bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigations of a Staged Fuel Nozzle for Aeroengines by Multi-Sector Combustor Test
Authors: Yamamoto Takeshi , Shimodaira Kazuo , Kurosawa Yoji , Yoshida Seiji , Matsuura Kazuaki
Published: January 2011

The reduction of NOx emissions from aeroengines is very important to protect the local air quality near the airports and prevent the climate change. ICAO CAEP has been stepped up the NOx standard frequently. Therefore, the engine manufacturers and national research institutes are actively working on the low-NOx technologies to meet the lower NOx emissions standard. JAXA is conducting research and development of the aeroengine technologies for the environmental adaptation in the TechCLEAN project. As a part of the project, combustion technologies have been developed with an aggressive target that is an 80% NOx reduction of CAEP/4. For the drastic reduction of NOx emissions, the fuel nozzles were designed based on the lean staged combustion concept. At first, five fuel nozzles were tested in a single-sector combustor at LTO cycle conditions of small aeroengine and it was confirmed that one fuel nozzle enabled 72% NOx reduction of CAEP/4. This lean low NOx fuel nozzle was tested in the present work in a multi-sector combustor at the same conditions with the single-sector combustor test. Test results showed that the combustor had combustion characteristics enabling 70% NOx reduction of CAEP/4, which was almost same with the single-sector combustor. For the improvement of combustion efficiency at middle power conditions, fuel staging among the main fuel injectors was also investigated at the MCL condition. The results showed that the fuel staging among the main fuel nozzles is effective to improve the combustion efficiency of the annular combustor.
Kinematical Analysis of a Novel Transmission Mechanism With Steady-Speed Output for Variable Speed Wind Turbines
Authors: Hwang Guan-Shyong , Tsay Der-Min , Kuang Jao-Hwa , Chern Tzuen-Lih
Published: January 2011

For the usage in variable speed wind turbines, a novel transmission mechanism with steady-speed output is proposed in this study. The proposed mechanism, named as independently controllable transmission (ICT), can produce a required angular velocity at the output shaft, which is independently manipulated by a controller and does not depend on the angular velocity of the input shaft. By applying the ICT mechanism to the variable speed wind power systems, the turbine fluctuation can be overcome and a constant speed can be provided for the input shaft of the generator. The ICT mechanism is fundamentally composed of two sets of planetary gear trains and two sets of transmission-connecting members. Four prototypes of the ICT mechanisms are installed to experiment their kinematical characteristics and to demonstrate their feasibility of engineering application.
Lean Premixed Turbulent Flame Front Structure and Implications for Modeling
Authors: Yuen Frank T. C. , Gu¨lder O¨mer L.
Published: January 2011

Premixed turbulent flames of methane-air and propane-air stabilized on a Bunsen type burner were studied to investigate the structure of the flame front at a wide range of turbulence intensities covering the range of interest in lean premixed combustors. The flame front data were obtained using planar Rayleigh imaging, and particle image velocimetry was used to measure instantaneous velocity field for the experimental conditions studied. The fuel-air equivalence ratio range was from lean 0.6 to stoichiometric for methane flames, and from 0.7 to stoichiometric for propane flames. The non-dimensional turbulent rms velocity, u′/SL, covered a range from 3 to 24. Flame front thickness and flame front curvature statistics were obtained from 2D measurements. Flame front thickness increased slightly with increasing non-dimensional turbulence rms velocity in both methane and propane flames, although the flame thickening was more prominent in propane flames. There was not any significant difference in flame thickening whether the flame thickness is evaluated at progress variable 0.5, corresponding to the reaction zone, or 0.3, corresponding to the preheat zone. Variations of front curvature and flame thickness are presented for different premixed combustion regimes and implications of these findings for modelling premixed turbulent combustion are discussed.
The Interaction Between Horseshoe Vortex and Longitudinal Vortices From the Vortex Generators
Authors: Andoh Masaharu , Motosuke Masahiro , Honami Shinji
Published: January 2011

A horseshoe vortex at the blade-endwall junction introduces the reduction of turbine blade performance due to the three dimensional separation near the stagnation point of the blade and the interaction of the two legs of the horseshoe vortex in the turbine cascade passage. In order to simulate the interaction of the leg vortices in the passage, a pair of vortex generators which produces the longitudinal vortices from the tip of the generator wings is installed upstream of the blade. The experiments are made under the different configuration of the longitudinal vortex generators. NACA 0024 airfoil at zero angle of attack is used as the blade in the wind tunnel where the undisturbed momentum thickness Reynolds number is 1700. The detailed measurements on the three-components of time-averaged and fluctuated velocities are conducted by a small size of rotating X-probe hot-wire anemometer with a miniature stepping motor at the prong. The location of the leg of the horseshoe vortex can be controlled by changing the spacing of the longitudinal vortex generators. The strong dependence of the spacing of the longitudinal vortex generators on the profiles of Reynolds stress and the temporal velocity is clarified.
Statistical Evaluation of Ignition Phenomena in Turbojet Engines
Authors: Lang Andreas , Lecourt Renaud , Giuliani Fabrice
Published: January 2011

