bluuebunny/crossref_metadata_2025 huggingface dataset:
Alumina-Forming Austenitic Alloys for Advanced Recuperators
Authors: Pint Bruce A. , Shingledecker John P. , Brady Michael P. , Maziasz Philip J.
Published: March 2009

Materials selection for thin-walled recuperators has been extensively investigated over the past decade. In the latest generation of recuperated turbine engines, type 347 stainless steel has been replaced by higher alloyed steels and Ni-base chromia-forming alloys. However, high (linear) rates of chromia evaporation in exhaust gas fundamentally limits the oxidation lifetime of these chromia-forming alloys. One solution is to use alumina-forming alloys that are more resistant to this environment. The lower scale growth kinetics and resistance to evaporation in the presence of water vapor suggests an order of magnitude increase in lifetime for alumina-forming alloys. A significant problem with this strategy was the large drop in creep strength with the addition of sufficient Al to form an external alumina scale. However, new Fe-base austenitic compositions have been developed with sufficient strength for this application above 700°C.
Asynchronous Dynamic Coefficients of a Three Lobe Air Bearing
Authors: Ruiz Rafael O. , Di Liscia Marcelo H. , Medina Luis , Di´az Sergio
Published: March 2009

The study of dynamic whirl behavior of air bearings is fundamental for an adequate rotordynamic analysis and future validation of numerical predictions. This work shows the dynamic response of the air film on a three lobe bearing under non-synchronous whirl motion. One-dimensional multifrequency orbits are used to characterize the bearing rotordynamic coefficients. The test rig uses two magnetic bearing actuators to impose any given orbits to the journal. The dynamic forces are measured on the test bearing housing by three load cells. Journal whirling excitation is independent of the rotating speed, thus allowing asynchronous excitations. The multi frequency excitation is applied at each rotating speed up to 11000rpm allowing the non-synchronous characterization of the air film. The experimental procedure requires two linearly independent excitation sets. Thus, vertical and horizontal one-dimensional multi-frequency orbits are applied as perturbations. Results show the synchronous and asynchronous dynamic coefficients of the air bearing. Asynchronous experimental results are compared to numerical estimation of the bearing force coefficients through solution of the isotropic ideal gas journal bearing Reynolds equation. Numerical dynamic coefficients are obtained as the effective coefficient values of the bearing when subject to a given orbit. A full characterization of the non-synchronous rotordynamics coefficients of the bearing is presented in three dimensional maps.
An Airfoil Diffuser With Variable Stagger and Solidity for Centrifugal Compressor Applications
Authors: Abdelwahab Ahmed
Published: March 2009

Airfoil diffusers have been extensively used in industrial centrifugal compressors. However, the majority of these diffusers are two-dimensional and have fixed solidity. This paper presents a numerical investigation of a new three-dimensional airfoil diffuser, i.e. variable stagger, which has a varying solidity in the span wise direction. The premise of this configuration is to better align the diffuser blade with the non uniform flow leaving the compressor impeller as well as to combine the benefits of the known wide operating range of the low solidity diffusers with the high performance of the high solidity diffusers. Numerical simulations of several impeller-diffuser configurations are presented. The first configuration uses a three-dimensional variable solidity airfoil diffuser while the others use conventional diffusers with different solidities. The results of the simulations are presented in terms of the aerodynamic performance of both the impeller and diffusers as well as the overall stage performance. The analysis indicates that the three dimensionality of the flow path of the proposed diffuser greatly impacts the diffuser as well as the impeller aerodynamic performance. The analysis also indicates the superiority of the proposed new diffuser geometry over the analyzed conventional airfoil diffusers in extending the operating range of the compressor stage as well as improving its efficiency.
Off-Design Performance Investigation of a Low Calorific Value Gas Fired Generic Type Single-Shaft Gas Turbine
Authors: Orbay Raik C. , Genrup Magnus , Eriksson Pontus , Klingmann Jens
Published: March 2009

When low calorific value gases are fired, the performance and stability of gas turbines may deteriorate due to a large amount of inert ballast and changes in working fluid properties. Since it is rather rare to have custom-built gas turbines for low Lower Heating Value (LHV) operation, the engine will be forced to operate outside its design envelope. This, in turn, poses limitations to usable fuel choices. Typical restraints are decrease in Wobbe-index and surge- and flutter-margins for turbomachinery. In this study, an advanced performance deck has been used to quantify the impact of firing low-LHV gases in a generic type gas turbine. A single-shaft gas turbine characterized by a compressor and an expander map is considered. Emphasis has been put on predicting the off-design behavior. The combustor is discussed and related to previous experiments which include investigation of flammability limits, Wobbe-index, flame position, etc. The computations show that at constant turbine inlet temperature (TIT), the shaft power and the pressure ratio will increase, however the surge margin will decrease. Possible design changes in the component level are also discussed. Aerodynamic issues (and necessary modifications) that can pose severe limitations on the gas turbine compressor- and turbine sections are discussed. Typical methods for axial turbine capacity adjustment are presented and discussed.
Variable Displacement Vane Pump for Turbine Engine Applications
Authors: Paluszewski Paul J. , Desai Mihir C. , Millar Richard C.
Published: March 2009

