bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Exhaust Gas Recirculation on Combustion Instabilities in CH4 and H2/CH4 Fuel Mixtures
Authors: Ferguson Don , Ranalli Joseph A. , Strakey Peter
Published: January 2011

This paper evaluates the impact of two strategies for reducing CO2 emissions on combustion instabilities in lean-premixed combustion. Exhaust gas recirculation can be utilized to increase the concentration of CO2 in the exhaust stream improving the efficiency in the post-combustion separation plant. This coupled with the use of coal derived syngas or hydrogen augmented natural gas can further decrease CO2 levels released into the environment. However, changes in fuel composition have been shown to alter the dynamic response in lean-premixed combustion systems. In this study, a fully premixed, swirl stabilized, atmospheric burner is operated on various blends of H2/CH4 fuels with N2 and CO2 dilution to simulate EGR. Acoustic pressure and velocity, and global heat release measurements were performed at fixed adiabatic flame temperatures to evaluate the impact of fuel composition and dilution on various mechanisms that drive the instabilities.
Design and Optimization of Radial Flow Wheels for a Waste Heat Recovery Double Supersonic Stage Turbo-Expander
Authors: Del Turco Paolo , Scotti Del Greco Alberto , Natali Daniele , Borys Robert , Biagi Roberto
Published: January 2011

Waste heat recovery cycles equipped with radial inflow turbines (turbo-expanders) typically dictate large pressure ratios per stage in order to increase the overall cycle efficiency. Depending on the operating conditions, supersonic flow may be reached at some location within the stage. The design of turbo-machinery in such an environment poses several challenges, the most important of which are preventing performance deterioration and High Cycle Fatigue (HCF) failure of the rotating, stressed material by avoiding resonance frequencies in the operating range. Turbo-expander wheels, being uncooled components, are generally not affected by high temperature gradients; therefore LCF (Low Cycle Fatigue) doesn’t constitute their main limiting life factor. This paper describes the process used in GE Oil & Gas to design and optimize the wheels of a 17MW double supersonic stage turbo-expander. The initial design phases, preliminary design assessments, CFD analyses and structural analysis optimization are described. Special focus is given to the modal analysis and resonance identification (i.e., Modal Cyclic Analysis) used in the design phase. A critical review of the use of the SAFE interference diagram in place of the Campbell diagram is also provided.
Rotor Health Monitoring by Wireless Localized Sensing
Authors: Gyekenyesi Andrew L. , Haase Wayne C.
Published: January 2011

This study presents early results for a localized, in-situ sensing approach for detecting cracks in turbine engines. A wireless slip ring system was developed for capturing and transmitting acoustic emissions data from rotors during operation. The wireless communication between the rotor and the stator is accomplished through capacitive coupling. The antennas are fashioned as a ring within a ring set-up. Here, tests were conducted under both static and rotating conditions in order to document the abilities of the system concerning signal accuracy after modulation and demodulation. Results showed that the prototype wireless slip ring was able to accurately recreate fixed frequency or arbitrary input signals, generated using a pulse/function generator or lead breaks imitating fracture events, in the frequency range of a few hundred Hz to 850 KHz. Planned improvements as well as strategies for implementation are also discussed.
Effects of Thermal Radiation on Air Plasma Spray (APS) Coated Gas Turbine Blade
Authors: Akwaboa Stephen , Mensah Patrick , Diwan Ravinder
Published: January 2011

Thermal barrier coatings (TBCs) are used to protect hot gas path (HGP) components such as the first two stages of turbine blades and vanes of land-based turbine engines against high temperature environment, corrosion and oxidation. The continuing thrust towards higher thermal efficiencies of gas turbines has resulted in a continuous increase of turbine inlet temperatures (TITs). This has resulted in the increase of heat load on the turbine components especially the high pressure side of the turbine necessitating the need to protect the HGP components from the heat of the exhaust gases using novel TBCs such as air plasma spray (APS) TBCs which are transparent and reflective to radiation. This paper focuses on the combined effects of radiation and conduction heat transfer in the semitransparent yttria-stabilized zirconia (YSZ) coatings used to offer thermal protection to turbine blade. The temperature distribution in the turbine blade depends on the surface convection, reflectivity and refractive index of the grey semitransparent YSZ coatings. The temperature distributions in the metal substrate and the TBC systems are determined by solving the steady state heat diffusion equation and the radiative transport equation simultaneously using ANSYS FLUENT 12.0 CFD commercial package. Preliminary results indicate that substrate metal temperature reduction of about 100K results with the use of the TBC. This temperature drop reduces the thermally activated oxidation rate of the bond coat in the TBC and so delays failure of TBC by oxidation. Furthermore, by taking into account the effect of radiation, the temperature distribution in the metal substrate with TBC exceeds the temperature distribution without radiation by about 40 K, signifying the importance of including radiation in the thermal modeling of TBCs for high temperature applications.
The Effects of Localized Blade Endwall Suction on Secondary Flows and Heat Transfer
Authors: Hollis Rebecca , Bons Jeffrey P.
Published: January 2011

