bluuebunny/crossref_metadata_2025 huggingface dataset:
Tip-Clearance and Secondary Flows in a Transonic Compressor Rotor
Authors: Gerolymos G. A. , Vallet I.
Published: December 2014

The purpose of this paper is to numerically investigate tip-clearance and secondary flows in a transonic compressor rotor. The computational method used is based on the numerical integration of the Favre-Reynolds-averaged 3-D compressible Navier-Stokes equations, using the Launder-Sharma near-wall k-ε turbulence closure. In order to accurately describe the flowfield through the tip and its interaction with the main flow, a fine O-grid is used to discretize the tip-clearance-gap. A patched O-grid is used to discretize locally the mixing-layer region created between the jet-like flow through the gap and the main flow. An H-O-H grid is used for the computation of the main flow. In order to substantiate the validity of the results comparisons with experimental measurements are presented for the NASA_37 rotor near peak efficiency using 3 grids (of 106, 2 × 106, and 3 × 106 points, with 21, 31, and 41 radial stations within the gap respectively). The Launder-Sharma k-ε model underestimates the hub corner stall present in this configuration. The computational results are then used to analyze the interblade-passage secondary flows, the flow within the tip-clearance gap and the mixing downstream of the rotor. The computational results indicate the presence of an important leakage-interaction-region where the leakage-vortex after crossing the passage shock-wave mixes with the pressure-side secondary flows. A second trailing-edge-tip-vortex is also clearly visible.
Application of Stress Relaxation Testing in Metallurgical Life Assessment Evaluations of GTD111 Alloy Turbine Buckets
Authors: Daleo Joseph A. , Ellison Keith A. , Woodford David A.
Published: December 2014

Stress relaxation and constant displacement rate tensile tests were performed on poly-crystalline GTD111 alloy material removed from General Electric MS6001B first stage combustion turbine buckets. Samples were examined in the standard heat treated condition, thermally exposed at 900°C for 5000 hours and from service run buckets. Creep rates of the material were measured and evaluated directly in terms of temperature capability at 850°C and 900°C. Stress relaxation tests done at 0.8% total strain indicated that the creep rate properties in the service exposed airfoil were an order of magnitude higher than the material properties in the standard heat treated condition measured in the root form. In terms of temperature capability, the creep rate properties of the service run airfoil material had decreased by the equivalent of almost 40°C.

The stress relaxation test method was demonstrated to be a very useful tool in quantifying the degradation of creep properties in service run components. Creep data that would require years to gather using conventional creep tests was generated in a few days. This now makes realistic life assessment and repair / replace decisions possible during turbine overhauls.

The test method’s unique ability to measure changes in creep rate over a large stress range, enabled the technique to distinguish between changes in creep strength due to (normal) microstructural evolution from the combined effects of microstructural evolution and strain related creep damage.

A method for estimating standard constant load creep rupture life from the stress relaxation creep rate data is also presented along with time-temperature parameter correlations. The data sets examined in this study indicate that creep rupture lives can be estimated within a factor of three from the stress relaxation data.

The information and analysis techniques described in this paper are directly applicable to metallurgical life assessment evaluations and the re-qualification of repaired General Electric buckets in Frame 3, 5, 6, 7 and 9 engine models.
Investigation of Discrete-Hole Film Cooling Parameters Using Curved-Plate Models
Authors: Berhe Mulugeta K. , Patankar Suhas V.
Published: December 2014

Computations have been conducted on curved, three-dimensional discrete-hole film cooling geometries that included the mainflow, injection hole, and supply plenum regions. Both convex and concave film cooling geometries were studied. The effects of several film cooling parameters have been investigated, including the effects of blowing ratio, injection angle, hole length, hole spacing, and hole staggering. The blowing ratio was varied from 0.5 to 1.5, the injection angle from 35° to 65°, the hole length from 1.75D to 6.0D, and the hole spacing from 2D to 3D. The staggered-hole arrangement considered included two rows. The computations were performed by solving the fully elliptic, three dimensional Navier-Stokes equations over a body fitted grid. Turbulence closure was achieved using a modified k-ε model in which algebraic relations were used for the turbulent viscosity and the turbulent Prandtl number. The results presented and discussed include plots of adiabatic effectiveness as well as plots of velocity contours and velocity vectors in cross-stream planes. The present study reveals that the blowing ratio, hole spacing, and hole staggering are among the most significant film cooling parameters. Furthermore: (1) the optimum blowing ratios for curved surfaces are higher than those for flat surfaces, (2) a reduction of hole spacing from 3D to 2D resulted in a very significant increase in adiabatic effectiveness, especially on the concave surface, (3) the increase in cooling effectiveness with decreasing hole spacing was found due to not only the increased coolant mass per unit area, but also the smaller jet penetration and the weaker counter-rotating vortices, (4) for all practical purposes, the hole length was found to be a much less significant film cooling parameter.
Zero Emission MATIANT Cycle
Authors: Mathieu Ph. , Nihart R.
Published: December 2014

