bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Hybrid Method for Wind Power Forecasting Based on Wavelet Decomposition and Artificial Neural Networks
Authors: De Giorgi Maria Grazia , Tarantino Marco , Ficarella Antonio
Published: May 2012

Depending on their input, wind power forecasting models are classified as physical or statistical approaches or a combination of both. Physical models use physical considerations, as meteorological information (Numerical Weather Prediction) and technical characteristics of the wind turbines (hub height, power curve, thrust coefficient). Statistical models use explanatory variables and online measurements, usually employing recursive techniques, like recursive least squares or artificial neural networks (ANNs) which perform a non-linear mapping and provide a robust approach for wind prediction. In this paper a new hybrid method (mixing physical and statistical approaches) is proposed, based on the wavelet decomposition technique and on artificial neural networks, in order to predict power production of a wind farm in different time horizons: 1, 3, 6, 12 and 24 hours. In particular, two approaches are compared, both based on the time series of on-line measured wind power and on the Numerical Weather Predictions; in the first approach, the forecast is carried out only through the training of a neural network which, in the second approach is, instead, used in combination with the wavelet decomposition technique, improving the performance especially over the short time horizons. The error of the different forecast systems is investigated for various forecasting horizons and statistical distributions of the error are calculated and presented.
Comparison of Various Supersonic Turbine Tip Designs to Minimize Aerodynamic Loss and Tip Heating
Authors: Shyam Vikram , Ameri Ali
Published: May 2012

The rotor tips of axial turbines experience high heat flux and are the cause of aerodynamic losses due to tip clearance flows, and in the case of supersonic tips, shocks. As stage loadings increase, the flow in the tip gap approaches and exceeds sonic conditions. This introduces effects such as shock-boundary layer interactions and choked flow that are not observed for subsonic tip flows that have been studied extensively in literature. This work simulates the tip clearance flow for a flat tip, a diverging tip gap and several contoured tips to assess the possibility of minimizing tip heat flux while maintaining a constant massflow from the pressure side to the suction side of the rotor, through the tip clearance. The CFD code GlennHT was used for the simulations. Due to the strong favorable pressure gradients the simulations assumed laminar conditions in the tip gap. The nominal tip gap width to height ratio for this study is 6.0. The Reynolds number of the flow is 2.4×105 based on nominal tip width and exit velocity. A wavy wall design was found to reduce heat flux by 5% but suffered from an additional 6% in aerodynamic loss coefficient. Conventional tip recesses are found to perform far worse than a flat tip due to severe shock heating. Overall, the baseline flat tip was the second best performer. A diverging converging tip gap with a hole was found to be the best choice. Average tip heat flux was reduced by 37% and aerodynamic losses were cut by 2.84%.
Sub-Miniature Five-Hole Probe Calibration Using a Time Efficient Pitch and Yaw Mechanism and Accuracy Improvements
Authors: Town Jason , Camci Cengiz
Published: May 2012

A five-hole probe is a proven aerodynamic tool for the accurate measurement of flow fields, but is traditionally difficult to calibrate manually in an acceptable range of pitch and yaw angles. With advancements in computer technology, it is possible to improve the calibration process that is made up of tedious and repeating angular pitch and yaw angle movements. This paper proposes a way to increase the accuracy of measurements. The proposed approach uses computer automation, a mechanical pressure scanner, and precision rotary tables to significantly reduce the amount of time required to complete the calibration sequence. A five-hole probe is fastened to a precision calibration mechanism in a wind tunnel test section. This mechanism varied the pitch and yaw angle of the probe accurately via two computer controlled rotary tables. This approach allowed for a much greater degree of accuracy and a way to increase the number of data points taken, better defining the non-linear portions of the calibration maps. The scanivalve system minimized the number of transducers required from seven to one. While it takes more time than having multiple transducers, this approach lowered the overall equipment costs and helped to reduce measurement errors. The data acquisition device provides an interface between the rotary table stepper controllers, the scanivalve controller, and the transducer. A LabVIEW interface was then used to control all of the devices, while simultaneously retrieving data from the transducer and turning it into the coefficients needed to make the calibration map. The program allows for a degree of flexibility, allowing the user to choose the range of angles and the degrees between each point.
Experimental Investigation on Leakage Loss and Heat Transfer in a Straight Through Labyrinth Seal
Authors: Micio Mirko , Facchini Bruno , Innocenti Luca , Simonetti Francesco
Published: May 2012

