bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Studies of the Boundary Conditions Leading to Oil Fire in the Bearing Chamber and in the Secondary Air System of Aeroengines
Authors: Willenborg K. , Busam S. , Roßkamp H. , Wittig S.
Published: February 2009

The continuous increase of the temperature and pressure levels in modern aeroengines has significantly increased the demands on the design of the lubrication system. Among other things the oil/air system of a gas turbine engine has to ensure that engine operation does not permit oil coking or oil fires in order to guarantee high reliability and safety of the engine. To improve existing and develop new design rules, a fundamental study of the conditions leading to oil firing within an oil contaminated environment has been initiated. Three ignition mechanisms relevant for the triggering of an oil fire in the bearing chamber or in the secondary air system are investigated in detail: the spontaneous ignition of the lubricant (autoignition), the ignition of the lubricant near a hot surface (hot surface ignition) and the propagation of a flame within a vent pipe into the bearing chamber (vent pipe flashback). The present paper focusses on the experimental approach and procedure. The different test rigs are presented and their functioning is demonstrated by means of initial results.
In-Engine Measurements of Temperature Rises in Axial Compressor Shrouded Stator Cavities
Authors: Lewis Leo V.
Published: February 2009

Although many axial compressors in large aero engines use shrouded stators to retain aerodynamic efficiency, the temperature rises generated within the stator well cavities can be detrimental to the mechanical design of the disc rim or the shroud itself. These temperature rises are poorly understood and have not been widely reported. This paper presents the temperature measurements from the HP compressor stator wells of full size development engine tests, concentrating on two particular tests for the majority of its information. It is shown how standard formulae for windage and mass flows on rotor discs and in labyrinth seals can, if suitably factored, explain the observed temperatures in the first test. Inferences are drawn regarding the windage losses in the compressor, in kW, and swirl velocities, as fractions of the disc rim rotational velocity, in the stator wells. The second test is used to demonstrate the significant further temperature rise which can be caused at the front stage of the compressor by forward leakage: further analysis shows that the temperature rise is dependent on the number of stages of axial disc rim fixings behind the first stage, and that this mechanism can produce higher temperature rises than those due to windage.
Thermal and Economic Considerations for Optimizing HRSG Design
Authors: Pasha Akber , Ragland Andrew S. , Sun Suichu
Published: February 2009

The design, operation and usage of Heat Recovery Steam Generators (HRSG) has undergone considerable changes in the last 30 years. Nowadays, instead of as an option item, HRSGs are a major part of the Combined Cycle Power Plant. This makes it necessary to optimize the design and operation of the HRSG so that it can be integrated with the total plant. However, because of the complexity, it is not always feasible to evaluate all possible configurations for selecting the most optimum one within the given time constraints. An attempt is made here to present the parametric effect of various variables through descriptive graphs. These graphs are developed for general cases but can be applied to specific cases to give the trend rather than the absolute values. Cycle designers can use those to narrow down the cycle HRSG configurations. Plant operators may be able to use these to improve the performance by simple additions or modifications.
Enhanced TF40B Gas Turbine Engine Development Program
Authors: Yee Roger , Myers Lee , Braccio Ken , Dvornak Mike
Published: February 2009

The Navy Landing Craft Air Cushion (LCAC) Service Life Extension Program (SLEP) upgrades the current TF40B gas turbine engine and analog control system on the LCAC to an Enhanced TF40B (ETF40B) gas turbine with a Full Authority Digital Engine Control (FADEC) system. This upgrade and enhancement will provide additional engine horsepower, increased engine reliability, and modern digital engine control equipment to the LCAC. The success of the ETF40B engine development program has been an ongoing effort between the Navy, the LCAC craft builder Textron Marine & Land Systems (TM&LS), and the engine manufacturer Honeywell Engine and Systems. This paper will document and outline the differences between the TF40B and ETF40B and the efforts of the ETF40B 150 hour endurance qualification test.
A Bulk Flow Model for Off-Centered Honeycomb Gas Seals
Authors: Soulas Thomas , San Andres Luis
Published: February 2009

A computational analysis for prediction of the static and dynamic forced performance of gas honeycomb seals at off-centered rotor conditions follows. The bulk-flow analysis, similar to the two-control volume flow model of Kleynhans and Childs [1], is brought without loss of generality into a single-control volume model, thus simplifying the computational process. The formulation accommodates the honeycomb effective cell depth, and existing software for annular pressure seals is easily upgraded for damper seal analysis. An analytical perturbation method for derivation of zeroth- and first-order flow fields renders the seal equilibrium response and frequency-dependent dynamic force impedances, respectively. Numerical predictions for a centered straight-bore honeycomb gas seal show good agreement with experimentally identified impedances, hence validating the model and confirming the paramount influence of excitation frequency on the rotordynamic force coefficients of honeycomb seals. The effect of rotor eccentricity on the static and dynamic forced response of a smooth annular seal and a honeycomb seal is evaluated for characteristic pressure differentials and rotor speeds. Leakage for the two seal types increases slightly as the rotor eccentricity increases. Rotor off-centering does have a pronounced non-linear effect on the predicted (and experimentally verified) dynamic force coefficients for smooth seals. However, in honeycomb gas seals, even large rotor center excursions do not sensibly affect the effective local film thickness, maintaining the flow azimuthal symmetry. The current model and predictions thus increase confidence in honeycomb seal design, operating performance and reliability in actual applications.
Unsteady Aerodynamic Forces on Vibrating Annular Cascade Blades: Cross-Validation of the Linear Unsteady CFD Calculations Using the TVD Scheme and the Double Linearization Theory
Authors: Yamasaki Nobuhiko , Hamabe Masaaki , Namba Masanobu
Published: February 2009

