Heat Flux Reduction With Cylindrical Holes Embedded in a Transverse Trench
Authors: Harrison Katharine L. , Dorrington John R. , Dees Jason E. , Bogard David G. , Bunker Ronald S.
Published: March 2009

Film cooling adiabatic effectiveness and heat transfer coefficients for cylindrical holes embedded in a 1d transverse trench on the suction side of a simulated turbine vane were investigated to determine the net heat flux reduction. For reference, measurements were also conducted with standard inclined, cylindrical holes. Heat transfer coefficients were determined with and without upstream heating to isolate the hydrodynamic effects of the trench and to investigate the effects of the thermal approach boundary layer. Also the effects of a tripped versus an un-tripped boundary layer were explored. For both the cylindrical holes and the trench, heat transfer augmentation was much greater with no tripping of the approach flow. A further increase in heat transfer augmentation was caused by use of upstream heating, with as much as a 150% augmentation with the trench. With a tripped approach flow the heat transfer augmentation was much less. The net heat flux reduction for the trench was found to be significantly higher than for the row of cylindrical holes.
Rotordynamic Response and Identification of AMB Machining Spindle
Authors: Sawicki Jerzy T. , Maslen Eric H.
Published: March 2009

Active magnetic bearings (AMBs) are a very promising technology for machining applications. They offer a number of advantages compared to classical bearings, such as high speed capability, rotation accuracy, high stiffness, and possibility of active displacement tracking. This paper presents a modeling approach for a high-speed machining spindle-AMBs system based on finite-element model analysis coupled to experimental modal identification. The extracted frequency response functions, measured between the magnetic bearing journals and the sensor locations, are compared with the responses of a rotor model, and a calibration procedure is applied to reduce the discrepancies between the model and the measured data.
Performance Analysis of an Auxiliary Power Unit Based on Static/Dynamic Mathematic Modeling
Authors: Kim SooYong , Yepifanov Sergey V.
Published: March 2009

Present work is about performance analysis of an auxiliary power unit (APU) based on mathematic modeling of static and dynamic regime. Climatic and load characteristic of the engine are investigated with air bleed off and power takeoff conditions. Transient analysis with variation in external and control actions were also made. Present results can be used as input data for designing the automatic control system (ACS).
Effect of Higher-Order Hydrocarbons on Methane-Based Fuel Chemistry at Gas Turbine Pressures
Authors: Bourque Gilles , Healy Darren , Curran Henry , Simmie John , de Vries Jaap , Antonovski Viktorio , Corbin Benjamin , Zinner Christopher , Petersen Eric
Published: March 2009

A chemical kinetics mechanism designed for the oxidation of methane-hydrocarbon blends at elevated pressures was used to study the effect of higher-order hydrocarbons on ignition delay time and flame speed at gas turbine conditions. The mechanism was developed from recent data and modeling conducted by the authors, including pressures above 30 atm, temperatures as low as 700 K, and alkane additives from C2H6 through C5H12. Calculations focused on three target natural gas mixtures containing CH4 mole fractions from 62.5 to 98%. The results show the effects that pressure, temperature, and hydrocarbon content have on the combustion chemistry of the fuel-air mixtures. For example, autoignition times exhibit nonlinear trends with increasing pressure and decreasing temperature. Experiments in the authors’ laboratories are ongoing, and an overview of the related facilities is provided.
Significance of Solar Radiation on Aircraft Engine Under Cowl Temperature
Authors: Abu Talib A. R. , Jaafar A. A. , Mokhtar A. S. , Razali A. H.
Published: March 2009

Literature on solar radiation effect on aircraft engine under cowl temperature is very limited. This paper describes an experimental work to quantify the effect of solar radiation levels on a range of aircraft engine nacelle surface finish and orientation in a representative way. The investigation was carried out on four aircraft engine nacelle representations during static ground running conditions. The nacelle models were fabricated using aluminium and surface coated with four different aircraft paint finish. Thermocouples were mounted at locations around the nacelle model. Effects of different solar radiation levels on the temperature distributions on the nacelles were presented. The contributions of radiative and convective heat transfer on the overall distribution of temperature inside the under cowl were quantified.
PIV Measurements of Combustor Turbulence Fields
Authors: Spencer Adrian , Hollis David , Carrotte Jon
Published: March 2009

