bluuebunny/crossref_metadata_2025 huggingface dataset:
3-D Finite Element Simulation of Shear Spinning for Investigation of Effect of Roller Nose Radius and Feed Rate on the Reaction Forces of Roller
Authors: Zoghi Hamed , Sayeaftabi Mojtaba , Fallahi Arezoodar Alireza
Published: January 2011

A 3-D Dynamic explicit finite element model of metal shear spinning, is developed and solved for different nose radii and feed rates. Several amounts are applied to spinning roller nose radius and feed rate, then Axial, tangential and normal forces are calculated for each combination of parameters. The results are checked with a series of experimental tests in which the process parameters are varied according to the finite element model. The experimental values are shown to be in relatively good agreement with the outcomes of the finite element model.
Simulation and Field Experiments With an Agricultural Tractor of a Robust Control for a Complete Fluid Power Circuit Using a New Electro-Hydraulic Pump: Part II—Control
Authors: Borodani Pandeli , Colombo Davide , Forestello Marco , Turco Patrizio , Morselli Riccardo
Published: January 2011

The plant under control is the hydraulic circuit arranged by CNH in a prototype agriculture tractor of medium segment, where instead of the conventional main hydraulic pump, a new device electronically piloted, is installed. The main purpose is basically to obtain some advantages according to the energetic point of view, by means of an appropriate control structure, managing the electronic variable displacement pump. The frontier of the new systems requires the employment of the advanced control techniques, in order to assure the levels of precision, reliability, robustness demanded from systems. The control design methodology employed in the present case is based on robust H∞ optimization techniques, where robust stability properties are guaranteed in presence of unaccountable dynamics and other destabilizing factors. The effectiveness of the proposed control approach is tested on the demonstrative tractor realized from the CNH Agriculture at Modena plants, in all real conditions.
Simulation and Field Experiments With an Agricultural Tractor of a Robust Control for a Complete Fluid Power Circuit Using a New Electro-Hydraulic Pump: Part I—Modelling
Authors: Forestello Marco , Borodani Pandeli , Colombo Davide , Turco Patrizio , Morselli Riccardo
Published: January 2011

Recently, agricultural tractors fuel consumption is growing, as a consequence of an increased number of components supplied. Otherwise, the increased sensitivity for environmental protection and global market competition are pointing out evermore urgent needs for significant improvement of fuel economy. With normal components of standard production tractors, dimensioned for the worst case operating conditions, is difficult to reduce consumptions. In this study, it is dealt with an innovative configuration where, the main hydraulic pump is substituted with a new electro-hydraulic one, with aim to optimize the operating points. To manage the pump by an appropriate control strategy, is fundamental to understand the characteristics and the dynamic properties of the hydraulic circuit fed by the pump. The purpose of this part of the paper is to describe the modeling activity that cover this necessity.
Dynamic Analysis of Surface Scanning for Tactile Perception
Authors: Fagiani Ramona , Massi Francesco , Chatelet Eric , Berthier Yves
Published: January 2011

The human hand works in a perfect accord with the brain for an efficient exploration of physical world and objects perception according to man’s purposes. During the haptic sensing, the fingertip slides on a surface activating the receptors located under the skin allowing the brain to identify objects and information about their properties. In fact, in order to create the contact, the hand must exercise a force causing the fingertip to deform, generating a stress-state that contains the information on the object in contact. The information concerning the object surface is represented by the vibrations induced by the friction between the skin and the rubbed object in contact. The mechanoreceptors have the key role of transducing the stress state into an electrical impulse conveyed to the brain. Nevertheless, the vibration spectra induced by the finger/surface rubbing and the consequent activation of the mechanoreceptors on the skin were rarely investigated. A clear understanding of the mechanisms of the tactile sense is basilar for manifold applications, like the development of artificial tactile sensors for intelligent prostheses or robotic assistants, and for the ergonomics. In this context, it is fundamental to realize appropriate dynamic analysis of the signals that characterize the characteristics of the contact. In other words, it is necessary to investigate the vibration spectrum measured on the finger, in order to identify the frequency range of measured spectra (that should correspond to the expected one given by the mechanoreceptors activation frequency range [2–500 Hertz]). An experimental set-up is developed to recover the contact global dynamics by detecting the contact force and the induced vibrations; the bench test has been designed to guarantee the measurements reproducibility and, at cause of the low amplitude of the vibrations of interest, to perform measurements without introducing external noise. In particular, in this paper, the interest will be focused on the changes shown in vibration spectra with respect to variations of the scanning velocity and surface roughness characteristics.
The Effect of Drilling Mud on Nonlinear Instability Threshold of Drill String
Authors: Jafari Ali Asghar , Kazemi Reza , Faraji Mahyari Mohammad
Published: January 2011

