bluuebunny/crossref_metadata_2025 huggingface dataset:
The Development of Aerodynamic Performance Measurements in a Transient Test Facility
Authors: Atkins Nicholas R. , Miller Robert J. , Ainsworth Roger W.
Published: November 2008

Transient test facilities offer the potential for the simultaneous study of turbine aerodynamic performance, unsteady flow phenomena and the heat transfer characteristics of a turbine stage. This paper describes the development of aerodynamic performance measurement techniques in the Oxford Rotor Facility (ORF). The solutions to the technological issues involved with transient testing presented in this paper are expected to achieve levels of precision uncertainty comparable with traditional steady flow test rigs. The theoretical background to the measurement of aerodynamic performance is presented together with a comprehensive pre-test uncertainty analysis. The instrumentation scheme for the measurement of stage mass flow rate is discussed in detail, the measurements of shaft power, total inlet enthalpy, and stage pressure ratio are also outlined. The current working section features a 62% scale, 1-1/2 stage, high-pressure shroudless transonic turbine. The required inlet flow conditions are provided by an Isentropic Light Piston Tunnel (ILPT) with a quasi-steady state run time of approximately 70ms. The testing is conducted at engine representative specific speed, pressure ratio, gas-to-wall temperature ratio, Mach number and Reynolds number.
Contact Dynamic Response With Misalignment in a Flexible Rotor/Magnetic Bearing System
Authors: Keogh Patrick S. , Cole Matthew O. T.
Published: November 2008

This paper investigates the vibration characteristics of rotor displacement signals in a magnetic bearing system under conditions when rotor contact with auxiliary bearings is possible. Since these signals may be used for feedback control, it is necessary to determine how they may affect the ability of the controller to regain rotor levitation. An experimental system is used to demonstrate the sensitivity of the rotor non-linear dynamic behavior to unbalance, which is sufficient to cause contact during rotor run up through rigid body and flexural mode critical speeds. Complex rotor dynamics may involve contact with more than one auxiliary bearing or bush. Application of appropriate rotating forces to the rotor through a magnetic bearing is also shown to induce similar contact dynamics. Thus an alternative procedure for assessing the non-linear rotor dynamic behavior is established with the potential for identification of appropriate control forces. The contact dynamics are also considered in the presence of auxiliary bearing misalignment. Misalignment may arise through physical translation of a housing or through steady state offset errors in sensor measurements. A misalignment of 50% of the nominal radial clearance is applied at an auxiliary bearing. Various contact modes are evident as the rotor is run up in speed. During run down different contact dynamics may be encountered and the level of such hysteresis is assessed.
Flame Transfer Function for Swirled LPP Combustion From Experiments and CFD
Authors: Armitage Carol A. , Riley Alex J. , Cant R. Stewart , Dowling Ann P. , Stow Simon R.
Published: November 2008

Combustion oscillations that arise in gas turbines can lead to plant damage. One method used to predict these oscillations is to analyse the acoustics using a simple linear model. This model requires a transfer function to describe the response of the heat release to flow perturbations. A transfer function has been obtained for a swirled premixed combustion system using experiments under atmospheric conditions and CFD. These results have been compared with analytical models. The experimental and computational transfer functions both indicate a low frequency zero. A time-delay spread model gives a good representation of the computational transfer function. The experimental transfer function is described well by a model that combines a time-delay spread with a constant gain.
The Effects of a Trip Wire and Unsteadiness on a High Speed Highly Loaded Low-Pressure Turbine Blade
Authors: Vera M. , Hodson H. P. , Vazquez R.
Published: November 2008

This paper presents the effect of a single spanwise 2D wire upon the downstream position of boundary layer transition under steady and unsteady inflow conditions. The study is carried out on a high turning, high-speed, low pressure turbine (LPT) profile designed to take account of the unsteady flow conditions. The experiments were carried out in a transonic cascade wind tunnel to which a rotating bar system had been added. The range of Reynolds and Mach numbers studied includes realistic LPT engine conditions and extends up to the transonic regime. Losses are measured to quantify the influence of the roughness with and without wake passing. Time resolved measurements such as hot wire boundary layer surveys and surface unsteady pressure are used to explain the state of the boundary layer. The results suggest that the effect of roughness on boundary layer transition is a stability governed phenomena, even at high Mach numbers. The combination of the effect of the roughness elements with the inviscid Kelvin-Helmholtz instability responsible for the rolling up of the separated shear layer (Stieger [1]) is also examined. Wake traverses using pneumatic probes downstream of the cascade reveal that the use of roughness elements reduces the profile losses up to exit Mach numbers of 0.8. This occurs with both steady and unsteady inflow conditions.
Numerical and Experimental Investigations Into the Aerodynamic Performance of a Supersonic Turbine Blade Profile
Authors: Parvizinia Manuchehr , Berlich Carsten , Truckenmu¨ller Frank , Stu¨er Heinrich
Published: November 2008