Two methods of flow control were designed to mitigate the effects of the horseshoe vortex structure (HV) at an airfoil/endwall junction. An experimental study was conducted to quantify the effects of localized boundary layer removal on surface heat transfer in a low-speed wind tunnel. A transient infrared technique was used to measure the convective heat transfer values along the surface surrounding the juncture. Particle image velocimetry was used to collect the time-mean velocity vectors of the flow field across three planes of interest. Boundary layer suction was applied through a thin slot cut into the leading edge of the airfoil at two locations. The first, referred to as Method 1, was directly along the endwall, the second, Method 2, was located at a height ∼1/3 of the approaching boundary layer height. Five suction rates were tested; 0%, 6.5%, 11%, 15% and 20% of the approaching boundary layer mass flow was removed at a constant rate. Both methods reduced the effects of the HV with increasing suction on the symmetry, 0.5-D and 1-D planes. Method 2 yielded a greater reduction in surface heat transfer but Method 1 outperformed Method 2 aerodynamically by completely removing the HV structure when 11% suction was applied. This method however produced other adverse effects such as high surface shear stress and localized areas of high heat transfer near the slot edges at high suction rates.
The Role of Density Ratio and Blowing Ratio on Film Cooling in a Vane Passage
Authors: Post James W. , Acharya Sumanta
Published: January 2011

Temperature and heat flux measurements have been obtained in a film-cooled, heated fixed-vane cascade. The cascade facility has the capability to deliver high-pressure air through the vane passages at high flow rates (3.5 lbm/s; 1.59 kg/s). Prior to entering the vane test section, pressurized mainstream air has been heated by a natural gas-burning combustor, which produces realistic density ratios for the film-cooling air. Measurements are reported for a vane pressure ratio of around 1.5 and for coolant blowing ratios (M) in the range of 1.0–3.0, with coolant-to-freestream density ratios (DR) in the range of 1.1–2.2. Data presented include endwall and vane surface normalized metal temperatures (NMT), and surface heat fluxes, q″, in both local and averaged form. Generally, a higher density coolant film tends to provide greater cooling effectiveness along the endwall at higher M, with local increases in NMT of as much as 0.2, but the opposite trend is observed for lower M along the endwall, with potential lowering in NMT of 0.1 in the early-passage regions. Along the vane, a higher DR tends to produce lower NMT (peak reductions of the order of 0.1, average reductions in the range of 0.05–0.1). Higher blowing ratios (above 1.0) usually give better cooling performance due to the increased coolant flow rate.
A Comparison of the Steady-State and Dynamic Performance of First- and Second-Generation Foil Bearings
Authors: Conlon M. J. , Dadouche A. , Dmochowski W. M. , Payette R. , Be´dard J.-P.
Published: January 2011

Oil-free foil bearing technology has advanced intermittently over the years, driven by research efforts to improve both steady-state and dynamic performance characteristics, namely: load capacity, stiffness, and damping. Bearing designs are thus classified according to “generation”, with first-generation bearings being the most primitive. This paper presents an experimental evaluation of a first- and a second-generation foil bearing, and aims to provide the high-fidelity data necessary for proper validation of theoretical predictive models of foil bearing performance. The aforementioned test bearings were fabricated in-house, and are both 70mm in diameter with an aspect ratio of 1; bearing manufacturing details are provided. The work makes use of a facility dedicated to measuring both the steady-state and dynamic properties of foil bearings under a variety of controlled operating conditions. The bearing under test is placed at the midspan of a horizontal, simply-supported, stepped shaft which rotates at up to 60krpm. Static and dynamic loads of up to 3500N and 450N (respectively) can be applied by means of a pneumatic cylinder and two electrodynamic shakers. The bearings’ structural (static) stiffnesses are highly nonlinear, and this affects the accuracy of the dynamic coefficient determination. Both dynamic stiffness and damping are found to vary nonlinearly with excitation frequency, and are over-predicted by a structural experimental evaluation — the film plays an important role in bearing dynamics. The second-generation bearing is found to have a higher load capacity, dynamic stiffness, and damping than the first-generation bearing.
Solar Retrofit to Combined Cycle Power Plant With Thermal Energy Storage
Authors: Bonadies Monica F. , Mohagheghi Mahmood , Ricklick Mark , Kapat J. S.
Published: January 2011