Labyrinth seals are extensively used in turbomachinery to prevent high pressure gas from flowing into a region of low pressure. Because of thermal expansions and centrifugal forces, the actual seal clearance can vary based on engine conditions. Pressure ratio, Reynolds number, tip geometry, and seal clearance all affected the sealing performance. This paper deals with its influence on the leakage flow and heat transfer coefficient through a thirteen teeth straight through labyrinth seal. Three gaps were experimentally investigated using a stationary test rig. The experiments covered a range of Reynolds numbers between 5000 and 50000 and pressure ratios between 1.0 and 2.7. Cavity pressure measurements along the seal were also performed in order to characterize each constriction. In addition, 2D PIV measurements were made on the plane containing the seal teeth to obtain a high local resolution of the velocity distribution and the flow field within the seal. Experimental results show a strong influence of clearance on both leakage loss and heat transfer as well as on the development of the flow fields. A simplified model to calculate the leakage mass flow rate is presented and validated comparing its prediction capability with experimental data. In order to improve the agreement between numerical and experimental results a correction of published correlations is proposed.
Performance Improvement of Turbomachinery Using Plasma Actuators
Authors: De Giorgi Maria Grazia , Traficante Stefania , Ficarella Antonio
Published: May 2012

This work deals with the computational modeling of the single dielectric barrier discharge (SDBD) plasma actuator and its applications as a flow actuator. In the literature, plasma actuators have been used especially in order to control boundary layer separation. The plasma acts as a momentum source to the boundary layer allowing it to remain attached throughout a large portion of the airfoil. The RANS simulations are performed using a CFD code in which the plasma force have been modeled as paraelectric force acting on the charged particles in the working flow. Using this numerical model, different cases have been simulated on NACA 0015 airfoil, depending on the direction of the force, to study the effect of the force on the flow and on the boundary layer. The best flow control solutions have been displayed when body force component in the direction straight along the flow is positive and the component normal to the flow is considered. Finally, this numerical simulation methodology has been used for the investigations on the potential of plasma actuators, to suppress the flow separation over a compressor blade. Specifically, the analysis has been focused to evaluate the increasing of the compressor performance depending on the actuator strength and position on the blade.
Gas Path Analysis and Gas Turbine Re-Mapping
Authors: Cerri Giovanni , Chennaoui Leila , Giovannelli Ambra , Salvini Coriolano
Published: May 2012

The paper deals with the relevant problem of establishing the statuses of degraded performance of Gas Turbine based Power Plant Components and with the remapping of the simulator models. The methodology is based on physical models including Reality and Actuality Functions that modify the model source terms of the Governing Conservation Equations. Inverse calculations based on Neural Networks are illustrated and the application to two GE LM6000 PA aeroderivative Gas Turbines is widely discussed.
Investigation of the Effect of Rotation on the Flow in a Two-Pass Cooling System With Smooth and Ribbed Walls Using PIV
Authors: Schroll Michael , Lange Lena , Elfert Martin
Published: May 2012

A rotating cooling system with a 180 deg turn is investigated experimentally using the 2C PIV technique to measure the flow inside. This cooling configuration consists of two ducts of arbitrary cross-sections representing a two-pass front part of an idealized but nevertheless engine relevant turbine blade cooling design. The system has been investigated with ribbed walls in both passages for cooling enhancement as well as with smooth walls as a reference version in order to identify the effects induced by ribs. The rib orientation on the walls is 45 deg. With a rib height of 0.1 of hydraulic duct diameter and a pitch of 10 times rib height, a representative well-established rib lay-out was selected. This paper presents measurements of the axial flow during rotation of this two-pass system for rotation numbers up to 0.1. Together with previously obtained stationary results [1], this data completes the investigation of the secondary flow field with rotational results acquired with a two-component PIV measuring technique with improved sequencer technique [2]. The Two-Pass Cooling System was analyzed on the rotating test rig using two-component Particle Image Velocimetry (2C PIV) a non-intrusive optical planar measurement technique. PIV is capable of obtaining complete flow maps of the instantaneous as well as averaged flow field even at high turbulence levels, which are typical for the narrow serpentine-shaped ribbed cooling systems. An in-house developed synchronization device enables very accurate control of the laser flashes and image acquisition with regard to the angular position of the measurement plane (light sheet) and thereby very accurately stabilizes the position of the channel within the image during PIV recording which then leads to very accurate mean velocities. The presented investigations were conducted in stationary and rotating mode. The results demonstrate the combined interaction of different vortices induced by several effects such as the inclination of ribs, Coriolis forces due to rotation and inertial forces within the bend. Additionally, a flow separation was observed at the divider wall downstream of the bend (in the second pass) that has a strong impact on the flow field depending on the rotational speed. The axial flow maps presented in this paper in combination with the secondary flow maps published previously are of sufficient high quality and spatial resolution to serve as a benchmark test case for the validation of flow solvers. The turbulent channel flow was investigated at a Reynolds number of 50,000 and at rotation numbers of 0.0 and 0.1.
Integration of Unknown Input Observers and Classification for Turbofan Engine Diagnosis
Authors: Tan Daoliang , He Ai , Kong Xiangxing , Wang Xi
Published: May 2012