In this paper, a novel technology based on the zero CO2 emission MATIANT (contraction of the names of the 2 designers: MATHIEU and IANTOVSKI) cycle is presented. This latter is basically a gas cycle and consists of a supercritical CO2 Rankine-like cycle on top of regenerative CO2 Brayton cycle. CO2 is the working fluid and O2 is the fuel oxidizer in the combustion chambers. The cycle uses the highest temperatures and pressures compatible with the most advanced materials in the steam and gas turbines. In addition, a reheat and a staged compression with intercooling are used. Therefore the optimized cycle efficiency rises up to around 45% when operating on natural gas. A big asset of the system is its ability to remove the CO2 produced in the combustion process in liquid state and at high pressure, making it ready for transportation, for reuse or for final storage. The assets of the cycle are mentioned. The technical issues for the predesign of a prototype plant are reviewed.
The Creep Damage Behavior of the Plasma-Sprayed Thermal Barrier Coating System NiCr22Co12Mo9-NiCoCrAlY-ZrO2/7%Y2O3
Authors: Schmidt Uli T. , Vöhringer Otmar , Löhe Detlef
Published: December 2014

During creep loading metallic substrates impose deformation on deposited ceramic thermal barrier coatings (TBC). Strain accomodation of the TBC is not attained by plastic deformation, but by means of crack initiation, crack opening, crack propagation or sliding of adjacent crack faces. In technical applications a distinction is made between tolerated or desired cracks perpendicular to the surface, and detrimental cracks parallel to the substrate-coating interface. Thus, TBC can respond to creep deformation by segmentation or spallation, the latter being referred to as failure.

The parameters influencing the probability of either segmentation or spallation are temperature, creep rate, magnitude of creep deformation, layer thickness and microstructure of the TBC. It can be stated that spallation failure probability increases with increasing creep rate, creep deformation and layer thickness. The presence of pores between single spraying layers also strongly augments the likelyhood of spallation. No significant influence of temperature on spallation failure probability can be found in the range from 850°C to 1050°C.

Light microscopy and scanning electron microscopy investigations show that the microstructure of the ceramic TBC changes during creep, and that the density of cracks detected on micrographs with low magnification (x50), increases with increasing creep deformation. On the other hand, the density of microcracks visible with high magnification (x500) is constant, or even decreases with increasing creep deformation. These findings are explained by sintering processes enabled by stress relaxation due to formation of macroscopic cracks perpendicular to the surface as a response to creep deformation.

A relationship between microstructural changes and the emission of acoustic signals recorded during creep is presented.
Development and Test of a Catalytic Combustor for an Automotive Gas Turbine
Authors: Lipinski John J. , Brine Philip R. , Buch Rajesh D. , Lester George R.
Published: December 2014

A catalytic combustor was designed and tested for a small recuperated gas turbine engine for use in a hybrid electric vehicle (HEV). Combustor rig and engine tests were performed with DF-2 diesel fuel, kerosene, and automotive gasoline. Rig test steady-state emissions were measured over the full engine operating range. Nitrogen oxides (NOx) emissions were insensitive to operating condition, and were almost strictly a function of fuel nitrogen content. For low-nitrogen kerosene, NOx emissions less than 1 ppm(vol) (at 15 percent O2) were demonstrated. Startup emissions were measured for conditions modeling engine spoolup from ignition to full speed.

Laboratory engine tests on DF-2 over a range of speeds and loads demonstrated tailpipe emissions less than 10 ppm(vol) NOx and less than 1 ppm(vol) unburned hydrocarbons (HC). NOx, HC, and carbon monoxide (CO) emissions were less than the California State Ultra-Low Emissions Vehicle (ULEV) standards for steady-state operation, corrected for assumed vehicle load and fuel consumption rate.
Sliding Mode Output Feedback Control of a Flexible Rotor via Magnetic Bearings
Authors: Lewis A. S. , Sinha A. , Wang K. W.
Published: December 2014

A sliding mode feedback algorithm is proposed to control the vibration of a flexible rotor supported by magnetic bearings. It is assumed that the number of states is greater than the number of sensors. A mathematical model of the rotor/magnetic bearing system is presented in terms of partial differential equations. These equations are then discretized into a finite number of ordinary differential equations through Galerkin’s method. The sliding mode control law is designed to be robust to rotor imbalance and transient disturbances. A boundary layer is introduced around each sliding hyperplane to eliminate the chattering phenomenon. The results from numerical simulations are presented which not only corroborate the validity of the proposed controller, but also show the effects of various control parameters as a function of the angular speed of the rotor. In addition, results are presented that indicate how the current required by the magnetic bearings is affected by control parameters and the angular speed of the rotor.
Influence of the Interface on the Energy Absorption Mechanisms of CMCs
Authors: Puente Iñigo , Elizalde Reyes , Sánchez José M. , Martínez-Esnaola José M. , Martín-Meizoso Antonio , Fuentes Manuel
Published: December 2014