Turbojet engines must demonstrate their ability to be ignited on high altitude airfields or reignited in flight. These extreme conditions require the ignition of the engine in a large field of aerodynamic and thermodynamic conditions. Usually, a Mach-Altitude domain in which combustion can be established is used to represent the ignition performances of the aircraft engine. Nowadays, the prediction of this domain during the design process is mostly based on empirical rules. On the contrary, for the steady regimes, thanks to the use of computer aided design (CAD) and computational fluid dynamics (CFD) the combustor design is mainly done on the workstation. Finally the validation of the ignition configuration and the determination of the ignition domain demand an expensive experimental program. In an industrial context, it is therefore very important to include the ignition system design in the CAD process to reduce the costs of the experimental testing of the ability of a turbojet engine to be ignited. This requires the elaboration of a well tuned CFD model that is able to simulate the ignition phenomena properly. The aim of this study was therefore to gather experimental data on ignition to get a database for statistical evaluation of the ignition phenomena. A sample of 150 experiments at same operating conditions was performed. The experimental data were analyzed regarding the number of sparks needed to ignite and the ignition delay time. Further on, the probability that a certain spark will lead to ignition was computed. The paper discusses how the sample was statistically treated and the ignition probability was computed. Further the results on ignition probability are presented. The results of this study will be used to validate the ignition module of the AVBP LES CFD-Code at CERFACS in future works.
Prediction of Separation-Induced Transition Using a Correlation-Based Transition Model
Authors: Corral Roque , Gisbert Fernando
Published: January 2011

A correlation-based transition model has been introduced in a RANS solver to improve the prediction of the transition from laminar to turbulent flow regime in low-pressure turbine blades. The model has been validated by comparing the numerical results against experimental data. The transition model correctly predicts the transition process due to the separation of the laminar boundary layer in a wide range of situations, ranging from steady two-dimensional simulations to unsteady multirow three-dimensional simulations with cavities, improving in all cases the sensitivity of the RANS solver to variations in the Reynolds number.
Rotordynamic Performance of an Oil-Free Turbocharger Supported on Gas Foil Bearings: Effects of an Assembly Radial Clearance
Authors: Kim Tae Ho , Lee Jangwon , Kim Chang Ho , Lee Yong-Bok
Published: January 2011

Oil-free turbochargers (TCs) will increase power and efficiency of internal combustion (IC) engines, sparking ignition (SI) and compression ignition (CI), without engine oil lubricant feeding and scheduled maintenance. Implementing gas foil bearings (GFBs) into passenger vehicle TCs enables compact, light weight, oil-free systems along with accurate shaft motions, while engine oil lubricated TCs with floating ring bearings (FRBs) are prone to show severe sub synchronous motions over a wide range of shaft speeds due to instability. The paper presents static load-deflection tests of TC GFB structure, and rotordynamic performance measurements of an oil-free TC unit supported on test GFBs. Three metal shims inserted under the bump-strip layers and in contact with the bearing housing create a mechanical preload, which induces a hydrodynamic wedge in the assembly radial clearance to generate more film pressure for the shimmed GFB. Static load-deflection tests estimate the assembly radial clearances of the shimmed GFB smaller than that of the original GFB. Model predictions agree well with test data. The discrepancy between the model predictions and test data is attributed to fabrication inaccuracy of the top foil and bump strip layers. The rotordynamic TC test rig is driven by pressurized air. The test TC rotor, of 335 gram weight and 117 mm length, is coated using commercially available wear-resistant solid lubricant, Amorphous M, to prevent severe wears during start up and shutdown in the absence of an air film. Pressure sensors measure the driving turbine inlet air pressure and a control valve changes the air mass flow manually. A pairs of optical proximity probes positioned orthogonally at the compressor end record the lateral rotor motions. Rotordynamic test results show that the shimmed GFB attenuates significantly the large amplitude of subsynchronous whirl motions arising for the original GFBs. Mechanical preloads, which determine the assembly radial clearance of the shimmed GFB, causes the increase in the rotor-bearing system natural frequency.
Investigation of Compressor Tip Clearance Flow Structure
Authors: Matzgeller Roland , Burgold Yves
Published: January 2011

By the use of decomposition for the three-dimensional flow field in compressors into independent through flow and cross flow as first proposed by Chen et al., the tip gap flow structure for different tip gap heights and boundary conditions is examined. Tracing the roll up of a shear layer in planes normal to the blade camber line the position of the tip leakage vortex is presented in a non-dimensional formulation. Tests for different boundary conditions, i.e. the distinction between a stationary and a rotating end-wall as well as the use of different fluid models are made to quantify their influence on the tip leakage vortex position. By comparing the analytical result to data extracted from three-dimensional RANS computations and to measurement data the validity of the model is presented. Finally, an attempt is made to find a criterion for the occurrence of tip leakage vortex induced stall of tip critical rotor blades. This is done by a correlation based on the previously derived non-dimensional vortex trajectory and the stagger angle. This criterion is again tested on results of a three dimensional RANS computation proving its validity.
Characterisation of the Uncertainties of the Operating Conditions in Turbomachinery Design
Authors: Kipouros Timoleon , Pachidis Vassilios , Ghisu Tiziano , Templalexis Ioannis
Published: January 2011