The paper presents the formulation to compute numerically the unsteady aerodynamic forces on the vibrating annular cascade blades. The formulation is based on the finite volume method, the type, and the TVD scheme, following the UPACS code developed by NAL, Japan. By applying the TVD scheme to the linear unsteady calculations, the precise calculation of the peak of unsteady aerodynamic forces at the shock wave location like the delta function singularity becomes possible without empirical constants. As a further feature of the present paper, results of the present numerical calculation are compared with those of the double linearization theory (DLT), which assumes small unsteady and steady disturbances but the unsteady disturbances are much smaller than the steady disturbances. Since DLT requires far less computational resources than the present numerical calculation, the validation of DLT is quite important from the engineering point of view. Under the conditions of small steady disturbances, a good agreement between these two results is observed, so that the two codes are cross-validated. The comparison also reveals the limitation on the applicability of DLT.
Using CFD to Reduce Resonant Stresses on a Single-Stage, High-Pressure Turbine Blade
Authors: Clark J. P. , Aggarwala A. S. , Velonis M. A. , Gacek R. E. , Magge S. S. , Price F. R.
Published: February 2009

The ability to predict levels of unsteady forcing on high-pressure turbine blades is critical to avoid high-cycle fatigue failures. In this study, 3D time-resolved computational fluid dynamics is used within the design cycle to predict accurately the levels of unsteady forcing on a single-stage high-pressure turbine blade. Further, nozzle-guide-vane geometry changes including asymmetric circumferential spacing and suction-side modification are considered and rigorously analyzed to reduce levels of unsteady blade forcing. The latter is ultimately implemented in a development engine, and it is shown successfully to reduce resonant stresses on the blade. This investigation builds upon data that was recently obtained in a full-scale, transonic turbine rig to validate a Reynolds-Averaged Navier-Stokes (RANS) flow solver for the prediction of both the magnitude and phase of unsteady forcing in a single-stage HPT and the lessons learned in that study.
Maximum Amplification of Blade Response Due to Mistuning: Localization and Mode Shapes Aspects of the Worst Disks
Authors: Rivas-Guerra Alejandro J. , Mignolet Marc P.
Published: February 2009

This paper focuses on the determination and study of the maximum amplification of the steady state forced response of bladed disks due to mistuning. First, an optimization strategy is proposed in which partially mistuned bladed disks are considered as physical approximations of the worst case disk and the mistuned properties are sought to maximize the response of a specific blade. This approach is exemplified on both a reduced order model of a blisk and a single-degree-of-freedom per blade disk model an extensive parametric study of which is conducted with respect to blade-to-blade coupling, damping, and engine order. A mode shape-based formulation of the amplification factor is then developed to clarify the findings of the parametric study in the strong coupling/small damping limit. In this process, the upper bound of Whitehead is recovered for all engine orders and number of blades and the conditions under which this limit is exactly achieved or closely approached are clarified. This process also uncovers a simple yet reliable approximation of the resonant mode shapes and natural frequencies of the worst disk.
Analytical Formulation of Friction Interface Elements for Analysis of Nonlinear Multi-Harmonic Vibrations of Bladed Discs
Authors: Petrov E. P. , Ewins D. J.
Published: February 2009

An analytical formulation for the vectors of contact forces and the stiffness matrix of the non-linear friction contact interface is developed for the analysis of multi-harmonic vibrations in the frequency domain. The contact interface elements provided here an exact description of friction and unilateral contact forces at the interacting surfaces, taking into account the influence of the variable normal load on the friction forces, including the extreme cases of separation of the two surfaces. Initial gaps and interferences at the contact nodes, which affect the normal force, as well as the unilateral action of the normal force at the contact surface, are all included in the model. The accurate calculation of the force vector and the tangent stiffness matrix provides a very reliable and fast convergence of the iteration process used in the search for the amplitudes of nonlinear vibrations of bladed discs. Numerical investigations demonstrate excellent performance with respect to speed, accuracy and stability of computation.
Improving Turbine Efficiency Using Non-Axisymmetric End Walls: Validation in the Multi-Row Environment and With Low Aspect Ratio Blading
Authors: Harvey N. W. , Brennan G. , Newman D. A. , Rose M. G.
Published: February 2009

