bluuebunny/crossref_metadata_2025 huggingface dataset:
Nature of Vibratory Waves in Bladed Disks
Authors: Klompas Nicholas
Published: July 2014

An elemental explanation of the longstanding puzzler, peak splitting, is advanced and correlated with published experimental results. The peaks are shown to represent two singular speeds of a traveling wave, at each of which a portion of the blades jump from subcritical to supercritical response, or vice versa. Only one blade, of two with slightly different natural frequency and spaced approximately 90 deg apart, passes through full resonant condition in each jump. Interaction with engine whirl is produced.

Aeroengine vibrations associated with bladed disk flexing/whirl interaction are examined:

• A nonconservative, either stabilizing or destabilizing, inertial force due to linear flexing is introduced.

• Previous definition of a nonlinear friction induced limit cycle, attendant to the interlocked shroud enabling the high-bypass turbofan, is now reviewed and completed by explanation of the necessary frictional backward driving torque.
Optimization of Intentional Mistuning Patterns for the Reduction of the Forced Response Effects of Unintentional Mistuning: Formulation and Assessment
Authors: Choi Byeong-Keun , Lentz Jeff , Rivas-Guerra Alejandro , Mignolet Marc P.
Published: July 2014

The focus of the present investigation is on the use of intentional mistuning of bladed disks to reduce their sensitivity to unintentional random mistuning. The class of intentionally mistuned disks considered here is limited, for cost reasons, to arrangements of two types of blades (A and B, say). A two-step procedure is then describe to optimize the arrangement of these blades around the disk to reduce the effects of unintentional mistuning. First, a pure optimization effort is undertaken to obtain the pattern(s) of the A and B blades that yields small/the smallest value of the largest amplitude of response to a given excitation in the absence of unintentional mistuning. Then, in the second step, a pattern screening technique based on a recently introduced measure of localization is used to determine which of the patterns does have a large/small sensitivity to random unintentional mistuning. In this manner, expensive Monte Carlo simulations can be eliminated. Examples of application involving both simple bladed disk models and a 17-blade industrial rotor clearly demonstrate the significant benefits of using this class of intentionally mistuned disks.
The Periodical Interaction of the Tip Clearance Flow in the Blade Rows of Axial Compressors
Authors: Mailach Ronald , Sauer Helmut , Vogeler Konrad
Published: July 2014

Current models on the tip clearance flow in turbomachines only describe the time-averaged behaviour of the flow structures. However, the real tip clearance flow is periodically fluctuating in time. This fact has to be considered for the design of turbomachine bladings especially with regard to blade vibrations and tip clearance noise.

Detailed experimental investigations on the time-resolved behaviour of the flow in the rotor blade tip region were carried out in a four-stage low-speed research compressor. A strong time-periodic interaction of the blade tip vortices of adjacent blades can be shown for relatively large tip clearance of the rotor blades for operating points near the stability limit of the compressor. The resulting flow pattern, which frequency is not related to the rotor frequency, moves along the blade row. It can be described as a multicell configuration with strongly fluctuating cell number and size. The structure and propagation of the flow instability can be summarized in a model of the periodic fluctuating tip clearance flow (Mailach et al., 2000).

Additional experiments were carried out in a straight cascade to improve the understanding of this flow phenomenon. It can be shown by means of time-resolved measurements that the same disturbance exists for comparable inlet flow conditions in the blade tip region of the cascade. Flow visualizations show that the blade tip vortex is strongly fluctuating and moves sometimes ahead of the leading edge of the adjacent blade. The result of this is a short-lengthscale flow pattern, which is propagating along the blade row. These experiments confirm the model of the time-periodic tip clearance flow proposed for compressors. A Strouhal-number for the estimation of the frequency of the flow fluctuation will be presented, which includes both design and aerodynamic parameters.
Analysis of Two Automotive Turbocharger Compressor Radial Vaneless Diffusers for Use in Improving a Performance Prediction Technique
Authors: Meese H. M. , Swain E.
Published: July 2014

An experimental and analytical investigation of two automotive centrifugal compressors with a radial vaneless diffusers has been conducted. Static pressure measurements together with 1-D flow assumptions have been used to determine the fluid properties throughout the diffuser and this has provided quantitative estimates of the location and value of the losses occurring in this region.

A correlation of diffuser loss for the two specific geometry’s has been developed. This correlation has been used to extend a 1-D prediction technique to include the vaneless diffuser, enabling the operating range and performance of the diffuser to be predicted from the geometry.
Analysis of Diffusers With Different Number of Vanes in a Centrifugal Compressor Stage
Authors: He N. , Tourlidakis A.
Published: July 2014

In this paper, a computational analysis of a high-speed centrifugal compressor stage for turbocharger applications is presented. Emphasis is focused on the effect of different number of diffuser vanes, and for this reason four different designs of the vaned diffuser are analysed. The first three of the diffusers consist of 11, 22 and 33 vanes, respectively, with their leading edge at a radius of 1.075 times the radius of the impeller tip. The fourth one consists of 22 vanes with its leading edge at 1.15 times the radius of the impeller tip. All the above vane designs are of double circular arc shape.

