bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and Testing of CFCC Shroud and Combustor Components
Authors: Dean Anthony J. , Corman Gregory S. , Bagepalli Bharat , Luthra Krishan L. , DiMascio Paul S. , Orenstein Robert M.
Published: December 2014

This paper presents initial results in the development and testing of SiC-based Continuous Fiber Ceramic Composites (CFCC) materials for combustor and stage 1 shroud components of large utility-class gas turbines. Use of CFCC’s for these components has the potential for increasing output power and thermal efficiency and reducing emissions.

First stage turbine shroud components were fabricated using five material systems including three SiC/SiC-Si systems made by silicon melt infiltration (MI), chemical vapor infiltrated (CVI) enhanced SiC-SiC and directed metal oxidation (DIMOX) Al2O3-SiC composite. A combustor liner was made of MI CFCC. Before and after testing the components were inspected by several NDE techniques including IR thermography, resonance testing and visual examination.

A novel, high pressure test rig was used to test four shroud components and a combustor liner simultaneously. Components were exposed to hot gas temperature of 1200°C at 12.5 bar in cyclic and steady-state tests. Cyclic testing simulated engine trip conditions with 200 flame-on, flame-off cycles. Steady state testing involved 100 hours of exposure at high temperature and pressure with hot combustion gases. At the conclusion of the first phase of testing there was visible damage to two pieces of one of the material systems. Destructive testing of the components following rig exposure showed little degradation to the MI composite materials. In summary, high pressure combustion rig testing of these components demonstrated excellent performance with little degradation among the material systems.
Rolls Royce RB211-DLE Combustor Diffuser Design Optimisation
Authors: Schweiger Tom , Underhill Richard M. , Livingston Duncan W.
Published: December 2014

This paper presents a technique for optimising the performance of a diffuser in an industrial gas turbine using validated CFD modelling. The combustor module of the Rolls Royce RB211-DLE industrial engine was modelled from diffuser inlet to combustor inlet, using a hybrid meshing procedure. A CFD model of the current RB211-DLE diffuser and casing was validated against perspex single sector rig data, including pressure probe measurements, oil dot flow tests and a sensitivity analysis. A three-dimensional design process was then undertaken to determine how the shape of the diffuser affects the loss through the system, and hence which type of diffuser would provide the best opportunity for maximising the engine performance. The best two general diffuser designs were optimised using an iterative two-dimensional design process. The performance of these optimised designs was then confirmed by full three-dimensional modelling. This work suggests that a significant improvement in sfc (based on a constant turbine temperature) would be achieved if the optimum diffuser design is installed into the RB211-DLE engine.
The Siemens Westinghouse Advanced Turbine Systems Program
Authors: Diakunchak Ihor S. , Krush Mark P. , McQuiggan Gerry , Southall Leslie R.
Published: December 2014

This paper summarizes progress on Siemens Westinghouse’s Advanced Turbine Systems (ATS) Program. The ATS program, which is supported by U.S. Department of Energy, Office of Fossil Energy, has the ultimate objective of introducing into the utility market electricity generating systems capable of achieving greater than 60% LHV based net plant thermal efficiency, less than 10 parts per million NOx emissions, 10% electricity cost reduction and state-of-the-art reliability-availability-maintainability. Work has been in progress over the last few years on developing the required advanced technologies and designing the W501ATS gas turbine. The main thrust of the technology development effort was in the areas of compressor aerodynamics, turbine aerodynamics, heat transfer/cooling, sealing, combustion/emissions, single crystal casting, materials, and coating systems. These technologies were incorporated into the W501ATS engine design to ensure that the ATS Program goals will be achieved.
Flowfield Measurements for a Highly Turbulent Flow in a Stator Vane Passage
Authors: Radomsky R. W. , Thole K. A.
Published: December 2014

Turbine vanes experience high convective surface heat transfer as a consequence of the turbulent flow exiting the combustor. Before improvements to vane heat transfer predictions through boundary layer calculations can be made, we need to understand how the turbulent flow in the inviscid region of the passage reacts as it passes between two adjacent turbine vanes. In this study, a scaled-up turbine vane geometry was used in a low-speed wind tunnel simulation. The test section included a central airfoil with two adjacent vanes. To generate the 20% turbulence levels at the entrance to the cascade, which simulates levels exiting the combustor, an active grid was used. Three-component laser Doppler velocimeter measurements of the mean and fluctuating quantities were measured in a plane at the vane mid-span. Coincident velocity measurements were made to quantify Reynolds shear stress and correlation coefficients. The energy spectra and length scales were also measured to give a complete set of inlet boundary conditions that can be used for numerical simulations. The results show that the turbulent kinetic energy throughout the inviscid region remained relatively high. The surface heat transfer measurements indicated high augmentation near the leading edge as well as the pressure side of the vane as a result of the elevated turbulence levels.
Highly Turbulent Mainstream Effects on Film Cooling of a Simulated Airfoil Leading Edge
Authors: Johnston Christopher A. , Bogard David G. , McWaters Marcus A.
Published: December 2014

