bluuebunny/crossref_metadata_2025 huggingface dataset:
Health Monitoring of Turbine Engine Gas Path Components and Measurement Instruments
Authors: Lee Y. H. , Singh R.
Published: February 2015

A performance simulation program has been used to simulate deteriorated performance of a new augmented turbofan engine developed for fighter aircraft and generate a fault pattern library.

This fault pattern library forms a basis for both understanding degradation trends of engine usage and in developing an engine health monitoring system. An efficient health monitoring method is proposed to identify the engine faults along with measurement uncertainties and faulty instruments, and to reduce false alarms. A pattern matching method is used to discriminate the engine faults by matching the measurement patterns throughout the fault pattern library.

The comparison of this approach to conventional gas path analysis has demonstrated that this approach has comparable ability to monitor engine gas path performance degradation, and provides some capability to handle measurement uncertainties and faults. It also provides a good base for future capability in conjunction with other engine inspection and/or monitoring methods.
Propulsion System Considerations for Future Supersonic Transports: A Global Perspective
Authors: Mercure Robert A.
Published: February 2015

With research and technology (R&T) development activities for the next generation SuperSonic Transport (SST) being pursued globally over the past few years, the options to proposed airframe and engine concepts appears to be converging. The United States, the Europeans, and the Japanese are all engaged in developing the technologies needed for a future SST that is environmentally compatible and economically practical. Boeing and McDonnell Douglas are part of the team under an R&T contract with the National Aeronautics and Space Administration to develop critical components and enabling materials that will allow industry to make a production decision by 2003. Europe’s three main aircraft manufacturer’s — i.e., Aerospatiale, British Aero-space, and Deutsche Aerospace — comprise the European Supersonic Research Program (ESRP). A primary Japanese effort called the Hypersonic Transport Propulsion System Research (HYPR) project consists of a consortium of four international engine manufacturers and the National Japanese Laboratory. The manufacturers are: Ishikawajima-Harima Heavy Industries Co. Ltd., the Kawasaki Heavy Industries Co. Ltd., Mitsubishi Heavy Industries Co. Ltd., and General Electric Aircraft Engines Company, USA. A recent study by the Japan Aircraft Development Corporation (Reference 1) also addressed the technology requirements for the next generation SST.

There are basically three major challenges that must be met before a new SST can become a reality. They are the technical, environmental, and economic challenges. The technical challenges of the propulsion system primarily reduce the development of new materials capable of sustaining higher temperatures and vibration (high and low frequency) over longer exposure times as well as capable of being produced at reasonable costs. Low emission combustors and low exhaust jet noise are the primary environmental challenges, which are a technical challenge in themselves. The economic challenge is to produce an aircraft and propulsion system that allows the manufacturers to recover development and manufacturing costs as well as realize a reasonable Return-On-Investment (ROI). In addition, Life Cycle Costs (LCC) must not be substantially above future subsonic airliners in order to justify premium fares the public would be willing to pay for the time savings of long-distance flights and still be profitable to the airlines.
A Review of Recent Research on Contra-Rotating Axial Flow Compressor Stage
Authors: Sharma P. B. , Adekoya A.
Published: February 2015

Aero compressor technology has seen a significant advancement during the last two decades. Research on Rotor-Stator stage has focused on improvements in the design as well as off-design performance. Work has also been carried out to improve the clearance losses, stage loading as well as the stability of the operation. In this connection, the work on end-bend rotor-stator and variable geometry stators is specially significant. These efforts have however, yielded marginal improvements as far as the capability of the stage to produce pressure rise and its through-flow capacity are concerned. The interest in contra-rotation has emerged with a view to achieve considerable high pressure rise per stage besides its effects on stability of the stage to rotating stall/surge suppression. Contra-rotation concept has already found its acceptability in the development of future fuel efficient gas turbine plants and aero engines.

This paper presents a review of the experimental and theoretical investigations on the aero-dynamic and aero-acoustic performance of the contra-rotating pressure stage. The areas of future work on contra-rotation are also outlined.
Analytical Solution of Whirl Speed and Mode Shape for Rotating Shafts
Authors: Yang S. M. , Sheu G. J. , Yang C. D.
Published: February 2015

The analytical solution of whirl speed and mode shape of a rotating shaft in six boundary conditions is presented in this paper. The shaft is modelled by a Rayleigh beam with rotatory inertia and gyroscopic effects, and the boundary conditions are (1) short-short, (2) long-long, (3) long-free, (4) free-free, (5) long-short, and (6) short-free bearings. It is shown that the whirl speed can be written analytically by a function of the whirl ratio (λ) defined by the rotating speed over the whirl speed and the slenderness ratio (l) defined by the length of the shaft over its radius. The number of whirl speeds, contrary to common belief, is finite when λ > 1/2. For the first time, the rotating system’s unbalanced response can be written analytically in an exact form by a finite number of vibration modes with the corresponding generalized coordinates.
The Thermal-Mechanical Behavior of Selected Si3N4 and SiC Ceramics
Authors: Hecht Norman L. , Rho Hongsang , Osborne Nora R. , McCullum Dale E. , Goodrich Steven M.
Published: February 2015