In computational engineering design the robust analysis comprises a prerequisite towards the successful development of future gas turbines. However, reliable determination of the statistical characteristics of variation of the operating conditions in a turbomachine is crucial. Initially, the variability of the physical operating conditions along the operating line on the compressor map is developed with the assistance of a through flow analysis tool. The probability density functions of the variability of the pressure profiles, mass flow, input angles, etc. of each individual stage of the compressor can be extracted and processed accordingly for 3D aerodynamic shape robust design. In this way, flexibility in detailed design is developed leading to innovative and creative thinking in modern turbomachinery design, but at the same time the intelligence and level of robust design is improved, and hence the quality of the designed product. For a particular compression system of a turbo-shaft engine all the details can be extracted, along the whole operating line, covering all the possible scenarios of individual operating conditions of each component. With this methodology the appropriate information is developed for robust analysis at the preliminary or detailed design phases of a compression system.
Aerodynamic Performance of Stepped Labyrinth Seals for Gas Turbine Applications
Authors: Kang Y. , Kim T. S. , Kang S. Y. , Moon H. K.
Published: January 2011

This paper presents the leakage performance of various stepped labyrinth seals. A stationary seal test rig was set up and the leakage characteristics of three seal configurations with different numbers of steps and teeth were investigated for wide operating ranges in terms of pressure ratio and tip clearance. Both the solid and honeycomb land structures were tested. In the honeycomb case, two different sizes were used. The seal was shaped, typical of labyrinth seals for gas turbine applications. The influences of seal configuration, and clearance and honeycomb sizes on the leakage performance were investigated. The relative performances between different seal configurations were compared and their dependence on the land structure was investigated. The honeycomb structure was found to increase leakage for all test conditions. The leakage ratio (honeycomb/solid) was analyzed in terms of geometric variables.
Performance Model “Zooming” for In-Depth Component Fault Diagnosis
Authors: Aretakis N. , Roumeliotis I. , Mathioudakis K.
Published: January 2011

A method giving the possibility for a more detailed gas path component fault diagnosis, by exploiting the “zooming” feature of current performance modelling techniques, is presented. A diagnostic engine performance model is the main tool that points to the faulty engine component. A diagnostic component model is then used to identify the fault. The method is demonstrated on the case of compressor faults. A 1-D model based on the “stage stacking” approach is used to “zoom” into the compressors, supporting a 0-D engine model. A first level diagnosis determines the deviation of overall compressor performance parameters, while “zooming” calculations allow a localization of the faulty stages of a multistage compressor. The possibility to derive more detailed information with no additional measurement data is established, by incorporation of empirical knowledge on the type of faults that are usually encountered in practice. Although the approach is based on known individual diagnostic methods, it is demonstrated that the integrated formulation provides not only higher effectiveness but also additional fault identification capabilities.
Dynamic Analysis of Fretting-Wear in Joint Interface by a Multiscale Harmonic Balance Method Coupled With Explicit or Implicit Integration Schemes
Authors: Salles Loi¨c , Gouskov Alexander M. , Blanc Laurent , Thouverez Fabrice , Jean Pierrick
Published: January 2011

Assembled bladed disks have many contact interfaces (blade-disk joint, blade shrouds, friction damper, etc). Because of relative displacements at these interfaces, fretting-wear can occur, which shortens the life expectancy of the structure. Moreover, vibrations that occur in bladed-disks can increase this fretting-wear phenomenon. Two previous papers in Turboexpo have introduced a numerical method based on the Dynamical Lagrangian Frequency Time algorithm (DLFT) to calculate worn geometry, especially wear of bladed-disks’ dovetail roots. Numerical investigations have illustrated the performances of this method and shown the coupling between dynamical and tribological phenomena. The basic idea of the DLFT-with-wear method is to separate time in two scales, slow scale for tribological phenomena and fast scale for dynamics. In the present paper, implicit and explicit integration schemes on the slow time scale are compared. An ad hoc prediction-correction method is used in both methods to accelerate the convergence of the non-linear solver. Numerical experiments on bladed-disk show that the implicit scheme is more appropriate to deal with fretting-wear under dynamical loading.
Theoretical Prediction of the Lift-Off Speed in Aerodynamic Compliant Foil Journal Bearings
Authors: Qi Shemiao , Ho Y. S. , Geng Haipeng , Yu Lie
Published: January 2011

