bluuebunny/crossref_metadata_2025 huggingface dataset:
The NEREUS Installation — The Nuclear Part (HTR)
Authors: Crommelin Gulian A. K.
Published: December 2014

The paper highlights on-going studies and design efforts by a team of several specialists in aspects related to a type of power generation installation, which consists of a directly coupled closed-cycle gas turbines (the Light Water Reactors have a double loupe energy transfer system coupled by a heat exchanger) to an inherently safe nuclear heat source. In particular the NEREUS installation will be discussed. NEREUS is the God for shipping in Greek mythology, but in this case it stands for: a Naturally safe, Efficient, Reactor, Easy to operate, Ultimately simple and Small. This describes very well the aims of the design team. This part will explain the inherently safe character of the nuclear heat source, the way the energy production in the heat source is controlled, the type of nuclear fuel and the treatment of the nuclear waste, the refuelling, the weight, the dimensions and the construction of the nuclear part of the NEREUS installation.

Part two will describe the non-nuclear part of the installation, the possible applications, its potential markets and the technical and financial indications from the on-going study.

This paper should be read in conjunction with the paper “The NEREUS installation — the Non-Nuclear part (GT)”.
Effects of Periodic Wake Passing Upon Aerodynamic Loss of a Turbine Cascade: Part I — Measurements of Wake-Affected Cascade Loss by Use of a Pneumatic Probe
Authors: Funazaki Ken-ichi , Tetsuka Nobuaki , Tanuma Tadashi
Published: December 2014

This paper reports on an experimental investigation of aerodynamic loss of a low-speed linear turbine cascade which is subjected to periodic wakes shed from moving bars of the wake generator. In this case, parameters related to the wake, such as wake passing frequency (wake Strouhal number) or wake turbulence characteristics, are varied to see how these wake-related parameters affect the local loss distribution or mass-averaged loss coefficient of the turbine cascade. Free-stream turbulence intensity is changed by use of a turbulence grid. In Part I of this paper a focus is placed on the measurements by use of a pneumatic five-hole yawmeter, which provides time-averaged stagnation pressure distributions downstream of the moving bars as well as of the turbine cascade. Spanwise distributions of wake-affected exit flow angle are also measured. From this study it is found that the wake passing greatly affects not only the profile loss but secondary loss of the linear cascade. Noticeable change in exit flow angle is also identified.
Development of Advanced Compressor Airfoils for Heavy-Duty Gas Turbines: Part I — Design and Optimization
Authors: Köller Ulf , Mönig Reinhard , Küsters Bernhard , Schreiber Heinz-Adolf
Published: December 2014

A new family of subsonic compressor airfoils, which are characterized by low losses and wide operating ranges, has been designed for use in heavy-duty gas turbines. In particular the influence of the higher airfoil Reynolds numbers compared to aeroengine compressors and the impact of these differences on the location of transition are taken into account. The design process itself is carried out by the combination of a geometrical code for the airfoil description, with a blade-to-blade solver and a numerical optimization algorithm. The optimization process includes the design-point losses for a specified Q3D flow problem and the off-design performance for the entire operating range. The family covers a wide range of inlet flow angle, Mach number, flow turning, blade thickness, solidity and AVDR in order to consider the entire range of flow conditions which occur in practical compressor design. The superior performance of the new airfoil family is demonstrated by a comparison with conventional controlled diffusion airfoils (CDA). The advantage in performance has been confirmed by detailed experimental investigations, which will be presented in Part II of the paper. This leads to the conclusion that CDA airfoils which have been primarily developed for aero engine applications are not the optimum solution, if directly transferred to heavy-duty gas turbines. A significant improvement in compressor efficiency is possible, if the new profiles are used instead of conventional airfoils.
Time-Resolved Numerical Analysis of the 2-D Aerodynamics in the First Stage of an Industrial Gas Turbine for Different Vane-Blade Spacings
Authors: von Hoyningen-Huene Martin , Hermeler Jürgen
Published: December 2014

A numerical 2D study of the unsteady flow in the first stage of an industrial axial flow gas turbine is presented. The study focuses on the influence of the axial spacing between stator and rotor on the unsteady flow field and relevant design parameters. For six different axial spacings between 18.5 % and 60 % of rotor chord length, time-averaged and time-resolved results are presented, focusing mainly on the pressure distribution on the rotor, stage efficiency and flow angle variation.

The instantaneous pressure and entropy contours at midspan are presented for different rotor positions. The underlying physical principles are described making a clear distinction between the impact of the potential flow interaction and the wake-blade interaction. The pressure fluctuations over the stator and rotor blades and the seal air injection gap as well as the effects of axial spacing are investigated. The major focus of this paper is to examine the variation of stage efficiency and rotor incidence angle with a changing axial gap.