Increasing airframe fueldraulic system pressures and flow requirements have put severe demands on fuel system thermal management techniques. Heat loads from a variety of sources are constantly increasing the temperatures at which modern aircraft fuel systems are required to operate. Variable Displacement Vane Pump (VDVP) based systems are a solution to thermally constrained high pressure turbine engine fuel supply and fueldraulic actuation systems (i.e. variable engine nozzle and/or variable engine geometry). VDVPs offer several benefits including exceptional thermal efficiency, fast response and contamination resistance comparable to legacy systems. Utilizing a simple pumping design in conjunction with recent advances in material and bearing technology, the VDVP has demonstrated high thermal efficiency for flow turndowns up to 100:1 in a range of displacements from 5 gpm (small engines) to 120 gpm (large turbofans). Based on testing to date, VDVP systems also have potential for high-pressure fueldraulics and are capable of cavitation-free operation for extended periods of time. The VDVP is easy to operate in flow or pressure control loops and can easily meet the slew requirements of modern engines. With over 15000 hours of testing under various pressure, flow and fuel temperature conditions this technology is approaching readiness for integrated test with some challenging gas turbine engine applications. The intent of this paper is to share the system level thermal management benefits, basic design principles, test data, and potential applications of the Goodrich VDVP.
Laminar Flame Speeds and Strain Sensitivities of Mixtures of H2 With CO, CO2and N2 at Elevated Temperatures
Authors: Natarajan J. , Lieuwen T. , Seitzman J.
Published: March 2009

Laminar flame speed and strain sensitivities have been measured for mixtures of H2/CO/CO2/N2/O2 with a wall stagnation flame technique at high preheat temperature (700 K) and lean conditions. The measurements are compared with numerical predictions based on two reaction mechanisms: GRI Mech 3.0 and a H2/CO mechanism (Davis et al.). For H2:CO 50:50 fuel mixtures, both models tend to over predict the temperature dependence of the flame speed especially at very lean conditions, which confirms the trend found in an earlier study employing a Bunsen flame technique. The predicted strain sensitivities are in good agreement with the measurements. For 50:50 H2:CO fuel mixtures diluted with 40% CO2, the amount of over prediction by the models is about the same as in the undiluted case, which suggests that radiation effects associated with CO2 addition are not important for this mixture at highly preheated lean condition. For low H2 content (5 to 20%) H2/CO fuel mixtures at 5 atm and fuel lean condition, the predicted unstrained flame speeds are in excellent agreement with the measurements, but the models fail to predicted the strain sensitivity as the amount of H2 increases to 20%. Results are also presented for pure H2 with N2 diluted air (O2:N2 1:9) over a range of equivalence ratios. At lean conditions, the models over predict the measured flame speed by as much as 30%, and the amount of over prediction decreases as the equivalence ratio increases to stoichiometric and rich condition. The measured strain sensitivities are three times higher than the model predictions at lean conditions. More importantly, the predicted strain sensitivities do not change with equivalence ratio for both models, while the measurements reveal a clear trend (decreasing and then increasing) as the fuel-air ratio changes from lean to rich.
Gas Turbine Life Cycle Assessment and Preliminary Risk Analysis
Authors: Gomes E. E. B. , Pilidis P.
Published: March 2009

The prediction of possible faults in gas turbines power systems can have a great impact on the maintenance program efficiency as they can allow generators optimize generation schedule and increase profits. This study provides an evaluation of the gas turbine life time during its operation over a life cycle and evaluates the risk involved in such assessment. A mathematical model was developed to calculate the principal variables that take part in life cycle assessment: time, temperature and stress loads. Because of stochastic nature of the failure mechanisms involved in life cycle assessment of gas turbines, a probabilistic risk analysis was carried out to properly evaluate the uncertainty involved. The work conditions of the gas turbine identify the mechanical failure mechanism that rules a gas turbine life. The risk analysis algorithm produces the expected window time in which the turbine blade is expected to failure and its respective probability. The gas turbine life cycle assessment and risk analysis described in this investigation are strategic and powerful tools for optimization of gas turbines power systems.
Reduction of Multistage Rotor Models Using Cyclic Modeshapes
Authors: Sternchu¨ss Arnaud , Balme`s Etienne
Published: March 2009

This study deals with the reduction of models of bladed disks assemblies through the use of mono-harmonic cyclic mode-shapes. The first part of this paper describes how the classical substructuring technique in cyclic symmetry can be extended to rotors in the case of non compatible meshes to compute mono-harmonic eigenvectors. The second part of the paper then presents the method employed by the authors to seek the full modes of the rotor in a subspace generated from a set of such modeshapes. All the concepts developed here are illustrated on a representative sample.
Assessing Performance Degradation in Gas Turbines for Power Applications: A Challenging Task
Authors: Zachary Justin
Published: March 2009