This paper presents the results of a long term program initiated in December of 1984 to investigate the effects of environment (temperature, atmosphere, and stress) on the mechanical behavior of eight Si3N4 and three SiC ceramics being considered for heat engine applications. Microstructure, chemistry, and physical properties were determined. The mechanical behavior of these materials was investigated from room temperature to 1400°C by employing tests for flexural and tensile strength, dynamic, static and cyclic fatigue, and fracture toughness. The results obtained from these evaluations showed that the thermal mechanical behavior was quite varied, depending on the composition and processing methods employed. Batch to batch differences were also found to cause variances in the property values measured. Insights gained from this work about the failure mechanisms and potential service life are also discussed.
Superduplex Stainless Steel Use in Manufacturing Highly Sour Gas Centrifugal Compressors
Authors: Millet François , Friez Patrick , Franzi Angelo , Bonnefois Bernard , Lardon Jean-Marc
Published: February 2015

More and more often, oil fields need to handle wet sour gases which contain high proportions of carbon dioxide and hydrogen sulphide. Furthermore, the liquid phase contains water with chlorides. Therefore, pitting corrosion and stress corrosion cracking may occur. Centrifugal compressors used on oil fields for increasing the pressure levels, require components which must be resistant to be efficient, but nevertheless cheap for an industrial solution. A corrosion resistant material with high mechanical characteristics is necessary. Duplex stainless steels which have been widely developed and experimented on off-shore applications, are a good way to achieve this challenge. They must be solution annealed to withstand severe corrosion conditions. This paper deals with the metallurgical aspects and the major influence of heat treatments, and with the manufacturing process of two major components : the casing and the rotor. This new centrifugal compressor, designed for a highly sour gas service, with 87% of acid compoaents, is dedicated to a process of sulphur elimination from the flare gas for environmental protection reasons. It has been operating since the beginning of 1995 by GASCO in Abu Dhabi.
Optimum Operation and Maintenance of Gas Turbines Offshore
Authors: Bakken Lars E. , Skorping Roald
Published: February 2015

At present, offshore gas turbines are operated encouraging high thermal efficiency and low power consumption. High thermal efficiency normally demands operation close to full load, which may increase the emission of specific components.

The present emission tax on CO2 has a substantial impact on gas turbine operation and maintenance costs. At present, it is of great importance to include the influence of emission taxes by focusing on optimum energy operation and maintenance.

The influence of gas turbine degradation on operating costs is high. Analysis based on operational experience and field test performance data show an extra cost due to deterioration up to NOK 4.5 million a year. To obtain optimum energy operation and maintenance for the gas turbine drivers on Sleipner A, analysis and developments are based on:

• on-line condition monitoring, to detect machinery condition and component degradation

• prediction routines, to forecast degradation “development” as a function of time

• optimisation routines, to predict optimum intervention time based on operating and maintenance costs

• sensitivity analysis, including site performance correction to actual operating condition

The developed procedure has resulted in increased flexibility and availability, in addition to reduced operating and maintenance costs. Total potential savings are estimated up to NOK 2.5 mill. per gas turbine a year. The system forms an important tool in future operation of the 60 gas turbines in present service.
Dry Low NOx Combustion Systems Development and Operating Experience
Authors: Strand Torsten
Published: February 2015

It is shown that emissions are becoming significant performance parameters. Dry Low NOx combustion is favourably evaluated in terms of fuel consumption when compared to NOx abatement with water injection or SCR.

The conversion of two industrial gas turbines to Dry Low NOx (DLN) Combustion summarised.

Four years experience of commissioning and operation of a number of DLN gas turbines is described.

Emission levels around 25 ppmv NOx on gas has been achieved. Operation on natural gas is generally very reliable, but some initial problems were encountered.

Emission measurements and especially continuos emission monitoring have proved to be unreliable and caused a lot of trouble during the commissioning of some plants.
Surface Temperature Measurement of Thermal Barrier Coatings Using Infrared Pyrometry
Authors: Ruud James A. , Lillquist Robert D. , Gray Dennis M.
Published: February 2015

A method for measuring surface temperature of semitransparent materials was developed and used to measure temperature gradients through a yttria-stabilized zirconia thermal barrier coating (TBC) heated on the front surface with a natural gas flame. A Pt stripe was deposited on the TBC surface, and its temperature was measured using infrared pyrometry at 10.6 μm. A model was developed to determine the radiant intensity emitted from a TBC on a metal substrate with a thermal gradient. The radiant intensity from TBCs was measured as a function of thermal gradient and compared with results of the model.
Isothermal and Cyclic Oxidation of an Air Plasma-Sprayed Thermal Barrier Coating System
Authors: Haynes J. Allen , Ferber Mattison K. , Porter Wallace D. , Rigney E. Douglas
Published: February 2015