The main goal of this research is to analyze the effect of drilling mud and WOB on instability threshold of drill string. To this end, the kinetic and potential energy of an element of drill string for axial and lateral vibration is written in an integral form. The effect of geometrical shortening is considered in potential energy. The effect of drilling mud is modeled by the Paidoussis model. The works done by external forces are calculated. The finite element method is employed to discretize the system. The effects of stabilizers are modeled by dropping the nodes coincided with them. Flutter instability analysis is employed to analyze drill string’s instability threshold. By this procedure, the instability threshold of drill string is obtained for different WOB and drilling mud flow. Also, the effects of stabilizers numbers and arrangements are also illustrated. These results may be used for choosing the safe domain of drilling process.
Mechanical Characterization of Fiber Fabrics
Authors: Birsan Iulian-Gabriel , Circiumaru Adrian , Bria Vasile , Roman Igor , Ungureanu Victor
Published: January 2011

Fabric reinforced or textile composites are increasingly used in aerospace, automotive, naval and other applications. They are convenient material forms providing adequate stiffness and strength in many structures. In such applications they are subjected to three-dimensional states of stress coupled with hydro-thermal effects. Assuming that a composite material is a complex structure it is obvious that is hard to describe all its properties in terms of its parts properties. The properties of the composite depend not only on the properties of the components but on quality and nature of the interface between the components and its properties. As reinforcement two types of fiber fabric were used; first one is a simple type fabric of untwisted tows of carbon filaments while the second one is also simple type but as yarn and fill are used alternately untwisted tows of carbon and aramide filaments. There were some problems to be solved before molding: fabric stability during handling, cutting, imbuing the carbon and aramide tows are slipping one on each other leading to fabric defects; generally the epoxy systems do not adhere to the carbon fiber; in order to obtain a valuable material the nature of interface must be the same for polymer-carbon fiber and polymer aramide fiber. In order to solve these problems the two fabrics were covered (by spraying) with a thin film of PNB rubber. Into the rubber solution were also dispersed small amounts of clay (to create a better interface) and carbon black (to improve the electrical conductivity). The rubber presence solves the fabric stability problem; ensures the same type of interface between fibers and polymer matrix; ensures a more elastic interface between fibers and polymer matrix. This treatment induces modification on tensile behavior of fabrics. This study is about mechanical evaluation of such fabrics.
Mathematical Modeling of a High Pressure Regulator With Safety Valve
Authors: Shahani Amir R. , Aryaei Ashkan , Esmaili Hamid , Najar Mosayeb , Mohammadi Sirvan
Published: January 2011

In this article, the mathematical modeling of a high pressure regulator with its safety valve is presented. In the first step, the performance of regulator and safety valve are investigated, separately. After that, the safety valve is connected to the output port of air regulator and the output pressure’s variation is investigated. For analyzing of air regulator and safety valve’s operation, the equation of motion of internal parts, continuity equations for chamber and the equations related to mass flow rate which passing from diverse ducts in regulator are derived, respectively. The motion’s equation consists of inertia, controlling spring force, pressurized air force and coulombs friction terms. Because of nonlinearity and coupling, these equations are solved by using numerical methods and the results are presented. Finally, the results obtained in steady state are validated by testing.
DEM Computational Modeling of Flow Over Wind-Turbine Sections Under Varying Wind Speed and Direction Conditions
Authors: Eraslan Arsev H. , Erturk R. Furkan , Onbasioglu Seyhan
Published: January 2011

A summary of the core computational algorithm of the Discrete Element Model (DEM) FLOWER code, which was developed by implementing Newton’s original “discrete” Moving-Material-Domain (MMD) concepts, as the EDAN (Euler Domain Assimilated Newtonian) formalism, was presented. New generation DEM code AERO-FLOWER was used for the simulation of fast-transient air-flow conditions over three selected blade-sections (NACA 4424, NACA 4421, DU 00-W2-401) of an AEOLUS II wind-turbine blade. For each blade-section, simulations were started from parked-blade (stationary) conditions, with the oncoming wind velocity considered as 10m/s or 20m/s, along the rotor-axis (zero yaw). The tangential-velocity conditions were started as 0m/s, and were increased, intermittently, as 10m/s, 20m/s, and 40m/s, until the Torque Termination Limit (TTL). The results for tangential-force and normal-force coefficients clearly indicated the continuous presence of gradually weakening, but persistent, fast-transient characteristics of the dynamic-stall regimes, which verified the critical need for Shedding-Eddies Simulation (SES) capabilities.
Static Pull-In Analysis of a Carbon Nano Tube (CNT)-Reinforced Microplate Under Electrostatic Actuation
Authors: Jalali Amir , Khadem Siamak E.
Published: January 2011