A simple design rule is derived in order to optimize the vane-blade spacing and it is shown that the gap chosen for the real life machine offers a good compromise between the opposing design requirements.
High Temperature Thermal Stability of JP-8+100 and Other Fuels
Authors: Binns Kenneth E. , Dieterle Gordon L.
Published: December 2014

An engine trend toward maximum use of fuel as a heat sink has created interest in thermal stability information on aviation fuels for high temperature applications. Testing of the fuels has been conducted in the Extended Duration Thermal Stability Test System. This system was established for evaluating the thermal stability of JP-8+100 fuel. The specific fuels evaluated were JP-8, JP-8+100, JPTS and JP-7. The testing has been conducted at temperature and residence times that represent future aircraft/engine fuel systems. Special thermal stability tests with copper doped fuels and at low oxygen content have also been conducted. Carbon deposition information of these fuels that occur in bulk fuel and on hot surfaces is covered in this paper. The description of the test system and its operating characteristics and the test results are also included.
Experimental and Numerical Studies of Two-Stage Ethane-Air Flames
Authors: Waly M. M. Y. , Li S. C. , Williams F. A.
Published: December 2014

This paper reports results of experimental and numerical investigations on ethane-air two-stage combustion in a counterflow burner where the fuel stream, which is partially premixed with air for equivalence ratios from 1.6 to 3.0, flows against a pure air stream. Similar to methane, the two-stage ethane combustion exhibits a green fuel-rich premixed flame and a blue diffusion flame. Flame structures, including concentration profiles of stable intermediate species such as C2H4, C2H2 and CH4, are measured by a gas chromatography and are calculated by numerical integrations of the conservation equations employing an updated elementary chemical-kinetic data base. The implications of the results from these experimental measurements and numerical predictions are summarized, the flame chemistry of ethane two-stage combustion at different degrees of premixing (or equivalence ratio) is discussed, and the relationship between NOx formation and the degree of premixing is established. The present work helps to increase understanding of flame chemistry of hydrocarbon fuels, identify important reactions for pollutant formation and suggest means to reduce emissions.
Non-Intrusive Temperature and Oxygen Concentration Measurements in a Catalytic Combustor Using Rotational Coherent Anti-Stokes Raman Spectroscopy
Authors: Bood Joakim , Bengtsson Per-Erik , Aldén Marcus
Published: December 2014

Rotational CARS (Coherent anti-Stokes Raman Spectroscopy) was used to measure temperature and relative oxygen concentrations in the exhaust gas of a catalytic combustor. This laser technique has the general advantages of such techniques, i.e. possibility of performing in-situ measurements with high spatial and temporal resolution, and non-intrusiveness. Profiles of temperature and oxygen concentrations are presented for a full-load condition, and the measured temperatures are compared with calculated values. Of great importance for the results is the accuracy of the technique, and a sensitivity analysis is performed to test the temperature and oxygen concentration dependence on uncertainties in experimental parameters. It was shown that the accuracy of temperature and oxygen concentration could be improved by fitting the nonresonant susceptibility in the evaluation procedure. The measurements were performed as a project in the European gas turbine program AGATA with the aim to develop a catalytic combustor with ceramic structural components and producing low emissions of pollutants.
PIV Investigation of the Flow Characteristics in an Internal Coolant Passage With 45deg Rib Arrangement
Authors: Schabacker J. , Boelcs A. , Johnson B. V.
Published: December 2014

Flow characteristics in a model of a stationary two-pass internal coolant passage were measured with the stereoscopic PIV technique. From the PIV measurements, the 3D mean velocity field and turbulence quantities of the flow were obtained simultaneously with high spatial resolution, which allowed for an understanding of the flow phenomena in the coolant passage.

The model of the coolant passage consists of two square legs, each having a length of 19 hydraulic diameters that are connected by a sharp 180deg bend with a rectangular outer wall. In the two legs, 45deg ribs are mounted in a staggered arrangement on the bottom and top wall, with rib heights equal to 0.1 hydraulic diameter, and rib spacing of 10 rib heights. The measurements were carried out for a Reynolds number of 45,700 with air as working medium.

The paper presents results of the flow development in the straight legs of the passage and in the bend. The oblique ribs in the straight legs contribute to the development of secondary flows that transport fluid from the leg center towards the walls. In the bend of the passage, the interaction between rib-induced and bend-induced secondary flows leads to a three-dimensional flow. Downstream of the bend, the ribs quickly dominate the flow and thus lead to a fast recovery of the flow from the bend effect.
Heat Transfer Measurements on a Cooled Flat Plate Simulating Actual Size Turbine Hardware
Authors: Lepicovsky J. , Bencic T. J.
Published: December 2014