Thermogravimetric methods for evaluating bond coat oxidation in plasma-sprayed thermal barrier coating (TBC) systems were assessed by high-temperature testing of TBC systems with air plasma-sprayed (APS) Ni-22Cr-10Al-1Y bond coatings and yttria-stabilized zirconia top coatings. High-mass thermogravimetric analysis (at 1150°C) was used to measure bond coat oxidation kinetics. Furnace cycling was used to evaluate APS TBC durability. This paper describes the experimental methods and relative oxidation kinetics of the various specimen types. Characterization of the APS TBCs and their reaction products are discussed.
Development of Ceramic Turbine Rotors and Nozzles for the 100kW Automotive Ceramic Gas Turbine Program
Authors: Yamada Satoru , Watanabe Keiichiro , Masuda Massaki
Published: February 2015

NGK Insulators, Ltd. (NGK) fabricates ceramic turbine rotors and nozzle components for the Automotive Ceramic Gas Turbine development program (CGT program), conducted by the Petroleum Energy Center (PEC) of Japan. Both the rotor and nozzle components are made of silicon nitride. The turbine rotor is a radial type having a 127 mm tip diameter, and the segment type nozzle is formed integrally with either three or four vanes and shrouds. This paper discusses various processes of fabricating the ceramic components, dependence of the fabrication processes on dimensional accuracy, and the performance of each of the processes.
Evaluation of New Process Options for Co-Generation in the Sugar Industry
Authors: Gabra M. A. , Kjellström B. O.
Published: February 2015

Biomass fuelled combined cycle with gas turbine for co-generation, has the promise of being able to produce electricity at competitive cost. The sugar cane industries in the developing countries are targets for near term-applications of this technology.

Different options for increasing the electricity generation in the sugar mills by using more advanced steam process and combined cycle technology, using cane trash and bagasse as a fuel for has been analyzed. The TPC sugar mill in Tanzania was selected as a case study for investigation. Introduction of a combined gas turbine/steam turbine process will make it possible to increase the electricity output from 2.5 MW to 30 MW at this plant during milling season. By using cane trash as fuel during the off-season period, the electricity generation can be increased by a factor of 20 compared to what is generated at TPC sugar factory today.

The financial evaluation indicated that the annual profit would range from US$ 3.5 million for the advanced steam process with 6.5 years pay-back time, to be US$ 4.7 million for the combined gas turbine/steam turbine process with 6.8 years pay-back time.
A Simultaneous Solution Method Based on a Modular Approach for Power Plant Analyses and Optimized Designs and Operations
Authors: Cerri Giovanni
Published: February 2015

A general method capable to solve optimization power plant problems simultaneously with the solution of equations describing the plant behavior is discussed.

The method has been implemented into CGSPO code whose main features as the plant modular structure and its automatic assembling are described.

Procedures foreseen in the code are: cycle calculations, sizing of components and off-design analysis. Examples showing the capabilities and the flexibility of the method are given.

The code is suitable for the analysis of plant including commercially available machines whose modifications to match with other components may be investigated.
Numerical Investigation of the Unsteady Transonic 3D-Flow in Stator and Rotor Cascades With Oscillating Blades
Authors: Peitsch Dieter , Gallus Heinz E. , Weber Stefan
Published: February 2015

Subject of this paper is a numerical method for the simulation of flutter in three dimensional oscillating cascades. Unsteadiness can be caused by bending and torsional oscillation modes simultaneously. The goal of the investigation is the evaluation of the resulting blade forces and moments. The flow is assumed to be time-dependent and inviscid. By solving the Euler equations in a nonlinear way, large oscillations as well of the airfoil as of existing shocks can be treated.

The numerical solution follows a Godunov-type upwind scheme, formulated in node centered finite volume technique. An approximative Riemann solver proposed by Roe is used to determine the fluxes over the surfaces of the control volume. Since unphysical expansion shocks have to be suppressed, a modification of the transonic characteristic speeds is included. The extrapolation of the flow values onto the control volumes’ surfaces is done by means of the MUSCL technique, embedded in a TVD-scheme with the flux limiter by van Albada. The computational domain is restricted to only one channel and the periodic values are stored over one period of oscillation. A special technique is introduced, which reduces both the effort in CPU-time and in computer memory. Results are included for compressor and turbine geometries in sub- and transonic flow.
CFD Based Sensitivity Study of Flow Parameters for Engine Like Film Cooling Conditions
Authors: Baldauf Stefan , Scheurlen Michael
Published: February 2015