An analysis of energy absorption in a tensile test of a CAS/SIC ceramic matrix composite is presented. The analysis is based on the principal parameters related to the strain and fracture mechanisms, as are the pullout length and the matrix crack spacing. The micro-mechanical properties of the material, the interfacial debonding, the frictional stress along the interface and the debonding energy are the core of the analysis. Using these parameters, the energy absorbed during the test, and the elastic energy released after fracture are calculated. The results are compared with those obtained in twenty-one tensile tests at room temperature, in which the strain energy density has been calculated and the permanent strain has been measured.
Testing, Analysis, and CFD Modeling of a Profiled Leading Edge Groove Tilting Pad Journal Bearing
Authors: Edney Stephen L. , Heitland Gregory B. , DeCamillo Scan M.
Published: December 2014

Testing and analysis of a profiled leading edge groove tilting pad journal bearing developed for light load operation is described. This bearing was designed for a generic, small, high speed steam turbine operating at projected loads of less than 25 psi (172.4 kPa) and journal surface speeds to 400 ft/s (122 m/s). On the second turbine application, a rotor instability was experienced with the oil flowrate reduced to optimize bearing steady state performance. This instability was eliminated by machining a taper on the exit side of the feed groove on each pad. At the reduced flowrate, the profiled groove bearing greatly improved the operating characteristics of the rotor system by reducing vibration amplitudes and stabilizing operation at speed.

This paper is divided into two sections. The first section compares the rotordynamics analysis with test data that shows improved unbalance response and operating stability with the profiled groove bearing. The second section provides original insight of the effect of the profiled geometry on the bearing flow field using computational fluid dynamics models.
A Fast Method to Obtain the Nonlinear Response of Multi-Mode Rotors Supported on Squeeze Film Dampers Using Planar Modes: Part I — Theory
Authors: Yakoub R. Y. , El-Shafei A.
Published: December 2014

This paper describes the development of an extremely fast method to obtain the unbalance response of multiple mode rotors supported on Squeeze Film Dampers (SFDs). Planar modal analysis theory is used to model the rotor-SFD system. Undamped critical speed analysis is performed to obtain the rotor eigenvalues and eigenvectors. The SFD nonlinear forces are included in the modal force vector. The system differential equations are constructed for the system and are uncoupled using the orthogonal properties of modal vectors. Assuming circular orbit, consistent with planar modes, the differential equations are converted into algebraic ones. A polynomial in speed is obtained through algebraic manipulations. This polynomial represents the steady state behavior of the rotor-SFD system. The full unbalance response is directly obtained by finding the roots of the polynomial for each particular orbit. This method is extremely fast compared to numerical integration and to iterative methods. The developed method is useful in performing parametric studies and optimum design of SFDs. Twenty five orders of magnitude computer lime savings are reported. Part II of the paper presents parametric studies of an aircraft gas turbine fan rotor supported by an SFD.
Computation of Subsonic and Transonic Compressor Rotor Flow Taking Account of Reynolds Stress Anisotropy
Authors: Arima Toshiyuki , Sonoda Toyotaka , Shirotori Masatoshi , Yamaguchi Yoshihiro
Published: December 2014

A two-layer k-ε/algebraic Reynolds stress model (ARSM) has been adopted to the three-dimensional, Reynolds-averaged, Navier-Stokes code to include explicitly the Reynolds stress anisotropy. The code has been used to study the complex flow fields of a transonic axial compressor rotor (i.e., NASA Rotor 37) and a subsonic centrifugal compressor impeller (i.e., the backswept impeller of Krain, first reported in 1988). The computed results have been compared with those from a Baldwin-Lomax model, a low-Reynolds number k-ε turbulence model and actual experimental data. Calculated results for the axial compressor are compared with data reported by Suder in 1994. The suitability of the turbulence model to predict accurately the overall performance of the rotor, spanwise distributions of aerodynamic characteristics, and the wake flow profiles is assessed. Calculations for the centrifugal compressor impeller are compared with the experimental data reported by Hah and Krain in 1989. The usefulness of the turbulence models to predict accurately the overall performance of the impeller, the impeller-exit-velocity profile, and the meridional velocity and flow angle profiles at the cross-channel planes (via L2F measurements) has also been investigated. For modeling the turbulence of both the rotor and the impeller, reasonably good predictions have been obtained with the ARSM and the low-Reynolds number k-ε models, but have not been attainable using the Baldwin-Lomax model. The solutions obtained with the ARSM show better agreement with experimental data than those obtained with the other models. However, in some cases, the predicted differences between the ARSM and the low-Reynolds number k-ε models are not significant. The computed secondary flow and the relative helicity have also been used to investigate the effect of wall curvature and frame rotation on the flow field inside the centrifugal impeller for three operating conditions (i.e., design point, choke, and near surge) and the results are discussed.
Surge in a Low-Speed Radial Compressor
Authors: Meuleman Corine , Willems Frank , de Lange Rick , de Jager Bram
Published: December 2014