A steady CFD analysis is carried out using the Reynolds-Averaged Navier-Stokes solver TASCflow at design and off-design operating conditions. An averaging approach is used at the interface between the impeller and the diffuser. A detailed comparison between the predicted and the available experimental data is performed in terms of pressure rise and efficiency characteristics, and very good agreement is accomplished. In addition, detailed flow distributions are compared and critically analysed.

One of the most important conclusions is that while maintaining the overall throat area and the location of the leading and trailing edges of the diffuser, as the number of diffuser vanes increases, the pressure recovery coefficient at the semi-vaneless space at surge condition was found to reduce, the wake pattern becomes more pronounced and the velocity distribution at vaneless and semi-vaneless space becomes more distorted when passing the same mass flow rate and therefore the diffuser has a narrower flow range. On the other hand, it was found that the diffuser outlet to throat area ratio is not the dominant factor to influence the flow range when the number of vanes changes.
Improved Compressor Exit Diffuser for an Industrial Gas Turbine
Authors: Orth U. , Ebbing H. , Krain H. , Weber A. , Hoffmann B.
Published: July 2014

Cycle studies carried out for the medium pressure ratio gas turbine THM 1304 of 10 MW power output manufactured by MAN Turbomaschinen AG GHH BORSIG predicted that the overall efficiency of the multi stage compressor, composed of a 10 stage axial and a single stage centrifugal compressor, would improve by 0.8% if the efficiency of the back stage centrifugal unit could be raised by 4%. It was expected that this would result in a noticeable improvement of the thermal gas turbine efficiency.

The paper describes the aerodynamical design process used for the stage optimization applying today’s advanced design tools for blade generation and three dimensional aerodynamic calculation methods. Additionally it describes the manufacturing procedure for the resulting three-dimensional blades and the experimental verification of the design approach.
Redesign of a 12-Stage Axial-Flow Compressor Using Multistage CFD
Authors: Wellborn Steven R. , Delaney Robert A.
Published: July 2014

A multistage turbomachinery computational fluid dynamics (CFD) system was developed and used to redesign an industrial core compressor for improved performance. Overall performance improvement goals of a 1% increase in the design point adiabatic efficiency and a 5% increase in high-speed surge margin were established for this first attempt at using this new system. Outlined in this paper are the details of how advanced multistage tools were incorporated into the existing design system. Data from the baseline and redesigned configurations are presented that illustrate the capabilities of the system. The redesign activities are reviewed, with emphasis placed on the ability of the tools to adequately predict axial stage matching.

A simple and economical means to increase compressor performance was found using the new CFD system. Test data confirmed that the redesign of the target compressor was successful. Engine results demonstrated a 2% increase in design speed compressor efficiency and a 4% drop in the high speed operating line with the redesigned blading installed, thereby exceeding the original efficiency improvement goal. This increase in compressor efficiency produced a 4% increase in engine shaft horsepower with a 16% decrease in the heat rate near the design turbine inlet temperature.
Unsteady Rotor/Stator Interaction: An Improved Unstructured Approach
Authors: Adami P. , Belardini E. , Martelli F. , Michelassi V.
Published: July 2014

A full-3D unstructured solver based on an upwind TVD finite volume scheme is developed and applied to the simulation of an unsteady turbine stage. Two different approaches are considered for the time accurate inviscid simulation of the unsteady stator/rotor interaction. The first consists of a classical explicit time accurate multi-step Runge-Kutta scheme. The second is based on a dual-time stepping strategy, which exploits the implicit time-marching Newton-Krylov method. In this case the linear solver of the implicit scheme consists of a preconditioned GMRES and ILU(0) incomplete factorisation. Both the explicit and implicit approaches are designed to run on parallel cluster of workstations. The development of the numerical strategy is discussed with particular concern on the validation of the unsteady model through a comparison against experiments, NISRE approach and a 3D steady stage computation. The results compare favourably with a set of time averaged and unsteady experimental data available for the turbine stage under investigation, which is representative of a wide class of aero-engines. Both the accuracy of the solver and the capability of the computational model are discussed.
Conservative Interfacing for Turbomachinery Applications
Authors: Cali Philip M. , Couaillier Vincent , Jameson Antony
Published: July 2014

This paper presents the development of a conservative interface technique designed for turbomachinery applications involving multiple rows of blades. Instead of interpolating solution information between blade rows, unique patch boundaries are defined at rotor/stator interfaces on which numerical fluxes are evaluated directly. The fluxes are then distributed to both sides of the interface in a fully conservative fashion. Accuracy is maintained by representing the primitive variables in each interface cell using a system of quadratic polynomials. The coefficients of each polynomial are calculated using neighboring flow information from both sides of the interface. In order to make the reconstruction process more tenable, the current implementation is restricted to pairs of blade rows which maintain identical axisymmetric radial distributions of points at their juncture. Preliminary inviscid flow results show significant improvements in solution quality relative to calculations conducted using conventional nonconservative interpolation techniques.
Studies of Jet Fuel Freezing by Differential Scanning Calorimetry and Cold-Stage Microscopy
Authors: Ervin J. S. , Widmor N. , Zabarnick S. , Vangness M.
Published: July 2014

