bluuebunny/crossref_metadata_2025 huggingface dataset:
Materials Issues for High-Temperature Components in Indirectly-Fired Cycles
Authors: Wright Ian G. , Stringer John
Published: December 2014

Indirectly-fired cycles provide one means of using a fuel other than natural gas or distillates of various purities to generate power using a gas turbine. In a closed cycle, the fuel typically is used to heat a clean working fluid which is then expanded through a gas turbine, after which it is cooled and recompressed before being recirculated through the heating circuit. In an open cycle, the heated working fluid (usually air) is exhausted to the atmosphere after expansion in the turbine and passage through heat recovery devices. In both cases, the temperature of the working fluid may be boosted before entry to the turbine by supplementary firing of a premium fuel such as natural gas in a topping combustor. A major advantage of such indirectly-fired cycles is that the concerns arising from the use of a dirty fuel in other advanced cycles are confined to the fireside surfaces of the heat exchange equipment, whereas the gas turbine is exposed to a relatively benign environment. One limitation of such systems is that the emissions problems are the same as for a conventional coal-fired boiler although, on an power output-normalized basis, the emissions from an indirectly-fired cycle may be lower. The requirements of the potential candidate materials for the various components in the circuit are discussed, and the critical issues for each are identified.
Chemically Reactive Flow of Hot Combustion Gases in an Aircraft Turbo-Jet Engine
Authors: Godin Th. , Harvey S. , Stouffs P.
Published: December 2014

Current progress in gas turbine performance is achieved mainly by increasing the turbine inlet temperature. State-of-the-art military aircraft gas turbines operate with turbine inlet temperatures exceeding 2000 K, and future development plans call for even higher temperature levels. At such high temperatures, the hot combustion gases can no longer be considered as chemically inert, and it becomes important to account for the chemically reactive nature of the expanding flow. In this paper, the authors present a one-dimensional model of the chemically reactive flow through the first turbine stage of an aircraft turbo-jet engine. The model is used to study the impact of chemical reactivity on pollutant emission characteristics and engine performance (i.e., overall efficiency and specific thrust). Three different flight conditions are considered: sea-level static operation (take-off), subsonic cruising at 10000 meters altitude, and supersonic flight at 20000 meters altitude. The results of this study show that typical flight conditions and operating parameters of turbo-jet engines produce high pollutant emission levels and decrease overall efficiency and specific thrust.
Acoustically Controlled Combustor NOx
Authors: Vermeulen Peter J. , Ramesh Venkataramanayya
Published: December 2014

Successful NOx measurements in the end plane of the primary zone of a small tubular gaseous fuelled combustor of conventional gas turbine design, employing acoustic driving of the combustor via the air inlet pipe, have been made at scaled 1/8 load operating conditions. The acoustic drive caused partial blockage of the combustor primary zone air flow which increased the equivalence ratio in the plane of the NOx measurements. The mixing was acoustically augmented which together with the blockage richening significantly changed the combustor mean NOx-mean equivalence ratio characteristic in the end plane of the combustor primary zone. Under lean-conditions at 1/8 load and “with-drive” at 246 Hz mean NOx was reduced indicating that a value of 10ppm (50% reduction) is possible, confirming previous results. Under rich-conditions NOx “with-drive” at 246 Hz might be reduced by 23%, relative to previous results, and even might reach the “no-drive” value of about 25ppm, which was possibly due to acoustic augmentation of the primary zone aerodynamics. The NOx at the combustor exhaust “with-drive” should be even lower than that measured “with-drive” because of normal dilution. Therefore, the technique has the potential to create a low NOx conventional combustor without requiring the complicated design-changes of current industry efforts.
Contaminants in a Gas Turbine Fuel System and Thermal Shock
Authors: Newbound Timothy D. , Norek Richard. S.
Published: December 2014

Thermal shock has emerged as a probable cause of random cracking in gas turbine hot gas path parts fueled by sweet gas from Eastern Province gas plants in Saudi Arabia. Fuel is distributed to combustion gas turbines in a central Ghawar water injection plant approximately 50 km away through a series of pipelines above grade. To combat the damaging effects of condensates in fuel gas, two stage particle/demister filters were installed on the gas turbines at this plant. Inspections of the filters that protect five WIP drivers, model MS-5002B/AT, have been carried out after 13,000 to 17,000 operating hours. An analytical evaluation of solids recovered from the filters revealed evidence of condensates in the fuel gas including water soluble salts, iron hydroxides and heavy hydrocarbons. There was damage to four out of five particulate filter elements, elemental sulfur found in filter catches, erosion of a stop valve stem, and cracks in the turbine nozzles with no cracks in the buckets’ coating. All of these problems could be attributed to the presence of solid and liquid contaminants in the fuel gas. HYSIM calculations on upstream fuel gas samples support the potential for condensate and gas hydrates, particularly in cooler weather. The results of this study have led to the recommendation to install coalescing filters on gas turbines operating on this sweet gas fuel system. Suspected sources of moisture and heavy hydrocarbons resulting in sudden changes in fuel gas composition and the potential for damage due to thermal shock will be presented.
Redesign of the MS6001 First Stage Bucket for Improved Cooling and Extended Life
Authors: Jaqueway Jerry K. , Pistor Robert J.
Published: December 2014