The degradation of thermal performance is playing a significant role in the economic viability of the highly competitive merchant power plants. Since most of the gas turbines are used in Combined Cycles applications, the degradation is applicable not only to the traditional performance guaranteed values of power output and heat rate but also to exhaust flow and exhaust temperature. While the performance degradation of turbo machinery has been a widely accepted fact, an accurate quantitative assessment of the phenomenon is extremely difficult and costly. The paper will review the potential causes of degradation, related to variability in the manufacturing of the equipment, site configuration, fuel composition quality, operational requirements and maintenance practices. The article will also address the impact on the performance guarantees, due to qualifications applied to degradation process terms such as “new and clean condition”, “fired and equivalent operating hours”, and “bench mark testing”. In a combined cycle configuration, due to lengthy commissioning activities of various systems, acceptance performance tests are conducted only after a significant number of hours in operation have been accumulated. The article will discuss the viability and merits of conducting comparative testing during this commissioning period, aimed at the actual measurement of short-term deterioration. The potential obstacles and challenges of this testing program, associated with changes in the control system, hardware modifications and measurement uncertainty, will also be analyzed in details. The alternative option to account for the expected degradation is the use of correction curves supplied by the equipment manufacturers. The paper will review the suitability to specific project conditions of generically developed curves. In addition, the document will touch on how degradation evaluation may affect the Long Term Service Agreements (LTSA) between Owners and Equipment Manufacturers. Finally, the article will offer suggestions on how performance and fuel quality continuous monitoring, careful operations and maintenance scheduling could reduce the actual degradation and provide a substantial economic benefit to the Owner.
A Sensitivity-Based Method for Direct Stochastic Analysis of Nonlinear Forced Response for Bladed Discs With Friction Interfaces
Authors: Petrov E. P.
Published: March 2009

An efficient method is developed to calculate stochastic and uncertainty characteristics of forced response for nonlinear vibrations of bladed discs with friction and gap contact interfaces. Uncertainty ranges, statistical characteristics and probability density functions for forced response levels are determined directly without any sampling procedure. The method uses approximations of the forced response level based on derived analytically and calculated extremely fast and accurately sensitivity coefficients of forced response with respect to friction contact interface parameters. The method effectiveness allows analysis of strongly nonlinear vibration of bladed discs using realistic large-scale FE element models. The method is implemented in a program code developed at Imperial College and numerical examples of application of the method for stochastic analysis of a realistic blisc with underplatform dampers are provided.
Development and Application of an Eight-Step Global Mechanism for CFD and CRN Simulations of Lean-Premixed Combustors
Authors: Novosselov Igor V. , Malte Philip C.
Published: March 2009

In this paper, the development of an eight-step global chemical kinetic mechanism for methane oxidation with nitric oxide formation in lean-premixed combustion at elevated pressures is described and applied. In particular, the mechanism has been developed for use in computational fluid dynamics (CFD) and chemical reactor network (CRN) simulations of combustion in lean-premixed gas turbine engines. Special attention is focused on the ability of the mechanism to predict NOx and CO exhaust emissions. Applications of the eight-step mechanism are reported in the paper, all for high-pressure, lean-premixed, methane-air (or natural gas-air) combustion. The eight steps of the mechanism are as follows: 1. Oxidation of the methane fuel to CO and H2O. 2. Oxidation of the CO to CO2. 3. Dissociation of the CO2 to CO. 4. Flame NO formation by the Zeldovich and nitrous oxide mechanisms. 5. Flame NO formation by the prompt and NNH mechanisms. 6. Post-flame NO formation by equilibrium H-atom attack on equilibrium N2O. 7. Post-flame NO formation by equilibrium O-atom attack on equilibrium N2O. 8. Post-flame Zeldovich NO formation by equilibrium O-atom attack on N2.
Transonic Compressor Rotor Design Using Non-Monotonic Meanline Angle Distribution
Authors: Hu Zongjun , Zha Gecheng , Montgomery Matthew , Roecken Thomas , Orosa John
Published: March 2009

A non-monotonic meanline angle distribution technique with local negative camber is applied to a transonic rotor blade from the hub area to tip with the inlet Mach number varying from subsonic to low supersonic. The blade passage area is controlled by the non-monotonic meanline angle distribution, which results in reduced peak Mach number and weakened or removed shock wave. The negative camber is used downstream of the throat and hence it does not affect the flow passing capability of the blade section. The design point efficiency is significantly increased and the stall margin at part speed is also improved. Detailed results are given in the paper.
An IPRP (Integrated Pyrolysis Regenerated Plant) Microscale Demonstrative Unit in Central Italy
Authors: Fantozzi Francesco , D’Alessandro Bruno , Desideri Umberto
Published: March 2009