The influence of a high mainstream turbulence was examined in an experimental study of film cooling on a simulated turbine blade leading edge. Detailed heat transfer coefficient and adiabatic effectiveness values were measured under conditions representative of actual environments in a gas turbine engine. The two parameters were also combined for a net heat flux reduction analysis. Turbulence levels of Tu = 17% were achieved by modifying a cross-jets turbulence generator with a large cylinder element. A quarter cylinder geometry was used to simulate the turbine blade leading edge. Two staggered rows of nine holes each were incorporated with a geometry consistent with current industry design practices. One row was positioned nominally on the stagnation line, x/d = 0, while the other was located 25° from the stagnation line. The holes were spaced at S/d = 7.64 with a shallow injection angle of 20° and oriented at 90° to the streamwise direction. Comparisons were made to previous studies of heat transfer rates and adiabatic effectiveness values under low turbulence (Tu < 0.5%) conditions. Adiabatic effectiveness was generally decreased by about 20% due to the high mainstream turbulence, although a much greater decrease occurred at the stagnation line at lower blowing rates. The relative increase in heat transfer coefficient due the coolant injection was found to be significantly smaller for the high mainstream turbulence case compared to the low mainstream turbulence case. This was particularly important when evaluating the overall performance of this film cooling hole configuration, since the much smaller relative increase in heat transfer coefficient resulted in good performance in terms of net heat flux reduction.
In Situ Detailed Chemistry Calculations in Combustor Flow Analyses
Authors: James S. , Anand M. S. , Razdan M. K. , Pope S. B.
Published: December 2014

In the numerical simulation of turbulent reacting flows, the high computational cost of integrating the reaction equations precludes the inclusion of detailed chemistry schemes, therefore reduced reaction mechanisms have been the more popular route for describing combustion chemistry, albeit at the loss of generality. The in situ adaptive tabulation scheme (ISAT) has significantly alleviated this problem by facilitating the efficient integration of the reaction equations via a unique combination of direct integration and dynamic creation of a look-up table, thus allowing for the implementation of detailed chemistry schemes in turbulent reacting flow calculations. In the present paper, the probability density function (PDF) method for turbulent combustion modeling is combined with the ISAT in a combustor design system, and calculations of a piloted jet diffusion flame and a low-emissions premixed gas turbine combustor are performed. It is demonstrated that the results are in good agreement with experimental data and computations of practical turbulent reacting flows with detailed chemistry schemes are affordable.
Numerical Simulation of Turbulent Premixed Combustion Using a Joint-PDF Approach Based on a Systematically Reduced Multi-Step Reaction Mechanism
Authors: Bohn Dieter E. , Lepers Joachim
Published: December 2014

Based on the characteristics of turbulent combustion in lean-premix combustion chambers, this paper presents a combustion model which solves transport equations for six chemical species. The source terms are calculated by probability weighted integration of 35 elementary reaction rates. The model presented here does not include any adjustable parameters. Therefore, it is universal in its character for conditions of highly turbulent premixed lean to stoichiometric combustion.

The model is applicable to fuel compositions including methane, carbon monoxide, and hydrogen. The application is shown for a test case burning methane in lean-premixed mode.
Combustor Flow Analysis Using an Advanced Finite-Volume Design System
Authors: Anand M. S. , Zhu J. , Connor C. , Razdan M. K.
Published: December 2014

An advanced design system has been developed for combustor flow analysis. The system is based on the finite-volume methodology and is of second-order numerical accuracy. Use of co-located grids and Cartesian velocities offers significant advantages over previous staggered-grids, covariant-velocities based schemes. The physicochemical effects are simulated by the standard k-ε model for turbulence, the eddy-breakup model with a two-step general hydrocarbon chemistry for combustion, and a stochastic Lagrangian transport and evaporation model for spray. The developed design system has been applied to analyze a production gas turbine combustor configuration and several design changes. The calculated exit-plane temperature profiles compare well against full-scale rig data. The trends of the exit temperature profiles, showing the effect of design changes to the geometry and flow-splits of various combustor features, are well predicted. The study demonstrates the developed design system to be a robust and viable tool for analyzing and guiding combustor design.
Velocity Measurements and Gas Mixing Characterization at the Exit of an Isothermal Model of a Gas Turbine Premixer
Authors: Burattini Paolo , Talamelli Alessandro , Tanzini Giordano , Mariotti Gaudenzio , Turrini Fabio
Published: December 2014

Premixed flames have shown to provide sufficient low NOx emission levels in gas turbine combustor. To achieve this goal several issues are to be addressed. Highly uniform fuel air ratio along with proper velocity profiles at the flame front has to be achieved. Vortex generators are commonly employed inside lean premixed combustor to generate a swirling flow that can assure the two aspects above. An experimental parametric study of the isothermal swirl flow of a non-confined prototype premixer is presented. Several different geometrical details have been considered for two different fuel air ratios. Velocity fields and mixing distribution between fuel and air at the premixer exit are described. Velocity and turbulence data can be related to formation of flashback and temporal homogeneity of the mixture respectively while the degree of spatial mixing, in terms of segregation factor, is connected with NOx rate of formation. In both cases the vigorous and high responsive character of the vortex generated by the swirler plays a major role. The final objective is twofold: to define an optimum geometrical arrangement to be tested in subsequent combustion tests and to demonstrate the feasibility of a rapid assessment method of degree of mixing between fuel and air.
Introduction and Performance Prediction of a Nutating-Disk Engine
Authors: Korakianitis T. , Meyer L. , Boruta M. , McCormick H. E.
Published: December 2014