An experimental study has been conducted on a full-scale, three-sector, isothermal model of a gas turbine combustor. PIV has been used as the main instrumentation technique and this has been validated against LDA and hot-wire velocity measurements of the same geometry. These data combine to provide high quality boundary condition and validation data for CFD predictions. Substantial care has been taken in assuring the quality of the PIV data. In high turbulence intensity flow fields, low pass spatial filtering can artificially reduce the Reynolds stresses calculated from the PIV measured velocities. The level of this filtering depends upon the ratio of the integral lengthscales in the flow field to the size of the measurement volume of the PIV interrogation cell. Within the highly turbulent flow field of a combustor there exist a very wide range of turbulent length scales. Consideration should therefore be given to any measurements taken in a combustor, hot or cold, to take account of this sub-grid filtering effect. A method is described to overcome this problem and it is demonstrated to be successful by comparing with LDA and PIV data (at increased magnification) that does not suffer this problem. Sparse LDA and HWA data for the combustor is thus complemented by more dense planar PIV data to allow a more complete mapping of the velocity field. This has allowed better understanding of the processes occurring in the combustor such as the jet impingement process and the fuel injector swirler flow interaction with the primary jets. In addition detailed information on turbulence statistics, integral lengthscales, spatial correlation and energetic structure identification is available.
Review of Heat Exchanger Studies for High-Efficiency Gas Turbines
Authors: Jeong Ji Hwan , Kim Lae Sung , Lee Jae Keun , Ha Man Yeong , Kim Kui Soon , Ahn Young Cheol
Published: March 2009

Air transportation has been being expanded remarkably, and its growth is expected to continue in the coming decades. Environmental issues and airlines require gas turbine manufacturers to produce environmentally friendly gas-turbine engines with lower emissions and improved specific fuel consumption. These requirements can be met by incorporating heat exchangers into gas turbines for intercooling and recuperation. Relevant research in such areas as the design of a heat exchanger matrix, materials selection, and manufacturing technology and optimization has been carried out by a variety of researchers. These works are reviewed in this paper. The recent advance in technologies appears to herald the development of intercoolers and recuperators for civil aeroplane gas turbines. Based on results reported in previous studies, potential heat exchanger designs for an aero gas turbine recuperator, intercooler, and cooling-air cooler are suggested.
Performance Testing of Microturbine Generator System Fueled by Biodiesel
Authors: Chiang Hsiao-Wei D. , Chiang I-Che , Li Hsin-Lung
Published: March 2009

Using microturbine generator systems for distributed power generation has become the recent trend. To face the impact of the global energy crisis, one of the options is to use biofuels including biodiesel. To this end, this program is to perform study on biodiesel microturbine testing and analysis. A 150kW microturbine generator set with twin rotating disk regenerators was used. Designed as a vehicular microturbine engine, the twin rotating ceramic disk regenerators dramatically improve fuel consumption by transferring heat energy from the exhaust gas stream to compressor discharge. This paper involved testing of the microturbine generator set at different load conditions using 10%–30% biodiesel fuel. A software program was used to predict the performance of the microturbine generator set at different operating conditions in order to compare with the test results. Both biodiesel and petrodiesel fuels are used on the microturbine generator system in this study and the results will be compared.
Effect of Strain Rate and Pressure on the Flame Structure and Emission Characteristics of Syngas Flames
Authors: Som Sibendu , Rami´rez Anita I. , Hagerdorn Jonathan , Saveliev Alexei , Aggarwal Suresh K.
Published: March 2009