A great deal of attention has been attracted in the analytical model-based engine diagnostics over the past years. Meanwhile, an increasing number of researchers and practitioners make an attempt to gain an intelligent diagnoser in a pattern recognition way. A question naturally emerges of how to combine the two techniques to improve the robustness of an on-board diagnostic system. In this context, this paper suggests an integrated approach that combines the unknown input observer (UIO) with the support vector machine (SVM) technique to aircraft engine fault diagnosis. Sensor faults and actuator faults are separately considered. To reduce the effect of engine disturbances on diagnostic performance, we first design a bank of UIOs, each of which is sensitive to all sensor and actuator faults but only one signal. Then, the magnitudes of a set of residuals between the UIO-based estimations and the engine measurements are fed into an SVM classifier to detect and isolate engine faults. Experimental results demonstrate an encouraging potential of the suggested method and that the UIO-oriented approach is superior or competitive to the Kalman-based algorithm.
Potential Flow Field Generated by Downstream Moving Bars and Propagated on a Turbine Blade at Low Reynolds Number
Authors: Penin Ve´ronique , Kulisa Pascale , Bario Franc¸ois
Published: May 2012

During the last few decades, the size and weight of turbo-machinery have been continuously reduced. However, by decreasing the distance between rows, rotor-stator interaction is strengthened. Two interactions now have the same magnitude: wake interaction and potential effect. Studying this effect is essential to understand rotor-stator interactions. Indeed, this phenomenon influences the whole flow, including the boundary layer of the upstream and downstream blades, ergo the stability of the flow and the efficiency of the machine. A large scale turbine cascade followed by a specially designed rotating cylinder system is used. Synchronised velocity LDA measurements on the vane profile show the flow and boundary layer behavior due to the moving bars. To help the general understanding and to corroborate our experimental results, numerical investigations are carried out with an unsteady three dimensional Navier-Stokes code. Moreover, the numerical study informs about the potential disturbance to the whole flow of the cascade.
Integrating Systems Engineering Into the USAF Academy Capstone Gas Turbine Engine Course
Authors: Rolling August J. , Byerley Aaron R. , Wisniewski Charles F.
Published: May 2012

This paper is intended to serve as a template for incorporating technical management majors into a traditional engineering design course. In 2002, the Secretary of the Air Force encouraged the USAF Academy to initiate a new interdisciplinary academic major related to systems engineering. This direction was given in an effort to help meet the Air Force’s growing need for “systems” minded officers to manage the development and acquisition of its ever more complex weapons systems. The curriculum for the new systems engineering management (SEM) major is related to the “engineering of large, complex systems and the integration of the many subsystems that comprise the larger system” and differs in the level of technical content from the traditional engineering major. The program allows emphasis in specific cadet-selected engineering tracks with additional course work in human systems, operations research, and program management. Specifically, this paper documents how individual SEM majors have been integrated into aeronautical engineering design teams within a senior level capstone course to complete the preliminary design of a gas turbine engine. As the Aeronautical engineering (AE) cadets performed the detailed engine design, the SEM cadets were responsible for tracking performance, cost, schedule, and technical risk. Internal and external student assessments indicate that this integration has been successful at exposing both the AE majors and the SEM majors to the benefits of “systems thinking” by giving all the opportunity to employ SE tools in the context of a realistic aircraft engine design project.
Design, Model, and Virtually Fly: Investigation of the B-1A Cruise Performance With F101 Engines Compared With Its Re-Engined Performance Using F119 Engines
Authors: Rolling August J.
Published: May 2012

This paper examines application of AEDSYS and MATLAB design tools to virtually fly an engine in a platform through a mission. The primary objective of this effort was to develop the procedures for this process as an instructional tool. The secondary objective was application of the process to an actual case study, the re-engine of the B-1A. The resulting modular software uses performance data from engine models for the F101, F119, and a cadet designed engine built in AEDSYS; a B-1A drag polar model; as well as atmospheric and geospatial mapping tools available in MATLAB. The resulting simulation provides a relatable means of presenting this complicated information. This tool gives the cadets the opportunity to virtually fly their engine. This visualization gives them full insight into how the integrated system performs. Aside from providing a great means of discussing many aspects for consideration in engine design, it also provides an incentive to develop a higher performance engine through competition.
Numerical Investigation of a Highly Loaded Axial Compressor Stage With Inlet Distortions
Authors: Lesser Andreas , Iseler Jens , Niehuis Reinhard
Published: May 2012