In aerodynamic bearings, since the supporting air film is generated by rotor motion, there is no support at the start of motion. As in all such bearings, there is dry rubbing until the rotor achieves sufficient speed to lift-off. Thus, the lower the lift-off speed, the less will be the rubbing and so the greater will be the life of the bearing. This paper focuses on the theoretical prediction of lift-off speed in aerodynamic compliant foil journal bearings based on a generalized solution of elasto-aerodynamically coupled lubrication for compliant foil bearings. A computational method is presented which is used to predict the lift-off speed in aerodynamic foil journal bearings with eccentricity ratio greater than or equal to 1.0. Special emphasis is placed on investigating the effects of the load imposed on the bearing, the nominal radial clearance and the bearing radius on the lift-off speed. The numerical results obtained indicate that lift-off speed decreases with the decrease of load and nominal radial clearance, but with an increase in bearing radius. The eccentricity ratios are all greater than 1.0 at the lift-off speed for the aerodynamic compliant foil journal bearings used in this study.
Investigations of Gaseous Alternative Fuels at Atmospheric and Elevated Temperature and Pressure Conditions
Authors: Bagdanavicius Audrius , Shelil Nasser , Bowen Philip J. , Syred Nick , Crayford Andrew P.
Published: January 2011

Increasing interest in alternative fuels for gas turbines stimulates research in gaseous fuels other than natural gas. Various gas mixtures, based on methane as the main component, are considered as possible fuels in the future. In particular, methane enrichment with hydrogen or dilution with carbon dioxide is of considerable interest. Some experiments and numerical calculations have been undertaken to investigate methane-hydrogen and methane-carbon dioxide gas flames, however most of these investigations are limited by particular pressure or temperature conditions. This paper presents the investigation of the combustion of methane–carbon dioxide mixtures at atmospheric and elevated temperature and pressure conditions. Two experimental rigs were used, a Bunsen burner and swirl burner. Bunsen burner experiments were performed in the High Pressure Optical Chamber, which is located within the Gas Turbine Research Centre of Cardiff University — at 3 bara and 7 bara pressure, and 473 K, 573 K and 673 K temperature conditions for lean and rich mixtures. Planar Laser Tomography (PLT) was applied to investigate turbulent burning velocity. Burning velocity of the gas mixture was calculated using two different image processing techniques and the difference in the results obtained using these two techniques is presented and discussed. Laser Doppler anemometry (LDA) was utilised to define turbulence characteristics such as turbulence intensity and integral length scale. Due to the variability of the velocity flow field and turbulence intensity across Bunsen burners, the importance of measuring position and conditions is discussed. The sensitivity of this variance on the flame regime as defined in the Borghi diagram is evaluated. In the second part of the study, a generic swirl burner was used to define the flame flashback limits for methane–carbon dioxide mixtures at atmospheric conditions. The gas mixture stability graphs are plotted, and the effect of CO2 addition are discussed.
Calculation of Steady and Periodic Unsteady Blade Surface Heat Transfer in Separated Transitional Flow
Authors: Pacciani Roberto , Rubechini Filippo , Arnone Andrea , Lutum Ewald
Published: January 2011

In this work aerothermal investigations of a highly loaded HP turbine blade are presented. The purpose of such investigations is to improve the physical understanding of the heat transfer in separated flow regions, with the final goal of optimizing cooling configurations for aerodynamically highly loaded turbine designs. The analysis is focused on the T120 cascade, that was recently tested experimentally in the framework of the European project AITEB-2 (Aero-thermal Investigation of Turbine Endwalls and Blades). Such a cascade has a relatively low solidity that is responsible for the formation of a laminar separation bubble on the suction side of the blade. Separated-flow transition and transonic conditions downstream of the throat result in a flow configuration that is very challenging for traditional RANS solvers. Moreover, the separated flow transition pattern was found to have a strong impact on both the aerodynamic and thermal aspects. The study was carried out using a novel three-equation, transition-sensitive, turbulence model. It is based on the coupling of an additional transport equation for the laminar kinetic energy to the Wilcox k–ω model. Such an approach allows one to take into account the increase of the non-turbulent fluctuations in the pre-transitional and transitional region. Comprehensive aerodynamic and heat transfer measurements were available for comparison purposes. In particular, heat transfer measurements cover different Mach and Reynolds numbers, in both steady and periodic unsteady inflow conditions. A detailed comparison between measurements and computations is presented, and the impact of transition-related aspects on the surface heat transfer is discussed.
Internal Flow and Noise Investigations About the Cross-Flow Fan With Different Blade Angles
Authors: Li You , Ouyang Hua , Tian Jie , Zheng Zhiming , Du Zhaohui
Published: January 2011

The experimental and numerical studies have been carried out to investigate the flow and the noise characters of the three impellers with different blade angles in a cross-flow fan (CFF). Firstly, the aerodynamic performances of the fan with these impellers are obtained experimentally and the averaged flow patterns inside the impellers are measured by the three-hole probe. Secondly, the far-field noise generated by CFF with different impellers has been measured in a semi-anechoic chamber under different throttling conditions. Thirdly, the two-dimensional unsteady CFD simulations have been performed by commercial software. The internal flow patterns influenced by the different blade angles have been summarized through the computational results. The accuracy of the calculations is validated by the corresponding experimental ones. The detail analysis has been carried out on the unsteady vortex flow properties of the three impellers, which is considered to be the main factor that influences the aerodynamic and aeroacoustic performance of the CFF. Finally, the relative far field noise generated by different impellers are evaluated by an empirical formula based on the assumption that the total sound pressure levels are proportional to the sixth power law of the relative velocity on the outer and inner circumferences of the impeller. The circumferential distributions of relative velocity are provided from the numerical solutions. The varying trends of predicted results agree well with the actual relative noise of the CFF with three different impellers.
Redesign of High-Lift LP-Turbine Airfoils for Low Speed Testing
Authors: Marconcini Michele , Rubechini Filippo , Pacciani Roberto , Arnone Andrea , Bertini Francesco
Published: January 2011

