bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Investigations of Flow Separation Control for a Low Pressure Turbine Blade Using Steady and Pulsed Vortex Generator Jets
Authors: Liu Xiaomin , Zhou Haiyang
Published: January 2011

This paper investigated numerically the application of Vortex Generator Jets (VGJs) to control flow separation on the suction side of a low pressure turbine blade. Firstly, numerical simulations of flow separation for a LPT blade, which based on Menter’s SST k-ω turbulence model coupled with Langtry-Menter transition model, were performed for different Reynolds numbers Re∼100,000, 75,000, 50,000 and 25,000, for three freestream turbulence intensity (FSTI) of 0.08%, 2.35% and 6.0%. The pressure distributions around the turbine blade and streamline plots showing the flow separation were presented in this paper. Good agreement of the numerical and experimental results also showed the validity of the numerical scheme for simulating the flow separation occurring on a low pressure turbine blade. And then, steady Vortex Generator Jets (steady VGJs) having pitch angle of 30°, skew angle of 90°, blowing ratio of 2.0 were used to control the flow separation in the suction side of the low pressure turbine blade. Although steady VGJs have been illustrated to be extremely robust at suppressing low Reynolds number separation, the practical application of VGJs in the low pressure turbine engine is in the pulsed mode. The injection mass flow requirements of pulsed Vortex Generator Jets (pulsed VGJs) can be reduced drastically when similar flow control effect is obtained using steady VGJs. For pulsed VGJs, the pulse frequency has been found to be an important control parameter for the flow separation control. In this paper, cases with the duty cycle of 0.5 were studied for the pulse frequency ranging from 2.5Hz to 10Hz at Re = 25,000 and freestream turbulence level of 0.08%. The numerical results showed that pulsed VGJs can effectively reduce and even eliminate the flow separation on the blade suction surface while there is an optimal pulse frequency. The flow control mechanism of VGJs on LPT blade was also revealed.
The Deduction of the Integral and the Estimation of the Local Core Rotation Ratio by Telemetric Pressure Measurements in a Two Cavity Test Rig
Authors: Uffrecht Wieland , Gu¨nther Andre´
Published: January 2011

The heat transfer in rotating cavities as found in the internal air system of gas turbines is mainly governed by the flow passing through these specific machine structures. Therefore the understanding of the local heat transfer in the rotating cavities relies on the knowledge about the flow structure created by the specific flow modes of interest. The core rotation ratio represents the circumferential velocity, which is suspected to be a flow parameter of significant influence on the heat transfer in rotating cavities flown through in radial direction. Therefore this paper is focussed on the deduction of the core rotation ratio and the estimation of its local distribution using telemetric pressure measurements. The local core rotation ratio is connected to the radial pressure distribution in the rotating cavity system. This permits to deduce an integral core rotation ratio from pressure measurements in the rotating cavity system. A flow structure based approximation of the measurements permits to estimate the radial distribution of the core rotation ratio in the rotating cavity. The results of the measurements with varied flow rates and revolving speeds is presented as well as a discussion of the fit parameters and its dependency on the operation mode of the test rig.
Aerodynamics and Aeroelasticity of Impeller Vane Interactions in a High Pressure Ratio Centrifugal Compressor
Authors: Krishnababu S. K. , Imregun M. , Green J. S. , Hoyniak D.
Published: January 2011

The interaction between impeller and diffuser in a high-pressure ratio centrifugal compressor is considered to have a strong influence on the unsteady flow field, the impeller response and the performance of the compressor. A computational study was performed to investigate the interactions between a backswept impeller and its downstream vaned diffuser with emphasis on the impeller response at 2 different vane settings. The unsteady computations were conducted using two different modelling levels of increasing fidelity. The computational domain included an impeller with 15 main and 15 splitter blades and 22-vane wedge diffuser. A steady-state stage calculation with a mixing-plane interface between the impeller trailing edge and the vane leading edge was conducted first to assess the performance. A whole-annulus unsteady stage calculation was conducted to study the response of the impeller. The effect of radial gap between the impeller trailing edge and the vane leading edge on the performance of the impeller was investigated in some detail. In agreement with other similar studies, the results suggest that there is an optimum value of the radius ratio for best performance.
Experimental Investigation Into Unsteady Effects on Film Cooling
Authors: Fawcett Richard J. , Wheeler Andrew P. S. , He Li , Taylor Rupert
Published: January 2011

The benefits of different film cooling geometries are typically assessed in terms of their time averaged performance. It is known that the mixing between the coolant film and the main turbine passage flow is an unsteady process. The current study investigates the forms of unsteadiness which occur in engine-representative film cooling flows, and how this unsteadiness affects the mixing with the mainstream flow. Cylindrical and fan-shaped cooling holes across a range of hole blowing ratios have been studied experimentally using Particle Image Velocimetry and High Speed Photography. Coherent unsteadiness is found in the shear layer between the jet and the mainstream, for both cylindrical and fan-shaped cooling holes. Its occurrence and sense of rotation is found to be controlled by the velocity difference between the mainstream flow and the jet which is largely determined by the blowing ratio.
Rotor Dynamic Analysis on Partial Admission Control Stage in a Large Power Steam Turbine
Authors: Gao Lin , Dai Yiping
Published: January 2011