Solar thermal power plants have been constructed over the past two decades to reduce harmful emissions and provide a long-term solution for oil independent electricity generation. Of the solar power plant solutions, Rankine cycle based machines have most widespread uses. This study focuses on the modeling of a solar retrofit to a typical combined cycle power plant. The goal is to operate the plant 17 hours per day, making use of thermal storage capability so that the plant may operate even during a portion of the night time. The plant will be located in Orlando, Florida to take advantage of the abundance of sun in that geographic location. On the cycle side, the amount of solar collectors, the working fluid, and the turbine are considered. The thermal storage system, on the other hand, must be designed based upon a balance between cost and storage density. A decision will be made from existing sensible heat solid storage materials. The storage material evens out the energy supplied to the turbine working fluid between the peak solar radiation of the day time and the absence of solar radiation at night. This plant can be implemented in two ways: as a completely newly constructed power plant or as an addition to a HRSG (Heat Recovery Steam Generation) configuration, which can be retrofitted to an existing combined cycle power plant to increase its overall efficiency. In this study, the addition of a solar air collection system with a storage unit to a HRSG combined cycle power plant is proposed. The HRSG will be designed using a series of energy balances for each component. This proposed plant will then be compared with a similar solar plant to examine its feasibility in terms of land area. The storage unit devised comprises 1377 m3 and stores approximately 3900 GJ of thermal energy, which equates to 8 hours of run time when solar radiation is not available. The benefit of this addition to the plant is that the storage reduces the gas turbine run time necessary to provide hot gas to the HRSG. The total cost of the storage medium is approximately $8 million.
Effects of Hydrogen Addition on Swirl-Stabilized Flame Properties
Authors: Zhu Shengrong , Acharya Sumanta
Published: January 2011

The role of hydrogen addition to swirl-stabilized methane flames is studied experimentally. Of specific interest are flame properties including flame surface density and curvature. The measurements are based on Particle Image Velocimetry (PIV), Mie-scattering and CH-chemiluminescence imaging. Identification of the flame front and its geometric characterization provides an understanding of the flame properties. Compared to the non-reacting flow, the methane flame broadens the central recirculation zone. Hydrogen enriched flames reduce the central recirculation zone and scales down the characteristic length of the flow. With hydrogen addition, the distribution of the flame front curvature is broadened and flame surface density is increased. This indicates that hydrogen addition increases the reaction front thermo-diffusive instability, causing the flame front to be more wrinkled, and increasing the flame surface area leading to an increase in the burning velocity.
Squealer Tip Heat Transfer With Film Cooling
Authors: Acharya Sumanta , Kramer Gregory , Moreaux Louis , Nakamata Chiyuki
Published: January 2011

Heat transfer coefficients and film cooling effectiveness values were obtained numerically on a film cooled 2-D gas turbine blade tip model featuring a cutback squealer. In addition, pressure distributions were obtained at 50% and 98% spans. The calculations were performed for a single blade with periodic boundary conditions imposed along the two mid-passage boundaries formed by the adjacent blades. The calculations were performed with the realizable k-ε turbulence model and non-equilibrium wall function using 1.1 million elements. The numerical results are obtained for 4 blowing ratios and for Reynolds number based on axial chord and inlet velocity of 75,000. Limited experimental measurements of the blade pressure distributions and the uncooled tip heat transfer coefficients were performed for validation of the numerical results. The experiments were conducted in a six-blade low-speed wind tunnel cascade at a Reynolds number of 75,000. The heat transfer experiment involved a transient infrared thermography technique. Experimental heat transfer coefficients were extracted using a transient technique. The predicted pressure distributions agree very well with the measurements while the heat transfer coefficient predictions show qualitative agreement. From the numerical results, it can be seen that as the blowing ratio is increased, larger regions of film cooling effectiveness were seen with higher effectiveness values between the camber line and suction side. Heat transfer coefficients were largest near the leading edge for all cases.
Evolution of Combustion-Generated Particles at Tropospheric Conditions
Authors: Tacina Kathleen M. , Heath Christopher M.
Published: January 2011

This paper describes particle evolution measurements taken in the Particulate Aerosol Laboratory (PAL). The PAL consists of a burner capable of burning jet fuel that exhausts into an altitude chamber that can simulate temperature and pressure conditions up to 13,700 m. After presenting results from initial temperature distributions inside the chamber, particle count data measured in the altitude chamber are shown. Initial particle count data show that the sampling system can have a significant effect on the measured particle distribution: both the value of particle number concentration and the shape of the radial distribution of the particle number concentration depend on whether the measurement probe is heated or unheated.
Practical Jet Noise Reduction for Tactical Aircraft
Authors: Martens Steve , Spyropoulos John T.
Published: January 2011