The objective of this paper is to critically review the cooling design for the MS6001 first stage buckets and examine alternate designs for improved cooling. Several basic designs were considered to improve cooling performance, extend service life, and improve the reliability of the first stage bucket. Of the designs being considered and compared with existing and past designs, two options containing 13 and 13M (modified) cooling holes were investigated. The target for the design which was met by the 13M design, was to reduce bucket bulk metal temperature by an average of 13.9°C (25°F), while maintaining current unit performance and bucket integrity. Finite element analysis was performed to evaluate the aerofoil thermal gradients and the results demonstrate that a cooler core and an overall reduction in bulk metal temperature was obtained with the modified designs. In addition to the design analysis, bucket alloys were reviewed and IN-738 was chosen for its reliability and predictable performance.
Developing a Cooperative International Program in Graduate Education and Research
Authors: Oliveras Juan , Barrett Lloyd E. , Flack Ronald D.
Published: December 2014

This paper describes cooperative research and graduate instructional activities by the University of Virginia (UVA) and Universidad Simon Bolivar (USB) which focus on research and developments in rotor dynamics and turbomachinery, including gas turbines. The cooperative efforts have been underway since 1991. Both universities have independently developed programs in this area with strong ties to industry. At the University of Virginia a program has been in place for 25 years that specializes in rotor dynamics, bearings, seals, turbomachine flows; including an industrial consortium base of over 40 companies. The program at the University of Virginia comprises the typical curricula in the US for Master of Engineering, Master of Science, and Doctoral degrees. Universidad Simon Bolivar has more recently developed a Postgraduate Program for engineers in the Venezuelan oil and petrochemical industry. The course focuses on turbomachinery issues, has the typical academic structure of a Master of Engineering with a duration of two years, and is tailored to the needs of students working full time in industry. Multiple cooperative efforts have proceeded in a number of areas. UVA faculty have taught portions of the Postgraduate courses at USB; USB and UVA faculty have developed joint research projects; USB faculty have conducted research activities and taught at UVA; and several USB faculty have attended UVA to obtain graduate degrees. Discussions between the two universities are underway to permit the exchange of course credits for graduate degrees; the final aim is to establish a Doctoral Program in the turbomachinery area at USB.
Failure Probability Prediction of Fast-Fractured NT451 SiAlON Diesel Exhaust Valves
Authors: Wereszczak Andrew A. , Kirkland Timothy P. , Ferber Mattison K. , Corum James M. , Peralta Alonso
Published: December 2014

The fast-fracture failure probability of a prototype NT451 SiAlON diesel exhaust valve was predicted using volume-censored flexure and tensile strength data. A tandem set of life prediction codes developed by AlliedSignal Engines was used to make these predictions in this exercise; these codes also yielded 95% confidence estimates on determined two-parameter Weibull distributions and failure probabilities. The prediction of fast-fracture failure probability was compared to actual NT451 SiAlON valve fast-fracture strengths. All the valves failed from volume-flaws, so volume-censored input strength data were required for the fast-fracture failure probability predictions. In addition to the failure probability predictions, the effects of several independent parameters on strength, and ultimately on the failure probability, were also examined in this exercise: the specimen geometry tested; specimen machining parameters consisting of grinding direction and grinding wheel grit size; and the utilization of a post-machining anneal. Within 95% confidence estimates, the effect of specimen geometry, machining parameters, and a post-machining anneal had no effect on the calculated Weibull Moduli and scaling parameters and the consequential predicted reliability.
Creep Life Prediction of Ceramic Components Subjected to Transient Tensile and Compressive Stress States
Authors: Jadaan Osama M. , Powers Lynn M. , Gyekenyesi John P.
Published: December 2014

The desirable properties of ceramics at high temperatures have generated interest in their use for structural applications such as in advanced turbine systems. Some of these ceramic components, such as vanes and rotors, are subjected to concurrent tensile and compressive stress fields. Design lives for such systems can exceed 10,000 hours. Such long life requirements necessitate subjecting the components to relatively low stresses. The combination of high temperatures and low stresses typically places failure for monolithic ceramics in the creep regime. The objective of this paper is to present a design methodology for predicting the lifetimes of structural components subjected to concurrent transient tensile and compressive creep stress states. In this methodology, failure generally starts at or near the most highly stressed point and subsequently propagates across the section. The creep rupture life is divided into two stages. The first is called the stage of latent failure. During this stage the damage accumulates until it becomes critical at some point within the component, and failure begins. Damage due to compressive stresses is assumed to be negligible. Subsequently, the second stage, named the propagation of failure, takes place. Component failure occurs at the end of this stage when the total carrying capacity of the structure is expended. This methodology utilizes commercially available finite element packages and takes into account the time varying creep stress distributions (stress relaxation). The creep life of a component is divided into short time steps, during which, the stress distribution is assumed constant. The damage is calculated for each time step based on a modified Monkmon-Grant creep rupture criterion. Failure is assumed to commence when the normalized accumulated damage at a point in the body is equal or greater than unity. For tensile/compressive stress states, rupture is assumed to take place when the damage zone is large enough so that the component is no longer able to sustain load. The corresponding time will be the creep rupture life for that component. Flexural and C-ring data of siliconized silicon carbide KX01 material are used to test the viability of this methodology. The NASA integrated design code CARES/Creep (Ceramics Analysis and Reliability Evaluation of Structures/Creep) which utilizes this damage accumulation model was used for this purpose. It was found that the methodology described in this paper yielded reasonable creep rupture life predictions given the amount of scatter in the data.
Effect of Machining Conditions on the Strength Distributions of Ground Ceramics
Authors: Kanematsu Wataru , Yamauchi Yukihiko , Ito Shoji
Published: December 2014

