bluuebunny/crossref_metadata_2025 huggingface dataset:
Combustion Characteristics of a Multiple-Injection Combustor for Dry Low-NOx Combustion of Hydrogen-Rich Fuels Under Medium Pressure
Authors: Dodo Satoschi , Asai Tomohiro , Koizumi Hiromi , Takahashi Hirokazu , Yoshida Shouhei , Inoue Hiroshi
Published: May 2012

An oxygen-blown integrated coal gasification combined cycle (IGCC) plant with pre-combustion carbon dioxide capture and storage (CCS) is one of the most promising means of zero-emission generation of power from coal. In an IGCC plant with CCS, hydrogen-rich syngas with a wide variation of hydrogen contents is supplied to a gas turbine. Such hydrogen-rich syngas poses a great challenge to a low NOx combustor based on premixed combustion technology, because its high flame speed, low ignition energy, and broad flammability limits can cause flashback and / or auto-ignition. On the other hand, a diffusion combustor suffers from the high flame temperature of syngas and the resulting high NOx emission. The authors applied a “multi-injection burner” (cluster burner) concept to a preliminary burner for hydrogen-rich syngas simulating that from IGCC with CCS. In a preliminary experiment under atmospheric pressure, the multi-injection burner worked without any flashback or any blowout. A prototype multi-cluster combustor based on the results of that preliminary study was made to be a dry low NOx combustor for hydrogen-rich syngas of IGCC with CCS. It was tested in experiments, which were carried out under medium pressure (0.6MPa) using test fuels simulating syngas from IGCC with a 0% carbon capture rate, a 30% carbon capture rate and a 50% carbon capture rate. The test fuels contained hydrogen, methane and nitrogen, and had hydrogen content ranging from 40% to 65%. The following conclusions were drawn from the test results: (1) The tested combustor allows stable combustion of fuels simulating 0%, 30%, and 50% CCS. (2) A convex perforated plate swirler is effective to suppress combustion oscillation, which allows NOx emissions to be less than 10ppm through the variation of fuel simulating 0%, 30% and 50% CCS.
A Three-Dimensional Diffuser Design for the Retrofit of a Low Pressure Turbine Using In-House Exhaust Design System
Authors: Yoon Sungho , Stanislaus Felix Joe , Mokulys Thomas , Singh Gurnam , Claridge Martin
Published: May 2012

The performance of the last stage of a Low Pressure (LP) steam turbine is strongly coupled with the downstream exhaust hood performance. In particular, the effect of the diffuser within the exhaust hood on the pressure recovery is very important in retrofitting existing machines, which dictate many geometric constraints. Alstom’s in-house Exhaust Design System (EDS) simulates the three-dimensional flow in the exhaust hood by coupling the last stage blades and the exhaust hood. This EDS system can be used to design an LP diffuser in the exhaust hood and to achieve the required performance targets. In the first part of this paper, the EDS system is validated against measurements within model turbines, which represent both a standard machine as well as a retrofit machine. In the second part of this paper, an LP diffuser was redesigned to improve the performance using the EDS method. To begin with, an axi-symmetric diffuser was designed using numerical simulations of a passage in the last stage turbine as well as a slice of the diffuser and the exhaust hood. By carefully controlling the profile of the diffuser casing, the flow separation at the original casing walls was reduced significantly and this, in turn, improved the performance of the turbine substantially. Then, the full geometry of the exhaust hood was modeled in order to investigate the effect of the three-dimensional flow features. Based on the examined flow features, an asymmetric change was introduced to the diffuser casing to improve the three-dimensional flow structure. This new asymmetric diffuser was found to maximize the exhaust performance.
Comparison Between the Steady Performance of Double-Entry and Twin-Entry Turbocharger Turbines
Authors: Romagnoli Alessandro , Copeland Colin , Martinez-Botas Ricardo , Rajoo Srithar , Seiler Martin , Costall Aaron
Published: May 2012

Most boosting systems in internal combustion engines utilize ‘pulse turbocharging’ to maximize the energy extraction by the turbine. An internal combustion engine with more than four cylinders has a significant overlap between the exhaust pulses which, unless isolated, can decrease the overall pulse energy and increase the engine pumping loss. Thus, it is advantageous to isolate a set of cylinders and introduce the exhaust gases into two or more turbine entries separately. There are two main types of multiple entry turbines depending on the method of flow division: the twin-entry and the double-entry turbine. In the twin-entry design, each inlet feeds the entire circumference of the rotor leading edge regardless of inlet conditions. In contrast, the double-entry design introduces the flow from each gas inlet into the rotor leading edge through two distinct sectors of the nozzle. This paper compares the performance of a twin and double-entry mixed flow turbine. The turbines were tested at Imperial College for a range of steady-state flow conditions under equal and unequal admission conditions. The performance of the turbines was then evaluated and compared to one another. Based on experimental data, a method to calculate the mass flow under unequal admission from the full admission maps was also developed and validated against the test results.
Thermo-Economic Optimization of the CCPP Design With Supplementary Firing Considering Off-Design Performance and Operating Profile
Authors: Conte Enrico , Pedretti Camille
Published: May 2012