Synthesis gas or “Syngas” is being recognized as a viable energy source worldwide, particularly for stationary power generation due to its wide flexibility in fuel sources. There are gaps in the fundamental understanding of syngas combustion and emissions characteristics, especially at elevated pressures, high strain rates and in more practical conditions. This paper presents a numerical and experimental investigation to gain fundamental understanding of combustion and emission characteristics of syngas with varying composition, pressure and strain rate. Two representative syngas fuel mixtures, 50% H2 / 50% CO and 5% H2 / 95% CO (% vol.), are chosen, three detailed chemical kinetic models are used namely, GRI 3.0, Davis et al. and Li et al. mechanisms. Davis et al. mechanism agrees best with the experimental data hence is used to simulate the partially premixed flame structures at all pressures. Results indicate that for the pressure range investigated, a typical double flame structure was observed characterized by a rich premixed reaction zone (RPZ) on the fuel side and a nonpremixed reaction zone (NPZ) at the oxidizer side nozzle with the stabilizing due to the H2 chemistry rather than the CO chemistry. Sensitivity analysis to mass burning rates for unstretched laminar flame shows that flames are more sensitive to H2 chemistry. For both representative mixtures an increase in pressure leads to a significant increase in NO due to increase in flame temperature. The emission index for these flames is also found to follow a similar behavior with pressure. Although flame temperatures were higher for flame A, total NO is lower for these flames due to increases in reburn characteristics. Thermal route dominates NO production while, prompt route is negligible. Experimental analysis on the stability of nonpremixed syngas/air flames showed that the flames were very stable for the range of strain rates investigated. At low strain rates it required 0.5% H2 to establish a stable flame.
Gas Turbine Diagnostics Under Variable Operating Conditions
Authors: Loboda Igor , Feldshteyn Yakov , Yepifanov Sergiy
Published: March 2009

Operating conditions (control variables and ambient conditions) of gas turbine plants and engines vary considerably. The fact that health monitoring has to be uninterrupted creates the need for a run time diagnostic system to operate under any conditions. The diagnostic technique described in this paper utilizes the thermodynamic models in order to simulate gaspath faults and uses neural networks for the faults localization. This technique is repeatedly executed and the diagnoses are registered. On the basis of these diagnoses and beforehand known faults, the correct diagnosis probabilities are then calculated. The present paper analyses the influence of the operating conditions on a diagnostic process. In the technique, different options are simulated of a diagnostic treatment of the measured values obtained under variable operating conditions. The mentioned above probabilities help to compare these options. The main focus of the paper is on the so called multipoint (multimode) diagnosis that groups the data from different operating points (modes) to set only a single diagnosis.
Integrated Technology Investment Plan for Aeropropulsion Testing at Arnold Engineering Development Center
Authors: Rouser Kurt , Vining Charles , McAmis Robert
Published: March 2009

This paper presents the integrated investment plan that Arnold Engineering Development Center (AEDC) has established for aeropropulsion testing technology. Near and far term technology drivers are addressed in the forecast for test and evaluation capability requirements. Recent technology advancements are described and related to current AEDC testing capabilities. Technology investment areas include intrusive and non-intrusive diagnostics, modeling and simulation, test protocols, and data acquisition and processing. Focus is given to the integration of these technologies with each other, with AEDC facility capabilities, and with forecasted workload requirements. Anticipated budget downsizing has motivated AEDC to prioritize current capabilities and consider partnerships with other federal entities, along with commercial industry and academic institutions. Detailed treatment of particular technology initiatives is presented here along with current collaborative efforts. This paper provides both strategic and tactical vision for continued development of aeropropulsion testing technology at AEDC.
Combined Steam-Turbine Power Producing Concept With Recirculating Steam Compressor
Authors: Stankovic Branko
Published: March 2009

This concept shows that an efficient combined cycle, comprising topping & bottoming cycle, does not have to be privilege of gas turbine plants only, but could also be achieved with steam turbine plants. An efficient power-producing concept of a combined steam-turbine cycle with addition of a recirculating steam compressor is disclosed. Topping part of such a combined steam-turbine cycle operates at elevated steam turbine inlet temperature and pressure, while its “waste heat” is recovered by the bottoming part of the combined cycle in a heat-recovery boiler (steam heat exchanger). The recirculating steam compressor pumps the cooled majority of the entire steam flow to the maximum cycle pressure, while smaller steam flow fraction continues its full expansion to some low pressure in a condenser. The cycle waste heat could be transferred to the bottoming part of the combined cycle in a variety of modalities, depending on the chosen main high-temperature steam-turbine inlet temperature and inlet pressure (supercritical/subcritical). At an assumed constant steam-turbine inlet temperature of 900°C (∼300 bar), a very high gross cycle thermal efficiency could potentially be achieved, ranging from 56 to 62% with the high-temperature steam-turbine pressure ranging from subcritical (30 bar) to supercritical (300 bar). Such a combined steam-turbine cycle seems to be a suitable energy conversion concept that could be applied in classic thermal power plants powered by coal, but also seems as an ideal option for application in the new generation of gas-cooled nuclear rectors, where the gaseous reactor coolant, heated up to 1000°C, would indirectly transfer its heat content to working fluid (superheated steam) of the topping part of the combined steam-turbine cycle. Alternatively, the proposed concept may be combined with renewable energy sources of a sufficient temperature level.
Shutdown Modelling to Extend Operation to Extreme Ambient Conditions
Authors: Svensdotter Susanne , Skelton Lee , Ingle John
Published: March 2009