Aircraft which fly at high altitude or encounter extremely cold environments have the potential for fuel freezing and, consequently, catastrophic failure of the fuel system. Thus, it is important to study the freezing of hydrocarbon jet fuels. In the current work, a differential scanning calorimeter is used to study thermal characteristics and phase transitions of freezing jet fuel. In addition, a cold-stage microscope is used to record images of the resulting crystalline microstructure. A kinetic representation for the freezing of jet fuel is presented. Kinetic mechanisms that describe the liquid-to-solid phase transformation in fuels are necessary for the development of computational fluid dynamics models that can be used by aircraft designers.
Efficiency Upgrading of an Ambient Pressure MCFC Plant Through the Introduction of an Indirect Heated Gas Turbine
Authors: Lunghi Piero , Ubertini Stefano
Published: July 2014

The efficient end environmentally friendly production of electricity is undoubtedly one of the 21st century priorities. Since renewable sources will be able to guarantee only a share of the future demand, the present research activity must focus on innovative energy devices and improved conversion systems and cycles. Great expectations are reserved to fuel cell systems. The direct conversion from chemical to electrical energy eliminates environmental problems connected with combustion and bypass the stringent efficiency limit due to Carnot’s principle.

Still in infancy high temperature Fuel cells present the further advantage of feasible cycle integration with steam or gas turbines.

In this paper, a Molten Carbonate Fuel Cell plant is simulated in a cycle for power generation. The introduction of an external combustion Gas Turbine is evaluated with the aim of efficiency and net power output increase. The results show that the proposed cycle can be conveniently used as a source of power generation. As compared to internal combustion Gas Turbine hybrid cycles found in literature the plant is characterized by fuel cell greater simplicity, due to the absence of pressurization, and gas turbine increased complexity, due to the presence of the heat exchange system.
Degradation Effects on Combined Cycle Power Plant Performance: Part 1 — Gas Turbine Cycle Component Degradation Effects
Authors: Zwebek A. , Pilidis P.
Published: July 2014

This paper describes the effects of degradation of the main gas path components of the gas turbine topping cycle on the Combined Cycle Gas Turbine (CCGT) plant performance. Firstly the component degradation effects on the gas turbine performance as an independent unit are examined. It is then shown how this degradation is reflected on a steam turbine plant of the CCGT and on the complete Combined Cycle plant.

TURBOMATCH, the gas turbine performance code of Cranfield University was used to predict the effects of degraded gas path components of the gas turbine have on its performance as a whole plant. To simulate the steam (Bottoming) cycle, another Fortran code was developed. Both codes were used together to form a complete software system that can predict the CCGT plant design point, off-design, and deteriorated (due to component degradation) performances.

The results show that the overall output is very sensitive to many types of degradation, specially in the turbine of the gas turbine. Also shown is the effect on gas turbine exhaust conditions and how this affects the steam cycle.
Performance Simulation of Turboprop Engine for Basic Trainer
Authors: Kong Changduk , Ki Jayoung
Published: July 2014

A performance simulation program for the turboprop engine (PT6A-62), which is the power plant of the first Korean indigenous basic trainer KT-1, was developed for more precise performance prediction, development of an EHMS (Engine Health Monitoring System) and the flight simulator.

Characteristics of components including compressors, turbines, the combustor and the constant speed propeller were required for the steady state and transient performance analysis with on and off design point analysis. In most cases, these were substituted for what scaled from similar engine components’ characteristics with the scaling law.

The developed program was evaluated with the performance data provided by the engine manufacturer and with analysis results of GASTURB program, which is well known for the performance simulation of gas turbines. Performance parameters such as mass flow rate, compressor pressure ratio, fuel flow rate, specific fuel consumption ratio and turbine inlet temperature were discussed to evaluate validity of the developed program at various cases. The first case was the sea level static standard condition and other cases were considered with various altitudes, flight velocities and part loads with the range between idle and 105% rotational speed of the gas generator.

In the transient analysis, the Continuity of Mass Flow Method was utilized under the condition that mass stored between components is ignored and the flow compatibility is satisfied, and the Modified Euler Method was used for integration of the surplus torque.

The transient performance analysis for various fuel schedules was performed. When the fuel step increase was considered, the overshoot of the compressor turbine inlet temperature occurred. However, in case of the fuel ramp increase longer than the fuel step increase, the overshoot of the compressor turbine inlet temperature was effectively reduced.
Modelling the Air-Cooled Gas Turbine: Part 2 — Coolant Flows and Losses
Authors: Young J. B. , Wilcock R. C.
Published: July 2014

This paper is Part II of a study concerned with developing a formal framework for modelling air-cooled gas turbine cycles. It deals with the detailed specification of coolant flowrates and losses. For accurate performance assessment it is necessary to divide the turbine expansion into individual stages with stator and rotor rows being treated separately. Particular care is needed when deriving the equations for the rotor and it is shown how all required flow variables can be estimated from minimal data if design values are unavailable.

