bluuebunny/crossref_metadata_2025 huggingface dataset:
Position-Mode Haptic-Based Control of Teleoperated Hydraulic Actuators
Authors: Zarei-nia Kurosh , Sepehri Nariman
Published: May 2012

A control scheme for teleoperation of hydraulic actuators, using a haptic device, is developed and experimentally evaluated in this paper. In the control laws, the position error between the displacement of the haptic device and the hydraulic actuator movement is used at both master and slave sides to maintain good position tracking at the actuator side while providing a haptic force to the operator. Lyapunov’s stability theory and LaSalle’s invariant set theorems are employed to prove the asymptotic stability of the system. It is shown that beside stability, the system performs well in terms of position tracking of the hydraulic actuator and providing a feel of telepresence to the operator. Proposed controller only needs system’s pressures and displacements that are easy to obtain via on-line measurements. Additionally, the controller does not need any information about the parameters of the system. These characteristics make the controller very attractive from the implementation view point.
Dynamic Model of the Piston-Ring Assembly Using Curved Beam Finite Elements
Authors: Hakeem Mohannad , Chalhoub Nabil G. , Schihl Peter
Published: May 2012

A dynamic model for the crankshaft/connecting-rod/piston-assembly for a single cylinder engine is developed. The model considers the rigid body motion of the crank-slider mechanism including the piston secondary motions such as the piston-slap and piston-tilting. The formulation considers the ring to have three rigid body degrees of freedom in addition to its longitudinal and in-plane transverse deformations. The structural flexibility terms are approximated by using curved beam finite element method. The dynamic model has a variable structure whereby the number of degrees of freedom depends on the piston-liner and piston-ring interactions. Its formulation does not include frictional losses. The simulation results illustrate the piston secondary motions along with the ring tilting angles relative to the piston orientation for the total duration of the engine cycle. In addition, they exhibit the translational motion of the ring within the piston groove.
Scalybot: A Snake-Inspired Robot With Active Control of Friction
Authors: Marvi Hamidreza , Meyers Gregory , Russell Geoffrey , Hu David L.
Published: May 2012

Snakes are one of the world’s most versatile locomotors, at ease slithering through rubble or ratcheting up vertical tree trunks. Their adaptations for movement across complex dry terrain thus serve naturally as inspirations for search-and-rescue robotics. In this combined experimental and theoretical study, we perform experiments on inclined surfaces to show a snake’s scales are critical anatomical features that enable climbing. We find corn snakes actively change their scale angle of attack by contracting their ventral muscles and lifting their bodies. We use this novel paradigm to design Scalybot, a two-link limbless robot with individually controlled sets of belly scales. The robot ascends styrofoam plates inclined up to 45°, demonstrating a climbing ability comparable to that of a corn snake in the same conditions. The robot uses individual servos to provide a spatial and temporal dependence of its belly friction, effectively anchoring the stationary part of its body while reducing frictional drag of its sliding section. The ability to actively modulate friction increases both the robot’s efficiency over horizontal surfaces and the limiting angles of inclination it can ascend.
Model of Neonatal Infant Blood Oxygen Saturation
Authors: Krone Bradley , Fales Roger , Amjad Ramak
Published: May 2012

In this work, three different black box models were designed to model the blood oxygen saturation (SpO2) of a neonatal infant. The inputs into each of the models where fraction of inspired oxygen, heart rate, and respiratory rate. The three modeling types used were fuzzy logic, neural network, and a transfer function model. Each model was trained on a window of data. The models were tuned using a design of experiments and the optimum window size was found for each model. The models were tested to see how long the model adequately represents the future SpO2. The best model was found to be the transfer function model which adequately modeled the future SpO2 for an average of 51.8 seconds.
Nonlinear Model Based Diagnostic of Gas Turbine Faults: A Case Study
Authors: Liu Yongwen , Su Ming
Published: May 2012

During the lifetime of a gas turbine, its gas path components deteriorate gradually and sometimes serious problems happened. Direct physical and indirect model based methods can be used in health monitoring systems for gas turbines. The gas turbine under study is run as part of a combined cycle generation unit, sited in the BAO Steel Power Plant. The basic health monitoring system is based on vibration signal. After the vibration monitoring system failed to detect foreign object damage (FOD) fault, a health monitoring system based thermodynamic model is tried to explain quantitatively why the performance degradation happened, with the foreseeable usage as part of the online health monitoring system. The present work is based upon component level nonlinear gas turbine model, so errors caused by linearization can be avoided. The component level model of gas turbine is built as dynamic model, and the off-design performance of gas turbine is evaluated as the steady-state solution of the dynamic model. A dynamic tracking filter, which tracking field measurements with PI control loops, is incorporated into the gas turbine dynamic model. Output of the dynamic tracking filter is called correction factors, which are used as multiplicative corrective values of component performance parameters (i.e., flow or efficiency) in the gas turbine model. With dynamic tracking filter and aero-thermal dynamic model, the model based fault diagnosing of gas turbine is implemented as a three step process. As a case study, several measurement data sets are tried to detect and isolate FOD fault happened. The result demonstrates that a model based gas path analysis can detect and isolate fault even when no vibration level alarm is reported.
Experimental and Numerical Analysis of the Flow Field in the Impeller of a Centrifugal Compressor Stage at Design Point
Authors: Guidotti Emanuele , Tapinassi Libero , Toni Lorenzo , Bianchi Lorenzo , Gaetani Paolo , Persico Giacomo
Published: May 2012

