bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of Cassette-Tube Airheaters as a Way to Improve the Mass-Size Characteristics of Regenerative Gas-Turbine Units
Authors: Soudarev A. V. , Soudarev B. V. , Soudarev V. B. , Kondratiev A. A. , Avran P.
Published: December 2014

To produce a new generation of gas-pumping units and to upgrade the existing ones, the producer needs to update their heat exchange equipment. The aim of the update is to decrease its mass and sizes and to reduce its manufacturing and assembly costs. Heat-hydraulic calculations and experiments with models of the gas-turbine plant cassette-tube airheaters demonstrated that application of profiled U-tubes of a small hydraulic diameter to manufacture the matrices of such heat exchangers provides a high compactness and low metal consumption rate typical for plate heat exchangers. Simplicaty, reliability, elasticity and maintainability which are typical characteristics of tube heat exchangers are retaned.
Rotordynamic Force Prediction of Whirling Centrifugal Impeller Shroud Passages Using Computational Fluid Dynamic Techniques
Authors: Moore J. Jeffrey , Palazzolo Alan B.
Published: December 2014

The demand for higher efficiencies and performance of modern centrifugal turbomachinery requires improved knowledge of critical design factors in strength of materials, aerodynamics, and rotordynamics. While tremendous strides in finite element stress analysis and computational fluid dynamics (CFD) have addressed the first two areas, the lack of accurate prediction tools for centrifugal impellers typically leaves rotordynamics out of the design loop. While several authors have analyzed the rotordynamic forces arising from shrouded centrifugal impellers, there has been no study to couple the secondary shroud passage with the three-dimensional primary flow model. The strong interaction between these domains makes this approach advantageous. The current study utilizes CFD techniques to analyze the full 3D viscous, primary/secondary flow field in a centrifugal pump impeller to determine rotordynamic forces. Multiple quasi-steady solutions of an eccentric, 3D model at different precessional frequency ratios yield the rotordynamic impedance forces. Performing a second order, least-squares analysis generates the skew-symmetric stiffness, damping, and mass matrices. The results show good correlation with experiment for both performance and rotordynamic forces.
A Proposal for Integration of Wind Tunnel and Engine Test Programs for the Evaluation of Airframe-Propulsion Compatibility Using Numerical Simulations
Authors: Davis Milt , Baker William , Power Greg , Beale Dave
Published: December 2014

The current high-performance aircraft development programs, and the trends in research and development activities suggest a rapidly increasing level of aircraft subsystem integration, particularly between the airframe/inlet and the propulsion system. Traditionally these subsystems have been designed, analyzed, and tested as isolated systems. The interaction between the subsystems is modeled primarily through evaluating inlet distortion in an inlet test and simulating this distortion in engine tests via screens or similar devices. In the current paper, an overview of current techniques for inlet performance and distortion characterization and engine distortion testing is presented. A review of the current state-of-the-art in inlet analysis is also presented along with a discussion of current engine analysis techniques, from a semi-empirical approach to high-fidelity full Navier-Stokes simulations. Finally, a proposal to coordinate the existing test techniques and analysis capabilities to provide a truly integrated inlet-engine test and evaluation capability is outlined.
Study of the Filtration Process Through a Ceramic Candle Filter
Authors: Al-Hajeri M. , Aroussi A. , Pickering S. J.
Published: December 2014

Ceramic candle filters have been developed for cleaning high-temperature high-pressure (HTHP) gas streams. They meet environmental and economical considerations in Combined cycle power plant, where gas turbine blades can be protected from the erosion that occurs due to using HTHP exhaust from the fluidized bed. Ceramic candle filters are the most promising hot gas filtration technology, which has demonstrated high collection efficiencies at high-temperature high-pressure conditions.

This paper reports a computational fluid dynamics (CFD) investigation of a candle filter. Constant filtration velocity boundary models have been used to investigate the filter in cross flow conditions using the CFD code FLUENT. Different approach (inlet) velocity to filter face velocity ratios and different face velocities (ranging from 2 to 5 cm/s) are used in the CFD calculation. Particles in the diameter range 1 to 100 microns are tracked through the domain. The radius of convergence (or the critical trajectory) is compared and plotted as a function of many parameters. The deposition process and the factors that affect the build up of the filter cake have also been studied.
3D Modelling of NOx Emissions From an Aircraft Afterburner
Authors: Foster T. J. , Wilson C. W. , Pourkashanian M. , Williams A.
Published: December 2014

Aircraft fitted with afterburner systems for increased thrust have been observed to have NOx emissions with a higher proportion of nitrogen dioxide (NO2) than non-augmented aircraft. These emissions are generally characterised by a brown plume and has implications for aircraft visibility and stealth as well as environmental considerations. This paper describes the CFD modelling of NOx emissions from a modern afterburner system with particular emphasis on the formation of nitric oxide (NO) and the subsequent conversion of NO to NO2.