This paper presents the latest developments of a methodology for the initial design of the water/steam cycle in combined-cycle power plants, which aims at delivering optimal designs from an operator’s perspective. To this end, an evolutionary algorithm optimization toolbox is coupled to a process model of the water/steam cycle. The process model requires the definition of a number of boundary conditions (like GT type and ambient conditions) and the selection of the cycle configuration (number of pressure levels, single or double reheat, supplementary firing, heat integration with GT coolers, fuel gas preheating, steam extraction from the steam turbine and type of cold end, among others). Based on a number of thermodynamic parameters assigned by the optimizer, the process model derives an initial dimensioning and/or selection of the key components and systems from the OEM’s portfolio: HRSG (full, geometry-based technical dimensioning), piping, steam turbines, condenser and generator, among others. For each of those, realistic designs are ensured by checking and enforcing the component design rules. Finally, performance and cost are derived. In the latest development, the process model computes the plant performance in a number of off-design conditions, specified in a plant operating profile. These may include different ambient conditions, GT loads, power augmentation (e.g. supplementary firing, inlet fogging and evaporative cooling) and steam exports (e.g. to district heating, desalination plant, carbon capture system) or imports (e.g. from a solar field). The cost of electricity (CoE), net present value (NPV) or average efficiency of the plant design in the given operating profile is the feedback to the optimization algorithm. This guides the process towards the definition of a plant design that gives the best thermo-economic performance under the specified economic boundary conditions and operating scenario. In a typical example, an air-cooled peaking plant needs to be optimized to maximize NPV in an operating scenario characterized by large spikes of the electricity price in hot summer days, during which the plant operator wants to use supplementary firing to boost power production. The described methodology is applied to find the most advantageous dimensions of the supplementary firing to be installed and the right HRSG design pressure at design conditions, ensuring that all design rules and technical limits are respected in all operating conditions. In this way, an optimal point is found in the trade-off between amount of supplementary firing and dimensions of HRSG and air-cooled condenser, delivering the highest possible benefit to the plant operator.
LP Turbine Secondary Vortices: Reynolds Lapse
Authors: Kuerner Matthias , Reichstein Georg A. , Schrack Daniel , Rose Martin G. , Staudacher Stephan , Gier Jochen , Engel Karl
Published: May 2012

A two-stage turbine is tested in a cooperation between the Institute of Aircraft Propulsion Systems (ILA) and MTU Aero Engines GmbH (MTU). The experimental results taken in the Altitude Test Facility (ATF) are used to assess the impact of cavity flow and leakage on vortex structures. The analysis focuses on a range of small Reynolds numbers, from as low as 35,000 up to 88,000. The five hole probe area traverse data is compared to steady multistage CFD predictions behind the second vane. The numerical model compares computations without and with cavities modeled. The simulation with cavities is superior to the approach without cavities. The vortex induced blockage is found to be inversely proportional to Reynolds number. The circulation of the vortices is dependent on the Reynolds number showing a reversing trend to smallest Reynolds numbers. The steady numerical model as of yet is unsuitable to predict these trends. A first unsteady simulation suggests major improvements.
Prediction of Separation-Induced Transition on High Lift Low Pressure Turbine Blade
Authors: Benyahia Abdelkader , Castillon Lionel , Houdeville Robert
Published: May 2012

This paper deals with the development and validation of the Menter and Langtry correlation-based transition model in the RANS code elsA. Two types of experimental linear cascades of low pressure turbine (LPT) airfoils having different loading distributions have been considered for the validation: the T106C and T108 blades. Experimental data have been provided by the Von Karman Institute in the framework of the European program TATMo. Different Reynolds numbers varying from 80 000 to 250 000 and different freestream turbulence intensities have been investigated. The results obtained for the T106C blade are in good agreement with the experimental data: the bubble size and the kinetic energy losses are well predicted. Sensitivity to freestream turbulence is also well demonstrated for the considered Reynolds numbers. However the results for the T108 blade show the limitations of the current version. These limitations are explained and discussed in this paper. The second part of this paper deals with the numerical and physical aspects of periodical unsteady inlet conditions which are introduced in order to take into account the incoming wakes. The original Menter and Langtry transition model has required a modification for performing correct unsteady computations of wake induced transition which is discussed in this paper. The unsteady results obtained with elsA are in quite good agreement with the experimental data.
Experimental Investigation of Louver Cooling Scheme on Gas Turbine Vane Suction Side
Authors: Elnady T. , Hassan O. , Hassan I. , Kadem L. , Lucas T.
Published: May 2012

