bluuebunny/crossref_metadata_2025 huggingface dataset:
A Dual-Mesh Approach to Enhance Accuracy of the Boundary Conditions for Unstructured Grid Modeling of Turbomachinery Flows
Authors: Yang Hong , Jiang Leiyong
Published: January 2011

Although unstructured grids have gained wide acceptance in many engineering applications, they still suffer from difficulties in achieving high accuracy at the inflow, outflow and mixing-plane interface boundaries of multi-stage turbomachinery configurations. To overcome these difficulties and hence to increase the accuracy of unstructured grid methods, a novel dual mesh approach is proposed. In contrast to conventional CFD techniques, the dual mesh approach works on two sets of meshes at the boundaries: one is the original mesh and the other is an auxiliary surface mesh created at run time. By properly coupling of such double meshes, the dual mesh approach can effectively increase the accuracy and conservation of the solutions at the inflow, outflow and mixing-plane interface boundaries, and it can also enjoy most of the sophisticated numerical algorithms originally developed for the structured-grid boundary conditions. With both compressor and turbine test cases, the dual mesh approach is demonstrated to be superior to the conventional method while its CPU-time penalty is marginal. Additionally the dual mesh approach may be also useful for any structured CFD solvers subject to some restrictions on the structured grid distributions at the inflow, outflow and mixing-plane interface boundaries, e.g. mesh uniformity in the circumferential direction.
Optimizing Maintenance for Multi-Unit Industrial Gas Turbine Installations
Authors: Bohlin Markus , Wa¨rja Mathias
Published: January 2011

High levels of availability and reliability are essential in many industries where production is subject to high costs due to downtime. Examples where gas turbines are used include the mechanical drive in natural gas pipelines and power generation on oil platforms, where it is common to use redundant gas turbines to mitigate the effects of service outage. In this paper, component-level maintenance of parallel multi-unit systems is considered, allowing production at a reduced level when some of the units are not operational. Units are themselves assumed to be composed out of components in a serial configuration; maintenance of one component implies shutdown of the unit. Parallel installations allow maintenance to be performed on one or a few gas turbines without taking down the entire installation. This allows maintenance to be optimized even further than in a serial system. However, the maintenance optimization process is made more complicated, since there now exist both positive and negative grouping effects. The positive grouping effects come from shared setup activities and costs, and the negative effects come from resource limitations, in this case the limited number of gas turbines which can be maintained at the same time. In the approach presented in this paper, each component has its individual preventive maintenance schedule, which is updated at inspections, changes in production and when indicated using remote condition monitoring. A minimal repair model for noncritical routine inspections and service tasks is assumed, which does not affect component state. In addition, previously developed procedures for estimating and measuring residual component lifetime for individual components during operation are used. The procedures are based on a Retirement For Cause (RFC) approach where components are not replaced until a potential failure has been detected. To maximize revenues for an operator, the available information is evaluated using software where scenario analysis and optimization is performed. To show the possible economic effects, gas turbine operation data is used together with maintenance and operator requirements as input for optimization of a production line consisting of a natural-gas compressor station having three SGT-600 gas turbines. Savings can be substantial compared to a traditional preventive maintenance plan.
Experiments on Flame Flashback in a Quasi-2D Turbulent Wall Boundary Layer for Premixed Methane-Hydrogen-Air Mixtures
Authors: Eichler Christian , Sattelmayer Thomas
Published: January 2011

Premixed combustion of hydrogen-rich mixtures involves the risk of flame flashback through wall boundary layers. For laminar flow conditions, the flashback mechanism is well understood and is usually correlated by a critical velocity gradient at the wall. Turbulent transport inside the boundary layer considerably increases the flashback propensity. Only tube burner setups have been investigated in the past and thus turbulent flashback limits were only derived for a fully-developed Blasius wall friction profile. For turbulent flows, details of the flame propagation in proximity to the wall remain unclear. This paper presents results from a new experimental combustion rig, apt for detailed optical investigations of flame flashbacks in a turbulent wall boundary layer developing on a flat plate and being subject to an adjustable pressure gradient. Turbulent flashback limits are derived from the observed flame position inside the measurement section. The fuels investigated cover mixtures of methane, hydrogen and air at various mixing ratios. The associated wall friction distributions are determined by RANS computations of the flow inside the measurement section with fully resolved boundary layers. Consequently, the interaction between flame back pressure and incoming flow is not taken into account explicitly, in accordance with the evaluation procedure used for tube burner experiments. The results are compared to literature values and the critical gradient concept is reviewed in light of the new data.
A Methodology for on the Fly Acoustic Characterization of the Feeding Lines Impedances in a Turbulent Swirled Combustor
Authors: Lamraoui A. , Richecoeur F. , Schuller T. , Ducruix S.
Published: January 2011

