bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Optimisation of Longitudinal Ribs in Variable Geometry Ducts
Authors: Naik S. , Probert S. D.
Published: December 2014

Augmenting the heat transfer rates in the internal flow passages of several components of a gas turbine, such as the turbine blades, vanes and combustor walls is an important pre-requisite for maintaining their structural integrity. This is particularly paramount when higher turbine inlet temperatures and pressure ratios are utilised for enhancing the thermal efficiencies of the gas turbine plant.

In this study, the heat transfer enhancement, which can be achieved by longitudinal ribs in a variable geometry duct, has been examined. With the base of the ribs maintained at a constant temperature, it was observed that the optimal rib spacing, which corresponded to the maximum heat transfer from the ribs, was a strong function of the rib height to length ratio and the Reynolds number but relatively insensitive to the amount of clearance above the ribs. A design correlation is proposed which shows the distribution of this optimal rib spacing for a wide range of rib geometrical and operational conditions.

Comparisons of the longitudinal ribs with pin fin arrays indicated that at rib height to length ratios of ≥ 0.24, higher heat transfers can be achieved with the longitudinal ribs. The frictional characteristics of the longitudinal ribs is comparable to those of circular pin fins.

Measurements of the local heat transfer coefficient for the rib surfaces indicate that it is highly non-uniform along the rib height and length and also significantly influenced by the amount of clearance above the ribs. For all the cases examined, it was observed that developing flow conditions (thermally and hydrodynamically) were prevalent within the longitudinal rib channels.
Prospect of Advanced Generation Technologies in a Competitive Marketplace
Authors: Guha Manoj K.
Published: December 2014

To meet the challenge of deregulation and customer demands for a free competitive market, the electric utility industry in the U.S. (and, for that matter, throughout the world) will experience tremendous changes over the next five years. These changes will be driven by two major forces: the deregulation of the industry and, therefore, no guaranteed return on investment but more importantly, the demands of customers for a free competitive market in the electric utility industry where they can achieve the lowest cost for the commodity. This will force utility companies to position themselves as low-cost producers. Although low cost does not necessarily mean success, it is obvious that cutting and/or reducing capital expenditures will play the most important role.

Unregulated markets encourage product diversity, as firms look for “niche” profit opportunities. A pervasive lesson from other industries that have recently been deregulated clearly shows that unless properly planned, these companies will not only do poorly but may be completely wiped out from the market Generation Planning (base load vs. peak load, long-term vs. short-term) will become more important since two-thirds of the capital investment is tied to generation facilities. While low-cost utilities will have greater flexibility in adapting to competition, they will be far from immune to industry changes.

Under a fully competitive marketplace, all generating plant assets/investments will come out of a rate base. Since all companies will be exposed to competition, high-cost generating assets would no longer be subsidized by ratepayers. This will force the utility companies to invest in low capital cost generation only, at least during the next ten to fifteen years.

This paper will briefly discuss the status of various advanced generation technologies with respect to their costs, applicability and limitations, where these technologies are expected to be cost effective and finally how these technologies compare with the state-of-the-art combined cycle gas-turbine technology. It is predicted that as environmental regulations tighten on pollution, advanced generation technologies may benefit at the expense of current fossil fuel technologies. However, it is not certain whether economic growth in the U.S. can be sustained if new regulations on pollution force to add new plants with advanced generation technologies, compared to continuing with today’s generation mix. It will be examined how, when and where the advanced generation technologies would play an important role in penetrating the market on their own merits.
Advanced Gas Turbine System Utilizing Partial Oxidation Technology for Power Generation
Authors: Maslennikov Victor M. , Batenin Vlacheclav M. , Shterenberg Victor Ja. , Vyskubenko Yury A. , Tsalko Edward A.
Published: December 2014

A number of options for power generating unit repowering by installing topping gas turbine units, using the novel natural gas “partial oxidation” technology on basis of heavy duty and aeroderivative gas turbines, intended for modernization of existing natural gas fired steam power plants have been examined. A comparative thermodynamic, technical and economic analysis of these repowering options has been made. The additionally generated useful power and the efficiency of production of additional electricity have been used as the most important parameters for comparison with traditional repowering options. Pages 8, Figures 8, Tables 6.
Local Heat Transfer Coefficients on Flat Continuous, Flat Interrupted and Corrugated External Cooling Fins
Authors: Robertson Andrew J. , Neely Andrew J. , Ireland Peter T. , Harper Les R.
Published: December 2014

An experimental investigation into the performance of gas turbine engine component external cooling fins has been carried out using the transient liquid crystal technique in a low speed wind tunnel. Full fin surface local heat transfer coefficient distributions have been determined. Measurements with this level of resolution are not previously reported in the literature.

In addition to the flat continuous fins, interrupted and corrugated fin geometries have been tested. These geometries enhance heat transfer coefficients by disrupting the thermal and velocity boundary layers which grow down the length of the fin.