Partial admission is used widely for steam turbines to match their output power to the load demand. The occurrences or thresholds of most self-induced low-frequency vibrations are under partial admission conditions. But the destabilizing forces which cause rotor instability are seldom investigated under partial admission conditions especially for large power steam turbines. Full 3D CFD model is built for the control stage of a 600 MW steam turbine applying commercial codes. N-S equations are solved to investigate the flow fields in the control stage including all the blade passages and the labyrinth seal over the shroud. Interesting flow distributions are observed for the seal spaces at partial admission conditions. A correction formula is presented for partial admission labyrinth seal based on the classical one and a method is discussed for the estimation of partial-admission phase-angle-dependent stiffness coefficients. The destabilizing forces acting on the rotor system are calculated for different eccentricity angles and are compared with those under the concentric condition. The stiffness coefficients are solved under typical partial admission conditions. They are found to change dramatically with the phase angle. The results may be helpful for a deep understanding of the low-frequency variation problems of large power steam turbines under partial admission conditions.
Development of Non-Destructive Heat Resistance Evaluation System for TBC on Gas Turbine Blade
Authors: Fujii Tomoharu , Takahashi Toshihiko , Sakai Eiji , Fujioka Terutaka
Published: January 2011

The use of thermal barrier coatings (TBCs) is the key technique for realizing high-efficiency gas turbine combined cycles. Hence, TBCs are applied to various hot gas path components such as combustors, blades, and vanes. The application of a TBC causes a significant decrease in the temperature of the base metal surface. Consequently, the lifetime of the component is increased. However, it is reported that under high-temperature operating conditions, the heat resistance of the TBC decreases gradually because of sintering and erosion of the TBC layer. Accurate evaluation of changes in the TBC heat resistance is very important for evaluating the residual lifetime of a given component. We have previously developed a nondestructive technique for measuring the heat resistance of TBCs applied on the inner surface of a combustion liner. In this technique, the TBC surface is heated by a laser beam, and the temperature change of this heated point is measured by an IR camera. The heat resistance is calculated from the measured temperature. On the basis of this concept, we have made improvements to this technique so that it can be used to measure the heat resistance of a TBC layer on a blade surface. However, several difficulties are encountered when using this technique for the abovementioned purpose. For example, the blade has a three-dimensional (3D) surface and complex internal cooling paths, as opposed to the combustion liner, which has a simple cylindrical shape. Hence, it is difficult to keep the same heating condition at any surface. To overcome these difficulties, we propose a new concept and develop a system for measuring the heat resistance of the TBC layer on a blade. This system is mainly composed of a carbon dioxide laser, a robot arm, and an IR camera. In this paper, we present an overview of the developed system.
A 3-D Compressible Flow Model for Weak Rotating Waves in Vaneless Diffusers: Part I—The Model
Authors: Chen Hua , Shen Fen , Zhu Xiao-cheng , Du Zhao-hui
Published: January 2011

A three-dimensional compressible flow model is presented to study the occurrence of weak rotating waves in vaneless diffusers of centrifugal compressors. The diffuser considered has two parallel walls, and the undisturbed flow is assumed to be circumferentially uniform, isentropic and to have no axial velocity. Linearised 3D compressible Euler eqns. were casted on a rotating coordinate system traveling at the same angular speed as the wave cells. A disturbance of radial velocity at the inlet and a uniform static pressure at the outlet of the diffuser were imposed. Complex functions of the solutions to the eqns. were obtained by a second order finite difference method and the Singular Value Decomposition technique. The influences of the inlet Mach number on the rotating waves were studied and preliminary results show that the critical flow angle and rotating wave speed are both affected by the Mach number. However, the angle only increases slightly with the Mach number while the wave speed increases rapidly with the Mach number.
Heavy Duty Gas Turbine Simulation: A Compressor IGV Airfoil Off-Design Characterization
Authors: Carcasci Carlo , Da Soghe Riccardo , Silingardi Andrea , Astrua Pio , Traverso Stefano
Published: January 2011

The correct simulation of power plant behavior over a variety of operating conditions has to be extremely detailed in order to provide reliable help to the turbomachinery developers. The latter instance implies for designers and commercial personnel to be equipped with reliable calculation tools (in-house developed or commercial). In particular, Performance Analysis Codes (PACs) allow the designers to analyze different system configurations. To predict off-design behavior, these codes need to be not limited to thermodynamic analysis, but also able to perform a simplified description of each component that require a specific set of correlations. The selection of suitable correlation sets for compressor IGV airfoils could be very difficult. This paper deal with a procedure based on 2D-CFD analysis to provide a reliable evaluation of compressor IGV airfoils deviation and profile loss coefficients in a wide range of operating condition. The analysis were set up on the IGV of the Ansaldo Energia AE94.3A compressor and the developed correlations were successfully implemented in an in-house PAC called ESMS.
Factors Affecting Oil Removal From an Aeroengine Bearing Chamber
Authors: Chandra Budi , Simmons Kathy , Pickering Stephen , Tittel Marc
Published: January 2011