A standard CFD code with two-layer k-ε-model was used to calculate film cooling effectiveness of flat plate test cases. Experimental data from the literature were taken to perform extensive validation of the code for film cooling effectiveness prediction. Emphasis was put on injection of cooling gas through one row of cylindrical holes in the streamwise direction. Blowing ratio, density ratio, blowing angle, pitch, and hole length to diameter ratio were varied in a wide range. It was found that the code is well suited for the prediction of lateral averaged film cooling effectiveness for common film cooling conditions. A similarity analysis is presented for the prescribed film cooling problem to isolate the influence parameters of flow properties and geometry. A reduction of the parameters of influence was achieved using physical implications. The magnitude of the remaining parameters was compared for literature reported experimental results and gas turbine applications. It was found that experimental realized Reynolds and Eckert numbers are mostly far from turbine engine conditions. Therefore the validated CFD code was used to extrapolate the experimental configuration to engine like conditions. It was found that the examined Reynolds and Eckert numbers had no significant impact on lateral averaged film cooling effectiveness. It is hence possible to present a reduced but complete set of the governing influence parameters on the discussed film cooling problem.
Development of the Sequential Combustion System for the ABB GT24/GT26 Gas Turbine Family
Authors: Joos Franz , Brunner Philipp , Schulte-Werning Burkhard , Syed Khawar , Eroglu Adnan
Published: February 2015

The 60Hz, 165MW gas turbine GT24 and the 50Hz, 240MW gas turbine GT26 are the first two members of ABB’s Sequential Combustion System gas turbine family. These turbines are designed to offer increased output at up to 4% efficiency advantage over today’s engines. Whereas the first combustor is based on the proven EV-combustor technology, an extensive research and development program has been carried out in developing the lean premixed, self-igniting second combustor.

This paper reports the basic research work concerning the lean premixing burners with self-ignition. The development of the burner and the combustor was based on wind tunnel and water channel experiments, CFD-calculations and combustion tests at atmospheric and high pressure.

Moreover an innovative cooling technology was developed to fullfill all conditions of the self-igniting premix combustor requiring minimal cooling air consumption. Special attention was paid both to a low sensitivity of the cooling effectiveness to variations of the imposed boundary conditions and to a robust hardware construction.

Tests of real engine parts at real engine conditions will be demonstrated in detail. Finally the paper demonstrates the potential of the sequential combustion system to reach single digit NOx levels by unveiling the results of the extensive testing program.
Experimental Assessment of the Emissions Benefits of a Ceramic Gas Turbine Combustor
Authors: Smith K. O. , Fahme A.
Published: February 2015

Three subscale, cylindrical combustors were rig tested on natural gas at typical industrial gas turbine operating conditions. The intent of the testing was to determine the effect of combustor liner cooling on NOx and CO emissions.

In order of decreasing liner cooling, a metal louvre-cooled combustor, a metal effusion-cooled combustor, and a backside-cooled ceramic (CFCC) combustor were evaluated. The three combustors were tested using the same lean-premixed fuel injector.

Testing showed that reduced liner cooling produced lower CO emissions as reaction quenching near the liner wall was reduced. A reduction in CO emissions allows a reoptimization of the combustor air flow distribution to yield lower NOx emissions.
International Standardization Activities for Fine Ceramics: Status of ISO/TC 206 on Fine Ceramics
Authors: Kanno Takashi
Published: February 2015

In response to a proposal of “Early-Stage Standardization” by the ISO/IEC Presidents’ Advisory Board on Technological Trends, the Technical Committee ISO/TC 206 on Fine Ceramics was established in 1992. The scope of ISO/TC 206 is a standardization in the field of fine ceramic materials and products in all forms: powders, monoliths, coatings and composites, intended for specific functional applications including mechanical, thermal, chemical, electrical, magnetic, optical and combinations thereof. The term “fine ceramics” is defined as “a highly engineered, high performance, predominantly nonmetallic, inorganic material having specific functional attributes”. A summary overview is given of membership, organization structure, work program and future work of ISO/TC 206.
The Offshore Application of a Dual-Mode Injection Centrifugal Compressor and Improvements to Rotating Stall
Authors: Lynghjem Arne , Svendsen Ove , Underbakke Harald
Published: February 2015

This paper covers the experience from the retrofit of a new dual-mode injection compressor into the existing gas compression facilities on an offshore platform. The implementation of this new and innovative compressor technology made it possible to fulfil new requirements to higher throughput, different kind of service, improved safety level and economical operation.

But then the compressor exhibited gas dynamic instability — determined as rotating stall in the impeller — a phenomenon not well understood. The literature on this topic is scare. The rotating stall phenomenon caused a significant reduction in useful operational area of the compressor. An improvement program was carried out. Changes in the impeller geometry led to restoration of the expected operational range. The magnitude of the phenomenon has diminished partially also. Rotating stall criteria proved to be useful in order to improve or avoid rotating stall problems in a centrifugal compressor.

The dual-mode injection compressor allowed decommissioning of a whole equipment module, which represents a very useful experience factor in the design of new offshore platforms. The compressor has been in operation since November 1994, and it has been able to fulfil all specified operating requirements.
Using an Auxiliary Power Unit (APU) Gas Turbine Engine to Start the LSD-41 Class Diesel Engines
Authors: Patterson Jeffrey S.
Published: February 2015

The LSD-41 Whidbey Island Class of Amphibious dock landing ships are powered by two Colt-Pielstick PC2.5V Block 16 cylinder Main Propulsion Diesel engines. These engines represent the largest diesels in the U.S. Navy. Currently, they are started without the use of a mechanical starter, by injecting 100 cfm [47.2 LPs] of 3,000 psig [206.9 barr] high pressure air, reduced to 425 psig [29.3 barr] directly into one block of eight engine cylinders. Naval Surface Warfare Center, Carderock Division (NSWCCD) was tasked to perform a proof of concept test that would demonstrate the capability of an Auxiliary Power Unit (APU) gas turbine engine to start these large, medium speed diesel engines.