The Integrated Pyrolysis Regenerated Plant (IPRP) concept is based on a Gas Turbine (GT) fuelled by pyrogas produced in a rotary kiln slow pyrolysis reactor; pyrolysis process by-product, char, is used to provide the thermal energy required for pyrolysis. An IPRP demonstration unit based on an 80 kWE microturbine was built at the Terni facility of the University of Perugia. The plant is made of a slow pyrolysis rotary kiln pyrolyzer, a wet scrubbing section for tar and water vapor removal, a micro gas turbine and a treatment section for the exhaust gases. This paper describes the plant layout and expected performance with different options for waste heat recovery.
Effect of Stagnation Regions on Film Cooling Effectiveness
Authors: Rodri´guez S. , Kersten S. , Zuniga H. A. , Ling J. C. , Kapat J. S.
Published: March 2009

Over the last decades, researchers have investigated many aspects of film cooling. The present study investigates the impact of stagnation region created by a downstream airfoil on endwall film cooling effectiveness. Experimental measurements are presented for a single row of cylindrical holes inclined at 35° with hole length to diameter ratio, L/D = 7.5, pitch to diameter ratio, PI/D = 3 with a constant density ratio of 1.26 and with nitrogen as the coolant. Five different configurations were studied. Configuration 0 is the baseline, this configuration consist of a single row of cylindrical holes. Configuration I-III consisted of an airfoil positioned downstream of the injection point at x/D = 6.4, 12.7 and 25.4. The presence of wake is also investigated on configuration IV. This configuration in addition to the airfoil, also has a wake plate at x/D = −12.7, upstream of the injection location. The experimental data shows that slightly higher averaged effectiveness values are observed for configuration I for low blowing ratios. Configuration III average effectiveness is higher for mid and high blowing ratios. For all configurations, the average effectiveness increase with increasing blowing ratio at a x/D further downstream of the injection point where the jet has reattached. Higher blowing ratio increase lateral spreading of the jet promoting jet to jet interaction and mainstream interaction enhancing mixing.
Flow-Induced Vibration Analyses of Stator and Moving Rotor Cascade With Viscosity Effects
Authors: Kim Dong-Hyun , Oh Se-Won , Kim Yu-Sung , Park Oung
Published: March 2009

In this study, nonlinear dynamic responses considering fluid-structure interactions have been conducted for a stator-rotor cascade configuration. Advanced computational analysis system based on computational fluid dynamics (CFD) and computational structural dynamics (CSD) has been developed in order to investigate detailed dynamic responses and flutter stability of general stator-rotor cascade configurations. Especially, effects of relative motions of the rotor cascade with respect to the stator cascade are considered in numerical analyses. Fluid domains are modeled using the unstructured grid system with dynamic moving and local deforming techniques. Unsteady, Reynolds-averaged Navier-Stokes equations with Spalart-Allmaras and SST k-ω turbulence models are solved for unsteady flow problems. A fully implicit time marching scheme based on the Newmark direct integration method is typically used for computing the coupled aeroelastic governing equations of the cascade fluid-structure interaction problems. Detailed dynamic aeroelastic responses for different stator-rotor interaction flow conditions are presented to show the physical vibration characteristics in the time-domain.
A Simplified Method to Evaluate the Impact of Component Design on Engine Performance
Authors: Montella Francesco , van Buijtenen J. P.
Published: March 2009

This paper presents a simplified and fast method to evaluate the impact of a single engine component design on the overall performance. It consists of three steps. In the first step, an engine system model is developed using available data on existing engines. Alongside the cycle reference point, a sweep of operating points within the flight envelop is simulated. The engine model is tuned to match a wide range of conditions. In the second step, the module that contains the engine component of interest is analyzed. Different correlations between the component design and the module efficiency are investigated. In the third step, the deviations in efficiency related to different component configurations are implemented in the engine baseline model. Eventually, the effects on the performances are evaluated. The procedure is demonstrated for the case of a two-spool turbofan. The effects of tip leakage in the low pressure turbine on the overall engine performance are analyzed. In today’s collaborative engine development programs, the OEMs facilitate the design process by using advanced simulation software, in-house available technical correlations and experience. Suppliers of parts have a limited influence on the design of the components they are responsible for. This can be rectified by the proposed methodology and give subcontractors a deeper insight into the design process. It is based on commercially available PC engine simulation tools and provides a general understanding of the relations between component design and engine performance. These relations may also take into account of aspects like production technology and materials in component optimization.
A Post Test Analysis of a High-Speed Two-Stage Axial Flow Compressor
Authors: Adamczyk John J. , Hansen Jeffrey L. , Prahst Patricia S.
Published: March 2009