In this paper, nonlinear vibration characteristics of a viscoelastic microplate under electrostatic actuation have been obtained. The microplate has been assumed as a CNT-reinforced simply supported square plate and an electrostatic actuation applied on it. The nonlinear equations of motion have been derived and solved, by using combined Galerkin method and indeterminate coefficient procedure. Static pull-in instability of the microplate has been also derived. It has been shown that the pull-in voltage, natural frequency and deflection of the system depend on the value of electrostatic actuation and viscoelastic characteristics of the microplate and differ from those obtained in elastic one. So, good selection of composite components (nanotube, base matrix) can result in better controlling of the microplate due to increasing/decreasing of the pull-in voltage.
Analysis of Spatial Steady-State Vibrations of a Layered Anisotropic Plate Using the Green’s Functions
Authors: Karmazin Alexander , Kirillova Evgenia , Seemann Wolfgang , Syromyatnikov Pavel
Published: January 2011

Spatial steady-state harmonic vibrations of a layered anisotropic plate excited by the distributed sources are considered. The work is based on the classical methods of the integral Fourier transforms and integral representations of the Green’s functions. In Fourier transform domain, the displacement vector is represented in terms of the Green’s matrix transform and the transform of the surface load vector. The two-dimensional inverse Fourier transform of the displacement vector is computed by reducing double integral to the iterated one with integrating along a contour, which deviates from the real axis while bypassing the real poles, and with subsequent integrating along the wave propagation angle. Three numerical algorithms of computing related iterated integrals are presented. The features of the application of these algorithms for the near- and far-field zones of the source are discussed. All of presented methods are compared for the numerical examples of vibrations on the surface of 24-layer symmetrical composite.
Simulation of Indirect Internal Reforming With Self-Sustained Electrochemical Promotion Catalysts in a Planar Solid Oxide Fuel Cell Anode
Authors: Pramuanjaroenkij Anchasa , Zhou Xiang Yang , Tongkratoke Amarin , Kakac¸ Sadık
Published: January 2011

Low operating temperature SOFCs permit a larger range of choices for materials, higher durability, and less volume and mass of a SOFC system. However, the low operating temperature poses a difficulty for the reforming of the hydrocarbon fuel: external reforming and internal reforming (IR). In this work, we develop a numerical model for simulating an indirect internal reforming section to introduce effects of the electrochemical promotion and coupling between selective anode catalysts and selective cathode catalysts in the catalyst pack in a planar solid oxide fuel cell operating at an intermediate temperature. The model employs a simplified geometrical model of an indirect internal reforming section in the anode chamber of the planar solid oxide fuel cell. However, the model includes very complicated combination of conventional reforming processes, electrochemical promotion and coupling. The model is simulated by using an in-house computer code. The results predict that the electrochemical promotion and coupling in a microscopic scale can enable a significant reforming and production of hydrogen at a relatively low temperature (500°C) with different conditions.
Experimental Analysis of Small Scale Cogenerators Based on Natural Gas Fired Reciprocating Internal Combustion Engine
Authors: Roselli Carlo , Sasso Maurizio , Sibilio Sergio , Tzscheutschler Peter
Published: January 2011

The European Union recently established an ambitious target by 2020 that consists of increasing the utilization of renewable energy up to 20%, reducing its overall pollutant emissions to at least 20%, and achieving a primary energy saving of 20% compared to reported 1990 levels. This aim could be reached only with strong effort in different sectors, such as residential, commercial, industry, tertiary, transportation, .... In particular in the European Union a remarkable contribution to energy consumption and CO2 emissions is concentrated in residential and commercial sector. The introduction of more efficient technologies in these sectors could help in achieving the results expected by 2020. An option is given by cogeneration, defined as the combined “production” of electric and/or mechanical and thermal energy starting from single energy source, that could be considered one of the first elements to save primary energy, to avoid network losses and to reduce the greenhouse gas emissions. In particular, our interest will be focused on the microcogeneration (electric power ≤ 15 kW), which represents a valid and interesting application for residential and light commercial users. The energetic, economic and environmental implications due to the use of small scale cogeneration systems were reported, starting by an experimental research activity performed by the authors and other researchers.
Diagnosis and Solution of High Noise and Vibration Issues After a Propylene Refrigeration Compressor Re-Rate
Authors: Liu Zheji , Kuzdzal Mark J. , Atkins Kenneth E. , Rials Randy
Published: January 2011

High noise and vibration levels were experienced in a propylene refrigeration centrifugal compressor piping system. The noise and vibration problems began after an ethylene plant re-rate that accomplished its aero-thermal performance expectations. The high noise and vibration was measured as a discrete source with the peak noise and vibration frequency occurring near 480 Hz. Fatigue failures of small bore piping appurtenances had also occurred. Comprehensive site measurements were performed to diagnose the root cause of the noise and vibration. In-pipe pressure pulsations, piping vibration, pipe wall strain levels, external sound pressure, and pipe surface sound intensity were measured to identify the excitation source. Analysis of the measured data indicated that the 480 Hz acoustic source originated within the compressor, upstream of the side stream discharge nozzle. Typically centrifugal compressors tend to produce dominant noise at the blade passing frequency and its harmonics. The blade passing frequency (1544 Hz) was well above the 480 Hz measured dominant frequency. Further analysis of the data lead to the belief that an acoustic standing wave inside the compressor flow path was responsible for the noise and vibration. This paper will discuss the source of the issue, how the issue was diagnosed, and what solution was implemented to address the issue. A considerable amount of data gathering and analysis will be described in the paper to support the diagnosis of the root cause of the noise and vibration. After the excitation source was correctly identified, a duct resonator array was designed and installed upstream of the discharge pipe to minimize the acoustic energy entering the pipe. The noise and vibration solution was validated with actual field data measured before and after the installation of the duct resonator array.
An Algebraic Sub-Grid Scale Turbulent Combustion Model
Authors: Wang F. , Leboeuf F. , Huang Y. , Zhou L. X. , Sayma A. I.
Published: January 2011