This paper will present the background, installation and initial testing for this proof of concept test. The background section will discuss the test philosophy, the LSD-41 Land Based Engineering Site (LBES) and initial prototype testing. The installation section will discuss the modifications made to the LBES for this test and the characteristics and specifications of the test hardware. The testing section will discuss the test plan and the test procedures.

This paper will not present any results or data analysis from this proof of concept test. Test site availability and equipment procurement delays postponed the start of this test until March, 1996. Therefore, the test results will be discussed at the upcoming Turbo Exposition conference.
Dynamic Modeling of Single-Shaft Industrial Gas Turbine
Authors: Bettocchi R. , Spina P. R. , Fabbri F.
Published: February 2015

In the paper the dynamic non-linear model of single shaft industrial gas turbine was developed as the first stage of a methodology aimed at the diagnosis of measurement and control sensors and gas turbine operating conditions.

The model was calibrated by means of reference steady-state condition data of a real industrial gas turbine and was used to simulate various machine transients.

The model is modular in structure and was carried out in simplified form, but not so as to compromise its accuracy, to reduce the calculation time and thus make it more suitable for on-line simulation.

The comparison between values of working parameters obtained by the simulations and measurements during some transients on the gas turbine in operation provided encouraging results.
A Modal Coupling for Fluid and Structure Analyses of Turbomachine Flutter: Application to a Fan Stage
Authors: Moyroud Francois , Jacquet-Richardet Georges , Fransson Torsten
Published: February 2015

The paper presents an approach for the modal aeroelastic analysis of three-dimensional turbomachinery bladings with several fluid and structure analyzers. Structure analyzers are three-dimensional solvers for static and dynamic analyses of axisymmetric/cyclic-symmetric blade-shroud-disk-shaft assemblies with/without elastic coupling between blades. Fluid analyzers are two-dimensional/three-dimensional solvers for single/multi-stage steady/unsteady turbomachinery flows. An automatic interfacing procedure for exchanging data at the incompatible fluid-structure boundary and the development of a multi-model interfacing software are discussed. The modal aeroelastic analysis of a first stage shrouded fan is carried out to illustrate the main issues of the paper. In particular, two structural models for the elastic coupling of the part-span shrouds are discussed. The results show the strong dependence of the structure dynamics and aeroelastic analysis on this modelling.
Experimental Determination of the Influence of Foreign Particle Ingestion on the Behavior of Hot-Section Components Including Lamilloy®
Authors: Weaver Matthew M. , Dunn Michael G. , Heffernan Tab
Published: February 2015

The effect of foreign particle ingestion on hot-section components has been investigated with a series of experiments performed using a one-quarter sector F100-PW-100 annular combustor. The combustor was operated so that the engine corrected conditions were duplicated. The experiments were designed to determine the influence of cooling hole size, hole roughness (laser-drilled vs. EDM), combustor exit temperature and dust concentration on the cooling capability of the component in the presence of dust particles. Cylindrical Lamilloy® specimens, film cooled Inconel cylinders, and F100-PW-220 first stage turbine vanes were investigated. The size distribution of the foreign particles injected into the air stream just upstream of the combustor was consistent with distributions measured at the exit of high compressors for large turbofan engines. The foreign material was a soil composition representative of materials found around the world. Pre- and post-test bench flow measurements suggested that none of the test specimen’s cooling passages or holes were clogged by the foreign particles. Foreign particle deposition on the specimens was experienced with approximate values for the minimum combustor exit temperature and minimum specimen wall temperature for deposition measured.
A Technique to Achieve Uniform Stress Distribution in Compressive Creep Testing of Advanced Ceramics at High Temperatures
Authors: Liu Kenneth C. , Stevens Christopher O. , Brinkman Charles R. , Holshauser Nicholas E.
Published: February 2015

A technique to achieve stable and uniform uniaxial compression is offered for creep testing of advanced ceramic materials at elevated temperatures, using an innovative self-aligning load-train assembly. Excellent load-train alignment is attributed to the inherent ability of a unique hydraulic universal coupler to maintain self-aligning. Details of key elements, design concept, and principles of operation of the self-aligning coupler are described. A method of alignment verification using a strain-gaged specimen is then discussed. Results of verification tests indicate that bending below 1.5% is routinely achievable with the use of the load-train system. A successful compression creep test is demonstrated using a dumb-bell shaped silicon nitride specimen tested at 1300°C for a period in excess of 4000 h.
Wavelet Analysis for Gas Turbine Fault Diagnostics
Authors: Aretakis N. , Mathioudakis K.
Published: February 2015