An experimental investigation has been performed to measure the film cooling performance of louver scheme over a scaled vane of high-pressure gas turbine using a two-dimensional cascade. Two rows of axially oriented louver scheme are used to cool the suction side and their performance is compared with two similar rows of standard cylindrical holes. The effect of hole location on the cooling performance is investigated for each row individually, then the row interaction is investigated for both rows at four different blowing ratios ranging from 1 to 2 with a 0.9 density ratio. The exit Reynolds number based on the true chord is 1.5E5 and exit Mach number is 0.23. The temperature distribution on the vane is mapped using a transient Thermochromic Liquid Crystal (TLC) technique to obtain the local distributions of the heat transfer coefficient and film cooling effectiveness. The louver scheme shows a superior cooling effectiveness than that of the cylindrical holes at all blowing ratios in terms of protection and lateral coverage. The row location highly affects the cooling performance for both the louver and cylindrical scheme.
An Experimental and Modeling Study of Laminar Flame Speeds of Alternative Aviation Fuels
Authors: Kick Thomas , Kathrotia Trupti , Braun-Unkhoff Marina , Riedel Uwe
Published: May 2012

The present work reports on measurements of burning velocities of synthetic fuel air mixtures exploiting the cone-angle method, as part of the EU project ALFA-BIRD. The GtL (Gas-to-Liquid)-air mixtures — (i) 100% GtL and (ii) GtL+20% hexanol, respectively — were studied at atmospheric pressure, with values of the equivalence ratio φ ranging between φ ∼ 1.0 and φ ∼ 1.3, at preheat temperatures To = 423 K (GtL+20% hexanol) as well as To = 473 K (for 100% GtL and GtL+20% hexanol). A comparison between experimentally obtained burning velocities and predicted values of laminar flame speed is presented, too. In general, good agreement was found between predicted and measured data for the range of conditions considered in the present study. The predictive capability of the detailed reaction model consisting of 3479 reactions involving 490 species will be discussed focusing on the laminar flame speed and the combustion of the components (n-decane, iso-octane, and 1-hexanol) of the surrogate used.
Theory and Application of Axisymmetric Endwall Contouring for Compressors
Authors: Kro¨ger Georg , Voß Christian , Nicke Eberhard , Cornelius Christian
Published: May 2012

Engine operating range and efficiency are of increasing importance in modern compressor design for heavy duty gas turbines and aircraft engines. These highly challenging objectives can only be met if all components provide high aerodynamic performance and stability. The aerodynamic losses of highly loaded axial compressors are mainly influenced by the leakage flow through clearance gaps. Especially the leakage flow due to the radial clearances of rotor blades affects negatively both, the efficiency and the operating range of the engine. Recent publications showed that the clearance flow and the clearance vortex can be influenced by an additional static pressure gradient at the outer casing, which is created by an axisymmetric wavy casing shape. A notable performance increase of up to 0.4% stage efficiency at design point conditions was reported for high pressure stages with large tip clearance heights [1] as well as for a transonic stage with a relatively small radial clearance gap [2]. An analytic approach to predict the effects of axisymmetric casing contouring has been developed at DLR, Institute of Propulsion Technology, and is outlined in the first part of this work. The characteristic behavior of the clearance vortex in an adverse pressure gradient is discussed by means of an inviscid vortex model [3]. The critical vortex parameters are isolated and related to the static pressure increase due to the casing contour. The second part illustrates the application of an axisymmetric endwall contour. A three dimensional optimization of the outer casing and the corresponding blade tip airfoil section of a typical gas turbine high pressure compressor stage with a high number of free variables is presented. The optimization led to a significant increase in aerodynamic performance of about 0.8% stage efficiency and to a notable reduction of the endwall blockage at ADP conditions. Furthermore, an improved off-design performance was found and a simple design rule is given to transfer both, the casing contour and the blade tip section modification on similar high pressure compressor blades. Based on these design rules the results of the optimized stages were applied to the rear stages of a Siemens gas turbine compressor CFD model. An increase of 0.3% full compressor performance was reached at design point conditions.
Stability of Centrifugal Compressors by Applications of Damper Seals
Authors: Memmott Edmund A.
Published: May 2012

This paper surveys the applications of damper seals to provide the stable operation with respect to rotordynamics of centrifugal compressors. Damper seals are applied as sealing devices at the division wall of back-to-back compressors and at the balance piston of in-line compressors. They consist of a roughened surface on the stator that is typically created by a pattern of holes. Rotordynamically stable operation is shown by a lack of or a small bounded amount of SSV (subsynchronous vibration) at the first fundamental lateral critical frequency. Experience plots showing the use of damper seals will be presented. Case histories of the use of damper seals will be given. Stability analysis and full load full pressure test results will be reviewed. The test results show no SSV at the first critical frequency with the damper seals.
The Effect of the Operating Conditions of the Last Turbine Stage on the Performance of an Axial Exhaust Diffuser
Authors: Opilat Victor , Seume Joerg R.
Published: May 2012