This paper presents results of numerical and experimental investigations in order to validate the aerodynamic performance of a supersonic tip section profile which will be used in the next generation low pressure steam turbines. The tip section profile design was derived using the “design-by-analysis” method with respect to the supersonic inlet and outlet conditions. The measurements were taken in the high speed cascade wind tunnel of Siemens Power Generation in Mu¨lheim, Germany. The outlet Mach number ranged from Ma2 = 1.2 to Ma2 = 1.8, where one subsonic and one supersonic inlet Mach number were set. The Reynolds number was Re2 = 4.5 E05 and superheated steam was used as a working medium. As a very important geometrical parameter, the pitch-to-chord ratio was varied for different aerodynamic parameters. The experiments include detailed measurements of the blade surface pressure distribution, flow visualization measurements using the Schlieren technique, wake flow measurements employing pneumatic probes as well as side wall pressure measurements. The computational investigations were carried out using an inviscid Euler method coupled with a fast viscous integral boundary-layer method. This paper is organized into two main areas including firstly, a description of the experimental set up, secondly, the discussion and comparison on the results of experimental and numerical investigations.
New Optimization Criteria for the Design of Three-Dimensional Bladings Applied to Compound Lean Nozzles of an Axial Turbine
Authors: Wingelhofer Franz , Haselbacher Hermann
Published: November 2008

The performance of axial turbines can be improved by the application of three-dimensionally shaped bladings. The performance improvement by three-dimensionally shaped bladings is perceptible only within a stage, leading to a time-accurate three-dimensional optimization. The paper describes two objective functions that, if applied to an isolated turbine blade row, may help to reduce the range of feasible geometries. The quality of the objective functions is tested in a parametric study, in which the stator row geometry is parameterized by only one parameter. The stage efficiency, obtained by evaluation of the time-accurate flows through turbine stages with different stator rows, is used as criterion. An optimization of compound lean nozzles parameterized by two parameters is performed with the more accurate objective function resulting in high performance compound lean nozzles.
Large Eddy Simulation of the Developing Region of a Stationary Ribbed Internal Turbine Blade Cooling Channel
Authors: Sewall Evan A. , Tafti Danesh K.
Published: November 2008

This study reports on a Large Eddy Simulation (LES) of the entrance section of a gas turbine blade internal cooling passage. The channel is fitted with in-line turbulators orthogonal to the flow, and the domain studied covers the first six ribs of the channel. The rib height-to-hydraulic diameter ratio (e/Dh) is 0.1, and the rib pitch-to-rib height ratio (P/e) is 10. A constant temperature boundary condition is imposed on the walls and the ribs, and the flow Reynolds number is 20,000. Results indicate that the mean flow is essentially fully developed by the fifth rib. Turbulent kinetic energy near the ribbed wall approaches fully developed values very quickly by the third or fourth ribs. However, turbulent intensities at the center of the duct are not fully developed by the sixth rib. As a consequence, heat transfer augmentation on the ribbed walls reaches a fully developed state quickly after the third rib, whereas, the smooth wall heat transfer augmentation shows a slight but steady increasing trend toward the fully developed value up to the sixth rib. Both augmentation ratios are to within 10% of their fully developed values after the third rib.
Large Eddy Simulation of the Developing Region of a Rotating Ribbed Internal Turbine Blade Cooling Channel
Authors: Sewall Evan A. , Tafti Danesh K.
Published: November 2008

This study focuses on a Large Eddy Simulation (LES) of the entrance region of a gas turbine blade internal cooling duct. The square channel is fitted with in-line turbulators orthogonal to the flow. The rib height-to-hydraulic diameter ratio (e/Dh) is 0.1, and the rib pitch-to-rib height ratio (P/e) is 10. A constant temperature boundary condition is imposed on the walls and the ribs; the flow Reynolds number is 20,000; and the rotation number is 0.3. Results from these calculations indicate that flow development length is much longer than in a stationary channel because of the large effect of rotational Coriolis forces on mean flow and heat transfer, which only begin to exert a substantial influence after 3 to 4 rib pitches from the entrance to the duct. During the development length, heat transfer augmentation increases on the trailing and smooth walls, while it decreases on the leading wall. At the ninth rib, the mean augmentation ratios are to within −12% and −14% of their fully developed values on the trailing and smooth walls, respectively. At both walls there is a gradual increasing trend which suggests that fully developed conditions have not been achieved by the heat transfer coefficient. On the leading wall, however, all results indicate that the heat transfer coefficient has achieved its fully developed augmentation ratio. The calculation clearly shows that the direct effect of Coriolis forces on turbulent structure and intensity have a much stronger effect on heat transfer augmentation than the effect of secondary flows.
Transient Analysis of Solid Oxide Fuel Cell Hybrids: Part A — Fuel Cell Models
Authors: Magistri Loredana , Trasino Francesco , Costamagna Paola
Published: November 2008