Surge is measured in a low-speed radial compressor with a vaned diffuser. For this system, the flow coefficient at surge is determined. This coefficient is a measure for the inducer inlet flow angle and is found to increase with increasing rotational speed. Moreover, the frequency and amplitude of the pressure oscillations during fully-developed surge are compared with results obtained with the Greitzer lumped parameter model. The measured surge frequency increases when the compressor mass flow is throttled to a smaller flow rate. Simulations show that the Greitzer model describes this relation reasonably well except for low rotational speeds. The predicted amplitude of the pressure rise oscillations is approximately two times too small when deep surge is met in the simulations. For classic surge, the agreement is worse. The amplitude is found to depend strongly on the shape of the compressor and throttle characteristic, which are not accurately known.
Does User-Oriented Gas Turbine Research Pay Off?
Authors: Rooth Rudy A.
Published: December 2014

In 1994, the Dutch utilities started a five-year program aimed at 1) reduction of the forced unavailability of their gas turbine fleet and 2) keeping the operational and maintenance cost down. The project approaches its completion so now is the time to evaluate what it has delivered. Subjects of the project were the development of on-line and off-line diagnostic techniques, blade life management systems, optimization strategies for maintenance, air filtration and compressor washing, evaluation of NOx control techniques and evaluation and development of test methods for repair and reconditioning techniques. This paper gives an overview of the project achievements and a look at the evolution of the unavailability in the course of the years until 1995.

New (on-line) techniques developed are e.g. a flame stability monitoring system, correlating operational parameters to burner characteristics, a pyrometer with high spatial resolution and a tip shroud deflection monitor. Off-line inspection techniques include the development of a combined in-situ crack detection and sizing instrument as well as a method for measuring alumina depletion from coatings. REMLIF6, a life estimating algorithm for GE Frame 6 turbine blade and nozzles has been completed. Recommendations for optimized filter exchange and compressor washing schedules have been formulated. Development of the forced unavailability shows less problems related to turbine blading, possibly related to better knowledge on blade temperatures, and liners. An increase in burner related problems is noticeable, associated with the introduction of Low-NOx combustion. Overall the forced unavailability figures are going down and a number of problems in recent years has been solved quicker because of tools and knowledge developed in the project. The evolution of maintenance cost is under study.
Gas Turbine Inlet Air Cooling System With Liquid Air
Authors: Tanaka T. , Ishikawa A. , Aoyama K. , Kishimoto K. , Yoshida Y. , Toda K. , Atsumi M. , Kawamura H.
Published: December 2014

Gas turbine performance, especially power output and efficiency, is strongly dependent on ambient air temperature. Gas Turbine Inlet Air Cooling (GTIAC) has the effect of enhancing gas turbine capacity during peak hours in summer season. This paper presents an unique GTIAC system with liquid air, which will produce and store liquid air during off peak periods and spray it directly into the compressor inlet during peak hours. In the summer of 1996, an experimental study using a 150MW base load gas turbine was successfully performed on Chita Power Station to prove this new GTIAC performance. Test results show that the new GTIAC has a big advantage of increasing gas turbine capacity flexibly and economically for peak demands or emergencies.
Propulsion Aspects of the Thrust Asymmetry Compensation System (TAC) on the Boeing 777 Airplane
Authors: Ostrom Grace Balut
Published: December 2014

The Boeing 777 airplane has been designed with a Thrust Asymmetry Compensation System (TAC). This system reduces flight crew workload during single-engine flight operation by automatically commanding rudder deflection to compensate for different levels of thrust between the left and right engines. The airplane is equipped with two Engine Data Interface Units (EDIU) which compute thrust based on engine parameters. This paper will describe the thrust calculation, the fault detection requirements and the resultant fault monitors, and the processes used to validate the EDIU logic.
Advanced Instrumentation Technology for the Integrated-High-Performance-Turbine-Engine-Technology and High-Cycle-Fatigue Programs
Authors: Stange William A. , Navarra Kelly R.
Published: December 2014

This paper presents an overview of current research efforts aimed at improving turbine-engine structural-instrumentation capabilities. Emphasis is placed on non-intrusive concepts that will be applicable to the advanced engines currently in use, or concepts being developed for initial operational testing shortly after the turn of the century. Technologies to be described include: blade-tip deflection sensors to determine dynamic stress, thermographic phosphors to measure metal temperature, pressure-sensitive paints and air etalons to measure dynamic pressure, and micro-electro-mechanical systems to assess a variety of parameters. Advantages, potential problems and limitations of each system are presented, and an assessment of the applicability of each system to either the Integrated High Performance Turbine Engine Technology or the High Cycle Fatigue initiative is made.
Effects of Compound Angle Injection on Flat-Plate Film Cooling Through a Row of Conical Holes
Authors: Chen Ping-Hei , Ai Di , Lee Szu-Hsien
Published: December 2014

This paper presents the measured heat transfer and film cooling results over a flat plate as the secondary flow is ejected into the mainstream through a row of conical holes. A transient liquid crystal thermography was employed to derive the film cooling performance and heat transfer distribution over the test flat plate. Each conical injection hole, with a pitch-to-diameter ratio of 3 on the exit plane, had an expanded angle of 8 degrees. The effects of changing the spanwise injection angles and blowing ratios on both film cooling and heat transfer distributions were investigated. Test pieces in this study used different spanwise injection angles of β = 0°, 45°, and 90° but maintained the same inclination angle of γ = 35°. For each test piece, four different blowing ratios of 0.5, 1.0, 1.25 and 1.5 were tested at Re = 44,000, Tu = 2.3%, δ1/d = 0.22, p/d = 3, and R = 1.06. A baseline check was also conducted for the flat-plate film cooling through the use of straight circular holes. In addition, a comparison was made between the film cooling results using conical holes with those using straight circular holes.