A direct numerical simulation (DNS) of three-dimensional turbulent reacting channel flows taking into account the buoyancy effect was carried out using a spectral method. The statistical results from the DNS database are used to validate an algebraic sub-grid scale combustion model (ASSCM), which was studied in gas combustion previously. Comparison between the exact solution and the results of the correlations in the ASSCM model show good agreement in some cases while the results were acceptable other cases. A methane-air gas flame and a methanol-air two-phase spray flame were also simulated using the ASSCM model. The LES predicted temperature profile in both flames were close to the experimental data demonstrating the accuracy of the model.
A Performance Autopsy of Three Centrifugal Compressors for a Small Gas Turbine
Authors: Rodgers Colin , Brown Dan
Published: January 2011

Three 140mm tip diameter centrifugal compressors were designed and tested to determine the one exhibiting the best performance most suitable for eventual application to a small 60KW radial flow type gas turbine. The design features, and stage test results of these three moderately high pressure ratio impellers are presented, together with a comparison of their respective test and CFD computed performance maps.
Comparative Studies of Alternative HPC Configurations for the NEWAC IRA Engine
Authors: Calvert W. John , Swain Ed , Woods Ian , Dempsey Mark , Schmidt-Eisenlohr Uwe
Published: January 2011

One of the core configurations being considered under the EU NEWAC (NEWAero-engine Core concepts) programme is for an intercooled recuperative aero-engine (IRA). The IRA concept exploits the heat of the engine exhaust gas and maximises the heat pick up capacity of the combustor inlet air by intercooling in front of the high pressure compressor (HPC). The datum configuration adopted for the HPC is a single stage radial compressor, but comparative design studies into alternative configurations have also been carried out. The ducting arrangements for the HPC in the IRA engine are more complicated than in a conventional turbofan engine, with the inlet flow coming from the intercooler via a C-shaped duct and the outlet flow going to the heat exchangers in the exhaust stream via 8 pipes on the outside of the engine core. A radial compressor fits quite neatly into this configuration, but the size required for a 70,000 lbf (310kN) thrust engine is significantly larger than for existing designs. In addition, the use of intercooling reduces the flow coefficient below the optimum value. By contrast, an axial compressor is likely to achieve higher efficiency, but it will be longer and have considerably more aerofoils. Therefore, preliminary designs for axial, radial and axial-CF configurations have been set up and analysed using CFD and finite element methods to assess their aerodynamic performance and to investigate their mechanical requirements. Each configuration has some advantages and disadvantages, and the results from the current studies quantify these for current levels of compressor technology.
Mistuning Identification for Integrally Bladed Disks Based on the SNM Technique
Authors: Wang Shuai , Yao Jianyao , Wang Jianjun
Published: January 2011

A new mistuning identification method based on the Subset of Nominal Modes (SNM) theory for the integrally bladed disk is presented. In this approach, steady-state responses from experiments are used as input parameters for identification without requiring the knowledge of the applied forces. This makes the input data more reliable and reduces the measurement difficulty. The method is especially suitable for the bladed disk situation in which the high modal density or relatively high damping leads the isolation of normal modes more difficult. The submatrix method enables the definition of mistuning parameters more freely and adds the model modification function to this identification method. The improved identification method introduced in this paper could simultaneously identify both the blade mistuning parameters and tuned natural frequencies to avoid the adverse influences of the errors in tuned natural frequencies and greatly increase the accuracy of identified mistuning. Finally, numerical example of a fan bladed disk is preformed to validate the effectiveness of the proposed identification method.
Effects of Trenched Holes on Film Cooling of a Contoured Endwall Nozzle Vane
Authors: Barigozzi Giovanna , Franchini Giuseppe , Perdichizzi Antonio , Ravelli Silvia
Published: January 2011