This paper describes how the Intermediate Pressure (IP) turbine model rig of the Rolls-Royce Trent 500 engine was redesigned by applying non-axisymmetric end walls to both the vane and blade passages. The blading aerofoil shapes, the turbine operating point and the overall flow conditions were unaltered from the original design. The results from testing of the model rig are presented and compared with those obtained previously for the datum design. A feature of this is that the IP turbine was tested in a “two-shaft” arrangement with the (upstream) Trent 500 High Pressure (HP) model turbine. Previously, non-axisymmetric end wall profiling had been shown to achieve a 0.59 ± 0.25% improvement in the stage efficiency of the Trent 500 HP model turbine when tested as a single stage, Rose et al. [1]. This had exceeded the design expectation of 0.4% improvement, Brennan et al. [4] — based on previous linear cascade research at Durham University, see Harvey et al. [2] and Hartland et al. [3]. The IP and HP turbines with profiled end walls were tested together, while for the datum test both model turbines had blading with axisymmetric end walls. The results have met expectations with an improvement in the IP turbine stage efficiency of 0.9 ± 0.4% at the design point. The turbine characteristics are shown to change significantly from the datum test.
The Investigation of Turbine and Exhaust Interactions in Asymmetric Flows: Part 1 — Blade-Row Models Applied
Authors: Liu J. J. , Hynes T. P.
Published: February 2009

Part 1 of this paper describes the blade-row models applied to the asymmetric flow field coupling between turbine and exhaust system. Numerical actuator is applied to represent a turbine blade row around whole annulus and flow properties across the disc can jump to achieve required flow turning and entropy rise. The derivation of disc boundary conditions and the implementation in CFD solvers are described in detail. Validation of the actuator disc model and sample application of the present numerical approach are presented.
Experimental Investigation of Turbine Wake Flow by Interferometrically Triggered PIV and LDV Measurements
Authors: Woisetschla¨ger J. , Mayrhofer N. , Lang H. , Hampel B.
Published: February 2009

The process of vortex shedding had been investigated in a a linear turbine blade cascade by non-invasive optical measurement techniques. The experiments were carried out in the wake behind a linear arrangement of turbine profiles (VKI-1) with a chord length of 58 mm at an isentropic exit Mach number of 0.7 and a Reynolds number of 9.75×105. Shedding frequency was approx. 18.2 kHz. Density fluctuations in the vortex street were measured by guiding the beam of a Laser Vibrometer (LV) through the turbine blade cascade behind the trailing edge and a frequency analysis was performed. These interferometrically detected density fluctuations had then been used to trigger two-dimensional velocity measurements by Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV) in the turbine wake flow, by means of an analog filter. This resulted in phase resolved measurements of the flow field during vortex shedding at this high frequency. Results of these velocity measurements within the wake flow are presented with a decomposition of the velocity into mean, periodic and turbulent components performed.
Analysis of Rotor-Rotor and Stator-Stator Interferences in Multi-Stage Turbomachines
Authors: He L. , Chen T. , Wells R. G. , Li Y. S. , Ning W.
Published: February 2009

A nonlinear harmonic methodology is adopted to analyse interactions between adjacent stages in multi-stage compressors. Of particular interest are the effects of circumferential ‘aperiodic’ distributions and the relative circumferential positioning (‘clocking’) of blades. The main feature of the present approach is that both the aperiodic and clocking effects are very efficiently included with circumferential ‘steady’ harmonic disturbances. Consequently, a single run of the nonlinear harmonic solver using a single-passage domain can produce the whole annulus unsteady and aperiodic time-averaged flow field. In addition, performance variation at any clocking position can be obtained simply by post-processing the result. A case study is presented for a two and half stage transonic compressor, and the present results show much stronger rotor-rotor interaction than stator-stator interaction. A mechanism leading to strong rotor-rotor interference seems to be the interaction between upstream rotor wakes and the downstream rotor passage shock waves. A rotor-rotor clocking study illustrates a qualitatively different loss variation with respect to clocking position in a transonic flow compared to that in a subsonic flow.
Radial Impeller Forces Using CFD: Part II — A Comparison Between Compressible and Incompressible Flows
Authors: Baun Daniel O. , Flack Ronald D.
Published: February 2009

Lateral centrifugal impeller forces are calculated using the CFD model developed in Part I of this paper. The impeller forces are evaluated by integrating the pressure and momentum profiles at both the impeller inlet and exit planes. Direct impeller lateral force measurements were made using a magnetic bearing supported pump rotor. Comparisons between the simulated and measured forces are first made for both average and transient impeller forces with water as the working fluid. Air was then substituted as the working fluid in the validated CFD model and the effect of impeller Mach number and Reynolds number on the static impeller lateral forces was investigated. The non-dimensional lateral impeller force characteristics as a function of normalized flow coefficient are similar in character between the incompressible and compressible case. At the matching point flow coefficient the non-dimensional impeller force magnitude was the same for all compressible and incompressible simulations. For any normalized flow rate other than the matching point flow rate, the magnitude of the non-dimensional impeller force increased as the Mach number increased. As the choke condition was approached the magnitude of the impeller force increased exponentially. As the Mach number increased the transition of the force orientation vector from the low flow asymptote to the high flow asymptote occurred over a progressively smaller range of flows.
A Study on Impeller-Diffuser Interaction: Part II — Detailed Flow Analysis
Authors: Ziegler Kai U. , Gallus Heinz E. , Niehuis Reinhard
Published: February 2009