Measured results showed that the laterally averaged heat transfer coefficient increases with the blowing ratio for both straight circular and conical hole configurations. For the simple injection, a conical configuration was found to have better film cooling protection only at higher blowing ratio (M = 1.25 and 1.5). Compound angle injection does not have specific advantage for the film cooling protection in the case of conical configuration.
Separated-Flow Transition: Part 1 — Experimental Methodology and Mode Classification
Authors: Hatman Anca , Wang Ting
Published: December 2014

This first part of the paper presents techniques implemented for the experimental investigation of the transition mechanism in 2-D pressure driven separated boundary layer flows over a flat plate at inlet free-stream turbulence intensities ranging from 0.3 to 0.6% and imposed adverse pressure gradients ranging from K = − 0.68 × 10−6 to − 6.25 × 10−6. The structure and behavior of the separation bubble were investigated for various flow conditions. The separated-flow transition modes were identified and classified. The distribution end strength of the adverse pressure gradient were obtained by varying the test section outer wall divergence angle.

Specific methods identifying the main parameters that characterize separated-flow transition are introduced and issues regarding measurements of reverse flow are discussed. The methods implemented in determining the separation point, maximum displacement location, the unsteady reattachment region, the start and end of transition, etc. are described.
High-Temperature Properties of SiC-Si3N4 Particle Composites
Authors: Woetting Gerhard , Caspers Bernhard , Gugel Ernst , Westerheide Ralf
Published: December 2014

Due to promising results in literature, SiC-Si3N4 particle composites in the range 0–100% SiC were evaluated. Focusing on high-temperature properties, mainly Y2O3 was used as sintering additive. Consolidation occurred primarily by hot-pressing, sintering tests were performed for comparison. Besides short-term properties like strength, toughness etc., long-term properties like creep and oxidation behavior were determined.

Results as a function of SiC-content and microstructure were discussed with respect to materials’ performance at high temperatures and possibilities of their production on a technical scale.
Effects of Inlet Flow Field Conditions on the Performance of Centrifugal Compressor Diffusers: Part 2 — Straight-Channel Diffuser
Authors: Deniz Sabri , Greitzer Edward M. , Cumpsty Nicholas A.
Published: December 2014

This is Part 2 of an examination of influence of inlet flow conditions on the performance and operating range of centrifugal compressor vaned diffusers. The paper describes tests of straight-channel type diffuser, sometimes called a wedge-vane diffuser, and compares the results with those from the discrete-passage diffusers described in Part 1. Effects of diffuser inlet Mach number, flow angle, blockage, and axial flow non-uniformity on diffuser pressure recovery and operating range are addressed.

The straight-channel diffuser investigated has 30 vanes and was designed for the same aerodynamic duty as the discrete-passage diffuser described in Part 1. The ranges of the overall pressure recovery coefficients were 0.65–0.78 for the straight-channel diffuser and 0.60–0.70 for the discrete-passage diffuser; the pressure recovery of the straight-channel diffuser was roughly 10% higher than that of the discrete-passage diffuser. Both types of the diffusers showed similar behavior regarding the dependence on diffuser inlet flow angle and the insensitivity of the performance to inlet flow field axial distortion and Mach number. The operating range of the straight-channel diffuser, as for the discrete-passage diffusers was limited by the onset of rotating stall at a fixed momentum-averaged flow angle into the diffuser, which was for the straight-channel diffuser, αcrit = 70° ±0.5°.

The background, nomenclature and description of the facility and method are all given in Part 1.
Measurement and Computation of Energy Separation in the Vortical Wake Flow of a Turbine Nozzle Cascade
Authors: Carscallen W. E. , Currie T. C. , Hogg S. I. , Gostelow J. P.
Published: December 2014