The design of high efficiency modern centrifugal compressor stages with a wide operating range is challenging and demanding. To achieving the best design, numerical tools and test equipments for performance prediction and validation need to be at the state-of-the-art. Test data are also necessary to validate and continuously improve the numerical techniques used for performance prediction during the design phase. This paper presents the experimental and computational analysis of the flow field in a modern high flow, high Mach centrifugal compressor stage at the design point. Phase-resolved flow measurements for total pressure, static pressure and flow angle were carried out at the exit section of the centrifugal impeller. The measurements were performed using a Fast Response Aerodynamic Pressure Probe (FRAPP), traversed from the impeller hub up to the shroud; the key experimental results are presented as two-dimensional distributions as well as hub-to-shroud profiles. A CFD analysis was also carried out using an in-house CFD code to compare the results of the computational models with the FRAPP. In particular two different approaches, which combined accuracy and reasonable computational time, were used for the CFD computations: one is the standard methodology with only the flow-path modeled; the second also includes modeling of the leakage cavities. In fact the correct prediction of the flow profiles at the impeller exit and downstream, at the diffuser exit, is fundamental for the accurate design of the non-rotating downstream parts. Historically, the standard CFD approach has been found to be weak in capturing these profiles, especially close to the hub wall. Instead the CFD model including cavities was able to match to within a good approximation the profiles from the FRAPP probe.
Separation of Particles in the Secondary Air System of Gas Turbines
Authors: Garci´a Vi´llora Natalia , Dullenkopf Klaus , Bauer Hans-Jo¨rg
Published: May 2012

Particles contaminating the secondary air system of land based gas turbines or aero-engines can cause serious problems in various engine components, particularly in the cooling system. The capability of the pre-swirl system in separating particles will be described in this paper. So far, only a few publications can be found on experimental investigations on this subject. The work presented in this paper attempts to give a contribution to fill this gap and thus represents a further step towards a better understanding of the behaviour of solid contaminants in the secondary air system. Due to the strong swirl in the pre-swirl cavity, the aero-dynamical forces can be used to separate particles, thus preventing depositions inside the turbine blades or even block-age of the film cooling holes. Numerous experiments in a pre-swirl system have been performed using spherical particles and non-spherical particles. As reference cases, three types of spheres, with two size ranges and different materials, were used to understand how size and density influence the separation efficiency. For further experiments, irregularly-shaped particles, more similar to the ones found in real aero-engines, were used too. The separation efficiency was investigated at different pre-swirl nozzle pressure ratios, rotational speeds and radial mass flows. The results are presented in relation to the particle Reynolds numbers, drag coefficients, Stokes numbers and swirl ratios in the pre-swirl cavity.
Flow Visualization and Conjugate Heat Transfer Study From Shower Head Impinging Jets
Authors: Panda Rajesh Kumar , Prasad B. V. S. S. S.
Published: May 2012

Computational and experimental investigations on a flat circular disk are reported with a constant heat flux imposed on its bottom surface and a shower head of air jets impinging on the top surface. The shower head consists of a central jet surrounded by four neighboring perimeter jets. Lamp black flow visualization technique and computations using shear stress transport (SST) κ-ω turbulence model are employed to describe the complex interaction of the wall jets and the associated flow structure. Thermochromic liquid crystal measurement technique is used for surface temperature measurement. The formations of saddle point, nodal point of attachment, nodal point of separation, flow separation line and the up-wash flow are identified. It is observed that the flow topology is practically independent of Reynolds number within the investigated range but is significantly altered with the spacing between the jet orifice and the target surface. A strong correlation between the Nusselt number and the pressure distribution is noticed. Local variation of heat transfer rate with varying plate spacing to jet diameter ratio is significant but its effect on the area weighted average heat transfer rate is small. When compared with a single jet of equal mass flow rate and Reynolds number, the shower head jets provide higher heat transfer rate but require more power for pumping.
Determination of the Heat Release Distribution in Turbulent Flames by a Model Based Correction of OH* Chemiluminescence
Authors: Lauer Martin , Zellhuber Mathieu , Sattelmayer Thomas , Aul Christopher J.
Published: May 2012