The interaction between impeller and diffuser is considered to have strong influence on the flow in highly loaded centrifugal compressors. However, the knowledge about this influence is still not satisfying. This two-part paper presents an experimental investigation of the effect of impeller-diffuser interaction on the unsteady and the time averaged flow configuration in impeller and diffuser and the performance of these components. The flat wedge vaned diffuser of the investigated stage allows an independent adjustment of diffuser vane angle and radial gap between impeller exit and diffuser vane inlet. Attention is mainly directed to the radial gap, as it determines the intensity of the impeller-diffuser interaction. In part I it was shown that smaller radial gaps improve diffuser pressure recovery, whereas impeller efficiency is hardly affected. Part II focuses on the reasons for these effects. Measurements with a laser-2-focus velocimeter in the highly unsteady flow field between the impeller exit region and diffuser throat were performed at three different diffuser geometries allowing a detailed flow analysis. Especially the unsteady results show that for a smaller radial gap more impeller wake fluid is conveyed towards the highly loaded diffuser vane pressure side reducing its loading and leading to a better diffusion in the diffuser channel. Concerning the impeller flow, it was found that a smaller radial gap is leading to a noticeable reduction of the wake region at impeller exit. The experimental results are intended to be published as an open CFD testcase under the name “Radiver”.
Non-Linear Effects of Vibration in Gas Turbine Engines With Two or Three Rotors
Authors: Pismenny J. , Levy Y.
Published: February 2009

The dependence of the vibration characteristics of gas turbine engines on the rotor speeds becomes highly complicated in engines with two and three rotors, both because of the simultaneous dynamic action of the multiple rotors and the ambiguous relationships between their speeds. In this paper, the gas turbine engine is analyzed in the context of the theory of non-linear oscillation — as a complex system comprising a large number of non-linear elements and multiple periodical forces of different frequencies (defined by the rotor speeds). This paper presents results, which indicate that the level of vibration can obtain critical values at certain relationships between the rotor speeds. As a practical application of this phenomena it is shown that the number of three-spool engines returns from the aircraft to the engine manufacturer, due to different kinds of malfunctions, for example due to activation of the “intensified vibration” alarm, may be approximately three times that of returns of analogous two-rotor engines.
Fast Calculation of the Statistics of the Forced Response of Mistuned Bladed Disk Assemblies With Friction Contacts
Authors: Sextro Walter , Panning Lars , Go¨tting Florian , Popp Karl
Published: February 2009

In turbomachinery one major problem is still the calculation and the optimization of the spatial vibrations of mistuned bladed disk assemblies with friction contacts. Friction contacts are widely used to reduce dynamic stresses in turbine blades. Due to dry friction and the relative motion of the contact planes energy is dissipated. This effect results in a reduction of blade vibration amplitudes. In the case of a tuned bladed disk cyclic boundary conditions can be used for the calculation of the dynamic response. For a mistuned bladed disk the complete system has to be modeled and simulated. To reduce the computation time the so-called substructure method is applied. This method is based on the modal description of each substructure, especially disk and blades, combined with a reduction of the degrees of freedom, to describe the dynamics of each component. The spatial dynamical behavior of each component is considered and described by the mode shapes, natural frequencies and modal damping ratios. Using the Harmonic Balance Method the nonlinear friction forces can be linearized. From here it is possible to calculate the frequency response functions of a mistuned bladed disk assembly with friction contacts. In many cases Monte-Carlo simulations are used to find regions, where the system response is sensitive to parameter uncertainties like the natural frequencies of the blades. These simulations require a large computation time. Therefore, an approximate method is developed to calculate the envelopes of the frequency response functions for statistically varying natural frequencies of the blades. This method is based on a sensitivity analysis and the Weibull-distribution of the vibration amplitudes. From here, a measure for the strength of localization for mistuned cyclic systems is derived. Regions, where localization can occur with a high probability, can be calculated by this method. The mean value and the standard deviation of the vibration amplitudes are calculated by simulation and by the approximate method. The comparisons between the approximate method and the Monte-Carlo simulations show a good agreement. Therefore, applying this method leads to remarkable reduction of computation time and gives a quick insight into the system behavior. The approximate method can also be applied to systems, that include the elasticity of the disk and/or the coupling by shrouds or other friction devices.
Optimization of the Contact Geometry Between Turbine Blades and Underplatform Dampers With Respect to Friction Damping
Authors: Panning Lars , Sextro Walter , Popp Karl
Published: February 2009

