bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and Characterization of Micro-Compressor Impellers
Authors: Sirakov Borislav , Gong Yifang , Epstein Alan , Tan Choon
Published: November 2008

A study has been conducted, using steady three-dimensional Reynolds-averaged Navier-Stokes simulations (FLUENT) to investigate dominant performance limiting mechanisms for micro-scale, high-speed compressor impellers with diameter in the range of 5mm to 10mm and peripheral speed ∼ 500 ms−1. Heat transfer to impeller flow (hence non-adiabatic in contrast to nearly adiabatic macro-scale centrifugal compressors for aircraft engine application), casing drag, and impeller passage boundary layer loss are identified as micro-scale impeller performance limiting mechanisms. Heat transfer could lead to up to 25 efficiency points penalty, casing drag to about 10–15 points, and passage boundary layer loss to another 10 points for the investigated micro-impellers. Micro-impeller efficiency of up to 90% is achievable if design is directed at mitigating these performance limiting mechanisms. The effect of heat addition on impeller performance is detrimental and depends on a single non-dimensional parameter (ratio of added heat to inlet stagnation enthalpy). The performance penalty is associated with the physical fact that compression at high temperatures requires more work. Casing drag associated with impeller rotating relative to stationary casing results in a torque on the flow near the casing and impeller blade tip that can be characterized in terms of rotational Reynolds number and ratio of tip clearance to impeller radius. Channel boundary layer loss can be characterized in terms of Reynolds number, geometry (impeller exit-to-inlet diameter ratio, blade angles, chord-to-inlet diameter ratio, average-to inlet span ratio, inlet diameter-to-inlet span ratio), and exit-to-inlet temperature ratio related to work input (rotor geometry and speed). A physics-based model is developed for quantifying each of these performance-limiting processes, given the key design parameters. The results from the models are in accord with CFD (FLUENT) data. Implications on impeller design are discussed and design guidelines are formulated. The paper reports a quantitative investigation of micro-turbomachinery performance limiting mechanisms and offers design guidelines based on physical understanding.
Numerical Investigations About the Vaneless Counter-Rotating Turbine for Cold-Air Test
Authors: Ji L. C.
Published: November 2008

Vaneless Counter-Rotating Turbine (VCRT) is taken as an important component technique to greatly improve the performance of aircraft engine. However design problems involved in a practicable VCRT is far from being resolved. Based on previous studies, the design process of a VCRT for cold-air test is presented. The design target is for practical use. The design is based on iterations between airfoil blading and numerical analysis of 3D steady viscous flow. Results indicate the performance of VCRT might be proper for practical use. To investigate the control problem in engines that use this type of VCRT, variable vane is tested numerically. Off-design operations are also simulated. The engine with the VCRT shows severe control problems. Variable vane and changing exhaust nozzle area may be two selectable ways.
Nuclear Desalination the Small and Peaceful Way
Authors: Crommelin Gulian A. K. , Crommelin Walter F.
Published: November 2008

This study is about a much discussed and recommended application of a nuclear gas turbine and was undertaken at the request of many visitors to the Nuclear Gas Turbine stand at the ASME IGTI 2002 in Amsterdam. Apparently, the specifications of the NEREUS plant led their thoughts to small-scale energy production combined with fresh water production. This thought fits well into the basic idea that: Energy equals Electricity, Heat and Fresh Water. The NEREUS project is a non-profit organisation seeking to expand the use of Small Scale Nuclear Power Generation. This paper discusses the possibilities to produce fresh water with a NEREUS inherently safe nuclear power plant. The acronym NEREUS describes very well the goals of this project and stands for: A Natural safe, Efficient, Reactor, Easy to operate, Ultimately simple and Small. Fresh water can be produced using any fossil fuelled energy conversion unit, but this study works out how the advantages of a gas turbine in combination with an inherently safe and well-proven nuclear heat source combines the advantages of a gas turbine with the logistic advantages of nuclear power. The paper starts with an introduction on why the energy conversion branch should pay more attention to fresh water production. Secondly the paper gives an overview of the main characteristics of the nuclear heat source. Thirdly the paper briefly explains the most common methods used for fresh water produced. Finally the paper will discuss the conclusion of this study, which was: The ENERGY demand of 27648 people can be fully and affordably satisfied in both quantity and quality, with a well-proven, inherently safe, self controlling nuclear pebble-bed 20 MWth reactor. Such a reactor is suitable for unmanned operation with a three year refuelling and maintenance cycle, and with the dimensions of 10 × 10 × 10 meters.
Flow Field and Structure of Swirl Stabilized Non-Premixed Natural Gas Flames at Elevated Pressure
Authors: Janus Bertram , Dreizler Andreas , Janicka Johannes
Published: November 2008