Low pressure turbine airfoils of the present generation usually operate at subsonic conditions, with exit Mach numbers of about 0.6. To reduce the costs of experimental programs it can be convenient to carry out measurements in low speed tunnels in order to determine the cascades performance. Generally speaking, low speed tests are usually carried out on airfoils with modified shape, in order to compensate for the effects of compressibility. A scaling procedure for high-lift, low pressure turbine airfoils to be studied in low speed conditions is presented and discussed. The proposed procedure is based on the matching of a prescribed blade load distribution between the low speed airfoil and the actual one. Such a requirement is fulfilled via an Artificial Neural Network (ANN) methodology and a detailed parameterization of the airfoil. A RANS solver is used to guide the redesign process. The comparison between high and low speed profiles is carried out, over a wide range of Reynolds numbers, by using a novel three-equation, transition-sensitive, turbulence model. Such a model is based on the coupling of an additional transport equation for the so-called laminar kinetic energy (LKE) with the Wilcox k–ω model and it has proven to be effective for transitional, separated-flow configurations of high-lift cascade flows.
An Efficient Method for the Optimization of Viscoplastic Constitutive Model Constants
Authors: DeMarco James P. , Hogan Erik A. , Stewart Calvin M. , Gordon Ali P.
Published: January 2011

Constitutive modeling has proven useful in providing accurate predictions of material response in components subjected to a variety of operating conditions; however, the high number of experiments necessary to determine appropriate constants for a model can be prohibitive, especially for more expensive materials. Generally, up to twenty experiments simulating a range of conditions are needed to identify the material parameters for a model. In this paper, an automated process for optimizing the material constants of the Miller constitutive model for uniaxial modeling is introduced. The use of more complex stress, strain, and temperature histories than are traditionally used allows for the effects of all material parameters to be captured using significantly fewer tests. A graphical user interface known as uSHARP was created to implement the resulting method, which determines the material constants of a viscoplastic model using a minimum amount of experimental data. By carrying out successive finite element simulations and comparing the results to simulated experimental test data, both with and without random noise, the material constants were determined from 75% fewer experiments. The optimization method introduced here reduces the cost and time necessary to determine constitutive model constants through experimentation. Thus it allows for a more widespread application of advanced constitutive models in industry and for better life prediction modeling of critical components in high-temperature applications.
Direct Outer Ring Cooling of a High Speed Jet Engine Mainshaft Ball Bearing: Experimental Investigation Results
Authors: Gloeckner Peter , Dullenkopf Klaus , Flouros Michael
Published: January 2011

Operating conditions in high speed mainshaft ball bearings applied in new aircraft propulsion systems require enhanced bearing designs and materials. Rotational speeds, loads, demands on higher thrust capability, and reliability have increased continuously over the last years. A consequence of these increasing operating conditions are increased bearing temperatures. A state of the art jet engine high speed ball bearing has been modified with an oil channel in the outer diameter of the bearing. This oil channel provides direct cooling of the outer ring. Rig testing under typical flight conditions has been performed to investigate the cooling efficiency of the outer ring oil channel. In this paper the experimental results including bearing temperature distribution, power dissipation, bearing oil pumping and the impact on oil mass and parasitic power loss reduction are presented.
Prediction of the Influence of Upstream Wake Passing on Downstream Blade Row External Heat Transfer Coefficient: A New Physically-Based Method
Authors: Chana K. S. , Haller B. R.
Published: January 2011

For gas turbines, accurate prediction of the external heat transfer coefficient on the high pressure (HP) turbine rotor blades is of immense importance, as this component is critical and operates at material limits. Furthermore the external heat load is the governing boundary condition for the design of the internal cooling system of the blade. There is a continuous drive to increase the turbine entry temperature to increase the cycle efficiency, whilst developing blade cooling systems with higher efficiency (i.e. using less cooling air). A new systematic procedure has been developed and validated to predict the external heat transfer to a blade surface. The procedure allows for the unsteady effects caused by the passing of upstream nozzle guide vane (NGV) wakes. The early part of the suction surface was shown to have a pessimistic prediction of external heat transfer coefficient which resulted in unnecessary over-cooling of the blade in this region. The heat transfer aspect is found from the well-known TEXSTAN differential boundary layer method, developed by Mike Crawford at Texas University from the original approach of Spalding & Patankar. The method is validated against the MT1 turbine tested in the QinetiQ Turbine Test Facility. Predictions and comparisons have also been carried out on the VKI turbine stage. The level of agreement with the test data is shown to be good.
Effect of Surface Roughness on Loss Behaviour, Aerodynamic Loading and Boundary Layer Development of a Low-Pressure Gas Turbine Airfoil
Authors: Montis Marco , Niehuis Reinhard , Fiala Andreas
Published: January 2011