Imaging of OH* or CH* chemiluminescence with intensified cameras is often employed for the determination of heat release in premixed flames. Proportionality is commonly assumed, but in the turbulent case this assumption is not justified. Substantial deviations from proportionality are observed, which are due to turbulence-chemistry interactions. In this study a model based correction method is presented to obtain a better approximation of the spatially resolved heat release rate of lean turbulent flames from OH* measurements. The correction method uses a statistical strain rate model to account for the turbulence influence. The strain rate model is evaluated with time-resolved velocity measurements of the turbulent flow. Additionally, one-dimensional simulations of strained counterflow flames are performed to consider the non-linear effect of turbulence on chemi-luminescence intensities. A detailed reaction mechanism, which includes all relevant chemiluminescence reactions and deactivation processes, is used. The result of the simulations is a lookup table of the ratio between heat release rate and OH* intensity with strain rate as parameter. This lookup table is linked with the statistical strain rate model to obtain a correction factor which accounts for the non-linear relationships between OH* intensity, heat release rate, and strain rate. The factor is then used to correct measured OH* intensities to obtain the local heat release rate. The corrected intensities are compared to heat release distributions which are measured with an alternative method. For all investigated flames in the lean, partially premixed regime the corrected OH* intensities are in very good agreement with the heat release rate distributions of the flames.
High Pressure Turbine Low Radius Radial TOBI Discharge Coefficient Validation Process
Authors: MirzaMoghadam A. V. , Riahi A. , Morris M.
Published: May 2012

A TOBI (tangential on board injection) or preswirl system is a critical component of a high pressure turbine cooling delivery system. Its efficient performance and characterization are critical because the blade and disk life depend on the accuracy of delivering the required flow at the correct temperature and pressure. This paper presents a TOBI flow discharge coefficient validation process applied to a low radius radial configuration starting from a 1D network flow analysis to a 3D frozen rotor CFD analysis of the rotor cooling air delivery system. The analysis domain commences in the combustor plenum stationary reference frame, includes the TOBI, transitions to the rotating reference frame as the flow travels through the rotating cover plate orifice, continues up the turbine disk into the slot bottom blade feed cavity, and terminates in the turbine blade. The present effort includes matching a 1D network model with 3D CFD results using simultaneous goal-matching of pressure predictions throughout the circuit, defining test rig pressure measurements at critical “non-disturbing” locations for quanification of pressure ratio across the TOBI, and finally comparing the TOBI flow coefficient resulting from stationary cold flow tests with what was obtained from the 3D CFD results. Analysis of the results indicates that the discharge coefficient varies with pressure ratio and that the traditional method of using a constant discharge coefficient extracted from a cold flow test run under choked conditions leads to over-predicting turbine cooling flows. TOBI flow coefficient prediction for the present study compares well with the stationary data published by author researchers for the configuration under investigation, and the process described in this paper is general for any TOBI configuration.
Impact on Adiabatic Film Cooling Effectiveness Using Internal Cyclone Cooling
Authors: Lerch Andreas , Schiffer Heinz-Peter , Klaubert Daniela
Published: May 2012

The internal heat transfer of turbine blades can be augmented using cyclone cooling, but the consequential impact on the external film cooling may be significant. To determine these effects, the distribution of adiabatic film cooling effectiveness was measured on the surface of a symmetrical blade model containing a cylindrical leading-edge channel. This channel feeds one row, respectively two opposite rows, of eight cooling holes each. Inside this channel two different types and directions of swirl are generated. The resulting adiabatic effectiveness distributions, which are measured using the calibrated ammonia diazo technique, are compared to those measured with a channel flow without swirl (datum configuration). The operating points are defined by blowing ratio (0.6–1.0) and film cooling discharge coefficient (20%–50%). A high full-range resolution over the adiabatic effectiveness is achieved using a weighting average method with multiple experiments per operating point. The lateral-averaged adiabatic effectiveness is presented up to 30 diameters downstream of the cooling holes. These effectiveness values show a high dependency on the configurations and reach values of about 0.3 to 2 times the reference configuration values. This is due to the strong variation of the flow structure inside the cooling holes. PIV-measurements and basic numerical simulations of the channel flow structure and dynamic pressure measurements at the cooling hole exits are carried out to support the results of film cooling effectiveness.
Disk Crack Detection and Prognosis Using Non Contact Time of Arrival Sensors
Authors: Chana Kam , Cardwell Dave , Gray Lauren , Hall Ben
Published: May 2012

Early detection of cracks in engine rotors can prevent uncontained engine fractures. A detection system may also reduce maintenance costs by increasing the time between inspections and reducing the number of spares required. Currently, the only method to monitor engine rotor degradation is through periodic removal of the engine from service, disassembly, and inspection of each rotor. The objective of this study was to propagate a crack in a cyclic engine test and evaluate the ability of an eddy current sensor and Reasoner software system to isolate a crack and predict its remaining useful life. The engine used for these tests was a Spey RB168 Mk 101 engine with titanium blades. Prior to the engine test, low cycle fatigue (LCF) spin-pit testing was carried out on a pre-flawed disk to validate understanding of the disk crack growth and reduce the risk of fracture during engine testing. Time of arrival data was collected using the QinetiQ eddy current sensor based tip timing system, to investigate the blade movement caused by crack growth in the disk. A greater understanding of the different types of faults that might exist in a rotor assembly and the ability to differentiate between them using the tip timing system is essential if the true nature of a fault is to be diagnosed and reported. A software Reasoner, using physics-based structural transfer functions to relate blade tip timing measurements to the damage state of the disk, was validated during the spin-pit test and was subsequently used on the cracked disk test at MoD Shoeburyness. The Reasoner provided real-time monitoring of the crack growth and remaining useful life of the component.
Taking-Off Under Tropical Storm: A New Steam and Water Injection Feature in the K9 Combustion Test Rig of DGA Aero-Engine Testing
Authors: Plana Vincent , Hervy Franck , Serre Je´roˆme
Published: May 2012