The relationship between strength distribution or ground ceramics and machining condition was examined. The strength of ground silicon carbide ceramics at the failure probability of 1 percent, which is termed 1 % strength, was estimated as a function of the maximum grain depth of cut g, which is used as an index of grinding conditions. It is assumed that the fracture is governed by the competing failure mechanism between pre-existing flaws and machining cracks and that the Weibull modulus of machining cracks was independent of grinding condition. The deviation from estimated value is noticeable in small g region although experimental data of the 1% strength of ground specimen approaches that of polished ones with diminishing g. The observed discrepancy is inferred to be attributed to an increase in stress intensity factor by the interaction between a pre-existing flaw and its adjacent machining crack.
Status of Silicon Nitride Component Fabrication Processes, Material Properties, and Applications
Authors: Pollinger John P.
Published: December 2014

Silicon nitride monolithic structural ceramic components have recently been introduced as production parts in commercial aircraft turbomachinery pump and seal applications to take advantage of their unique thermomechanical properties. Additionally, extensive efforts are in progress to develop, evaluate, and productionize silicon nitride components for commercial aircraft turbomachinery hot sections, industrial power generation turbines, and automotive hybrid vehicle turbogenerators. AlliedSignal Ceramic Components has developed a family of in-situ reinforced silicon nitride materials for these applications and is developing and implementing a suite of component fabrication processes to achieve production-viable manufacturing of complex shaped components, including turbine seals, blades, nozzles, wheels, and combustors. A key focus of the manufacturing process development is the need to achieve low cost fabrication of components in order to meet cost targets required for commercial introduction. Finally, the status and plans for a number of aerospace, industrial, and automotive turbomachinery applications are discussed, including commercial aircraft turbomachinery production components (pump and seal parts) and development components (auxiliary power unit turbine blades and nozzles, and propulsion engine wheels and starter wheels), nozzle, blade, wheel and combustor components for automotive hybrid vehicle turbogenerators, and turbine blades and nozzles for industrial power generation gas turbines.
HIPed Silicon Nitride Components for AGATA — A European Gas Turbine for Hybrid Vehicles
Authors: Lundberg Robert
Published: December 2014

The European EUREKA project, EU 209, otherwise 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 an hybrid electric vehicle. These three components, which are of critical importance to the achievement of low emissions and high efficiency, have been designed and developed and will be 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. Silicon nitride ceramics play an important role both in the development of the catalytic combustor and for the radial turbine wheel. This paper outlines the main results of the AGATA project with special emphasis to the development of HIPed Si3N4 combustor and turbine wheel. AC Cerama has developed a HIPed Si3N4 material designated CSN 101. This material has been selected for the catalytic combustor afterburner as well as for the radial turbine wheel. Mechanical properties of the CSN 101 Si3N4 have been found to be at the level of the best available high temperature Si3N4 materials. A new glass encapsulation technique using an interlayer between the glass and the silicon nitride has been shown to give material with excellent strength and creep resistance with as-HIPed surface finish.
Dynamic Instabilities in Natural-Circulation Evaporators of Vertical HRSGs
Authors: Payrhuber Klaus , Halozan Hermann
Published: December 2014

Dynamic instabilities become increasingly one of the design criteria for natural-circulation evaporators in Heat Recovery Steam Generators (HRSGs) of combined cycle power plants, especially in systems with a vertical gas duct. To calculate such instabilities, the computer program DEDYN is being developed. The calculation method has been presented at the ASME Cogen-Turbo Power 1995 in Vienna (Payrhuber, 1995).

This publication deals with modeling of a natural-circulation evaporator. The evaporator investigated in this paper consists of 340 parallel finned tubes in 4 layers of 16 meters (total tube length of one tube is 64 meters) and a total heat transfer surface of 16400 square meters. This heat exchanger bundle of a HRSG with a vertical duct is divided in 8 sub-ducts, which permits a calculation with local heating medium (= flue gas) temperatures. The inlet and outlet headers of this bundle are connected to a drum.