The exhaust diffusers studied in this paper are installed behind the last turbine stage of gas turbines, including those used in combined cycle power plants. For the design of efficient diffusers, the effects caused by the last turbine stage need to be taken into account. In the present paper, results are presented to estimate the performance of a diffuser operating under a variation of multiple modelling parameters: tip leakage flow, the swirl, and the rotating blade wakes. To provide a better understanding of the flow parameters, a test facility with a turbine stage simulator is used to model these flow effects and an optical endoscopic planar measurement technique based upon Particle Image Velocimetry (PIV) is applied. The pressure recovery is estimated for various turbine conditions using a variety of relevant parameters. Within a range of conditions, a PIV study is performed to try to understand the typical flow phenomena which influence the performance of axial diffusers. The rise of turbulent energy in the inlet flow positively affects the diffuser performance. A small positive swirl angle in the inlet flow (behind the rotating bladed wheel in experiments) has a stabilizing effect on the diffuser. The tip leakage flow from the last turbine stage can also positively affect the pressure recovery in the diffuser.
Influence of Unsteady Turbine Flow on the Performance of an Exhaust Diffuser
Authors: Kuschel Marcus , Seume Joerg R.
Published: May 2012

For the design of highly efficient turbine exhaust diffusers, it is important to take into account the unsteady flow field induced by the last turbine stage. A 1/10 scale model of a gas turbine exhaust diffuser consisting of an annular followed by a conical diffuser is used to investigate the influence of the unsteady flow conditions on the performance of the diffuser. To reproduce the outflow of the last turbine stage, a NACA profiled rotor is placed at the inlet of the diffuser. Measurements with 3D hot-wire probes are conducted in order to resolve the unsteady flow mechanisms inside the annular diffuser. Additionally, unsteady pressure transducers are installed at the shroud of the diffuser and on the surface of the NACA blades to detect rotating instabilities generated by the rotor. For operating points with a high flow-coefficient, vortices are generated at the tip of the blades. They support the boundary layer at the shroud with kinetic energy up to the half-length of the annular diffuser, which leads to a high pressure recovery. For operating conditions without generated vortices, the pressure recovery is significantly lower. The analysis of the pressure signals at the shroud and at the rotating blades with auto- and cross-correlations show that the number of generated vortices at the tip of the blades is lower than the number of blades. For the operating point with the highest flow coefficient, it can be shown that fourteen vortices are generated at the tip of the thirty blades. In modern RANS-model based CFD-codes, turbulence is modeled as isotropic flow. By comparing the three Reynolds Stress components behind the rotor it can be shown that the flow field especially in the wake of the blades is non-isotropic. This shows that diffuser flows should be modeled with turbulence models which account for non-isotropy.
Influence of Different Rim Widths on Leakage Flow
Authors: Wang Jin , Zeng M. , Wang Q. W.
Published: May 2012

Three-dimensional simulations of squealer tip on GE-E3 blade with eight film cooling holes were numerically studied. The effect of the rim width and the blowing ratio on the blade tip flow was revealed. Numerical simulations were performed to predict the leakage flow and the tip heat transfer with the k-ε model. For the squealer tip, the depth of the cavity is the same and the width of the shoulder varies to form a narrow rim and a wide cavity, which can decrease the coolant momentum and the tip leakage flow velocity. This cavity contributes to the improvement of the cooling effect in the tip zone. To investigate the leakage flow influenced by the rim width, numerical simulations were made at four different models which have different rim widths of 0.58%, 0.89%, 1.16% and 1.74% axial chord (0.5mm, 0.77mm, 1 mm and 1.5mm, respectively) on both the pressure side rim and the suction side rim. From the simulated results, mathematical equations of mass flow rate of the leakage flow and the blowing ratio were proposed. With different rim widths, the effect of different global blowing ratios of M = 0.5, 1.0 and 1.5 is investigated. In addition, calculation results of squealer tip and flat tip were compared. The simulation results are validated with some limited experimental data in the open literatures.
An Investigation Into Improving Off-Design Performance in a Turbocharger Turbine Utilizing Non-Radial Blading
Authors: Walkingshaw Jason , Spence Stephen , Ehrhard Jan , Thornhill David
Published: May 2012

Off-design performance now plays a vital role in the design decisions made for automotive turbocharger turbines. Of particular interest is extracting more energy at high pressure ratios and lower rotational speeds. In this region of operation the U/C value will be low and the rotor will experience high values of positive incidence at the inlet. The positive incidence causes flow to separate on the suction surface and produces high blade loading at inlet, which drives tip leakage. A CFD analysis has been carried out on a number of automotive turbines utilizing non-radial fibred blading. To help improve secondary flows yet meet stress requirements a number of designs have been investigated. The inlet blade angle has been modified in a number of ways. Firstly, the blading has been adjusted as to provide a constant back swept angle in the span wise direction. Using the results of the constant back swept blading studies, the back swept blade angle was then varied in the span wise direction. In addition to this, in an attempt to avoid an increase in stress, the effect of varying the leading edge profile of the blade was investigated. It has been seen that off-design performance is improved by implementing back swept blading at the inlet. Varying the inlet angle in the span wise direction provided more freedom for meeting stress requirements and reduces the negative impact on blade performance at the design point. The blade leading edge profile was seen to offer small improvements during off-design operation with minimal effects on stress within the rotor. However, due to the more pointed nature of the leading edge, the rotor was less tolerant to flow misalignment at the design point.
A Study of Steam-Cooled Humidified Gas Turbine Cycles
Authors: Tang Ching-Jen C. J.
Published: May 2012