The main goal of this work is the transient analysis of Hybrid Systems based on Solid Oxide Fuel Cells. The work is divided into three parts: in the first the fuel cell transient models are presented and discussed, while in the following papers the anodic recirculation system (Part B) and the entire hybrid transient performance (Part C) are investigated. In this paper the transient behavior of a Solid Oxide Fuel Cell is analyzed through the use of two different approaches: macroscopic and detailed SOFC models. Both models are presented in this paper and their simulation results are compared to each other and to available experimental data. As a first step the transient response of the fuel cell was studied using very detailed model in order to completely describe this phenomenon and to highlight the critical aspects. Subsequently some modifications were made to this model to create an apt simulation tool (Macroscopic Fuel Cell Model) for the whole plant analysis. The reliability of this model was verified comparing several transient responses to the results obtained with the detailed model. In the following papers (Parts B and C) the integration of the macroscopic fuel cell model into the whole plant model will be described and the transient study of the hybrid plant will be presented.
Transient Analysis of Solid Oxide Fuel Cell Hybrids: Part C — Whole-Cycle Model
Authors: Magistri Loredana , Ferrari Mario L. , Traverso Alberto , Costamagna Paola , Massardo Aristide F.
Published: November 2008

A Solid Oxide Fuel Cell-Hybrid System is mainly composed of three parts: the stack, the anodic recirculation system with fuel feeding, and the cathodic side (air side) where turbomachinery and heat exchangers are installed. In Part A of this work the transient models of the fuel cell are described, while in Part B the anodic side is investigated. Many previous studies have been carried out on the cathodic side at the Thermochemical Power Group facility to simulate the transient behavior of the main components such as compressors, expanders and heat exchangers. In this paper attention is focused on the integration of the transient models of the hybrid system components. Following the on and off-design analysis of the SOFC-HS the transient response of the system from an electrochemical, fluid dynamic and thermal point of view has been studied at several operating conditions.
Axial Compressor Response to Inlet Flow Distortions by a CFD Analysis
Authors: Charalambous Nikolaos , Ghisu Tiziano , Iurisci Giuseppe , Pachidis Vassilios , Pilidis Pericles
Published: November 2008

The usual approach to compressor design considers uniform inlet flow characteristics. Especially in aircraft applications, the inlet flow is quite often non uniform, and this can result in severe performance degradation. The magnitude of this phenomenon is amplified in military engines due to the complexity of inlet duct configurations and the extreme flight conditions. CFD simulation is an innovative and powerful tool for studying inlet distortions and can bring this inside the very early phases of the design process. This project attempts to study the effects of inlet flow distortions in an axial flow compressor trying to minimize the use computer resources and computational time. The first stage of a low bypass ratio compressor has been analyzed and its clean and distorted performance compared outlining the principal changes due to uneven flow distribution: drop in mass flow, increase in pressure and temperature ratios, decrease in surge margin. Three different studies have then been conducted to better understand the effects of the level, the type and the frequency of the distortion.
Development of an Improved High Cycle Fatigue Criterion
Authors: Scott-Emuakpor Onome , Shen M.-H. Herman , Cross Charles , Calcaterra Jeffrey , George Tommy
Published: November 2008

An integrated computational-experimental approach for prediction of total fatigue life applied to uniaxial stress state is developed. The approach consists of the following elements: (1) development of a vibration based fatigue testing procedure to achieve low cost bending fatigue experiments and (2) development of a life prediction and estimation implementation scheme for calculating effective fatigue cycles. A series of fully reversed bending fatigue tests were carried out using a vibration-based testing procedure to investigate the effects of bending stress on fatigue limit. The results indicate that the fatigue limit for 6061-T6 aluminum is approximately 20% higher than the respective limit in fully reversed tension-compression (axial). To validate the experimental observations and further evaluate the possibility of prediction of fatigue life, an improved high cycle fatigue criterion has been developed, which allows one to systematically determine the fatigue life based on the amount of energy loss per fatigue cycle. A comparison between the prediction and the experimental results was conducted and shows that the criterion is capable of providing accurate fatigue life prediction.
Advancements in the Structural Stiffness and Damping of a Large Compliant Foil Journal Bearing: An Experimental Study
Authors: Salehi Mohsen , Heshmat Hooshang , Walton James F.
Published: November 2008

This paper presents the results of an experimental investigation into the dynamic structural stiffness and damping characteristics of a 21.6 cm (8.5inch) diameter compliant surface foil journal bearing. The goal of this development was to achieve high levels of damping without the use of oil, as is used in squeeze film dampers, while maintaining a nearly constant dynamic stiffness over a range of frequencies and amplitudes of motion. In the experimental work described herein, a full compliant foil bearing was designed, fabricated and tested. The test facility included a non-rotating journal located inside the bearing. The journal was connected to an electrodynamic shaker so that dynamic forces simulating expected operating conditions could be applied to the structurally compliant bump foil elements. Excitation test frequencies to a maximum of 400 Hz at amplitudes of motion between 25.4μm to 102μm were applied to the damper assembly. During testing, both compressive preload and unidirectional static loads of up to 1335N and 445N, respectively, were applied to the damper assembly. The experimental data from these tests were analyzed using both a single degree of freedom model and an energy method. These methods of data analysis are reviewed here and results are compared. Excellent agreement in results obtained from the two methods was achieved. Equivalent viscous damping coefficients as high as 1050 N.s/cm (600 lbf.s/in) were obtained at low frequencies. Dynamic stiffness was shown to be fairly constant with frequency.
Abradable Seals for Gas Turbines and Other Rotary Equipment
Authors: Hajmrle Karel , Fiala Petr , Chilkowich Anthony P. , Shiembob Lawrence T.
Published: November 2008