Aerodynamic measurements on the linear low-pressure turbine cascade T106C were conducted in a high speed test facility, in order to investigate the effect of surface roughness on loss behaviour, aerodynamic loading, and boundary layer development. Three different roughnesses were investigated, with a ratio of the center line average roughness to the profile chord of 0.8·10−5, 5·10−5 and 25·10−5. Tests were carried out under design outlet Mach number (Ma2th = 0.6), outlet Reynolds number ranging from Re2th = 5·104 to Re2th = 7·105 and inlet turbulence level Tu1 = 3% and Tu1 = 6%. The flow field downstream of the cascade and the loading distribution on the profiles were measured for each investigated operating point using five hole probes and surface static pressure taps. Additional measurements with a hot-wire probe in the suction surface (SS) boundary layer were also conducted, in order to investigate the differences in boundary layer development due to surface roughness. From loss and blade loading measurements it was found that roughness has no influence on the pressure distribution on the profile, although the highest investigated roughness produces a significant loss reduction at low Reynolds numbers. Hot-wire probe surveys show that at Re2th = 9·104 the boundary layer for the highest roughness immediately upstream of the flow separation point on the SS is substantially thinner than for the middle roughness and the smooth profile.
Effects of Vane/Blade Relative Positions and Showerhead Film Cooling on a Stationary Blade: Heat Transfer
Authors: Lee Dong Hyun , Rhee Dong-Ho , Kim Kyung Min , Cho Hyung Hee
Published: January 2011

The present study investigates the effects of relative position on heat transfer distributions of a showerhead film-cooled stationary rotor blade. Detailed heat/mass transfer coefficients were measured using the naphthalene sublimation method. A low-speed wind tunnel was used, with a single annular turbine stage consisting of sixteen guide vanes and blades. The axial chord length of the test blade was 136 mm. The inlet and exit angles of the test blade were 56.4° and −62.6°, respectively, which produced a turning angle of 119.0°. Three rows of film cooling holes were drilled in the leading edge region of the blade. Each row had 10 circular cooling holes along the spanwise direction, and the diameter of each cooling hole was 1.2 mm. Detailed heat transfer coefficients were measured at two different guide vane and rotor blade relative positions, while changing the blowing rate (M) from 1.0 to 2.0. The inlet Reynolds number was fixed at 1.3×105 based on the blade axial chord length. As the blowing rate increased, overall heat transfer rates increased, and the lower peaks formed on the pressure side by the separation bubble were reduced, and disappeared at M = 2.0. The effects of vane/blade relative position were significant because the incoming flow condition was changed. However, the spanwise average Sherwood number became similar as the blowing rate increased.
A Novel Quasi 3-D Design Method for Centrifugal Compressor Meridional Plane
Authors: Nili-Ahmadabadi Mahdi , Durali Mohammad , Hajilouy-Benisi Ali
Published: January 2011

This paper is concerned with a quasi-3D design method for centrifugal compressor impeller in the meridional plane. The method links up a novel inverse design algorithm, called Ball-Spine Algorithm (BSA), and a quasi-3D analysis code. The Euler equation is solved on the meridional plane for a numerical domain of which some unknown boundaries (hub and shroud) are iteratively modified under the BSA until a prescribed pressure distribution is reached. In BSA, the unknown walls are composed of a set of virtual balls that move freely along the specified directions called spines. The difference between target and current pressure distribution causes to deform flexible boundary at each modification step. In order to validate the quasi-3D analysis code, an existing compressor is investigated by some experiments in which several static pressure points on the shroud, the flow parameters at the compressor inlet and outlet are measured. Comparison of the quasi-3D analysis results with experimental results shows good agreement. Also, a full 3D Navier-Stokes code is used to analyze the existing and designed compressor numerically. The results show that the momentum decrease near the shroud wall in the existing compressor is removed by hub-shroud modification resulting an improvement in performance by 0.6 percent.
Modeling of Surge Characteristics in Turbo Heat Pumps
Authors: Kim Hye Rim , Song Seung Jin
Published: January 2011

This paper presents a new analytical model of surge dynamics in turbo heat pumps. Turbo heat pumps use refrigerants as the working fluid and consist of a centrifugal compressor, condenser, expansion valve, and evaporator. Compared to a gas turbine engine, the turbo heat pump system introduces additional complexities. First, the turbo heat pump forms a closed-loop system. Second, the system has two plenums — condenser and evaporator — which are coupled to each other. Third, the heat pump runs on a refrigeration cycle with two phases — vapor and liquid. Fourth, heat transfer effects of evaporation and condensation have to be considered. Fifth, unlike air, a refrigerant has strong real gas effects and thus cannot be modeled as an ideal gas. The new model addresses such additional complexities on the basis of the first principles of conservation of mass, momentum, and energy. When applied to a gas turbine system, the new model’s predictions become identical to those from the Greitzer’s model. Furthermore, comparison with the available experimental data shows that the model can also accurately predict surge behavior in actual turbo heat pumps. Finally, the effects of Greitzer’s B parameter and the ratio of evaporator and condenser volume have been examined. Parameter B influences both surge shape and frequency. Finally, surge frequency is extremely sensitive to the ratio of the two plenum volumes.
Development of a Low-NOX Hydrogen-Fuelled Combustor for 10 MW Class Gas Turbines
Authors: Cocchi Stefano , Sigali Stefano
Published: January 2011