In 1991 under a Space Act Agreement between then Allison Gas Turbine Division (Rolls-Royce), NASA Lewis (NASA Glenn), and the Army Propulsion Directorate, a combined experimental and analytical research program was initiated to assess the capability of advanced computational fluid dynamics (CFD) codes to predict the aerodynamic performance of high-speed, high-aerodynamic- loaded axial flow compressors. Both two-stage compressors that were designed, fabricated, and tested in this study and reported upon in this paper had a design pressure ratio of 5:1. In addition, several tests were run of the first stage of each of these two-stage machines in isolation. Extensive use was made of CFD codes to support the aero-design process. The objective of this paper is to report upon what was learned from this aero- design exercise. Both experimental and post-test CFD simulation results are presented. The original build of the two stage compressor fell short of meeting the targeted aero-performance goals. The shortcomings of this design are attributed to the failure of the CFD simulations conducted in support of the design to capture key phenomena which limited the aero-performance of the compressor. This failure is not due to the inability of the CFD code to account for these key phenomena. Rather the fault lies in not accounting for them in the simulations that were conducted in support of the aerodynamic design. Finally the paper outlines the steps taken in the aerodynamic design of the second build to overcome the shortcomings of the first build.
Direct Numerical Simulation of Pulsating Jet Mixing
Authors: Yun Sangsig , Boulanger Joan , Jiang Leiyong
Published: March 2009

In lean premixed combustors, the fuel/air ratio oscillation can cause a serious problem since it can produce pressure and heat release fluctuations, and further, combustion instability if it is well phased with them. In order to design a system where such air/fuel ratio fluctuation is well suppressed, it is important to understand the mixing process and its interaction with the flow structures inside a premixer. In this study, the flow-field of a pulsating jet and the mixing of the jet with the co-flow are examined using direct numerical simulation. The effects of the frequency and amplitude of the imposed pulsation on the flow structures and mixing process are investigated in detail. It is found that the modulation amplitude has a favorable effect on mixing, but the dependency on frequency is more complicated.
Additional Investigations Into the Natural Frequencies and Critical Speeds of a Rotating, Flexible Shaft-Disk System
Authors: Greenhill Lyn M. , Lease Valerie J.
Published: March 2009

Traditional rotor dynamics analysis programs make the assumption that disk components are rigid and can be treated as lumped masses. Several researchers have studied this assumption with specific analytical treatments designed to simulate disk flexibility. The general conclusions reached by these studies indicated disk flexibility has little effect on critical speeds but significantly influences natural frequencies. This apparent contradiction has been reexamined by using axisymmetric harmonic finite elements to directly represent both disk and shaft flexibility along with gyroscopic effects. Results from this improved analysis show that depending on the thickness-to-diameter (slenderness) ratio of the disk and the axial position of the disk on the shaft, there are significant differences in all natural frequencies, for both forward and backward modes, including synchronous crossings at critical speeds.
The Effect of Steam Ingestion on Transonic Rotor Stall Margin
Authors: Gannon A. J. , Hobson G. V. , Payne T. A. , Zarro S. E.
Published: March 2009

The adverse effect of high temperature water vapor on the stall margin of a transonic compressor rotor is investigated. This type of flow condition is experienced during the takeoff of carrier born aircraft. An experiment is designed to replicate these flow conditions on a transonic compressor test rig. The transient inlet conditions are measured and the changes in gas properties as well as the reduction in stall margin for differing steam inlet pressures are presented. High speed data measurements are used to investigate the initial conditions of the compressor before steam is introduced to the flow. Evidence of pre-cursors rotating at near half rotor speed are found and the strength of these appear to give an indication of the compressor’s susceptibility to stall.
Transition on the T106 LP Turbine Blade in the Presence of Moving Upstream Wakes and Downstream Potential Fields
Authors: Opoka Maciej M. , Hodson Howard P.
Published: March 2009

Boundary layer measurements were performed on a cascade of the T106 high lift low-pressure (LP) turbine blades that was subjected to upstream wakes and a moving downstream potential field. Tests were carried out at a low level of inlet freestream turbulence (0.5%) and at a higher (4.0%). It is found that perturbations in the freestream due to both disturbances are superposed on each other. This affects the magnitude of the velocity perturbations at the edge of the boundary layer under the wakes as well as the fluctuations in the edge velocity between the wakes. Furthermore, the fluctuations in the adverse pressure gradient on the suction surface depend on the relative phase of the upstream and downstream disturbances, providing an additional stimulus for clocking studies. Time-mean momentum thickness values calculated from LDA traverses performed near the suction surface trailing edge are used to identify the optimum relative phase angle of the combined interaction. Unsteady suction surface pressures, quasi wall shear stress and LDA data illustrate the resulting multimode process of transition, which is responsible for the observed clocking effects. The optimum relative phase angle of the upstream wake and the downstream potential field can produce 0.25% of efficiency improvement, through the reduction of the suction surface boundary layer loss. This reduction is mainly related to the calmed region and the laminar flow benefits that can be more effectively utilised than when only the upstream wakes are present. During the remaining parts of the cycle the features that are usually associated with the wake and the potential field effects are still present.
Challenges Facing Performance Evaluations of IGCC Power Plants
Authors: Zachary Justin J. , Horazak Dennis
Published: March 2009