Application of thin-film thermocouples and temperature sensitive paint to surface temperature and heat transfer rate measurement on a flat plate with internal cooling is described in this paper. The test arrangement was designed to model flow and heat transfer conditions in terms of gas (external) and coolant (internal) Reynolds numbers that are typical for cooled turbine components. The test article is geometrically simple; however, from the heat transfer point of view it represents a fairly complex case. For both flows, internal and external, the hydrodynamic boundary layers start well ahead of the thermal boundary layers. The thermally active surface is preceded by an adiabatic starting length. Also, the heat transfer occurs under nonisothermal wall conditions and nonuniform heat flux conditions. The heat transfer experiments were carried out for a range of Mach number and Reynolds number on the gas side from 0.17 to 0.53 and from 135 000 to 580 000, respectively. On the coolant side, the corresponding ranges were from 0.3 to 0.52 for the flow Mach number, and from 20 000 to 65 000 for the Reynolds number. Measured bulk heat transfer rates demonstrated expected trends as functions of external (gas) and internal (coolant) Reynolds numbers. Local heat transfer rates measured along the mid-span line behaved as expected in relation to the internal (coolant) Reynolds number. However, they seem to be insensitive to changes in the external (gas) Reynolds number — at least for the particular test arrangement. Local heat transfer rates, however, strongly depend on the location with respect to the width of the cooling passage. These results were not expected; they may be caused by three dimensional nature of heat convection and conduction in this test arrangement.
Predictions of a Film Coolant Jet in Crossflow With Different Turbulence Models
Authors: Hoda Asif , Acharya Sumanta
Published: December 2014

This study investigates the performance of several existing turbulence models for the prediction of film coolant jet in a crossflow. Two equation models employing k-ε and k-ω closures, broadly categorized as high Reynolds number formulations, low Reynolds number formulations, DNS based formulation and non-linear formulations have been used to simulate the flow. In all, seven different turbulence models have been tested. Predictions with different models have been compared with experimental results of Ajersch et al. (1995) and with each other to critically evaluate model performance. The assessment of models has been done keeping in mind that all models have been formulated for wall bounded flows and may not be well suited for the jet-in-a-crossflow situation. Close agreement with experimental results was obtained at the jet exit and far downstream of the jet injection region, but all models typically overpredicted the magnitude of the velocities in the wake region behind the jet. The present study clearly underscores the deficiencies of the current models, and demonstrates the need for improvements.
Modeling Transfer Matrices of Premixed Flames and Comparison With Experimental Results
Authors: Schuermans Bruno B. H. , Polifke Wolfgang , Paschereit Christian Oliver
Published: December 2014

A combined analytical/experimental investigation of the thermoacoustic properties of a gas turbine burner with a premixed, turbulent, swirl-stabilized flame is presented. In an enclosed flame, an interaction occurs between acoustic fluctuations and non-steady heat release, which may lead to thermoacoustic instabilities. This interaction may be characterized by the transfer matrix of the burner with flame. The transfer matrix describes the coupling between fluctuations of acoustic pressure and velocity on both sides of burner and flame, incorporating also the effects of heat release fluctuations on the acoustic quantities. The transfer matrix has been modeled and validated with experimental results. For the burner, an analytical model is proposed, which is based on the Bernoulli equation for instationary flow through compact elements. The model is based on the Rankine-Hugoniot relations across a thin heat source. The fundamental assumption underlying the model is that acoustic fluctuations cause modulations of fuel concentrations at the fuel injector, which result, after a certain time lag, in a fluctuating heat release rate at the flame. The oscillating heat release couples with pressure and velocity fluctuations in the combustion chamber, thereby creating a feedback loop between combustor acoustics and flame dynamics which may result in self-excited combustion instability.

The transfer matrix of the burner with flame has been determined experimentally in an atmospheric combustion test facility. The test rig was equipped with loudspeakers and microphones in order to measure the response to an acoustical excitation. Our new flame model shows to be in agreement with the measured results.
The Effect of Schmidt Number on Turbulent Scalar Mixing in a Jet-in-Crossflow
Authors: He Guangbin , Guo Yanhu , Hsu Andrew T. , Brankovic A. , Syed S. , Liu N.-S.
Published: December 2014

The adequacy and accuracy of the constant Schmidt number assumption in predicting turbulent scalar fields in jet-in-crossflows are assessed in the present work. A round jet injected into a confined crossflow in a rectangular tunnel has been simulated using the Reynolds-Averaged Navier-Stokes equations coupled with the standard k-ε turbulence model. A semi-analytical qualitative analysis was made to guide the selection of Schmidt number values. A series of parametric studies were performed, and Schmidt numbers ranging from 0.2 to 1.5 and jet-to-crossflow momentum flux ratios from 8 to 72 were tested. The principal observation is that the Schmidt number does not have an appreciable effect on the species penetration, but it does have a significant effect on species spreading rate in jet-in-crossflows, especially for the cases where the jet-to-crossflow momentum flux ratios are relatively small. A Schmidt number of 0.2 is recommended for best agreement with data. The limitations of the standard k–ε turbulence model and the constant Schmidt number assumption are discussed.
On the Development and Application of the FRAP® (Fast-Response Aerodynamic Probe) System in Turbomachines: Part 3 — Comparison of Averaging Methods Applied to Centrifugal Compressor Measurements
Authors: Köppel Pascal , Roduner Christian , Kupferschmied Peter , Gyarmathy Georg
Published: December 2014