The present paper investigates the effects of the application of trenched holes in the front part of a contoured film cooled endwall. Two trench configurations were tested, changing the trench depth. Tests have been carried out at low speed (M2is = 0.2) and low inlet turbulence intensity level, with coolant mass flow rate ratio varied within the 0.5–2.5% range. Pressure probe traverses were performed downstream of the vane trailing edge to show the secondary flow field modifications and to evaluate trench additional losses. Endwall distributions of film cooling effectiveness have been obtained by TLC technique. For each injection condition energy loss coefficient and film cooling effectiveness distributions were analyzed and compared to the ones obtained from rows of cylindrical holes. Laterally and area averaged effectiveness as well as pitch and mass averaged kinetic energy loss coefficient were computed to enlighten any change induced by the introduction of trenched holes. A uniform and high thermal coverage was obtained in the region just downstream of the trench, but it quickly decayed, because of enforced mixing of coolant with main-flow. Compared to the cylindrical hole configuration, trenches are able to provide a higher global cooling effectiveness, but a larger amount of coolant injection is required. The introduction of both trenches is responsible for a secondary thermodynamic loss increase of about 0.7%, at low coolant injection rates. Increasing blowing rates, the additional loss is going to vanish.
An Assessment of Gas Foil Bearing Scalability and the Potential Benefits to Civilian Turbofan Engines
Authors: Bruckner Robert J.
Published: January 2011

Over the past several years the term oil-free turbomachinery has been used to describe a rotor support system for high speed turbomachinery that does not require oil for lubrication, damping, or cooling. The foundation technology for oil-free turbomachinery is the compliant foil bearing. This technology can replace the conventional rolling element bearings found in current engines. Two major benefits are realized with this technology. The primary benefit is the elimination of the oil lubrication system, accessory gearbox, tower shaft, and one turbine frame. These components account for 8–13% of the turbofan engine weight. The second benefit that compliant foil bearings offer to turbofan engines is the capability to operate at higher rotational speeds and shaft diameters. While traditional rolling element bearings have diminished life, reliability, and load capacity with increasing speeds, the foil bearing has a load capacity proportional to speed. The traditional applications for foil bearings have been in small, lightweight machines. However, recent advancements in the design and manufacturing of foil bearings have increased their potential size. An analysis, grounded in experimentally proven operation, is performed to assess the scalability of the modern foil bearing. This analysis coupled to the requirements of civilian turbofan engines. The application of the foil bearing to larger, high bypass ratio engines nominally at the 120 kN (∼25000 pound) thrust class has been examined. The application of this advanced technology to this system was found to reduce mission fuel burn by 3.05%.
Primary Surface Recuperator Alloy Oxidation: A Comparison of Accelerated Engine Testing to Field Operation
Authors: Matthews Wendy J. , More Karren L. , Walker Larry R.
Published: January 2011

The Capstone C65 MicroTurbine Primary Surface Recuperator (PSR) core has been manufactured from Haynes alloy HR-120 since 2005. When exposed to the harsh operating environment of the microturbine PSR, HR-120 forms a protective oxide scale that is resistant to the effects of the water vapor present in the exhaust gas. Long-term accelerated microturbine testing, with samples in a modified PSR with a removable aft dome, is on-going at an elevated Turbine Exit Temperature (TET) ∼100°F higher than normal operation. The elevated TET test engine is operated at steady state conditions and the engine is shut down at pre-determined intervals for sample removal. Material characterization of the elevated TET samples has been carried out by Capstone Turbine Corporation in collaboration with Oak Ridge National Laboratory. The surface oxide scale formation and associated alloy compositional changes have been evaluated for elevated TET samples with operating lives ranging from ∼1,800 – ∼26,500 hours. In addition, field operated HR-120 recuperators have been sectioned and samples have been evaluated for operating lives ranging from ∼5,500 – ∼18,000 hours. Results from the microstructural and compositional analyses of both the long-term steady-state elevated TET HR-120 samples, and the field operated HR-120 recuperator samples, will be presented and compared.
Hybrid Electric Design Enters Navy Service: A Report on the Early Service Experience From LHD 8 -USS Makin Island
Authors: Mako C. David , Mccullough Shane , Boughner Abe
Published: January 2011

The LHD 8 amphibious assault ship utilizes a hybrid propulsion plant, where the ship has the capability to be propelled by electric propulsion motors or gas turbine engines all of which is controlled and monitored by a state-of-the-art Machinery Control System (MCS). Unlike the previous ships of the class which were steam powered, the hybrid drive is designed to allow economical low speed fuel efficiency on electric motors as well as a traditional gas turbine power plant for all other mission areas. This will yield significant fuel savings over the life of the ship. The integrated machinery control system is likewise expected to reduce life cycle costs through reduced manning. After a successful series of sea trials, the LHD 8, Makin Island was delivered to the US Navy on April 2009 and departed the builders’ yard in July 2009 for a transit around the tip of South America to her homeport of San Diego, CA. The paper discusses the results of Builders and Acceptance Trials as well as the in-service experience of the ship on her maiden voyage. Examples are given of predicted vs. expected fuel consumption rates, design issues encountered and corrective measures taken as well as feedback from operators on the overall machinery plant design the MCS and its ease of operation. Included in the paper are ship drawings, photos and diagrams.
Importance of Auxiliary Power Consumption on Combined Cycle Performance
Authors: Gu¨len S. Can
Published: January 2011