This paper presents a discussion of heat soak-back for various gas turbine engine shutdown scenarios, compares with experimental data and discusses how the temperatures at the shutdown point can be used to approximately determine a suitable shutdown procedure for ambient and hot ambient conditions in order to control the bearing soak back peak. The investigation was performed by running the test vehicle at various engine conditions and shutdown procedures while measuring the temperatures at the bearing outer tracks. The data acquisition continued after the engine shutdown until the temperature data showed that the soak-back peak temperature had passed. The tested engine conditions were replicated in a FEM model of the turbine, from which knowledge was gained of the turbine discs temperatures during the shutdown and subsequent cooling down. It was shown that the bearing soak-back and cooling down after shutdown is determined by the cooling down of the turbine discs. The discs are directly affected by the blade temperature reduction, which in turn is depending on how the air trapped in the main gas annulus after the engine has stopped rotating is cooling down. The cooling down of the main annulus air is due to free convection and conduction to the surrounding metal, and cannot be readily predicted with current tools (the air is not moving). Therefore, an approximation of the temperature behaviour is needed. It was decided for the present study to investigate the correlation between the disc temperature at the shutdown point with the bearing soak-back peak temperature and time. It was found that the disc rim temperature at the shutdown point could be used to determine an approximate soak-back peak and thereby the need for motor-overs (MO). The conclusions are that various shutdown procedures and motor over cooling can be used in order to extend the engine operability without expensive bearing redesign.
Hybrid-Grid Simulation of Unsteady Wake-Boundary Layer Interaction on a High Lift Low Pressure Turbine Airfoil
Authors: Yang Hong , Roeber Thomas , Kozulovic Dragan
Published: March 2009

The unsteady wake-boundary layer interaction on a high lift low pressure (LP) turbine airfoil T106C was investigated by applying the hybrid structured-unstructured RANS solver developed at the DLR. The simulation domain was split into two parts: a translational one with moving bars and a stationary one with turbine airfoils, and in between was a sliding mesh interface. An unstructured grid was generated around the moving bars with particular clustering along the wake path to have a sharp resolution of the shedding vortex street, whereas the stationary blade airfoil subject to the incoming wakes was meshed with a block-structured grid to ease the implementation of the laminar-turbulent transition model around the airfoil. The Wilcox two-equation k-ω turbulence model was applied in conjunction with a multi-mode transition model developed by the authors taking into account several modes of transition, namely natural/bypass, separated-flow and wake-induced transition modes. In this paper, the hybrid-grid modeling is first validated against measurements from the VKI, and then the unsteady flow mechanisms associated with the shedding vortices and the multi-mode transition on the blade airfoil are analyzed. Furthermore, the quasi-steady mixing-plane model on the hybrid grids is also assessed by a comparison with the time-mean of the unsteady state solutions. In particular, different chopping to the incoming vortex street at the blade leading edge is found to have different effects on the separation and transition over the blade suction surface. At the end a composite picture of the boundary-layer development over the suction surface is summarized.
Carbon Capture and Reduced Irreversibility Combustion Using Chemical Looping
Authors: McGlashan Niall R. , Heyes Andrew L. , Marquis Andrew J.
Published: March 2009