A methodology is proposed to determine on the fly the acoustic impedances at the boundaries of a combustor under operation and without the need of external forcing device. The methodology is applied hereby to obtain the reflection coefficients of the air and fuel feeding lines supplying a swirled combustor operating in lean conditions and featuring an unstable regime. It is based on a three-microphone technique and uses the combustion roar noise inside the chamber to get estimates of the boundary impedances in the low frequency limit. Conditions under which this method yields reliable results for the reflection coefficient are examined, and a criterion based on the coherence between microphone signals is proposed to determine the frequency band width for impedance reconstruction. The method also takes into account the flow Mach number in the supplying pipes, which can be non negligible because of their reduced diameter. The technique is validated against data obtained in a dedicated impedance measurement setup equipped with a high-efficiency loudspeaker.
A Generalized Axisymmetric Boundary Condition Method for Parallel Unstructured Field Solvers
Authors: Hyams Daniel G. , Webster Robert , Sreenivas Kidambi
Published: January 2011

A generalized interpolative interface is developed to provide an axisymmetric boundary condition for multielement unstructured field solvers, including those that require highly stretched anisotropic meshes. The method centers around an extruded interpolative interface that does not require matched unstructured grids on the corresponding axisymmetric surfaces. Arc-based mesh extrusions are constructed from each periodic interface, which allow for closure and the solution of control volumes that lie on the interface. For each extruded point, a corresponding virtual point is created in order to control the exact location at which the client data interpolations are performed; for axisymmetric surfaces, the virtual points are rotated and placed inside of the opposite side of the domain. Special procedures, such as utilization of surface projections and parallel boundary layer displacement algorithms, are required for support of highly stretched anisotropic grids commonly used in the resolution of boundary layers in fluid flow solvers. All algorithms used to extrude the interpolative surface, place virtual points, and interpolate for the client data must be parallelized for compatibility with modern parallel field solvers. No restrictions are to be placed on the subdomain decomposition. To this end, fully general parallel mechanisms are implemented in order to transport data from its native storage to a possibly remote location. This overall axisymmetric boundary condition scheme is implemented in the Tenasi code for testing. Interpolation requires a parallel unstructured multielement search algorithm, which is a concerted effort by itself, and is the subject of an upcoming paper. This axisymmetric interface scheme is validated on an empty rotor passage, as well as on a Rotor 37 standard test case at full design speed. For these simulations, the two equation Menter SST [1] turbulence model is utilized. Profiles of the relative Mach number aft of the blade and pressure ratio data match very well with experimental results, demonstrating the validity of the proposed approach.
Evaluation of a Particulate Sampling Methodology From a Gas Turbine Exhaust Using Real-Time Size and Number Analysis at Simulated Aircraft Conditions
Authors: Sevcenco Yura A. , Crayford Andrew P. , Marsh Richard , Bowen Philip J. , Miller Michael N. , Johnson Mark P.
Published: January 2011

Two differential mobility spectrometers (DMS 500) were used to measure particulate size distributions and particulate matter losses in the exhaust of a simulated gas turbine combustor test rig. The rig is a stable gas turbine combustor simulator providing particles of physicochemical properties analogous to real aircraft engines. The rig ran at three operating conditions, giving a range of organic to elemental carbon distributions, allowing different aerosol compositions to be formed for comparison and analysis of transport losses. Smoke number from a recognised filter stain method and gas analysis of the exhaust were also taken to prove representative engine conditions. The two instruments were separated by 10m of heated stainless steel sample line and a range of transitional to turbulent flow rates from 19L/min to 64L/min were utilised for the comparative analysis. The aerosols showed measureable transport losses dependant on organic fraction, while flow rate showed substantial effects dependent on the flow state within the line. Comparisons made to the particle transport loss model from United Technologies Research Center show agreement in trend losses relative to size distribution of the particulate matter, but with losses being higher than predicted.
Optimal Lay-Out and Operation of District Heating and Cooling Distributed Trigeneration Systems
Authors: Buoro Dario , Casisi Melchiorre , Pinamonti Piero , Reini Mauro
Published: January 2011

The paper deals with the optimization of a distributed urban district heating and cooling cogeneration system. The model is based on a Mixed Integer Linear Program (MILP) and includes a set of micro-cogeneration gas turbines and a district heating network potentially connecting each considered building to all the others. Absorption machines, supplied with cogenerated heat, can be used instead of conventional electrical chiller to face the cooling demand. In addition, a district cooling network can be introduced, independently from the district heating one. The objective of the paper is to obtain the optimal synthesis and operation strategy of the whole system, in terms of Total Annual Cost for owning, maintaining and operating the system. The solution has to specify the kind, the number and the location of cogeneration equipment and absorption machines, the size and the position of district heating and cooling pipelines as well as the optimal operation of each component. The effects of different plant options, comparing cogeneration and tri-generation machines adoption and district heating and cooling pipelines installation, are considered.
Computational and Experimental Study of Premixed Combustion at Ultra Wet Conditions
Authors: Go¨ke Sebastian , Go¨ckeler Katharina , Kru¨ger Oliver , Paschereit Christian O.
Published: January 2011