Specification of the cooling flowrates is based on a modified Holland and Thake procedure which can be formalised in terms of averaged parameters. Thermal barrier coatings can be included if present. The importance of allowing for fluctuations in combustor outlet temperature is stressed and procedures for dealing with end-wall and disk cooling are suggested.

There is confusion in the literature concerning cooling losses and it is shown how these may be defined and sub-divided in a consistent way. The importance of representing losses in terms of irreversible entropy creation rather than total pressure loss is stressed. A set of models for the components of the cooling loss are presented and sample calculations are used to illustrate the division and magnitude of the loss.
CAES: Reduced to Practice
Authors: Daly John , Loughlin R. M. , DeCorso Mario , Moen David , Davis Lee
Published: July 2014

With the deregulation of the power industry, the use of peaking power solutions such as Compressed Air Energy Storage (CAES) is receiving increasing attention. The CAES plant located in McIntosh, Alabama, owned and operated by Alabama Electric Cooperative, Inc. (AEC) is the subject of this paper. It is the only such plant in the USA and one of two in the world. In off-peak hours the plant pressurizes a cavern with compressed air. During peak hours the stored cavern air is then valved through the combustion turbines to produce any level of peaking power required between 10 and 110 megawatts. This prototype plant began operating in May 1991 and its reliability has been steadily improved. This paper describes the learning process and plant-wide equipment modifications that were made to bring the plant to its present state of reliable operation. Because the CAES operating conditions and operating modes differ from conventional gas turbines, anticipated and unanticipated problems arose. The plant is made up of “combustion turbine” type components, but because of the way the plant operates (- valving of air input - relatively high pressure and air flows at startup - abrupt air flow shutoff at shutdown), certain operating experiences are unique to a CAES plant and not seen on standard gas turbine plants. Among the areas discussed are: controls, stand-by combustor, low-pressure (LP) expander, cavern well liner, lube oil, exhaust flow damper, high-pressure (HP) combustors, LP combustors, fuel injectors, fuel handling, and hot gas path instrumentation. These topics are discussed in the problem, solution, recommendation format. The learning process described in the paper will serve as an invaluable guide to plant designers as future CAES plants are built.
Thermal Field and Flow Visualization Within the Stagnation Region of a Film Cooled Turbine Vane
Authors: Cutbirth J. Michael , Bogard David G.
Published: July 2014

To develop quality computational codes for the film cooling of a turbine vane, a detailed understanding is needed of the physical mechanisms of the mainstream-coolant interactions. In this study flow visualization, thermal profiles, and laser Doppler velocimetry measurements were used to define the thermal and velocity fields of the film cooled showerhead region of a turbine vane. The showerhead consisted of six rows of spanwise oriented coolant holes, and blowing ratios ranged from 0.8 to 2.5. Performances with low and high mainstream turbulence levels were tested. Coolant jets from the showerhead were completely separated from the surface even at relatively low blowing ratios. However, the interaction of the coolant jets from laterally adjacent holes created a barrier to the mainstream flow, resulting in relatively high adiabatic effectiveness.
Ductility Loss in Aluminized CoCrAlY Coatings Exposed to In-Service Environment
Authors: Shinohara N. , Ito A. , Sugiyama K. , Sugita Y. , Kameda J. , Bloomer T. E. , Sakurai S.
Published: July 2014

By applying a small punch testing technique, it has been previously shown that near-surface aluminized CoCrAlY coatings of unused advanced gas turbine blades had very low ductility due to the formation of Al and Cr rich phases, compared to internal and near-interface regions. Thus, it is important to examine how in-service operation affects the mechanical properties of the internal, near-interface coatings and substrates to maintain the integrity of gas turbines. This study attempts to compare the effects of in-service operation for 20,000 h under combustion of liquefied natural gas and thermal ageing in air. The in-service operation led to a larger ductility loss in concave coatings near the tailing edge, although the ductility slightly improved above testing temperature at 950 °C. Substrate used in-service had lower ductility at 950 °C than the used concave coatings. The ductility of used internal coatings depended on the blade location. In convex coatings near the leading edge, in-service degradation was not significant and the ductility was about two-fold greater than in the thermally aged blade. The in-service degradation mechanism of the aluminized CoCrAlY coatings is discussed in light of the operating temperature distribution and microstructural evolution.
Dwell Sensitive Fatigue Response of Titanium Alloys for Power Plant Applications
Authors: Bache Martin R. , Evans W. John
Published: July 2014

The phenomenon of “dwell sensitivity” in the α+β and near α titanium alloys and the intrinsic relationship with quasi-cleavage facet formation is discussed. In the present paper, particular emphasis is placed upon the role of “cold creep” and ambient temperature strain accumulation under cyclic loading. A process of stress redistribution between microstructurally distinct regions that demonstrate different strengths is proposed as the fundamental cause of facet development and subsequent dwell failures. A model to describe the redistribution process is validated through a matrix of fatigue testing designed to assess the effects of microstructural form, stress axiality and periods of dwell loading at peak stress on cyclic strain accumulation.
Pressure Surface Separations in Low Pressure Turbines: Part 2 of 2 — Interactions With the Secondary Flow
Authors: Brear Michael J. , Hodson Howard P. , Gonzalez Paloma , Harvey Neil W.
Published: July 2014