Power generation traditionally depends on combustion to ‘release’ the energy contained in fuels. Combustion is, however, an irreversible process and typically accounts for a quarter to a third of the lost work generation in power producing systems. The source of this irreversibility is the large departure from chemical equilibrium that occurs during the combustion of hydrocarbons. Chemical looping combustion (CLC) is a technology initially proposed as a means to reduce the lost work generation in combustion equipment. However, renewed interest has been shown in the technology since it also facilitates carbon capture. CLC works by replacing conventional “oxy-fuel” combustion with a two-step process. In the first, a suitable oxygen carrier (typically a metal) is oxidised using air. This results in an oxygen depleted air stream and a stream of metal oxide. The latter is then reduced in the second reaction step using a hydrocarbon fuel. The products of this second step are a stream of reduced metal, which is returned to the oxidation reaction, and a stream of CO2 and H2O that can be separated easily. The thermodynamic benefits of CLC stem from the fact that the oxygen carrier is recirculated and can thus be chosen with a reasonable degree of freedom. This enables the chemistry to be optimised to reduce the lost work generation in the two reactors – the reactions can then be operated much closer to chemical equilibrium. It is widely accepted in the literature that a key issue in CLC is identifying the most effective oxygen carrier. However, most previous work appears to consider systems in which a solid phase metallic oxygen carrier is recirculated between two fluidised bed reactors. In the current paper, we explore the possibility of using liquid or gas phase reactions in the two reaction steps since it is hypothesised that these might be compatible with a wider range of fuels including coal. The paper, however, starts by reviewing the existing literature on CLC and the basic thermodynamics of a conceptual CLC power plant. The thermodynamic analysis is extended to include a general method for calculating the lost work generation in a given chemical reactor. Finally, this method is applied to the oxidation reaction of a proposed CLC reaction scheme.
A Hybrid LES/RANS Calculation of Subsonic, Supersonic Hot Jet Noise
Authors: Cai Xiaodan , Ladeinde Foluso
Published: March 2009

In this paper, pure RANS and hybrid LES/RANS procedures have been investigated for the simulation of jet noise from subsonic and supersonic, hot jets. The aerodynamic predictions from the RANS calculations agree well with experimental measurements. It is emphasized that the RANS-based acoustic analogy method used is incapable of capturing the sound characteristics at small jet angles, which are dominated by the sound radiated from large-scale turbulent structures. The hybrid LES/RANS approach investigated by Shur et al is examined. The preliminary results for a subsonic, hot jet (Set Point 46 in Tanna’s experiment) have shown that this method can capture, satisfactorily, the near-filed velocity and pressure signatures induced by large-scale turbulent structures. It is our goal to establish the feasibility and advantages of using a high-fidelity tool for predicting both small scale and large-scale supersonic jet noise with arbitrary complex geometries and under realistic flight conditions.
Characteristics in Response Integration and Bifurcation of a Forced Duffing Oscillator
Authors: Jeng Jang-Der , Kang Yuan , Chang Yeon-Pun , Shyr Shyh-Shyong
Published: March 2009

The Duffing oscillator is well-known models of nonlinear system, with applications in many fields of applied sciences and engineering. In this paper, a response integration algorithm is proposed to analyze high-order harmonic and chaotic motions in this oscillator for modeling rotor excitations. This method numerically integrates the distance between state trajectory and the origin in the phase plane during a specific period and predicted intervals with excitation periods. It provides a quantitative characterization of system responses and can replace the role of the traditional stroboscopic technique (Poincare´ section method) to observe bifurcations and chaos of the nonlinear oscillators. Due to the signal response contamination of system, thus it is difficult to identify the high-order responses of the subharmonic motion because of the sampling points on Poincare´ map too near each other. Even the system responses will be made misjudgments. Combining the capability of precisely identifying period and constructing bifurcation diagrams, the advantages of the proposed response integration method are shown by case studies. Applying this method, the effects of the change in the stiffness and the damping coefficients on the vibration features of a Duffing oscillator are investigated in this paper. From simulation results, it is concluded that the stiffness and damping of the system can effectively suppress chaotic vibration and reduce vibration amplitude.
Validation of MISES 2-D Boundary Layer Code for High Pressure Turbine Aerodynamic Design
Authors: Andrew Philip L. , Kahveci Harika S.
Published: March 2009

Avoiding aerodynamic separation and excessive shock losses in gas turbine turbomachinery components can reduce fuel usage, and thus reduce operating cost. In order to achieve this, blading designs should be made robust to a wide range of operating conditions. Consequently, a design tool is needed which can be executed quickly for each of many operating conditions, and on each of several design sections which will accurately capture loss, turning and loading. This paper presents the validation of a boundary layer code, MISES, versus experimental data from a 2-D linear cascade approximating the performance of a moderately-loaded, mid-pitch section from a modern aircraft high-pressure turbine [1–2]. The validation versus measured loading, turning, and total pressure loss is presented for a range of exit Mach numbers from ≈ 0.5 to 1.2, and across a range of incidence from −10° to +14.5° relative to design incidence.
Simultaneous Thermochromic Liquid Crystal Calibration and Calculation of Heat Transfer Coefficients
Authors: Ferguson James R.
Published: March 2009