All geometries are tested at a range of flow speeds and comparisons are made with the relevant literature.
Measurements of Secondary Flows in a Turbine Cascade at Off-Design Incidence
Authors: Benner M. W. , Sjolander S. A. , Moustapha S. H.
Published: December 2014

The present study is part of an on-going project concerned with the effects of off-design incidence on losses. Previous work has examined the profile losses (Benner et al., 1995). This study focusses on the secondary flow, the endwall flow in the absence of tip clearance. This paper describes an experimental study in a large-scale, low-speed, linear turbine cascade for which the incidence was varied. Three different values of incidence were investigated: 0, +10 and +20 degrees. Detailed flow field measurements were made upstream and downstream of the cascade and static pressure distributions were measured on the blade surfaces. The data were supplemented by extensive surface oil flow visualization. This paper concentrates on the physical insights into the relationship between the behaviour of secondary flows and incidence which have been gained from the measurements and the flow visualization. A preliminary discussion of the effect of incidence on the losses is also included.
Grid Dependency Study for the NASA Rotor 37 Compressor Blade
Authors: Arnone Andrea , Carnevale Ennio , Marconcini Michele
Published: December 2014

The NASA Rotor 37 has been computed by several authors in the last few years with relative success. The aim of this work is to present a systematic grid dependency study in order to quantify the amount of uncertainty that comes from the grid density. The computational domain is divided onto several regions (i.e. leading edge, trailing edge, shear layer …) and for each of them, the impact of the grid density is investigated.

By means of this analysis, substantial improvement has been obtained in the prediction of efficiency and exit angle. On the contrary, the improvement achieved in total pressure and total temperature ratio is less remarkable. It is believed that only after a systematic grid dependency study can the contribution of turbulence modeling, laminar-turbulent transition, and boundary conditions be analyzed with success.
Stagnation Point Heat Transfer With a Thermal Barrier Coated Cylinder
Authors: Abuaf N. , Dorri B. , Lee C. P. , Flodman D. A.
Published: December 2014

A warm wind tunnel test facility operating in a transient mode was demonstrated with thin wall metal cylinders and with a thin wall linear airfoil cascade to generate local temperature variations with time which were used with a lumped parameter heat transfer assumption to calculate the external gas side heat transfer coefficients (Abuaf et al. [1995]). The present work extends the transient test methodology to Thermal Barrier Coated (TBC) thin wall metallic cylinders. The central cylinder had thermocouples imbedded and brazed in the thin metal wall and then was coated with a relatively smooth Plasma Vapor Deposited (PVD) thermal barrier coating. Transient tests were conducted at three inlet free stream turbulence intensities of 2%, 7% and 14% and at several air flow rates covering a range of Reynolds numbers from 15,000 to 100,000 based on the inlet flow conditions and the cylinder diameter. The recorded cylinder metal wall transient temperature data, were analyzed by means of an inverse conduction code. The inverse conduction code used the transient metal wall temperature data, the test cylinder geometry and the metal and TBC properties to calculate the stagnation point heat transfer coefficients acting at the surface of the TBC coating. The cylinder stagnation point Nusselt numbers are in agreement with correlations existing in the literature.
Turbocharger-Design Effects on Gasoline-Engine Performance
Authors: Korakianitis T. , Sadoi T.
Published: December 2014

Specification of a turbocharger for a given engine involves matching the turbocharger performance characteristics with those of the piston engine. Theoretical considerations of matching turbocharger pressure ratio and mass flow with engine mass flow and power permits designers to approach a series of potential turbochargers suitable for the engine. Ultimately, the final choice among several candidate turbochargers is made by tests. In this paper two types of steady-flow experiments are used to match three different turbochargers to an automotive turbocharged-intercooled gasoline engine. The first set of tests measures the steady-flow performance of the compressors and turbines of the three turbochargers. The second set of tests measures the steady-flow design-point and off-design-point engine performance with each turbocharger. The test results show the design-point and off-design-point performance of the over-all thermodynamic cycle, and this is used to identify which turbocharger is suitable for different types of engine duties.
Low-Aspect-Ratio Rib Heat Transfer Coefficient Measurements in a Square Channel
Authors: Taslim M. E. , Korotky G. J.
Published: December 2014