The K9 combustion test facility enables characterization of combustors at sea level with a new steam injection feature to simulate ingestion of rain and hail by the combustor. By providing steam and water directly to the combustor, DGA is now able to check its stability and its loss of efficiency under the most severe test conditions. In this paper, the description of this new water supply will be made and a brief description of quality of the spray used for the production of steam will be presented. A specific study has been made concerning the air flow measurement with some corrections due to the presence of high concentration of steam in the air. The second part of this paper is dedicated to the control of the vaporization of water, the correct control of the steam / air ratio in the flow and the consequences on the thermal behavior of the facility.
Friction Factor Behavior From Flat-Plate Tests of 12.15 mm Diameter Hole-Pattern Roughened Surfaces
Authors: Asirvatham Thanesh Deva , Childs Dara W. , Phillips Stephen
Published: May 2012

A flat-plate tester is used to measure the friction-factor behavior for a hole-pattern-roughened surface facing a smooth surface with compressed air as the medium. Measurements of mass flow rate, static pressure drop and stagnation temperature are carried out and used to find a combined (stator + rotor) Fanning friction factor value. In addition, dynamic pressure measurements are made at four axial locations at the bottom of individual holes of the rough plate and at facing locations in the smooth plate. The description of the test rig and instrumentation, and the procedure of testing and calculation are explained in detail in Kheireddin in 2009 and Childs et al. in 2010. Three hole-pattern flat-plates with a hole-pattern diameter of 12.15 mm were tested having depths of 0.9, 1.9, and 2.9 mm. Tests were done with clearances at 0.254, 0.381, and 0.653 mm, and inlet pressures of 56, 70 and 84 bar for a range of pressure ratios, yielding a Reynolds-number range of 100,000 to 800,000. The effects of Reynolds number, clearance, inlet pressure, and hole depth on friction factor are studied. The data are compared to friction factor values of three hole-pattern flat-plates with 3.175 mm diameter holes with hole depths of 1.9, 2.6, and 3.302 mm tested in the same rig described by Kheireddin in 2009. The test program was initiated mainly to investigate a “friction-factor jump” phenomenon cited by Ha et al. in 1992 in test results from a flat-plate tester using facing hole-pattern plates where, at elevated values of Reynolds numbers, the friction factor began to increase steadily with increasing Reynolds numbers. Friction-factor jump was not observed in any of the current test cases.
Synthetic Jet Fuel Combustion: Experimental and Kinetic Modeling Study
Authors: Dagaut P. , Mze´-Ahmed A. , Hadj-Ali K. , Die´vart P.
Published: May 2012

Fischer-Tropsch liquid fuels synthesized from syngas, also called synthetic paraffinic jet fuel (SPK), can be used to replace conventional petroleum-derived fuels in jet engines. Whereas currently syngas is mostly produced from coal of natural gas, its production from biomass has been reported. These synthetic liquid fuels contain a very high fraction of iso-alkanes, while conventional jet fuels contain large fractions of n-alkanes, cycloalkanes (naphtenes), and aromatics. In that contest, a jet-stirred reactor (JSR) was used to study the kinetics of oxidation of a 100% SPK and a 50/50 SPK/Jet A-1mixture over a broad range of experimental conditions (10 atm, 560 to 1030K, equivalence ratios of 0.5 to 2, 1000 ppm of fuel). The temperature was varied step-wise, keeping the mean residence time in the JSR constant and equal to 1s. Three combustion regimes were observed over this temperature range: the cool-flame oxidation regime (560–740K), the negative temperature coefficient (NTC) regime (660–740K), and the high-temperature oxidation regime (>740K). More than 15 species were identified and measured by Fourier transform infrared spectrometry (FTIR), gas chromatography/mass spectrometry (CG/MS), flame ionization detection (FID), and thermal conductivity detection (TCD). The results consisting of concentration profiles of reactants, stable intermediates and products as a function of temperature showed similar kinetics of oxidation for the fuels considered, although the 100% SPK was more reactive. A surrogate detailed chemical kinetic reaction mechanism was used to model these experiments and ignition experiments taken from the literature. The kinetic modeling showed reasonable agreement between the data and the computations whereas model improvements could be achieved using more appropriate surrogate model fuels. Kinetic computations involving reaction paths analyses and sensitivity analyses were used to interpret the results.
Experimental Studies of Crude Oil Combustion in a Top-Mounted Silo Combustor
Authors: Nowak Dariusz , Dobski Tomasz , Slefarski Rafal , Jankowski Radoslaw , Magni Fulvio
Published: May 2012