Aeroengines incorporate various bearing chambers that house the shaft bearings and the oil used to cool and lubricate these bearings must subsequently be recovered from these chambers. Effective oil removal (scavenge) is essential to avoid heat generation through unnecessary working of the oil which can lead to excessive heat generation and reduced overall efficiency. Therefore the design of the scavenge region (sump) in a bearing chamber, as well as the ability to assess its performance is very important. An ongoing research program into bearing chamber scavenge comprising experimental and computational components is being conducted at the University of Nottingham Technology Centre in Gas Turbine Transmission Systems. This program is enhancing understanding of sump performance and design. In this paper an experimental study into a simplified but representative scavenge is reported. This experimental work helps to further understanding of the complex two-phase flow physics in a bearing chamber, particularly in the scavenge region, by means of various measurements and flow visualization. For the study a bespoke test rig has been built. It consists of a simplified, generic bearing chamber with simple sump geometry constructed entirely of Perspex to allow visualization. A shaft in the centre of the chamber capable of rotating up to 15,000 rpm is employed to introduce a windage flow in the chamber. Water (the working fluid) is fed to the chamber via an inlet pump and an outlet pump removes liquid from the chamber, closing the circuit. Several pneumatic pinch valves are installed in the flow circuit to allow residence volume measurement. A completely air-tight reservoir with internal baffle functions as a simple liquid-gas separator, allowing measurement of gas volumetric flow rate in the off-take pipe; hence the scavenge ratio (ratio of total exit volume to liquid volume) can be obtained. Residence volume measurements highlight the importance of sump geometry as an ill-designed sump can lead to an undesirable increase in residence volume.
Parametric Modelling of a Spiral Bevel Gear Using CFD
Authors: Webb Thomas , Eastwick Carol , Morvan Herve´
Published: January 2011

Initial results investigating windage power loss on a rotating shrouded spiral bevel gear using a parametric solid model and Computational Fluid Dynamics (CFD) are presented. The context behind this study is a desire to use CFD as a tool to investigate heat-to-oil within gas turbine bearing chambers and gearboxes in order to reduce costly rig-based experiments. This paper contains the methodology for creation of the parametric model of a spiral bevel gear in Pro/Engineer, formulation of a mesh in ICEM CFD and the subsequent CFD analysis in Fluent 6.2.26 and 12.0.16. A single tooth segment of a 91 teethed spiral bevel gear is produced with periodic boundaries imposed to reduce computational cost. Validation against experimental results for a single control gear is shown with particularly good correlation between static pressure rise across the face of the gear. Mesh verification is also presented. Using the model to change the module of the gear (effectively the number of teeth), investigations show that windage power loss reduces when the number of teeth increases. Analysis of the static pressure variation throughout the domain shows that all gears tested exhibit a linearly increasing relationship between non-dimensional mass-flow-rate and the pressure drop through the shroud restriction. The control gear was seen to have only a weak increase in static pressure gain across the gear tooth as the mass-flow-rate increases; however, a far larger increase exists for the module cases tested — at comparable mass-flow-rates to the control gear. As the number of teeth increase, the pressure gain across the gear reduces, and vice-versa. It is this difference between the gears that results in dissimilar windage power losses.
An Energy-Based Experimental-Analytical Torsional Fatigue Life-Prediction Method
Authors: Wertz John N. , Shen M.-H. Herman , George Tommy , Cross Charles , Scott-Emuakpor Onome
Published: January 2011

An energy-based fatigue life prediction framework for calculation of torsional fatigue life and remaining life has been developed. The framework for this fatigue prediction method is developed in accordance with our previously developed energy-based axial and bending fatigue life prediction approaches, which state: the total strain energy dissipated during a monotonic fracture and cyclic processes is the same material property, where each can be determined by measuring the area underneath the monotonic true stress-strain curve and the area within a hysteresis loop, respectively. The energy-based fatigue life prediction framework is composed of the following entities: (1) development of a shear fatigue testing procedure capable of assessing strain energy density per cycle in a pure shear stress state and (2) incorporation of an energy-based fatigue life calculation scheme to determine the remaining fatigue life of in-service gas turbine materials subjected to pure shear fatigue.
Validation and Development of Loss Models for Small Size Radial Turbines
Authors: Suhrmann Jan F. , Peitsch Dieter , Gugau Marc , Heuer Tom , Tomm Uwe
Published: January 2011