Abradable seals are typically used in compressors of aircraft and industrial gas turbines to decrease clearance between the stator casing and rotor blade tips, and hence, to increase compressor efficiency and decrease fuel consumption. The abradable seal concept originally developed for aircraft gas turbine applications is presently applied to other types of rotary equipment such as steam turbines and turbochargers. Among the most important variables influencing the choice of abradables for a particular section of a gas turbine are: application temperature, material of the rubbing element (titanium, nickel or iron alloy), the rubbing element geometry (blade, knife edge), seal durability (aircraft engines are refurbished more often than land based turbines), and of course the installed cost. In order to satisfy all the seal requirements, the chemical composition and structure of an abradable seal have to be carefully designed and controlled. The main challenge is to optimize the contradictory requirements such as durability and abradability. The process for choosing the best material starts with identifying the main variables and choosing the most suitable systems to fulfill all the requirements. This choice must be confirmed by a series of laboratory tests that simulate the actual application. The tests, test equipment and test results on a new seal system will be described to demonstrate the influence of all important parameters on seal performance. A new generation of abradable seals that, for example, can rub against titanium alloy blades at any temperature in the titanium alloy application range, will be presented. Emphasis will be put on the seal performance in “aged” conditions, i.e. after exposure to air at high temperatures for prolonged periods of time. Such results are necessary to evaluate the seal performance after extended service in the gas turbine when rubbing can still occur.
Role of Tip-Leakage Vortices and Passage Shock in Stall Inception in a Swept Transonic Compressor Rotor
Authors: Hah Chunill , Rabe Douglas C. , Wadia Aspi R.
Published: November 2008

The current paper reports on investigations aimed at advancing the understanding of the flow field near the casing of a forward-swept transonic compressor rotor. The role of tip clearance flow and its interaction with the passage shock on stall inception are analyzed in detail. Steady and unsteady three-dimensional viscous flow calculations are applied to obtain flow fields at various operating conditions. The numerical results are first compared with available measured data. Then, the numerically obtained flow fields are interrogated to identify the roles of flow interactions between the tip clearance flow, the passage shock, and the blade/endwall boundary layers. In addition to the flow field with nominal tip clearance, two more flow fields are analyzed in order to identify the mechanisms of blockage generation: one with zero tip clearance, and one with nominal tip clearance on the forward portion of the blade and zero clearance on the aft portion. The current study shows that the tip clearance vortex does not break down, even when the rotor operates in a stalled condition. Interaction between the shock and the suction surface boundary layer causes the shock, and therefore the tip clearance vortex, to oscillate. However, for the currently investigated transonic compressor rotor, so-called breakdown of the tip clearance vortex does not occur during stall inception. The tip clearance vortex originates near the leading edge tip, but moves downward in the spanwise direction inside the blade passage. A low momentum region develops above the tip clearance vortex from flow originating from the casing boundary layer. The low momentum area builds up immediately downstream of the passage shock and above the core vortex. This area migrates toward the pressure side of the blade passage as the flow rate is decreased. The low momentum area prevents incoming flow from passing through the pressure side of the passage and initiates stall inception. It is well known that inviscid effects dominate tip clearance flow. However, complex viscous flow structures develop inside the casing boundary layer at operating conditions near stall.
U.S. Navy Refinement of Electronic Fuel Controls and Air Assist Fuel Nozzles to Meet Upgraded Power Requirements for the 501-K34 Marine Gas Turbines
Authors: Hoffman Matthew G. , Connery Brian J. , Kozuhowski Helen J. , Pin˜eiro Iva´n
Published: November 2008

The U.S. Navy operates Rolls Royce 501-K34 powered Gas Turbine Generators (GTGs) on DDG 51 Class destroyers. The design of these GTGs has evolved significantly over the course of the shipbuilding program. One significant change is that GTGs on DDG 51 to 90 are rated to provide 2,500 KW while those on DDG 91 and follow are rated at 3,000 KW. The 3,000 KW rating has been accepted by the Navy and demonstrated on several new GTGs during qualification testing. However, test results indicate that one area where very little performance margin exists is full load transient response. This paper discusses extensive transient testing performed on a DDG 51 Class GTG at the U.S. Navy’s Land Based Engineering Site (LBES) in Philadelphia, Pennsylvania. It details control system modifications that optimize performance and explores changes to GTG transient response that result from operation with a new type of 501-K34 fuel nozzle.
Operation of a Mesoscopic Gas Turbine Simulator at Speeds in Excess of 700,000 rpm on Foil Bearings
Authors: Salehi Mohsen , Heshmat Hooshang , Walton James F. , Tomaszewski Michael
Published: November 2008