This paper deals with the numerical flow-simulation of a transonic compressor stage, which has been investigated for baseline as well as distorted inflow conditions at the Institute of Propulsion Technology of the DLR in Cologne (Dunker [1] and Lecht [2]). The inlet distortions are generated in the experiment upstream of the compressor stage by non-rotating steel bars, while in the numerical calculations the total pressure and inflow angle distribution measured downstream of the bars are taken as inflow boundary conditions. The circumferential extent of the generated total pressure and inflow angle distortion is 120 degrees. Numerical simulations were performed for uniform inflow conditions at 85% and 100% rotational speed. For disturbed inflow conditions, a full-annulus calculation has been carried out for an operational point at peak efficiency. The object of the investigations is to validate the flow solver for compressor flow with distorted inflow. The results from time-averaged numerical and experimental data are compared extensively. The experimental trends are qualitativly and in the most part also quantitativly well reproduced in the numerical calculations.
Centrifugal Compressor Design Challenges for CO2 and Other Acid Gas Injection Services
Authors: Gupta Manoj K.
Published: May 2012

Centrifugal compressors are the preferred compression equipment for its higher reliability. However, when centrifugal compressors are designed to handle high CO2 and other acid gases such as H2S, special challenges must be addressed. Some of the key challenges are thermodynamic performance, materials selection, phase changes, hydrate formation, stability, and sealing. This paper presents how centrifugal compressors can be designed to meet these challenges.
Exhaust Gas Recirculation Performance in Dry Low Emissions Combustors
Authors: Elkady A. M. , Brand A. R. , Vandervort C. L. , Evulet A. T.
Published: May 2012

In a carbon constrained world there is a need for capturing and sequestering CO2. Post-combustion carbon capture via Exhaust Gas Recirculation (EGR) is considered a feasible means of reducing emission of CO2 from power plants. Exhaust Gas Recirculation is an enabling technology for increasing the CO2 concentration within the gas turbine cycle and allow the decrease of the size of the separation plant, which in turn will enable a significant reduction in CO2 capture cost. This paper describes the experimental work performed to better understand the risks of utilizing EGR in combustors employing dry low emissions (DLE) technologies. A rig was built for exploring the capability of premixers to operate in low O2 environment, and a series of experiments in a visually accessible test rig was performed at representative aeroderivative gas turbine pressures and temperatures. Experimental results include the effect of applying EGR on operability, efficiency and emissions performance under conditions of up to 40% EGR. Findings confirm the viability of EGR for enhanced CO2 capture; In addition, we confirm benefits of NOx reduction while complying with CO emissions in DLE combustors under low oxygen content oxidizer.
Negative Stiffness in Gas Turbine Leaf Seals
Authors: Jahn Ingo H. J. , Owen Andrew K. , Franceschini Gervas , Gillespie David R. H.
Published: May 2012

The stiffness of contacting shaft seals such as brush seals and leaf seals is a required characteristic to accurately predict their performance and life in the gas turbine engine. This paper describes the results of a test campaign in which a series of eccentric rotor excursions are applied at low rotational speed and engine representative pressure differences to characterise the behaviour of a prototype leaf seal. A phenomenon that may best be described as negative seal stiffness is reported. Here, the displacement of the seal rotor to an eccentric position causes a resultant force, which, rather than trying to return the rotor to a central position, acts to amplify its displacement. These data were used to develop an empirical model of the seal behaviour. It was possible to model the negative stiffness phenomenon and show that it is caused by a combination of two effects: the inherent mechanical stiffness of the leaf pack, and the aerodynamic stiffness of the seal. The latter is caused by the pressure distribution and changes in the flow field through the leaf pack as a result of the displacement of the rotor.
Concentrated Solar Thermal Downstream of the Solar Field: Design and Optimization of the Associated Power Generation Cycle
Authors: Zachary Justin , Jones Natasha , Golant Aslan
Published: May 2012

While major design efforts are dedicated to the development and improvement of solar energy collection technologies, the downstream power generation cycle is often considered a straightforward exercise. The diverse nature of the heat sources and their cyclic behavior make the design of the turbo-machinery and associated balance-of-plant equipment for solar plants quite different from the design for use in conventional fired power plants. The high capital cost of these renewable energy facilities and the limited hours of operation are powerful drivers to increase equipment efficiency and reduce the startup time. This paper reviews the state of the art regarding hardware selection and design considerations for tower, trough, and Fresnel solar thermal technologies from an engineering, procurement, and construction (EPC) contractor’s perspective. It also describes the benefits and limitations of each method and the impact of flow and temperature on cycle efficiency. In particular, it addresses the turbine design challenges for repeated fast startups and plant size optimization. Special emphasis is given to heat sink design in consideration of water scarcity. In conclusion, the paper provides recommendations for achieving a balance between the economics of generation and cost of equipment and reliability for the downstream power generation system.
Effect of Geometric Changes in an Idealised Contacting Brush Seal Bristle Pack on Typical Key Performance Measures
Authors: Pekris Michael J. , Franceschini Gervas , Gillespie David R. H.
Published: May 2012