Based on present integrated gasification combined cycle (IGCC) development activities and the renewed role of coal as the primary fossil fuel for power generation, there is a high probability that several IGCC projects will materialize in the near future. A challenge facing Owners, engineering, procurement, and construction (EPC) contractors, and original equipment manufacturers (OEMs) is to define performance guarantee criteria and the practical means to determine them. In anticipation of this, the ASME Performance Test Committee developed a Performance Test Code for IGCC plants — PTC 47. Currently, a final draft of PTC 47 is in the approval stage. IGCC performance plant testing is facing many unique challenges. However, by offering guidelines for accurate testing, this code should play an important role in the full commercialization of this technology.
Investigation of Unsteady Wake-Separated Boundary Layer Interaction Using Particle-Image-Velocimetry
Authors: Uzol Og˘uz , Zhang Xue Feng , Cranstone Alex , Hodson Howard
Published: March 2009

The current paper presents an experimental investigation of the interaction between unsteady wakes and the separated boundary layer on the suction side of an ultra-high-lift low-pressure turbine airfoil. Two-dimensional Particle Image Velocimetry (PIV) measurements of the unsteady boundary layer over the T106C LP turbine profile were performed in a low speed linear cascade facility, at selected phases of passing wakes. The wakes are created by moving cylindrical bars across the inlet of the test section. Various phenomena were investigated such as separation and transition characteristics, vortex structures within the unsteady boundary layer, their interaction and effects on the transition process, the corresponding vortex shedding mechanisms and the unsteady behaviour of the separation bubble due to the wake- boundary layer interaction. The current measurements suggest that rollup vortices are generated as the wake approaches the separated shear layer on the suction surface before the wake centerline starts impinging on the blade. At this instant, the bubble is sufficiently high for the free shear layer to roll up into a vortex and the incoming wake is highly distorted (strained) due to the velocity field within the blade passage, and the turbulence distribution within the wake is not symmetrical. Vortices within the boundary layer, identified using the swirl strength distributions calculated from the eigenvalues of the velocity gradient tensor, seem to be coalescing and forming bigger scale structures, which in turn break up into smaller but higher swirl strength eddies. In between the passing wakes, the separation bubble grows in both in height and length, trying to return to its steady state shape.
An Experimental and Computational Parametric Investigation of Flow Conditions in Intersecting Circular Passages
Authors: Nowlin Scott R. , Gillespie David R. H. , Ireland Peter T. , Romero Eduardo , Mitchell Mark
Published: March 2009

In some industrial applications such as turbine airfoil film cooling, coolant passage configurations must maintain sufficient pressure margin to prevent hot gas ingestion whilst using holes of large enough diameter to avoid foreign object blockage. This frequently means that some regions of a film-cooled surface are provided with excess air, or that exhausting film jets are over-blown, adversely amplifying local mixing or coolant separation and therefore enhancing heat flux. A cooling system featuring intersecting passages would allow a high pressure margin to be obtained using discrete, localized loss mechanisms where flows intersect. The degree of loss could be tailored to the local internal and external flow conditions by altering the intersection extent (i.e. the degree of intersecting passage offset), thereby optimizing the use of coolant. Furthermore, localized in-passage convective heat transfer enhancements caused by thin boundary layers and impinging flows in the vicinity of the intersections would improve total heat flux (Watts per square meter) despite surface area lost to intersection voids. As the heat transfer and loss enhancements do not rely on intricately manufactured flow features, the cooling performance is likely to be robust in industrial applications, extending component life. An experimental and computational investigation of the flow through two intersecting cylindrical pipes has been carried out at turbine engine-representative conditions to test these hypotheses. While previous workers have characterized loss and heat transfer in co-planar intersecting holes, this first-of-a-kind study parametrically investigates both fully and partially-intersecting passages, accounting for passage offsets due to typical manufacturing tolerances or purpose-built localized loss enhancements. The loss coefficient across the intersection has been experimentally determined for a range of intersection angles and degrees of intersection in a large scale model running at near atmospheric conditions. The results are used to develop an empirical correlation for the loss coefficient for the isolated intersecting circular channel. A commercial computational fluid dynamics (CFD) code, FLUENT©, has been used to model heat transfer locally within selected intersecting geometries, and thus to examine the average heat transfer coefficient compared to that predicted by the well-known Dittus-Boelter correlation and other investigators. Insight gained from the CFD predictions enables a first-order estimate of the impact of adding intersections to the convective cooling performance of these advanced cooling configurations. Results show that even an imperfectly machined (i.e. partial) intersection can provide a significant improvement to heat transfer as well as enhanced loss.
Study of Sloped Trench Casing Treatment on Performance and Stability of a Transonic Axial Compressor
Authors: Zhang Hui , Ma Hongwei
Published: March 2009