The application of wavelet analysis to diagnosing faults in Gas Turbines is examined in the present paper. Applying the Wavelet Transform to time signals obtained from sensors placed on an engine, gives information which is in correspondence to their Fourier Transform. Diagnostic techniques based on Fourier analysis of signals can therefore be transposed to the Wavelet analysis. In the paper the basic properties of wavelets, in relation to the nature of turbomachinery signals, are discussed. The possibilities for extracting diagnostic information by means of wavelets are examined, by studying the applicability to existing data from vibration, unsteady pressure and acoustic measurements. Advantages offered, with respect to existing methods based on harmonic analysis, are discussed as well as particular requirements related to practical application.
Aerodynamically Induced Radial Forces in a Centrifugal Gas Compressor: Part 2 — Computational Investigation
Authors: Flathers Michael B. , Bache George E.
Published: February 2015

Radial loads and direction of a centrifugal gas compressor containing a high specific speed mixed flow impeller and a single tongue volute, were determined both experimentally and computationally at both design and off-design conditions. The experimental methodology was developed in conjunction with a traditional ASME PTC-10 closed-loop test to determine radial load and direction. The experimental study is detailed in Part 1 of this paper (Moore and Flathers, 1996). The computational method employs a commercially available, fully-3D viscous code to analyze the impeller and the volute interaction. An uncoupled scheme was initially used where the impeller and volute were analyzed as separate models using a common vaneless diffuser geometry. The two calculations were then repeated until the boundary conditions at a chosen location in the common vaneless diffuser were nearly the same. Subsequently, a coupled scheme was used where the entire stage geometry was analyzed in one calculation, thus eliminating the need for manual iteration of the two independent calculations. In addition to radial load and direction information, this computational procedure also provided aerodynamic stage performance. The effect of impeller front face and rear face cavities was also quantified. The paper will discuss computational procedures, including grid generation and boundary conditions, as well as comparisons of the various computational schemes to experiment. The results of this study will show the limitations and benefits of Computational Fluid Dynamics (CFD) for determination of radial load, direction, and aerodynamic stage performance.
Development of Blade Profiles for Low Pressure Turbine Applications
Authors: Curtis E. M. , Hodson H. P. , Banieghbal M. R. , Denton J. D. , Howell R. J. , Harvey N. W.
Published: February 2015

This paper describes a programme of work, largely experimental, which was undertaken with the objective of developing an improved blade profile for the low-pressure turbine in aero-engine applications.

Preliminary experiments were conducted using a novel technique. An existing cascade of datum blades was modified to enable the pressure distribution on the suction surface of one of the blades to be altered. Various means, such as shaped inserts, an adjustable flap at the trailing edge, and changing stagger were employed to change the geometry of the passage. These experiments provided boundary layer and lift data for a wide range of suction surface pressure distributions. The data was then used as a guide for the development of new blade profiles. The new blade profiles were then investigated in a low-speed cascade that included a set of moving bars upstream of the cascade of blades 10 simulate the effect of the incoming wakes from the previous blade row in a multistage turbine environment.

Results are presented for two improved profiles that are compared with a datum representative of current practice. The experimental results include loss measurements by wake traverse, surface pressure distributions, and boundary layer measurements. The cascades were operated over a Reynolds Number range from 0.7 × 105 to 4.0 × 105. The first profile is a “laminar flow” design that was intended to improve the efficiency at the same loading as the datum. The other is a more highly loaded blade profile intended to permit a reduction in blade numbers. The more highly loaded profile is the most promising candidate for inclusion in future designs. It enables blade numbers to be reduced by 20%, without incurring any efficiency penalty. The results also indicate that unsteady effects must be taken into consideration when selecting a blade profile for the low-pressure turbine.
Rotordynamic Forces due to Turbine Tip Leakage: Part II — Radius Scale Effects and Experimental Verification
Authors: Song Seung Jin , Martinez-Sanchez Manual
Published: February 2015

This paper presents a radius scale actuator disc model which describes the flow response to a whirling/spinning rotor in an unshrouded turbine. At each azimuth, the upstream-downstream flow variables are matched by the results from a steady blade scale analysis presented in a companion paper, with allowance for mass storage in the stator-rotor Pregion. The new model can accurately predict the magnitude of both direct and cross excitation forces as well as their breakdown into work extraction and pressure effects. The trends versus the mean flow coefficient and interblade distance are predicted. While underpredicted, a trend versus mean rotor tip clearance height is also indicated. Thus, the new model captures the dominant physical effects caused by a whirling/spinning rotor in an unshrouded turbine.
Ceramic Gas Turbine Technology Development
Authors: Easley M. L. , Smyth J. R.
Published: February 2015

Under the U.S. Department Of Energy/National Aeronautics and Space Administration (DOE/NASA) funded Ceramic Turbine Engine Demonstration Program, AlliedSignal Engines is addressing the remaining critical concerns slowing the commercialization of structural ceramics in gas turbine engines. These issues include demonstration of ceramic component reliability, readiness of ceramic suppliers to support ceramic production needs, and enhancement of ceramic design methodologies.