Crude oil is still an attractive fuel for electricity production due to its low extraction costs in relation to other fuels. However, combustion of crude oil in modern gas turbines must meet certain criteria, which mainly include the reduction of harmful gas emissions, the elimination of harmful dust from the exhaust gas, the improvement of turbine efficiency, the limiting of the power degradation process and elimination of hard deposits. Experimental studies are always needed to meet these requirements because of common complexity in CFD crude oil combustion models. This paper presents experimental investigations of the combustion process of crude oil. Using different sorts of crude oil, all experiments are performed in the atmospheric test rig of a top-mounted combustor, which was scaled down from the baseline system. The test rig was optimized for the typical silo gas turbine boundary conditions. The combustion process is described and quantified with the measured temperature and velocity field distributions in the top-mounted combustion chamber for different injector design’s parameters. Additionally, measured profiles of the molar fraction of CO2, are discussed and compared with respect to the injector parameters. Finally, based upon the experimental results gathered, the possibility of fuel flexibility in the top-mounted combustor chamber is discussed.
Diagnostics of Highly Degraded Industrial Gas Turbines Using Bayesian Networks
Authors: Kestner Brian K. , Lee Young K. , Voleti Gautham , Mavris Dimitri N. , Kumar Viren , Lin TsungPo
Published: May 2012

This paper presents an offline fault diagnostics method for highly degraded industrial gas turbines. The method recasts gas path analysis to an inference problem using Bayesian networks where the health condition of each component is quantified in comparison to an expected value. The health parameters are inferred from available gas path measurements, which are sometimes erroneous due to sensor faults or miscalibration. The sensor errors should be inferred as well as the health parameters. Thus, typically in gas path analysis the unknowns are more than the knowns. To address this issue, the present method uses multiple Bayesian network models each of which contains a subset of the unknowns. Their results are averaged according to how much each of the models is supported by the data. Although this method has been reported successful for the faults affecting a few unknowns, its results are still less accurate and confident when it is applied to highly degraded gas turbines. Such gas turbines are likely to have health parameters deviated from the new and clean condition as well as have component faults and sensor errors. Because of this, the present method must infer too many unknowns at the same time to result in a solution with high confidence. In addition, this method cannot differentiate normal or expected degradation from an actual fault. These issues are resolved by fusing extra information to the method. First of all, a sensor calibration report, if available, eliminates the sensor errors from the unknowns. Consequently, the number of possible subsets decreases, and so does the number of Bayesian models. Second, a degradation model provides meaningful prior guesses for the health parameters. It is equivalent to change the point of reference from a brand new gas turbine to a normally degraded one. It will be demonstrated that the method accompanying with the degradation model and the sensor calibration report shows significant improvement in accuracy and confidence.
Computational Study of Kelvin-Helmholtz Instability Created by Interaction of the Mainstream Flow and the Seal Flow in Gas Turbines
Authors: Rabs M. , Benra F.-K. , Domnick C. , Schneider O.
Published: May 2012

The present paper gives a contribution to a better understanding of the emergence of Kelvin-Helmholtz instabilities (KHI) in gas turbines. In an earlier paper of the authors, the occurrence of the KHI’s near the rim cavity of a 1.5 stage gas turbine has been examined by use of CFD methods. It is shown that the KHI’s occur, when the swirl component of the hot gas flow is very strong. Due to the fact, that a high swirl is produced by the guide vanes of the first stage, this matter concerns all common gas turbines. In order to get a basic theoretical background of the emergence of the KHI’s, 2D CFD investigations of the flow behind a splitter plate have been performed showing the development of KHI’s downstream of the splitter plate. To validate the numerical results a comparison to test rig data is used. This shows that the numerical method can simulate the characteristics of the KHI’s. Furthermore, a parameter study is conducted to extract parameters describing the appearance of KHI’s, the vortex periodicity and stability criteria. The main intention of this paper is to deliver “KHI parameters”, which are able to describe the development of the KHI in gas turbine rim cavities.
Experimental Investigation of Geometrical Parameters on the Pressure Recovery of Low Pressure Steam Turbine Exhaust Hoods
Authors: Finzel Conrad , Schatz Markus , Casey Michael V. , Gloss Daniel
Published: May 2012

The three-dimensional inhomogeneous flow in the exhaust hoods of low pressure steam turbines is a major cause of losses and the design of low-loss exhaust hoods remains a challenge, particularly in retrofit units. This paper examines the sensitivity of certain geometrical exhaust hood parameters on the pressure recovery of the whole exhaust system of low pressure steam turbines. The experimental investigations are carried out in a scaled exhaust system test rig operating at full-scale Mach numbers and near design flow conditions. The measurements for all exhaust hood configurations have been performed on two axial-radial diffuser geometries at two different load points, which represent the outflow in the design point of a last stage rotor with and without shrouds. The flow measurements make use of pneumatic probes and wall pressure taps. The influence of the exhaust hood area, the flow area in the horizontal joint plane and the location of the steam inlet are examined. The sensitivity of the pressure recovery on these parameters is evaluated. The flow area in the horizontal joint plane is identified as the most sensitive geometrical parameter in the exhaust hood of low pressure steam turbines.
Flame Transfer Function Measurements in a Single Nozzle Combustor
Authors: Wehe Shawn D. , Li Hejie , McManus Keith R.
Published: May 2012