This paper describes a study of the interaction between the pressure surface separation and the secondary flow on low pressure turbine blades. It is found that this interaction can significantly affect the strength of the secondary flow and the loss that it creates. Experimental and numerical techniques are used to study the secondary flow in a family of four low pressure turbine blades in linear cascade. These blades are typical of current designs, share the same suction surface and pitch, but have differing pressure surfaces.

A mechanism for the interaction between the pressure surface separation and the secondary flow is proposed and is used to explain the variations in the secondary flows of the four blades. This mechanism is based on simple dynamical secondary flow concepts and is similar to the aft-loading argument commonly used in modern turbine design.
TERTS: A Generic Real-Time Gas Turbine Simulation Environment
Authors: Visser Wilfried P. J. , Broomhead Michael J. , van der Vorst Jasper
Published: July 2014

Real-time simulation of gas turbine engine performance is used in a variety of aerospace applications. For simulation of propulsion system performance in flight-simulators, fidelity requirements become increasingly stringent. Significant improvements in simulation fidelity can be obtained when using thermodynamic models instead of the customary (piece-wise) linear real-time models. However, real-time thermodynamic models require sophisticated methods to efficiently solve the model equations on a real-time basis with sufficient speed.

NLR has developed the ‘Turbine Engine Real-Time Simulator’ (TERTS) generic real-time engine simulation environment for full thermodynamic simulation of various gas turbine engine configurations. At NLR’s National Simulator Facility (NSF), research is performed on pilot-in-the-loop simulation of complex aircraft and helicopter configurations such as thrust-vectoring and Integrated Flight Propulsion Control (IFPC) concepts. For this application, high-fidelity real-time gas turbine models are required. TERTS has an efficient method for solving the engine model equations real-time. The system is implemented in Matlab-Simulink®, which offers advantages in terms of control system modeling flexibility. With TERTS, detailed thermodynamic real-time engine models can easily be implemented in NSF providing an excellent means to analyze a variety of engine effects on pilot-in-the-loop aircraft performance.

In this paper the TERTS modeling environment will be described including the numerical solutions used to comply with the real-time requirements. A TERTS model of a military afterburning turbofan will be presented including simulation results.
Disc-Type Airborne Vehicle and Radial Flow Gas Turbine Engine Used Therein
Authors: Heuvel Norman L.
Published: July 2014

An annular, radial flow gas turbine engine and airborne vehicle utilizing same for jet propulsion. The engine comprises counter-rotating rotors and a compressor section with counter-rotating annular rows of intermeshing compressor blades, an annular combustion section common to both rotors wherein the combustion zone is defined by oppositely rotating rotor walls, and a turbine section made up of annular rows of counter-rotating exhaust turbine blades. No stator blades are present in either the compressor or the turbine sections. The craft comprises a central hub on which the engine rotors rotate on thrust bearings, and speed-staged bearings maintain rotor tolerances with respect to each other and to nonrotating shell portions above and below the engine rotors. Air inlet guide vanes leading to the compressor section are also housed in the hub portion of the craft. Exhaust gases emitting from the turbine section are selectively ducted through the annularly arranged-downwardly directed lift thrust producing ducts and/ or rearwardly directed ducts or vanes for generation of forward propulsion. Directional control during hovering and low speed flight is by selective braking of one or the other of the rotors. and during high speed flight also by selective control of spoiler surfaces arranged in the upper and lower external surfaces of the craft.
Oxidation Behavior of Prospective Silicon Nitride Materials for Advanced Microturbine Applications
Authors: Schenk Bjoern , Strangman Tom , Opila Elizabeth J. , Robinson R. Craig , Fox Dennis S. , Klemm Hagen , Taut Christine , More Karren , Torterelli Peter
Published: July 2014

Various laboratory tests have shown that high-pressure water vapor environments combined with elevated temperatures and intermediate gas velocities (current facilities limited to about 50 m/s) can cause grain boundary degradation and material recession in silica formers. Recent tests include burner rig testing conducted by NASA [1], Honeywell Engines & Systems [2], Siemens Power Generation [3], CRIEPI in Japan [4, 5], “Keiser rig” testing at Oak Ridge National Laboratory (ORNL) [6], and engine testing in the Allison 501K industrial gas turbine [7]. This paper presents a summary of oxidation test data of candidate silicon nitride materials for advanced microturbine applications. These data are of interest to microturbine component designers in order to determine the limits of safe unprotected component operation with respect to the given turbine environment, as well as to understand the behavior of ceramic microturbine components once local spallation of the protective environmental barrier coating has occurred.