The AlliedSignal/Garrett Model 331-200[CT] Auxiliary Power Unit (APU) is being used as a ceramics test bed engine. For this program, the APU First-stage turbine blades and nozzles were redesigned using ceramic materials, employing the design methods developed during the earlier DOE/NASA funded Advanced Gas Turbine (AGT) and Advanced Turbine Technologies Application Project (ATTAP) programs. The present program includes ceramic component design, fabrication, and testing, including component bench tests and extended engine endurance testing and field testing. These activities will demonstrate commercial viability of the ceramic turbine application. In addition, manufacturing process scaleup for ceramic components to the minimum level for commercial viability will be demonstrated.

Significant progress has been made during the past year. Engine testing evaluating performance with ceramic turbine nozzles has accumulated over 910 hours operation. Ceramic blade component tests were performed to evaluate the effectiveness of vibration dampers and high-temperature strain gages, and ceramic blade strength and impact resistance. Component design technologies produced impact-resistance design guidelines for inserted ceramic axial blades, and advanced the application of thin-film thermocouples and strain gages on ceramic components. Ceramic manufacturing scaleup activities were conducted by two ceramics vendors, Norton Advanced Ceramics (East Granby, CT) and AlliedSignal Ceramic Components (Torrance, CA). Following the decision of Norton Advanced Ceramics to leave the program, a subcontract was initiated with the Kyocera Industrial Ceramics Company Advanced Ceramics Technology Center (Vancouver, WA). The manufacturing scaleup program emphasizes improvement of process yields and increased production rates.

Work summarized in this paper was funded by the U.S. Dept. Of Energy (DOE) Office of Transportation Technologies, part of the Turbine Engine Technologies Program, and administered by the NASA Lewis Research Center, Cleveland, OH under Contract No. DEN3-335.
Stall Precursor Identification in High Speed Compressor Stages Using Chaotic Time Series Analysis Methods
Authors: Bright Michelle M. , Qammar Helen K. , Weigl Harald J. , Paduano James D.
Published: February 2015

This paper presents a new technique for precursor identification in high speed compressors. The technique is a pseudo-correlation integral method referred to as the correlation method. To provide a basis for comparison, the traveling wave energy technique, which has been used extensively to study pre-stall data, is also briefly presented and applied. The correlation method has a potential advantage over the traveling wave energy method because it uses a single sensor for detection. It also requires no predisposition about the expected behavior of the data to detect “changes” in the behavior of the compressor. Both methods are used in this study to identify stall procursive events in the pressure fluctuations measured from circumferential pressure transducers located at the front face of the compressor rig. The correlation method successfully identified stall formation or changes in the compressor dynamics from data captured from four different configurations of a NASA Lewis single stage high speed compressor while it was transitioned from stable operation into stall. This paper includes an exposition on the use of nonlinear methods to identify stall precursors, a description of the methodologies used for the study, information on the NASA high speed compressor rig and experimental data acquisition, and results from the four compressor configurations. The experimental results indicate that the correlation method provides ample warning of the onset of rotating stall at high speed, in some tests on the order of 2000 rotor revolutions. Complementary features of the correlation method and the traveling wave energy method are discussed, and suggestions for future developments are made.
Evaluation of Flow Field Approximations for Transonic Compressor Stages
Authors: Dorney Daniel J. , Sharma Om P.
Published: February 2015

The flow through gas-turbine compressors is often characterized by unsteady, transonic and viscous phenomena. Accurately predicting the behavior of these complex multi-blade-row flows with unsteady rotor-stator interacting Navier-Stokes analyses can require enormous computer resources. In this investigation, several methods for predicting the flow field, losses and performance quantities associated with axial compressor stages are presented. The methods studied include, 1) the unsteady fully-coupled blade row technique, 2) the steady coupled blade row method, 3) the steady single blade row technique, and 4) the loosely-coupled blade row method. The analyses have been evaluated in terms of accuracy and efficiency.
The Effect of Misalignment on Rotor Vibrations
Authors: Nikolajsen Jorgen L.
Published: February 2015

Rotors with three or more fluid-film bearings (or fluid seals) have ‘redundant’ supports, and therefore interdependent bearing loads which are generally unknown both in magnitude and direction. The steady-state bearing eccentricities and the dynamic stiffness and damping coefficients of the bearings are therefore also unknown, since both are functions of the bearing loads. Thus, the dynamic behaviour of multi-bearing rotors generally cannot be predicted with good accuracy without access to a procedure for calculating the steady-state bearing loads and eccentricities. This paper outlines such a procedure in terms of both the influence coefficient method, the transfer matrix method, and the finite element method. Radial bearing misalignment and flexibility of the bearing back-up structures are accounted for. Once the eccentricities are available, the bearing stiffness and damping coefficients can be calculated in the usual way and used to predict critical speeds, instability threshold speed and rotor response to imbalance. A numerical example is presented which illustrates some of the non-linear effects of bearing support redundancy, notably the large variations in instability threshold speed with radial bearing misalignment. The example shows how the method can be used to determine the level of bearing misalignment which leads to optimum rotor stability. It is concluded that no simple guide lines exist by which optimum stability can be achieved. Neither perfect bearing alignment nor equal load sharing between bearings necessarily lead to optimum stability.
Unsteady Flow in Oscillating Turbine Cascade: Part 1 — Linear Cascade Experiment
Authors: He L.
Published: February 2015