This paper describes an experimental investigation of Flame Transfer Function (FTF) behavior where the response of a swirl-stabilized, natural gas fueled combustor is measured for partially premixed conditions. Controlled perturbations of the combustor inlet flows are produced using a siren and the combustor response is observed using several measurement techniques. The fuel/air equivalence ratio fluctuation is measured using a diode laser absorption sensor operating near 1.6 μm. Measurements of global heat release perturbations are obtained using a three-color optical emission technique and velocity measurements are obtained using the two-microphone method. FTFs are derived from these measurements for a frequency range commensurate with field-observed tones. Typical experimental investigations of dynamic signals involve the use of Fourier methods to obtain average signal amplitudes and phase. In this investigation, standard Fourier techniques are used to verify the driving frequencies, but they are coupled with a homodyne detection algorithm to measure time-dependent gain and phase behavior of a FTF.
Study on Fault Diagnostics of a Turboprop Engine Using Inverse Performance Model and Artificial Intelligent Methods
Authors: Kong Changduk , Lim Semyeong
Published: May 2012

Recently, the health monitoring system of major gas path components of gas turbine uses mostly the model based method like the Gas Path Analysis (GPA). This method is to find quantity changes of component performance characteristic parameters such as isentropic efficiency and mass flow parameter by comparing between measured engine performance parameters such as temperatures, pressures, rotational speeds, fuel consumption, etc. and clean engine performance parameters without any engine faults which are calculated by the base engine performance model. Recently, the expert engine diagnostic systems using the artificial intelligent methods such as Neural Networks (NNs), Fuzzy Logic and Genetic Algorithms (GAs) have been studied to improve the model based method. Among them the NNs are mostly used to the engine fault diagnostic system due to its good learning performance, but it has a drawback due to low accuracy and long learning time to build learning data base if there are large amount of learning data. In addition, it has a very complex structure for finding effectively single type faults or multiple type faults of gas path components. This work builds inversely a base performance model of a turboprop engine to be used for a high altitude operation UAV using measured performance data, and proposes a fault diagnostic system using the base engine performance model and the artificial intelligent methods such as Fuzzy logic and Neural Network. The proposed diagnostic system isolates firstly the faulted components using Fuzzy Logic, then quantifies faults of the identified components using the NN leaned by fault learning data base, which are obtained from the developed base performance model. In leaning the NN, the Feed Forward Back Propagation (FFBP) method is used. Finally, it is verified through several test examples that the component faults implanted arbitrarily in the engine are well isolated and quantified by the proposed diagnostic system.
Method to Evaluate Service Boundary Conditions for Gas Turbine Stator Structure by Using Inverse Analysis
Authors: Hayasaka Y. , Sekihara M.
Published: May 2012

The service conditions and structures of gas turbines are so complex that it is very difficult to determine boundary conditions for thermal-mechanical analyses of these turbines. To improve the accuracy of the analyses, an analytical method for estimating the service boundary conditions for the whole gas turbine stator has been developed. This method consists of FEAs (finite element analyses), a DOE (design of experiments), and measured metal temperatures in an actual gas turbine. The FEAs, with varied boundary conditions, are analyzed using an orthogonal array. In each analysis, the differences between results of an FEA and the measured results are estimated. The model is modified to reduce the difference by using analyses of variance. The method was applied to a 150kW micro gas turbine stator and the good agreement between the analysis results and the measured data confirmed the validity of the method. The modified model is applied to the clearance setting and life assessment of the gas turbine.
Use of an Immersed Mesh for High Resolution Modelling of Film Cooling Flows
Authors: Lad B. , He L.
Published: May 2012

The development of a high pressure turbine requires the accurate prediction of flow within and around film cooling holes. However the length scales inherent to film cooling flows produce a large disparity against those of the mainstream flow, hence they can not be resolved by a mesh generated for an aerodynamics analysis. Furthermore, the process of meshing cooling holes is not only time consuming but cumbersome; thus making the parametric study of film cooling effectiveness for a given blade geometry, using hole geometry and distribution very difficult in a design environment. In this paper an immersed mesh block (IMB) approach is proposed which allows the refined mesh of a cooling hole to be immersed into the coarser mesh of an NGV and solved simultaneously whilst maintaining mass conservation. By employing two-way coupling, the flow physics in and around cooling holes is able to interact with the mainstream, hence the length scales of both types of flow are appropriately resolved. A generic cooling hole design can then be mapped to a given aerofoil geometry multiple times to achieve an appropriate distribution of cooling holes. The results show that for a realistic transonic blade, a configuration consisting of up to 200 cooling holes can be efficiently and accurately calculated — whilst retaining the original aerodynamic mesh but with a much enhanced resolution for the film cooling.
Preliminary Experimental Results of IGFC Operation Using Hardware Simulation
Authors: Traverso Alberto , Tucker David , Haynes Comas L.
Published: May 2012