A small mesoscopic gas turbine engine (MGTE) simulator was tested at speeds over 700,000 rpm. The MGTE was operated with specially designed miniature compliant foil journal and thrust air bearings. The operation of the simulator rotor and foil bearing system is a precursor to development of turbine powered micro aerial vehicles and mesoscopic power generators. The foil bearings use a new fabrication technology in which each bearing is split. This feature permits the use of these bearings in highly advanced engines where single piece ceramic rotors may be required. The simulator weighed 56 grams (including the 9 gram rotor) and included two non-aerodynamic wheels to simulate the compressor and turbine wheels. Each compliant foil journal bearing had a diameter of 6 mm and was located equidistant from each end of the rotor. Experimental work included operation of the simulator at speeds above 700,000 rpm and at several different orientations including having the spin axis vertical. Results of the rotor bearing system dynamics are presented along with experimentally measured natural frequencies at many operating speeds. Good correlation between measurement and analysis is observed indicating the scalability of the analysis tools and hardware used. The rotor was very stable and well controlled throughout all testing conducted. Based on this successful testing it is expected that the goal of operating the rotor at speeds exceeding 1 million rpm will be achieved.
Modeling and Control of Combustion Dynamics in Industrial Gas Turbines
Authors: McManus Keith , Han Fei , Dunstan Wayne , Barbu Corneliu , Shah Minesh
Published: November 2008

The thermoacoustic response of an industrial-scale gas turbine combustor to fuel flow perturbations is examined. Experimental measurements in a laboratory combustor along with numerical modeling results are used to identify the dynamic behavior of the combustor over a variety of operating conditions. A fast-response actuator was coupled to the fuel system to apply continuous sinusoidal perturbations to the total fuel mass flow rate. The effects of these perturbations on the combustor pressure oscillation characteristics as well as overall operability of the system are described. The results of this work suggest that persistent excitation of the fuel system may present a viable means of controlling combustion dynamics in industrial gas turbine and, in turn, enhance their performance.
Combustion Oscillation Monitoring Using Flame Ionization in a Turbulent Premixed Combustor
Authors: Chorpening B. T. , Thornton J. D. , Huckaby E. D. , Benson K. J.
Published: November 2008

To achieve very low NOx emission levels, lean-premixed gas turbine combustors have been commercially implemented which operate near the fuel-lean flame extinction limit. Near the lean limit, however, flashback, lean blowoff, and combustion dynamics have appeared as problems during operation. To help address these operational problems, a combustion control and diagnostics sensor (CCADS) for gas turbine combustors is being developed. CCADS uses the electrical properties of the flame to detect key events and monitor critical operating parameters within the combustor. Previous development efforts have shown the capability of CCADS to monitor flashback and equivalence ratio. Recent work has focused on detecting and measuring combustion instabilities. A highly instrumented atmospheric combustor has been used to measure the pressure oscillations in the combustor, the OH emission, and the flame ion field at the premix injector outlet and along the walls of the combustor. This instrumentation allows examination of the downstream extent of the combustion field using both the OH emission and the corresponding electron and ion distribution near the walls of the combustor. In most cases, the strongest pressure oscillation dominates the frequency behavior of the OH emission and the flame ion signals. Using this highly instrumented combustor, tests were run over a matrix of equivalence ratios from 0.6 to 0.8, with an inlet reference velocity of 25 m/s. The acoustics of the fuel system for the combustor were tuned using an active-passive technique with an adjustable quarter-wave resonator. Although several statistics were investigated for correlation with the dynamic pressure in the combustor, the best correlation was found with the standard deviation of the guard current. The data show a monotonic relationship between the standard deviation of the guard current (the current through the flame at the premix injector outlet) and the standard deviation of the chamber pressure. Therefore, the relationship between the standard deviation of the guard current and the standard deviation of the pressure is the most promising for monitoring the dynamic pressure of the combustor using the flame ionization signal. This addition to the capabilities of CCADS would allow for dynamic pressure monitoring on commercial gas turbines without a pressure transducer.
Tip Leakage/Main Flow Interactions in Multi-Stage HP Turbines With Short-Height Blading
Authors: Lampart Piotr , Yershov Sergey , Rusanov Andrey , Szymaniak Mariusz
Published: November 2008

Interaction of the main flow with tip leakage over shrouded rotor blades in a multi-stage turbine is studied numerically. The flow in blade-to-blade channels is computed with the aid of a 3D Navier-Stokes solver FlowER with the Menter SST turbulence model. In this paper, the labyrinth seals are not computed but the numerical scheme is modified to include the source/sink-type boundary conditions at places at the endwalls referring to design locations of injection of leakage flows into, or their extraction from, the blade-to-blade passage. Without considering complete labyrinth seal geometries, the tip leakage jet is represented by its flow rate and direction at re-entry to the blade-to-blade passage, as if referring to the performance of a range of different labyrinth seal arrangements. The effect of direction of tip leakage re-entry on the downstream flow and efficiency of the turbine stage (stage group) is studied. The calculation method is validated on a model air stator/rotor turbine.
Comparative Performance Assessment of CRGT Power Plants Fuelled by Hydrogen Energy Carriers
Authors: Cocco Daniele , Tola Vittorio
Published: November 2008