This study reports on measurements in a generic non-premixed gas turbine combustor segment. Flow and scalar field were characterized using advanced laser diagnostic methods. The optically accessible burning chamber allowed for measurement of inflow conditions close-by the nozzle important for comparisons with numerical simulations. The generic nozzle design is sufficiently simplified to be precisely reproduced by block structured computational grids but shows typical features of gas turbine applications. To expose the influence of heat release on the flow field properties both isothermal and combusting conditions were investigated. Striking features of the present configuration are a detached flame, multiple recirculation zones, and complex coherent flow structures.
Optimization of Three-Dimensional Angled Ribs With RANS Analysis of Turbulent Heat Transfer
Authors: Kim Hong-Min , Kim Kwang-Yong
Published: November 2008

A numerical optimization procedure for the shape of three-dimensional channel with angled ribs mounted on one of the walls to enhance turbulent heat transfer is presented. The response surface based global optimization with Reynolds-averaged Navier-Stokes analysis of fluid flow and heat transfer is used. Shear stress transport (SST) turbulence model is used as a turbulence closure. Computational results for local heat transfer rate show a reasonable agreement with the experimental data. The pitch-to-height ratio of the rib and rib height-to-channel height ratio are set to be 9.0 and 0.1, respectively, and width-to-rib height ratio and attack angle of the rib are chosen as design variables. The objective function is defined as a linear combination of heat-transfer and friction-loss related terms with the weighting factor. Full-factorial experimental design method is used to determine the data points. Optimum shapes of the channel have been obtained in the range from 0.0 to 0.1 of the weighting factor.
Effect of Tip Clearance on Stall Evolution Process in a Low-Speed Axial Compressor Stage
Authors: Inoue Masahiro , Kuroumaru Motoo , Yoshida Shinichi , Minami Takahiro , Yamada Kazutoyo , Furukawa Masato
Published: November 2008

Effect of the tip clearance on the transient process of rotating stall evolution has been studied experimentally in a low-speed axial compressor stage with various stator-rotor gaps. In the previous authors’ experiments for the small tip clearance, the stall evolution process of the rotor was sensitive to the gaps between the blade rows. For the large tip clearance, however, little difference is observed in the evolution processes independently of the blade row gap. In the first half process, it is characterized by gradual reduction of overall pressure-rise with flow rate decreasing, and the number of short length-scale disturbances is increasing with their amplitude increasing. In the latter half a long length-scale disturbance develops rapidly to result in deep stall. Just before the stall inception the spectral power density of the casing wall pressure reveals the existence of rotating disturbances with broadband high frequency near a quarter of the blade passing frequency. This is caused by the short length-scale disturbances occurring intermittently. A flow model is presented to explain mechanisms of the rotating short length-scale disturbance, which includes a tornado-like separation vortex and tip-leakage vortex breakdown. The model is supported by a result of a numerical unsteady flow simulation.
Chemical Looping Combustion-Analysis of Natural Gas Fired Power Cycles With Inherent CO2 Capture
Authors: Naqvi Rehan , Bolland Olav , Brandvoll O̸yvind , Helle Kaare
Published: November 2008

In this paper an alternative to so-called ‘oxy-fuel’ combustion has been evaluated. Chemical Looping Combustion (CLC) is an innovative concept of CO2 capture from combustion of fossil fuels in power plants. CLC is closely related to oxy-fuel combustion as the chemically bound oxygen reacts in a stoichiometric ratio with the fuel. In CLC, the overall combustion takes place in two steps. In a reduction reactor fuel is oxidised by the oxygen carrier i.e. the metal oxide MeO which is reduced to metal oxide with a lower oxidation number, Me. Me flows to an oxidation reactor where it is oxidised by oxygen in the air. In this way pure oxygen is supplied to fuel without using an energy intensive traditional air separation unit. This paper presents thermodynamic cycle analysis of a CLC-power plant. A steady-state model has been developed for the solid-gas reactions occurring in the reactor system. The model is applied to analyse the system under two configurations; a combined cycle and a conventional steam cycle. A turbine-cooling model has also been implemented to evaluate the turbine cooling penalty in the combined cycle configuration. Effects of exhaust recirculation for coking prevention and incomplete fuel conversion have also been investigated. Performance of the oxygen carrier has been idealised except for the degrees of reduction and oxidation. Energy needs for CO2 capture have properly been taken into account. The results show that an optimum efficiency of 49.7% can be achieved under given conditions with a CLC-combined cycle at zero emissions level. With turbine cooling, efficiency falls by 1.2% points under the same conditions. The CLC-steam cycle is capable of achieving 40.1% efficiency with zero emissions. The results show that CLC has high potential for power generation with inherent CO2 capture. This work will be useful in designing CLC systems after the reactor system has been analysed experimentally for long-term operations.
Influence of Hot Streak Circumferential Length-Scale in Transonic Turbine Stage
Authors: He L. , Menshikova V. , Haller B. R.
Published: November 2008