Humidified gas turbines (HGT), operating with humidified air, promise a higher efficiency compared to dry gas turbines, as well as reduced NOx emissions. In this study, premixed, near-stoichiometric combustion was investigated for gas turbine applications at ultra wet conditions with steam levels up to 35w%. Based on a generic burner, an experimental study was conducted for the combustion of natural gas at atmospheric pressure. The influence of humidity on emissions and flammability limits was investigated for different inlet temperatures, swirl numbers, and fuel injection strategies. At near-stoichiometric conditions, a degree of humidity of 35w% was achieved with a stable flame and single-digit NOx and CO emissions. In experiments conducted in a water tunnel, the flow field of the combustor was investigated using Laser Doppler Anemometry and Laser-induced Fluorescence. In addition to the experiments, a kinetic assessment of the emission formation was conducted with a reactor network, using a combination of several perfectly stirred reactors. The results of these simulations confirm the experimental findings.
Compressor Performance 2D Modelling at Reverse Flow Conditions
Authors: Gallar L. , Tzagarakis I. , Pachidis V. , Singh R.
Published: January 2011

After a shaft failure the compression system of a gas turbine is likely to surge due to the heavy vibrations induced on the engine after the breakage. Unlike at any other conditions of operation, compressor surge during a shaft over-speed event is regarded as desirable as it limits the air flow across the engine and hence the power available to accelerate the free turbine. It is for this reason that the proper prediction of the engine performance during a shaft over-speed event claims for an accurate modelling of the compressor operation at reverse flow conditions. The present study investigates the ability of the existent two dimensional algorithms to simulate the compressor performance in backflow conditions. Results for a three stage axial compressor at reverse flow were produced and compared against stage by stage experimental data published by Gamache. The research shows that due to the strong radial fluxes present over the blades, two dimensional approaches are inadequate to provide satisfactory results. Three dimensional effects and inaccuracies are accounted for by the introduction of a correction parameter that is a measure of the pressure loss across the blades. Such parameter is tailored for rotors and stators and enables the satisfactory agreement between calculations and experiments in a stage by stage basis. The paper concludes with the comparison of the numerical results with the experimental data supplied by Day on a four stage axial compressor.
Effects of Fuel Nozzle Condition on Gas Turbine Combustion Chamber Exit Temperature Distributions
Authors: Bishop Kristen , Allan William
Published: January 2011

The effects of fuel nozzle condition on the temperature distributions experienced by the nozzle guide vanes have been investigated using an optical patternator. Average spray cone angle, symmetry, and fuel streaks were quantified. An ambient pressure and temperature combustion chamber test rig was used to capture exit temperature distributions and to determine the pattern factor. The rig tests matched representative engine operating conditions by matching Mach number, equivalence ratio, and fuel droplet size. It was observed that very small deviations (± 10° in spray cone angle) from a nominal distribution in the fuel nozzle spray pattern correlated to increases in pattern factor, apparently due to a degradation of mixing processes, which created larger regions of very high temperature core flow and smaller regions of cooler temperatures within the combustion chamber exit plane. The spray cone angle had the most measureable influence while the effects of spray roundness and streak intensity had slightly less influence. Comparisons were made with published studies conducted on the combustion chamber geometry, and recommendations were made for fuel nozzle inspections.
Fault Diagnosis of Jet Engines by Using a Multiple Model-Based Approach
Authors: Meskin N. , Naderi E. , Khorasani K.
Published: January 2011

In this paper, a novel real-time fault detection and isolation (FDI) scheme that is based on the concept of multiple model approach is proposed for jet engines. A modular and a hierarchical architecture is proposed which enables the detection and isolation of both single as well as permanent concurrent faults in the engine. The nonlinear dynamics of the jet engine is linearized in which compressors and turbines maps are used for performance calculations and a set of linear models corresponding to various operating modes of the engine (namely healthy and different fault modes) at each operating point is obtained. Using the multiple model approach the probabilities corresponding to each operating point of the engine are generated and the current operating mode of the system is detected based on evaluating the maximum probability criteria. It is shown that the proposed methodology is also robust to the failure of pressure and temperature sensors and extensive levels of noise outliers in the sensor measurements. Simulation results presented demonstrate the effectiveness of our proposed multiple model FDI algorithm for both structural faults and actuator fault in the jet engine.
An Approach to Compact, Wet Gas Compression
Authors: Gilarranz R. Jose´ L. , Kidd H. Allan , Chochua Gocha , Maier William C.
Published: January 2011