A new type of internal combustion engine and its thermodynamic cycle are introduced. The core of the engine is a nutating non-rotating disk, with the center of its hub mounted in the middle of a Z-shaped shaft. The two ends of the shaft rotate, while the disk nutates. The motion of the disk circumference prescribes a portion of a sphere. A portion of the area of the disk is used for intake and compression, a portion is used to seal against a center casing, and the remaining portion is used for expansion and exhaust. The compressed air is admitted to an external accumulator, and then into an external combustion chamber before it is admitted to the power side of the disk. The accumulator and combustion chamber are kept at constant pressures. The engine has a few analogies with piston-engine operation, but like a gas turbine it has dedicated spaces and devices for compression, burning and expansion. The thermal efficiency is similar to that of comparably-sized simple-cycle gas turbines and piston engines. For the same engine volume and weight, this engine produces less specific power than a simple-cycle gas turbine, but approximately twice the power of a two-stroke engine and four times the power of a four-stroke engine. The engine has advantages in the 10 kW to 200 kW power range. This paper introduces the geometry and thermodynamic model for the engine, presents typical performance curves, and discusses the relative advantages of this engine over its competitors.
Heat Transfer and Flow on the First Stage Blade Tip of a Power Generation Gas Turbine: Part 2 — Simulation Results
Authors: Ameri A. A. , Bunker R. S.
Published: December 2014

A combined experimental and computational study has been performed to investigate the detailed distribution of convective heat transfer coefficients on the first stage blade tip surface for a geometry typical of large power generation turbines (>100MW). This paper is concerned with the numerical prediction of the tip surface heat transfer. Good comparison with the experimental measured distribution was achieved through accurate modeling of the most important features of the blade passage and heating arrangement as well as the details of experimental rig likely to affect the tip heat transfer. A sharp edge and a radiused edge tip was considered. The results using the radiused edge tip agreed better with the experimental data. This improved agreement was attributed to the absence of edge separation on the tip of the radiused edge blade.
Three-Dimensional Performance Prediction of Multistage Axial Flow Compressors With a Repeating Stage Model
Authors: Li Y. G. , Tourlidakis A. , Elder R. L.
Published: December 2014

In this paper, a method for the performance prediction of multistage axial flow compressors through a steady, three-dimensional, multi-block Navier-Stokes solver is presented.

A repeating stage model has been developed aiming at the simplification of the required global aerodynamic boundary conditions for the simulation of the rear stages of multistage axial compressors where only mass flow rate and exit average static pressure are required. The stage inlet velocity distribution is fixed to be equal to the one calculated at the stage exit and the exit static pressure distribution is fixed to have the same shape to that at inlet but maintain its own average value. A mixing plane approach is used to exchange information between neighbouring blade rows which allows both radial and circumferential variations at both sides of the interface.

A pressure correction method with the standard k–ε turbulence model is used in combination with Stone’s two step procedure for the solution of the algebraic system of the discretised equations. A global iteration is carried out in order to establish the physical consistency between the blade rows.

A combination of two structured grid blocks for the rotor blade row, one for the main passage and a second for the modelling of the tip clearance, is used for a detailed representation of the leakage flows.

Computational results from two methods, the first by using the repeating stage model and the second by setting stage inlet velocity profile, are presented from the analysis of the third stage of the four-stage Cranfield Low Speed Research Compressor (LSRC). Good agreements with the experimental data are obtained in terms of total pressure, static pressure and velocity distributions at the inlet, exit and interface planes proving that the repeating stage model is a very economical and accurate alternative to the very expensive complete multistage simulations.
Exposure of Ceramics and Ceramic Matrix Composites in Simulated and Actual Combustor Environments
Authors: More Karren L. , Tortorelli Peter F. , Ferber Mattison K. , Walker Larry R. , Keiser James R. , Miriyala Narendernath , Brentnall William D. , Price Jeffrey R.
Published: December 2014

A high-temperature, high-pressure, tube furnace has been used to evaluate the long term stability of different monolithic ceramic and ceramic matrix composite materials in a simulated combustor environment. All of the tests have been run at 150 psia, 1204°C, and 15% steam in incremental 500 h runs. The major advantage of this system is the high sample throughput; >20 samples can be exposed in each tube at the same time under similar exposure conditions. Microstructural evaluations of the samples were conducted after each 500 h exposure to characterize the extent of surface damage, to calculate surface recession rates, and to determine degradation mechanisms for the different materials. The validity of this exposure rig for simulating real combustor environments was established by comparing materials exposed in the test rig and combustor liner materials exposed for similar times in an actual gas turbine combustor under commercial operating conditions.
Nitrogen Oxide Reduction by Staged Combustion of Biomass Gas in Gas Turbines — A Modeling Study of the Effect of Mixing
Authors: Coda Zabetta Edgardo G. , Kilpinen Pia T. , Hupa Mikko M. , Leppälahti Jukka K. , Ståhl C. Krister O. , Cannon Michael F. , Nieminen Jorma J.
Published: December 2014