A computational study is carried out on the influence of turbine inlet temperature distortion (hot streak). The hot streak effects are examined from both aeromechanical (forced blade vibration) and aero-thermal (heat transfer) points of view. Computations are firstly carried out for a transonic HP turbine stage, and the steady and unsteady surface pressure results are compared with the corresponding experimental data. Subsequent analysis is carried out for hot-streaks with variable circumferential wavelength, corresponding to different numbers of combustion burners. The results show that the circumferential wavelength of the temperature distortion can significantly change unsteady forcing as well as the heat-transfer to rotor blades. In particular, when the hot-streak wavelength is the same as the nozzle guide vane (NGV) blade pitch, there is a strong dependence of the preferential heating characteristics on the relative clocking position between hot-streak and NGV blade. However, this clocking dependence is shown to be qualitatively weakened for the cases with fewer hot streaks with longer circumferential wavelengths.
Methods and Tools for Multidisciplinary Optimization of Axial Turbine Stages With Relatively Long Blades
Authors: Moroz Leonid , Govoruschenko Yuri , Romanenko Leonid , Pagur Petr
Published: November 2008

An effective methodology for optimal design of axial turbine blades is presented. It has been used for achieving stage maximal efficiency meeting both stress-strain and vibration reliability requirements and taking into account technological limitations.
Degradation Mechanism Characterization and Remaining Life Prediction for NiCoCrAlY Coatings
Authors: Chan K. S. , Cheruvu N. S.
Published: November 2008

The cyclic oxidation behaviors of two NiCoCrAlY coatings, which are PWA 286 and CT102 (GT33-like), were characterized using one-hour thermal cycles between ambient temperature and a peak temperature at either 1010°C or 1066°C. Weight change curves were generated as a function of thermal cycles. During cyclic oxidation testing, selected test specimens were removed and sectioned to characterize the coating degradation processes, such as oxidation attack, type and morphology of oxides, Al depletion, β-phase exhaustion, microstructural changes, and thermal fatigue crack formation. These experimental data were utilized in conjunction with a coating lifing model, called COATLIFE, to develop coating life diagrams that depicts the useful life of the coatings as a function of cycle time. Application of the COATLIFE approach and the coating life diagrams to predicting the remaining lives of GT33-like and PWA 286 coatings are demonstrated for turbine blades in land-based combustion gas turbines.
High Vacuum Brazing of Fe-Cr-Al-Y Honeycomb
Authors: Sporer Dieter R. , Reinkensmeier Ingo
Published: November 2008

M-Cr-Al-Y and in particular Fe-Cr-Al-Y alloys with high aluminium matrix content have a tendency to form thin, stable and tightly adherent alumina scales even at low oxygen partial pressures. This forms the basis of their superior hot gas oxidation, carburization and sulfidation resistance when used at high temperatures. However, the same tendency makes the alloys more difficult to braze because the easily formed and highly stable ceramic surface layers significantly reduce wettability and hence braze flow. Fe-Cr-Al-Y alloys have recently been suggested as promising alloys for use in gas turbine engines as abradable honeycomb gas path seals. This paper reviews the vacuum brazing of honeycombs made from highly alloyed Fe-Cr-Al-Y foils to metal backing members. Most suitable Fe-Cr-Al-Y materials, commercial braze filler alloys and braze cycles are presented. Emphasis is placed on industrial equipment rather than laboratory vacuum furnaces. Brazing under high vacuum conditions in all-metal furnaces is recommended as a brazing procedure for honeycomb made from MI 2100, which is high in aluminium content, to various commonly used carrier structure alloys.
Performance Evaluation of Hybrid (Ceramic on Steel) Bearings With Advanced Aircraft Engine Oils for Lubrication
Authors: Wang L. , Wood R. J. K. , Powrie H. E. G. , Streit E. , Care I.
Published: November 2008

Hybrid bearings (silicon nitride rolling elements and steel raceways) are being developed for the new generation of gas turbine engines, as they offer weight savings, reduced heat rejection and can operate at higher DN (bore diameter in mm × shaft rotational speed in rpm) values than conventional steel bearings. In the present study, various advanced synthetic aviation oils were tested on a pin-on-disc tribometer. Conditions were chosen to simulate engine low load and ambient start up, where sliding is a factor. The tests used a silicon nitride ball sliding against an M50NiL bearing steel disc. Fresh oils were tested for the hybrid contacts under high sliding speed of 7 ms−1 and normal aircraft engine bearing contact pressure of 2.8 GPa [1]. The results showed that most of the synthetic aviation oils in use today would provide similar protection for the hybrid contacts against scuffing. Initial studies, aimed at identifying the influence of oil degradation and effects of additive depletion are also presented. The oils were ranked based on the contact wear rate. Electrostatic charge measurements were made along with wear, friction and surface temperature measurements to monitor the on-line wear conditions [2–3]. Electrostatic sensing shows promise as a monitoring technique for oil lubricated hybrid contacts. Polishing wear mechanisms and iron-based material transfer from disc to ball were identified by Field Emission Gun Scanning Electron Microscopy (FEG-SEM) and Energy-Dispersive X-ray (EDX) as the dominant degradation process in these hybrid contacts.
Set Up of a Robust Neural Network for Gas Turbine Simulation
Authors: Bettocchi R. , Pinelli M. , Spina P. R. , Venturini M. , Burgio M.
Published: November 2008