This paper intends to give materials and engine development engineers some guidance with respect to the different test facility capabilities and the prevailing oxidation/recession mechanisms to better understand/interprete the oxidation test results when developing new ceramic material compositions and environmental barrier coating systems.
Mechanical Behavior of Notched SiC/SiC Composites
Authors: Morscher Gregory N. , Gyekenyesi John Z. , Gyekenyesi Andrew L.
Published: July 2014

Gas turbine components such as combustor liners or turbine vanes are subject to regions of high stress-concentration, e.g. attachment to the frame or at cooling holes. Ceramic matrix composites (CMCs) are potential materials for high temperature applications in gas turbines. They offer some capability to relieve stress at regions of high stress-concentration via matrix damage accumulation. In this study notch sensitivity was examined for woven SiC fiber reinforced, melt-infiltrated SiC matrix composites with a BN interphase, utilizing either Hi-Nicalon™ fibers or the stiffer Sylramic® fibers. The double-edge notched tensile test approach was used for a wide range of notch sizes and specimen widths. Both composite systems exhibited mild notch sensitivity similar to other CMC systems. Acoustic emission, detected during the tensile tests, indicated that matrix cracking occurred around notches at net-section stresses below the stress where matrix cracking first occurs in unnotched specimens. However, thermoelastic stress analysis did not show any measurable stress relief around notches after the specimens were preloaded.
Probabilistic Residual Strength Model for Stress Rupture of SiC/SiC Composites
Authors: Thomas David J.
Published: July 2014

A probabilistic residual strength (PRS) model for the stress rupture behavior of composites is presented. The material’s initial ultimate strength, time-to-failure, and intermediate residual strength are all considered to be random variables. A Kachonov style rate equation is assumed to model the strength degradation. Data requirements for model calibration are outlined and the calibration process is presented. Model capabilities are demonstrated using experimental data for a SiC/SiC [0/90] 5-harness satin weave material system. The PRS model has the potential to generate design curves and aid in the development of design practices for use with brittle composite structures.
Developing Engineering Leadership Skills
Authors: Cloyd Scott T. , DiCavallucci Richard J.
Published: July 2014

The Engineering Development Program at Siemens Westinghouse Power Corporation was implemented to develop the leadership skills of highly talented college graduates. The benefits of this program for the participants and company are presented with descriptions of the rotational assignments and training classes.
Numerical and Experimental Investigations on Endwall Contouring in a Four-Stage Turbine
Authors: Bonn Dieter E. , Funke Harald , Sürken Norbert , Kreitmeier Franz
Published: July 2014

Secondary flows and leakage flows create complex vortex structures in the 3-D flow field of a turbine stage. Aerodynamic losses are the consequence. Reducing the aerodynamic losses by endwall contouring is subject of an actual investigation of the flow field in a 4-stage test turbine with repeating stages.

Numerical 4-stage simulations are performed for a reference case of a turbine without endwall modifications and two different geometric configurations with endwall contouring. The numerical results for the reference case are compared to corresponding experimental investigations. Both, the experiment and the CFD focus on the stage exit flow field of the second, the third and the fourth stage of the actual four stage turbine. The 3-D flow field is calculated by application of a steady 3-D Navier-Stokes code.

The numerical results of an arc-like endwall contouring at the casing are presented a) with a maximum deviation from the reference contour in the axial gap within the stages (“arc contour”) and b) with a maximum deviation in the axial gap between the stages (“off-set arc contour”). The results show a significant influence of the bumps on the blade’s profile pressure distribution near the radial gap, the leakage flow and the radial pressure field. A detailed secondary flow analysis shows the influence of the different endwall contours on the leakage vortex development.

Finally, the aerodynamic efficiencies of the geometric configurations are compared. It is predicted that the off-set arc contour has a remarkable positive influence on the machine’s performance.
Aerodynamic Tip Desensitization of an Axial Turbine Rotor Using Tip Platform Extensions
Authors: Dey Debashis , Camci Cengiz
Published: July 2014

Aerodynamic losses due to the formation of a leakage vortex near the tip section of rotor blades form a significant part of viscous losses in axial flow turbines. The leakage flow, mainly induced by the pressure differential between the pressure side and suction side of a rotor tip section, usually rolls into a streamwise vortical structure near the suction side part of the blade tip. The current study uses the concept of a tip platform extension that is a very short “winglet” obtained by slightly extending the tip platform in the tangential direction. The use of a pressure side tip extension can significantly affect the local aerodynamic field by weakening the leakage vortex structure. Phase averaged, time accurate total pressure measurements downstream of a single stage turbine facility are provided from a total pressure probe that has a time response of 150 kHz. Complete total pressure maps in all of the 29 rotor exit planes are measured accurately. Various pressure and suction side extension configurations are compared against a baseline case. The current investigation performed in the Axial Flow Turbine Research Facility (AFTRF) of the Pennsylvania State University shows that significant total to total efficiency gain is possible by the use of tip platform extensions.
Numerical Simulation of the 3D Viscous Flow in the Exhaust Casing of a Low-Pressure Steam Turbine
Authors: Xu X. , Kang S. , Hirsch Ch.
Published: July 2014