Chemically Recuperated Gas Turbines (CRGT) perform the exhaust heat recovery through the endothermic steam reforming process of the primary fuel, which produces an H2-rich fuel. In particular, methanol, ethanol and DME are very suitable fuels for CRGT power plants owing to their low reforming temperature, which leads to a very effective waste heat recovery, especially in comparison with CRGT solutions fuelled by natural gas. This paper reports a comparative performance analysis of CRGT power plants fuelled by methanol, ethanol and DME. The performance analysis has been carried out with reference of two 40 MW class commercial turbines (the aeroderivative GE LM6000 unit and the heavy-duty GE PG6561 one). The best operating conditions have been pointed out by considering different operating parameters for the reforming process (pressure, temperature and water/fuel molar ratio). Thermochemical recuperation in CRGT power plants allows to achieve a significant performance improvement in comparison with the performance of the reference gas turbines without any exhaust heat recovery. In particular, the CRGT solutions here considered show maximum efficiencies in the range 54–57%, according to the primary fuel considered, with a corresponding increase of the power output and a decrease of the specific CO2 emissions.
Turbulent Augmentation of Internal Convection Over Pins in Staggered Pin Fin Arrays
Authors: Ames F. E. , Dvorak L. A. , Morrow M. J.
Published: November 2008

The objective of this reserch was to investigate pin fin midline heat transfer in terms of our understanding of stagnation region heat transfer for cylinders in cross flow and turbine airfoils. An experimental investigation was conducted in a staggered pin fin array at Reynolds numbers of 3000, 10,000, and 30,000 based on the maximum velocity between cylinders. Midline distributions of static pressure and heat transfer were acquired for rows 1 through 8 at the three Reynolds numbers. Turbulence measurements and velocity distributions were acquired at the inlet and in between adjacent pins in rows using hot wire anemometry. One dimensional power spectra were calculated to determine integral and energy scales. Midline heat transfer distributions are reported as Nusselt number divided by the square root of Reynolds number as a function of angle. In these terms, heat transfer was found to increase through row 3 for a Reynolds number of 30,000. After row 3, heat transfer diminished slightly. Reynolds number for each row was recast in terms of an effective approach velocity, which was found to be highest in row 3 due to the upstream blockage of row 2. Based on this effective velocity Nusselt number divided by the square root of Reynolds number increased through row 4. These data indicate that heat transfer is highest in row 3 pins due to the highest effective velocity while heat transfer augmentation due to turbulence is highest in row 4 and beyond. Hot wire measurements show higher turbulence intensity and dissipation rates upstream of row 4 compared to upstream of row 3. Generally pressure, heat transfer, and turbulence measurements were taken at all rows providing a better understanding of turbulent transport from pin fin arrays.
Operation and Performance Limitations for Solid Oxide Fuel Cells and Gas Turbines in a Hybrid System
Authors: Kemm Miriam , Hildebrandt Andre , Assadi Mohsen
Published: November 2008

Temperature limitations of Solid Oxide Fuel Cells (SOFC) in transient single operation and steady-state Hybrid System (HS) operation with Gas Turbines (GT) are presented. For transient SOFC simulations, an unsteady-state SOFC model was developed by upgrading a detailed validated steady-state model. As critical SOFC single operation modes, concerning the risk of material cracking due to exceeding SOFC transient temperature gradients, heat-up and cool-down are investigated. For minimization of transient SOFC temperature gradients at start-up and shut-down, a stepwise heat-up and cool-down procedure is proposed. Concerning HS off-design and part-load operation, the impact of SOFC temperature limitations on the operational window is investigated. Results show a reduced operational window due to exceeding local SOFC temperature gradients, which can be reduced by optimal adaptation of GT to SOFC size.
Coupling of Biomass Steam Gasification and an SOFC-Gas Turbine Hybrid System for Highly Efficient Electricity Generation
Authors: Proell Tobias , Rauch Reinhard , Aichernig Christian , Hofbauer Hermann
Published: November 2008

An energetic model of an internal reforming solid oxide fuel cell (IRSOFC) is developed. It is integrated in a process coupling fluidized bed steam gasification of biomass and an IRSOFC-gas turbine hybrid cycle. Process simulation is performed using the software package IPSEpro. The model of the gasification and gas conditioning section is based on data from the 8 MW (fuel power) plant in Guessing/Austria, while the fuel cell is modeled based on recent literature data. Heat utilization for power generation is considered covering both hybrid cycle exhaust and heat from the gasification process. Electric efficiencies up to 43% are expected for combined heat and power application even at small plant capacities in the range of 8 MW fuel power.
Flow Mechanism for Stall Margin Improvement Due to Circumferential Casing Grooves on Axial Compressors
Authors: Shabbir Aamir , Adamczyk John J.
Published: November 2008