A newly developed Integrated Gasification Fuel Cell (IGFC) hybrid system concept has been tested using the Hybrid Performance (Hyper) project hardware-based simulation facility at the U.S. Department of Energy, National Energy Technology Laboratory. The cathode-loop hardware facility, previously connected to the real-time fuel cell model, was expanded by the inclusion of a real-time model of a gasifier of solid fuels, in this case biomass fuel. The fuel cell is operated at the compressor delivery pressure, and it is fuelled by an updraft atmospheric gasifier, through the syngas conditioning train for tar removal and syngas compression. The system was brought to steady-state; then, several perturbations in open loop (variable speed) and closed loop (constant speed) were performed in order to characterize the IGFC behavior. Experiments have shown the feasibility of relatively fast control of the plant as well as a possible mitigation strategy to reduce the thermal stress on the fuel cell as a consequence of load variation and change in gasifier operating conditions. Results also provided an insight into the different features of variable vs constant speed operation of the gas turbine section.
Numerical Study on the Effects of Blade Lean on High-Pressure Centrifugal Impeller Performance
Authors: Oh JongSik , Buckley Charles W. , Agrawal Giri L.
Published: May 2012

Blade lean and sweep are additional degrees of freedom for the three dimensional blade design. When compared to blade sweep, the influence of blade lean on the performance is not extensively described in the public literature. The effects of blade lean on the aerodynamic performance of a high-pressure ratio centrifugal impeller were investigated using a CFD (Computational Fluid Dynamics) approach. For total of 15 variations of blade lean given at the impeller inlet and outlet, while blade angles at the impeller inlet and outlet were unchanged, numerical solutions of the impeller with a vaneless diffuser were obtained at the design speed from a maximum choke flow to a minimum flow available. Compressor performance maps were generated to compare overall characteristics, and details of internal flow structure at 5 different quasi-orthogonal planes were investigated to see the effects of blade lean on the development of secondary flows. It was found that a positive lean at the impeller exit shroud helps mitigate the wake region to contribute to more uniform flows, resulting in an increase of the impeller pressure and efficiency. A negative lean at the impeller exit causes a limited head rise due to a reduced blade loading on the shroud. A negative inlet lean at the shroud provided the worst performance.
Turbulent Consumption Speed Scaling of H2/CO Blends
Authors: Venkateswaran Prabhakar , Marshall Andrew D. , Noble David R. , Seitzman Jerry M. , Lieuwen Tim C.
Published: May 2012

This paper describes measurements and analysis of global turbulent consumption speeds, ST,GC, of hydrogen/carbon monoxide (H2/CO) mixtures. The turbulent flame properties of such mixtures are of fundamental interest because of their strong stretch sensitivity and of practical interest since they are the primary constituents of syngas fuels. Data are analyzed at mean flow velocities and turbulence intensities of 4 < U0 < 50 m/s and 1 < u′rms/SL,0 < 100, respectively, for H2/CO blends ranging from 30–90% H2 by volume. Data from two sets of experiments are reported. In the first, fuel blends ranging from 30–90% H2 and mixture equivalence ratio, Φ, were adjusted at each fuel composition to have nominally the same un-stretched laminar flame speed, SL,0. In the second set, equivalence ratios were varied at constant H2 levels. The data clearly corroborate results from other studies that show significant sensitivity of ST,GC to fuel composition. For example, at a fixed u′rms, ST,GC of a 90% H2 case (at Φ = 0.48) is a factor of three times larger than the baseline Φ = 0.9, CH4/air mixture that has the same SL,0 value. We also describe physics-based correlations of these data, using leading points concepts and detailed kinetic calculations of their stretch sensitivities. These results are used to develop an inequality for negative Markstein length flames that bounds the turbulent flame speed data and show that the data can be collapsed using the maximum stretched laminar flame speed, SL,max, rather than SL,0.
Optimization of a Transonic Axial Compressor Considering Interaction of Blade and Casing Treatment to Improve Operating Stability
Authors: Kim Jin-Hyuk , Choi Kwang-Jin , Kim Kwang-Yong
Published: May 2012

A multi-objective optimization of a transonic axial compressor with circumferential casing grooves has been carried out in the present study. A hybrid multi-objective evolutionary algorithm coupled with response surface approximation is used to optimize the stall margin and design speed efficiency of the transonic axial compressor. Three-dimensional Reynolds-averaged Navier-Stokes equations with the shear stress transport turbulence model are discretized by finite volume approximations and solved on hexahedral grids for the flow analysis. The stall margin and peak adiabatic efficiency are used as objective functions for the optimization. Tip clearance and angle distribution at blade tip are considered as design variables in addition to the depth of the circumferential casing grooves which was more sensitive variable than the width in the previous work (GT2010-22396). Latin-hypercube sampling as design-of-experiments is used to generate twenty five design points within the design space. A fast non-dominated sorting genetic algorithm with an ε–constraint strategy for the local search is applied to determine the global Pareto-optimal solutions. The trade-off between two objectives is determined and discussed with respect to the representative clusters in the Pareto-optimal solutions compared to the smooth casing.
Investigation of Gas Composition Effects on the Aerothermal Characteristics of a Film-Cooled Flat Plate at High-Temperature Conditions
Authors: Zou Xin , Yuan Xin
Published: May 2012