Several variations have been investigated like changing the operation pressure, different heights of the drum, subcooling when entering the downcomer, as well as parallel flow or counter flow through the evaporator tube bundle. The paper shows the boundary conditions for preventing or at least damping mass flow oscillations in the evaporator.
A Review of Some Current Problems in Gas Turbine Secondary Systems
Authors: Turner A. B. , Long C. A. , Childs P. R. N. , Hills N. J. , Millward J. A.
Published: December 2014

This paper reviews the current position of five major problem areas in gas turbine secondary air system design. Although the problems are of primary interest to the designer of the coolant flow paths, since they directly affect the temperature, the stresses and thus the life of the major rotating components, three of the problems interact with the main gas path and are thus also the concern of the mainstream aerodynamicist.

The five problems reviewed are: prediction of the flow distribution and heat transfer in the high pressure compressor drive cone cavity from the turbine to the rim of the HP compressor running underneath the combustion chamber, the flow penetration and heat transfer in the multiple rotating cavities formed by the multiple discs of the high pressure compressor with a rotating shaft running through the bores; the control of ingestion of hot turbine mainstream gas into the rotor-stator wheelspaces through the rim-seals; the problem of compressor and turbine stator-well heating, particularly compressor stator-wells in which excessive temperatures have been occasionally measured and finally, the pre-swirl coolant system which has to take the blade cooling air across from the stationary casing to the rotating turbine disc in the most advantageous manner.
Computational and Experimental Investigations of Straight-Through Labyrinth Seals
Authors: Prasad B. V. S. S. S. , Sethu Manavalan V. , Nanjunda Rao N.
Published: December 2014

Computational and experimental investigations are carried out to estimate leakage flow rate in a static straight-through labyrinth seal. Tests were conducted over a range of pressure ratios, varying from 1.003 to 1.897, for three clearance values of 0.2, 0.36 and 0.6 mm respectively. The measured values of leakage flow parameter are corroborated with the results obtained from the simulations using FLUENT computer package. The agreement was within 8.6%. The flow details, e.g., the stream line pattern, velocity vectors, static pressure and turbulent kinetic energy in a typical seal passage, are presented.
Turbine Airfoil External Heat Transfer Measurement in a Hot-Cascade
Authors: Zhang Luzeng J. , Glezer Boris
Published: December 2014

Detailed knowledge of local external heat transfer around a turbine airfoil is critical for an accurate prediction of metal temperature and component life. This paper discusses the results of measurements of the local gas side heat transfer coefficient distribution which were performed in an annular gas turbine vane hot-cascade test facility and provides comparisons with analytical predictions. The steady state tests were performed at simulated engine operating conditions. The tests were conducted on an internally cooled airfoil with the intent to provide close to uniform coolant temperature at the mid-span of the airfoil and also to obtain a high heat flux through the wall, minimizing uncertainty. Internal coolant side heal transfer coefficients were measured through calibration tests outside the cascade by a wire heater. A calibrated infrared pyrometer was used to provide detailed airfoil surface local temperatures and the corresponding external heat transfer coefficients. The airfoil was instrumented with a number of thermocouples for both calibration and temperature measurement. A 12% freestream turbulence was generated by a turbulence grid upstream of the test cascade. The static pressure measured over the test vane agreed well with invicid predictions. Heat transfer coefficients were measured and compared to a TEXSTAN boundary layer code prediction. The influence of Reynolds number and Mach number on the airfoil external heat transfer coefficient were also studied and is presented in the paper.
Quantitative Visualization of Full-Coverage Discrete-Hole Film Cooling
Authors: Fric Thomas F. , Campbell Robert P. , Rettig Mark G.
Published: December 2014

Water tunnel experiments were carried out to study full-coverage discrete-hole film cooling for geometries applicable to gas turbine combustor liners. The cooling holes were spaced at a pitch to diameter ratio of 6.5 and had an injection angle of 20° to the cooled surface. The mainstream flow direction was in line with the cooling holes. Blowing ratios from 0.5 to 5.7 were studied, which is a range typical of combustor liners.

A unique multiple plane PLIF (planar laser-induced fluorescence) technique was used to measure time-averaged film cooling concentration at various heights above the surface to be cooled. Three-dimensional data sets were generated to quantitatively visualize cooling-jet film coverage, structure, and interaction. Film coverage as close as 0.25 mm (0.010 in.) from the surface was measured, thereby yielding data that approach adiabatic film effectiveness. Two sets of film cooling experiments were conducted. One set used a model with a relatively small array of 2.54 mm (0.100 in.) holes, meant to be a large-scale model of hole sizes encountered in combustor liners. The second set used a large array of 0.51 mm (0.020 in.) nominal diameter laser-drilled holes, manufactured in the same manner as combustor liner cooling holes.