Today an increasing need for gas turbines with extremely low flow rates can be noticed in many industrial sectors, e.g. power generation, aircraft or automotive turbo chargers. For any application it is essential for the turbine to operate at best possible efficiency. It is known that for turbines the specific optimum achievable power output decreases with smaller size. A major contribution for this reduction in efficiency comes from the relative increase of aerodynamic losses in smaller turbine stages. In the early turbine design stage, easy and fast to use two-dimensional calculation codes are widely used. In order to produce qualitatively good results, all of these codes contain a diversity of loss models that more or less exactly describe physical effects which generate losses. It emerges to be a real problem that most of these empirical models were derived for rather large scale turbo machines and that they are not necessarily suitable for application to small turbines. In this paper many of the commonly known and well established loss models used for the preliminary design of radial turbines were collected, reviewed, and validated with respect to their applicability to small-size turbines, i.e. turbines of inlet diameter smaller than 40 mm. Comprehensive numerical investigations were performed and the results were used to check and verify the outcome of loss models. Based on the results, loss models have been improved. Furthermore, new correlations were developed in order to raise the quality of loss prediction especially for the design of small-size turbines. After receiving an optimum set of loss prediction models, all of them were implemented into a two-dimensional solver program for the analytical iterative solution of a complete turbine stage. Hence a powerful tool for preliminary radial turbine design has been created. This program enables the user to analytically evaluate the effects of changing key design properties on performance. These are amongst others the optimum rotor inlet flow angle according to the slip-factor definition, the value of flow deviation, and hence the optimum blade outlet angle for a minimum adverse flow-swirl at turbine outlet. Complementarily the turbine key performance indicators, e.g. pressure ratio, power output, rotational turbine speed, and mass flow can be calculated for optimum efficiency of a given turbine geometry. The paper presents the most important loss models implemented in the new code and weights their relative importance to the performance of small size radial turbines. The data acquisition was done using the new code itself as well as accompanying full 3D CFD calculations.
CFD Prediction and Test Results of Stiffness and Damping Coefficients for Brush-Labyrinth Gas Seals
Authors: Pugachev Alexander O. , Deckner Martin
Published: January 2011

This paper presents ongoing investigations on calculation and measurement of rotordynamic coefficients for brush-labyrinth gas seals. The seals are tested on static and dynamic test rigs to measure leakage, pressure distribution, and seal specific forces. To predict seal performance a full three-dimensional eccentric CFD model is considered. Rotordynamic coefficients are calculated using the whirling rotor method. The bristle pack of the brush seal is modeled using the porous medium approach. The prediction results show some deviations in absolute values of stiffness and damping coefficients in comparison with the experimental values, but the trends are similar. Comparing with a staggered labyrinth seal, the brush seal improves rotordynamic characteristics in most cases. Position of the brush seal in sealing configuration has a great influence on the stiffness and damping coefficients, while leakage performance remains relatively unaffected. The capability of the brush seal model based on the porous medium approach to predict rotordynamic coefficients is discussed.
Aerodynamic Analysis and Redesign of an Inlet Segment for a Heavy-Duty Gas Turbine Engine
Authors: Abdel-Wahab Samer , Vogel Gregory
Published: January 2011

For heavy-duty gas turbines with silo combustors, the transition section between the combustor and the turbine poses unique aerodynamic design challenges due to the non-axis symmetrical shape of the transition from the combustor (pipe), to hot gas casing (torus), to turbine inlet (annulus). The inlet segment is the transition piece located between the hot gas casing and the outer radius of the turbine. The shape of the inlet segment is designed such that it provides minimum pressure loss of the hot gas flowing from the silo combustor to the turbine inlet. Another requirement of the inlet segment shape is to provide as homogeneous as possible flow conditions at the turbine inlet. This paper shows the results from CFD analysis of an inlet segment. The results agree very well with pressure tap measurements in the engine at several discrete circumferential locations. In addition, thermal crystal measurements mounted at several leading edge locations of the vanes at the inlet of the turbine were able to confirm from the CFD the radial and circumferential temperature distribution typically produced in a silo combustor. A new inlet segment profile shape has been designed to produce an equivalent pressure distribution for the turbine inlet but with a reduced surface area, which helps to reduce the cooling requirements for this part.
Tip Leakage in Small Radial Turbines: Optimum Tip-Gap and Efficiency Loss Correlations
Authors: Kammeyer Jasper , Natkaniec Christoph , Seume Joerg R.
Published: January 2011

The tip-leakage flow mechanisms in turbocharger turbines used for downsized internal combustion engines and the associated losses are investigated over a range of operating conditions. Experiments are performed on a small, 35 mm diameter turbocharger turbine with varying tip-gap heights in a turbocharger test facility and numerical simulations are presented for extending the parameter range to sizes not covered experimentally. The sensitivity of turbine efficiency to tip-gap is evaluated and correlations for the estimation of tip-leakage related loss of efficiency are developed. An optimum applicable tip-gap size for radial turbines is suggested. The results show that the magnitude of the tip-leakage losses, e.g. in downsizing turbocharger turbines, provides a high potential for their improvement.
Vibration Analysis of a Nonlinear System With Cyclic Symmetry
Authors: Grolet Aure´lien , Thouverez Fabrice
Published: January 2011