Typically several hundred million data points arise from a comprehensive measurement campaign carried out in a centrifugal compressor test rig with the FRAP® system (see Part 1). In order to obtain a maximum of information about the unsteady flow at any position in this turbo machine the time-resolved data processing method has to be optimized. In contrast to the standard time-averaged flow measurements with pneumatic probes, the objective of FRAP® measurements and of data processing is to extract novel information about crucial unsteady phenomena like turbulence, row-to-row interaction, modal or rotating stall, leakage flow effects etc. In such cases the simultaneous measurement of static and total pressures and flow vectors is of particular interest. Novel information means the analysis of averaged and time-resolved (wavelet) spectra, autocorrelations or time averages properly conserving physical fluxes, etc..

Different averaging methods are applied to compress the time dependent data measured by a 1-sensor-probe (see Part 2) in a centrifugal compressor. Such results could be used for comparison with pneumatic sensor measurements and CFD calculations. The comparison of averaging methods includes the averaging theories by Traupel and by Dzung which are compared to simple arithmetic time averaging. From there the specific stage work is calculated.

In analysing the time dependency several ensemble-averaging procedures for flow pressure and velocity are utilized for separating deterministic from stochastic fluctuations, extracting blade row finger prints or investigating low-frequency surge type fluctuations.

With respect to the selection and overall optimization of data processing methods an overview of generic tools is given and the modularity of the processing procedures is discussed.
Simulations of the Unsteady Flow Through the Fastrac Supersonic Turbine
Authors: Griffin Lisa W. , Dorney Daniel J.
Published: December 2014

Analysis of the unsteady aerodynamic environment in the Fastrac supersonic turbine is presented. Modal analysis of the turbine blades indicated possible resonance in crucial operating ranges of the turbopump. Unsteady computational fluid dynamics (CFD) analysis was conducted to support the aerodynamic and structural dynamic assessments of the turbine. Before beginning the analysis, two major problems with current unsteady analytical capabilities had to be addressed: modeling a straight centerline nozzle with the turbine blades and exit guide vanes (EGVs), and reducing run times significantly while maintaining physical accuracy. Modifications were made to the CFD code used in this study to allow the coupled nozzle/blade/EGV analysis and to incorporate Message Passing Interface (MPI) software. Because unsteadiness is a key issue for the Fastrac turbine (and future rocket engine turbines such as for the Reusable Launch Vehicle (RLV)], calculations were performed for two nozzle-to-blade axial gaps. Calculations were also performed for the nozzle alone, and the results were imposed as an inlet boundary condition for a blade/EGV calculation for the large gap case. These results are compared to the nozzle/blade/EGV results.
A Combined Experimental and Numerical Investigation of the Flow in a Heated Rotor/Stator Cavity, With a Radial Inflow
Authors: Laroche E. , Desportes S. , Djaoui M. , Debuchy R. , Paté L.
Published: December 2014

A combined experimental and numerical study has been conducted in order to investigate the turbulent flow in a heated rotor-stator cavity of low gap ratio, subjected to a superposed centripetal flow. In the scope of this work, the fluid can be considered as incompressible, with the consequence that the heat transfer process is dissociated from the dynamical effects. The flowfield is characterized by two separated Ekman layers and a core region.

Detailed velocity measurements have been carried out. Reynolds stresses were examined in great detail using hot wire measurements, whereas temperature-velocity correlations were obtained using combined hot wire–cold wire measurements. The temperature distribution was specified on the stator and heat fluxes were measured with fluxmeters.

Numerical simulations of the above configuration have been carried out with the following turbulence models: a two equation k-1 model, an Explicit Algebraic Reynolds Stress Model (EARSM), and an anisotropic thermal extension of the k-1 ASM model. The agreement between experimental and numerical results is generally good for the nondimensional velocities, except in the Ekman layer region. A comparison of Reynolds Stresses is also provided. The heat flux on the stator appears to be underestimated, due to the poor prediction of the Ekman layer zone.

The numerical study reveals the critical importance of the inlet conditions, and in particular of the nondimensional tangential velocity on the flow inside the cavity. A comparison with experimental data also confirms that the anisotropy is of importance mainly in the Ekman layer region.
Unsteady Wake Effect on Film Temperature and Effectiveness Distributions for a Gas Turbine Blade
Authors: Teng Shuye , Sohn Dong Kee , Han Je-Chin
Published: December 2014

The film effectiveness and coolant jet temperature profile on the suction side of a gas turbine blade were measured using a transient liquid crystal and a cold-wire technique, respectively. The blade has only one row of film holes oear the gill hole portion on the suction side of the blade. Tests were performed on a five-blade linear cascade in a low-speed wind tunnel. The mainstream Reynolds number based on cascade exit velocity was 5.3×105. Upstream unsteady wakes were simulated using a spoke-wheel type wake generator. Coolant blowing ratio was varied from 0.6 to 1.2. Wake Strouhal number was kept at 0 and 0.1. Results show that unsteady wake reduces film cooling effectiveness. Results also show that film injection enhances local heat transfer coefficient while the unsteady wake promotes earlier boundary-layer transition. The development of coolant jet temperature profiles could be used to explain the film cooling performance.
Computation of Flow and Heat Transfer in Rotating Two-Pass Square Channels by a Reynolds Stress Model
Authors: Chen Hamn-Ching , Jang Yong-Jun , Han Je-Chin
Published: December 2014