In this paper, Neural Network (NN) models for the real-time simulation of gas turbines are studied and developed. The analyses carried out are aimed at the selection of the most appropriate NN structure for gas turbine simulation, in terms of both computational time of the NN training phase and accuracy and robustness with respect to measurement uncertainty. In particular, feed-forward NNs, with a single hidden layer and different numbers of neurons, trained by using a back-propagation learning algorithm are considered and tested. Finally, a general procedure for the validation of computational codes is adapted and applied to the validation of the developed NN models.
Endwall Boundary Layer Control in Compressor Cascades
Authors: Mu¨ller Ralf , Vogeler Konrad , Sauer Helmut , Hoeger Martin
Published: November 2008

Recent investigations have shown a reduction of secondary losses in compressor cascades using a bulb like modification of the profile at the endwall. This paper is focussed on experimental work in comparison of 5 different endwall modifications at a compressor cascade. The cascade is modified near the endwall with a bulb, a medium and a large fillet. The fillet configurations are modified by an axial blunt cut-off at the leading edge. The investigations have been carried out at a profile developed from a hub section of the Dresden Low Speed Research Compressor (LSRC) blade, a compressor profile with a nominal turning of 18 deg. A datum configuration and the 5 other configurations were tested at the Low Speed Cascade Windtunnel (LSCW). For the bulb configuration, an intensified horse shoe vortex was suspected and observed counterrotating to the passage vortex with an influence on its propagation. The interaction of the passage vortex and the suction side profile boundary layer is influenced. The superposition of both is minimized and the losses developing from this effect are significant lower. For the fillet and blunt-fillet configurations, a fillet vortex develops and was observed co-rotating to the passage vortex with an influence on the mentioned interaction as well. Blunt leading edges produce additional losses but the superposition of the growing vortices may reduce the overall losses. The cases show a reduction in losses of 1.9% for 3 deg incidence and a range of 1.2% rise to 1.9% reduction in dependence of the incidence. This equals a reduction of the isolated secondary losses up to 28% with respect to the reference profile. Detailed results of the experiments are presented for the reference and all modified cascades.
A Correlation-Based Transition Model Using Local Variables: Part II — Test Cases and Industrial Applications
Authors: Langtry R. B. , Menter F. R. , Likki S. R. , Suzen Y. B. , Huang P. G. , Vo¨lker S.
Published: November 2008

A new correlation-based transition model has been developed, which is built strictly on local variables. As a result, the transition model is compatible with modern CFD methods using unstructured grids and massive parallel execution. The model is based on two transport equations, one for the intermittency and one for the transition onset criteria in terms of momentum thickness Reynolds number. The proposed transport equations do not attempt to model the physics of the transition process (unlike e.g. turbulence models), but form a framework for the implementation of correlation-based models into general-purpose CFD methods. Part I of this paper gives a detailed description of the mathematical formulation of the model and some of the basic test cases used for model validation. Part II (this part) of the paper details a significant number of test cases that have been used to validate the transition model for turbomachinery and aerodynamic applications, including the drag crisis of a cylinder, separation induced transition on a circular leading edge and natural transition on a wind turbine airfoil. Turbomachinery test cases include a highly loaded compressor cascade, a low-pressure turbine blade, a transonic turbine guide vane, a 3-D annular compressor cascade and unsteady transition due to wake impingement. In addition, predictions are shown for an actual industrial application, namely a GE Low-Pressure turbine vane. In all cases good agreement with the experiments could be achieved and the authors believe that the current model is a significant step forward in engineering transition modeling.
Nonlinear Heat-Release/Acoustic Interactions in a Gas Turbine Combustor
Authors: Bellows Ben , Lieuwen Tim
Published: November 2008

This paper describes an experimental investigation of the response of the flame in a lean, premixed combustor to imposed acoustic oscillations. The ultimate objective of this work is to develop capabilities for predicting the amplitude of combustion instabilities in gas turbines. Simultaneous measurements of CH* and OH* chemiluminescence, pressure, and velocity were obtained over a range of forcing amplitudes and frequencies. These data show that nonlinearity in the heat release/acoustic transfer function is manifested in two ways. First, the flame chemiluminescence response to imposed oscillations saturates at pressure and velocity amplitudes on the order of p’/po ∼0.02 and u’/uo∼0.3. In addition, the phase between the CH* or OH* oscillations and acoustic oscillations exhibits some amplitude dependence, even at disturbance amplitudes where the amplitude transfer function is linear. We also find that the response of this swirling, highly turbulent flame exhibits similarities to those of simple, laminar flame configurations. First, the “linear”, low amplitude flame response is similar to the laminar, V-flame measurements and predictions of Schuller et al. [1]. Also, at large disturbance amplitudes, the subharmonic characteristics of the oscillations exhibit analogous characteristics to those observed by Bourehla & Baillot [2] in a conical Bunsen flame, and Searby & Rochwerger [3] in a flat flame.
High Resolution Infrared Thermography for Airfoils Boundary Layer Inspection in Passive Mode
Authors: Desideri Umberto , Rossi Gianluca , Giovannozzi Alessandro , Maggiorana Paolo
Published: November 2008