The key product of a combined cycle power plant is electric power generated for industrial, commercial and residential customers. In that sense, the key performance metric that establishes the pecking order among thousands of existing, new, old, and planned power plants is the thermal efficiency. This is a ratio of net electric power generated by the plant to its rate of fuel consumption in the gas turbine combustors and, if applicable, heat recovery boiler duct burners. The term in the numerator of that simple ratio is subject to myriad ambiguities and/or misunderstandings, resulting primarily from the lack of a standardized definition agreed upon by all major players. More precisely, it is the lack of a standardized definition of the plant auxiliary power consumption (or load) that must be substracted from the generator output of all turbines in the plant, which then determines the net contribution of that power plant to the electric grid. For a combined cycle power plant, the key contributor to the plant’s auxiliary power load is the heat rejection system. In particular, any statement of combined cycle power plant thermal efficiency that does not specify (i) the steam turbine exhaust pressure, and (ii) the exhaust steam cooling system to achieve that pressure at the site ambient and loading conditions is subject to conjecture. Furthermore, for an assessment of the realism associated with the two in terms of economic and mechanical design feasibility, it is necessary to know the steam turbine exhaust end size and configuration. Using fundamental design principles, this paper provides a precise definition of the plant auxiliary load and quantifies its ramification on the plant’s net thermal efficiency. In addition, four standard auxiliary load levels are quantitatively defined based on a rigorous study of heat rejection system design considerations with a second-law perspective.
LES Predictions of Noise Emissions From a Low-Bypass Ratio Military Gas Turbine Engine
Authors: Sinha N. , Erwin J. , Kannepalli C. , Arunajatesan S.
Published: January 2011

A practical framework for predicting jet structure and noise from military aircraft is described, which is developmental and has been examined for some fundamental jet flow problems. The framework currently utilizes RANS methodology for geometrically complex internal propulsive flowpaths and LES methodology for the jet structure downstream of the nozzle exit. Temporal data from the LES solution is stored on a flared-cylindrical surface surrounding the jet, to be used for noise propagation to the farfield. Earlier applications of RANS methodology combined with the use of analogy-based jet noise codes proved inadequate due to the inability of the noise codes to treat complex 3D flows such as those associated with multiple nozzles and/or with varied jet noise reduction concepts. Restricting the use of LES (or RANS/LES) methodology to free shear flows remedies the severe grid resolution issues that would be encountered with utilization of LES for modeling internal propulsive flows. The issue of “adequately” initiating the LES solution from a RANS solution profile just downstream of the nozzle exit has been the focus of our exploratory studies, and is clearly more complex than standard procedures such as recycling and rescaling techniques used for simple wall bounded flows. Approaches examined are discussed and unified RANS / LES solutions for several flows are described. The application of this framework to more complex flows requires no fundamental modifications as will also be discussed.
Computation of Laminar-Turbulent Transition in Turbumachinery Using the Correlation Based γ-Reθ Transition Model
Authors: Kelterer M. E. , Pecnik R. , Sanz W.
Published: January 2011

The accurate numerical simulation of the flow through turbomachinery depends on the correct prediction of boundary-layer transition phenomena. Especially heat transfer and skin friction investigations demand a reliable simulation of the transition process. Many models have been developed to simulate the transition process, ranging from simple algebraic models to very sophisticated transport models. But nearly all models suffer from the need to determine boundary layer parameters and from their difficult application in three-dimensional flows. Therefore, in this work the correlation based γ-Reθ transition model developed by Menter and Langtry is implemented into the in-house Reynolds-averaged Navier-Stokes solver. This model avoids the calculation of non-local parameters and is thus very suitable for three-dimensional general flow situations. Two additional transport equations, one for the intermittency and one for the momentum thickness Reynolds number, which is a criterion for the transition onset, are added to the well known SST turbulence model by Menter. Instead of the proprietary model correlations by Menter et al. the authors used correlations by other research groups within the in-house code and tested these correlations for simple flat-plate test cases. The non-satisfying results indicate a strong code dependency of the model. Therefore also in-house correlations are presented and validated. A comprehensive study of the model performance on the well known ERCOFTAC flat plate test cases is performed. After this validation the model is applied to the steady flow in a T106A and a T106 turbine cascade.
Effect of Surface Roughness Location and Reynolds Number on Compressor Cascade Performance
Authors: Back Seung Chul , Hobson Garth V. , Song Seung Jin , Millsaps Knox T.
Published: January 2011