This paper presents a numerical investigation of effects of sloped trench casing treatment over the rotor tip on the aerodynamic performance and stability of a transonic axial compressor rotor (NASA Rotor 37). The axially cutting tip of blade is the marked characteristic of the casing treatment which is differ with casing treatments without adjustment of the blade tip. The numerical method has been verified by experimental results in the case of the smooth casing with the tip clearance of 0.356 mm at the design wheel speed (17188.7 rpm). The simulation results are well consistent with the measurement results. The experiment results of NASA Rotor 37 cite from NASA Lewis Research Center. The simulation results show a performance improvement of the compressor on the sloped trench casing. The flow fields of the smooth and sloped trench casings were compared, and results show the sloped trench geometry provides a barrier to minimize the forward flow from the tip clearance vortex. In addition, the sloped trench allows the forward facing step at the aft end to be replaced by an aerodynamically smooth transition to guide the flow from the recess into the mainstream. These results show a performance improvement of the compressor.
Influence of Stagger Angle Variation on Aerodynamic Damping and Frequency Shifts
Authors: Sladojevic´ I. , Sayma A. I. , Imregun M.
Published: March 2009

The paper presents the results of a study focusing on aerodynamic non-uniformities and their effect on frequency and damping variations. Small tolerances of stagger angle or camber can affect the aerodynamic loading of rotor blades, without significantly altering the structural properties. This investigation looks into the degree of change of natural frequencies and damping of the aeroelastic model caused by blade stagger angle variations. The model used in the study is a simplified aero-engine fan model. The investigation involved three different patterns at two operating speeds. The results suggest that damping in a mis-staggered structure is more prone to variation than frequencies.
Life Prediction Based on Material State Changes in Ceramic Matrix Composite Materials
Authors: Reifsnider Ken , Case S. W.
Published: March 2009

Monolithic ceramics and continuous fiber reinforced ceramic composites are being developed for use in high temperature applications such as combustor liners in gas turbines, thrust deflectors for jet engines, and thruster nozzles. Ceramic composite materials possess the high temperature resistance properties of ceramics, but have better creep and cyclic properties. However, the properties of these materials change somewhat with time at service temperatures, i.e., their material state changes as a function of service conditions and history. The authors have developed a methodology for representing and combining the effects of high temperature material state changes in CMCs, along with changes in applied stress / strain conditions during service, to estimate remaining strength and life of ceramic composite materials and components. Fatigue, creep rupture, and time dependent deformation are combined by a strength metric in integral form to create a time-resolved, point-wise estimate of current remaining strength and life in material elements. Application of this methodology in discrete element representations of mechanical behavior of structural elements with nonuniform stress / strain states has been implemented.
Measured Endwall Flow and Passage Heat Transfer in a Linear Blade Passage With Endwall and Leading Edge Modifications
Authors: Mahmood Gazi I. , Acharya Sumanta
Published: March 2009

The role of contouring via leading edge fillets or 3-dimensional end wall contouring is examined and compared. The contour endwall profile varies along both the pitch-direction and the axial direction and represents full-passage contouring. The fillets are employed at the corner of blade leading edge and endwall and extend about one-third of the blade axial chord along the blade. Both the endwall contouring and leading edge fillet are employed at the passage bottom endwall. Measurements are obtained for static pressure, pitchwise velocity, flow yaw angle, streamwise vorticity, and Nusselt number on the endwall. The Reynolds number based on the axial chord and passage inlet velocity for the measurements is 2.39×105. The blade surface static pressure coefficients near the endwall indicate no effects of the leading fillet on the blade surface. However, the static pressure difference from the blade-pressure to the blade-suction surface near the endwall shows that the pressure differences generally decrease with the contour endwall and leading edge fillet. This results in less turning of the endwall region flow from the pressure side to suction side in the passage as indicated by reductions in the flow yaw angles and pitchwise velocity with the structural modifications. The streamwise vorticity of the passage vortex is also affected indicating weaker secondary flows in the endwall region for the contour endwall and leading edge fillet cases. The endwall Nusselt numbers are smaller especially upstream of the throat region for the contour endwall and fillet cases.
Rotordynamic Force Prediction of Centrifugal Compressor Impellers Using Computational Fluid Dynamics
Authors: Moore J. Jeffrey , Ransom David L. , Viana Flavia
Published: March 2009