In thermo-fluid-dynamics, the important role played by the boundary layer phenomena is well known. In order to set up an experimental tool, able to measure fluid dynamic magnitudes in the boundary layer, many efforts have been made and some advanced measurements have been developed. Since the mid-sixties, infrared thermography has been applied as a measurement technique. Primarily, this technique was used in space missions where the protection of space vehicles in the reentry phase was of prime importance. Nowadays, thermography is one of the most advanced non-intrusive measurement techniques and present many advantages such as no-needs for particular settings of system under analysis. Therefore, considering that boundary layer continues to be a fundamental aspect in fluid-dynamics studies, the present work wants to dwell on the possibility to enlarge the application of the infrared measurement technique, in particular for subsonic flows in passive mode. These conditions point out important problems of measurement for the low energy content and for the type of thermal exchange that can not be simplified as it is traditionally made in supersonic flows. Either the possibility to operate with modern infrared cameras or the improvements of new theoretical models in the data reduction process will be described in this paper and an application to an airfoil will be presented. The measurement technique used in this paper can be applied to any aerodynamic profile and can be easily used as a non intrusive technique to characterize the flow fields of blade cascades for gas tubrines and turbomachinery in general.
Influence of Blade Sweep on the Energetic Behavior of Axial Flow Turbomachinery Rotors at Design Flow Rate
Authors: Vad Ja´nos , Kwedikha Ali R. A. , Jaberg Helmut
Published: November 2008

Experimental and computational studies were carried out in order to survey the energetic aspects of forward and backward sweep in axial flow rotors of low aspect ratio blading for incompressible flow. It has been pointed out that negative sweep tends to increase the lift, the flow rate and the ideal total pressure rise in the vicinity of the endwalls. Just the opposite tendency was experienced for positive sweep. The local losses were found to develop according to combined effects of sweep near the endwalls, endwall and tip clearance losses, and profile drag influenced by re-arrangement of the axial velocity profile. The forward-swept bladed rotor showed reduced total efficiency compared to the unswept and swept-back bladed rotors. This behavior has been explained on the basis of analysis of flow details. It has been found that the swept bladings of low aspect ratio tend to retain the performance of the unswept datum rotor even in absence of sweep correction.
Effects of Spray Parameters and Operating Conditions on an Industrial Gas Turbine Washing System
Authors: Mund Friederike C. , Pilidis Pericles
Published: November 2008

Gas turbines for power generation are exposed to a variety of ambient conditions and are therefore bound to breathe contaminated airflow, thus degrading the engines internal gas path. In particular, accumulated debris on the compressor blades reduces engine efficiency. To recover this performance loss, online compressor washes may be performed. Cleaning fluid is injected through the nozzles upstream of the compressor to wash off the debris from the blades. This paper presents a numerical study of a generic compressor washing system based on an application case for a heavy duty gas turbine power plant. The inlet duct of the engine was modeled and droplet trajectories were calculated. Different spray patterns including single jet and full cone have been investigated for different ranges of injection velocity and droplet size. The spray angle was evaluated experimentally and was used to model the full cone spray pattern. The boundary conditions for the airflow were iterated with a performance simulation tool to match pressure loss and mass flow. To investigate the effect of different operating conditions on the airflow and spray distribution, an installation scenario of the engine at altitude on a hot summer day was modeled. The scenario was based on a review of plant installations and local meteorological conditions. Fluid concentration plots at the compressor inlet plane were evaluated for the different computational cases. Generally with lower injection momentum, the water droplets were significantly deflected by the main airflow. Higher injection velocity and droplet size reduced the effect of the main airflow. Different operating conditions and the significant change of air mass flow affected the spray distribution of the washing system at the compressor inlet. This can be compensated by adjusting the injection angles.
High Temperature Stability of MGCs Gas Turbine Components in Air and Combustion Gas Flow Environments
Authors: Nakagawa Narihito , Ohtsubo Hideki , Shibata Kohji , Mitani Atsuyuki , Shimizu Kazutoshi , Waku Yoshiharu
Published: November 2008

Melt growth composites (MGCs) have a unique microstructure, in which continuous networks of single-crystal phases interpenetrate without grain boundaries. Therefore, the MGCs have excellent high-temperature strength characteristics, creep resistance, oxidation resistance and thermal stability in an air atmosphere at very high temperature. To achieve ultra-high thermal efficiency and low NOx emission for gas turbine systems, non-cooled turbine nozzle vanes and heat shield panels of combustor liners has been fabricated on an experimental basis. These components are thermally stable after heat treatment at 1700°C for 1000 hours in an air atmosphere. In addition, we have just started the exposure tests to evaluate the influence of combustion gas flow environment on MGCs.
Investigation of a Novel Secondary Flow Feature in a Turbine Cascade With End Wall Profiling
Authors: Ingram Grant , Gregory-Smith David , Harvey Neil
Published: November 2008