An experimental and computational study has been carried out on a linear cascade of low pressure turbine blades with the middle blade oscillating in a torsion mode. The main objectives of the present work were to enhance understanding of the behaviour of bubble type of flow separation and to examine the predictive ability of a computational method. In addition, an attempt was made to address a general modelling issue: was the linear assumption adequately valid for such kind of flow?

In Part 1 of this paper, the experimental work was described. Unsteady pressure was measured along blade surfaces using off-board mounted pressure transducers at realistic reduced frequency conditions. A short separation bubble on the suction surface near the trailing edge and a long leading-edge separation bubble on the pressure surface were identified. It was found that in the regions of separation bubbles, unsteady pressure was largely influenced by the movement of reattachment point, featured by an abrupt phase shift and an amplitude trough in the 1st harmonic distribution. The short bubble on the suction surface seemed to follow closely a laminar bubble transition model in a quasi-steady manner, and had a localized effect. The leading-edge long bubble on the pressure surface, on the other hand, was featured by a large movement of the reattachment point, which affected the surface unsteady pressure distribution substantially. As far as the aerodynamic damping was concerned, there was a destabilizing effect in the separated flow region, which was however largely balanced by the stabilizing effect downstream of the reattachment point due to the abrupt phase change.
Unsteady Flow in Oscillating Turbine Cascade: Part 2 — Computational Study
Authors: He L.
Published: February 2015

Unsteady flow around a linear oscillating turbine cascade has been experimentally and computationally studied, aimed at understanding the bubble type of flow separation and examining the predictive ability of a computational method. It was also intended to check the validity of the linear assumption under an unsteady viscous flow condition.

Part 2 of the paper presents a computational study of the experimental turbine cascade as discussed in Part 1. Numerical calculations were carried out for this case using an unsteady Navier-Stokes solver. The Baldwin-Lomax mixing length model was adopted for turbulence closure. The boundary layers on blade surfaces were either assumed to be fully turbulent or transitional with the unsteady transition subject to a quasi-steady laminar separation bubble model. The comparison between the computations and the experiment were generally quite satisfactory, except in the regions with the flow separation. It was shown that the behaviour of the short-bubble on the suction surface could be reasonably accounted for by using the quasi-steady bubble transition model. The calculation also showed that there was a more apparent mesh dependence of the results in the regions of flow separation.

Two different kinds of numerical tests were carried out to check the linearity of the unsteady flow and therefore the validity of the Influence Coefficient method. Firstly calculations using the same configurations as in the experiment were performed with different oscillating amplitudes. Secondly calculations were performed with a tuned cascade model and the results were compared with those using the Influence Coefficient method. The present work showed that nonlinear effect was quite small, even though for the most severe case in which the separated flow region covered about 60% of blade pressure surface with a large movement of the reattachment point. It seemed to suggest that the linear assumption about the unsteady flow behaviour should be adequately acceptable for situations with bubble type flow separation similar to the present case.
Inlet Distortion Generated Forced Response of a Low Aspect Ratio Transonic Fan
Authors: Manwaring Steven R. , Rabe Douglas C. , Lorence Christopher B. , Wadia Aspi R.
Published: February 2015

This paper describes a portion of an experimental and computational program (ADLARF) which incorporates, for the first time, measurements of all aspects of the forced response of an airfoil row, i.e., the flow defect, the unsteady pressure loadings and the vibratory response. The purpose of this portion was to extend the knowledge of the unsteady aerodynamics associated with a low aspect ratio transonic fan where the flow defects were generated by inlet distortions. Measurements of screen distortion patterns were obtained with total pressure rakes and casing static pressures. The unsteady pressure loadings on the blade were determined from high response pressure transducers. The resulting blade vibrations were measured with strain gages. The steady flow was analyzed using a 3D Navier–Stokes solver while the unsteady flow was determined with a quasi–3D linearized Euler solver.

Experimental results showed that the distortions had strong vortical, moderate entropic and weak acoustic parts. The 3D Navier–Stokes analyses showed that the steady flow is predominantly two–dimensional, with radially outward flow existing only in the blade surface boundary layers downstream of shocks and in the aft part of the suction surface. At near resonance conditions, the strain gage data showed blade–to–blade motion variations and thus, linearized unsteady Euler solutions showed poorer agreement with the unsteady loading data than comparisons at off–resonance speeds. Data analysis showed that entropic waves generated unsteady loadings comparable to vortical waves in the blade regions where shocks existed.