A multiblock numerical method has been employed for the calculation of three-dimensional flow and heat transfer in rotating two-pass square channels with smooth walls. The finite-analytic method solves Reynolds-Averaged Navier-Stokes equations in conjunction with a near-wall second-order Reynolds stress (second-moment) closure model and a two-layer k–ε isotropic eddy viscosity model. Comparison of second-moment and two-layer calculations with experimental data clearly demonstrate that the secondary flows in rotating two-pass channels have been strongly influenced by the Reynolds stress anisotropy resulting from the Coriolis and centrifugal buoyancy forces as well as the 180° wall curvatures. The near-wall second-moment closure model provides the most reliable heat transfer predictions which agree well with measured data.
Diagnosis of Gas Turbine Operating Conditions by Means of the Inverse Cycle Calculation
Authors: Bettocchi R. , Spina P. R.
Published: December 2014

This paper presents a method for the analysis of gas turbine operating state, which uses the Cycle-Deck developed by gas turbine manufacturers and the measurements taken by means of the standard machine instrumentation. The gas turbine operating condition analysis is performed “adapting” the characteristic geometric and performance parameters (i.e., characteristic flow passage areas and efficiencies of the compressor and turbine, combustor efficiency, etc …), used as inputs by the Cycle-Deck, until the computed estimates of the measurable parameters agree with the values measured on the gas turbine. This is done by minimizing an objective function built as the sum of the squared residuals between the computed and measured values of the same parameters. The analysis of the variations between computed and expected values of the characteristic parameters allows the localization of inefficient operations due to deterioration and faults.
Experimental Investigation of Particle Rebound Characteristics on Turbomachinery Leading Edge Geometry
Authors: Siravuri S. , Tabakoff W. , Gunaraj J. A.
Published: December 2014

Aircraft gas turbines, steam turbines, coal utilization turbines and many other systems operating under particulate flows are exposed to erosion wear and performance deterioration. This paper describes an experimental technique to evaluate particle rebound characteristics on turbomachinery leading edge geometry using laser velocimetry and high-speed photography. The experimental work was conducted with silica sand particle sizes of 1000–1500 microns and velocity of 15 and 30 m/s. Stainless Steel was the target material. Mach Number and Reynolds Number of the flow were 0.09 and 105 (Based on inlet velocity and test section width) respectively. Wollensax Fastax high-speed camera was used. A camera speed of 2500 frames per second was used. The data were analyzed using x-v, image-processing software. Velocity restitution ratio at various impact locations was calculated. The measured velocity restitution ratio could be used in the numerical simulation to predict particle trajectories, subsequently could be used to identify the critical zones and to predict the erosion rates.
On Instability of Overhung Centrifugal Compressors
Authors: Berot François , Dourlens Hervé
Published: December 2014

This paper describes the synchronous vibration instability problem that occurred on a series of large overhung centrifugal compressors. The first part of this paper deals with the identification and display of the instability phenomenon: cyclic vibration amplitude variations and phase angle rotation occuring during testing of overhung centrifugal compressors. After numerical simulations and analysis of the test results, the bearing design has been identified as the cause of the problem. The second part describes the numerical study of the instability of the compressor. This problem is related to the eccentricity of the shaft in the bearing and to the shape of its orbit. We have investigated and propose different solutions to avoid this unstable dynamic behavior. These solutions have been tested on different compressors and have confirmed the results of the numerical analysis. The third part reminds a link between the thermal effect occurring in the bearings, the numerical results and the tested dynamic behavior of the compressor.

Recently, some authors such as Keogh et al. (1994) and Liebich et al. (1994) have noticed and studied this unstable behavior. Althougth the nature of the phenomenon seems to be known (de Jongh et al., 1984) (Faulkner et al., 1997a, 1997b), no universal technical solution to this important problem has been found. The contribution of this work is to present another case of the influence of the thermal effect on the dynamic behavior of an overhung compressor. We present the typical symptoms of the phenomenon, explain it, and propose the solutions we have used to avoid the problem.
Imbalance Response and Damping Force Coefficients of a Rotor Supported on End Sealed Integral Squeeze Film Dampers
Authors: De Santiago Oscar C. , San Andrés Luis A.
Published: December 2014