The results show that near-wall film coverage is minimum for blowing ratios from 1.7 to 3.3. At blowing ratios less than 1.7 and greater than 3.3, the film coverage was improved. Jet structure and interaction was also observed. In particular, jet separation behavior and coalescence were visualized, and both were generally a function of blowing ratio.
Self-Oscillating-Impinging-Jet as a Gas Turbine Cooling Enhancement System
Authors: Herr Frank , Camci Cengiz
Published: December 2014

Impinging jets are widely used in local enhancement of heat removed from internal passages of gas turbine blades. Arrays of stationary jets are usually impinged on inner surfaces of gas turbine blades exposed to severe thermal/hydrodynamic environment of hot mainstream gases. The current practice is to benefit from the high heat transfer coefficients existing in the immediate vicinity of the jet impingement region on a target wall. The present study shows that a self-oscillating impinging-jet configuration can be extremely beneficial in enhancing the heat removal performance of a conventional stationary impinging jet. In addition to a highly elevated stagnation line Nusselt number, the area coverage of the impingement zone is significantly enlarged because of the sweeping motion of the oscillating coolant jet. When an oscillating jet (Re = 14,000) is impinged on a plate normal to the jet axis (x/d = 24 hole to plate distance), a typical enhancement of Nu number on the stagnation line is shown to be 70 %. The present paper explains detailed fluid dynamics structure of the oscillating jet by using a triple decomposition technique on a crossed hot wire signal. High resolution heat transfer measurements are also presented in a Re number range between 7,500 and 14,000 (24<x/d<60). The current heat transfer enhancement levels achieved suggest that it is possible to implement the present self-oscillating-impinging-jet concept in future gas turbine cooling systems, on rotating disks, in electronic equipment cooling, aircraft de-icing systems and heat exchanger systems.
Effects of Incomplete Premixing on NOx Formation at Temperature and Pressure Conditions of LP Combustion Turbines
Authors: Rutar Teodora , Martin Scott M. , Nicol David G. , Malte Philip C. , Pratt David T.
Published: December 2014

A probability density function/chemical reactor model (PDF/CRM) is applied to study how NOx emissions vary with mean combustion temperature, inlet air temperature, and pressure for different degrees of premixing quality under lean-premixed (LP) gas turbine combustor conditions. Inlet air temperatures of 550, 650 and 750 K, and combustor pressures of 10, 14 and 30 atm are examined in different chemical reactor configurations. Primary results from this study are: incomplete premixing can either increase or decrease NOx emissions, depending on the primary zone stoichiometry; an Arrhenius-type plot of NOx emissions may have promise for assessing the premixer quality of lean-premixed combustors; and decreasing premixing quality enhances the influence of inlet air temperature and pressure on NOx emissions.
The Design of an Instructional Cogeneration Laboratory
Authors: Banta Andrew
Published: December 2014

California State University, Sacramento has designed and constructed a cogeneration laboratory for the instruction of students in modern electrical generation. This facility serves about 100 senior level students per year. The major components are a 75 kW gas turbine generator, a waste heat boiler and a small absorption chiller. Future plans include the addition of a 50 kW steam turbine.

The analytical design of this plant is described from concept to final layout with particular emphasis on cycle analysis, selection and sizing of components and instrumentation, and the layout of the equipment. A diagram showing the entire cycle on a scaled temperature entropy plot provides an interesting graphical interpretation of the plant’s operation. While the gas turbine has a relatively low pressure ratio of 3.3:1 and thus a low thermal efficiency, the addition of the other components improves the performance significantly.

An aspect of the analysis of particular interest is relating the cooling of the chiller to an equivalent work term thus enabling the determination of an overall thermal efficiency. If all of the steam were to be used for cooling the plant efficiency would improve slightly from 10% for the turbine alone; when made equivalent to other types of refrigeration the improvement is more than 6%. When all of the steam is used in the proposed steam turbine the efficiency will improve to about 17%. Using the chiller to cool inlet air to the gas turbine—thus increasing performance—is discussed at length. Student use of the laboratory is discussed briefly.

While the plant is quite small and intended for laboratory use, the design analysis is applicable to similar plants which might be used in remote locations, or as stand-by or peaking power supplies.
Full Coverage Discrete Hole Film Cooling: Investigation of the Effect of Variable Density Ratio (Part II)
Authors: Bazdidi-Tehrani F. , Andrews G. E.
Published: December 2014

Experimental results of the corrective film heat transfer coefficient at the hot gas-side of the wall for full coverage discrete hole film cooling are presented for a range of practical geometries. The results are reported for various hot gas mainstream-to-coolant temperature (density) ratios, in the realistic range of 1.0–3.2. For combustor wall and turbine blades film cooling applications, the corrective film heat transfer coefficient was influenced significantly by the design parameters. It decreased with an increase in the number of holes per unit wall surface area, over the range of 4306–26910 m−2 and with an increase in the hole size, in the range of 1.0–2.2 mm, due to the improvement in film cooling. This was supported by the overall cooling effectiveness results, as reported previously (Bazdidi-Tehrani and Andrews 1994). A comparison between the two approaches for the prediction of the convective film heat transfer coefficient was made. It showed that the higher wall overall heat transfer, obtained using the present measurements of the wall overall heat transfer coefficient, resulted in a considerably higher film heat transfer coefficient than that predicted using the summation of the hole approach surface correlation of Sparrow (1982) and the internal hole correlation of Mills (1962). The variation of the mainstream-to-coolant temperature ratio did not establish consistent trends for various configurations and its effect on the film cooling performance was shown to be small.
Detailed Off Design Flow Measurements in a Centrifugal Compressor Vaned Diffuser
Authors: Pinarbasi Ali , Johnson Mark W.
Published: December 2014

Three component hot wire measurements in the vaneless space and vane region of a low speed centrifugal compressor vaned diffuser are presented. These comprise mean velocity and turbulence level distributions for a below and above design flow rate for three vane-to-vane locations at each of five radial measurement stations.