GE and NAVAIR are working together to find and develop practical techniques to reduce jet noise on legacy tactical aircraft such as the F/A-18. Noise is an important issue for the Navy that has grown dramatically over the last number of years. The two most important issues are the hearing loss induced during operations of these aircraft on aircraft carriers and the impact to communities around Naval Air Bases and training sites. A near term noise reduction goal of 3 dB has been established by NAVAIR as the first step in a much longer term plan to significantly reduce the noise felt in both of these situations. A near term solution for noise reduction implies that it can be implemented in the existing fleet with relatively little impact to the current air vehicle and the way it is operated, deployed, maintained, and funded. These constraints quickly limit the magnitude and types of changes that can be made to legacy engines or exhaust systems. In 2009, a static acoustic test on an F404 engine demonstrated that chevrons are equally effective at reducing noise all the way to full afterburner conditions. This test also measured thrust and the chevrons were demonstrated to result in very minimal performance impact at sea level static conditions. These two results are very important, as this was the first demonstration at full scale of practical noise reduction at afterburner conditions with minimal thrust impact. This paper will report on this latest test.
On the Frequency Response of a Spinning Disk With Large Deformations
Authors: Khorasany Ramin M. H. , Hutton Stanley G.
Published: January 2011

In this paper, the effect of geometrical nonlinear terms, caused by a space fixed point force, on the frequencies of oscillations of a rotating disk with clamped-free boundary conditions is investigated. The nonlinear geometrical equations of motion are based on Von Karman plate theory. Using the eigenfunctions of a stationary disk as approximating functions in Galerkin’s method, the equations of motion are transformed into a set of coupled nonlinear Ordinary Differential Equations (ODEs). These equations are then used to find the equilibrium positions of the disk at different discrete blade speeds. At any given speed, the governing equations are linearized about the equilibrium solution of the disk under the application of a space fixed external force. These linearized equations are then used to find the oscillation frequencies of the disk considering the effect of large deformation. Using multi mode approximation and different levels of nonlinearity, the frequency response of the disk considering the effect of geometrical nonlinear terms are studied. It is found that at the linear critical speed, the nonlinear frequency of the corresponding mode is not zero. Results are presented that illustrate the effect of the magnitude of disk displacement upon the frequency response characteristics. It is also found that for each mode, including the effect of the geometrical nonlinear terms due to the applied load causes a separation in the frequency responses of its backward and forward traveling waves when the disk is stationary. This effect is similar to the effect of a space fixed constraint in the linear problem. In order to verify the numerical results, experiments are conducted and the results are presented.
Total Cooling Effectiveness on a Staggered Full-Coverage Film Cooling Plate With Impinging Jet
Authors: Jung Eui Yeop , Lee Dong Hyun , Oh Sang Hyun , Kim Kyung Min , Cho Hyung Hee
Published: January 2011

In the present study, total cooling performance was experimentally investigated on a full-coverage film cooling plate with an impingement jet cooling array. The detailed temperature distributions on the film cooled surface were measured using an infra-red thermographic technique. The test plate was made of polycarbonate (k = 0.2 W/m·K) and an array jet impinged underneath the test plates. The measured cooling effectiveness is a combined result of film cooling on the surface and convective heat transfer by a jet impingement array underneath the test plate. The diameter (d) of both film cooling and impingement jet cooling holes was 5 mm. Both the streamwise and spanwise hole spacing-to-hole diameter ratios (p/d) were 3 on the film cooled plate and impingement nozzle plate. The inclination angles of the film cooling holes and impingement jet holes were 35° and 90°, respectively. The holes on each plate were arranged in a staggered pattern. The jet Reynolds number based on the hole diameter varied from 3,000 to 7,000 and the equivalent blowing rate (M) changed from 0.3 to 0.7. The combined cooling effectiveness was measured by changing the gap distance between the jet plate and the film cooling plate from 1 to 5 times the hole diameter. The staggered film cooling hole arrangement showed a higher film cooling effectiveness than the inline film cooling hole arrangement. As the blowing rate increased, the cooling effectiveness decreased on the front part of film cooling plate for a fixed height to diameter ratio (H/d). The effect of H/d on the total cooling effectiveness was not significant for the fixed blowing rate (M) in the tested range.
Exploration of NDE Properties of AMB Supported Rotors for Structural Damage Detection
Authors: Sawicki Jerzy T. , Storozhev Dmitry L. , Lekki John D.
Published: January 2011

This paper addresses self-diagnostic properties of AMB (active magnetic bearing) supported rotors for on-line detection of the transverse crack on a rotating shaft. In addition to pure levitation, the rotor supporting bearing also serves as an actuator that transforms current signals additionally injected into the control loop into the superimposed specially selected excitation forces into the suspended rotor. These additional excitations induce combination frequencies in the rotor response, providing unique signatures for the presence of crack. The background of theoretical modeling, experimental and computer simulation results for the AMB supported cracked rotor with self-diagnostic excitation forces are presented and discussed.
Thick Airfoils With Blunt Trailing Edge for Wind Turbine Blades
Authors: van Dam C. P. , Cooperman A. , McLennan A. , Chow R. , Baker J.
Published: January 2011