To this date, squeeze film dampers (SFDs) are effective means to reduce vibrations and provide structural isolation in high performance aeroengine systems. Integral squeeze film dampers (ISFDs) offer distinct advantages such as reduced overall weight, accuracy of positioning, and a split segment construction allowing easier assembly, inspection and retrofit. An experimental study is conducted to evaluate the effectiveness of integral dampers in attenuating the imbalance response of a massive test rotor. Damping coefficients for end sealed dampers are identified from the peak rotor responses due to imbalances while passing through the fundamental critical speeds. Impact response measurements at null rotor speed are also conducted to identify system damping coefficients for increasing values of the lubricant temperature. The impact tests and imbalance response measurements demonstrate that end gap seals increase effectively the ISFD viscous damping coefficients and without a severe penalty in the flow through the dampers. The experiments further demonstrate that the amplitudes of rotor synchronous response are proportional to the imbalance displacements without subsynchronous frequencies or (nonlinear) jump responses.
Sliding Mode Control of Magnetic Bearings: a Hardware Perspective
Authors: Maslen Eric , Montie Dominick
Published: December 2014

The physical hardware of magnetic bearing systems has a very strong impact on the application of sliding mode control to this technology. Finite current slew rates affect the character of achievable reaching conditions; flexible rotors demand the use of state observers which then affect achievable robustness; finite controller throughput and use of switching power amplifiers has substantial impact on how chatter should be addressed.

This paper formulates the sliding mode control problem for realistic rotor/magnetic actuator systems considering rotor flexibility and finite amplifier voltages. The structure of the resulting class of controllers is examined for both rigid and for flexible rotors. It is demonstrated that, fundamentally, these controllers are conventional linear state observer based controllers acting through high speed switching amplifiers as in conventional magnetic bearing technology.
Complementary Use of CFD and Experimental Measurements to Assess the Impact of Shrouded and Cantilevered Stators in Axial Compressors
Authors: Campobasso M. S. , Mattheiss A. , Wenger U. , Amone A. , Boncinelli P.
Published: December 2014

The performance of an axial compressor with either shrouded or cantilevered stators has been analyzed. The two configurations have been compared both at design and near stall operating conditions, with the aid of CFD and experimental measurements.

Results show that shrouded or cantilevered stators impact differently on the overall performance of the tested compressor. A higher stall margin occurs with the cantilevered build, while the work coefficient and the efficiency of the shrouded build at design conditions are higher.

An overall comparison of the shrouded and cantilevered design concepts has been carried out, not only in aerodynamic but also in economic terms.
Active Control of Combustion Instability in a Liquid–Fueled Sector Combustor
Authors: Hibshman J. R. , Cohen J. M. , Banaszuk A. , Anderson T. J. , Alholm H. A.
Published: December 2014

A system for the active control of combustion instabilities in liquid-fueled, lean, premixed combustors was demonstrated in a three-nozzle sector combustor, using full-scale engine hardware. Modulation of a portion of the premixed fuel flow led to a reduction of 6.5 dB (2.1X) in the amplitude of the dominant instability mode. Combustor emissions were not adversely affected by the control.
Flow Characteristics of a Highly Rotating Turbine Cavity System With Discharge Hole
Authors: Maeng D. J. , Lee J. S. , Jakoby R. , Kim S. , Wittig S.
Published: December 2014

An experimental investigation is performed to analyze the flow characteristics of a turbine cavity system containing discharge holes installed in a rotating disk. The turbine cavity system is composed of a rotating disk and two stationary disks on both sides of the rotating disk. The air flow is induced into the upstream cavity, and then discharged into the downstream cavity through 8 discharge holes in the rotating disk. The flow field in each cavity at high-speed rotation of the rotor was measured by a three-dimensional LDV system. The measured flow field is analyzed to understand the flow structures, and further provide information for studying the heat transfer behaviors of the turbine disk system. The overall flow field in the upstream cavity shows a negligible axial velocity with a relatively small rotational velocity, less than 10% of the rotor speed. The downstream cavity flow has a high rotational velocity close to the rotational speed of the discharged jets, due to the direct circumferential momentum transfer from the discharged jets. The interaction between the discharged jet and the downstream stator disk induces an asymmetric development of the spreading wall jet, which results in a relative circumferential motion to the revolving discharged jet. The whole flow field in the downstream cavity is divided into several flow regions according to their features.
In-Service Damage Assessment and Life Prediction of Stage 1 Buckets in a Frame 9E CCGT
Authors: Kallianpur V. , Yoshioka Y. , Claeys J. , Beltran A. , Kashiwaya H. , Fujiyama K. , Tezuka H. , Sakurai T. , Aoki M.
Published: December 2014

In-service degradation of hot gas path components were evaluated for life extension purpose in a combined cycle power plant. In this paper only results for stage 1 bucket evaluation are discussed. The study included a detailed thermal and structural analysis of the hardware simulating typical operation of the TEPCO power plant, together with nondestructive and destructive examination of the parts condition at various hot gas path inspections. The analytic predictions of critical locations compared well versus actual, and the damage trends were tracked to quantify the damage evolution in the hardware. The destructive tests also verified temperature gradients based on γ microstructure measurements at near-surface, and internal locations.