In recent years, several papers have been written regarding the use of centrifugal compression technology to handle applications in which the process gas entering the equipment contains a significant amount of liquids, and can therefore be considered a wet gas. One such application that is currently being considered by many oil and gas operators is the installation of processing and compression equipment on the sea bed, to directly handle the process gas stream in close proximity to the wellhead. Other applications also exist topside, in which the operator would benefit from the installation of additional compression and processing capabilities at brown field facilities. Most of these existing installations have limited space for expansion and have strict size and weight limitations that have to be met by the additional equipment. This, in many cases, hinders the utilization of traditional compression and processing equipment, which is typically arranged using the large and heavy multi deck approach. A novel integrated compression system (ICS) has recently been developed to address the current need for compact compression systems that can handle wet process gas. The ICS makes use of centrifugal compressor stages driven directly by a high-speed, close-coupled electric motor, and incorporates a proprietary integrated centrifugal gas-liquid separation unit within the compressor case. This compact compression unit is packaged with process gas coolers in a single-lift module, providing a complete compression system that can be applied to all markets — upstream, midstream and downstream. With this integrated approach, the total footprint and weight of a conventional module or equipment layout can be greatly reduced. This paper is part of a series of publications that will describe the attributes of the new integrated compression system, and will serve to introduce the ICS and the benefits associated to the integration of the centrifugal separator into the compressor casing. The paper will focus on the OEM’s approach to Wet Gas Compression, with emphasis on the benefits of handling the liquid and vapor phases as separate streams, making the system more efficient and reliable than alternate solutions, including the ones that handle the wet gas directly. Finally the paper will provide a comparison between a traditional compression train and the new ICS to show how the latter system offers significant size and weight advantages.
Design and Testing of a Micromix Combustor With Recuperative Wall Cooling for a Hydrogen Fuelled μ-Scale Gas Turbine
Authors: Robinson A. E. , Funke H. H.-W. , Hendrick P. , Wagemakers R.
Published: January 2011

For more than a decade up to now there is an ongoing interest in small gas turbines downsized to micro-scale. With their high energy density they offer a great potential as a substitute for today’s unwieldy accumulators, found in a variety of applications like laptops, small tools etc. But micro-scale gas turbines could not only be used for generating electricity, they could also produce thrust for powering small unmanned aerial vehicles (UAVs) or similar devices. Beneath all the great design challenges with the rotating parts of the turbomachinery at this small scale, another crucial item is in fact the combustion chamber needed for a safe and reliable operation. With the so called regular micromix burning principle for hydrogen successfully downscaled in an initial combustion chamber prototype of 10 kW energy output, this paper describes a new design attempt aimed at the integration possibilities in a μ-scale gas turbine. For manufacturing the combustion chamber completely out of stainless steel components, a recuperative wall cooling was introduced to keep the temperatures in an acceptable range. Also a new way of an integrated ignition was developed. The detailed description of the prototype’s design is followed by an in depth report about the test results. The experimental investigations comprise a set of mass flow variations, coupled with a variation of the equivalence ratio for each mass flow at different inlet temperatures and pressures. With the data obtained by an exhaust gas analysis, a full characterisation concerning combustion efficiency and stability of the prototype chamber is possible. Furthermore the data show a full compliance with the expected operating requirements of the designated μ-scale gas turbine.
Conjugate Heat Transfer Analysis of NASA C3X Film Cooled Vane With an Object-Oriented CFD Code
Authors: Mangani Luca , Cerutti Matteo , Maritano Massimiliano , Spel Martin
Published: January 2011

This paper presents the developments done on a CFD unstructured solver, based on the OpenFOAM® CFD libraries, to perform conjugate heat transfer simulations in turbomachinery applications. The solver uses a SIMPLE-C All-Mach algorithm with a special treatment for the pressure corrector equation to deal with highly compressible flows. Moreover, the solver provides an exhaustive turbulence model library, specific for heat transfer calculations and an implicit treatment for fluid-to-fluid and solid-to-fluid boundaries using a generic grid interface (GGI) that allows a greater mesh generation flexibility. The development of the generic grid interface is described in the current paper. The conjugate numerical methodology was employed to predict the metal temperature of a three-dimensional first stage gas turbine blade at realistic operating conditions. The validation case is based on the 1988 NASA C3X experimental setup of a internally and film cooled vane. The stator vane was internally cooled by an array of radial cooling channels of constant cross-sectional area an externally by rows of film cooling holes. The mesh has been generated with GridPRO®, using a multi block structured approach. The optimization methods used in the grid generator provide a full hex grid maintaining mesh orthogonality at the walls and within the domain and allowing the nodes to be moved to an optimal position. Numerical and experimental results are compared in terms of pressure and temperature distribution on the blade wall at mid-span, as well as heat transfer coefficient profiles.
Numerical Investigation of the Influence of Real World Blade Profile Variations on the Aerodynamic Performance of Transonic Nozzle Guide Vanes
Authors: Edwards R. , Asghar A. , Woodason R. , LaViolette M. , Goni Boulama K. , Allan W.
Published: January 2011