A commercial CFD code, was used to solve a three dimensional model of a “burn then mix” afterburner system under investigation. A post processor package has been developed and was used to calculate both NO and NO2 concentrations. Four reheat settings were investigated; minimum, 25%, 50% and maximum reheat. For all conditions investigated the bulk of NOx emission was found in the core, stemming from the vitiated combustor air flow. NOx was also formed in the bypass stream, the production zone was found to be close to the fuel sprayers and flame stabiliser at minimum reheat, but moved downstream towards the exit nozzle as reheat power was increased. The model showed that for all the conditions under investigation, over 90% of the NOx produced in the reheat system was formed via the thermal-NO route.

The model has been compared with centre-line traverse data measured at the exit nozzle of the engine on a sea level static test bed. The predicted NOx emissions agreed quantitatively with the experimental measurements to within ± 5%.
A New Durable Gas Turbine Recuperator
Authors: Oswald James I. , Dawson David A. , Clawley Lee A.
Published: December 2014

A new recuperator has been developed at Rolls-Royce, specifically designed to address the problems recuperators traditionally experience in withstanding thermal cycling and high cost associated with production complexity. Unlike existing recuperators it is made from two continuous sheets of metal wound into a spiral form. It is believed to be the only recuperator in the world manufactured as a continuous process and therefore has inherently lower cost. A significant increase in thermal fatigue resistance relative to state of the art recuperators is achieved due to the compliant structure and careful design of the heat exchanger matrix.

A technology acquisition programme has been carried out which has involved the design, manufacture and rig testing of recuperator cores. The success of the work is now leading to the continuation of the programme to address the application of this technology to specific engine developments from microturbines of 40kW to large industrial and marine turbines of 20MW.
Upgrading of a Small Size Gas Turbine to HAT Cycle Operation: Thermodynamic and Economic Analysis
Authors: Desideri Umberto , Di Maria Francesco
Published: December 2014

A detailed study is presented in this paper concerning the changes required to transform a GE/Nuovo Pignone PGT2 gas turbine into a humid air turbine (HAT). The PGT2 is a 2 MW single-shaft gas turbine with a two stage centrifugal compressor and single can combustor. These features of the compressor and the combustion chamber are very important, because they reduce to a minimum the modifications necessary to add all the components required for operation in HAT cycle mode.

This paper shows the performance of the PGT2 gas turbine in three different modified configurations: 1) regenerated cycle, 2) intercooled-regenerated cycle and 3) HAT cycle with flue gas condensation. A detailed economic study is presented of the regenerated and the HAT cycles. The intercooled-regenerated cycle was not considered in the economic analysis, because it does not reach the performance of the HAT cycle but it has not the advantage of being a dry cycle.

All the components being added to the PGT2 are sized to determine with a sufficient accuracy their cost. The economic analysis presents a detailed cost analysis of the optimal configurations for maximum efficiency, and allows the calculation of the capital cost of the modified gas turbine. Return of investment is also presented in different economic situations with varying electricity and fuel prices.
The Influence of a Variable Capacity Turbine in the Performance of a Variable Cycle Engine
Authors: Dodds Martin , Pilidis Pericles
Published: December 2014

An investigation was conducted to examine the effects of a variable flow low pressure turbine on a variable cycle engine’s performance.

One of the greatest challenges, during the design of a variable cycle engine is how to optimise the various cycles and then to match then to the capabilities of the engine components, the use of extensive variable geometry is required to achieve this.

A method of matching variable cycle engines that was developed Cranfield University was adapted to cater for the use of a variable flow low pressure turbine. It was discovered that the implementation of variable geometry within the low pressure turbine could significantly reduce the requirements for variable geometry within the compressor system, at the cost of replacing well proven compressor variable geometry with high risk technology within the LP turbine.

Utilising the variable flow turbine to expand the bypass ratio range of the engine was studied. Increasing the LPM bypass ratio to 1.1 and 1.2 yielded SFC reductions of 3% and 5% respectively, reducing the bypass ratio of the HPM to 0.1 gave a 20% increase in specific thrust. It was found that the performance benefits gained from expanding the bypass ratio are large enough to warrant further investigation into this concept.
Handling of a Semiclosed Cycle Gas Turbine With a Carbon Dioxide-Argon Working Fluid
Authors: Ulizar Inaki , Pilidis Pericles
Published: December 2014

This paper outlines the handling of a semi closed cycle gas turbine, its working fluid is carbon dioxide and the fuel is low heating value gas from coal. At startup however, air and natural gas are used. The objective of the machine is to produce clean electricity with the smallest efficiency penalty.

Many aspects of the operation of the engine are examined here; these include starting requirements, stator vane and bleed valve scheduling and the working fluid transition from air to carbon dioxide. Other features highlighted are the compressor operating lines and surge margins. The present paper describes the salient features of the three main stages into which the engine operation has been divided. These stages are: startup to synchronous idle, change of working fluid (from air to Carbon Dioxide-Argon) and fuel (from natural gas to coal synthetic gas) at synchronous idle and part load operation.