In the context of a research project launched in 2006 (partially funded by Regione Veneto, a local institution in the Northeast of Italy), ENEL and GE Oil & Gas are developing an innovative “zero emission” gas turbine cycle suitable for power generation. The gas turbine, a GE10-1 model, is manufactured by GE Oil & Gas and features a single can silo-type combustion chamber. A hydrogen-fuelled GE10-1 prototypical unit has been installed in Fusina (Venice), at ENEL’s coal-fired power plant, and has been in operation since September, 2009. The prototypical unit is equipped with a diffusive flame combustor, and the NOx emission level is kept below contractual limits by means of steam injection. In the mean time, further research activities have been carried out to develop an upgraded diffusive combustor, to be operated with 100% H2 and with NOx emissions reduced to below 50% of the current contractual limits. CFD has been extensively used (in cooperation with several Italian universities and research centers) in order to model and assess the behavior of the prototype combustor, and to define the preliminary design of modified burners and liners. Subsequently, the most promising configurations were engineered, procured and tested on a full-scale full-pressure combustion rig at ENEL’s experimental facility in Sesta (Tuscany). The behavior of alternative components has been monitored, with a focus on metal temperatures, pattern factor, pressure pulsations, and NOx emissions, and the performance has been compared to that of the prototypical combustor. As expected, the lowest NOx emissions were achieved with configurations having a lean primary combustion zone. Such configurations have proven to be capable of significantly reduced NOx emissions without increasing the amount of steam.
Effects of the Swirl Velocity of a Jet in Crossflow From Fan Assemblies Mounted on Lifting Surfaces
Authors: Terzis Alexandros , Kazakos Charilaos , Papadopoulos Nikolaos , Kalfas Anestis I. , Zachos Pavlos K. , Pilidis Pericles
Published: January 2011

The penetration of a jet of fluid into a traversal moving stream is a basic configuration of a wide range of engineering applications, such as film cooling and V/STOL aircrafts. This investigation examines experimentally the effect of blowing ratio of fans in cross flow, and numerically, the effect of the swirl velocity of jets in cross flow, downstream of the injection hole. The experimental results indicated an agreement with typically straight jets in cross flow (no vorticity), illustrating that the trace of the jet, remains close to the wall and subsequently enhance cooling at low blowing ratios in the case of turbine blade applications. However, the rotation of the jet results in an imparity between the two parts of the counter rotating vortex pair (CVP), and as a consequence, the injected fluid not only bends in the direction of the main stream but also diverts in the direction of the rotation, in order to conserve its angular momentum. The induction of the swirl velocity on the injected jet destructs one of the two parts of the kidney vortex which entrains fluid from the cross flow to the jet promoting the mixing between the two fluids, while the trace of a swirled jet remains closer to the wall downstream of the injection hole. Finally, the use of contra rotating jet or fan configurations reduces the wall shear stress in a very great extent, leading to better thermal protection of turbine blades, as well as cancels out the yaw torques of each fan separately, resulting in better flight control of typical lift surface.
The Mixed Flow Forward Swept Turbine for Next Generation Turbocharged Downsized Automotive Engines
Authors: Fredriksson Carl , Baines Nick
Published: January 2011

In automotive turbochargers, the nature of the performance characteristics of a conventional radial turbine are such that it does not make good use of the exhaust gas energy of the engine, because the efficiency is lowest when the exhaust manifold pressure is highest, i.e. at the peak of the exhaust pulse, and the point at which most exhaust gas energy is theoretically available. The turbine design is also seriously compromised by requirements of size and inertia to improve the transient response of the engine. In this study, the use of forward swept rotor blading to improve the efficiency characteristic is investigated. Stress considerations mean that a mixed flow turbine geometry is required for this purpose. By comparing a baseline radial and two mixed flow turbines in engine simulations, it is shown that under steady-state conditions, a large increase in engine torque at low speed (before the wastegate opens) is obtained with the mixed flow turbines. The simulated response of the engine to a load step also shows that the same transient torque (and therefore vehicle response) can be achieved with the mixed flow turbine, even allowing for large increases in rotating inertia. The use of forward swept blades, and the improvement in exhaust energy recovery that stems from it, compensates for increases in inertia required by the mixed flow geometry and increases in overall turbine size.
Effects of Reynolds Number and Heat Transfer on Scaling of a Centrifugal Compressor Impeller
Authors: Ma Yan , Xi Guang
Published: January 2011