This work is devoted to the study of non linear dynamics of structures with cyclic symmetry under geometrical nonlinearity using the harmonic balance method (HBM). In order to study the influence of the non-linearity due to large deflection of blades a simplified model has been developed. It leads to nonlinear differential equations of the second order, linearly coupled, in which the nonlinearity appears by cubic terms. Periodic solutions in both free and forced cases are sought by the HBM coupled with an arc length continuation and stability analysis. In this study, a specific attention has been paid to the evaluation of nonlinear modes and to the influence of excitation on dynamic responses. Indeed, several cases of excitation have been analyzed: punctual one and tuned or detuned low engine order. The paper shows that for a localized, or sufficiently detuned, excitation, several solutions can coexist, some of them being represented by closed curves in the Frequency-Amplitude domain. Those different kinds of solution meet up when increasing the force amplitude, leading to forced nonlinear localization. As the closed curves are not tied with the basic nonlinear solution they are easily missed. They were calculated using a sequential continuation with the force amplitude as a parameter.
An Overview of Advanced Ni-Base Superalloys for Small Turbines and Missile Engine Applications
Authors: Wahl Jacqueline B. , Harris Ken
Published: January 2011

Ni-base superalloy cast materials provide an outstanding balance of high temperature strength, fatigue resistance, oxidation resistance and coating performance and can be produced to very tight tolerances in extremely complex configurations, such as axial and centrifugal integral cast turbine wheels. As a result, cast superalloys are used in the most demanding applications of aero and industrial gas turbine engines. Use of these materials is expanding to smaller microturbine, turbojet, turbocharger and missile engine applications due to this unique combination of desirable properties. This paper will present an overview of the application of investment cast Ni-base superalloys and process capability to small turbine and missile engines. Alloy property data will be presented, including advanced equiax alloys CM 247 LC®, CM 681 LC® and CM 939 Weldable®, directionally solidified alloys CM 247 LC and CM 186 LC® and single crystal alloy CMSX-4®, along with typical or candidate applications for each.
Investigation of Auto-Ignition of a Pulsed Methane Jet in Vitiated Air Using High-Speed Imaging Techniques
Authors: Meier Wolfgang , Boxx Isaac , Arndt Christoph , Gamba Mirko , Clemens Noel
Published: January 2011

An experimental arrangement for the investigation of auto-ignition of a pulsed CH4 jet in a co-flow of hot exhaust gas from a laminar lean premixed H2/air flame at atmospheric pressure is presented. The ignition events were captured by high-speed imaging of the OH* chemiluminescence associated with the igniting flame kernels at a frame rate of 5 kHz. The flow field characteristics were determined by high-speed PIV and Schlieren images. Further, high-speed imaging of laser-induced fluorescence of OH was applied to visualize the exhaust gas flow and the ignition events. Auto-ignition was observed to occur at the periphery of the CH4 jet with high reproducibility in different runs concerning time and location. In each measurement run several hundred consecutive single shot images were recorded from which sample images are presented. The main goals of the study are the presentation of the experimental arrangement and the high-speed measuring systems and a characterization of the auto-ignition events occurring in this system.
Prediction of the Vibratory Behaviour of Monoblock Sectorised Stator Vanes
Authors: Sall Amadou C. , Thouverez Fabrice , Blanc Laurent , Jean Pierrick , Ottavy Xavier
Published: January 2011

Stator vanes which are found at different stages in axial compressors are subject to major aerodynamic load fluctuations, due to cyclic excitations induced by the wakes of the rotors located upstream and also due to the pressure waves generated by the blade rows located downstream. In a vibratory fatigue context, it is important to ensure the structural strength of these stator vanes. A new technology of monoblock sectorised stator vanes has been developed to provide an easier manufacturing process and lower costs; in return, cyclic symmetry properties, which make the prediction studies easier, are lost in this case. Besides, these kinds of monoblock sectors are characterized by low damping which increases the criticality of the blade modes localization. The division into sectors of stator vanes creates a high density of eigenmodes in some short frequency ranges; this phenomenon is accompanied by non-negligible modal participations of neighbouring eigenmodes. Moreover, stator vanes sectors have shown a strong sensitivity to mistuning, making their vibratory behaviour prediction more difficult by means of deterministic prediction methods. In this paper, a phenomenological approach is followed to quantify the mistuning. Thus, several sensitivity to mistuning numerical studies were performed. They allowed to have first results about the relative predictable errors that could be done, depending on the mistuning. Some engine tests were also performed with gauges-equipped stator vanes sectors.
Effect of Temperature Nonuniformity on Heat Transfer in an Unshrouded Transonic HP Turbine: An Experimental and Computational Investigation
Authors: Qureshi Imran , Smith Andy D. , Chana Kam S. , Povey Thomas
Published: January 2011