This paper addresses the primary concerns regarding the aerodynamic performance characteristics of thick airfoils with blunt trailing edges (or so-called flatback airfoils) and the utilization of these section shapes in the design of rotor blades for utility-scale wind turbines. Results from wind tunnel and computational fluid dynamic studies demonstrate the favorable impact of the blunt trailing edge on the aerodynamic performance characteristics including higher maximum lift coefficient and reduced sensitivity of lift to premature boundary layer transition. The negative effect of the blunt trailing edge on drag can be partially mitigated through simple trailing edge treatments such as splitter plates. Studies on the effect of these section shapes on wind turbine rotor performance show that at attached flow conditions this inboard blade modification does not adversely affect rotor torque output. Blade system design studies involving the collective optimization of aerodynamic performance, structural strength and weight, and manufacturing complexity demonstrate the overall favorable impact of the flatback concept.
Analysis of Fluid-Structure Interaction in a Steam Turbine Throttle Valve
Authors: Tecza Joseph , Chochua Gocha , Moll Randy
Published: January 2011

Throttle valves in steam turbines often operate at very small lift positions during turbine startup. The large pressure differentials across these valves, combined with the very small openings at the valve seat, result in large pressure drops across these valves and high local steam Mach numbers. A steam turbine throttle valve operated under these conditions was found to be undergoing self-excited vibration. Stress and structural dynamic finite element analyses (FEA) were performed to identify the structural mode for the valve oscillations. A three-dimensional transient computational fluid dynamics (CFD) analysis of the valve revealed an unsteady fluid dynamics phenomenon in the pressure balancing arrangement that served as a forcing function for this vibration. Valve modifications were implemented as a result of these analyses. The improved valve has performed successfully, and the design modifications have been incorporated in other production valves.
Numerical Simulations of the Aerodynamics of Circulation Control Wind Turbines Under Yawed Flow Conditions
Authors: Sankar Lakshmi N. , Tongchitpakdee Chanin , Zaki Mina , Englar Robert
Published: January 2011

The aerodynamic performance of a wind turbine rotor equipped with circulation control technology is investigated using a three-dimensional unsteady viscous flow analysis. The National Renewable Energy Laboratory (NREL) Phase VI horizontal axis wind turbine (HAWT) is chosen as the baseline configuration. Experimental data for the baseline case is used to validate the flow solver, prior to its use in exploring these concepts. Steady and pulsed Coanda jet calculations have been performed for axial and yawed flows at several wind conditions. Results presented include radial distribution of the normal and tangential forces at selected radial locations, shaft torque, and root flap bending moments. At low wind speeds where the flow is fully attached, it is found that steady and pulsed Coanda jets at the trailing edge are both effective at increasing circulation resulting in an increase of lift and the chordwise thrust force. This leads to an increased amount of net power compared to the baseline configuration for moderate blowing coefficients. Preliminary calculations are also shown to demonstrate how Coanda jets may be used as jet spoilers to alleviate structural loads under extreme wind conditions.
FT8-3 Advanced Low Emissions Combustor Design
Authors: Reddy Urmila C. , Blanchard Christine E. , Schlein Barry C.
Published: January 2011

Pratt & Whitney has developed a novel water-injected Industrial Gas Turbine (IGT) combustor liner design that has demonstrated significant reduction in CO emissions when compared to typical film cooled combustor designs. The CO reduction demonstrated in a prototype test shows that the CO quenching due to cooler film temperatures near the liner wall is a significant source of CO emissions in a conventional water-injected combustor operating on natural gas fuel. This finding paved the way for a combustor design that reduces CO emissions while still maintaining low levels of NOx emissions. This design also has potential for lower NOx since the low CO emissions characteristic enables increased water-injection. This paper presents the emissions characteristics measured on prototype hardware and the design of the engine hardware for future validation. Significant reduction in gaseous emissions was demonstrated with the testing of a prototype at the United Technologies Research Center in East Hartford, CT. This reduction in emissions compared to the baseline film-cooled design for a given operating condition has many benefits to the customer, including reduced need for exhaust catalyst cleanup and extended operating times while still meeting site permits specified in CO tons per year. Other benefits may include the ability to guarantee lower NOx emissions through increased water injection for the current CO emissions output.
Experimental Study of Surface Roughness Effects on a Turbine Airfoil in a Linear Cascade: Part II—Aerodynamic Losses
Authors: Lorenz M. , Schulz A. , Bauer H.-J.
Published: January 2011