In this paper, the influence of Reynolds number and heat transfer on scaling of a small scale centrifugal compressor impeller was investigated. The flow solver EURANUS, integrated in the FINE/Turbo interface, was used in the numerical simulation. With the application of the similarity principle, the baseline impeller was scaled with a factor of 1/5 and 5 respectively. Using the baseline impeller as reference, an exponential relation between efficiency loss and Reynolds number was used in this study. By comparing Reynolds exponent n of the scaled-up and the scaled-down impellers under adiabatic wall condition, the effect of Reynolds number on scaling of this small scale impeller was studied. The effect of heat transfer was investigated by comparing the results under two different wall conditions (isothermal and adiabatic). This work provides general guidelines for performing scaling designs for small scale centrifugal impellers.
Interface Treatment for Harmonic Solution in Multi-Row Aeromechanic Analysis
Authors: Rahmati M. T. , He L. , Wells R. G.
Published: January 2011

In the present work, an interface treatment method has been developed to extend a non-linear harmonic solution method for aeromechanic analysis in multiple blade row configurations. The main emphasis is two folds. Firstly the method will enable efficient and accurate analysis of blade aerodynamic forcing and damping characteristics under the influence of adjacent bladerows. Secondly, it will warrant that the same steady/mean base flow as defined by the aerothermal designers is used consistently in the aeromechanical analysis. For passing the harmonic disturbance across a rotor-stator interface, the present method employs the time series reconstruction in conjunction with a temporal Fourier transform. On the other hand, the consistency with a conventional steady multistage solution for the base flow is achieved by applying an extended mixing plane method. The validity and effectiveness of the method are examined and demonstrated.
Simulation Framework Development for Aircraft Mission Analysis
Authors: Goulos Ioannis , Pachidis Vassilios , Celis Cesar , D’Ippolito Roberto , Stevens Jos
Published: January 2011

Since the very beginning of first commercial flight operations, aircraft mission analysis has played a major role in minimizing costs, increasing performances and satisfying regulations. The operational trajectory of any aircraft must comply with several constraints that need to be satisfied during its operation. The nature of these constraints can vary from Air Traffic Control (ATC) regulations, to emissions regulations and any combination between these two. The development of an integrated tool capable of determining the resources required (fuel and operational time) for a given aircraft trajectory, as well as assessing its environmental impact, is therefore essential. The present work illustrates the initial steps of a methodology developed in order to acquire the optimal trajectory of any specified aircraft under specific operational or environmental constraints. The simulation framework tool is the result of a collaborative effort between Cranfield University (UK), National Aerospace Laboratory NLR (NL) and LMS International (BE). With this tool, the optimal trajectory for a given aircraft can be computed and its environmental impact assessed. In order to simulate the characteristics of a specific trajectory, as well as to evaluate the emissions that are produced during the aircraft operation within it, three computational models developed at Cranfield University have been integrated into the simulation tool. These models consist of an aircraft performance model, an engine performance model and an emission indices model. The linking has been performed with the deployment of the OPTIMUS process and simulation integration framework developed by LMS International. The optimization processes carried out were based on OPTIMUS’ built-in optimizing algorithms. A comparative evaluation between an arbitrarily defined baseline trajectory and optimized ones has been waged for the purpose of quantifying the operational profit (in terms of fuel required or operational time) gained by the aircraft operation within the path of an optimized trajectory. Trade-off studies between trajectories optimized for different operational and environmental constraints have been performed. The results of the optimizations revealed a substantial margin available for reduction in fuel consumption as well as required operational time compared to a notional baseline. The optimal trajectories for minimized environmental impact in terms of produced emissions have been acquired and their respective required resources (fuel required and operational time) have been evaluated.
FLOX® Combustion at High Power Density and High Flame Temperatures
Authors: Lammel Oliver , Schu¨tz Harald , Schmitz Guido , Lu¨ckerath Rainer , Sto¨hr Michael , Noll Berthold , Aigner Manfred , Hase Matthias , Krebs Werner
Published: January 2011

In this contribution, an overview of the progress in the design of an enhanced FLOX® burner is given. A fuel flexible burner concept was developed to fulfill the requirements of modern gas turbines: high specific power density, high turbine inlet temperature, and low NOx emissions. The basis for the research work is numerical simulation. With the focus on pollutant emissions a detailed chemical kinetic mechanism is used in the calculations. A novel mixing control concept, called HiPerMix®, and its application in the FLOX® burner is presented. In view of the desired operational conditions in a gas turbine combustor this enhanced FLOX® burner was manufactured and experimentally investigated at the DLR test facility. In the present work experimental and computational results are presented for natural gas and natural gas + hydrogen combustion at gas turbine relevant conditions and high adiabatic flame temperatures (up to Tad = 2000 K). The respective power densities are PA = 13.3 MW/m2/bar (NG) and PA = 14.8 MW/m2/bar (NG + H2) satisfying the demands of a gas turbine combustor. It is demonstrated that the combustion is complete and stable and that the pollutant emissions are very low.