Humidified Gas Turbine (HGT) cycles such as the Evaporative Gas Turbine (EGT) and the Steam-Injected Gas Turbine (STIG) using humid air as the working medium do not require a complete steam turbine bottoming cycle; thus, their initial capital costs are not as high as those for the conventional combined cycles. The performance of a HGT cycle could be comparable to a state-of-the-art combined cycle for small loads. The availability of the steam from a HGT cycle presents opportunities for designing steam-cooled blades. Since the specific heat capacity for steam is higher than that for air, steam could potentially be a better coolant for turbine blades than air, resulting in higher cycle efficiency. In this study, three known HGT cycles are evaluated in terms of their electrical efficiencies and power outputs: the STIG, the Part-flow Evaporative Gas Turbine (PEvGT), and the combined STIG cycles. All the three HGT cycles are analyzed in two cooling options: steam and air coolings. The HGT cycles will be evaluated using consistent thermodynamic properties and assumptions. Like a simple gas turbine cycle, the HGT cycles are based on the well-known Brayton cycle whose performance is dictated by the cycle pressure ratio and turbine inlet temperature. Therefore, the electrical efficiencies and power outputs of the HGT cycles will be calculated as a function of the cycle pressure ratio and turbine inlet temperature. The steam-cooled cycles provide advantages over the air-cooled cycles in the electrical efficiency, power output, and combustion stability. The steam cooling improves the electrical efficiency by approximately 1.4 percentage points for the STIG cycle, by approximately 1.7 percentage points for the PEvGT cycle, and by approximately 1 percentage point for the combined STIG cycle. The maximum electrical efficiency of the steam-cooled PEvGT cycle is 54.6%, only 0.2 percentage points higher than that for the steam-cooled combined STIG cycle. The steam cooling generally results in more power output than the air cooling does for all the HGT cycles at most operating conditions. In addition, the steam cooling reduces the water content of the humid air entering the combustor, leading to significantly improved combustion stability.
Injection of Subcritical and Supercritical Aviation Kerosene Into a High-Temperature and High-Pressure Crossflow
Authors: Xue Xin , Gao Wei , Xu Quanhong , Lin Yuzhen , Sung Chih-Jen
Published: May 2012

In the present experimental study, injection of subcritical and supercritical kerosene into a high-temperature and high-pressure subsonic crossflow was investigated. Visualization and characterization of the jet structures were performed using schlieren imaging, from which the jet penetration trajectory was determined. For the conditions tested, a correlation of jet penetration trajectory was developed, with momentum ratio as the primary parameter. An analysis based on one-dimensional isentropic flow was also conducted to calculate the flow parameter variations in the nozzle and along the jet trajectory. Using a three-component kerosene surrogate, the phase transition processes for supercritical and subcritical kerosene jets were illustrated in the thermodynamic phase diagram. Experimental and analytical results demonstrated that the behavior and penetration of supercritical kerosene injection into high temperature and high pressure crossflow were closer to those of the case with gas jet injecting into a gas crossflow than the case with liquid kerosene injection.
Algebraic Anisotropic Eddy-Viscosity Modeling for Application to Turbulent Film Cooling Flows
Authors: Li Xueying , Ren Jing , Jiang Hongde
Published: May 2012

Under-predicting the spanwise spreading of film cooling is a big problem in the film cooling computation. This is mainly due to the incorrect simulation of the spanwise transport of the jet in crossflow by conventional isotropic eddy viscosity turbulent models. An improved algebraic anisotropic eddy viscosity method including both the influence of the wall and the strain of the mean flow field to the anisotropic ratio has been raised by the authors in the paper, referred to as Algebraic Anisotropic Eddy Viscosity (AAEV) method. An equation derived from the algebraic Reynolds stress transport equations is applied to compute the anisotropic eddy-viscosity ratio. The variation of the anisotropic eddy-viscosity ratio is a function of both the dimensionless wall distance and the local mean flow field. This method is applied to the two layer k-ε model with a one-equation model in near-wall region to form a new turbulent model- AAEV k-ε model. The new model is tested for the computation of a flat plate film cooling flow with an inclined row of streamwise injected jets. Comparison of the results between the AAEV k-ε model and two-layer k-ε model with the measured adiabatic film-cooling effectiveness distributions indicates that the AAEV k-ε model can correctly predict the spanwise spreading of the film and reduce the strength of the secondary vortices.
Validation of Advanced Steam Turbine Technology: A Case Study of an Ultra Super Critical Steam Turbine Power Plant
Authors: Quinkertz Rainer , Thiemann Thomas , Gierse Kai
Published: May 2012