This paper addresses the issue of aerodynamic consequences of small variations in airfoil profile. A numerical comparison of flow field and cascade pressure losses for two representative repaired profiles and a reference new vane were made. Coordinates for the three airfoil profiles were obtained from the nozzle guide vanes of refurbished turboshaft engines using 3D optical scanning and digital modeling. The repaired profiles showed differences in geometry in comparison with the new vane, particularly near the leading and trailing edges. A numerical simulation was conducted using a commercial CFD code which uses the finite element approach for solving the governing equations. The computational predictions of the aerodynamic performance were validated with experimental results obtained from a transonic cascade consisting of blades with the same airfoil profiles. A CFD analysis was performed for the cascade at subsonic inlet and transonic exit conditions. Boundary layer growth, wake formation, and shock boundary layer interactions were observed in the two-dimensional computations. The flow field showed the presence of shock waves downstream of the passage throat and near the trailing edges of the blades. A conspicuous change in flow pattern due to subtle variation in airfoil profile was observed. The calculated flow field was compared with the flow pattern visualized in the experimental test rig using the Schlieren method. The total pressure calculation for the cascade exit showed an increase in pressure loss for one of the off-design profiles. The pressure loss calculations were also compared with the multi-hole total pressure probe measurement in the transonic cascade rig.
Detached Eddy Simulation of Unsteady Stall Flows of a Full Annulus Transonic Rotor
Authors: Im Hong-Sik , Chen Xiangying , Zha Ge-Cheng
Published: January 2011

This paper uses the advanced Delayed-Detached Eddy Simulation (DDES) of turbulence to simulate rotating stall inception of NASA Rotor 67. The rotor is a low-aspect-ratio transonic axial-flow fan with a tip speed of 429 m/s and a pressure ratio of 1.63. A full annulus simulation was employed with the time accurate compressible Navier-Stokes code in order to accurately capture the the formation of long-length disturbance and a short-length inception (spike). The validation for all numerical methods used in this study was accomplished by the comparisons of the CFD solutions with the test data in advance of unsteady simulations. Self-induced rotating stall development is simulated holding the same back pressure at the near stall experiment without any throttling. Spike type rotating stall occurs and rotates at roughly 50% of rotor speed counter to the rotation. After spike onset, rotating stall fully develops approximately within 2 rotor revolutions. Two distinct characteristics that can advance the mechanism of spike type rotating stall are observed. First, the passage shock is fully detached from rotor and decays during the spike inception. Consequently the shifted sonic line at the upstream of rotor allows stalling flow to propagate to the neighboring passage. Second, the trailing edge back flow contributes to the build up of a fully developed stall cell by pushing tip clearance flow toward blade leading edge and inducing tip spillage flow. Tip vortex originated from the leading edge dies out during spike inception as the swirl angle of incoming tip flow decreases, while in the unstalled passages it develops without breakdown. DDES challenge for the complete blade row reflects well the sequence of rotating stall and its unsteady behavior.
Experimental Investigation of the Steady and Unsteady Flow Field in a Single Stage Low Pressure Axial Compressor With a Circumferential Groove Casing Treatment
Authors: Van de Wyer N. , Farkas B. , Desset J. , Brouckaert J. F. , Thomas J.-F. , Hiernaux S.
Published: January 2011

This paper deals with the experimental investigation of the influence of a circumferential groove casing treatment on the performance and stability margin of a single stage low pressure axial compressor. The design of the compressor stage is representative of a booster stage for the new counter-rotating turbofan engine architecture and is characterized by unusually high loading and flow coefficients. The choice of the circumferential groove is described on the basis of a numerical parametric study on the number of grooves, the axial position, the depth and width of the groove. The experiments were performed at a Reynolds number corresponding to cruise conditions in the von Karman Institute closed loop high speed compressor test rig R4. The detailed performance characterization of the compressor stage with casing treatment was mapped at four operating points from choke to stall at design speed. The compressor stall limit was determined at several other off-design speeds. Detailed steady and unsteady measurements were performed to determine the flow field characteristics of the rotor and of the complete stage. Conventional pressure, temperature and directional probes were used along with fast response pressure sensors in the rotor casing and in the groove. Simultaneous traverses with a fast response total pressure probe were used to map the unsteady flow field at the rotor exit allowing an experimental capture of the tip leakage vortex path and extension through the rotor passage. A comparison of the flow features with and without casing treatment was performed and the results are discussed against 3D viscous computational predictions. The casing treatment did not present any improvement of the compressor stall margin but no significant performance degradation was observed either. The CFD predictions showed a good agreement with the measurements and their analysis supported the experimental results.
A Simplified Method With Local Correlations for the Analysis of Multistage Axial Turbines
Authors: Ratto Luca , Satta Antonio
Published: January 2011