A computational study is carried out to understand the physical mechanism responsible for the improvement in stall margin of an axial flow rotor due to the circumferential casing grooves. It is shown that the computational tool used predicts an increase in operating range of the rotor when casing groves are present. A budget of the axial momentum equation is carried out at the rotor casing in the tip gap in order to uncover the physical process behind this stall margin improvement. It is shown that for the smooth casing the net axial pressure force at the rotor casing in the tip gap is balanced by the net axial shear stress force. However in the presence of casing grooves the net axial shear stress force acting at the casing is augmented by the axial force due to the radial transport of axial momentum, which occurs across the grooves and power stream interface. This additional force adds to the net axial viscous shear force and thus leads to an increase in the stall margin of the rotor.
Practical Implications of Integrating Turbomachinery Into the Air Turborocket
Authors: Clough Joshua A. , Lewis Mark J.
Published: November 2008

The development of new reusable space launch vehicle concepts has lead to the need for more advanced engine cycles. Many two-stage vehicle concepts rely on advanced gas turbine engines that can propel the first stage of the launch vehicle from a runway up to Mach 5 or faster. One prospective engine for these vehicles is the Air Turborocket (ATR). The ATR is an innovative aircraft engine flowpath that is intended to extend the operating range of a conventional gas turbine engine. This is done by moving the turbine out of the core engine flow, alleviating the traditional limit on the turbine inlet temperature. This paper presents the analysis of an ATR engine for a reusable space launch vehicle and some of the practical problems that will be encountered in the development of this engine.
Improvements to an Air Bypass System on a Kawasaki M1A-13X Engine
Authors: Vilayanur Suresh R. , Battaglioli John
Published: November 2008

A new bypass system using an improved design has been fabricated and tested on a Kawasaki M1A-13X gas turbine engine. The engine and catalytic combustor are currently installed at the City of Santa Clara’s Silicon Valley Power municipal electrical generating stations and connected to the utility grid. The use of a bypass system with a catalytic combustor, incorporating the Xonon Cool Combustion™ technology, on an M1A-13X system increases the low emissions load turndown and ambient operating range without impacting engine efficiency. The increased operating range is achieved because the bypass system provides the required adiabatic combustion temperature (Tad) in the combustor’s post-catalyst burn out zone without changing the turbine inlet temperature. A detailed measurement of the pressure drops, in the old bypass system, revealed that there were large flow losses present, particularly in the re-injection spool piece and the extraction plenum. Since it was determined that the spool had the highest pressure loss, this was the component targeted for improvement. The analysis coupled with detailed measurements on the reinjection piece revealed that the effective area actually varied with flow As the flow changed, so did the flow mechanics inside and exiting the spool piece. Therefore, in order to achieve the design target, the flow area of the spool piece had to be optimized at the predicted capacity flow rate. CFD analysis of the spool piece revealed the regions of losses in the re-injection piece. This analysis along with a one-dimensional flow analysis of the entire system enabled the design of new spool re-injection piece. Once the design was completed, the new bypass system was fabricated and tested. Bypass flow capacity was increased by about 22%. This was achieved by alleviating regions of flow losses and also by using a new “scoop” design for the bypass reinjection tubes. As expected, engine turndown capacity and ambient operating range were improved with the new design.
Subsurface Stress Fields in FCC Single Crystal Anisotropic Contacts
Authors: Arakere Nagaraj K. , Knudsen Erik C. , Swanson Gregory R. , Duke Gregory , Ham-Battista Gilda
Published: November 2008

Single crystal superalloy turbine blades used in high pressure turbomachinery are subject to conditions of high temperature, triaxial steady and alternating stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent high cycle fatigue (HCF) failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes, and noncrystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single crystal turbine blades. This paper presents analytical and numerical techniques for evaluating two and three dimensional subsurface stress fields in anisotropic contacts. The subsurface stress results are required for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single crystal nickel-base superalloy turbine blades. An analytical procedure is presented for evaluating the subsurface stresses in the elastic half-space, based on the adaptation of a stress function method outlined by Lekhnitskii [1]. Numerical results are presented for cylindrical and spherical anisotropic contacts, using finite element analysis (FEA). Effects of crystal orientation on stress response and fatigue life are examined. Obtaining accurate subsurface stress results for anisotropic single crystal contact problems require extremely refined three-dimensional (3-D) finite element grids, especially in the edge of contact region. Obtaining resolved shear stresses (RSS) on the principal slip planes also involves considerable post-processing work. For these reasons it is very advantageous to develop analytical solution schemes for subsurface stresses, whenever possible.
Vortex-Wake-Blade Interaction in a Shrouded Axial Turbine
Authors: Schlienger J. , Kalfas A. I. , Abhari R. S.
Published: November 2008