The flow entering the diffuser closely resembles the classic jet-wake flow characteristic of centrifugal impeller discharges. A strong upstream influence of the diffuser vanes is observed which results in significant variations in flow quantities between the vane-to-vane locations. The circumferential variations due to the passage and blade wakes rapidly mix out in the vaneless space, although some variations are still discernible in the vaned region. Comparison with results in a vaneless diffuser suggest that the presence of the vanes accelerates this mixing out process.
Perspective on a Combustion-Free Gas Turbine to Meet Power Generation Needs in the 21st Century
Authors: McDonald Colin F.
Published: December 2014

The combustion gas turbine, operating in both simple and combined cycle modes, is rapidly becoming the preferred prime-mover for electrical power generation for both new plants, and in the repowering of old power stations. In replacing Rankine cycle plants the combustion gas turbine could become dominant in the power generation field early in the next century. Fired currently with natural gas, and later with gasified coal these gas turbines will operate for many decades with no concern about resource depletion. This paper addresses an extension of high efficiency gas turbine technology but uses a combustion and emission-free heat source, namely a high temperature gas cooled nuclear reactor. The motivation for this evolution is essentially twofold, 1) to introduce an environmentally benign plant that does not emit greenhouse gases, and 2) provide electrical power to nations that have no indigenous natural gas or coal supplies. This paper presents a confidence-building approach that eliminates risk towards the goal of making the nuclear gas turbine a reality in the 21st century.
Oxidation Behavior of Ceramics for Gas Turbines in Combustion Gas Flow at 1500°C
Authors: Etori Y. , Hisamatsu T. , Yuri I. , Yasutomi Y. , Machida T. , Wada K.
Published: December 2014

In order to evaluate the durability of silicon-carbides (SiC) and silicon-nitrides (Si3N4), we studied the oxidation behavior of SiC and Si3N4 in 1500°C combustion gas flow. We found that the exposure to the combustion gas flow resulted in the weight losses of those ceramics due to the partial disappearance of the oxidized surface layer.

We investigated the effects of sintering aids and high speed gas flow as possible factors for the disappearance of the oxide layer. Two kinds of SiC, without sintering aids and sintered with B4C, were used as test specimens. After the exposure to combustion gas flow conditions of 1500°C, 150m/s, 0.18MPa, the weight loss rate and thickness of the oxide layer were quite the same for each specimen of SiC. The existence of sintering aids did not have any effect on the disappearance of the oxide layer. To investigate the effect of gas flow, we set each specimen in a tube made of SiC to protect it from the gas flow. The tube had two holes each acting both as inlet and exhaust vents. Consequently, the oxide layer formed thickly. But at the spots on the specimen facing the holes, the oxide layer was thin. Hollows occurred on the specimen of SiC at these spots. It seems that the existence of gas flow is a very important factor in the disappearance of the oxide layer.

Alumina (Al2O3) and zirconia (ZrO2) as oxide ceramics were exposed to the combustion gas flow. The weight of these also decreased. There is a possibility that the weight loss of ceramics in combustion gas flow is caused by degradation of oxide layer on their surface from erosion and hot corrosion due to some oxide scales coming from the test equipment.
A Finite Difference Simulation of the Heat Transfer Enhancement in a Typical Two Pass Ribbed Duct of a Cooled Turbine Blade Using Wall Functions
Authors: Visser Jan A. , Coetzer Calvyn B.
Published: December 2014

Optimisation of the internal cooling duct of a modern turbine blade, consisting of ribbed and pin finned sections, is essential as the coolant flow introduces losses that need to be minimised. In the ribbed sections large variations in turbulence levels occur and the secondary flows associated with these ribs are responsible for significant local heat transfer variations. This paper presents a finite difference simulation of the friction losses and heat transfer rates in a typical duct with two passes. A standard k-ε turbulence model with wall functions is used as a turbulence closure model. The results show predicted heat transfer enhancement in a typical two pass duct for both smooth walls and a duct with ribs on the top and bottom surfaces. In the case of a smooth duct, predicted and measured results were in good agreement in areas where no recirculation occurred. At the ribbed walls, and in the areas where recirculation occurs, the simulations presented poor results. From the results can be concluded that a wall function based turbulence model does not provide sufficiently accurate results when applied to ribbed ducts and in particular sharp turns.
The Analysis and Resolution of a Fatigue Failure of a Low Pressure Turbine Blade Caused by the Excitation of a Bladed Disc Mode of Vibration
Authors: Staddon Malcolm C. , Box Paul R. , Barnett Barry , Horton Tony , Ballans Geoff H.
Published: December 2014

A high cycle fatigue failure of a low pressure turbine blade was investigated. Strain gauge tests of a running engine indicated a high dynamic response of the blade at the nozzle passing frequency. This could be attributed to the excitation of a bladed disc mode of vibration. A Finite Element analysis of the low pressure turbine blades and discs, together with bench testing of the complete structure, confirmed the existence of a high frequency 2nd Nodal Diameter mode of vibration. The levels of dynamic strain determined through strain gauge tests were found to be sufficient enough to explain the failure at the given location.