The blades of rotating compressor or turbine disks are subjected to fluctuating fluid forces that cause blade vibrations. To avoid high resonance stresses, in many applications additional damping is introduced into the bladed disk assembly by means of friction damping devices such as underplatform dampers. These are mounted between adjacent turbine blades and pressed onto the platforms due to centrifugal forces to dissipate energy by the generated friction forces due to relative motions between the damper and the neighboring blades. In real turbomachinery applications, the rotating blades are subjected to spatial vibrations caused by a complex blade geometry and distributed excitation forces acting on the airfoil. Therefore, a spatial model is presented including an appropriate spatial contact model to predict the generalized contact forces acting between the damper and the blades accurately. Six degrees of freedom are considered for each contact between the damper and the respective neighboring blades. Roughness effects are considered that determine the real contact area with respect to the nominal contact area. Different spatial blade vibration modes are investigated with regard to the friction damping that is provided by the underplatform damper. To gain the maximum damping effect, the damper mass is optimized at different working conditions of the assembly like the excitation amplitudes and the engine order. Furthermore, the influence of the contact geometry upon the damping potential is investigated in detail including the damper as well as the blade platform geometry. In practice, different damper geometries are in operation. Studies will be presented that prove the capability of the developed model to compare the effectiveness of different damper and blade platform geometries. Asymmetric platform angles leading to different contact conditions at the left and right damper contact, respectively, are studied in detail to improve the damping effect.
Aerodynamic Performance and Turbulence Measurements in a Turbine Vane Cascade
Authors: Boyle R. J. , Lucci B. L. , Senyitko R. G.
Published: February 2009

Turbine vane aerodynamics were measured in a three vane linear cascade. Surface pressures and blade row losses were obtained over a range of Reynolds and Mach numbers for three levels of turbulence. Comparisons are made with predictions using a quasi-3D Navier-Stokes analysis. Turbulence intensity measurements were made upstream and downstream of the vane. The purpose of the downstream measurements was to determine how the turbulence was affected by the strong contraction through 75° of turning.
Low Speed Studies of Sweep and Dihedral Effects on Compressor Cascades
Authors: Roy Bhaskar , Laxmiprasanna P. A. , Borikar Vishal , Batra Amit
Published: February 2009

The use of three dimensional blade designs incorporating end bend, sweep and dihedral to reduce secondary flow related losses, improve efficiency and stable operating range has gained ground in the recent years. In the present study a straight cascade, a swept cascade, and a dihedral cascade have been considered. Effects of sweep and dihedral along the span are studied at 0° and +20° stagger. The study shows that both the sweep and the dihedral have lower end-wall losses compared to the straight cascade. However, lower losses are accompanied with lower diffusion factors. At mid-span also the lowering of losses is achieved along with some lowering of diffusion factor. While the dihedral seems to contribute for stable operation more near the end-wall, the swept blade contributes more near the mid-span. The swept blade is able to sustain the flow at higher angles of attack. While the end-wall loss benefits are welcome with lower loading, at mid-span lower loading obtained may need to be corrected by increasing the design angle of incidence.
Aerodynamic Design Optimization of an Axial Flow Compressor Rotor
Authors: Ahn Chan-Sol , Kim Kwang-Yong
Published: February 2009

Design optimization of a transonic compressor rotor (NASA rotor 37) using the response surface method and three-dimensional Navier-Stokes analysis has been carried out in this work. The Baldwin-Lomax turbulence model was used in the flow analysis. Three design variables were selected to optimize the stacking line of the blade. Data points for response evaluations were selected by D-optimal design, and linear programming method was used for the optimization on the response surface. As a main result of the optimization, adiabatic efficiency was successfully improved. It was found that the optimization process provides reliable design of a turbomachinery blade with reasonable computing time.
Numerical Assessment of Different Turbulence Models for Slot Jet Impinging on Flat and Concave Surfaces
Authors: Jia Rongguang , Rokni Masoud , Sunde´n Bengt
Published: February 2009

A numerical study has been carried out for slot jet impinging on flat and concave surfaces. Five turbulence models are employed for the predictions of these strongly strained turbulent flows, namely linear eddy viscosity model (LEVM), low-Re explicit algebraic Reynolds stress model (EASM) and three different V2F models. A bounded formulation for Cμ was also introduced to account for the better prediction of the wall jet development. The studied Reynolds numbers vary from 8,000 to 20,000, and nozzle-to-surface distance (H) is in the range of 1≤H/B≤8. Detailed comparison is made between the results from the models and available experimental data to test the ability of the models in predicting these fluid flow and heat transfer problems.
Measurements of the Effects of Periodic Inflow Unsteadiness on the Aerodynamics of a Fishtail Diffuser
Authors: Yaras M. I. , Orsi P.
Published: February 2009