This paper describes the observation, measurement and computation of vortex shedding behind a cascade of turbine nozzle guide vanes which have a blunt trailing edge. At subsonic discharge speeds periodic wake vortex shedding was observed at all times at a shedding frequency in the range 7–11 kHz. At high subsonic speeds the wake was susceptible to strong energy redistribution. The effect was greatest around an exit Mach number of 0.95 and results are presented for that condition. An unusually cold flow on the wake center line and hot spots at the edges of the wake were measured. These were found to be a manifestation of Eckert-Weise effect energy separation in the shed vortex street. Experimental identification of these phenomena was achieved using a new stagnation temperature probe of bandwidth approaching 100 kHz. Using phase averaging techniques it was possible to plot contours of time-resolved entropy increase at the downstream traverse plane. Computational work has been undertaken which gives qualitative confirmation of the experimental results and provides a more detailed explanation of the fine scale structure of the vortex wake. The topology of the wake vortical structures behind blunt trailing-edged turbine blades is becoming clearer. These measurements are the first instantaneous observations of the energy separation process occurring in turbine blade wake flows. This was also the first demonstration of the use of the probe in the frequency, Mach number and temperature ranges typical of operation behind the rotors of high performance turbomachines such as transonic fans.
Reduced Order Modeling and Vibration Analysis of Mistuned Bladed Disk Assemblies With Shrouds
Authors: Bladh Ronnie , Castanier Matthew P. , Pierre Christophe
Published: December 2014

This paper presents important improvements and extensions to a computationally efficient reduced order modeling technique for the vibration analysis of mistuned bladed disks. In particular, this work shows how the existing modeling technique is readily extended to turbomachinery rotors with shrouded blades. The modeling technique employs a component mode synthesis approach to systematically generate a Reduced Order Model (ROM) using component modes calculated from a Finite Element Model (FEM) of the rotor. Based on the total number of degrees of freedom, the ROM is typically two or three orders of magnitude smaller than the FEM. This makes it feasible to predict the forced response statistics of mistuned bladed disks using Monte Carlo simulations. In this work, particular attention is devoted to the introduction of mistuning into the ROM of a shrouded assembly. Mistuning is modeled by projecting the mistuned natural frequencies of a single, cantilever blade with free shrouds onto the harmonic modes of the shrouded blade assembly. Thus, the necessary mistuning information may be measured by testing individual blades.
Inlet and Exit Flow Characteristics of Mixed Flow Turbines
Authors: Arcoumanis C. , Martinez-Botas R. F. , Nouri J. M. , Su C. C.
Published: December 2014

The steady performance of mainly two high pressure ratio mixed flow turbines for an automotive turbocharger (expansion ratio of 2.9) has been investigated and the results indicated superior performance of the rotor with a constant inlet blade angle relative to that with a nominally constant incidence angle. These results have been confirmed by the measurement of the three components of velocity, the Reynolds normal stresses and the flow angle at the inlet and exit of the mixed-flow turbine rotors by laser Doppler velocimetry (LDV) under steady state conditions. The turbine testing conditions corresponded to the 50% and 70% design speeds, equivalent to 29,400 and 41,300 rpm respectively.

The velocity results have indicated that the flow upstream of the rotor varies significantly along the blade inlet plane, and this is more evident at the 50% design speed. The flow in the volute behaves as a free vortex except in regions close to the hub, while the exit flow revealed that the constant incidence design rotor has a significantly higher exit swirl angle than the constant blade design, in agreement with the higher exit kinetic energy loss in the former case.
Current Status of Ceramic Gas Turbine (CGT302)
Authors: Kobayashi Hirotake , Tatsumi Tetsuo , Nakashima Takashi , Takehara Isashi , Ichikawa Yoshihiro
Published: December 2014

In Japan, from the point of view of energy saving and environmental protection, a 300kW Ceramic Gas Turbine (CGT) Research and Development program started in 1988 and is still continuing as a part of “the New Sunshine Project” promoted by the Ministry of International Trade and Industry (MITT).

The final target of the program is to achieve 42% thermal efficiency at 1350°C of turbine inlet temperature (TIT) and to keep NOx emissions below present national regulations. Under contract to the New Energy and Industrial Technology Development Organization (NEDO), Kawasaki Heavy Industries, Ltd. (KHI) has been developing the CGT302 with Kyocera Corporation and Sumitomo Precision Products Co., Ltd.

By the end of the fiscal year 1996, the CGT302 achieved 37.0% thermal efficiency at 1280°C of TIT. In 1997, TIT reached 1350°C and a durability operation for 20 hours at 1350°C was conducted successfully. Also fairly low NOx was proved at 1300°C of TIT. In January 1998, the CGT302 has achieved 37.4% thermal efficiency at 1250°C TIT.

In this paper, we will describe our approaches to the target performance of the CGT302 and current status.
Through Flow Calculation in Axial Flow Turbines Using a Quasi-Orthogonal Solver
Authors: Noera F. , Satta A.
Published: December 2014

Application of CFD investigating and analysing axial flow turbomachines has reached, in the last years, a high level of accuracy and thus can be applied quite routinely in the prediction of different kinds of flow. The numerical investigation of axial flow turbine performance is of great interest because of the importance of correct product design and of the behaviour in off-design conditions.

In this paper a new formulation of the radial equilibrium equation is presented. This formulation is particularly suitable for turbomachinery numerical investigation, and is applied in a quasi-orthogonal through flow solver. All the terms involved in the proposed formulation have been taken into account in order to solve the more general problem.