Having understood the problem, the situation was resolved through the use of Finite Element analysis with a short term modification to the original blade aerofoil to prevent the mode from being excited.

An aero/mechanical re-design of both the low pressure turbine rotor and the stator was undertaken to resolve the problem by both returning the blade to avoid high frequency excitation, and also by reducing the forcing effect of the nozzle passing frequency. The new design has been validated through strain gauge tests and endurance tests. A further improvement in performance was also obtained.
Bond Strength and Stress Measurements in Thermal Barrier Coatings
Authors: Jordan Eric H. , Gell Maurice , Pease Doug M. , Shaw Leon , Clarke David R. , Gupta Vijay , Barber Brent , Vaidyanathan Krishna
Published: December 2014

The failure mode for thermal barrier coatings in gas turbine engines is spallation at or near the ceramic to metal interface. We propose that the two most important factors leading to this failure are the change in the bond strength and bond stress with cycling. Five methods of measuring stress near the ceramic bond coat interface and four methods of bond strength measurement were investigated. Laser fluorescence and enhanced laboratory x-ray methods have the most potential for stress measurement, while the promising bond strength measurement methods are direct pull testing, chevron notch fracture toughness, and laser induced ultrasonic spallation. The stress and strength as a function of thermal cycles was determined for one set of yttria stabilized zirconia coated single crystal samples. Both a decreasing residual compression stress in the oxide layer that joins the ceramic to the metal and a decreasing bond strength were measured as a function of thermal cycles.
Economics and Design Approaches for Small Commercial Turbogenerators
Authors: Myers Phillip F.
Published: December 2014

The successful development of small commercial turbogenerators for automotive and other applications presents a major economic challenge. Current aerospace turbogenerators in the 60 kilowatt power range sell for around $500 per kilowatt. Volume automotive turbogenerators prices must be $30 per kilowatt, or less — a 94% reduction. Turbogenerators for aerospace applications have drastically different requirements on almost all important criteria from automotive turbogenerators. The production of commercial turbogenerators requires a radically different organizational setting, mindset, and overhead structure from that necessary for the aerospace industry. Ground up designs which take an integrated approach to material selection, method of operation, fabrication techniques, supplier base, assembly methods, and low cost overheads will be necessary for commercial success. Significant innovation and simplification, and the natural effects of high volume production are also required. Success will likely require lean, agile, innovative, and specialized organizations.
Advances in Gas Turbine Blade Repair by Laser Welding
Authors: Gandini Ettore , Agnesone Franco , Taricco Federica , Arrighi Leonardo
Published: December 2014

Industrial gas turbine components are subject, in the course of their operating life, to various kinds of damages, requiring repair processes during periodical overhauling operations. Blades, in particular, suffer from creep, corrosion, wear phenomena.

The majority of blade damage is currently repaired by means of manual TIG welding, with a filler metal which is often different from the blade alloy. This leads to an inferior metallurgical and mechanical condition of the repaired area as compared to the base metal. Besides, the nickel superalloys of the blades are often subject to cracking during welding operations.

A process of laser welding for the repair of the airfoil tip has been introduced and optimized, to improve the characteristics of the repaired component. Powder of the same alloy of the part is used as filler metal, and the process is carried out using a Nd:YAG laser, equipped with a 6–axis CNC motion control. The original blade geometry is rebuilt by multi–layer cladding, then the blade is submitted to machining operations, NDT testing and heat treatment.

The optimizing activity has been performed with the aid of microstructural characterization, chemical composition checking (by EDX microanalysis), hardness and stress rupture testing of the welded specimens.
Improvement of Environmental Record of the Stationary Gas Turbines Run in Russia Through Combustors Update
Authors: Soudarev A. , Vinogradov E. , Zakharov Yu.
Published: December 2014

Some results of the NPP “EST” activities on improvement of the environmental record of the stationary gas turbines, viz.GTG-1500, FRAME 5, GTN-16, which are in use nowadays in Russia, are presented. Toxic emissions reduction is achieved through combustors update. The technique of directed dosed air blow-in into the maximum fire temperature zones allows to reduce the NOx emissions to 70–130 mg/Nm3 (converted to NO2 at 15% O2 concentration) via minimal combustor design modifications. Lower NOx emissions, amounting to 15–25 mg/Nm3, can be produced through combustion of lean premixed air and fuel in the 4-burner low-toxic module. When retrofitting the GTN-16 unit combustor, the standard dome was replaced with 20 such modules.
Numerical Simulation of Turbulent Heat Transfer and Flow in a Rotating Multiple-Pass Square Channel
Authors: Hwang Jenn-Jiang , Wang Wei-Jyh , Lai Dong-Yuo
Published: December 2014