This study examines the effects of periodic inflow unsteadiness on the flow development through fishtail diffusers utilized on small gas-turbine engines. The periodic unsteadiness is due to the distortion of the flow in the peripheral direction at the exit of the centrifugal compressor impeller, caused by the jet-wake type of flow discharging from each passage of the impeller. The study consists of detailed measurements in a large-scale fishtail diffuser rig with a geometry that is typical of those used in small gas turbine engines. An unsteady-flow generator is used to approximate the type of diffuser-inflow conditions that exist at the exit of centrifugal compressor impellers. Detailed measurements of the transient velocity field have been performed at the inlet and at four cross-sectional planes throughout the diffuser using a miniature 4-wire probe. These measurements involve frequencies of inflow unsteadiness corresponding to design as well as off-design operating conditions. The measured velocity field is analyzed in a time-averaged sense and in the context of previously-performed steady-flow measurements. Results show significant effects of inflow unsteadiness at lower frequencies on the flow field in the diffuser, which translates into a substantial impact on the pressure recovery of the diffuser. In addition to providing insight into the physics of this flow, the experimental results presented here constitute a detailed and accurate data set that can be used to validate computational-fluid-dynamics codes for this application.
One-Dimensional Unsteady Modeling of the Flow-Field in a Short Duration Facility
Authors: Frati G. , De´nos R.
Published: February 2009

The establishment of the flow field in the test section of a short duration test rig is a complex process. In order to gain understanding during the transient phase, the time-accurate 1D Euler equations have been solved. The code is validated with two test cases: a steady nozzle flow and an unsteady flow in a shock tube. It is also applied to the short duration facility with an instantaneous opening of the shutter valve. Then, the code is modified to model the progressive opening of the shutter valve using moving boundaries. Finally, pressure and heat losses are also implemented using appropriate additional terms in the momentum and energy equations. The results obtained for the three different cases (instantaneous shutter opening, progressive opening, pressure and heat losses) are compared and discussed. In spite of the simplified approach that is used, the present simulation is able to provide the basic structure and behaviour of the flow field at different locations in the facility. The results show strong transient shock waves that propagate first forward and then backward in the settling chamber and put into evidence oscillations for both pressure and temperature at the test section inlet. In the case of a progressive opening, the process is delayed and the oscillations are smoother. The pressure losses damp significantly the oscillations.
Characterization and Nozzle Test Experience of a Self Sealing Ceramic Matrix Composite for Gas Turbine Applications
Authors: Bouillon Eric P. , Ojard Greg C. , Habarou G. , Spriet Patrick C. , Lecordix Jean L. , Feindel David T. , Linsey Gary D. , Stetson Doug P.
Published: February 2009

Advanced materials have the potential to improve gas turbine engine durability. One general area of concern for durability is in the hot section components of the engine. Ceramic matrix composites offer improvements in durability at elevated temperatures with a corresponding reduction in weight for nozzles of gas turbine engines. Building on past material efforts, a next generation SiC/SiC composite with a self-sealing matrix has been developed for gas turbine applications. An extensive baseline test characterization has been done that shows the overall material suitability. Prior to ground engine testing, a reduced test matrix was undertaken to aggressively test the material in a long-term hold cycle at elevated temperatures and environments. This tensile low cycle fatigue testing was done in air and a 90% steam environment. While the steam environment aggressively attacked the material, no appreciable debit in material life was noted. Nondestructive testing and post test characterization of this testing were performed. After completion of the aggressive testing effort, two nozzle seals of constant thickness were fabricated and installed in an F100-PW-229 engine for accelerated mission testing. The self sealing CMC seals were tested for over 250 hours in accelerated conditions without damage. The results of the engine testing will be shown and overall conclusions drawn.
Development of a New Simulation Program for Combined Cycle System
Authors: Sanaye Sepehr , Moradi Arash
Published: February 2009

The turbine inlet gas temperature ( Toso ) is an important parameter in design and performance analysis of gas turbine cycles. By increasing Toso, air bleeding for blade cooling increases and it can be about 25 percent of compressor inlet air mass flow rate for Toso equal to 1600 K. Therefore air bleeding has an important impact on thermal efficiency, specific power output and the optimum compressor pressure ratio at which maximum efficiency occurs. For the gas turbine part of a combined cycle, these performance curves are obtained and shown using a developed simulation program (GTE). Also for heat recovery steam generator (HRSG) part of a combined cycle plant, HRSG simulates the transient and steady state temperature distribution of hot gases, steam and tube metal at different parts of HRSG. Any number of pressure levels (high, intermediate and low) and heating elements (superheater, evaporator and economizer) including desuperheater and deaerator can be included. GTE outputs show less than two percent difference from reported measured values. This difference was less than six percent for HRSG model.
Pressure-Side Bleed Film Cooling: Part II — Unsteady Framework for Experimental and Computational Results
Authors: Holloway D. Scott , Leylek James H. , Buck Frederick A.
Published: February 2009