Preliminary findings show that engine handling can be carried out effectively with variable stators. This is possible because of the two shaft gas generator. Another point of interest is the large increase of corrected speed relative to rotational speed experienced when the working fluid changes from air to carbon dioxide. In general the control of the engine does not seem to present any insurmountable problems despite the complexities arising from the need to change working fluid and fuel.
CM 186 LC® Alloy Single Crystal Turbine Vanes
Authors: Burkholder Phil S. , Thomas Malcolm C. , Helmink Randy , Frasier Donald J. , Harris Ken , Wahl Jacqueline B.
Published: December 2014

There is a need to introduce advanced turbine technology at reduced cost. SX superalloy vanes demonstrate excellent engine performance and durability benefits compared to their polycrystalline counterparts. However, their manufacturing cost can be prohibitive due to low casting and solution heat treatment yields due to rejectable grain defects. High purity (carbon and boron free), ultra high creep and fatigue strength SX alloys are limited to low angle boundaries (LABs) normally not exceeding 6° in critical airfoil locations. Carbon (C) and boron (B) containing SX superalloys (Ross, et al., 1996) can accommodate low angle boundaries in the 9°–12° range with an overall sacrifice in creep and fatigue properties. Aero engine vane segments with complex configurations, can result in not only LAB defects exceeding 9°–12° but also high angle grain boundary (HAB) defects ≥ 15° occurring during the SX solidification process. This is further excaberated by recrystallised grains occurring during solution heat treatment from residual casting stresses and associated strain.

CM 186 LC® is a hafnium (Hf) containing nickel-base superalloy developed for directionally solidified (DS) columnar grain turbine airfoils. SX casting experience — development and production — has shown the alloy can be readily cast into aero turbine multi-airfoil segments. Mechanical property and turbine engine testing show the alloy can accommodate grain boundaries at least up to 30° resulting in high SX casting yields. The SX vane components are either used as-cast or approximately 50% partial solutioned which avoid any recrystallisation (Rx) problems. Component costs can be < 50% of that of a conventional high purity SX alloy.

Mechanical property, oxidation and coating performance characterisation studies on SX CM 186 LC (including DS test pieces) and turbine engine test and application experience show a 72°F (40°C) metal temperature capability improvement (thin wall) over DS MAR M 002 alloy.
Protruded Four-Point Bending Testing Method and Characterization of Near Interface Cracking in Thermal Barrier Coatings
Authors: Zhang Zhehua , Bloomer T. E. , Kameda J. , Sakurai S.
Published: December 2014

A protruded four-point bending testing method has been developed to characterize the crack initiation of thermal barrier coatings (TBC) near the interface. Two types of protruded TBC specimens, with and without a reinforcement attached on the top of the protruded TBC, were prepared from in-service used transition ducts made of TBC (6% Y2O3 stabilized ZrO2) and bond coatings (NiCoCrAlY) plasma-sprayed over a superalloy substrate. In the unreinforced protruded TBC specimen tests, pre-existing TBC cracks extended in the transverse direction while near interface TBC cracking did not occur. The reinforced protruded TBC specimen hindered the transverse TBC cracking and allowed the formation of TBC cracks adjacent to the oxidized TBC/bond coating interface in a similar mode to in-service TBC spalling. The onset of TBC cracks was identified by a change in the loading rate in the elastic deformation regime. The local stress distribution at the edges of the reinforced protruded TBC was analyzed using finite element analysis. The critical local tensile stress for the initiation of TBC cracks near the interface was estimated for the in-service used transition duct. The near interface TBC cracking behavior in the protruded TBC tests is discussed in light of the applied and residual stress distribution.
NESTEM: A Computational Tool to Perform Probabilistic Structural Analysis of Components Subjected to Uncertain Mechanical and Thermal Loading
Authors: Patel Bhogilal M. , Strack William C. , Nagpal Vinod , Pai Shantaram S. , Murthy P. L. N.
Published: December 2014

This paper presents an overview of a newly developed code, NESTEM that analyzes structural components subjected to varying thermal and mechanical loads. This program is an enhanced version of NESSUS and has all the capabilities of NESSUS. In addition, it allows one to perform heat transfer analysis. The basic heat transfer variables can be included as random variables along with the mechanical random variables to quantify risk using probabilistic methods and to perform sensitivity analysis.