In an effort to reduce gas turbine specific fuel consumption and to increase specific thrust, advanced sealing technologies have been deployed for the purpose of secondary air flow management. One such technology, the brush seal, provides a more compliant seal and hence improved leakage performance over the legacy industry standard, the labyrinth seal. It is known that brush seal geometry has a strong effect on the loading, deformations, temperatures and flows in the bristle pack. There is limited understanding of the complex interactions between the geometric variables. This paper describes a methodology for the modelling of an idealised brush seal domain based on Computational Fluid Dynamics. Bristle pressure and force distributions, temperature distributions and tip contact forces are presented. This methodology is used to examine the sensitivity of these parameters to the geometric input variables for a contacting seal configuration, using a Design of Experiments approach. Inferences are drawn from the results to determine which of the geometric parameters are most influential in brush seal pack flow-induced behaviour, and the strength of the coupling between these parameters and the key performance indicators.
Supporting Windpower Within a Separate Electric Power Grid
Authors: Domachowski Zygfryd , Dzida Marek , Ghaemi M. Hossein
Published: May 2012

Utilization of windpower is considerably increasing in many countries around of the world. However, it produces an unreliable output due to the vagaries of the wind profile. To solve the problem, wind energy should be supported by local conventional sources. The requirements concerning the reliability and quality of electric energy supply can be most satisfactorily fulfilled when a windfarm is connected to a large electric power system. Then any electric power fluctuations, resulting either from wind turbulence or power demand variation, provoke system frequency variations. They should be damped by applying an appropriate control system of such a large power system. In this paper, the problem of control of a separate electric power system composed of windpower farm and supported by a gas turbine plant or a combined cycle has been investigated. First, the impact of wind turbulence on gas turbine plant control system has been modeled and simulated. This is carried out for different amplitudes and frequencies of wind speed. Next, the structure of gas turbine plant control system and its parameters have been adapted to limit the power and frequency fluctuations resulting from wind turbulence. Then the design is further developed by considering a combined cycle instead of a single gas turbine.
Effects due to the Temperature Measurement Section on the Performance Estimation of a Centrifugal Compressor Stage
Authors: Bianchini Alessandro , Ferrara Giovanni , Ferrari Lorenzo , Ballarini Valeria , Bianchi Lorenzo , Tapinassi Libero , Toni Lorenzo
Published: May 2012

A wide-ranging analysis was performed by GE Oil & Gas and the University of Florence to investigate the effects on the estimation of centrifugal compressor performance induced by a different choice of the total temperature measurement section. With this goal in mind, the study focused on the analysis of a commonly found discrepancy between the measurements at the impeller outlet section and at the stage exit section. Based on the experimental data collected on a centrifugal impeller, three main physical phenomena were analyzed and discussed in further detail. First the effect of the heat exchange was examined and its influence on the total temperature variation throughout the machine was extrapolated. Next, the influence of the heat-exchange phenomena affecting the temperature sensors was evaluated by means of numerical models and physical assumptions. Finally, the effects on the temperature measurement of the flow structure at the impeller outlet were investigated. In particular, a corrective model to account for the thermal inertia of the thermocouples normally applied in this section was applied to the experimental data. The corrected temperatures at the investigated measurement sections were then compared and their influence on the correct stage performance estimation is discussed in this study.
Measured and Predicted Transfer Functions Between Rotor Motion and Pad Motion for a Rocker-Back Tilting-Pad Bearing in LOP Configuration
Authors: Wilkes Jason C.
Published: May 2012

Many researchers have compared predicted stiffness and damping coefficients for tilting-pad journal bearings (TPJBs) to measurements. Most have found that direct damping is consistently overpredicted. Continuing to test TBJBs in the same fashion is not likely to produce an explanation for the discrepancies between measured and predicted damping. Most analytical models for TPJBs are based on the assumption that explicit dependence on pad motion can be eliminated by assuming a solution for rotor motion such that the amplitude and phase of pad motions are predicted by rotor-pad transfer functions. Direct measurements of pad motion during test excitation are needed to produce measured transfer functions between rotor and pad motion, and a comparison between these measurements and predictions is needed to identify model discrepancies. A test setup was designed to fulfill these objectives. Motion probes were added to the loaded pad to obtain accurate measurement of pad radial and tangential motion, as well as tilt, yaw and pitch. For the remainder of this work, the loaded pad refers to the pad whose pivot sits on the static load line. Testing was performed primarily at low speeds and high loads, since this is the operating region for which predictions are most erroneous. Single frequency excitations were performed ranging from 10–350 Hz, producing rotor and pad motion, acceleration, and force vectors. This motion was used to determine frequency-dependent bearing impedances and rotor-pad transfer functions. A new pad perturbation model is proposed including the effects of pad angular, radial, and circumferential pad motion. This model was implemented in a Reynolds-based TPJB code to predict the frequency-dependent bearing impedances and rotor-pad transfer functions. These predictions are compared with measurements and discussed. Good agreement was found between the amplitude of the measured and predicted transfer functions concerning tilt and radial motions for low to moderate loads, but deviated in accuracy at the highest loaded case. Circumferential (sliding) pad motion was predicted and observed; however, the effect of this degree of freedom on dynamic bearing coefficients has not been quantitatively assessed. For the bearing investigated, radial motion accounted for more than 67% of total motion of the fluid-film height at the leading and trailing edges of the pad when operating at 4400 rpm under heavily loaded conditions. The measurements show that predicting TPJB stiffness and damping coefficients without accounting for pad pivot deformation will not produce satisfactory outcomes.
Application of Endwall Contouring to Transonic Turbine Cascades: Experimental Measurements at Design Conditions
Authors: Taremi F. , Sjolander S. A. , Praisner T. J.
Published: May 2012