Cooling channels, roughened with repeated ribs, are commonly employed as a means of cooling turbine blades. The increased level of mixing induced by these ribs enhances the convective heat transfer in the blade cooling cavities. Many previous investigations have focused on the heat transfer coefficient on the surfaces between these ribs and only a few studies report the heat transfer coefficient on the rib surfaces themselves. The present study investigated the heat transfer coefficient on the surfaces of round-corner, low-aspect-ratio (ARrib = 0.667) ribs. Twelve rib geometries, comprising of three rib height-to-channel hydraulic diameter (blockage ratios) of 0.133, 0.167, and 0.25 as well as three rib spacings (pitch-to-height ratios) of 5, 8.5, and 10 were investigated for two distinct thermal boundary conditions of heated and unheated channel walls. A square channel, roughened with low-aspect-ratio ribs on two opposite walls in a staggered manner end perpendicular to the flow direction was tested. An instrumented copper rib was positioned either in the middle of the rib arrangements or in the furthest upstream location. Rib heat transfer coefficient as well as the channel friction factor for these low-aspect-ratio ribs were also compared with those of square ribs, reported previously by the authors. Heat transfer coefficients of the furthest upstream rib and that of a typical rib located in the middle of the rib-roughened region of the passage wall were also compared.
Coating Life Prediction Under Cyclic Oxidation Conditions
Authors: Chan Kwal S. , Cheruvu N. Sastry , Leverant Gerald R.
Published: December 2014

The hot gas path section components of land based turbines require materials with superior mechanical properties and good hot corrosion and oxidation resistance. These components are generally coated with either a diffusion coating (aluminide or platinum aluminide) or with an overlay coating (MCrAlY) to provide additional hot corrosion and/or oxidation protection. These coatings degrade due to inward and outward diffusion of elements during service. Outward diffusion of aluminum results in formation of a protective oxide layer on the surface. When the protective oxide spalls, aluminum in the coating diffuses out to reform the oxide layer. Accelerated oxidation and failure of coating occur when the Al content in the coating is insufficient to reform a continuous alumina film. This paper describes development of a coating life prediction model that accounts for both oxidation and oxide spallation under thermal mechanical loading, as well as diffusion of elements that dictate the end of useful life. Cyclic oxidation data for aluminide and platinum aluminide coatings were generated to determine model constants. Applications of this model for predicting cyclic oxidation life of coated materials are demonstrated. Work is underway to develop additional material data and to qualify the model for determining actual blade and vane coating refurbishment intervals.
Analysis of the Temperature Profile of Ceramic Composite Materials Exposed to Combined Conduction-Radiation Between Concentric Cylinders
Authors: Tremante Andrés , Malpica Freddy
Published: December 2014

A numerical study is made of the thermal characteristics of semitransparent materials exposed to simultaneous conduction and radiation between concentric cylinders. For extremely high-temperature applications, where radiative transfer plays an important role, ceramic-matrix composites, considered as semitransparent materials, are being explored for potential use in turbines and compressors components, spacecraft structures, engine control systems and nuclear reactors. Through the use of a gray model and the the two flux method, specialized equations are developed that generate a system of nonlinear ordinary differential equations. To facilitate the solution of this system, an iterative strategy is adopted. In order to demonstrate the versatility and accuracy of the proposed methodology, the results of several numerical experiments are presented and compared with benchmark solutions.
Blockage Development in a Transonic, Axial Compressor Rotor
Authors: Suder Kenneth L.
Published: December 2014

A detailed experimental investigation to understand and quantify the development of blockage in the flow field of a transonic, axial flow compressor rotor (NASA Rotor 37) has been undertaken. Detailed laser anemometer measurements were acquired upstream, within, and downstream of a transonic, axial compressor rotor operating at 100%, 85%, 80%, and 60% of design speed which provided inlet relative Mach numbers at the blade tip of 1.48, 1.26, 1.18, and 0.89 respectively. The impact of the shock on the blockage development, pertaining to both the shock / boundary layer interactions and the shock / tip clearance flow interactions, is discussed. The results indicate that for this rotor the blockage in the endwall region is 2–3 times that of the core flow region, and the blockage in the core flow region more than doubles when the shock strength is sufficient to separate the suction surface boundary layer.
An Efficient Computational Model for Premixed Turbulent Combustion at High Reynolds Numbers Based on a Turbulent Flame Speed Closure
Authors: Zimont Vladimir , Polifke Wolfgang , Bettelini Marco , Weisenstein Wolfgang
Published: December 2014

Theoretical background, details of implementation and validation results of a computational model for turbulent premixed gaseous combustion at high turbulent Reynolds numbers are presented. The model describes the combustion process in terms of a single transport equation for a progress variable; closure of the progress variable’s source term is based on a model for the turbulent flame speed. The latter is identified as a parameter of prime significance in premixed turbulent combustion and is determined from theoretical considerations and scaling arguments, taking into account physico-chemical properties of the combustible mixture and local turbulent parameters. Specifically, phenomena like thickening, wrinkling and straining of the flame front by the turbulent velocity field are considered, yielding a closed form expression for the turbulent flame speed that involves, e.g., speed, thickness and critical gradient of a laminar flame, local turbulent length scale and fluctuation intensity. This closure approach is very efficient and elegant, as it requires only one transport equation more than the non-reacting flow case, and there is no need for costly evaluation of chemical source terms or integration over probability density functions.