The analysis capabilities of NESTEM have been demonstrated by analyzing a cylindrical combustor liner. This analysis includes evaluating stresses and their variations at critical points on the liner using material properties, pressure loading and basic heat transfer variables as the random variables. The heat transfer variables are convection temperatures, film coefficients, radiation temperatures, emissivity, absorptivity and conductivity. Cumulative distribution functions and sensitivity factors, for stress responses, for mechanical and thermal random variables are calculated. These results can be used to quickly identify the most critical design variables, in order to optimize the design, to make it cost effective.
A Correlation for Tip Leakage Blockage in Compressor Blade Passages
Authors: Hoeger M. , Lahmer M. , Dupslaff M. , Fritsch G.
Published: December 2014

3D multistage Navier-Stokes simulations for compressor components, rigs and cascades have been analyzed to gain insight into the tip leakage blockage evolution. From pitch-averaged flow quantities the local displacement caused by tip leakage is determined by means of a novel technique. Close to the throat an additional displacement of about 1–4% axial chord is observed for unchoked flow conditions. With tip gap height, stagger and inlet Mach number as governing variables a correlation for the tip leakage blockage transition function in blade passages is established, which may be used to improve the predictive capability of S1/S2 compressor aerodesign systems.
Antisurge Control for Variable Geometry Compressors
Authors: Batson B. W.
Published: December 2014

Compressors used for industrial applications are sometimes fitted with some form of variable geometry. Centrifugal compressors may have adjustable inlet guide vanes on one or multiple stages, or diffuser guide vanes at the discharge of the compressor. Axial compressors often have variable inlet guide vanes or adjustable stators. Such variable geometry compressors are becoming more common in the petroleum and chemical industries.

For many variable geometry compressors (but not all), the boundary between the stable operating region and surge is a surface, not just a curve.

In this paper, we discuss which forms of variable geometry result in a surge limit curve and which forms spread out into a surface. We describe some methods for determining the location of the operating point relative to the surge limit. An example is included showing actual surge points as found in the field. Surge testing to determine the complete surge limit surface is discussed.
Recommendations for Achieving Accurate Numerical Simulation of Tip Clearance Flows in Transonic Compressor Rotors
Authors: Van Zante Dale E. , Strazisar Anthony J. , Wood Jerry R. , Hathaway Michael D. , Okiishi Theodore H.
Published: December 2014

The tip clearance flows of transonic compressor rotors are important because they have a significant impact on rotor and stage performance. While numerical simulations of these flows are quite sophisticated, they are seldom verified through rigorous comparisons of numerical and measured data because these kinds of measurements are rare in the detail necessary to be useful in high-speed machines. In this paper we compare measured tip-clearance flow details (e.g. trajectory and radial extent) with corresponding data obtained from a numerical simulation. Recommendations for achieving accurate numerical simulation of tip clearance flows are presented based on this comparison. Laser Doppler Velocimeter (LDV) measurements acquired in a transonic compressor rotor, NASA Rotor 35, are used. The tip clearance flow field of this transonic rotor was simulated using a Navier-Stokes turbomachinery solver that incorporates an advanced k-ε turbulence model derived for flows that are not in local equilibrium. Comparison between measured and simulated results indicates that simulation accuracy is primarily dependent upon the ability of the numerical code to resolve important details of a wall-bounded shear layer formed by the relative motion between the over-tip leakage flow and the shroud wall. A simple method is presented for determining the strength of this shear layer.
Ceramic Component Development for Agata
Authors: Lundberg Robert , Ferrato Marc
Published: December 2014

The European EUREKA project, EU 209, also known as AGATA (Advanced Gas Turbine for Automobiles), is a programme dedicated to the development of three critical ceramic components — a catalytic combustor, a radial turbine wheel and a static heat exchanger — for a 60 kW turbogenerator in a hybrid electric vehicle. These three components, which are of critical importance to the achievement of low emissions and high efficiency, have been designed, developed, manufactured and tested as part of a full scale feasibility study. AGATA is a joint project conducted by eight commercial companies and four research institutes in France and Sweden. This paper outlines the main results of the AGATA project with special emphasis to the development of ceramic components.
The Evaluation of CFCC Liners After Field-Engine Testing in a Gas Turbine
Authors: Miriyala Narendernath , Simpson Jane F. , Parthasarathy Vijay M. , Brentnall William D.
Published: December 2014

In a program sponsored by the U.S. Department of Energy (DOE), Solar Turbines Incorporated is currently investigating the use of ceramics in industrial gas turbines by selectively replacing cooled metallic components with uncooled ceramic parts. As part of this program, Solar has developed CFCC (SiC/SiC) combustor liners and demonstrated their potential for low emissions in three field-engine tests for a total duration of over 3000 hours. The durability of the SiC/SiC liners appears to be primarily limited by surface recession, composite embrittlement and fiber degradation (particularly for CG-Nicalon). The microstructural, mechanical properties, and nondestructive evaluation of the CFCC liners after the three field tests are discussed in this paper.
A Study of Combustion Characteristics of Gasified Coal Fuel
Authors: Hasegawa Takeharu , Sato Mikio , Nakata Toshihiko
Published: December 2014

The development of integrated, coal-gasification combined cycle (IGCC) systems provides cost-effective and environmentally sound options for meeting future coal-utilizing power generation needs in the world. The Japanese government and the Electric Power Industries in Japan promoted research and development of an IGCC system. We have being working on developing a low-NOx combustion technology used in gas turbine combustors for IGCC.