This paper presents the results of time-resolved flow field measurements of a multistage shrouded axial turbine. The unsteady interaction mechanism between the rotor’s secondary flow vortices, the rotor’s wake and the adjacent blading at the exit plane of the first turbine stage is of prime interest and analysed in detail. Three key phases are identified for one blade passing event. The first phase shows a quasi undisturbed convection of the rotor’s secondary flow field into the downstream stator. The second phase shows a migration of high loss fluid from the wake layer into the passage and horse-shoe vortices at the rotor hub section. The relative motion between the rotor and stator blades brings the two vortices closer to the wake layer and lets the flow features interact with each other. The third phase focuses on the rotor indigenous hub vortices that are bent and stretched around the stator’s leading edge. The signal analysis of the time-resolved flow field indicates a high level of unsteadiness at the stator’s pressure side. The associated unsteadiness within the flow field is evaluated and quantified on the basis of pitchwise averaged space-time diagrams. The obtained results are finally discussed and explained using two flow schematics within and at the end of the paper.
The Use and Performance of Oxidation and Creep-Resistant Stainless Steels in an Exhaust Gas Primary Surface Recuperator Application
Authors: Rakowski James M. , Stinner Charles P. , Lipschutz Mark , Montague J. Preston
Published: November 2008

Recuperation increases the efficiency of a gas turbine engine by extracting heat from the exhaust gas stream and using it to pre-heat the compressor discharge air. Oxidation of the thin metal foil recuperator walls is a major concern, necessitating the use of heat-resistant alloys. Water vapor, present in the exhaust gas as a by-product of combustion, has been shown to be detrimental to the elevated temperature oxidation resistance of some ferrous alloys currently used for recuperators, e.g., Type 347 stainless steel. The walls of the primary surface recuperator are also subjected to a complex state of stress. Creep deformation can cause the compressor discharge air passages to expand, thus restricting exhaust gas flow and increasing the turbine backpressure. The material of construction must, therefore, be resistant to both oxidation and creep deformation. Long-term oxidation, stress-rupture, and creep test results and analysis will be presented for both commercially available and developmental austenitic stainless steel foil materials. A 20Cr-25Ni austenitic stainless steel containing a small addition of Nb was found to exhibit good creep strength when compared to current alloys of construction. This alloy also possesses excellent resistance to attack in environments containing high levels of water vapor. Oxide volatility and breakaway oxidation were not observed after 10,000 hours of exposure at temperatures as high as 760°C (1400°F).
A Computational Study of Tip Desensitization in Axial Flow Turbines: Part 2 — Turbine Rotor Simulations With Modified Tip Shapes
Authors: Tallman James A.
Published: November 2008

This study used Computational Fluid Dynamics (CFD) to investigate modified turbine blade tip shapes as a means of reducing the leakage flow and vortex. The subject of this study was the single-stage experimental turbine facility at Penn State University, with scaled three-dimensional geometry representative of a modern high-pressure stage. To validate the numerical procedure, the rotor flowfield was first computed with no modification to the tip, and the results compared with measurements of the flowfield. The flow was then predicted for a variety of different tip shapes: first with coarse grids for screening purposes and then with more refined grids for final verification of preferred tip geometries. Part 2 of this two-part paper focuses on flow-field predictions with modified blade tip geometries, and the corresponding comparisons with the baseline, flat-tip solutions presented in Part 1. Fifteen different tip shapes were computed using the ADPAC CFD Solver and moderately sized grids (720,000 nodes). These modified tip shapes incorporated different combinations of blade tip edge rounding and squealer cavities, both square and rounded, as means of reducing the leakage flow and vortex. Rounding of the suction side edge of the blade tip resulted in a considerable reduction in the size and strength of the leakage vortex, while rounding of the pressure side edge of the blade tip significantly increased the mass flow rate through the gap. Rounded squealer cavities acted to reduce the mass flow through the gap and proved advantageous over traditional, square squealer cavities. The presence of a square squealer cavity without edge rounding showed no aerodynamic advantage over a flat tip. Final computations of two preferred tip shapes were then carried out using more refined grids (7.2 million nodes). The final, refined grid computations reconfirmed a reduction in the leakage flow and vortex, as well as their associated losses.
A Transonic Compressor Stage: Part 2 — CFD Simulation
Authors: Hobson G. V. , Gannon A. J. , Shreeve R. P.
Published: November 2008

The simulation of a transonic compressor stage is presented. This stage was designed using an Euler CFD code with the intent of minimizing the use of empirical design techniques. The stage has subsequently been built and tested. More recently an existing multi-block Navier-Stokes code with a steady averaging-plane to pass information between the blade rows was used to simulate the flow through the machine. Performance maps of stage pressure ratio and efficiency at 70, 80, 90 and 100% speeds from both the Euler and Navier-Stokes CFD codes are compared with the experimental results. Details of the internal flow from the Navier-Stokes code are presented. Comparison of the design Euler CFD and experimental results showed reasonable agreement and validated its use as a design tool. Agreement between experimental and the current Navier-Stokes CFD results was good, allowing the code to be used in the viewing of the internal flow field. Improvements to the initial design CFD method are discussed in light of the experimental program and more recent simulations.