High efficiency and flexible operation continue to be the major requirements for power generation because of the benefits of reduced emissions and reduced fuel consumption, i.e. reduced operating costs. Ultra super critical (USC) steam parameters are the basis for state of the art technology of coal fired power plants with highest efficiency. An important part of the development process for advanced steam turbines is product validation. This step involves more than just providing evidence of customer guaranteed values (e.g. heat rate or electric output). It also involves proving that the design targets have been achieved and that the operational experience is fed back to designers to further develop the design criteria and enable the next step in the development of highly sophisticated products. What makes product validation for large size power plant steam turbines especially challenging is the fact that, due to the high costs of the required infrastructure, steam turbine manufacturers usually do not have a full scope / full scale testing facility. Therefore, good customer relations are the key to successful validation. This paper describes an extensive validation program for a modern state of the art ultra supercritical steam turbine performed at an operating 1000 MW steam power plant in China. Several measuring points in addition to the standard operating measurements were installed at one of the high pressure turbines to record the temperature distribution, e.g. to verify the functionality of the internal cooling system, which is an advanced design feature of the installed modern high pressure steam turbines. Predicted 3D temperature distributions are compared to the actual measurements in order to verify and evaluate the design rules and the design philosophy applied. Conclusions are drawn regarding the performance of modern 3D design tools applied in the current design process and an outlook is given on the future potential of modern USC turbines.
Actuated Transition in an LP Turbine Laminar Separation: An Experimental Approach
Authors: Baumann Jenny , Rist Ulrich , Rose Martin , Ries Tobias , Staudacher Stephan
Published: May 2012

The reduction of blade counts in the LP turbine is one possibility to cut down weight and therewith costs. At low Reynolds numbers the suction side laminar boundary layer of high lift LP turbine blades tends to separate and hence cause losses in turbine performance. To limit these losses, the control of laminar separation bubbles has been the subject of many studies in recent years. A project is underway at the University of Stuttgart that aims to suppress laminar separation at low Reynolds numbers (60,000) by means of actuated transition. In an experiment a separating flow is influenced by disturbances, small in amplitude and of a certain frequency, which are introduced upstream of the separation point. Small existing disturbances are therewith amplified, leading to earlier transition and a more stable boundary layer. The separation bubble thus gets smaller without need of a high air mass flow as for steady blowing or pulsed vortex generating jets. Frequency and amplitude are the parameters of actuation. The non-dimensional actuation frequency is varied from 0.2 to 0.5, whereas the normalized amplitude is altered between 5, 10 and 25% of the free stream velocity. Experimental investigations are made by means of PIV and hot wire measurements. Disturbed flow fields will be compared to an undisturbed one. The effectiveness of the presented boundary layer control will be compared to those of conventional ones. Phase-logged data will give an impression of the physical processes in the actuated flow.
Altitude Testing of the E3E Core Engine
Authors: Klinger Holger , Bake Sebastian , Vogt Hans-Frieder , Knieschke Daniel , Schober Peter
Published: May 2012

Within the E3E framework of the German Aeronautics Research Program Rolls-Royce Deutschland developed key technologies for an all new core engine that incorporates major advances with regard to environmental friendliness, efficiency and economy. The derived E3E core engine will serve as a scalable baseline for the future two-shaft engine family in the medium take-off thrust range. The latest build of the core engine demonstrator has accomplished a 40 hours test campaign in 2010 aiming at functional testing up to the master design point as well as intensive altitude experiments. The core engine features a nine stage HP compressor with an innovative axial load compensation system to cope with the high pressure ratio of 22:1 in one spool. A staged lean burn combustor demonstrates altitude relight, quick windmill relights and cold start capability. The 2-stage shroudless HP turbine is designed for strong rubs into the ceramic liner material to retain high turbine efficiency. The results and analysis will be presented in this paper.
Start-Up Behavior of a Three-Bladed H-Darrieus VAWT: Experimental and Numerical Analysis
Authors: Bianchini Alessandro , Ferrari Lorenzo , Magnani Sandro
Published: May 2012

Despite increasing attention paid by both the industrial and the academic worlds, an effective diffusion of Darrieus wind turbines is still hindered by productivity lower than that of classical HAWTs, mainly connected to the critical behavior of these machines during the transient phases and in particular, during the start-up transitory, which has not been investigated in depth in the past. In this paper, a numerical code for the evaluation of the transient behavior of H-Darrieus turbines is presented. The time-dependent code was based on a theoretical approach derived from the Momentum Models and completed by several sub-models for the evaluation of the main secondary and parasitic effects. The new software was validated with an extended experimental campaign in a wind tunnel on a three-bladed H-Darrieus turbine, obtaining constant agreement with experimental data. A sensitivity analysis was then performed in order to investigate the start-up behavior of a generic small size three-bladed H-Darrieus rotor. In particular, for a fixed turbine layout, the influence of the airfoil type and the blade shape on the startup capabilities of the rotor was investigated as a function of the initial position of the rotor and the oncoming wind velocity.
Time-Resolved Numerical Investigation of the Interaction of Labyrinth Seal Leakage and Main-Flow in a 1.5-Stage LP Turbine
Authors: Biester Marc H.-O. , Mueller Lasse , Seume Joerg R. , Guendogdu Yavuz
Published: May 2012