Microstructure and mechanical properties of the base metal and coating for the service exposed conditions were compared versus new buckets for baseline referencing. Also, the material properties for the service exposed condition were compared versus the original material assumptions used in the design of the original part, which also included approx. 60,000 hrs of uninterrupted creep testing. Knock down factors were established for the original materials design data in order to establish the life extension capability, and design margin beyond its specified original design life.

Life extension capability was determined using cumulative damage considerations along with the thermal-mechanical stress and strain predictions and adjusted materials properties, both of which were unique for TEPCO’s operating profile.
The Methodology of Stochastic Optimization of Parameters and Control Laws for the Aircraft Gas-Turbine Engines Flow Passage Components
Authors: Egorov I. N. , Kretinin G. V. , Kostiuk S. S. , Leshchenko I. A. , Babi U. I.
Published: December 2014

This paper presents the main theses of stochastic approach to the multimeasure parameters and control laws optimization for the aircraft gas-turbine engines. The methodology allows us to optimize the engines taking into account the technological deflections which inevitably take place in the process of manufacturing of the engine’s components as well as engine’s control deflections. The stochastic optimization is able to find highly robust solutions, stable to inaccuracies in technological processes.

The effectiveness of the methodology is shown by example of optimization problem solution to find the control laws for the flow passage controllable elements of the 4-th generation aircraft mixed-flow turbofan engine. The use of information about the existing and advanced production technology levels during the optimization process, including some components manufacturing accuracy, allows us to considerably increase the probability of optimum solution implementation in practice. In real engine there are some components manufacturing deflections as well as control accuracy deflections. It results a certain engine’s performance deviation. An engine optimization classic deterministic approach can not take into account this circumstance, so the probability of an optimum design implementation is too low.
Combustor Liner Analysis by a Thermo-Mechanical Integrated Approach
Authors: Baldi A. , Vitale E. , Piccitto U.
Published: December 2014

In this paper we present a mixed thermofluidodynamical and mechanical approach to the life analysis of thermally-loaded components, and apply it to a combustor liner.

When studying this class of problems, we are mostly concerned with a) the material parameter identification and b) the load history definition. While testing may alleviate the need for point a), we must put a lot of care in b), since the distribution of temperature (i.e., the thermal gradient) inside components and their load history are very difficult to measure accurately.

To face these kind of problems we take as input the results of thermofluidodynamical calculations made with the FLUENT computer code[1] at the ENEL (Italian Electric Power Company) Research Centre of Pisa to simulate the experimental behaviour of a combustor liner under different load conditions (phase 1). The output data have been processed in order to use them with the MARC Finite Element (F.E.) code transient thermal analysis (phase 2). Finally we took the MARC thermal simulation results as input to the mechanical analysis (phase 3). To interface the FLUENT and MARC codes, we developed a numerical program to map grid data (FLUENT) to the Finite Element mesh (MARC) by means of an interpolation algorithm.

This way, once we got a likely temperature distribution inside the component by means of the first step, we were able to follow the load history during the second and the third phases.

By this approach we were able to a) simulate the evolution of the combustor liner under cyclic thermal loads, b) identify the critical areas and c) make estimations of the life of the component under these loads.
Time-Dependent Reliability of Ceramic Components Subjected to High-Temperature Loading in a Corrosive Environment
Authors: Brückner-Foit A. , Ziegler C.
Published: December 2014

The time-dependent reliability of ceramic components subjected to high temperature loading can be analysed using multiaxial Weibull theory and its generalisations. In this approach it is assumed that no additional flaws are initiated during exposure to high temperatures. However, this may not be true in a highly corrosive environment such as in a combustion chamber. Additional flaws can be generated by surface oxidation, volume damage or by formation of circular pits on the surface of the component. These cases are considered in this paper. The relations for the failure probabilities are derived starting from classical Weibull theory. A fastener bolt for the ceramic lining of a combustion chamber is considered as an example.
Back Side-Cooled Combustor Liner for Lean-Premixed Combustion
Authors: Smith Kenneth , Fahme Anthony
Published: December 2014

This paper describes the design and initial testing of a second generation, lean-premixed combustor for a 6100 horsepower industrial gas turbine. The full scale, prototype combustor liner employed augmented backside cooling (ABC) as a means of reducing NOx and CO emissions. A thermal barrier coating (TBC) was applied on the liner hot side to reduce thermal flux from the flame zone. The goal of the effort was to demonstrate that the avoidance of film-cooling for the combustor liner would allow emissions reductions in a lean-premixed combustion system.