Detailed chemical kinetic modeling has been used to study the reduction of nitrogen oxides at gas turbine (GT) combustor conditions. A gas from gasification of wood with air has been used as the fuel. An air-staged combustion technique has been adapted.

In our previous study a simple plug flow model was used to study the effects of pressure and temperature among others process variables. The air-fuel mixing was assumed perfect and instantaneous. Results showed the NOx reduction mainly affected by both pressure and temperature.

The aim of the present work is to establish the effect of air-fuel mixing delay on NOx predictions and to extrapolate indications options for GT. To model the mixing delay, a varying number of air sub-streams are mixed with the fuel gas during different time periods. Alternatively, a combination of a perfectly mixed zone followed by a plug flow zone is illustrated.

Results by any air-fuel mixing model show similar affect of process variables on NOx reduction. When a mixing delay is assumed instead of the instantaneous mixing the NOx reduction is enhanced, and only with delayed mixing NOx are affected by CH4.

Lower temperature and higher pressure in the GT-combustor can enhance the NOx reduction. Also air staging is an effective option: a 3 stages combustor designed for low mixing speed appear competitive compared to more complicate combustors. The fewer hydrocarbons in the gasification gas the high NOx reduction.
The Role of Sulfur in the Thermal Stability of Jet Fuel
Authors: Naegeli David W.
Published: December 2014

The autoxidation of Jet A, dodecane, and a dodecane-15%-cumene blend doped with sulfur compounds were studied at 433 K. Oxygen, hydro peroxide and soluble gum were monitored during the autoxidation. Dodecane, cumene, and the dodecane-15%-cumene blend autoxidized rapidly, while Jet A had an induction period followed by a relatively slow post autoxidation. The results suggest that an inhibitor formed early in the post autoxidation of Jet A. Gum formed in the autoxidation of Jet A, whereas none was detected in dodecane, cumene, or dodecane-15% cumene. However, gum was detected in dodecane and dodecane-15% cumene doped with thiols and disulfides. Alkyl thiols and disulfides reduced the rate of autoxidation of dodecane, and there was an induction period in the formation of gum. Traces of sulfur (≈4 ppm) inhibited the autoxidation of dodecane-15% cumene in a way that resembled the post autoxidation of Jet A. Adding an organic base increased the rate of post autoxidation in Jet A and prevented formation of the oxidation inhibitor. An inhibition mechanism is proposed in which phenois are formed via acid-catalyzed decomposition of benzylic hydro peroxides.
Fuel Droplet Evaporation in a Supercritical Environment
Authors: Zhu G. S. , Aggarwal S. K.
Published: December 2014

This paper reports a numerical investigation of the transcritical and supercritical droplet vaporization phenomena. The simulation is based on the time-dependent conservation equations for liquid and gas phases, pressure-dependent variable thermophysical properties, and a detailed treatment of liquid-vapor phase equilibrium at the droplet surface. The numerical solution of the two-phase equations employs an arbitrary Eulerian-Lagrangian, explicit-implicit method with a dynamically adaptive mesh. Three different equations of state (EOS), namely the Redlich-Kwong (RK), the Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) EOS, are employed to represent phase equilibrium at the droplet surface. In addition, two different methods are used to determine the liquid density. Results indicate that the predictions of RK-EOS are significantly different from those obtained by using the RK-EOS and SRK-EOS. For the phase-equilibrium of n-heptane-nitrogen system, the RK-EOS predicts higher liquid-phase solubility of nitrogen, higher fuel vapor concentration, lower critical-mixing-state temperature, and lower enthalpy of vaporization. As a consequence, it significantly overpredicts droplet vaporization rates, and underpredicts droplet lifetimes compared to those predicted by PR- and SRK-EOS. In contrast, predictions using the PR-EOS and SRK-EOS show excellent agreement with each other and with experimental data over a wide range of conditions. A detailed investigation of the transcritical droplet vaporization phenomena indicates that at low to moderate ambient temperatures, the droplet lifetime first increases and then decreases as the ambient pressure is increased. At high ambient temperatures, however, the droplet lifetime decreases monotonically with pressure. This behavior is in accord with the reported experimental data.
A Method for the Diagnosis of Gas Turbine Sensor Faults in Presence of Measurement Noise
Authors: Bettocchi R. , Spina P. R.
Published: December 2014

This paper presents a method for the detection and isolation of single gas turbine sensor faults, in presence of model inaccuracy and measurement noise.