In axial turbomachinery such as low pressure turbines, shrouded airfoils with labyrinth seals are commonly used. Among different sealing options, labyrinth seals in particular are characterized by long term durability and high sealing efficiency. Since a leakage flow is inevitable, a thorough understanding of how the leakage flow exits the cavities, its interaction with the main flow, and the induction of losses is necessary. In order to take into account unsteady effects, three-dimensional time resolved RANS computations of a 1.5 stage LPT rig in its design operating point are conducted. To capture effects in the boundary layer, a low Reynolds approach is used at the blade surface as well as on the hub and tip surfaces. To match the real geometry of the turbine blades, fillets have been modeled. Simulations were performed using the TRACE solver developed by the German Aerospace Center (DLR). The investigation shows how cavity flows have a significant influence on the main-flow aerodynamics and the loss generation. Steady and unsteady results with full spatially discretized cavities show a significant decrease of isentropic efficiency compared to simulations without cavities. The efficiency drop for the steady and time-averaged cavity computations can be explained with intensified secondary flow. The time resolved calculation shows a strong non-uniformity of the leakage flux depending on the instantaneous circumferential position of the up- and downstream blades. The time dependent ingress of cavity leakage results in the formation of a counter-rotating vortex pair. In terms of the influence on the main flow, it is shown that the interaction is limited to the end walls with almost no influence on the midspan flow.
Aerodynamic Investigation of the Performance of a Two Stage Axial Turbine at Design and Off-Design Conditions
Authors: Abdelfattah Sherif A. , Chibli Hicham A. , Schobeiri M. T.
Published: May 2012

This paper describes numerical aerodynamic investigations of a two-stage, high pressure axial turbine at design and off-design operating conditions. The flow field in a high pressure turbine is highly complex due to unsteadiness of the flow and the various effects of blade row interaction. Blade loss mechanisms generally include primary and secondary loss mechanisms. Examples of primary loss mechanisms include boundary layer losses, shock losses and mixing losses, whereas examples of secondary losses include tip leakage losses and end wall losses which both create secondary flow characteristics. Although modern numerical analysis techniques have provided good understanding of the flow field, it is still difficult to accurately predict impact due to the aforementioned loss effects. This is generally due to errors predicting in boundary layers, transition as well as false entropy generation due to numerical dissipation. When a turbine is operated at off-design conditions the primary and secondary loss effects are further increased and create further reductions in engine efficiency. In this study a numerical model of the two-stage axial turbine was constructed and run under boundary conditions designed to mimic the operating conditions applied during engine operation. The shear stress transport (SST) turbulence model was selected for its versatility in turbomachinery applications. A comparison was made between both experimentally measured efficiencies and numerically predicted efficiencies.
Conjugate Heat Transfer Analysis for a Film-Cooled Turbine Vane
Authors: Ni Ron Ho , Humber William , Fan George , Johnson P. Dean , Downs Jim , Clark J. P. , Koch P. J.
Published: May 2012

A conjugate heat transfer analysis methodology has been defined and applied to an Air Force film cooled turbine vane consisting of 648 cooling holes. An unstructured computational mesh was used to model both the fluid and metal sides of the turbine vane. A summary of the numerical methods employed by Code Leo is provided along with a description of the coupling procedure employed between the fluid and heat conduction computations. Numerical simulations were conducted at multiple mesh resolutions to assess accuracy and repeatability. A detailed review is presented for the numerical solution obtained from a fine mesh consisting of 24 million elements (8 million solid, 16 million fluid) covering all 648 film holes. Results showed that cooled air from the film holes formed a protective layer around the airfoil surfaces and endwalls as intended. Low metal temperatures were present not only on the external surfaces exposed to hot gas, but also around the entrances to the film cooling holes. Cooled air was also observed to pile up along the pressure surface at mid-span. Solution convergence was achieved in approximately 15,000 iterations and 100 hours elapsed time on a dual-socket Intel E5504 workstation. The combination of fast turnaround time with accurate metal temperature prediction will enable conjugate heat transfer analysis to be easily incorporated into routine design processes to better address durability goals.
Effect of Rib Spacing on Heat Transfer in a Two Pass Rectangular Channel (AR=2:1) at High Rotation Numbers
Authors: Lei Jiang , Han Je-Chin , Huh Michael
Published: May 2012

In this paper the effect of rib spacing on heat transfer in a rotating two-passage channel (AR=2:1) at orientation angle of 135° was studied. Parallel ribs were applied on leading and trailing walls of the rotating channel at the flow angle of 45°. The rib-height-to-hydraulic diameter ratio (e/Dh) was 0.098. The rib-pitch-to-rib-height (P/e) ratios studied were 5, 7.5, and 10. For each rib-spacing, tests were taken at five Reynolds numbers from 10,000 to 40,000 and for each Reynolds number, experiments were conducted at four rotational speeds up to 400 rpm. Results show that the heat transfer enhancement increases with decreasing P/e from 10 to 5 under non-rotation condition. However, the effect of rotation on the heat transfer enhancement remains about the same for varying P/e from 10 to 5. Heat transfer enhancement due to rotation can be correlated on all surfaces (leading, trailing, inner and outer walls and tip cap region) in the two-passage 2:1 aspect ratio channel.
Aerodynamic and Aerothermal Investigation of the Flow Around an HPT Rotor Shroud: PIV Measurements
Authors: Lehmann Knut , Kanjirakkad Vasudevan , Hodson Howard
Published: May 2012