Numerical results of the 3D viscous flow in a downward exhaust casing of a low-pressure steam turbine, obtained with the 3D Navier-Stokes solver Fine/TURBO, is presented. Comprehensive comparisons of the computational results with the available experimental data, such as velocity, static and total pressure coefficients, are given. A good agreement with the experimental data is obtained. The computational results reveal a complex vortex system, including a passage vortex, a secondary vortex, an endwall vortex and a separation vortex, within the casing model. It is found that of all the vortices, most portion of energy losses within the casing is contributed from the passage vortex.
Investigation of Flow in a Steam Turbine Exhaust Hood With/Without Turbine Exit Conditions Simulated
Authors: Liu Jianjun , Cui Yongqiang , Jiang Hongde
Published: July 2014

Experimental and numerical investigations for the flow in an exhaust hood model of large steam turbines have been carried out in order to understand the complex 3D flow pattern existing in the hood and also to validate the CFD solver. The model is a typical design for 300/600 MW steam turbines currently in operation. Static pressure at the diffuser tip and hub endwalls and at hood outer casing is measured and nonuniform circumferential distributions of static pressure are noticed. Velocity field at the model exit is measured and compared with the numerical prediction. The multigrid multiblock 3D Navier-Stokes solver used for the simulations is based upon the TVD Lax-Wendroff scheme and the Baldwin-Lomax turbulence model. Good agreement between numerical results and experimental data is demonstrated. It is found that the flow pattern and hood performance are very different with or without the turbine exit flow conditions simulated.
Midspan Flow-Field Measurements for Two Transonic Linear Turbine Cascades at Off-Design Conditions
Authors: Jouini D. B. M. , Sjolander S. A. , Moustapha S. H.
Published: July 2014

The paper presents detailed mid-span experimental results from two transonic linear turbine cascades. The blades for the two cascades were designed for the same service and differ mainly in their leading-edge geometries. One of the goals of the study was investigate the influence of the leading-edge metal angle on the sensitivity of the blade to positive off-design incidence. Measurements were made for incidence values of −10.0°, 0.0°, +4.5°, +10.0°, and +14.5° relative to design incidence. The exit Mach numbers varied roughly from 0.5 to 1.2 and the Reynolds numbers from about 4×105 to 106. The measurements include the midspan losses, blade loadings and base pressures. In addition, the axial-velocity-density ratio (AVDR) was extracted for each operating point The AVDR was found to vary from about 0.98 at −10.0° of incidence to about 1.27 at +14.5°. Thus, the data set also provides some evidence of the influence AVDR on axial turbine blade performance.

Detailed experimental results for turbine blade performance at off-design incidence are very scarce in the open literature, particularly for transonic conditions. Among other things, the present results are intended to expand the database available in the open literature. To this end, the key aerodynamic results are presented in tabular form, along with the detailed geometry of the cascades. The results could be used in the development of new or improved correlations for use in the early stages of design. They could also be used to evaluate the ability of current CFD codes to capture reliably the variation in losses and other aerodynamic quantities with variations in blade incidence.
Development of H Series Gas Turbine
Authors: Maekawa A. , Uematsu K. , Ito E. , Ohya T. , Hirokawa K. , Fukuizumi Y.
Published: July 2014

Mitsubishi Heavy Industries, Ltd. developed the M501H gas turbine to improve the efficiency and power of G series using closed steam cooling of stage 1 and 2 blades and vanes following the firm’s experience in the construction of the D, F and G series. Development included elementary tests for pre-verification and trial operation using a combined plant verification plant to reach 220MW in May 1999 and to verify the stability of the steam cooling rotor, cooling properties of blades and vanes, and the efficiency of major components. The few remaining items can be easily taken care of.

The next operation is planned to complete verification.
Past, Present and Future of Combined Cycle Power Plants: From an A/E’s Perspective
Authors: Singh Anup
Published: July 2014

In the 1970s, power generation from gas turbines was minimal. Gas turbines in those days were run on fuel oil, since there was a so-called “natural gas shortage”. The U.S. Fuel Use Act of 1978 essentially disallowed the use of natural gas for power generation. Hence there was no incentive on the part of gas turbine manufacturers to invest in the development of gas turbine technology.

There were many regulatory developments in the 1980s and 1990s, which led to the rapid growth in power generation from gas turbines. These developments included Public Utility Regulatory Policy Act of 1978 (encouraging cogeneration), FERC Order 636 (deregulating natural gas industry), Energy Policy Act of 1992 (creating EWGs and IPPs) and FERC Order 888 (open access to electrical transmission system). There was also a backlash from excessive electric rates due to high capital recovery of nuclear and coal-fired plant costs caused by tremendous cost increase resulting from tightening NRC requirements for nuclear plants and significant SO2/NOx/other emissions controls required for coal-fired plants. During this period, rapid technology developments took place in the metallurgy, design, efficiency, and reliability of gas turbines. In addition, U.S. DOE contributed to these developments by encouraging research and development efforts in high temperature and high efficiency gas turbines.