The method uses a fault matrix with a column-canonical structure (i.e., each matrix column having the same number of zeroes, but in different positions), in order to obtain the unambiguous fault isolation.

The fault matrix was obtained by using a number of ARX (Auto Regressive exogenous) MISO (Multi-Input/Single-Output) models equal to the number of measured gas turbine outputs, each model calculating an estimate of one measurable output as a function of other inputs or outputs measured on the machine.

Moreover, in order to reduce the threshold of fault detection and, therefore, the minimal detectable faults, digital filters were used, applied to the time series of data measured on the machine and computed by the models.

Finally, tests were performed in order to find the minimal sensor faults that can be detected and isolated.
Pyrometric Gas and Surface Temperature Measurements
Authors: Fralick Gustave , Ng Daniel
Published: December 2014

A multiwavelength pyrometer possessing advantages over the one- and two-wavelength designs is described. Results of its application to surface temperature measurements of ceramics is presented. Also described is a probe suitable for gas temperature measurements to temperatures > 2600 K. The design of the probe includes a multiwavelength pyrometer with fiber optic input.
Turbine Inlet Gas Temperature Sensor
Authors: Glasheen W. Michael , DeMilo Charles A. , Sivathanu Yudaya R.
Published: December 2014

A practical turbine inlet gas temperature sensor (TIGTS) has been designed, fabricated and evaluated both numerically and experimentally. The sensor remotely measures the hot gas spectral radiation intensities at several discrete wavelengths and obtains the Planck-function weighted temperature of the optical path using a look-up-table.

A high temperature optical head collects the radiation intensities emitted by hot gases along a narrow path. The radiation is transmitted using optical fibers to a quadrant detector which measures the intensities at four discrete wavelengths within the spectral bands of water vapor and carbon dioxide. After analog signal processing, under microprocessor control, the signals are digitized. They are input to a look-up-table which was obtained with stochastically generated gas concentrations and temperatures in conjunction with the narrow-band radiation calculation model, RADCAL.
Ceramic Gas Turbine Technology Development
Authors: Schenk Bjoern
Published: December 2014

AlliedSignal Engines is addressing the critical concerns that are slowing commercialization of structural ceramics in gas turbines. The 331-200[CT] auxiliary power unit (APU) test bed features ceramic first-stage nozzles and blades. Fabrication of ceramic components provides manufacturing process demonstration scale-up to the minimum levels needed for commercial viability. On-site endurance tests are demonstrating component reliability, and additional field testing in APUs onboard commercial aircraft and stationary industrial engines is planned.

Manufacturing scale-up activities showed significant progress during 1998. Subcontractors AlliedSignal Ceramic Components (Torrance, CA) and Kyocera Industrial Ceramics Corporation (Vancouver, WA) transitioned process refinements to full demonstration. Both suppliers achieved demonstration capability of ceramic nozzle production at the rate of 100 pieces/month. These suppliers are also developing fixed processes to fabricate ceramic integrally-bladed turbine rotor disks (“blisks”).

Ceramic design technology advanced, and 776 hours engine operational testing of a ceramic blisk were successfully completed. Ceramic turbine nozzles were readied for planned field demonstrations, with 2.213 hours of engine endurance testing completed. High-temperature ceramic material tests in the cyclic oxidation test rigs were initiated, to establish functional operating temperature limits for current silicon nitride materials in gas turbine environments.

This work was funded as part of the Turbine Engine Technologies Program by the U.S. Dept. of Energy Office of Transportation Technologies under Contract No. DE-AC02-96EE50454.
Numerical Analysis of Rotating Flexible Blade-Disk-Shaft Systems
Authors: Repetski O. , Rygikov I. , Springer H.
Published: December 2014

The theory, the algorithms and program package BLADIS (BLAded DIsk Simulation) for strength calculations of rotating flexible blade-disk-shaft assemblies have been worked out. The formulation is based on a finite element analysis of the rotating cyclic structures and modal reduction. The stresses in different zones of the structural components due to influence of centrifugal and temperature forces using static analysis and vibration are calculated. The results obtained show, how shaft flexibility influence on stresses and frequencies. Analysis of influence of blade geometric parameters on disk-shaft stresses is presented. The results obtained by dynamic analysis show that the chosen reduction does not reduce the quality of the model and illustrate its capability to deal with rotating shafts usually calculated using the rotordynamic approach. Finally, the possible dynamic interactions between shaft and disk components are described. This information is used for bladed disks and rotors optimization leading to a reduction of resonance displacements, stress levels and shifts of natural frequencies of rotating flexible blade-disk-shaft assemblies from dangerous resonances. The numerical results are carried in leading machine building companies in Russia.
A Spread Sheet as a Tool in Turbomachinery Design
Authors: Engeda Abraham
Published: December 2014

Despite great advances in computations, industry still relies on empirical based one dimensional design in turbomachinery.

In colleges and universities that offer turbomachinery education, even the one dimensional design becomes a very complex exercise unless the procedure is programmed. Due to lengthy calculations and iterations, simple solutions are not possible. Design exercises have therefore been limited in the classroom. But recent advances in powerful spreadsheets have opened a simple and fast way of performing turbomachinery design.