Both experimental and computational investigations were carried out in this paper to study the influences of turbine inlet steam concentration on turbine flow and heat transfer under high-temperature and pressurized conditions. A high-temperature experimental facility has been built to study the steam concentration effects on turbine aerothermal characteristics for future advanced turbines in IGCC power systems. Preliminary data were obtained from experiment and used to validate the computational models presented in this paper. Results from computational modeling were compared qualitatively with previous studies and also quantitatively with our experimental measurements in this study, both of which proves the validation of the presented computational approach. Based on the validated computational models, a series of numerical investigations were conducted. Relationship between the change in gas inlet steam concentration and the corresponding change in dimensionless spanwise-averaged heat flux distribution was found to be well correlated with the form of power function. The influence of turbine inlet pressure and temperature on the aerothermal characteristics of turbine heat transfer is also considered and discussed. Finally, an overall correlation based on the numerical investigations were presented, and the capability of this correlation was validated with full CFD computation. The correlation can predict the trend of the dimensionless spanwise-averaged heat flux quite well with an acceptable accuracy.
Effects of Guide Vanes on the Tip Heat Transfer Enhancement of a Turbine Blade
Authors: Xie Gongnan , Sunde´n Bengt
Published: May 2012

Gas turbine blade tips encounter large heat load as they are exposed to the high temperature gas. A common way to cool the blade and its tip is to design serpentine passages with 180-deg turns under the blade tip-cap inside the turbine blade. Improved internal convective cooling is therefore required to increase the blade tip life time. This paper presents numerical predictions of turbulent fluid flow and heat transfer through two-pass channels with and without guide vanes placed in the turn regions using RANS turbulence modeling. The effects of adding guide vanes on the tip-wall heat transfer enhancement and the channel pressure loss were analyzed. The guide vanes have a height identical to that of the channel. The inlet Reynolds numbers are ranging from 100,000 to 600,000. The detailed three-dimensional fluid flow and heat transfer over the tip-walls are presented. The overall performances of several two-pass channels are also evaluated and compared. It is found that the tip heat transfer coefficients of the channels with guide vanes are 10∼60% higher than that of a channel without guide vanes, while the pressure loss might be reduced when the guide vanes are properly designed and located, otherwise the pressure loss is expected to be increased severely. It is suggested that the usage of proper guide vanes is a suitable way to augment the blade tip heat transfer and improve the flow structure, but is not the most effective way compared to the augmentation by surface modifications imposed on the tip-wall directly.
Detached Eddy Simulation of Transonic Rotor Stall Flutter Using a Fully Coupled Fluid-Structure Interaction
Authors: Im Hongsik , Chen Xiangying , Zha Gecheng
Published: May 2012

Detached eddy simulation of an aeroelastic self-excited instability, flutter in NASA Rotor 67 is conducted using a fully coupled fluid/structre interaction. Time accurate compressible 3D Navier-Stokes equations are solved with a system of 5 decoupled modal equations in a fully coupled manner. The 5th order WENO scheme for the inviscid flux and the 4th order central differencing for the viscous flux are used to accurately capture interactions between the flow and vibrating blades with the DES (detached eddy simulation) of turbulence. A moving mesh concept that can improve mesh quality over the rotor tip clearance was implemented. Flutter simulations were first conducted from choke to stall using 4 blade passages. Stall flutter initiated at rotating stall onset, grows dramatically with resonance. The frequency analysis shows that resonance occurs at the first mode of the rotor blade. Before stall, the predicted responses of rotor blades decayed with time, resulting in no flutter. Full annulus simulation at peak point verifies that one can use the multi-passage approach with periodic boundary for the flutter prediction.
Preventing Standstill Corrosion on LP Turbines Through Optimized Shutdown Procedures
Authors: Leidich Frank Udo , Theobald Markus
Published: May 2012

Caused by the deregulated market and the entrance of new power sources, like wind farms, solar power etc. into the market, conventional steam power plants are nowadays operated with frequent start-ups and shutdowns. During lay-up time, general corrosion or even localized pitting corrosion can take place if no preservation measures are applied. The CECD (Cold End Corrosion Diagnostics) diagnostic method by Alstom enables a cause-and-effect analysis of corrosive attacks — supported by analytical and instrumentation data — and can also be used for determining whether there is a high probability of corrosion in the exhaust-steam area of condensing turbines. In addition the method allows selective modification of shutdown procedures so that it will be impossible that corrosive attacks occur during short-term downtimes, e.g. during weekend standstills for which normally no special preservation measures are taken. The paper will give a brief description of the method and mainly focuses on examples already carried-out successfully.