Testing of the combustor was conducted in both low and high pressure environments. The testing demonstrated that the use of trip-strips for backside cooling provides an effective means of reducing CO emissions. The lower CO levels can be exploited by lowering flame temperatures to achieve lower NOx emissions. Reaction quenching associated with film cooling is indicated as the cause of the higher CO emissions in more conventional liners. Cyclic rig testing showed the TBC to have good short-term durability. Long-term field testing is getting underway.
Workshop Testing of GT140P: Part 2 — Tests and Experiences
Authors: Knudsen Knud , Nilsson Roland , Nilsson Ulf , Thörnblad Per
Published: December 2014

The first GT140P was tested in ABB STAL’s workshop in Finspong, Sweden. During about 550 hours of operation under different transient and stationary conditions, the function of the machine was tested and important performance and stress parameters were measured. On-line evaluation and subsequent analysis of recorded data showed, with a few exceptions, that the machine fulfilled the expectations. Modifications were introduced in those areas which did not perform satisfactorily, and the final tests verified that the changes had solved the earlier problems.
Internal Bearing Chamber Wall Heat Transfer as a Function of Operating Conditions and Chamber Geometry
Authors: Busam Stefan , Glahn Axel , Wittig Sigmar
Published: December 2014

Increasing efficiencies of modern aero-engines are accompanied by rising turbine inlet temperatures, pressure levels and rotational speeds. These operating conditions require a detailed knowledge of two-phase flow phenomena in secondary air and lubrication oil systems in order to predict correctly the heat transfer to the oil. It has been found in earlier investigations that especially at high rotational speeds the heat transfer rate within the bearing chambers is significantly increased with negative effects on the heat to oil management. Furthermore, operating conditions are reached where oil coking and oil fires are more likely to occur. Therefore, besides heat sources like bearing friction and churning, the heat transfer along the housing wall has to be considered in order to meet safety and reliability criteria.

Based on our recent publications as well as new measurements of local and mean heat transfer coefficients, which were obtained at our test facility for engine relevant operating conditions, an equation for the internal bearing chamber wall heat transfer is proposed. Nusselt numbers are expressed as a function of non-dimensional parameter groups covering influences of chamber geometry, flow rates and shaft speed.
Efficiency of Air-Purged Rotor-Stator Seals in Combustion Turbine Engines
Authors: Reichert A. W. , Lieser D.
Published: December 2014

Although the efficiency of air-purged rotor seals has been the subject of a number of different tests, and the results of these tests are available in the literature. Only a small number of tests actually also modeled the influence of the blading. Consideration of this influence is essential for combustion turbine applications.

Furthermore, the methods chosen for presenting experimental data on the influence of the blading differ from each other, and although the sealing efficiency is correlated to different parameters, the connection to the physical phenomena causing the hot gas ingestion into rotor-stator cavities does not become clear.

The objective of this paper is to improve this situation. The available experimental data are reviewed, and the given correlations for the sealing efficiency are discussed. Universally applicable parameters for the correlation of the sealing efficiency are recommended, and validity limits for this recommendation are discussed.
A Computational Visualization of Three Dimensional Flow: Finding Optimum Heat Transfer and Pressure Drop Characteristics From Short Cross-Pin Arrays and Comparison With Two Dimensional Calculations
Authors: Donahoo E. E. , Camci C. , Kulkarni A. K. , Belegundu A. D.
Published: December 2014

There are many heat transfer augmentation methods that are employed in turbine blade design, such as impingement cooling, film cooling, serpentine passages, trip strips, vortex chambers, and pin fins. The use of crosspins in the trailing edge section of turbine blades is commonly a viable option due to their ability to promote turbulence as well as supply structural integrity and stiffness to the blade itself. Numerous crosspin shapes and arrangements are possible, but only certain configurations offer high heat transfer capability while maintaining taw total pressure loss. This study preseots results from 3-D numerical simulations of airflow through a turbine blade internal cooling passage. The simulations model viscous flow and heat transfer over full crosspins of circular cross-section with fixed height-to-diameter ratio of 0.5, fixed transverse-to-diameter spacing ratio of 1.5, and varying streamwise spacing. Preliminary analysis indicates that endwall effects dominate the flow and heat transfer at lower Reynolds numbers. The flow dynamics involved with the relative dose proximity of the endwalls for such short crosspins have a definite influeoce on crosspin efficiency for downstream rows.
Computations of Flow and Heat Transfer in a Channel With Rows of Hemispherical Cavities
Authors: Lin Y.-L. , Shih T. I-P. , Chyu M. K.
Published: December 2014

Computations were performed to investigate the three-dimensional flow and heat transfer in a high aspect ratio channel in which one or two wall are lined with four rows of hemispherical cavities arranged in a staggered fashion with two Reynolds numbers (23,000 and 46,000). The focus is on understanding the flow induced by cavities and how that flow affects surface heat transfer. Computed results were compared with available experimental data.

This computational study is based on the ensemble-averaged conservation equations of mass, momentum (compressible Navier-Stokes), and energy closed by the low Reynolds number shear-stress transport k-ω turbulence model (wall functions were not used). Solutions were generated by a cell-centered finite-volume method that uses third-order accurate flux-difference splitting of Roe with limiters, multigrid acceleration of a diagonalized ADI scheme with local time stepping, and patched/overlapped structured grids.