Mesh generation and blade geometrical representation are simplified in order to reduce the pre-processing work. In order to evaluate cascade losses and deviation angle, Ainley- and Mathieson semi-empirical correlations and their correction proposed by Dunham and Came and Kacker and Okapuu have been utilised. The four stages Hannover experimental turbine and the Cambridge one have been analysed in different operating conditions; numerical results have been compared with the experimental ones to evaluate the level of accuracy of the proposed procedure.
Twin Web Disk — A Step Beyond Convention
Authors: Cairo Ronald R. , Sargent Kathleen A.
Published: December 2014

This paper will discuss a study of an innovative design for an advanced turbine rotor, that could have a great impact on future engines. The design challenge is to provide a minimum weight turbine rotor system that can withstand beyond state-of-the-art levels of AN2 (turbine annulus area multiplied by speed squared). An AN2 limit has been reached for High Pressure Turbine (HPT) disks configured in conventional (single web) geometry with state-of-the-art nickel alloys. The problem has reached the point where increased AN2 has been declared a “Break-Through” technology. The twin-web disk has the potential to provide this break through. This paper will present the history of this turbine rotor design, analytical results, material/component processing and concept validation results. All work was performed under an Air Force sponsored program entitled Composite Ring Reinforced Turbine (CRRT).
A Non-Local Theory for the Assessment of Multiaxial High Cycle Fatigue Failure
Authors: Sjödin Björn
Published: December 2014

Looking at HCF, the most critical component on the turbine is the blade.

At the present moment there is a need for a HCF criterion suitable for evaluation of stresses calculated with the Finite Element Method. Today there are some, such criterions e.g. Sines. However the criterion does not include important aspects such as the influence of; ‘geometrical size’, ‘stressed volume’ or ‘stress gradient’.

A better understanding of the HCF phenomena would give an increase in the design precision and an opportunity to increase the load on the blades.

A proposal is made for a new theory for HCF assessment. The input required by the theory is roughly the Haigh-diagram for a smooth test specimen.

The theory is a merger between the Sines criterion and the statistical approach made by Weibull. 3 basic assumptions are made; equivalent stresses are calculated according to Sines, ‘the weakest link assumption’ and finally that the fatigue limit for a smooth specimen has a statistical distribution.

Comparing the proposal to classical HCF assessment with Haigh-diagram, the following factors are incorporated:

1, stress concentration factor

2, fatigue notch factor (or notch sensitivity factor)

3, geometric volume dependence

4, different Haigh-diagrams for push-pull, bending and torsion

If the factors are incorporated partially or fully remains to be shown. It is also possible to give a geometrical quantification of the so called ‘stressed volume’.

Qualitative and quantitative tests have been made. Looking at them, the theory looks promising. However, it has to be tested further to get acquainted with any shortcomings of the theory.
Microstructure and Property Assessment of Conventionally Cast and Directionally Solidified Buckets Refurbished After Long-Term Service
Authors: Swaminathan V. P. , Cheruvu N. S. , Klein J. M. , Robinson W. M.
Published: December 2014

Conventionally cast GTD-111EA first stage buckets from GE Frame 5001P-NT engine after 42,000 hours of service, directionally solidified GTD-111DS Frame 5002C buckets after 49,000 hours of service, and conventionally cast IN-738 Frame 5002B buckets after 81,000 hours of service were evaluated before and after refurbishment. These buckets were coated with GT-29, GT-29 plus and RT-22 coatings respectively. Coating condition, microstructural degradation, tensile properties, and creep properties were evaluated in the service aged condition. Microstructure was assessed after the hot isostatic pressing (HIP) and solution heat treatment and again after the full refurbishment and recoating of the buckets. It was found that the GT-29 coating was breached 100% by oxidation in the 5001P engine after service. The GT-29 plus coating on the 5002C engine was breached very slightly and the majority of the coating was still in good condition. The RT-22 coating on the IN-738 bucket was stripped before it was received for evaluation at SwRI. Gamma prime growth, coalescence and agglomeration were found in all of the buckets. Continuous carbide network near the airfoil leading edge was found in the GTD-111EA bucket.

Significant improvement in the microstructural condition was observed after the refurbishment for the GTD-111 buckets. However, the gamma prime morphology was not normal for the IN-738 bucket. Both tensile and creep properties of the GTD-111 buckets showed significant improvement after refurbishment. However, for the IN-738 bucket little improvement on the mechanical properties was observed. The reasons for this and the correlation between the microstructure and properties are discussed in this paper.
Comparison of Design Intent and Experimental Measurements in a Low Aspect Ratio Axial Flow Turbine With Three-Dimensional Blading
Authors: Wallis A. M. , Denton J. D.
Published: December 2014

In recent years there has been considerable interest in improving turbine efficiency by the application of three-dimensional (3D) design techniques. However, there is no consensus on the optimum strategy to be adopted for this. The paper describes a strategy for the design of new 3D blading for a four stage model of a high pressure steam turbine. The new blading was tested and increased the turbine efficiency by 2% relative to the previous, very efficient 2D blading. Some details of the flow measurements in the turbine are presented and consideration is given to the effectiveness of current steady CFD codes to design this type of blading in the multistage environment.
Spray Characteristics of an Airblast-Simplex Nozzle for Liquid-Fueled Gas Turbine Combustors
Authors: Ibrahim Mounir , Sanders Terry , Yarwood Debra , Moawed Mohammed , Steinthorsson Erlendur , Benjamin Michael
Published: December 2014