This paper describes a typical current compressor design challenge in industry and how a student deals with the design and analysis using a spreadsheet.
Underplatform Dampers for Turbine Blades: Theoretical Modelling, Analysis and Comparison With Experimental Data
Authors: Sanliturk Kenan Y. , Ewins David J. , Stanbridge Anthony B.
Published: December 2014

This paper describes a theoretical model for analysing the dynamic characteristics of wedge-shaped underplatform dampers for turbine blades, with the objective that this model can be used to minimise the need for conducting expensive experiments for optimising such dampers. The theoretical model presented in the paper has several distinct features to achieve this objective including: (i) it makes use of experimentally-measured contact characteristics (hysteresis loops) for description of the basic contact behaviour of a given material combination with representative surface finish, (ii) the damper motion between the blade platform locations is determined according to the motion of the platforms, (iii) three-dimensional damper motion is included in the model, and (iv) normal load variation across the contact surfaces during vibration is included, thereby accommodating contact opening and closing during vibration.

A dedicated non-linear vibration analysis program has been developed for this study and predictions have been verified against experimental data obtained from two test rigs. Two cantilever beams were used to simulate turbine blades with real underplatform dampers in the first experiment. The second experiment comprised real turbine blades with real underplatform damper. Correlation of the predictions and the experimental results revealed that the analysis can predict (i) the optimum damping condition, (ii) the amount of response reduction and (iii) the natural frequency shift caused by friction dampers, all with acceptable accuracy. It has also been shown that the most commonly-used underplatform dampers in practice are prone to rolling motion, an effect which reduces the damping in certain modes of vibration usually described as the lower nodal diameter bladed-disc modes.
Friction Damper Optimisation: Simulation of Rainbow Tests
Authors: Sanliturk Kenan Y. , Ewins David J. , Elliott Robert , Green Jeff S.
Published: December 2014

Friction dampers have been used to reduce turbine blade vibration levels for a considerable period of time. However, optimal design of these dampers has been quite difficult due both to a lack of adequate theoretical predictions and to difficulties in conducting reliable experiments. One of the difficulties of damper weight optimisation via the experimental route has been the inevitable effects of mistuning. Also, conducting separate experiments for different damper weights involves excessive cost. Therefore, current practice in the turbomachinery industry has been to conduct so-called ‘rainbow tests’ where friction dampers with different weights are placed between blades with a predefined configuration. However, it has been observed that some rainbow test results have been difficult to interpret and have been inconclusive for determining the optimum damper weight for a given bladed-disc assembly.

A new method of analysis — a combination of Harmonic Balance Method and structural modification approaches — is presented in this paper for the analysis of structures with friction interfaces and the method is applied to search for qualitative answers about the so-called ‘rainbow tests’ in turbomachinery applications. A simple lumped-parameter model of a bladed-disc model was used and different damper weights were modelled using friction elements with different characteristics. Resonance response levels were obtained for bladed discs with various numbers of blades under various engine-order excitations. It was found that rainbow tests, where friction dampers with different weights are used on the same bladed-disc assembly, can be used to find the optimum damper weight if the mode of vibration concerned has weak blade-to-blade coupling (the case where the disc is almost rigid and blades vibrate almost independently from each other). Otherwise, it is very difficult to draw any reliable conclusion from such expensive experiments.
Secondary Flow Reduction in a Nozzle Guide Vane Cascade by Non-Axisymmetric End-Wall Profiling
Authors: Yan J. , Gregory-Smith D. G. , Walker P. J.
Published: December 2014

A linear cascade of HP steam turbine nozzle guide vanes was designed and built in order to study the effect of a non-axisymmetric profile for the endwall. The profile was designed by using CFD for the purpose of reducing the secondary flow. The method was to use convex curvature near the pressure surface to reduce the static pressure and concave curvature near the suction surface to increase it. Thus the cross passage pressure gradient which drives the secondary flow would be reduced. Detailed investigations of the flow field with a flat end-wall and the profiled end-wall were conducted. The effect of the profiled end-wall on the secondary flow development was determined and also compared with the CFD design predictions. It was found that the secondary loss and secondary kinetic energy were both reduced by about 20% with the shaped endwall, and a more uniform exit flow was also achieved.
The Flow Field in the Tip Clearance Region of an Axial Compressor Rotor
Authors: Arima Toshiyuki , Shirotori Masatoshi , Yamaguchi Yoshihiro
Published: December 2014