An experimental investigation has been conducted to characterize the influence of surface roughness location and Reynolds number on compressor cascade performance. Flow field surveys have been conducted in a low-speed, linear compressor cascade. Pressure, velocity, and flow angles have been measured via a 5-hole probe, pitot probe, and pressure taps on the blades. In addition to the entirely smooth and entirely rough blade cases, blades with roughness covering the leading edge; pressure side; and 5%, 20%, 35%, 50%, and 100% of suction side from the leading edge have been studied. All of the tests have been done for Reynolds number ranging from 300,000 to 640,000.Cascade performance (i.e. blade loading, loss, and deviation) is more sensitive to roughness on the suction side than pressure side. Roughness near the trailing edge of suction side increases loss more than that near the leading edge. When the suction side roughness is located closer to the trailing edge, the deviation and loss increase more rapidly with Reynolds number. For a given roughness location, there exists a Reynolds number at which loss begins to visibly increase. Finally, increasing the area of rough suction surface from the leading edge reduces the Reynolds number at which the loss coefficient begins to increase.
Spark Ignition Simulations and the Generation of Ignition Maps by Means of a Turbulent Flame Speed Closure Approach
Authors: Boyde Jan M. , Di Domenico Massimiliano , Noll Berthold , Aigner Manfred
Published: January 2011

This paper presents a numerical investigation of ignition phenomena in turbulent partially premixed methane/air flames. In this work, a turbulent flame speed closure model (TFC) is employed with an ignition delay module extension. The model is applied to two partially premixed test cases under standard conditions in the configuration of a shearless flame and a counter flow flame, respectively. For both setups, the flame kernel propagation and consequent establishment or extinction of the flame are examined. A shearless configuration represents the first test case under investigation. The study demonstrates the large influence of the mean flow parameters on achieving a successful ignition of the domain. The second test case under examination is a counterflow geometry. A sensitivity analysis with respect to spark ignition position and ignition energy is performed. The simulations show that flame kernel spreading is largely influenced by the magnitude of turbulence occurring in the flow, leading to an enhanced propagation in areas with a moderate turbulence degree, whereas high turbulence can be detrimental for the flame establishment due to extensive heat losses. Another observation is that a successful ignition of the domain can occur, even in cases in which the ignition energy is not placed in an area with flammable mixture. The comparison with experimental data shows a good agreement, both in terms of successful ignition and flame kernel propagation.
Laplace Correction of Confusion Matrices to Produce Statistically Representative Confidence Intervals
Authors: Davison Craig R.
Published: January 2011

During diagnostic algorithm development engine testing with implanted faults may be performed. The number of implanted faults is never large enough to truly capture the distribution in the confusion matrix. Misdiagnoses in particular are unlikely to be correctly represented. Misdiagnosis that could result in costly outcomes are frequently not captured in an implantation study, resulting in a deceptively reassuring zero value for the probability of it occurring. The Laplace correction can be applied to each element of the confusion matrix to improve the generated confidence interval. This also allows a confidence interval to be produced for zero value elements. Unfortunately, the choice of Laplace correction factor influences the size of the confidence interval, and without knowing the true distribution the best correction factor cannot be determined. The choice of correction factor depends on element probability, total sample size, number of faults and confidence level. The effect of the Laplace correction on the element probability is analytically examined to provide insight into the relative influence of the correction. This is followed by an examination of the influence of the element probability, total sample size, number of faults and confidence level on the required Laplace correction. This is achieved by sampling from known populations. A method of generating good confidence intervals on each element is proposed. This includes the production of a Laplace correction based on the sample size, number of faults and confidence level. This will allow consistent comparisons of Laplace corrected matrices rather than leaving the correction factor to each individual’s best engineering judgment.
Development of a Rotating Centrifugal Separator Technology for Centrifugal Compressors
Authors: Maier William , Chochua Gocha , Biba Yuri
Published: January 2011

This paper presents the development and testing of an advanced rotating centrifugal separator. This design extends separation technology to higher velocity and flowrate capabilities suitable for use as an inlet scrubber for industrial centrifugal compressors. Because of the inherent compact nature of the device it is particularly useful for oil and gas applications on offshore platforms where size and weight have high value. In addition to the separator design, a non-dimensional separation parameter is developed from first principles and is shown to be useful in accessing the degree of difficulty of separation for rotating centrifugal separator devices. An overview of a novel design evolution procedure used to optimize the rotating centrifugal separator is also presented.
Field Validation of a TBC Life-Prediction Model for Land-Based Gas Turbines
Authors: Chan K. S. , Cheruvu N. S.
Published: January 2011

The coating life-prediction model, COATLIFE, was previously developed for estimating the lifetimes of first-stage blades and vanes in land-based power-generation gas turbines on the basis of degradation mechanisms observed in laboratory and field data. For first-stage blades with thermal barrier coatings (TBCs), degradation mechanisms treated in COATLIFE include thermo-mechanical fatigue (TMF), Al depletion due to bond coat oxidation, sintering of voids and microcracks in TBC, and curvature effects. Material constants in COATLIFE were evaluated using laboratory data and subsequently utilized with the model to predict the remaining life of first-stage blades in the field. In the present study, the predictive capabilities of COATLIFE were evaluated against field data obtained from first-stage blades with TBC extracted from land-based power generation gas turbines. The ex-service blades were sectioned to characterize the conditions of the TBC and bond coat after various times of service. For coating characterization, the Al content and volume fraction of the β phase in the bond coat, as well as the extent of oxidation and microcracking in the TBCs and along the TBC/bond coat interface at various locations of the blade were determined. These results were compared against model predictions generated by COATLIFE. Good agreement between the field data and model predictions validates the predictive capabilities of COATLIFE for estimating the oxidation lives for first-stage blades with TBCs.
Numerical Simulation of Flow Instabilities in High Speed Multistage Compressors
Authors: Zhang Huan , Hu Jun , Tu Baofeng , Wang Zhiqiang
Published: January 2011