This study examines the unsteady transonic pressure-side bleed film cooling on the trailing edge of a turbine blade and resolves the key mechanism responsible for the unusual relationship between film cooling effectiveness and increasing blowing ratio. This study is meant to show that unsteadiness is the key mechanism causing the unexpected results seen in the experiments. It is believed that this unsteadiness is highly dependent on the ratio of the lip thickness to slot height and the shedding frequencies of the passage and coolant vortices, which depend on blowing ratio. For low blowing ratio, hot passage flow has the dominant vortices. For high blowing ratio, coolant flow has the dominant vortices. For intermediate blowing ratio, the vortices have the potential to interact and cause the unusual behavior seen in pressure-side bleed film cooling. On the basis of these observations, experiments were repeated with pressure probes used to acquire the shedding frequencies at the effectiveness measurement location, which showed that unsteadiness was indeed present. Realistic engine conditions are considered with lip thickness to slot height ratio of 0.9 and mainstream Mach numbers of 0.7 at the coolant injection point and expanding to sonic conditions at the exit plane of the test section. Numerical results are from a 2-D mid-plane cut of the original geometry and a full-pitch 3-D model. Computations use high quality grids, high order discretization schemes, and an advanced turbulence model. The 3-D grid consists of 4.4 million cells and a high quality, unstructured, multi-topology mesh with resolution of the viscous sublayer and y+ < 1 on all surfaces. The simulations are fully converged, time accurate, and grid-independent. A novel methodology is used to introduce unsteadiness into the simulations. Effects of blowing ratio are examined, where blowing ratio is equal to 1.0 for 3-D and ranges from 0.3 to 1.5 for 2-D with a density ratio of 1.52. By performing an unsteady simulation, the unusual relationship between the effectiveness and blowing ratio is demonstrated in an unsteady framework.
Flow and Heat (Mass) Transfer Characteristics in an Impingement/Effusion Cooling System With Crossflow
Authors: Rhee Dong Ho , Choi Jong Hyun , Cho Hyung Hee
Published: February 2009

The present study is conducted to investigate flow and heat/mass transfer characteristics in an impingement/effusion cooling system with crossflow. To simulate the impingement/effusion cooling system, two perforated plates are placed in parallel and staggered arrangements with a gap distance of 2 times of the hole diameter, and initial crossflow passes between the plates. Both the injection and effusion hole diameters are 10 mm, and the Reynolds number based on the hole diameter and hole-to-hole pitch are fixed to 10,000 and 6 times of the hole diameter, respectively. To investigate the effect of crossflow, the flow rate of crossflow is changed from 0.5 to 2 times of that of the impinging jet, and the results of impingement/effusion cooling with crossflow are compared with those of the crossflow in the channel and of an array of impingement jets and the effusion cooling system. A naphthalene sublimation method is used to determine the local heat/mass transfer coefficients on the upward facing surface of the effusion plate. The flow patterns are calculated numerically using a commercial package. With the initial crossflow, the flow and heat/mass transfer characteristics are changed significantly from the results without the crossflow. Jet flows ejected from the injection plate are deflected by the crossflow, so that the stagnation points of the impinging jets move downstream. The heat/mass transfer rates on the effusion (target) plate decrease as the velocity of crossflow increases, since the crossflow induces the locally low transfer regions formed at the mid-way between the effusion holes. However, the impingement/effusion cooling with crossflow presents higher heat/mass transfer rates than the array jet impingement cooling with the same initial crossflow.
CFD Optimization of Cooling Air Offtake Passages Within Rotor Cavities
Authors: Young Colin , Snowsill Guy D.
Published: February 2009

In modern gas turbine engines, up to 20% of the core airflow is bled off from various compressor stages to facilitate internal cooling, bearing chamber and rim sealing, as well as axial load management. As this secondary airflow makes no direct contribution to engine thrust, there are strong economic incentives to reduce the quantity and quality of offtake air and maximise its effective use. Secondary airflows are commonly bled off via circular drillings in the compressor rotor, thereby augmenting their swirl velocity. This results in the creation of vortices within the rotor cavity and strong radial pressure gradients opposing inflow. In the present work the relative performance of a series of non-circular offtake passages has been assessed using CFD techniques. The results of this work demonstrate the degree of control that may be exercised over swirl uptake, which can be used to suppress the creation of vortices in rotor cavities.
CMSX®-486: A New Grain Boundary Strengthened Single Crystal Superalloy
Authors: Harris Ken , Wahl Jacqueline B.
Published: February 2009

Modern turbine engine performance and life cycle requirements demand single crystal superalloy turbine airfoil and seal components. Complex SX vane segments can result in severe manufacturing cost challenges. This has resulted in the development of an improved creep-rapture strength SX superalloy designated CMSX®-486. This alloy is grain boundary strengthened through optimised additions of boron, carbon, hafnium and zirconium and is designed for use as-cast, to maximise complex casting yield through the use of generous grain specifications and without solution heat treatment recrystallisation problems. The paper in particular gives comprehensive low and high angle boundary creep-rupture properties of CMSX-486, enabling grain specifications to be developed depending upon component design requirements. The alloy has now entered its turbine application development phase.
Leading-Edge Film-Cooling Physics: Part III — Diffused Hole Effectiveness
Authors: York William D. , Leylek James H.
Published: February 2009