The energy industry depends on centrifugal compressors to produce, process, re-inject and transport many different gases. Centrifugal compressors use one or more impellers to impart momentum to the flowing gas and, thereby, produce an increase in pressure through diffusion. As the operating pressure in a compressor increases, the fluid-rotor interaction at the seals and impellers become more important. Also, the new generation of mega-scale Liquefied Natural Gas (LNG) compressors is dependent on accurate assessment of these forces. The aerodynamic forces and cross-coupled stiffness from the impellers cannot be accurately predicted with traditional methods and must be estimated with semi-empirical formulations. The result of these inaccuracies is a potential for compressor designs that can experience unexpected, dangerous, and damaging instabilities and subsynchronous vibrations. The current investigation is intended to advance the state-of-the-art to achieve an improved, physics-based method of predicted aerodynamic destabilizing cross-coupling forces on centrifugal compressor impellers using Computational Fluid Dynamics (CFD). CFD was employed in this study to predict the impeller-fluid interaction forces, which gives rise to the aerodynamic cross-coupling. The procedure utilized in this study was developed by Moore and Palazzolo [10], which applied the method to liquid pump impellers. Their results showed good correlation to test data. Unfortunately, no such data exists for centrifugal compressors. Therefore, in order to validate the present model, comparisons will be made to predict the instability of an industrial centrifugal compressor. A parametric CFD study is then presented leading to a new analytical expression for predicting the cross-coupled stiffness for centrifugal impellers.
Implementation of the Thickened Flame Model for Large Eddy Simulation of Turbulent Premixed Combustion in a Commercial Solver
Authors: Durand Ludovic , Polifke Wolfgang
Published: March 2009

The Thickened Flame model of Colin et al. for Large Eddy Simulation of turbulent premixed combustion has been implemented in a general purpose, commercial CFD solver. In this model, the computation of the filtered reaction rate involves a third order derivative operator acting on the velocity field. The evaluation of this operator is non-trivial even for cartesian grids, and indeed quite difficult for unstructured grids. Strategies to overcome these difficulties are discussed in the paper; in order to ease the implementation for unstructured grids in a commercial solver, a slight modification of the original thickened flame model is proposed. Both the original and the modified version of the thickened flame model are validated against experimental data (velocity distribution and flame position) for a turbulent, bluff-body stabilized, premix flame. A comparison against results obtained with the Turbulent Flame speed Closure LES-model proposed by Flohr and Pitsch is also presented.
Influences of Recess Geometry and Restrictor Dimension on Flow Patterns and Pressure Distribution of Hydrostatic Bearings
Authors: Chen Cheng-Hsien , Kang Yuan , Chang Yeon-Pun , Peng De-Xing , Yang Ding-Wen
Published: March 2009

This paper studies the influences of recess geometry and restrictor dimensions on the flow patterns and pressure distribution of lubricant film, which are coupled effects of hybrid characteristics of a hydrostatic bearing. The lubricant flow is described by using the Navier-Stokes equations. The Galerkin weighted residual finite element method is applied to determine the lubricant velocities and pressure in the bearing clearance. The numerical simulations will evaluate the effects of the land-width ratio and restriction parameter as well as the influence of modified Reynolds number and the jet-strength coefficient on the flow patterns in the recess and pressure distribution in lubricant film. On the basis of the simulation drawn from this study, the simulated results are expected to help engineers make better use of the design of hydrostatic bearing and its restrictors.
Electric Starter and Generator Systems (ESGS) for Gas Turbines: Making Platform Integration Easier
Authors: Quin˜ones Martin , Mason Steve , Green Allan
Published: March 2009

The US Navy has pursued gas turbine electric start systems since 2003. Such a system has been extensively tested at the Naval Surface Warfare Center, Carderock Division (NSWCCD) Land Based Engineering Site (LBES) in Philadelphia, PA. It was demonstrated on a General Electric (GE) LM2500 main propulsion engine as well as a Rolls Royce (RR) MT30 engine. Presently, the system is being refined and repackaged to undergo U.S. Navy qualification for production use. Given the performance success of electric start the next logical step is to extend its application to other engine lines such as the Ship Service Gas Turbine Generators (SSGTG). In order to facilitate platform integration, the electric start concept has been evolved into the Electric Start and Generation System (ESGS). As expected, this system has the ability to start a gas turbine by purely electrical means. Once the engine has reached idle speed or above, the ESGS becomes a generator capable of producing power. This power may be harnessed to address dark start capability on Surface Combatants. The ESGS configuration simplifies integration of bulk energy storage such as a flywheel device or battery pack. This will ensure availability to the engine under a loss of platform power scenario thus providing self-sustainability to all the gas turbine’s electrical functions. Another alternative is to continuously provide ESGS generated power back to the electrical grid in continuous support of the engine auxiliary systems. In this case, flywheels and batteries may be replaced by advanced transfer switches that redirect power where it is needed on demand. This paper describes a program undertaken by NSWCCD to carry out land based testing of an advanced design ESGS. An overview of system requirements is given from a perspective of platform integration. The system architecture is fully described. It is an evolution of ESGS technology that has been extensively tested on RR MT30 and GE LM2500 gas turbines at NSWCCD LBES. Compared with existing air and alternative hydraulic gas turbine starter systems, this system is more compact and provides the benefits of simplified platform integration. It incorporates energy storage to provide black start capability for the gas turbine. Battery and inertial energy storage technologies are discussed in detail for use with the ESGS.