A three-dimensional, Reynolds-averaged, compressible Navier-Stokes analysis (using a multi-block grid with the grid embedded in the tip-clearance space) has been developed to study the tip-clearance flow of an axial compressor rotor. A low-Reynolds number k-ε model have been used to reproduce the effects of turbulence. In order to assess the effect of the tip-clearance-grid treatment on prediction for the tip-clearance flow, calculations using a single-block grid (pinched grid topology) and multi-block grid (embedded grid topology) have been performed to calculate the flow field of NASA Rotor 37. The results are compared with experimental data. It has been found that both the single-block and multi-block approaches give a good agreement with the experimental data regarding the overall performance map of the rotor. For the prediction of the spanwise distributions of averaged aerodynamic properties downstream of the rotor, however, the orderly grid over the blade tip associated with the embedded grid has produced accurate predictions particularly from 40% to 80% span. In order to investigate the tip-clearance flow for different operating conditions, calculations have been performed for conditions at 100% (transonic inflow condition) and 60% (subsonic inflow condition) of the design point speed. Computed limiting streamlines at the blade tip surface and particle traces released from the tip-clearance have been used to study the tip-clearance flow. At the 100% speed, both separation and reattachment lines have been observed and a separation bubble occurs. At the 60% speed, the separation line shifts to the blade pressure side and the reattachment line can be partly observed near the leading edge of the blade tip surface. In order to investigate the interaction of the leakage vortex from the tip clearance with the main flow, the computed secondary flows on the cross-flow sections have been analyzed at the 100% and the 60% speeds. At the 100% speed, the vortex core apparently increases in size, as it moves downstream. At 60% speed, the second vortex, first reported by Suder and Celestina in 1994, is barely observable. Furthermore, the trajectory of vortex core identified using a semi-analytical method has also been used to study the vortex motion in the flow field near the blade tip.
Detailed Flow Measurements at the Exit of a Mixed Flow Turbine Under Steady Flow Conditions
Authors: Karamanis N. , Martinez-Botas R. F. , Su C. C.
Published: December 2014

A detailed flow investigation downstream of two mixed-flow turbocharger turbines has been carried out at 50% and 70% design speeds, equivalent to 29,400 and 41,300 rpm respectively. The measurement technique used was laser Doppler velocimetry (LDV). The measurements were performed at a plane 9.5 mm behind the rotor trailing edge, they were resolved in a blade-to-blade sense to fully examine the nature of the flow. The results confirmed the performance tests and indicated the improved performance of the rotor with a constant inlet blade angle relative to the rotor with a nominally constant incidence angle.
Effects of Alloy Composition on the Performance of Yttria Stabilized Zirconia–Thermal Barrier Coatings
Authors: Kimmel Josh , Mutasim Zaher , Brentnall William
Published: December 2014

Thermal barrier coatings (TBCs) provide an alloy surface temperature reduction when applied to turbine component surfaces. Thermal barrier coatings can be used as a tool for the designer to augment the power and/or enhance the efficiency of gas turbine engines. TBCs have been used successfully in the aerospace industry for many years, with only limited use for industrial gas turbine applications. Industrial gas turbines operate for substantially longer cycles and time between overhauls, and thus endurance becomes a critical factor. There are many factors that affect the life of a TBC including the composition and microstructure of the base alloy and bond coating. Alloys such as Mar-M 247, CMSX-4 and CMSX-10 are materials used for high temperature turbine environments, and usually require protective and/or thermal barrier coatings for increased performance. Elements such as hafnium, rhenium, and yttrium have shown considerable improvements in the strength of these alloys. However these elements may result in varying effects on the coatability and environmental performance of these alloys. This paper discusses the effects of these elements on the performance of thermal barrier coatings.
Ceramic Stationary Gas Turbine Development Program: Sixth Annual Summary
Authors: Price Jeffrey R. , Jimenez Oscar , Parthasarathy Vijay , Miriyala Narendernath
Published: December 2014

The Ceramic Stationary Gas Turbine (CSGT) program is being performed under the sponsorship of the United States Department of Energy, Office of Industrial Technologies. The objective of the program is to improve the performance of stationary gas turbines in cogeneration through the selective replacement of cooled metallic hot section components with uncooled ceramic parts. This review summarizes the progress on Phase III of the program which involves field testing of the ceramic components at a cogeneration end user site and characterization of the ceramic components following the field test exposure.

The Solar Centaur 50S engine, which operates a turbine rotor inlet temperature (TRIT) of 1010°C (1850°F), was selected for the developmental program. The program goals include an increase in the TRIT to 1121°C (2050 °F), accompanied by increases in thermal efficiency and output power. This will be accomplished by the incorporation of uncooled ceramic first stage blades and nozzles, and a “hot wall” ceramic combustor liner. The performance improvements are attributable to the increase in TRIT and the reduction in cooling air requirements for the ceramic parts. The “hot wall” ceramic liners also enable a reduction in gas turbine emissions of NOx and CO.