A proven computational methodology was applied to investigate film cooling from diffused holes on the simulated leading edge of a turbine airfoil. The short film-hole diffuser section was conical in shape with a shallow half-angle, and was joined to a plenum by a cylindrical metering section. The diffusion resulted in a film-hole breakout area of 2.5 times that of a cylindrical hole. In the present paper, predictions of adiabatic effectiveness for the cases with diffused holes are compared to results for standard cylindrical holes, and performance is analyzed in the context of extensive flowfield data. The leading edge surface was elliptic in shape to accurately model a turbine airfoil. The geometry consisted of one row of holes centered on the stagnation line, and two additional rows located 3.5 hole (metering section) diameters downstream on either side of the stagnation line. Film holes in the downstream rows were centered laterally between holes in the stagnation row. All holes were angled at 20° with the leading edge surface, and were turned 90° with respect to the streamwise direction (radial injection). The average blowing ratio was varied from 1.0 to 2.5, and the coolant-to-mainstream density ratio was equal to 1.8. The steady Reynolds-Averaged Navier-Stokes equations were solved with a pressure-correction algorithm on an unstructured, multi-block grid containing 4.6 million finite-volumes. A realizable k-ε turbulence model was employed to close the equations. Convergence and grid-independence was verified using strict criteria. Based on the laterally averaged effectiveness over the leading edge, the diffused holes showed a marked advantage over standard holes through the range of blowing ratios. However, ingestion of hot crossflow and thermal diffusion into the second row of film holes was observed to cause significant, and potentially detrimental, heating of the film-hole walls.
Film Cooling on a Modern HP Turbine Blade: Part III — Axial Shaped Holes
Authors: Ferguson Jeffrey D. , Leylek James H. , Buck Frederick A.
Published: February 2009

A well-tested computational methodology and high-quality data from a companion experimental study are used to analyze the physics of axial-injected, shaped-hole film cooling on the pressure and suction surfaces of a modern high-pressure turbine blade. Realistic engine conditions, including transonic flow, high turbulence levels, and a nominal density ratio of 1.52, are used to examine blowing ratios of 1.0, 1.5, and 2.0 on the suction surface (SS) and 1.5, 3.0, and 4.5 on the pressure surface (PS). SS results show excellent film-cooling performance with the hole shaping, but massive hot crossflow ingestion is found using similar hole shaping on the PS. Primary mechanisms governing the near and far-field cooling effectiveness and crossflow ingestion are identified, including: (1) the nature of the coolant entry into the film hole; (2) location of hole shaping relative to major coolant flow characteristics; and (3) susceptibility of low-momentum fluid to pressure gradients. Changes in blowing ratio, while not introducing new physical mechanisms, significantly alter the extent to which the mechanisms already present affect the flow. These effects are highly non-linear for both SS and PS geometries, highlighting the inadequacy of one-dimensional design practices and the potential usefulness of CFD as a predictive tool.
Full Coverage Film Cooling for Combustor Transition Sections
Authors: Ling John C. P. W. , Ireland Peter T. , Tumer Lynne
Published: February 2009

Concern for the environment has led to world-wide emissions legislation. Under such legislation, land based gas turbines in particular are required to meet stringent emissions levels of NOx and CO. In response, Rolls-Royce has designed and developed a retro fit dry low emission (DLE) module for the industrial RB211 aero-derivative engine. The DLE combustion system achieves low emissions through the use of staged premixed lean burn combustion. The paper reports detailed measurements of heat transfer coefficient and film cooling effectiveness for full coverage film cooling systems suitable for cooling the transition section between the combustor and the nozzle guide vanes. The experiments were performed at large scale using the transient liquid crystal method of measuring heat transfer. The film cooling data are unusual since the film injection angle is 20°. Extensive arrays with hole spacings of 16d and 10d have been investigated with air and with CO2 as the coolant. The latter tests achieved engine representative film to free-stream density ratios. The paper discusses in detail the experimental strategy and compares the data to results from the literature.
Inlet Fogging of Gas Turbine Engines: Part B — Fog Droplet Sizing Analysis, Nozzle Types, Measurement and Testing
Authors: Chaker Mustapha , Meher-Homji Cyrus B. , Mee Thomas
Published: February 2009

The inlet fogging of gas turbine engines for power augmentation has seen increasing application over the past decade yet not a single technical paper treating the physics and engineering of the fogging process, droplet size measurement, droplet kinetics, or the duct behavior of droplets, from a gas turbine perspective, is available. This paper provides the results of extensive experimental and theoretical studies conducted over several years, coupled with practical aspects learned in the implementation of nearly 500 inlet fogging systems on gas turbines ranging in power from 5 to 250 MW. Part B of the paper treats the practical aspects of fog nozzle droplet sizing, measurement and testing presenting the information from a gas turbine fogging perspective. This paper describes the different measurement techniques available, covers design aspects of nozzles, provides experimental data on different nozzles and provides recommendations for a standardized nozzle testing method for gas turbine inlet air fogging.