A novel secondary flow feature, previously unreported for turbine blading as far as the authors are aware, has been discovered. It has been found that it is possible to separate part of the inlet boundary layer on the blade row end wall as it is being over-turned and rolled up into the passage vortex. This flow feature has been discovered during a continuing investigation into the aerodynamic effects of non-axisymmetric end wall profiling. Previous work, using the low speed linear cascade at Durham University, has shown the potential of end wall profiling for reducing secondary losses. The latest study, the results of which are described here, was undertaken to determine the limits of what end wall profiling can achieve. The flow has been investigated in detail with pressure probe traversing and surface flow visualization. This has found that the inlet boundary locally separates, on the early suction side of the passage, generating significant extra loss which feeds directly into the core of the passage vortex. The presence of this new feature gives rise to the unexpected result that the secondary flow, as determined by the exit flow angle deviations and levels of secondary kinetic energy, can be reduced while at the same time the loss is increased. CFD was found to calculate the secondary flows moderately well compared with measurements. However, CFD did not predict this new feature, nor the increase in loss it caused. It is concluded that the application of non-axisymmetric end wall profiling, although it has been shown to be highly beneficial, can give rise to adverse features that current CFD tools are unable to predict. Improvements to CFD capability are required in order to be able to avoid such features, and obtain the full potential of end wall profiling.
Unsteady Flow Structures in Radial Swirler Fed Fuel Injectors
Authors: Midgley Kris , Spencer Adrian , McGuirk James J.
Published: November 2008

Many fuel injector geometries proposed for lean-premixed combustion systems involve the use of radial swirlers. At the high swirl numbers needed for flame stabilisation, several complex unsteady fluid mechanical phenomena such as vortex breakdown and recirculation zone precession are possible. If these unsteady aerodynamic features are strongly periodic, unwanted combustion induced oscillation may result. The present paper reports on an isothermal experimental study of a radial swirler fed fuel injector, and examines the dynamical behaviour of the unsteady aerodynamic flow structures observed. Particle Image Velocimetry (PIV) is used to capture the instantaneous appearance of vortex structures both internal to the fuel injector, and externally in the main flame-stabilising recirculation zone. Multiple vortex structures are observed. Vector field analysis is used to identify specific flow structures and perform both standard and conditional time averaging to reveal the modal characteristics of the structures. This allows analysis of the origin of high turbulence regions in the flow and links between internal fuel injector vortex breakdown and external unsteady flow behaviour. The data provide a challenging test case for Large Eddy Simulation methods being developed for combustion system simulation.
Developing a Combustor Simulator for Investigating High Pressure Turbine Aerodynamics and Heat Transfer
Authors: Barringer M. D. , Thole K. A. , Polanka M. D.
Published: November 2008

Within a gas turbine engine, the high pressure turbine vanes are subjected to very harsh conditions from the highly turbulent and hot gases exiting the combustor. The temperature and pressure fields exiting the combustor dictate the heat transfer and aero losses that occur in the turbine passages. To better understand these effects, the goal of this work is to develop an adjustable combustor exit profile simulator for the Turbine Research Facility (TRF) at the Air Force Research Laboratory (AFRL). The TRF is a high temperature, high pressure, short duration blow-down test facility that is capable of matching several aerodynamic and thermal non-dimensional engine parameters including Reynolds number, Mach number, pressure ratio, corrected mass flow, gas-to-metal temperature ratio, and corrected speed. The research objective was to design, install, and verify a non-reacting simulator device that provides representative combustor exit total pressure and temperature profiles to the inlet of the TRF turbine test section. This required the upstream section of the facility to be redesigned into multiple concentric annuli that serve the purpose of injecting high momentum dilution jets and low momentum film cooling jets into a central annular chamber, similar to a turbine engine combustor. The design of the simulator allows for variations in injection levels to generate turbulence and pressure profiles. It also can vary the dilution and film cooling temperatures to create a variety of temperature profiles consistent with real combustors. To date, the design and construction of the simulator device has been completed. All of the hardware has been trial fitted and the flow control shutter systems have been successfully installed and tested. Currently, verification testing is being performed to investigate the impact of the generated temperature, pressure, and turbulence profiles on turbine heat transfer and secondary flow development.
Analysis of Performance and Rotordynamic Force Coefficients of Brush Seals With Reverse Rotation Ability
Authors: Delgado Adolfo , San Andre´s Luis , Justak John F.
Published: November 2008