The use of thermochromic liquid crystals (TLCs) to indicate surface temperature in transient experiments designed to measure heat transfer coefficients requires careful calibration of the crystals. The calibration can be affected by lighting and viewing angles, light source spectral characteristics, surface preparation, and application procedure of the TLCs. A method is proposed whereby the calibration of the TLCs and calculation of heat transfer coefficients are conducted simultaneously using inverse techniques for the case of a suddenly heated semi-infinite wall. The calibration inherently accounts for the problems typically associated with the use of liquid crystals and results from simulated experiments indicate accuracy to within five percent is possible.
Dynamics and Stability Limits of Syngas Combustion in a Backward-Facing Step Combustor
Authors: Speth Raymond L. , Altay H. Murat , Ghoniem Ahmed F.
Published: March 2009

The stability bands and combustion dynamics of syngas under different operating conditions and fuel compositions are investigated. Pressure measurements and high-speed video data are used to distinguish three operating modes. A stable region near the lean flammability limit is characterized by the shedding of small-scale vortices in the shear-layer. A quasistable region is present at intermediate equivalence ratios. At high equivalence ratios, we observe an unstable operating mode characterized by the periodic interaction between a large vortex and the flame. As the amount of hydrogen in the fuel is increased, the lean flammability limit is extended and transitions between operating regimes moves to lower equivalence ratios. Numerical simulations performed using a vortex method correspond to the experimental measurements and confirm the observed instability mechanism.
Heat Transfer on Convective Surfaces With Pin-Fins Mounted in Inclined Angles
Authors: Chyu M. K. , Oluyede E. O. , Moon H.-K.
Published: March 2009

Casting of pin fins at the trailing edge of the turbine blades often presents some difficulties due to tight dimensional tolerances, leaving the pin fins inclined after the casting process. This study is to experimentally examine the effects of such an imperfect manufacturing phenomena on the heat transfer and friction characteristics over pin-fin arrays with different pin inclinations. The test model is a staggered short (H/D = 1) pin-fin array with an inter-pin spacing of 2.5 times the pin-diameter (S/D = 2.5) in both longitudinal and transverse directions. Detailed local heat transfer coefficients on both array endwalls and pin elements are determined using the transient liquid crystal technique, as the inclined angle θ varies from 40° to 90° and the Reynolds number ranges from 7.0 × 103 and 1.3 × 104. The measured data suggest that an increase in pin inclined angle relative to its normal orientation (90-degree) significantly reduces the level of heat transfer enhancement from the array. Such a reduction amounts to nearly 50% for the 40-degree case. The accompanied friction loss also decreases.
The Study of Thermal Properties and Micro Structures of YSZ
Authors: Guo S. M. , Silva M. B. , Mensah Patrick F. , Uppu Nalini
Published: March 2009

Thermal barrier coatings (TBCs) are used in gas turbine engines to achieve a better efficiency by allowing increased turbine inlet temperature and decreasing the amount of cooling air used. Plasma spraying is one of the most reliable methods to produce TBCs, which are generally comprised of a top coating of ceramic and a bond-coat of metal. Usually, the top coating is Yttria-Stabilized-Zirconia (YSZ), providing the thermal barrier effect. The bond-coat is typically a layer of M-Cr-Al-Y (where “M” stands for “metal”), employed to improve the attachment between the ceramic top-coat and the substrate. Due to the extreme temperature gradient presented in the plasma jet and the wide particle size distribution, during the coating process, injected ceramic powders may experience a significantly different heating process. Different heating history, coupled with the substrate preheating temperature, may affect the thermal properties of the YSZ layers. In this paper, four sets of mol 8% YSZ disks are fabricated under controlled temperatures of 1100°C, 1200°C, 1400°C and 1600°C. Subsequently the thermal properties and the microstructures of these YSZ disks are studied. The results indicate a strong microstructure change at a temperature slightly below 1400°C. For a high sintering temperature, a dense YSZ layer can be formed, which is good for gas tight operation; At low sintering temperature, say 1200°C, a porous YSZ layer is formed, which has the advantage of low thermal conductivity. For gas turbine TBC applications, a robust low thermal conductivity YSZ layer is desirable, while for Solid Oxide Fuel Cells, a gas-tight YSZ film must be formed. This study offers a general guideline on how to prepare YSZ layers, mainly by controlling the heating process, to form microstructures with desired properties.
A Subspace Method for Modal Identification of Bladed Assemblies Using Blade Tip-Timing Data
Authors: Salhi Bendali , Berthillier Marc , Lardies Joseph , Voinis Philippe , Bodel Charles
Published: March 2009