Each gaseous fuel produced from some raw materials contained CO and H2 as the main combustible components, and a small amount of CH4. Compositions and calorific values of gasified coal fuels varied widely depending on raw materials and gasifier types. Gaseous fuel, produced in various gasifiers, has a calorific value of 4–13MJ/m 3, which is about one-tenth to one-third that of natural gas. The flame temperatures of fuels increase as the fuel calorific value rises. When the fuel calorific value rises 8MJ/m 3 or higher, the flame temperature is higher than that of natural gas, and so NOx production from nitrogen fixation is expected to increase significantly. Also, some gasified coal fuels contain fuel nitrogen, such as ammonia, if the hot/dry type gas cleaning system is employed. These factors affect the combustion characteristics of the gasified coal fuel.

In this paper, we clarified the influence of gasified coal fuel properties on NOx and CO emissions through experiments using a small diffusion burner and through numerical analysis based on reaction kinetics. The main results were as follows:

(1) NH3 conversion to NOx increases with increasing CH4 concentration in gaseous fuel.

(2) If gaseous fuel contains CH4, there will be some specific equivalence ratio in the primary combustion zone for the minimum NH3 conversion to NOx in the two-staged combustion.

(3) Its specific equivalence ratio in the primary combustion zone increases with decreasing CH4 concentration in gaseous fuel.

(4) If the fuel contains a small percent of CH4, there is no influence of the CO/H2 molar ratio in the fuel on the conversion rate of NH3 to NOx, while there is an influence in the case where fuel contains no CH4. The conversion rate increases with rises in the CO/H2 molar ratio.

(5) As the pressure increases, the conversion rate of NH3 to NOx slightly decreases and the CO emission declines significantly.
Developmental Status of Hybrids
Authors: Layne Abbie , Samuelsen Scott , Williams Mark , Hoffman Patricia
Published: December 2014

Fuel cells are emerging as a major new power generation technology that is particularly suitable for distributed power generation, high-efficiency, and low pollutant emission. An interesting combined cycle, the “HYBRID,” has recently been scoped “on paper” that portends the potential of ultra-high efficiency (approaching 80%) in which a gas turbine is synergistically combined with a fuel cell into a unique combined cycle. This paper introduces hybrid technology to the gas turbine community as a whole, and summarizes the current and projected activities associated with this emerging concept.
The Need for Standards to Promote Low Emission, High Efficiency Gas Turbine Facilities
Authors: Klein Manfred
Published: December 2014

Gas turbine cogeneration and district energy plants can provide significant environmental improvements to the long term mix of energy production, in terms of low air pollutants and greenhouse gases. This paper is intended to discuss the fundamental need to integrate plant efficiency considerations into the environmental permitting rules to address all air issues at the same time, as described in the 1992 Canadian gas turbine emission guideline. The paper also compares the relevant air emissions, primarily nitrogen oxides (NOx) and carbon dioxide (CO2), from modern gas turbine plants, and the Canadian operating experience with cost-effective emission prevention methods.
Simulation and Optimized Dispatch of a Complex Cogenerating Combined Cycle in a Competitive Market
Authors: Griffin Patrick R. , Jia Gangyi , Gielen Martijn H. C. , Dalstra Nynke G.
Published: December 2014

A software system was developed to simulate technical performance and predict feasible, economically optimum operating arrangements for a multi-faceted cogenerating combined cycle. The software combines detailed technical performance data with commodity prices and contractual obligations to predict equipment loads that optimize net plant revenue subject to several operational constraints. The optimization technique is iterative due to the nonlinear behavior of the plant. Detailed production capability of each plant component is pre-simulated over the entire range of operation using a widely-accepted, commercially-available simulation package. Pre-simulated results are stored in look-up tables for fast evaluation during optimization calculations. This paper describes the plant equipment, the optimization technique, and illustrates how the software output guides plant management in strategic planning and operations in an evolving competitive electric and gas market.
Comparison of Theoretical and Experimental Data for an Oscillating Transonic Compressor Cascade
Authors: Carstens Volker , Schmitt Stefan
Published: December 2014

Numerical and experimental results are compared for a compressor cascade performing harmonic oscillations in transonic flow. The flow field was calculated by a Q3D Navier Stokes code, the basic features of which are the use of an upwind flux difference scheme for the convective terms, the implementation of an effective one-equation turbulence model and the use of deforming multi-block grids. The experimental investigations were performed in an annular cascade windtunnel where unsteady blade pressures were measured for two different operating conditions of the cascade.

The present data were all obtained for tuned torsional modes where the blades performed pitching oscillations with the same frequency and amplitude, but with a constant interblade phase angle. In the first test case the steady flow around the blades was purely subsonic. For the second test case the compressor cascade was run under transonic flow conditions where a normal shock in the front part of the blades’ suction side is followed by a blade passage shock.