An experimental investigation of the endwall flows in two transonic linear turbine cascades was presented at the 2010 ASME Turbo Expo (GT2010–22760). Endwall contouring was subsequently implemented in these cascades to control the secondary flows, and reduce the total pressure losses. The current paper presents experimental results from these cascades to assess the effectiveness of endwall contouring in the transonic flow regime. The experimental results include blade loadings, total pressure losses, streamwise vorticity and secondary kinetic energy distributions. In addition, surface flow visualization results are presented in order to interpret the endwall limiting streamlines within the blade passages. The flat-endwall and contoured-endwall cascades produce very similar midspan loading distributions and profile losses, but exhibit different secondary flows. The endwall surface flow visualization results indicate weaker interaction between the secondary flows and the blade suction surface boundary layers in the contoured cascades. Overall, the implementation of endwall contouring results in smaller and less intense vortical structures, and the reduction of the associated secondary kinetic energy (SKE) and exit flow angle variations. However, the mass-averaged losses at the main measurement plane, located 40% axial chord lengths downstream of the cascade (1.4CX), do not corroborate the numerically predicted improvements for the contoured cascades. This is in part attributed to slower mixing rates of the secondary flows in the compressible flow regime. The mass-averaged results at 2.0CX, on the other hand, show smaller losses for the contoured cascades associated with smaller SKE dissipation downstream of the cascades. Accordingly, the mixed-out row losses also show improvements for the contoured cascades.
Magnetic-Aerostatic Hybrid Bearing for Mini-Type High-Speed Air Turbine Cartridge
Authors: Wang Shih-Chun , Huang Kuang-Yuh
Published: May 2012

Under the development trend of high speed and high efficiency, mini-type air turbines have been widely applied to high-speed dental handpieces for decades. Bearing is the key component deciding efficiency of mini-type air turbine. Friction, collision and wear are the main causes to let the traditional ball and roller bearing not be able to reach higher efficiency. Although aerostatic bearing can realize very small sliding friction, but its weak bearing characteristic limits its application. In our research, we combined a magnetic levitation bearing with an aerostatic bearing to create a novel magnetic-aerostatic hybrid bearing, which can significantly promote the mini-type air turbine in a dental handpiece to achieve a better high-speed performance. The aerostatic bearing undertakes the function of radial bearing, and the magnetic levitation is responsible for the thrust bearing. The aerostatic bearing utilizes a composite orifice form with a large depth to width aspect ratio that can be realized by simple machining process. Its radial arranged orifices provide the spindle a sufficient and uniform radial support with high pressured air film. In consideration of operational safety and size constraint of the dental handpiece, the passive magnetic levitation method with repulsive NdFeB magnet rings is adopted for the thrust bearing. For comprehending their characteristics of the aerostatic and the magnetic levitation bearings, the finite element analytical method is employed to investigate the relationship between system parameters and performance and also to deduce the optimal construction for the prototype development. Our developed magnetic-aerostatic hybrid bearing is also experimentally approved to be able to provide stable and sustainable bearing capacity under low air pressure condition.
Blade Tip Measurement Advanced Visualization Using a Three Dimensional Representation
Authors: Hafner Michae¨l A. , Holst Thomas A. , Billington Scott A.
Published: May 2012