Unknown excitation forces are applied to bladed disk assemblies, such as turbines blades, leading to forced vibration responses. Non contact measurement of such vibrations using blade tip-timing data has become an industrial standard procedure and current research focuses on analysis methods for interpretation of measured vibrations. Our purpose is to develop a method for identification of the blade’s natural frequencies and damping ratios using blade tip-timing data. The method is based on a subspace analysis. Its performance is compared to the traditional Fast Fourier Transform analysis. A detailed description of these methods and results are presented.
The Sealing Behavior and Force Analysis of a Double-Laminate Single-Padded Finger Seal
Authors: Li Hongmin , Braun Minel J.
Published: March 2009

Finger seals represent a new type of non-contacting seals that allow leakages comparable, or lower than those of the brush seals, while at the same time eliminating the major brush seal drawback: contact and debris production at the shaft/seal interface. This paper presents a numerical investigation of the sealing behavior of a finger seal, which consists of a padded laminate, a padless laminate, and a backplate with a pressure dam. The flow, pressure, and the leakage through a full assembly are obtained by solving the combined full Navier-Stokes and energy equations. Results indicate that the leakage through the pressure chamber varies only with the axial pressure differential. Leakage depends on the axial pressure differential and the finger lifting distance. The lifting force on the pad bottom consists of the hydrodynamic lifting force and the pressure force due to the axial pressure differential. In order for the finger seal to be fully adaptive, the hydrodynamic lifting force has to be dominating over the axial effects.
Analysis of Turbulent Flow in 180° Turning Ducts With and Without Guide Vanes
Authors: Luo Jiang , Razinsky Eli H.
Published: March 2009

This paper presents a numerical study of the turbulent flows through a number of 2-D and 3-D 180° U-ducts, with and without guide vanes, using the Reynolds-averaged Navier-Stokes method. Computations have been first carried out for a 2-D U-duct flow (W/H = 1.0) with four turbulence models (V2F, k-ε, SST and Reynolds stress). The models’ capability for streamline curvature effects on turbulence and separation has been assessed, using flow and turbulence data. The effects of adding a guide vane inside the bend have been analyzed, to reduce/avoid flow separation. Three vanes with different radial locations have been studied, and the mechanism for pressure loss reduction has been examined. Analyses have been performed for turbulent flows in 3-D U-ducts with square cross-section and sharp 180° turning (W/D = 0.2), similar to the U-bends in typical turbine blade cooling passages. The predictions are compared with the data of outer wall pressure. The effects of the guide vane and outer-wall shape on the flow separation, secondary-flow vortices and pressure loss have been evaluated. The combined vane and uniform cross-section area provide a large benefit for the flow distribution and pressure loss reduction.
A Comparative Investigation of Round and Fan-Shaped Cooling Hole Near Flow Fields
Authors: Porter James S. , Sargison Jane E. , Walker Gregory J. , Henderson Alan D.
Published: March 2009

This study presents velocity and turbulence data measured experimentally in the near field of a round and a laterally expanded fan-shaped cooling hole. Both holes are fed by a plenum inlet, and interact with a turbulent mainstream boundary layer. Flow is Reynolds number matched to engine conditions to preserve flow structure, and two coolant to mainstream blowing momentum ratios are investigated experimentally. Results clearly identify regions of high shear for the round hole as the jet penetrates into the mainstream. In contrast, the distinct lack of high shear regions for the fan shaped hole point to reasons for improvements in cooling performance noted by previous studies. Two different CFD codes are used to predict the flow within and downstream of the fan shaped hole, with validation from the experimental measurements. One code is the commercially available ANSYS CFX 10.0, and the other is the density-based solver with low Mach number preconditioning, HYDRA, developed in-house by Rolls-Royce plc for high speed turbomachinery flows. Good agreement between numerical and experimental data for the center-line traverses was obtained for a steady state solution, and a region of reversed flow within the expansion region of the fan-shaped hole was identified.