Detailed experimental measurements have been performed to understand the effects of turbine inlet temperature distortion (hot-streaks) on the heat transfer and aerodynamic characteristics of a full-scale unshrouded high pressure turbine stage at flow conditions that are representative of those found in a modern gas turbine engine. To investigate hot-streak migration, the experimental measurements are complemented by three-dimensional steady and unsteady CFD simulations of the turbine stage. This paper presents the time-averaged measurements and computational predictions of rotor blade surface and rotor casing heat transfer. Experimental measurements obtained with and without inlet temperature distortion are compared. Time-mean experimental measurements of rotor casing static pressure are also presented. CFD simulations have been conducted using the Rolls-Royce code Hydra, and are compared to the experimental results. The test turbine was the unshrouded MT1 turbine, installed in the Turbine Test Facility (previously called Isentropic Light Piston Facility) at QinetiQ, Farnborough UK. This is a short duration transonic facility, which simulates engine representative M, Re, Tu, N/T and Tg /Tw at the turbine inlet. The facility has recently been upgraded to incorporate an advanced second-generation temperature distortion generator, capable of simulating well-defined, aggressive temperature distortion both in the radial and circumferential directions, at the turbine inlet.
The Influence of Cooling Flows on the Operating Conditions of the Ultra-Supercritical Steam Turbine Components
Authors: Kosman Wojciech
Published: January 2011

This paper presents the results of the analysis on the heat transfer in the inlet section of an ultra-supercritical steam turbine. Such power generating units become the foundation of new coal-fired power plants. The monitoring of their operation is in many aspects similar to the traditional, sub-critical steam turbines. However, higher live and reheat steam parameters result in several key differences, which must be taken into the consideration when assessing the thermal and strength states of the turbines main components for the diagnostic supervision. One of the main differences is the presence of the cooling and designs specific for ultra-supercritical steam turbines, which aim to protect their components against overheating. The research described in this paper investigates the inlet section of the turbines, which is the area exposed to the highest thermal loads. The scope of the research includes both, numerical modeling and laboratory testing. A test stand has been built for the analysis of the flows in the inlet section. Cooling flows are under special attention here as their temperature field is coupled to the temperature fields of the turbine components (the rotor and the inner casing) due to the relatively small amount of the coolant. The paper provides detailed description of the test stand and some early measurement results, which involve the operation with cooling. Also the numerical modeling results are shown and compared to the measurement data.
Aerodynamics and Heat Transfer for a Cooled One and One-Half Stage High-Pressure Turbine: Part II—Influence of Inlet Temperature Profile on Blade Row and Shroud
Authors: Mathison R. M. , Haldeman C. W. , Dunn M. G.
Published: January 2011

Heat-flux measurements are presented for the un-cooled blades of a one-and-one-half stage turbine operating at design corrected conditions with a fully cooled upstream vane row and with rotor disk cavity purge flow. The paper highlights the differences in blade heat flux and temperature caused by uniform, radial, and hot streak inlet temperature profiles. A general discussion of temperature profile migration is provided in Part I, and Part III presents data for hot streak magnitudes and alignments. The heat-flux and fluid-temperature measurements for the blade airfoil, platform, angel wing (near the root), and tip as well as for the stationary outer shroud are influenced by the vane inlet temperature profile. The inlet temperature profile shape can be clearly observed in the blade Stanton Number measurements, with the radial and hot streak profiles showing a greater redistribution of energy than the uniform case due to secondary flows. Hot gas segregation is observed to increase with the strength of the temperature distortion. Measurements for the hot streak profile show a segregation of higher temperature fluid to the pressure surface when compared to a uniform profile. The introduction of vane and purge cooling is found to further accentuate the flow segregation due to coolant migration to the suction surface.
Numerical Investigations of the Efficiency of Circulation Control in a Compressor Stator
Authors: Vorreiter A. , Fischer S. , Saathoff H. , Radespiel R. , Seume J. R.
Published: January 2011

Airfoil active flow control has been attempted in the past in order to increase the permissible loading of boundary layers in gas turbine components. The present paper presents a stator with active flow control for a high speed compressor using a Coanda surface near the trailing edge in order to inhibit boundary layer separation. The design intent is to reduce the number of vanes while — in order to ensure a good matching with the downstream rotor — the flow turning angle is kept constant. In a first step, numerical simulations of a linear compressor cascade with circulation control are conducted. The Coanda surface is located behind an injection slot on the airfoil suction side. Small blowing rates lead to a gain in efficiency associated with a rise in static pressure. In a second step, this result is transferred to a 4-stage high speed research compressor, where the circulation control is applied in the first stator. The design method and the first results are based on steady numerical calculations. The analysis of these results shows performance benefits of the concept. For both, the cascade and the research compressor, the pressure gain and efficiency are shown as a function of blowing rate and jet power ratio. The comparison is performed based on a dimensionless efficiency which takes into account the change of power loss.
Fast CFD Simulation of Horizontal Axis Wind Turbines
Authors: De Bellis Fabio , Catalano Luciano A. , Dadone Andrea
Published: January 2011