Today we are seeing a tremendous explosion of power generating facilities by electric utilities and Independent Power Producers (IPPs). A few years ago, Merchant Power (generation without power purchase agreements) was unheard of. Today it is growing at a very fast pace. Can this rapid growth be sustained? The paper will explore the factors that will play a significant role in the future growth of gas turbine-based power generation in the U.S. The paper will also discuss the methods and developments that could decrease the capital costs of gas turbine power plants resulting in the lowest cost generation compared to other power generation technologies.
An Argument for Enhancement of the Current Inlet Distortion Ground Test Practice for Aircraft Gas Turbine Engines
Authors: Davis Milt , Hale Alan , Beale Dave
Published: July 2014

The current high-performance aircraft development programs, and the trends in research and development activities suggest a rapidly increasing level of aircraft subsystem integration, particularly between the airframe/inlet and the propulsion system. Traditionally these subsystems have been designed, analyzed, and tested as isolated systems. The interaction between the subsystems is modeled primarily through evaluating inlet distortion in an inlet test and simulating this distortion in engine tests via screens or similar devices. For the current test methodology, the environment that is supplied by the inlet is simulated by the imposition of total pressure profiles at the aerodynamic interface plane (AIP). Unsteady or transient variation in total pressure is generally not considered to be important. In addition, angular flow, commonly called swirl, is also not considered important enough to be simulated. In the current paper, an overview of current techniques for inlet performance, distortion characterization, and engine distortion testing is presented. A numerical study was conducted on a single high-speed rotor to qualify potential effects on stability and performance and to support the concept that dynamic distortion and swirl may have large enough effects to affect the experimentally determined stability limit. This paper reports a numerical investigation using a 3D compression system simulation that supports the enhancement of the existing methodology to include the effects of time-dependent distortion and swirl effects. Based upon both experimental and numerical evidence, AEDC has embarked on efforts to develop inlet simulator technologies directed toward future airframe-propulsion integration requirements. This paper presents issues that require advancements in the simulation of inlet distortion techniques for direct-connect turbine engine tests.
Computational Study of Clocking an Embedded Stage in a 4-Stage Industrial Turbine
Authors: Dorney D. J. , Croft R. R. , Sondak D. L. , Stang U. E. , Twardochleb C. Z.
Published: July 2014

Multi-stage turbines have inherently unsteady flow fields because of relative motion between rotating and stationary airfoil rows. This relative motion leads to viscous and inviscid interactions between blade rows. As the number of stages increases in a turbomachine, the buildup of convected wakes can lead to progressively more complex wake/wake and wake/airfoil interactions. Variations in the relative circumferential positions of airfoils in adjacent rotating or non-rotating blade rows can alter these interactions, leading to different time-averaged losses and stage efficiencies. In addition, interaction between blade rows can intensify with increasing Mach number due to potential effects.

It has been shown in previous studies, both experimental and computational, that airfoil clocking can be used to improve the efficiency and reduce the unsteadiness in multiple-stage axial turbomachines with equal blade counts. While previous investigations have for the most part focused on two-stage turbines, the goal of the current research is to evaluate the effects of clocking an embedded stage within a larger turbine system. Quasi-three-dimensional simulations of airfoil clocking have been performed for a four-stage industrial turbine. Time-averaged and unsteady data (including performance quantities) are presented. The results show a 0.5% efficiency variation in the stage where the vanes were clocked, and smaller efficiency variations in the upstream and downstream stages. The overall efficiency of the turbine system varies with the efficiency of the clocked stage, although by a smaller amount.
Liquid Phase Diffusion Bond Repair of Siemens V84.2, Row 2 Vanes and Alstom Tornado, 2nd Stage Stator Segments
Authors: Miglietti Warren M. , Kearney John , Pabon Luis
Published: July 2014

During the industrial turbine engine operation of the Siemens V84.2, Row 2 vanes, and the Alstom Tornado, 2nd stage stator segments, “craze-cracking” and isolated thermal fatigue cracks develop during engine operation. Other damages found include pitting and dents resulting from corrosion/erosion and FOD (foreign object damage), respectively. Erosion and oxidation damage is also commonly found on the airfoils. This paper describes the vacuum LPDB (liquid phase diffusion bond) repair process used to repair all of the above-mentioned damage.

As a means of qualifying the high temperature diffusion bond process, both metallurgical and mechanical property evaluations were carried out. The metallurgical evaluation consisted of optical and scanning electron microscopy. The wide gap diffusion bonded area consisted of a fine-grained structure with intermetallic phases dispersed both intergranularly and intragranularly. An Energy Dispersive X-ray analysis was also conducted and the results are reported.

The chemistry of the repaired area is similar to the base metal which may explain why mechanical tests revealed properties equivalent to that of the base metal. The mechanical evaluations undertaken were tensile tests at room temperature and elevated temperature, as well as stress rupture tests. These results were equivalent to mechanical properties of the IN738 and IN939 Ni-based superalloys, which is the base metal that the above mentioned vanes and stator segments are manufactured from.