Multiple-shoed brush seals represent an alternative to resolve poor reliability resulting from bristle tip wear while also allowing for reverse rotation operation. The novel configuration incorporates pads contacting the shaft, and which under rotor spinning; lift off due to the generation of hydrodynamic pressures. The ensuing gas film prevents intermittent contact; thus lowering the operating temperature and thermal distortions, and even eliminating bristles’ wear. A computational analysis for the equilibrium and dynamic forced response of a brush seal with reverse rotation capability is presented. Small amplitude rotor motions about an equilibrium position lead to a nonlinear partial differential equation for the static pressure field, and a set of first order linear partial differential equations to determine the rotordynamic force coefficients, stiffness and damping, as function of the excitation frequency and other operating conditions. Predictions for the stiffness and damping coefficients of a 20 shoe-brush seal configuration operating over a range of rotor speeds are detailed. The parametric study varies the nominal gas film thickness, the supply to discharge pressure ratio, and the bristle bed structural loss (damping) coefficient. The results show that the film clearance and supply to discharge pressure ratio do not affect the shoed-brush seal force coefficients. On the other hand, the direct stiffness drops rapidly as the operating speed increases. The shoed-brush seal offers whirl frequency ratios much lower than 0.50 due to the (structural) damping arising from friction among the brush seal bristles.
Influence of Surface Roughness on Three-Dimensional Separation in Axial Compressors
Authors: Gbadebo Semiu A. , Hynes Tom P. , Cumpsty Nicholas A.
Published: November 2008

Surface roughness on a stator blade was found to have a major effect on the three-dimensional (3D) separation at the hub of a single-stage low-speed axial compressor. The change in the separation with roughness worsened performance of the stage. A preliminary study was carried out to ascertain which part of the stator suction surface and at what operating condition the flow is most sensitive to roughness. The results show that stage performance is extremely sensitive to surface roughness around the leading edge and peak-suction regions, particularly for flow rates corresponding to design and lower values. Surface flow visualization and exit loss measurements show that the size of the separation, in terms of spanwise and chordwise extent, is increased with roughness present. Roughness produced the large 3D separation at design flow coefficient that is found for smooth blades nearer to stall. A simple model to simulate the effect of roughness was developed and, when included in a 3D Navier-Stokes calculation method, was shown to give good qualitative agreement with measurements.
Active Flow Control Using Steady Blowing for a Low-Pressure Turbine Cascade
Authors: McAuliffe B. R. , Sjolander S. A.
Published: November 2008

The paper presents mid-span measurements for a turbine cascade with active flow control. Steady blowing through an inclined plane wall jet has been used to control the separation characteristics of a high-lift low-pressure turbine airfoil at low Reynolds numbers. Measurements were made at design incidence for blowing ratios from approximately 0.25 to 2.0 (ratio of jet-to-local freestream velocity), for Reynolds numbers of 25000 and 50000 (based on axial chord and inlet velocity), and for freestream turbulence intensities of 0.4% and 4%. Detailed flow field measurements were made downstream of the cascade using a three-hole pressure probe, static pressure distributions were measured on the airfoil suction surface, and hot-wire measurements were made to characterize the interaction between the wall jet and boundary layer. The primary focus of the study is on the low-Reynolds number and low-freestream turbulence intensity cases, where the baseline airfoil stalls and high profile losses result. For low freestream turbulence (0.4%), the examined method of flow control was effective at preventing stall and reducing the profile losses. At a Reynolds number of 25000, a blowing ratio greater than 1.0 was required to suppress stall. At a Reynolds number of 50000, a closed separation bubble formed at a very low blowing ratio (0.25) resulting in a significant reduction in the profile loss. For high freestream turbulence intensity (4%), where the baseline airfoil has a closed separation bubble and low profile losses, blowing ratios below 1.0 resulted in a larger separation bubble and higher losses. The mechanism by which the wall jet affects the separation characteristics of the airfoil is examined through hot-wire traverse measurements in the vicinity of the slot.
Modeling of Boundary-Layer Transition
Authors: Roberts S. K. , Yaras M. I.
Published: November 2008

This paper presents a mathematical model for predicting the rate of turbulent spot production. In this model, attached- and separated-flow transition are treated in a unified manner, and the boundary layer shape factor is identified as the parameter with which the spot production rate correlates. The model is supplemented by several correlations to allow for its practical use in the prediction of the length of the transition zone. Secondly, the paper presents a model for the prediction of the location of transition inception in separation-bubbles. The model improves on the accuracy of existing alternatives, and is the first to account for the effects of surface roughness.
Boundary-Layer Transition in Separation Bubbles Over Rough Surfaces
Authors: Roberts S. K. , Yaras M. I.
Published: November 2008

This paper documents the effects of surface roughness on boundary layer transition in separation-bubbles under low free-stream turbulence conditions (<1%). The experiments were performed on a flat surface, upon which a pressure distribution similar to those prevailing on the suction side of low-pressure turbine blades was imposed. The test matrix consists of four variations in the roughness conditions, including a reference test case with a smooth surface. The remaining roughness levels are typical of in-service turbine blades in gas turbine engines. The measurements were performed at flow Reynolds numbers of 350,000 and 470,000, based on the length of the test surface. The separation, transition inception, transition completion, and re-attachment locations, and the streamwise intermittency distributions in the transition region are documented for each of the test cases. Increasing surface roughness is shown to result in earlier transition inception, and consequently, a reduced size of the separation-bubble. However, the presence of surface roughness does not appear to have a significant effect on the rate of transition within the separation-bubble.
Thermomechanical Design of a Heat Exchanger for a Recuperative Aero Engine
Authors: Scho¨nenborn Harald , Ebert Ernst , Simon Burkhard , Storm Paul
Published: November 2008