A new through flow method, formulated in terms of pressure rather than velocity, for the analysis of multistage axial turbines is presented. It is designed to provide reliable radial distributions of circumferentially averaged values for the fundamental unknowns. This form of the radial equilibrium equation can represent also sharp velocity gradients in radial direction and interpret very realistic situations as discussed in the following applications. This result is more difficult to achieve if radial equilibrium is written in terms of velocity since this one approaches zero close to the wall. In order to demonstrate this statement, an experimental gas turbine, extensively analysed in literature, has been calculated and the results obtained by means of the proposed method have been compared with those circumferentially averaged derived from a 3D viscous calculation. Two stages of an industrial steam turbine have also been calculated with local semi-empirical correlations available in the open literature. Radial distributions of the fundamental quantities are successfully compared, in every station, with the mean circumferential values evaluated with a 3D viscous calculation. The differences are due to the approximations of the correlations employed.
Effect of Entraining Diffuser on the Performance of Bent Exhaust Ejectors
Authors: Maqsood Asim , Birk A. M.
Published: January 2011

This paper presents experimental data from subsonic air-air bent ejectors with ring type entraining diffusers. Three oblong ejectors with different degrees of bend in the mixing tubes were used in the study. The experiments were performed on a wind tunnel capable of providing air up to 2 kg/s. The performance was studied at different primary flow temperature and swirl conditions. Pressure, velocity and temperature was measured upstream of the primary nozzle and at the exit of the diffuser. Detailed traverses were done with 7-hole probes and thermocouples. As would be expected, the performance of the ejector decreases with the degree of bend. The diffusers were added to improve the pressure recovery in the ejector and for self cooling of the diffuser. Improved pressure recovery typically leads to improved pumping in ejectors. With the diffuser added, the overall length of the ejectors was increased from 2.5 to 3.8 times the mixing tube equivalent diameter. Different trends of pumping ratio with the swirl conditions were obtained with hot and cold primary flows.
Conceptual Studies of a Fuel-Flexible Low-Swirl Combustion System for the Gas Turbine in Clean Coal Power Plants
Authors: Smith Kenneth O. , Therkelsen Peter L. , Littlejohn David , Ali Sy , Cheng Robert K.
Published: January 2011

This paper reports the results of preliminary analyses that show the feasibility of developing a fuel flexible (natural gas, syngas and high-hydrogen fuel) combustion system for IGCC gas turbines. Of particular interest is the use of Lawrence Berkeley National Laboratory’s DLN low swirl combustion technology as the basis for the IGCC turbine combustor. Conceptual designs of the combustion system and the requirements for the fuel handling and delivery circuits are discussed. The analyses show the feasibility of a multi-fuel, utility-sized, LSI-based, gas turbine engine. A conceptual design of the fuel injection system shows that dual parallel fuel circuits can provide range of gas turbine operation in a configuration consistent with low pollutant emissions. Additionally, several issues and challenges associated with the development of such a system, such as flashback and auto-ignition of the high-hydrogen fuels, are outlined.
Aerothermal Research for Turbine Components: An Overview of the European AITEB-2 Project
Authors: Janke Erik , Wolf Torsten
Published: January 2011

The 6th European Frame Work Programme project AITEB-2 (Aero-thermal Investigations of Turbine Endwalls and Blades), started in March 2005 and was completed in August 2009. The project consortium of 17 partners brought together major European aero engine and gas turbine manufactures as well as leading European experts in the field of aero-thermodynamics to jointly address future challenges associated with the design of turbine components which are feasible from an aerodynamic, aero-thermal, economic and environmental point of view. The results presented show that the project was conducted successfully. Whereas not all of the ambitious project targets could be achieved, the outcome of both experimental and numerical efforts in the technical work packages lead to significant contributions to a) increased turbine efficiency, b) savings in cooling flows, c) aero-thermal technology for shorter turbine inter-ducts and, d) substantial savings in turn-around times within automated CFD based optimisation approaches.
Cogeneration Micro Turbine Fuelled by Solid Biomass: A Technical-Economic Study for Italy
Authors: Caresana Flavio , Comodi Gabriele , Pelagalli Leonardo , Vagni Sandro
Published: January 2011