It becomes apparent that under subsonic flow conditions the predicted aerodynamic damping coefficients are in resonable agreement with the experimental data, although the numerical pressure amplitudes are much higher than the measured ones. In transonic flow significant discrepancies between computed and experimentally determined pressure amplitudes are observed, whereas the accuracy of the pressure phase prediction is comparable to the subsonic test case. Another important result of these investigations is that oscillations of the blade passage shock lead to strong variations of the local aerodynamic damping of the blades, but do not significantly change the global damping coefficient of the tested compressor cascade.
Dynamic Stability in a Cracked Turbo Blade-Disk
Authors: Kuang J. H. , Huang B. W.
Published: December 2014

Analysis of the stability in a cracked blade-disk system is proposed. The effect of modal localization on the stability in a rotating blade-disk was studied. A crack near the root of a blade is regarded as a local disorder in this periodically coupled blade system. Hamilton’s principle and Galerkin’s method were used to formulate the equations of motion for the cracked blade-disk. The instability regions of this cracked blade-disk system were specified by employing the multiple scales perturbation method. Numerical results indicate that the rotation speed, shroud stiffness and crack depth in the blades affect the stability regions of this mistuned system significantly.
Instability Pathology of a High Speed Centrifugal Compressor
Authors: Oakes William C. , Lawless Patrick B. , Fleeter Sanford
Published: December 2014

An experimental investigation is performed to characterize a high-speed centrifugal compressor as it approaches instability and during subsequent surge cycles. To achieve this, data are analyzed from the inlet, the diffuser and the exit of the compressor. Analysis of the data indicates the presence of two rotating stall modes prior to and during surge cycles. A nine cell mode pattern is shown to erupt prior to the initial surge cycle. The second rotating stall mode is a single cell mode that coincides with the initiation of the surge cycles. Both stall modes are shown to be located at or near the diffuser.
Flow Field Measurements in an Annular Gas Turbine Exhaust Diffuser With Struts
Authors: Desideri Umberto , Ubertini Stefano
Published: December 2014

This paper presents the velocity and turbulence characteristics of the flow in an annular diffuser, which is a model of a gas turbine exhaust diffuser with six struts. The diffuser where the measurements were made is a scaled down model of a 10 MW gas turbine, built by GE/Nuovo Pignone.

In a previous paper (Desideri and Manfrida, 1995) 2-D turbulence and velocity measurements were presented with axial inlet velocity conditions.

In this paper a more detailed 3-D analysis of the design and off design behavior of the diffuser is presented. Turbulence characteristics were determined by means of two hot split-film probes, which allowed measuring axial, radial and tangential components of the mean velocity and their fluctuating components. The measuring point is moved inside the diffuser by means of two step-motors, which allow the rotation of the hub and the radial displacement of the probe.

Off-design behavior of the annular diffuser was determined by changing the inlet velocity angle of 10° from axial direction. The effect of swirl on the performance of the diffuser will be presented.

Turbulence microscales were also calculated in regions of interest inside the diffuser, with particular attention to the strut wake.
The 701F Gas Turbine Design Process: Upgrade and Innovations
Authors: Facchini B. , Carcasci C. , Ferrara G. , Innocenti L. , Coutandin D. , Monzi G. , Protto S.
Published: December 2014

In this paper, a Fiat Avio 701F gas turbine re-design process is presented. This already tested gas turbine has been modified, for a particular re-powering application: a reduction in the net power production is required, whereas efficiency and exhaust temperature have been improved by mean of increased hot gas temperature at the first nozzle inlet section. Consequently this re-powering solution clearly requires consistent re-design efforts to satisfy specific plant operating conditions.

The gas turbine power output has been tuned to the required value by reducing the air inlet mass flowrate; the combustion chamber setting has been modified with particular attention to the control of pollutant emission level. The increase of inlet stator turbine temperature necessitated a complete review of the three cooled turbine stages. The aim of greater overall efficiency with inlet and exit turbine temperature increase also involved the introduction of a new blade material. For design tool flexibility the blade cooling design procedure has been improved making better optimization of the cooling system possible.

In this paper a detailed description of the several gas turbine modifications with particular attention to the blade cooling design procedure and to the corresponding simulation results is reported. The modifications developed could also be introduced on the new version of the 701F, at full power capability, in order to get better efficiency and power.
Turbulence Intensity, Length Scale, and Heat Transfer Around Stagnation Line of Cylinder and Model Blade
Authors: Maslov V. P. , Mineev B. I. , Pichkov K. N. , Secundov A. N. , Vorobiev A. N. , Strelets M. Kh. , Travin A. K.
Published: December 2014

A hot-wire technique was used to measure turbulence characteristics in the vicinity of the stagnation line of circular cylinders and a turbine blade model (a chord length of 1 metre). Heat transfer intensity at the stagnation line of the cylinders was also measured by on-surface probes. The experiments were carried out in a wide range of the Reynolds number based on the blade leading edge/cylinder diameter, D (Re = 2.103–2.106) and integral length scale of free-stream turbulence, Le (Le = 0.1–10D) at two values of free stream turbulence intensity, Tu (Tu = 0.02 and 0.10). Along with the experimental data results of the 2D RANS computations are presented of the flow and heat transfer at the circular cylinder with the use of two turbulence models: a two-equation, k-ω SST, model of Menter, and a new two-equation, ν1-L, model developed in the course of the present study.
Coating Stripping Method for Refurbishing of Gas Turbine Blades and Vanes
Authors: Corcoruto Sergio , Guerreschi Umberto , Gandini Ettore
Published: December 2014

Hot gas path components (blades, vanes, heat shields...) in modern gas turbines are protected against hot corrosion and oxidation by MCrAlY overlay coatings deposited throughout Vacuum Plasma Spray (VPS) process. These coatings are designed to be consumed during the operation of the engine. To extend the life of the parts the exhausted coatings must be removed without damage to the base material, so already used parts could be reapplied with new coatings and returned to service.