An experimental study has been conducted to investigate the aerothermal performance of a shrouded high pressure turbine blade in a large scale rotating rig. The rotor blade and the associated shroud and casing geometry have been modelled in a large scale low speed turbine rig that was designed to investigate a novel passive shroud cooling methodology. The objective of the present paper is to provide a detailed description of the flow field around the rotor blade shroud. The improved physical understanding of the shroud flow gained from this study will be used to analyse the aerothermal performance of the shroud cooling strategy as reported in a companion paper, Lehmann et al. [1]. Experiments have been carried out using endoscopic PIV to identify and understand salient flow features that exist upstream and downstream of the shroud as well as within the shroud cavities. The measurements are complemented by steady and unsteady numerical computations of the turbine stage. The study identifies the existence of important vortical structures within the shroud cavities that not only interact with the main passage flow but also modify the amount and distribution of the shroud leakage flow in a manner that has major implications for shroud cooling and heat transfer. A detailed shroud flow model is derived and used to elucidate the causes and consequences of the flow pattern observed. The model emphasises the circumferentially asymmetric nature of the cavity flow structures caused by the presence of the inter shroud gap that in turn influences the production, interaction and dissipation of such vortical structures.
Experimental and Numerical Crossover Jet Impingement in a Rib-Roughened Airfoil Trailing-Edge Cooling Channel
Authors: Taslim M. E. , Fong M. K. H.
Published: May 2012

Local and average heat transfer coefficients were measured in a test section simulating a rib-roughened trailing edge cooling cavity of a turbine airfoil. The test rig was made up of two adjacent channels, each with a trapezoidal cross sectional area. The first channel, simulating the cooling cavity adjacent to the trailing-edge cavity, supplied the cooling air to the trailing-edge channel through a row of racetrack-shaped slots on the partition wall between the two channels. Eleven crossover jets, issued from these slots entered the trailing-edge channel, impinged on eleven radial ribs and exited from a second row of race-track shaped slots on the opposite wall in staggered or inline arrangement. Two jet angles of 0 and 5° and a range of jet Reynolds number from 10,000 to 35,000 were tested and compared. The numerical models contained the entire trailing-edge and supply channels with all slots and ribs to simulate exactly the tested geometries. They were meshed with all-hexa structured mesh of high near-wall concentration. A pressure-correction based, multi-block, multi-grid, unstructured/adaptive commercial software was used in this investigation. Standard high Reynolds number k–ε turbulence model in conjunction with the generalized wall function for most parts was used for turbulence closure. Boundary conditions identical to those of the experiments were applied and several turbulence model results were compared. The numerical analyses also provided the share of each crossover and each exit hole from the total flow for different geometries. The major conclusions of this study were: a) except for the first and last cross-flow jets which had different flow structures, other jets produced the same heat transfer results on their target surfaces, b) tilted crossover jets produced higher heat transfer coefficients on the target surface towards which they were tilted and lower values on the opposite surface and c) the numerical predictions of impingement heat transfer coefficients were in good agreement with the measured values for most cases thus CFD could be considered a viable tool in airfoil cooling circuit designs.
Hydrodynamic Analysis of Compliant Foil Bearings With Modified Top Foil Model
Authors: Xu Fangcheng , Liu Zhansheng , Zhang Guanghui , Xie Liang
Published: May 2012

The mathematical model of film thickness is developed with considering the compressibility of the gas and the deformation of the foil in this paper. By employing the Newton-Raphson method and the finite difference method, the compressible gas lubricated Reynolds equation and the film thickness equation are solved coupling together. The static characteristics such as pressure distribution and film thickness distribution for equivalent bump foil stiffness model are obtained to verify the validation of the proposed method. The gas film thickness model is modified by modeling the top foil as the one dimension curved beam, to meet the case of the real physical model. The numerical results of this modified structural model are compared with the other finite element top foil models. It indicates that the pressure distribution for bump foil gas bearing is in good agreement with the test data.
Effects of Axial Row-Spacing for Double-Jet Film-Cooling on the Cooling Effectiveness
Authors: Wang Zhan , Liu Jian-Jun , An Bai-tao , Zhang Chao
Published: May 2012

The effects of axial row-spacing for double jet film-cooling (DJFC) with compound angle on the cooling characteristics under different blowing ratios were investigated numerically. First, the flow fields and cooling effectiveness of DJFC on flat plate with different axial row-spacing were calculated. Film-cooling with fan-shaped or cylindrical holes was also calculated for the comparison. The results indicate that a larger axial row-spacing is helpful to form the anti-kidney vortex and to improve the cooling effectiveness. The DJFC was then applied to the suction and pressure surface of a real turbine inlet guide vane. Comparisons of film-cooling effectiveness with the cylindrical and fan-shaped holes were also conducted. The results for the guide vane show that on the suction surface the DJFC with a larger axial row-spacing leads to better film coverage and better film-cooling effectiveness than the cylindrical or fan-shaped holes. On the pressure surface, however, the film-cooling with fan-shaped holes is superior to the others.