Three-dimensional turbulent fluid flow and heat transfer characteristics are analyzed numerically for fluids flowing through a rotating periodical two-pass square channel. The two-pass channel is characterized by three parts: (1) a radial-inward straight channel, (2) 180-deg sharp turns, and (3) a radial-outward straight channel. The smooth walls of the two-pass channel are subject to a constant heat flux. A two-equation k-ε turbulence model with modified terms for Coriolis and rotational buoyancy is employed to resolve this elliptic problem. The effects of rotational buoyancy are examined and discussed. It is found that adjacent the 180-deg turn, the rotational buoyancy effect on the local heat transfer is nearly negligible due to the relatively strong entrance effect of 180-deg turns. Downstream the entrance length, the changes in local heat transfer due to the rotational buoyancy in the radially outward flow are more significant than those in the radially inward flow. However, the channel averaged heat transfer is affected slightly by the rotational buoyancy. Whenever the buoyancy effects are sufficiently strong, the flow reversal appears over the leading face of the radial outward flow channel. A comparison of the present numerical results with the available experimental data by taking buoyancy into consideration is also presented.
Update on Westinghouse’s Advanced Turbine Systems Program
Authors: Amos David J. , Diakunchak Ihor S. , McQuiggan Gerard , Southall Leslie R. , Wagner Gregg P.
Published: December 2014

This paper describes progress on Westinghouse’s Advanced Turbine Systems (ATS) Program. The ATS Program objective is to develop new utility gas turbines with greater than 60% net plant thermal efficiency, NOx emissions limited to less than 10 parts per million, reduced cost of electricity generation by 10% over current systems, and reliability-availability-maintainability equivalent to modern power generation systems. The Westinghouse ATS plant is a highly efficient combined cycle, based on an advanced gas turbine incorporating novel design concepts and enhancements of existing technologies. The 501 ATS engine is a fuel-flexible design operating on natural gas with provisions for future conversion to coal or biomass fuels. It is based on proven concepts employed in Westinghouse 501F and 501G engines. To achieve the required performance and reliability, the engine utilizes closed-loop steam cooling, advanced materials and coatings, and enhanced component performance. To minimize NOx emissions, an ultra-low NOx combustion system was incorporated. To ensure success, the necessary technologies were developed and integrated into the ATS engine design.
Application of CFD to DLN Combustion
Authors: Hornsby C. , Norster E. R.
Published: December 2014

This paper describes the methodology and application of Computational Fluid Dynamics (CFD) to Dry Low NOx (DLN) combustion systems throughout the range of small industrial gas turbines produced at European Gas Turbines (EGT) Lincoln UK.

The use of CFD in the development of such systems has been encouraged not only by the availability of a variety of general purpose CFD codes, but also by the inherent difficulties associated with direct measurement in such a harsh environment. Combusting flow analyses provide detailed predictions of local temperature and velocity fields together with exhaust emissions, enabling numerous conceptual studies to be undertaken without the usual associated mechanical difficulties.

In particular, the work EGT has concentrated on concerns the prediction of fuel / air mixing quality upstream of the flame front, in order to assess the effect of fuel injector design variables on NOx production. This methodology has accelerated injector development resulting in less than 10 ppmV NOx combustors.

Validation of the detailed features of the flow field is currently underway, though parametric comparisons have already proved consistently accurate in displaying the trends necessary for the development of an ultra low NOx combustion system. Correlations of rig emissions data with overall predictions have shown to be in good agreement.
Life Assessment of Gas Turbine Components Using Nondestructive Inspection Techniques
Authors: Walter Kurt , Greaves Wayne
Published: December 2014

The life expectancy of gas turbine components is strongly dependant on the service conditions in which they operate. Diverse factors can reduce the life dramatically, or can extend it far beyond what was originally predicted by the Original Equipment Manufacturer. In order to examine the condition of the casing, compressor blading, stationary turbine vanes, and rotating turbine blades, nondestructive inspection has been performed more frequently as part of an overhaul. During inspections, visual examination is usually the only method used. Hot corrosion, oxidation or overaging of the blades may not be obvious during such an inspection. The most accurate method of evaluation involves the removal of the parts from the unit, complete visual and penetrant inspection, metallurgical evaluation, and destructive mechanical testing. Yet, complete disassembly only takes place if obvious problems are found. Microstructural analysis and physical testing in such situations add much to the condition assessment. Although many in-situ techniques have been in place for years, applying them to the evaluation of gas turbine components has been limited. When nondestructive inspection is done regularly, the art of evaluation and life assessment can become more scientific. The risk of failure can be reduced and the component life extended. This paper describes the procedure for preparation and examination.