The paper presents part of the results of two studies, the European “Radar” (Raising Awareness on renewable energy Developing Agro-eneRgetic chain models) Project and the “Energy and environmental plan for the consortium of the municipalities of the Esino-Frasassi mountain area”, conducted in an area in central Italy. The area is characterized by huge forestry biomass resources and by substantial amounts of agricultural residues. The work presents a technical-economic study of a cogeneration plant using a solid biomass-fuelled micro turbine as the prime mover. The energy conversion of solid biomass can be achieved with different technologies, e.g. organic Rankine cycles, micro turbines with an external combustion chamber, or Stirling engines. The choice of the conversion system depends mainly on biomass availability and on the level of user demand. Of the conversion technologies mentioned above, the micro turbine is suitable to meet the requirements of the cogeneration plant examined here, which is applied to a low thermal demand public building. The work describes a micro turbine based on a regenerative Brayton cycle endowed with an external combustion chamber. The inlet air, after being compressed, passes through a regenerator and then through an external furnace fuelled by solid biomass, where it is further heated, and finally expands through the turbine. The outlet air of the turbine, before being funnelled through the chimney, passes through the regenerator and subsequently through a dry kiln, thereby reducing the humidity of the solid biomass. The micro turbine studied produces 75 kWe and 300 kWt. The biomass is made up of olive tree prunings. After the technical analysis, an economic study stresses the critical role of incentives systems (herein provided by the Italian legislation) in making the technology appealing to investors in renewable energy solutions. The energy and economic analysis considers different combinations of three different amounts of annual operation hours, of two operating modes (with/without cogeneration) and three purchase prices of the solid biomass. The incentives mechanism considered is the Feed-In Tariff (FiT) granted by the Italian legislation for plants < 1 MWe. The economic analysis highlights some influential factors for solid biomass-fuelled systems: contract with fuel suppliers, biomass price, availability, transportation, storage, and processing, and plant location. In particular, the purchase price of solid biomass is substantially negotiated between the manager of the energy conversion plant and suppliers. The work demonstrates the crucial role of the incentives mechanisms for economic sustainability; the strong influence of biomass price on investment profitability; and the role of cogeneration in further shortening the payback period.
An Experimental and Computational Investigation of Tip Clearance Flow and Its Impact on Stall Inception
Authors: Bennington Matthew A. , Ross Mark H. , Cameron Joshua D. , Morris Scott C. , Du Juan , Lin Feng , Chen Jingyi
Published: January 2011

A numerical and experimental study was conducted to investigate the tip clearance flow and its relationship to stall in a transonic axial compressor. The CFD results were used to identify the existence of an interface between incoming axial flow and the reverse tip clearance flow. A surface streaking method was used to experimentally identify this interface as a line of zero axial shear stress at the casing. The position of this line, denoted xzs, moved upstream with decreasing flow coefficient in both the experiments and computations. The line was found to be at the rotor leading edge plane when the compressor stalled. Further measurements using rotor offset and inlet distortion further corroborated these results, and demonstrated that the movement of the interface upstream of the leading edge leads to the generation of rotating (“spike”) disturbances. Stall was therefore interpreted to occur as a result of a critical momentum balance between the approach fluid and the tip-leakage flow.
Investigation of Unsteady Flow Effects in an Axial Compressor Based on Whole Annulus Computations
Authors: Ro¨ber Thomas , Ku¨geler Edmund , Weber Anton
Published: January 2011

Flows in the first stages of axial compressors are subject to a number of unsteady effects which are not generally taken into account in standard investigations, e.g. transition under the influence of impinging wakes as well as that of downstream potential effects, or the influence of unsteady blade row interactions. For numerical studies of these phenomena, usually, simplifications are made to the test case in question. These simplifications include domain scaling, quasi-unsteady modeling, or modeling assumptions regarding boundary layer development, like wall functions; and their impact on the final result can be quite high. This paper is concerned with the investigation of unsteady blade row interactions in a 4.5 stage research compressor without any of these simplifications. To this end, the whole annulus of the first two stages of the compressor was meshed and unsteady RANS simulations were carried out at two different operating points. Spatial and temporal resolutions were fine enough to allow the investigation of transitional phenomena on the blade surface using an integral multi-mode transition model. For each operating point, one revolution was recorded after computations reached a periodic state. Examination of the boundary layer parameters shows that transition plays a considerable role for the first two compressor stages which were investigated in more detail. It was evident that the development of the blade boundary layer depends not only on incoming wakes from upstream blade rows; the precise transition location is also highly dependent on the potential effect of downstream blade rows.
Use of Photo-Stimulated Luminescence Piezospectroscopy and Lifing Models to Evidence Film Cooling Effect on EB-PVD Ceramic Thermal Barriers of Ex-Service Blades
Authors: Rinaldi Claudia , de Maria Letizia , del Corno Ada
Published: January 2011