The numerical simulation of horizontal axis wind turbines (HAWT) has been analysed using computational fluid dynamics (CFD) with the aim of obtaining reliable but at the same time affordable wind turbine simulations, while significantly reducing required overall resources (time, computational power, user skills), for example in an optimization perspective. Starting from mesh generation, time required to extract preliminary aerodynamic predictions of a wind turbine blade has been shortened by means of some simplifications, i.e.: fully unstructured mesh topology, reduced grid size, incompressible flow assumption, use of wall functions, commercial available CFD package employment. Ansys Fluent software package has been employed to solve Reynolds Averaged Navier Stokes (RANS) equations, and results obtained have been compared against NREL Phase VI campaign data. The whole CFD process (pre-processing, processing, postprocessing) has been analysed and the chosen final settings are the result of a trade-off between numerical accuracy and required resources. Besides the introduced simplifications, numerical predictions of shaft torque, forces and flow distribution are in good agreement with experimental data and as accurate as those calcuted by other more sophisticated works.
Generation of Turbine Maps Using a Fusion of Validated Operational Data and Streamline Curvature Method
Authors: Zwingenberg M. , Benra F.-K. , Werner K. , Dobrzynski B.
Published: January 2011

This paper shows how operational data in combination with a calibrated stream line curvature method (SCM) and fleet statistics can be used for turbine map generation. The operational data storage system of industrial gas turbines can be used, in case the customer agreed to provide the data, for fleet statistics, degradation behavior investigation or component map generation. The generation of updated component maps using operational data is mainly necessary for older gas turbines types since the available numerical gas turbine models often do not represent the current state of knowledge. The process for component map generation based on operational data incorporates several steps explained in detail in this paper. The first step is a full thermodynamic evaluation, including the calculation of relevant parameters like isentropic efficiencies of compressor and turbine. Furthermore, the compressor mass flow and the turbine inlet temperature are determined. This step is accompanied with the calculation of systematic and random uncertainties for all required performance parameters. The thermodynamic evaluation is coupled with a data validation system. This system incorporates signal checks, a statistics based anomaly detection, a Kalman filter based single fault isolation und a fuzzy logic based multiple fault isolation. After the evaluation and validation of the data, aging effects are eliminated. In the next step, data sets from different sites are consolidated and shifted to meet the fleet average. The first step in calibrating the SCM is the rasterizing of the operational data. The Jacobian matrix of the SCM for the loss factors to be calibrated is generated automatically at the raster points. Afterwards, the calibration is done taking into account measurement uncertainties as well as different systematic uncertainties for the loss factors in order to achieve the minimum variance result. The updated SCM, calibrated to actual engine data, is then used for component map generation.
A New Reduced Order Modeling for Stability and Forced Response Analysis of Aero-Coupled Blades Considering Various Mode Families
Authors: Mayorca Mari´a A. , Vogt Damian M. , Ma˚rtensson Hans , Fransson Torsten H.
Published: January 2011

This paper presents the description and application of a new method for stability and forced response analyses of aerodynamically coupled blades considering the interaction of various mode families. The method, here referred as MLS (Multimode Least Square), considers the unsteady forces due to the blade motion at different modes shape families and calculates the aerodynamic matrixes by means of a least square (L2) approximations. This approach permits the prediction of mode families’ interaction with capabilities of structural, aerodynamic and force mistuning. A projection technique is implemented in order to reduce the computational domain. Application of the method on tuned and structural mistuned forced response and stability analyses is presented on a highly loaded transonic compressor blade. When considering structural mistuning the forced response amplitude magnification is highly affected by the change in aerodynamic damping due to mistuning. Analyses of structural mistuning without aerodynamic coupling might result in over-estimated or under-estimated response when the source of damping is mainly aerodynamic. The frequency split due to mistuning can cause that mode families’ interact due to reducing their frequencies separation. The advantage of the present method is that the effect of mode family interaction on aerodynamic damping and forced response is captured not being restricted to single mode families.
Influence of the Blade Count Ratio on Aerodynamic Forcing: Part I—Highly Loaded Transonic Compressor
Authors: Fruth Florian , Vogt Damian M. , Ma˚rtensson Hans , Mayorca Mari´a A. , Fransson Torsten H.
Published: January 2011