A microwave tip clearance sensor capable of measuring the hottest stages of industrial and aero gas turbines has been developed. This new microwave sensor has been integrated into a commercial package for online real-time monitoring of machine data. However, data analysis of large numbers of tip clearance probes makes standard industry graphic techniques cluttered. A method has been developed to reduce this data and visualize it in order to provide intuitive representations of the data from which a user can quickly draw the right conclusions about machine behavior. The main motivation for the development of a 3D graphical user interface is the density of information that can be shown to the user at one time. Tip clearance measurement is very data-rich, as every individual blade for each sensor mounted around the engine case is available. The result is that it may be difficult to find slight changes within hundreds of clearance trends. Only specialists with long experience in tip clearance measurement can synthesize all the data quickly enough using standard 2D plots. The 3D graphical user interface brings all of this data together to calculate the aggregated blade pattern, rotor positioning, and estimated case shape. All of these measurements are available to the user in a single visualization. Colors indicating alarm or clearance scale quickly draw attention to the most important data such as the minimum clearance point around the engine case where a rub may be likely to occur. This method is based about a case shape fitting algorithm that combines data from multiple sensors to make a case shape estimate based on fitting of a non-uniform rational B-spline (NURB). The scaling is also distorted in order to accentuate the graphics in a way that provides an intuitive understanding of the machine state. The method of applying this data accentuation is important so as to not be misleading. This innovative navigation interface presented in this paper capitalizes on modern advances in computer graphics to aid engineers and operators in understanding, access, monitoring, and analysis of tip clearance and air-gap measurements.
Vaporization Characteristics of Ethanol Droplets: Influence of the Environment Humidity
Authors: Saharin Sanisah , Lefort Benoiˆte , Morin Ce´line , Chauveau Christian , le Moyne Luis , Kafafy Raed
Published: May 2012

The study of the gasification of a droplet via vaporization, which involves heat, mass and momentum transfer processes in gas and liquid phases, and their coupling at the droplet interface, is necessary for better understanding and modeling of complex spray and mixture formation issues. A detailed description of the vaporization of an isolated droplet has been realized in this experimental study aimed at investigating the impact of the water vapor contained in the surrounding gas on the evaporation of an ethanol droplet. The experimental set-up consists of a heated chamber with a cross quartz fibers configuration as droplet support. An ethanol droplet is located at the intersection of the cross with a controlled initial diameter (300–550μm). Ambient temperature is varied from 350 to 850 K. The real impact of the water concentration on the vaporization rate of an ethanol droplet in a large range of temperature is examined, showing that the vaporization of an ethanol droplet is accompanied by the simultaneous condensation of water vapour on the droplet surface and thus the temporal evolution of the droplet squared diameter exhibits an unsteady behaviour. The histories of the instantaneous vaporisation rates calculated from the d2(t) curves confirms this non-stationary aspect of the phenomenon.
Wind Turbine Gearbox Fault Detection Using Multiple Sensors With Feature Level Data Fusion
Authors: Lu Yi , Tang Jiong , Luo Huageng
Published: May 2012

Fault detection in complex mechanical systems such as wind turbine gearboxes remains challenging, even with the recently significant advancement of sensing and signal processing technologies. For example, the non-stationary nature of the wind load may require the joint time-frequency domain feature extraction methods for the signals collected from the gearbox. In this paper, a harmonic wavelet based method is adopted, and a speed profile masking technique is developed to account for tachometer readings and gear meshing relationship. In such a way, those features with fault-related physical meanings can be highlighted. While multiple sensors yield redundant features, we fuse them through a statistical weighting approach based on principal component analysis. The fused data are fed to a simple decision making algorithm to verify the effectiveness. Using experimental data collected from a gearbox testbed emulating wind turbine operation, we can detect gear faults statistically for a given confidence level.
Optimization of a U-Bend for Minimal Pressure Loss in Internal Cooling Channels: Part I—Numerical Method
Authors: Verstraete Tom , Coletti Filippo , Bulle Je´re´my , Vanderwielen Timothe´e , Arts Tony
Published: May 2012

This two-parts paper addresses the design of a U-bend for serpentine internal cooling channels optimized for minimal pressure loss. The total pressure loss for the flow in a U-bend is a critical design parameter as it augments the pressure required at the inlet of the cooling system, resulting in a lower global efficiency. In this first part of the paper the design methodology of the cooling channel is presented. The minimization of the total pressure loss is achieved by means of a numerical optimization method that uses a metamodel assisted differential evolution algorithm in combination with an incompressible Navier-Stokes solver. The profiles of the internal and external side of the bend are parameterized using piece-wise Bezier curves. This allows for a wide variety of shapes, respecting the manufacturability constraints of the design. The pressure loss is computed by the Navier-Stokes solver, which is based on a two-equation turbulence model and is available from the open source software OpenFOAM. The numerical method predicts an improvement of 36% in total pressure drop with respect to a circular U-bend, mainly due to the reduction of the separated flow region along the internal side of the bend. The resulting design is subjected to experimental validation, presented in Part II of the paper.
Dual-Solution and Choked Flow Treatment in a Streamline Curvature Throughflow Solver
Authors: Tiwari Prashant , Stein Alex , Lin Yu-Liang
Published: May 2012