The component design and material selection have been definitized for the ceramic blades, nozzles and combustor liners. Each of these ceramic component designs were successfully tested in short term engine tests in the Centaur 50S engine test cell facility at Solar. Based on the results of the engine testing of the ceramic components, minor redesigns of the ceramic/metallic attachments were conducted where necessary. Based on their performance in a 100 hour cyclic in-house engine test, the ceramic components are approved for field testing. To date, four field installations of the CSGT Centaur 50S engine totaling over 4000 hours of operation have been initiated under the program at an industrial cogeneration site. This paper discusses the component design and material selection, in house engine testing, field testing, and component characterization.
Reductions in Acquisition Costs for State of the Art Fabrication of CFCC Turbine Engine Combustor Liners
Authors: Craig Phillip A. , Godfrey David
Published: December 2014

Through work in two U.S. Department of Energy cooperative programs with industry, the confidence level for utilization of ceramic composite SiC/SiC combustor liners has risen from a prototype curiosity to serious planning and addressing of hurdles for commercialization. One of the most significant hurdles for true commercialization is affordability of the ceramic composite combustor liners. To study the manufacturing costs for CFCC liners, a study was conducted to identify cost items and relationships. This report describes the effort, identifies the high impact areas of manufacturing costs, and recommends potential approaches to reducing the manufacturing costs.
Acoustic Instabilities in Syngas Fired Combustion Chambers
Authors: Klein Sikke A. , Kok Jim B. W.
Published: December 2014

Gas turbines fired on syngas may show thermo-acoustic combustion instabilities. The theory on these instabilities is well developed. From this theory it can be shown that the acoustic system of a combustion installation can be described as a control loop with a set of transfer functions. The transfer function of the flame plays a decisive role in the occurrence of combustion instabilities. It is however very difficult to predict this flame transfer function analytically. In this paper a numerical method will be presented to calculate the flame transfer function from time-dependent combustion calculations. Also an experimental method will be discussed to determine this flame transfer function. Experiments have been performed in a 25 kW atmospheric test rig. Also calculations have been done for this situation. The agreement between the measurements and CFD calculations is good, especially for the phase at higher frequencies. This opens the way to apply CFD-modeling for acoustics in a real gas turbine situation.
The Hybrid Cycle: Integration of Turbomachinery With a Fuel Cell
Authors: Ali Sy A. , Moritz Robert R.
Published: December 2014

In the deregulated electric utility environment, distributed power is expected to play a major role in meeting national power generation requirements of the 21st century. Compliance with environmental regulations and ultra-high efficiency will be attributes in penetrating distributed power markets. Fuel cell/turbomachinery hybrids are poised to become the first choice for these applications, yielding emissions of nitrogen oxides below 2 ppmv and low CO2 emissions due to high efficiency (>70% in 20 MW power packages). The challenges faced by hybrid systems are: system integration, power electronics/power conditioning, system controls, operational and transient dynamics, and commercial system cost. Opportunities to use existing gas turbines as the selected turbomachinery are being investigated, prompted by size flexibility and the savings in time and investment that this offers. This paper is an attempt to address the opportunities and challenges posed by a variety of fuel cell/turbomachinery hybrids.
Natural Gas Fired Combined Cycles With Low CO2 Emissions
Authors: Chiesa Paolo , Consonni Stefano
Published: December 2014

This paper assesses performances and economic viability of CO2 removal by chemical absorption from the flue gases of natural gas-fired Combined Cycles, more specifically for two configurations: one where CO2 is removed ahead of the stack without modifying the power cycle; the other where part of the flue gases is recirculated to the gas turbine, thereby reducing the flow to be treated by chemical absorption. In both cases sequestered CO2 is made available at conditions suitable to storage into deep oceanic waters.

Performances and cost of electricity are evaluated for systems based on large, heavy-duty turbines representative of state of the art “FA” technology. Carbon sequestration reduces net plant efficiency and power output by about 10% and increases the cost of electricity from 36 to about 50 mills/kWh. Flue gas recirculation warrants slightly higher efficiencies and lower costs.

CO2 removal is eventually compared with other strategies for the reduction of CO2 emissions, like switching existing coal-fired steam plants to natural gas or replacing existing steam plants with conventional CCs. At current fuel prices the latter appears the option of choice, with a cost of about 25 $ per tonn of avoided CO2 emission.
Identification of Mistuning Characteristics of Bladed Disks From Free Response Data — Part II
Authors: Mignolet Marc P. , Delor Jason P. , Rivas-Guerra Alejandro
Published: December 2014

The focus of the present investigation is on the estimation of the dynamic properties, i.e. masses, stiffnesses, natural frequencies, mode shapes and their statistical distributions, of turbomachine blades to be used in the accurate prediction of the forced response of mistuned bladed disks. As input to this process, it is assumed that the lowest natural frequencies of the blades alone have been experimentally measured, for example in a broach block test.

Since the number of measurements is always less than the number of unknowns, this problem is indeterminate in nature. Three distinct approaches will be investigated to resolve the shortfall of data. The first one relies on the imposition of as many constraints as needed to insure a unique solution to this identification problem. Specifically, the mode shapes and modal masses of the blades are set to their design/tuned counterparts while the modal stiffnesses are varied from blade-to-blade to match the measured natural frequencies. The second approach, based on the maximum likelihood principle, yields estimates of all the structural parameters of the blades through the minimization of a specified “cost function”. Finally, the third approach provides a bridge between the first two methods being based on the second but yielding a mistuning model similar to that of the first approach. The accuracy of these three techniques in predicting the forced response of mistuned bladed disks will be assessed on simple dynamic models of the blades.