The present experimental study is part of a comprehensive analysis accounting for heat transfer and aerodynamic losses on a highly loaded low pressure turbine blade with varying surface roughness. Whereas part I focuses on heat transfer measurements at airfoil midspan with different deterministic surface roughnesses, part II investigates surface roughness effects on aerodynamic losses of the same airfoil. A set of different arrays of deterministic roughness (the same as used in part I) is investigated in these experiments. The height and eccentricity of the roughness elements is varied, showing the combined influence of roughness height and anisotropy on the losses produced in the boundary layers. It is shown that the boundary layer loss is dominated by the suction side. Therefore, the investigations focus on measurements of the suction side boundary layer thickness at midspan directly upstream of the trailing edge. The experiments are conducted at several free-stream turbulence levels (Tu1 = 1.4% to 10.1%) and different Reynolds numbers. The measurements reveal that suction side boundary layer thickness is increased by up to 190% if surface roughness shifts the transition onset upstream. However, in some cases, at low Reynolds numbers and free-stream turbulence, surface roughness suppresses boundary layer separation and decreases the trailing edge boundary layer thickness by up to 30%.
Identification and Prediction of Force Coefficients in a Five-Pad and Four-Pad Tilting Pad Bearing for Load-on-Pad and Load-Between-Pad Configurations
Authors: Delgado Adolfo , Vannini Giuseppe , Ertas Bugra , Drexel Michael , Naldi Lorenzo
Published: January 2011

This paper presents the identification of the rotordynamic force coefficients for a direct lubrication five-pad and four-pad tilting pad bearing. The bearing is 110 mm in diameter with an L/D of 0.4. The experiments include load-on-pad (LOP) and load-between-pad (LBP) configurations, with a 0.5 and 0.6 pivot offset, for rotor speeds ranging from 7500 rpm to 15000 rpm. The bearing force coefficients are identified from multiple frequency excitations (20 to 300 Hz) exerted on the bearing housing by a pair of hydraulic shakers, and are presented as a function of the excitation frequency, rotor speed, for a 300 kPa unit load. The experimental results also include temperatures at the trailing edge of three pads. The direct force coefficients, identified from curve-fits of the complex dynamic stiffness, are frequency independent if considering an added mass term much smaller than the test device modal mass. The force coefficients from the four-pad bearing load-between-pad configuration show similar coefficients in the loaded and orthogonal direction. On the other hand, as expected, the five-pad bearing load-on-pad shows larger coefficients (∼25%) in the loaded direction. The maximum pad temperature recorded for the 0.5 pivot offset configurations are up to 20° C higher than those associated to the 0.6 offset configuration. Results from a predictive code are within 50% of the experimental results for the direct stiffness coefficients and within 30% for the direct damping coefficients.
Recent Advances in High Temperature Ceramic Regenerators for Externally Fired Gas Turbines: Theoretical and Experimental Results
Authors: Acun˜as Alfonso , Huete Jon , Amallobieta Ibon
Published: January 2011

Recent development in ceramic regenerators opens a vast range of new applications. Externally fired gas turbines have been limited by the efficiency of the process of transferring the heat to the turbine. So far, both the gasification process of the indirect routes and the heat exchanger efficiency of the direct routes have restricted the efficiency of the whole system to unacceptable values. A new concept of ceramic regenerator has been designed and tested, showing more than 95% efficiency at very high temperatures with low leakage and minimum pressure drop. The design, theoretical and experimental results are explained in the paper. The possibility of using solid biomass in small turbines and microturbines may turn out to be an attractive solution for agricultural and forestry residue revalorization.
An Innovative Approach to Emission Reductions and Heat Recovery: Comply Units
Authors: Littleford Wayne , Jolly Sanjeev
Published: January 2011

Emissions from power plants are increasingly becoming a global concern that is forcing countries to set tougher and tougher standards for meeting regulations. Compliance with these requirements comes at a cost — resources required to install and maintain the necessary equipment that is often exacerbated by a reduction in efficiency. These harmful emissions that are products of combustion (POC) are typically classified as NOx, SO2, CO2, UHC (unburned hydrocarbons) and Particulate and sometimes heavy metals like mercury, arsenic, etc. Currently there are specific methods available for reducing each of these emissions individually but there is no single system in use that can remove all these unwanted emissions simultaneously — at least not until now. With the proposed system, all these emissions can almost be entirely eliminated from the flue gases concurrently. The process essentially consists of ozone injection for NOx conversion, fogging spray mixed with hydrogen peroxide solution for SO2 conversion and condensing these along with other pollutants over coils to remove all pollutants from exhaust gas stream. As a result, the NOx and SO2 end up as nitric and sulfuric acid in the wastewater stream collected at the bottom of the unit. In addition, UHC and particulate are also removed during the condensation process along with some carbonic acid resulting from dissolved CO2. This waste water can then be treated accordingly and recycled. Another major advantage of this process is the heat absorbed by circulating water in the condensing coils that can be effectively utilized to improve plant performance and overall thermal efficiencies.
Large Eddy Simulation of an Oscillating Cylinder Close to a Wall
Authors: Huang Zhiyong , Larsen Carl M.
Published: January 2011