A stripping method has been developed in alternative to the acid stripping. The originality of the method is in using a spraying process to deposit onto the MCrAlY coating a layer of aluminium, followed by a diffusion heat treatment in vacuum. The resulting brittle aluminide layer is easily removed by mechanical means, like grit blasting.

The aluminium spraying process has been developed for turbine blades and vanes with a plasma gun positioned on a six axis robot, while uncoated areas are stopped off from aluminising. The penetration of aluminium is controlled by proper heat treatment parameters to guarantee uniformity and repeatability. The capability of recoating stripped parts as new ones has been verified.
Experimental Investigation on the Operational Stability of Multistage Centrifugal Compression Systems
Authors: Nie Chaoqun , Chen Jingyi , Jiang Haokang
Published: December 2014

The operational stability of three multistage centrifugal compression systems was studied experimentally. Two of the tested machines are four-stage centrifugal compressors arranged in two cylinders and used for air separation. The third machine is a ten-stage compressor in two cylinders and used for oxygen production. The measurement features conventional probes for describing performances and per-stage pressure transducers for recording dynamic characteristics. The performance measurement was conducted for the entire machine and also per stages. The signal of dynamic pressures was analyzed in both time and frequency domains. The result of per-stage performances clearly indicated which stage is first to lose the operational stability and how far it happens before the whole system runs into the stability boundary. This result is further demonstrated by the commencing time and location of stages of the strengthened dynamic pressure oscillation which differs from the most dangerous location in terms of maximum amplitude of the pressure oscillation during surge. The knowledge thus obtained for the operational stability should serve a good basis for monitoring and control purposes when running the machine in multistage compression environment.
Improvement of Flow Field in Vaned Diffuser for Centrifugal Compressor Through Flow Field Calculation
Authors: Tamaki Hideakl , Nakao Hidefumi
Published: December 2014

Flow field in the vaned diffuser was calculated with CFD code. In order to take the large flow angle difference of the impeller discharged flow between hub and shroud into account, measured total pressure and flow angle downstream of the impeller with vaneless diffuser were used as the inlet boundary condition. Calculated results were compared with the measured total pressure distribution at the exit of the vaned diffuser and the results of oil flow visualization at hub and shroud. According to the results of the calculation and measurements, the possibility of existence of the separated region near pressure surface at hub was shown from the compressor choke to peak efficiency. In order to reduce this separated region, the vaned diffuser whose shroud wall was pinched from just downstream of the diffuser throat to vaned diffuser exit was calculated and tested. The improvement of flow field and the pressure recovery in the vaned diffuser was confirmed with the measurement of the static pressure and the total pressure at the vaned diffuser exit. The efficiency of the compressor was also improved from the compressor choke to peak efficiency. This study shows that the reduction of separation near pressure side at hub is effective way to improve the vaned diffuser performance.
Optimization of a Vaned Diffuser Geometry for Radial Compressors: Part I — Investigation of the Influence of Geometry Parameters on Performance of a Diffuser
Authors: Kmecl Tomaz , Dalbert Peter
Published: December 2014

In the present investigation the influence of different diffuser geometry parameters on the stage efficiency and operating range of radial compressor stages has been studied. In addition to a parallel-walled vaneless diffuser, 20 vaned diffusers were experimentally tested with three different impellers having the same meridional contour. All diffusers were designed for industrial compressor stages with subsonic diffuser flow and had parallel sidewalls, diffuser vanes with simple circular are profiles of constant thickness and rounded leading edges.

In the first part of this investigation the length of the vaneless space, the number of diffuser vanes, the vane length, the inlet vane angle of a diffuser, and the solidity have been altered systematically.

The results show that the throat area of a diffuser, and consequently the number of diffuser vanes, are the most important parameters affecting the operating range of a diffuser. The vaneless space extent and the diffuser vane inlet angle have a significant effect on diffuser efficiency, while their effect on operating range is much smaller. Changing these two parameters induces primarily a shift of diffuser characteristics. The diffuser vane length is a very important parameter at overload, where high losses in a diffuser channel occur when using a long diffuser vane.
Stall Inception in a 5-Stage HP-Compressor With Increased Load due to Inlet Distortion
Authors: Jahnen Werner , Peters Thomas , Fottner Leonhard
Published: December 2014

Unsteady measurements of the flow and performance of a high speed 5-stage HP compressor have been carried out at different speeds under undistorted conditions and with swirl and total pressure inlet distortions. Distributions of incidence and diffusion factor have been derived from the test data which, together with hot-wire measurements of stall inception, provide new insights into the onset of stall with inlet distortion.