The very scattered life times of thermal barrier coatings used on the first stage rotating blades of GTs used in power generation plants encourage the development of reliable non destructive techniques to reliably detect degradation before spalling. Among the optical non contact techniques Photo stimulated Luminescence PiezoSpectroscopy (PLPS) is promising as it lets to measure the residual compressive stress values of the thermally grown oxide (σTGO) at the interface between the BC and the ceramic top coat of EB-PVD thermal barriers. This paper underlines the potentiality of the photoluminescence piezospectroscopy as a diagnostic tool to assess the actual local film cooling efficiency on ex service blades with EB-PD TBCs. TGO stress values measured by PLPS (well related to the local degradation level of the interface, as observed on metallographic sections) result to be correlated with holes positions at all the different height of the blade examined. Moreover the reliability of the NDT evaluation is shown to increase significantly with an automatic PLPS instrumentation able to map σTGO in the regions of interest. The recorded large number of σTGO values suitably elaborated give a statistically significant evaluation of the degradation level reached by the TBC/BC interface, before spallation. A quantitative relationship between spent life fraction and σTGO formulated in the literature is here extended to ex-serviced blades to quantify the NDT result in terms of spent life fraction. These results are discussed in the light of T and spent life fraction estimates made with a simplified life model of TBC coatings.
Analysis on the Effect of a Non-Uniform Inlet Profile on Heat Transfer and Fluid Flow in Turbine Stages
Authors: Simone Salvadori , Montomoli Francesco , Martelli Francesco , Chana Kam S. , Qureshi Imran , Povey Tom
Published: January 2011

This paper presents an investigation of the aerothermal performance of a modern unshrouded high pressure (HP) aeroengine turbine subject to non-uniform inlet temperature profile. The turbine used for the study was the MT1 turbine installed in the QinetiQ Turbine Test Facility (TTF) based in Farnborough (UK). The MT1 turbine is a full scale transonic HP turbine, and is operated in the test facility at the correct non-dimensional conditions for aerodynamics and heat transfer. Datum experiments of aero-thermal performance were conducted with uniform inlet conditions. Experiments with nonuniform inlet temperature were conducted with a temperature profile that had a non-uniformity in the radial direction defined by (Tmax−Tmin)/T = 0.355, and a non-uniformity in the circumferential direction defined by (Tmax−Tmin)/T = 0.14. This corresponds to an extreme point in the engine cycle, in an engine where the non-uniformity is dominated by the radial distribution. Accurate experimental area surveys of the turbine inlet and exit flows were conducted, and detailed heat transfer measurements were obtained on the blade surfaces and end-walls. These results are analysed with the unsteady numerical data obtained using the in-house HybFlow code developed at the University of Firenze. Two particular aspects are highlighted in the discussion: prediction confidence for state of the art computational fluid dynamics (CFD) and impact of real conditions on stator-rotor thermal loading. The efficiency value obtained with the numerical analysis is compared with the experimental data and a 0.8% difference is found and discussed. A study of the flow field influence on the blade thermal load has also been detailed. It is shown that the hot streak migration mainly affects the rotor pressure side from 20% to 70% of the span, where the Nusselt number increases by a factor of 60% with respect to the uniform case. Furthermore, in this work it has been found that a nonuniform temperature distribution is beneficial for the rotor tip, contrary to the results found in the open literature. Although the hot streak is affected by the pressure gradient across the tip gap, the radial profile (which dominates the temperature profile being considered) is not fully mixed out in passing through the HP stage, and contributes significantly to cooling the turbine casing. A design approach not taking into account these effects will underestimate to rotor life near the tip and the thermal load at mid-span. The temperature profile that has been used in both the experiments and CFD is the first simulation of an extreme cycle point (more than twice the magnitude of distortion all previous experimental studies): it represents an engine-take-off condition combined with the full combustor cooling. The research was part of the EU funded TATEF2 (Turbine Aero-Thermal External Flows 2) programme.
Pseudo-Density Approach to the Solution of a Thin Rotating Turbine Engine Disk
Authors: Jettappa Richard Rodrigues
Published: January 2011

This paper considers a rotating gas turbine engine disk. The governing equations lead to a non-linear, second order equation with thickness h as parameter. “Thin disk” assumption is made, implying plane stress conditions. In the present study, starting from the equations of equilibrium and compatibility, the author proposes the new approach of Pseudo Material Density. By introducing a pseudo material density, the problem is reduced to the Flat Disk Equation that can be solved easily. Introduction of pseudo density, however, throws up an additional equation — a fourth one — relating the pseudo density, actual density and the thickness parameter. The equation is solved to find the shape of the disk in terms of the actual density. This procedure allows modeling of the non-uniform profile disk as a disk with flat profile facilitating easier analysis. An unexpected, but important result that emerges from the present study pertains to the proof testing of rotating disks. It is shown that it is now possible to replace the external blade loading exactly with a radial extension of the disk itself.