Within the framework programs of the EU for Efficient and Environmentally Friendly Aero-Engines (EEFEA) MTU has developed a highly efficient cross-counter flow heat exchanger for the application in intercooled recuperated aero-engines. This very compact recuperator is based on the profile tube matrix arrangement invented by MTU and one of its outstanding features is the high resistance to thermal gradients. In this paper the combined thermomechanical design of the recuperator is presented. State-of-the-art calculation procedures for heat transfer and stress analysis are combined in order to perform a reliable life prediction of the recuperator. The thermal analysis is based upon a 3D parametric finite element model generation. A program has been generated, which allows the automatic generation of both the material mesh and the boundary conditions. Assumptions concerning the boundary conditions are presented as well as steady state and transient temperature results. The stress analysis is performed with a FEM code using essentially the same computational grid as the thermal analysis. With the static temperature fields the static loading of the profile tubes is determined. From transient thermal calculations successive 3D temperature fields are obtained which enable the determination of creep life and LCF life of the part. Finally, vibration analysis is performed in order to estimate the vibration stress of the profile tubes during engine operation. Together with the static stress a Goodman diagram can be constructed. The combined analysis shows the high life potential of the recuperator, which is important for economic operation of a recuperative aero-engine.
Evolution of the Tip Leakage Vortex in an Axial Compressor Rotor
Authors: Liu Baojie , Yu Xianjun , Wang Hongwei , Liu Huoxing , Jiang Haokang , Chen Maozhang
Published: November 2008

The evolution of tip leakage vortex is analyzed at both design and near stall conditions based on instantaneous and averaged velocity and vorticity distributions in cross flow sections measured with Stereoscopic Particle Image Velocimetry (SPIV) in a large-scale low-speed compressor facility. Formation, becoming unstable, and interaction of small-scale vortices and mainstream characterize the evolution of the tip leakage vortex in the compressor rotor. These processes influence the mainstream in very different ways. The process of leakage vortex becoming unstable is relatively smooth at design condition and vortex breakdown occurs at near stall condition for the case in the experiment. The main reason is that the critical condition occurs only in the core of tip leakage vortex at near stall condition. The effect of Coriolis force and centrifugal force on the stability of tip leakage vortex is analyzed theoretically with hypothesis of incompressible, inviscid and quasi-cylindrical swirling flow.
Selection and Sizing of Prime Movers in Combined Heat and Power Systems
Authors: Sanaye Sepehr , Shokrollahi Shahabeddin
Published: November 2008

Combined heat and power (CHP) is a technology with significant economical and environmental benefits. Proper sizing and operational strategy of CHP systems must take into account the time dependent character of electrical and thermal load requirements. Furthermore the CHP systems should be able to operate at off-design points with variable power and heat outputs. In this paper, the selection of type and combination of prime movers, their nominal powers and planning their operational strategy is performed. Three prime movers namely diesel engine, gas engine and gas turbine have been used to provide the required power and heat loads. Ambient conditions, and time dependent electrical/heat load curves are assumed to be the known variables, and thermal efficiency, engine exhaust gas temperatures, exhaust and fuel mass flow rate at partial load are estimated using relations obtained for prime movers mentioned in this paper. The presented approach successfully estimated the most economical combination of prime movers for a selected district heating plant.
Conjugate Calculations for a Film-Cooled Blade Under Different Operating Conditions
Authors: Kusterer Karsten , Bohn Dieter , Sugimoto Takao , Tanaka Ryozo
Published: November 2008

Conjugate heat transfer and flow calculation techniques (CCT: Conjugate Calculation Technique) developed by several numerical groups have been applied to more and more complex three-dimensional cooling configurations. With respect to gas turbine blade cooling, conjugate calculation codes are turning out as useful tools for the support of the thermal design process. Thus, the main focus of the present study is to investigate the applicability of the CCT on a realistic film-cooling configuration of a modern gas turbine blade under hot gas operating conditions. Thermal index paint measurements for the investigated configuration have been performed at KHI Gas Turbine R&D Center in order to provide thermal load data for comparison to results of conjugate blade analysis. The comparison shows that with respect to regions with high thermal load a qualitatively good agreement of the conjugate results and the measurements can be found although the calculation models contain several simplifications for the internal cooling configuration particularly. The tip region of the blade trailing edge is exposed to a high thermal load. This result can be found in the measurement data as well as in the numerical analysis. The influence of off-design flow conditions on the film cooling flow at the blade leading edge is also investigated. Despite the model simplification, the Conjugate Calculation Technique turns out to be applicable for the numerical testing of the cooling configuration investigated. With the numerical results, useful information for further improvement of the investigated cooling configuration can be provided.