A stall cell initiates as a disturbance in the distorted flow sector, which may decay as it passes through the undistorted sector. Stall inception occurs only when the damping of the disturbance in the undistorted sector is insufficient to prevail its growth. As this damping depends on the size of the disturbance, the Parallel Compressor model, based on the linear stability properties of the undistorted compressor alone, is unable to predict the stall inception with inlet distortion.
Catalytic Combustor Development Within the AGATA Program
Authors: Gabrielsson Rolf , Payen Gerard , Avran Patrick
Published: December 2014

The European AGATA programme (Advanced Gas Turbine for Automobiles), is a programme dedicated to the development of three critical ceramic components — a catalytic combustor, a radial turbine wheel and a static heat exchanger — for a 60 kW turbogenerator in a hybrid electric vehicle. These three components, which are of critical importance to the achievement of low emissions and high efficiency, have been designed, developed, manufactured and tested as part of a full-scale feasibility study. The AGATA partners represent car manufacturers as well as companies and research institutes in the turbine, catalyst and ceramic material fields in both France and Sweden. The AGATA project commenced in early 1993 and has occupied a 5-year period until April 1998. This paper summarises the results from the development of the catalytic combustor.

The catalytic combustor operates at temperatures in the catalytic section from inlet 935°C to the exhaust 1350°C. Therefore all structural components in the hot section are made of ceramic materials.

The testing and validation have been run through a component test campaign from which it was concluded that:

• The catalytic section substrates showed good behaviour during the high temperature tests.

• Palladium was chosen as the active catalytic material after extensive testing at pilot scale. Ageing at high temperature (1270°C) has a strong effect on catalyst deactivation.

• Emissions levels of the preheater are in agreement with the state of the an for small aero-engines according to the ICAO legislation.

The complete full scale combustor testing was run in the following steps:

• Initial gas analysis tests at inlet temperature 200° lower than the nominal value

• CARS and gas analysis

• Comparison diesel and ethanol fuels

• Final testing at maximum design temperatures and pressure

The catalytic combustor was run on diesel fuel during the complete test period. A test campaign comparing exhaust emissions when running on ethanol fuel was performed at Volvo Aero Turbines. These results showed that the catalyst reaction rate and CO/HC/NOx emissions were similar. This means that the chosen catalytic combustor can be used as a dual fuel combustor diesel/ethanol.

The final test campaign at ONERA, France, was run up to temperatures slightly above the specified maximum design temperatures. Inlet temperature 962°C (design 935°C) and exhaust temperature 1362°C (design 1350°C). These tests showed that NOx emission levels below 4 ppm @15% O2 were obtained when low CO and HC emissions levels were measured at full load conditions. This promising performance level was reached with technologies that still have to be thoroughly evaluated in terms of durability and low cost potential for industrial applications.
Probabilistic Analyses of HSCT Combustor Liner Components
Authors: Pai Shantaram S. , Murthy P. L. N.
Published: December 2014

Deterministic as well as probabilistic analysis results for a typical cylindrical combustor liner segment is presented in this paper. The type of liner segment analyzed in this report is a part of a HSCT combustor. In the analyses, thermal profiles, material stiffnesses, and mechanical loadings are considered random. Probabilistic static, stability and free vibration analysis were conducted and results are presented in the form of cumulative distribution functions for critical location stresses, and buckling load. The results indicated that scatter in thermal loads and thermal expansion coefficients have significant impact on the longitudinal and hoop stresses. Also, the thickness variations appeared to be most significant, in influencing the probabilistic buckling behavior. Collectively, the results provide an insight on dominant variables which could be used for reliable/robust combustor liner design.
An Interactive Methodology for Axial Compressor Design Teaching
Authors: Ramsden K. W.
Published: December 2014

The implementation of new technology in the gas turbine industry is accelerating at a rate which demands increasing specialisation by its engineering design staff. Simultaneously, this industry has been adopting concurrent engineering practices to reduce product lead-time. Accordingly, the industry now requires its engineers to acquire early competence in a wide range of technological disciplines. In addition, the individual must have a thorough understanding of the impact of component design decisions on both other components and on the engine as a whole.

Against this background, gas turbine educational providers must respond to these increasing demands with teaching programmes that facilitate a faster and deeper understanding of this very complex product. The ambition of the teacher, however, to adequately prepare the student will continue to be limited by time constraints within lecture courses. Hitherto, this has normally resulted in class worked examples which are necessarily narrow in scope and confined to a limited range of design cases.

This paper describes a teaching methodology which is structured to facilitate in-depth understanding of the key interactions between aerodynamics, thermodynamics and mechanical integrity arising in axial compressor design optimisation. This is achieved interactively through a combination of lectures, a hand worked multistage preliminary compressor design, a series of personal computer based design optimisation workshops and a final collective design assessment.