Experimental and computational (CFD) investigations were conducted on an Airblast Simplex (ABS) nozzle. A Phase Doppler Particle Analyzer (PDPA) was used to study the main characteristics of the nozzle. Water was used as the test liquid with pressure drops of 68.9, 172.3 & 689 kPa, while the air pressure drops were 2.49 & 34.5 kPa. PDPA data were obtained at three different axial distances from the nozzle exit (x = 2.5 (or 7), 17 & 40 mm). In the numerical simulations, the three-dimensional flow field for both air and liquid was computed. The combination of detailed experimental measurements and CFD provided excellent insight into the physics of the atomizer. The three-dimensional CFD simulation showed distinct jets originating the air swirler and secondary flows that cause multiple peaks in number density, volume flux and velocity distributions. The jets suggest why asymmetric distributions are common in sprays. The jetting effect from the swirler vanes emphasizes the importance of swirler and airflow design on the performance of a spray nozzle. The discrete jetting effect is not visually observable, nor is it easily measured using PDPA.

The ABS nozzle examined has several distinct advantages over a pressure swirl atomizer, including, (1) the distinct sheet from the hollow cone spray is dispersed within 17 mm in all cases studied herein, and (2) the spray volume does not change significantly with increasing air or liquid pressure drop. Therefore, careful design of ABS nozzle results in a spray with nearly constant spray volume and SMD over a wide range of Air/Liquid Ratios.
Detection of Precursor Waves Announcing Stall in Two 3-Stage Axial Compressors
Authors: Grauer F. , Volgmann W. , Stoff H. , Breuer T.
Published: December 2014

Rotating stall and surge limit the operating range of a compressor towards low throughflow and high pressure in the performance map. Usually a safety margin must be observed to prevent the compressor from entering unintentionally aerodynamic instabilities. As the range of highest performance and efficiency lies in the vicinity of the stability limit, efforts concentrate on recognizing imminent onset of unstable operation prior to its occurrence.

The present investigation centers on means of detecting information about onsetting instability from signals of pressure fluctuations in two transonic medium-pressure axial compressors of 3 stages. Fourier-transform-methods as well as artificial neural networks are applied for the data reduction of the time-dependent pressure signals. The methods of investigation presented here detected stall precursors announcing the onset of instability. Some of them seem appropriate to be used in connection with active stall control.
Steady and Unsteady Three Dimensional Flow Field Downstream of an Embedded Stator in a Multistage Axial Flow Compressor: Part 2 — Composite Flow Field
Authors: Suryavamshi N. , Lakshminarayana B. , Prato J.
Published: December 2014

In Part 1 of this paper, the unsteady velocity field derived from slanted hot-film measurements was presented and interpreted. In this part, the stagnation pressure (Kulite probe) and temperature data (Aspirating Probe) is integrated with the velocity data (hot-film probe) to derive a composite flow field description of the steady and unsteady flow behavior downstream of the second stator of a three stage axial flow compressor at the peak efficiency operating condition. Detailed mechanisms for various flow field features such as the hub clearance flow and the suction surface-casing endwall comer region have been analyzed based on the composite flow field. The feasibility of correlating the deterministic velocity and temperature distributions to develop stress and heat-flux terms to be used in Part 3 of this paper are explored. The results indicate that major blockage is caused in the stator hub endwall leakage flow and its possible subsequent rollup into a vortex and in the casing endwall region due to suction surface casing endwall comer and secondary flow region. These are also the regions with the highest levels of unsteadiness. From the ensemble averaged velocity, pressure and temperature field it was observed that very good comparison exists between these data sets for the wake properties such as width and depth. The transport of rotor wake towards the pressure side of the stator is confirmed through an integrated interpretation of all the flow properties.
Non-Axisymmetric Endwall Profiling in a Turbine Rotor Blade
Authors: Hartland J. C. , Gregory-Smith D. G. , Rose M. G.
Published: December 2014

A non-axisymmetric endwall profile has been designed using CFD with the aim of reducing endwall pressure non-uniformities downstream of a rotor blade. The purpose was to reduce coolant leakage as proposed by Rose (1994). This profile has been manufactured and fitted to the Durham linear cascade. The experimental endwall pressure distribution agrees very well with the CFD predictions giving a substantial reduction in pressure non-uniformity at the equivalent of the platform edge location downstream. Velocity and total pressure measurements have also been made within and downstream of the blade row to investigate the effects of the profile on the cascade secondary flow. Although the experimental results indicate no significant increase in the secondary flows, a small increase in loss is seen. The CFD predicts these trends also but to a smaller extent. This investigation suggests that with three-dimensional endwall design, the pressure field which provides the driving force of secondary flows can be modified without blade redesign.