In the present paper, a nonlinear multi “actuator disk” model is proposed to analyze the dynamic behavior of flow instabilities, including rotating stall and surge, in high speed multistage axial compressors. The model describes the duct flow fields using two dimensional, compressible and unsteady Euler equations, and accounts for the influences of downstream plenum and throttle in the system as well. It replaces each blade row of multistage compressors with a disk. For numerical calculations, the time marching procedure, using MacCormack two steps scheme, is used. The main purpose of this paper is to predict the mechanism of two dimensional short wavelength rotating stall inception, the interaction between blade rows in high speed multistage compressors and the influence of rotating inlet distortion on the stability. It has been demonstrated that the model has the ability to predict those phenomena, and the results show that some system parameters have a strong effect on the stall features as well. Results for a five stage high speed compressor are analyzed in detail, and comparison with the experimental data demonstrates that the model and calculating results are reliable.
Effects of Design Variations of Rotor Entry Cavity Geometry on Shrouded Steam Turbine Performance
Authors: Barmpalias K. G. , Kalfas A. I. , Abhari R. S. , Hirano Toshio , Shibukawa Naoki
Published: January 2011

This paper presents an experimental study of the effect of geometry variations of the rotor entry cavity on shrouded steam turbine performance. A series of experiments was carried out where different configurations of the geometry of the entry cavity were tested. Blade geometry and tip clearance remained unaltered for all cases examined. Interactions between cavity and main flow are carefully investigated and their consequences on shrouded steam turbine stage efficiency are examined. Geometry variations of the entry cavity were installed in a pre-existing ‘baseline’ case of high efficiency. Five different test cases were examined. For the first two of these cases a ring having a constant width of 2mm and 4mm in radial direction is used. The next two cases employ a non-uniform, wavy insert and for the last case a backwards slanted insert is used that covers most of the inlet to cavity area, maintaining a safety distance of 2mm from the downstream rotor. The cases are divided into two groups, based on the same inlet cavity volume. The first group of three cases has a cavity volume reduction of 14% compared to the baseline case, whereas in the second group two cases are examined which maintain a 28% cavity volume reduction compared to the baseline case. Stage performance and flow field data were acquired and analyzed. Strong interactions between cavity and main flow are observed for all cases, not only at the location where the variations were installed. An observed effect can also be seen downstream of the rotor affecting the stage performance. Measurements were performed with the use of miniature probes ensuring minimum blockage effects especially within the cavity, both at rotor inlet as well as downstream of the second rotor. The use of a uniform geometry variation for the inlet rotor cavity in both groups proved to be the best in terms of stage efficiency. Although more complex and non-uniform variations were also used, the simple design of uniform geometry caused the least disturbance in the flow downstream of the 2nd rotor, having at the same time a moderate positive influence at the exit of the 2nd stator. The use of a constant width insert ring (thickness = 2mm) showed an efficiency gain of at least 0.3% from cases with 14% cavity volume reduction, whereas in the cases with 28% cavity volume reduction the use of a uniform ring of 4mm width produced a marginal efficiency gain of 0.1% at the operational point.
Methane Oxy-Combustion for Low CO2 Cycles: Measurements and Modeling of CO and O2 Emissions
Authors: Amato Alberto , Hudak Robert , Noble David R. , Scarborough David , D’Carlo Peter A. , Seitzman Jerry M. , Lieuwen Tim C.
Published: January 2011

Concerns about green house gas emissions have encouraged interest in hydrocarbon combustion techniques that can accommodate carbon dioxide capture and sequestration. Oxy-fuel combustion, where the fuel is combusted in oxygen diluted with steam or CO2, is seen as one promising approach. In this paper we focus on CO2 dilution effects and, in particular, on CO and O2 emissions from these flames. The emissions issue must be considered from a different perspective than conventional power plants as the combustor effluents will be sequestered, and, thus, their interactions with the terrestrial atmosphere are not relevant. Equilibrium CO emissions from CO2 diluted systems are much higher than conventional air systems. In addition, for carbon sequestration application, pipeline specifications impose limitations on CO and O2 levels which also must then be controlled. Equilibrium and kinetic modeling of CH4/O2/CO2 combustion systems was performed in order to analyze CO2 dilution effects upon CO and O2 emissions level. Companion experiments were also performed in an atmospheric pressure, swirl stabilized combustor. These numerical and experimental results quantify the strong dependence of emissions on stoichiometry, CO2 dilution and residence time.