The influence of the Blade Count Ratio (BCR) on the aerodynamic forcing of a highly transonic compressor has been investigated. The focus has been put on the unsteady aerodynamics as well as mode excitability and thus High Cycle Fatigue (HCF) risk. A number of compressor stages were investigated that differed in blade count of the stator blade row. Time-resolved aerodynamic forcing results were acquired using a non-linear CFD approach. The results were decomposed into frequency content and combined with modal properties of the various components. It is found that the BCR is a key parameter to reduce generalized force and consequently vibratory HCF stresses. Furthermore a potential in avoiding and/or alleviating potential resonant crossings in the Campbell diagram is reported. The dependency of these aspects from BCR is largely non-linear and for the first time discussed in detail on the basis of a transonic compressor stage.
Measurements of Endwall Flows in Transonic Linear Turbine Cascades: Part I—Low Flow Turning
Authors: Taremi F. , Sjolander S. A. , Praisner T. J.
Published: January 2011

The current two part paper presents the results of an experimental investigation of the endwall flows in four transonic linear turbine cascades with two levels of flow turning: 90° and 112° of total flow turning, respectively. For each case, two levels of aerodynamic loading were examined. Part I of the paper examines the low-turning case. A seven-hole pressure probe was used to document the flow fields downstream of the cascades. The experimental results include blade surface pressure distributions, total pressure losses, secondary kinetic energy and streamwise vorticity distributions. The turbine cascades considered in Part I are referred to as SL3F and SL4F (exit Mach number ≈ 0.8). The airfoils have the same inlet and outlet design flow angles, but different aerodynamic loading levels: SL4F has a Zweifel coefficient that is 30% higher than that for SL3F. The midspan flow measurements indicate that SL4F produces higher profile losses than SL3F. SL4F also exhibits stronger secondary flow with larger exit flow-angle variations. Consequently, SL4F produces higher secondary losses. Growth of secondary losses has been documented by collecting additional measurements downstream of the SL3F cascade. Vortex dissipation and endwall boundary layer growth result in additional secondary losses. The loss coefficients and the secondary flow parameters are integrated over the entire measurement plane to present their individual contributions to total entropy generation. In this context, the profile and secondary loss results from two different loss-breakdown schemes are presented and compared. The treatment of near-endwall losses in the absence of detailed pressure probe results is also discussed here.
Unsteady CFD Methods in a Commercial Solver for Turbomachinery Applications
Authors: Biesinger Thomas , Cornelius Christian , Rube Christoph , Braune Andre´ , Campregher Rubens , Godin Philippe G. , Schmid Gregor , Zori Laith
Published: January 2011

Modern CFD flow solvers can be readily used to obtain time-averaged results on industrial size turbomachinery flow problem at low computational cost and overall effort. On the other hand, time-accurate computations are still expensive and require substantial resources in CPU and computer memory. However, numerical techniques such as phase shift and time inclining method can be used to reduce overall computational cost and memory requirements. The unsteady effects of moving wakes, tip vortices and upstream propagation of shock waves in the front stages of multi-stage compressors are crucial to determine the stability and efficiency of gas turbines at part-load conditions. Accurate predictions of efficiency and aerodynamic stability of turbomachinery stages with strong blade row interaction based on transient CFD simulations are therefore of increasing importance today. The T106D turbine profile is under investigation as well as the transonic compressor test rig at Purdue. The main objective of this paper is to contribute to the understanding of unsteady flow phenomena that can lead to the next generation design of turbomachinery blading. Transient results obtained from simulations utilizing shape correction (phase shift) and time inclining methods in an implicit pressure-based solver, are compared with those of a full transient model in terms of computational cost and accuracy.
Conceptual Study of Counter-Rotating Turbofan Engines
Authors: Gonza´lez Di´ez Ne´stor , Rao Arvind G. , van Buijtenen Jos
Published: January 2011

The dramatic growth that air traffic has experienced in the last years is not likely to slow down in the future. The situation for the airlines has however been critical due to the large share of the operating costs corresponding to fuel. On the other hand, the society demands quieter aircraft which is then translated into stricter regulations. The Advisory Council for Aeronautics Research in Europe (ACARE) has set an ambitious array of objectives to be accomplished by 2020. It is often claimed that complying with those targets will not require evolution but, rather, revolution. One of the potential future engine configurations being considered is the counter-rotating turbofan (CRTF) concept. This paper addresses the possibilities of improvement that the CRTF can offer with respect to the specific fuel consumption, emissions and noise as compared to the baseline engine, the GE90. Semi-empirical correlations and methodologies have been used for the study. First a Blade Element Method (BEM) is developed to estimate the performance of the fan and to build confidence upon the applied loss and deviation angle models. Next, the design methodology is applied to three cases: a single-stage fan featuring the reference properties of the GE90 engine; a counter-rotating fan (CRF) fan with similar properties as a GE90 fan, but with a lower rotational speed; and a CRF with higher fan pressure ratio (FPR) for lower specific fuel consumption. Finally, noise emission by all the three configurations are estimated by noise models available in the literature. Reductions of equivalent perceived noise level (EPNL) were found to be possible if a CRF is used instead of the baseline single-stage arrangement. Other noise descriptors are also reduced by a similar amount. Approximately equal noise levels are expected if the CRF is of higher pressure than the baseline.