The long term motivation for this work has been to find hydrodynamic coefficients needed to predict vortex induced vibrations (VIV) for free spanning pipelines. For such cases one must expect that the proximity of the seafloor will influence hydrodynamic forces, which means that coefficients found from experiments where wall effects have been eliminated are not necessarily valid. The paper presents results from a three dimensional large eddy simulation of flow over a forced oscillating cylinder close to a plane wall. Hydrodynamic forces are computed at a frequency of 0.425 Hz and Reynolds number of 24 000, and the motion amplitude is half diameter of the cylinder. The minimum gap distance between the cylinder and the wall has been varied from 0.2 to 2.5 D, where D is the diameter of the cylinder. The results show that the hydrodynamic forces on the cylinder are significantly influenced by the gap ratio. The excitation force shows a slight increase when the average gap is decreased from 2.5 to 0.5 D, but further reduction changes the trend so that the coefficient becomes negative for a minimum gap of 0.25 D. Hence, the dynamic lift force will change from being an excitation force to a damping force at this distance for the given flow and motion parameters. A sharp drop in drag force is observed at gap ratio less than 0.3 as the cylinder is still out of the boundary layer on the plane wall. The average lift force is also seen to be influenced by the gap. At a large distance from the wall, the average lift is obviously zero, but an average force that will push the cylinder away from the wall is found for gaps smaller than 0.3 D. Results are also reported for the cross-flow added mass as a function of varying gap. In addition to these results, spectra and time histories for the hydrodynamic forces are presented, and also coefficients for higher order force components. Vortex shedding is observed at the minimum gap ratio of 0.2. Some references to experimental work are made, but verification of these results cannot be obtained without new experiments.
Effect of Bracing Configurations on the Lateral Behavior of Jacket Type Offshore Platforms, Considering Pile-Soil-Structure Interaction
Authors: Agheshlui Hossein
Published: January 2011

The configuration of braces has a considerable influence in the lateral behavior of pile supported steel jacket type offshore platforms. In this paper nonlinear static push over analyses and hysteresis curves are used to investigate lateral behavior of a jacket type offshore platform considering different configurations for vertical bracings of the jacket. One sample platform, constructed in Persian Gulf, is precisely modeled using the finite element program Opensees. Since the lateral response of offshore platforms is completely dependent on their foundations’ behavior, an accurate model is used for modeling the foundation of this structure. Soil-pile-structure interaction is considered using Beam on Nonlinear Winkler Foundation model (BNWF). Lateral and vertical soil stiffness and end bearing were considered using p-y, t-z and q-z nonlinear models, respectively. Moreover, the buckling behavior of the braces is considered in the simulation of the platform to consider the behavior of the platform after buckling, and redistribution of the shear forces in the structure due to the bracings failures. The structure was modeled using nonlinear beam-column elements which have the ability to consider the spread of plasticity along the elements. The sections used for elements are fiber sections which are suitable for considering composite section of pile-grout-leg. Displacement controlled nonlinear static pushover analysis and cyclic loading analysis are conducted applying lateral load which its pattern is according to the predominant vibration modes. Three different configurations for lateral bracings are assumed and the behavior of the platform using these three bracing forms is investigated. The first configuration considered is the original bracing of the platform which is a combination of X and chevron braces; the second one is a case in that X braces were used in all of the bays of the jacket; and in the third form chevron braces are used for all of the bays. According to the push over and hysteresis curves, it is concluded that in the jacket modeled using X vertical braces, lateral load capacity, ductility, residual strength ratio and the absorbed energy in cyclic loadings are considerably more than the jackets which were modeled using a combination of chevron and X braces or just chevron braces. In comparison with the jacket modeled using only chevron braces, the jacket constructed using a combination of X and chevron bracings presents better lateral behavior and capacity.
Force Variations on Heave Compensating System for Ultra-Deepwater Drilling Risers
Authors: Sten Ronny , Rygaard Hansen Michael , Larsen Carl Martin , Sævik Svein
Published: January 2011

This paper discusses modeling aspects related to dynamic analysis of deep water drilling risers. These risers must have a heave compensator that maintains a near constant tension in the riser independent on platform motions. Traditional riser analysis will apply constant top tension or a simple parametric model that may give approximate tension variation. The present paper describes an alternative analysis procedure that consists of the following step: • Global riser analysis including calculation of dynamic stroke of the heave compensator from platform motions and riser dynamics. A “pipe-in-pipe” approach is used to represent the hydraulic cylinders. • Calculation of dynamic tension variation from an analysis of the hydraulic tensioner system. The dynamic stroke found from the first analysis is applied as known piston motions in this analysis. • Identification of parameters in a simple model for dynamic tension variation from the results from the second analysis. • Use of the simple model in a second global riser analysis. The difference between the two riser analyses can hence be found, which represents the error one must expect from a traditional riser analysis with constant riser tension. A case study with realistic data is reported. The conclusion is that the constant tension model is valid for small heave motions only, while the parametric tensioner model can give almost correct results for tension variation. However, the parametric model must be tuned for each case. Hence, an integrated model that accounts for riser dynamics and pressure variation in the tensioner system should preferably be developed.
Cost Efficient System Design for a North Sea High Pressure Water Injection Flexible Pipeline Development
Authors: Andreasen Steffen S. , Grytten Trond , Koldal O̸yvind
Published: January 2011