In most turbomachinery design systems streamline curvature based throughflow calculations makes the backbone of aero design process. The fast, reliable and easy to understand solution is especially useful in performing several multistage design iterations in a short period of time. Although the streamline curvature based technique enjoys many benefits for subsonic applications there are some challenges for transonic and supersonic flow applications, which is the focus of this paper. In this work it is concluded that three key improvements are required to handle transonic flows in a streamline curvature throughflow solver. These are: 1) ability to overcome dual sub- and supersonic solution and guide the solver towards supersonic flow solution where applicable; 2) suitable technique to calculate the streamline curvature gradient term which can avoid singularity at sonic meridional Mach number and high gradient values in transonic flows; 3) suitable technique to handle choked flow in the turbomachinery flowpath. Solution procedures for “dual-solution” and choked flow treatment are new and developed as part of this work. However, procedure for calculating streamline curvature gradient is leveraged from earlier work done by Denton [1] and Came [2]. Implementation of these improvements is performed in a streamline curvature based throughflow solver. Numerical improvements presented here have been tested for a range of compressor and turbine cases (both subsonic and supersonic). It is shown that the numerical improvements presented in this paper resulted in an enhanced version of streamline curvature throughflow solver. The new code produces consistent solution for subsonic applications with no sacrifice in accuracy of the solver. However, considerable robustness improvements are achieved for transonic turbine cases.
Aerodynamic Characterization of Transonic Turbine Vanes Optimized to Attenuate Rotor Forcing
Authors: Puente R. , Paniagua G. , Verstraete T.
Published: May 2012

A multi-objective optimization procedure is applied to the 3D design of a transonic turbine vane row, considering efficiency and stator outlet pressure distortion, which is directly related to induced rotor forcing. The characteristic features that define different individuals along the Pareto Front are described, analyzing the differences between high efficiency airfoils and low interaction. Pressure distortion is assessed by means of a model that requires only of the computation the steady flow field in the domain of the stator. The reduction of aerodynamic rotor forcing is checked via unsteady multistage aerodynamic computations. A well known loss prediction method is used to drive the efficiency of one optimization run, while CFD analysis is used for another, in order to assess the reliability of both methods. In both cases, the decomposition of total losses is performed to quantify the influence on efficiency of reducing rotor forcing. Results show that when striving for efficiency, the rotor is affected by few, but intense shocks. On the other hand, when the objective is the minimization of distortion, multiple shocks will appear.
Optimization of a U-Bend for Minimal Pressure Loss in Internal Cooling Channels: Part II—Experimental Validation
Authors: Coletti Filippo , Verstraete Tom , Vanderwielen Timothe´e , Bulle Je´re´my , Arts Tony
Published: May 2012

This two-part paper addresses the design of a U-bend for serpentine internal cooling channels optimized for minimal pressure loss. The total pressure loss for the flow in a U-bend is a critical design parameter as it augments the pressure required at the inlet of the cooling system, resulting in a lower global efficiency. In the first part of the paper the design methodology of the cooling channel was presented. In this second part the optimized design is validated. The results obtained with the numerical methodology described in Part I are checked against pressure measurements and Particle Image Velocimetry (PIV) measurements. The experimental campaign is carried out on a magnified model of a two-legged cooling channel that reproduces the geometrical and aerodynamical features of its numerical counterpart. Both the original profile and the optimized profile are tested. The latter proves to outperform the original geometry by about 36%, in good agreement with the numerical predictions. Two-dimensional PIV measurements performed in planes parallel to the plane of the bend highlight merits and limits of the computational model. Despite the well-known limits of the employed eddy viscosity model, the overall trends are captured. The study demonstrates that the proposed optimization method based on an evolutionary algorithm, a Navier-Stokes solver and a meta-model of it is a valid design tool to minimize the pressure loss across a U-bend in internal cooling channels.
Method and Measurement of Adiabatic Wall Temperature Downstream of a High Pressure Turbine Using Thin-Film Sensors
Authors: Pinilla V. , Solano J. P. , Paniagua G.
Published: May 2012

During engine development, heat loads in the turbomachinery are analyzed based on theoretical and numerical estimates together with correlations. Accurate models of the convective fluxes are vital to assess the thermo-mechanical integrity. This paper reports an experimental heat transfer research in a 1.5 turbine stage, the researched model is a the structural vane of a multi-splittered low pressure vane located downstream of a high pressure turbine stage. This concept is envisioned for ultra-high bypass-ratio aero-engines with a swan-neck diffuser between the high-pressure turbine and the low-pressure turbine. Measurements were performed in the large compression tube facility of the von Karman Institute, at representative conditions of modern aero-engines. Double-layered thin film gauges were employed for the measurement of the time-dependent temperature distribution around the airfoil. The initial temperature of the structural vane was adjusted using a heating system. The experimental procedure has allowed the determination of the time-mean and unsteady adiabatic wall temperature. Hence this technique allows the determination of the non-dimensional Nusselt number and proper scaling of the surface temperature to engine conditions. Furthermore, the analysis of the unsteady data reveals the contribution of the temperature fluctuations to the unsteady heat fluxes.