Due to the need of costly reel vessels and sophisticated long lead materials for rigid pipeline water injection systems, flexible flowlines with duplex inner carcass have lately been more used as they can be installed with less costly construction vessels and provide a cost effective, a competitive lead time and a compliant material system. The North Sea flexible Subsea water injection development consisted of installing a Subsea water injection template with a first time Subsea tieback to a very congested North Sea field. The conceptual design of the fast track field development was awarded in July 2008 and final tied-in system test was successfully performed in November 2009. This paper will present a cost efficient system design that reduced the project material, fabrication, installation and intervention costs. The paper will present how added value was given to the project by implementing a state of the art 3D in-place FE model in an optimized system design removing one expansion spool, significantly reducing amount of rock dump intervention and preventing modification to template design.
In-Place FE Modeling of Unbonded Flexible Pipelines Capturing Pressure Stiffening and Decoupled Axial/Nonlinear Bending Stiffness
Authors: Hanken Edvin , Hollingsworth Evelyn R. , Fagerland Lars S.
Published: January 2011

For fast track pipeline projects the need for costly installation vessels and sophisticated materials for rigid pipeline water injection systems, have made flexible pipelines a competitive alternative. They can be installed with less costly construction vessels, provide a competitive lead time and a corrosion resistant compliant material. Flexible pipelines have relative high axial stiffness and low non-linear bending stiffness which is a challenge to model correctly with FE for in-place analyses of pipelines. Whilst some FE programs can model the non-linear bending behaviour of a flexible pipeline at a given pressure, current FE tools do not include the effect of increased bending resistance as the system is pressurized. Therefore, a 3D FE model in ANSYS was developed to simulate the decoupled axial and nonlinear bending behaviour of a flexible, including the bend stiffening effect for increasing pressure. A description of the model is given in this paper. It will be demonstrated how the FE model can be used to simulate the 3D nonlinear catenary behaviour of an high pressure flexible pipeline tied into a manifold during pressurization. Due to high manifold hub loads during pressurization it is essential that such a model is capable of capturing all effects during pressurization to achieve an acceptable confidence level of the system integrity. It is also described how the FE model is used for upheaval buckling design, capturing non-linearities and load history effects that can reduce the conservatism in the design.
Particular Aspects Regarding the Lateral Buckling Analysis of Flowlines
Authors: Walker Alastair C. , Chee Kin Y. , Cooper Phil
Published: January 2011

The paper is concerned with the analysis of the effects of lateral buckling along a flowline. The analysis is considered to be relevant to the early stages of design, i.e. typically pre-FEED, and specifically addresses the significant effect that material strength properties has on the calculation of maximum strains along a flowline that could develop lateral deformations due to high temperature operating conditions. The analysis approach used here to generate the results presented in the paper is based on the assumed distances between sites of lateral buckling. This is generally known as the virtual anchor spacing (VAS). It is also assumed that the assessment of the acceptability of the deformations and the calculated maximum strain levels, with regard to the safety of the operating flowline, may validly be based on the displacement controlled methodology contained in guidance prepared by DNV. It is shown that the interaction between the material properties and the levels of lateral friction results in an ambiguity with regard to the relevant displacement patterns that can occur along the flowline at the site of a lateral buckle. It is concluded that the calculation models used even during early stages of design, should be based on the relevant pipe material properties and that compromise with these properties, perhaps to improve the stability of the numerical modelling, should be avoided. Another conclusion from the results relates to the assumption of symmetry boundary conditions in finite element and other models since this assumption could possibly underestimate the calculated levels of the maximum strain at the lateral buckle and thus undermine the use of the displacement controlled approach to safety assessment.
Retaining the Sustainability of Oil and Gas Operations: Qualifying the Best Available Techniques
Authors: Samarakoon S. M. S. M. K. , Gudmestad O. T.
Published: January 2011

By nature, oil and gas operations are sensitive to Health, Safety and Environment (HSE) requirements. Within the Norwegian Continental Self (NCS), it is mandatory to implement the Best Available Techniques (BAT) guidelines as required in the European Union’s Integrated Pollution Prevention and Control (IPPC) directive. The directive provides guidelines for selecting BAT in industrial activities while protecting the environment as a whole. One of the major challenges for an oil and gas operator is to satisfy the guidelines while confirming fitness for purpose with respect to the different technologies applied. Hence, the concept of technique qualification is paramount to reveal opportunities to improve system design, to minimize schedule risk and to reduce cost risks during operations by reducing uncertainties and increasing reliability. In this paper, we are concerned with the process of selecting a technique for supplying power from shore to an offshore unit. This paper discusses how we can give priorities to HSE concerns, while also satisfying financial objectives, in the context of implementing the BAT guidelines. The analysis aims to qualify the technique as a whole, considering the capability of satisfying the underlying objective of controlling environmental pollution.