The model was implemented in a finite-volume based computational fluid dynamics code and validated against detailed experimental data taken from a large scale atmospheric gas turbine burner test stand. The predictions of the model compare well with the available experimental results. It has been observed that the model is significantly more robust and computationally efficient than other combustion models. This attribute makes the model particularly interesting for applications to large 3D problems in complicated geometries.
Results of Experiments and Models for Predicting Stability Limits of Turbulent Swirling Flames
Authors: Hoffmann S. , Lenze B. , Eickhoff H.
Published: December 2014

Swirling flames are used in many industrial applications like process furnaces, boilers and gas turbines due to their excellent mixing, stability, emission and burnout characteristics. The wide-spread use of swirl burners in the process and energy industries and, in particular, new concepts for the reduction of NOx-emissions raise the need for simple-to-use models for predicting lean stability limits of highly turbulent flames stabilized by internal recirculation.

Based on recently published experimental data of the first author concerning the reaction structures of swirling flames operating near the extinction limit, different methods for predicting lean blow-off limits have been developed and tested. The aim of the investigations was to find stabilization criteria that allow predictions of blow-off limits of highly turbulent recirculating flames without the requirement for measurements in those flames.

Several similarity criteria based on volumetric flow rates, burner size and material parameters of the cold gases, were found to be capable of predicting stability limits of premixed and (in some cases) nonpremixed flames at varying swirl intensities, burner scales and fuel compositions. A previously developed numerical field model, combining a k,ϵ-model with a combined “assumed-shape Joint-PDF”/Eddy-Dissipation reaction model was also tested for its potential for stability prediction.
Modeling Unsteady Boundary Layer Transition on a Curved Plate Under Periodic Unsteady Flow Conditions: Aerodynamic and Heat Transfer Investigations
Authors: Chakka P. , Schobeiri M. T.
Published: December 2014

A boundary layer transition model is developed that accounts for the effects of periodic unsteady wake flow on the boundary layer transition. To establish the model, comprehensive unsteady boundary layer and heat transfer experimental investigations are conducted. The experiments are performed on a curved plate at zero-streamwise pressure gradient under periodic unsteady wake flow, where the frequency of the periodic unsteady flow is varied. The analysis of the time dependent velocities, turbulence intensities, and turbulence intermittencies has identified three distinct quantities as primarily responsible for the transition of an unsteady boundary layer. These quantities, which exhibit the basis of the transition model presented in this paper, are: (1) relative intermittency, (2) maximum intermittency, and (3) minimum intermittency. To validate the developed transition model, it is implemented in an existing boundary layer code, and the resulting velocity profiles and the heat transfer coefficients are compared with the experimental data.
Inner Workings of Aerodynamic Sweep
Authors: Wadia A. R. , Szucs P. N. , Crall D. W.
Published: December 2014

The recent trend in using aerodynamic sweep to improve the performance of transonic blading has been one of the more significant technological evolutions for compression components in turbomachinery. This paper reports on the experimental and analytical assessment of the pay-off derived from both aft and forward sweep technology with respect to aerodynamic performance and stability. The single stage experimental investigation includes two aft-swept rotors with varying degree and type of aerodynamic sweep and one swept forward rotor. On a back-to-back test basis, the results are compared with an unswept rotor with excellent performance and adequate stall margin. Although designed to satisfy identical design speed requirements as the unswept rotor, the experimental results reveal significant variations in efficiency and stall margin with the swept rotors. At design speed, all the swept rotors demonstrated a peak stage efficiency level that was equal to that of the unswept rotor. However, the forward-swept rotor achieved the highest rotor-alone peak efficiency. At the same time, the forward-swept rotor demonstrated a significant improvement in stall margin relative to the already satisfactory level achieved by the unswept rotor. Increasing the level of aft sweep adversely affected the stall margin. A three-dimensional viscous flow analysis was used to assist in the interpretation of the data. The reduced shock/boundary layer interaction, resulting from reduced axial flow diffusion and less accumulation of centrifuged blade surface boundary layer at the up, was identified as the prime contributor to the enhanced performance with forward sweep. The impact of tip clearance on the performance and stability for one of the aft-swept rotors was also assessed.
Intermittent Flow and Thermal Structures of Accelerating Transitional Boundary Layers: Part 2 — Fluctuation Quantities
Authors: Wang Ting , Keller F. Jeffrey
Published: December 2014

The conditionally sampled fluctuation quantities of non-accelerating and accelerating heated transitional boundary layers were analyzed. The results indicated that the values of u′, v′, uv, and ut in the turbulent part of the transitional flow were higher than those values in the fully-developed turbulent flow. These higher values were believed to be manifestations of the vigorous activities involved in the transition process. The contributions to the unconditioned u′ by “mean-step” change due to the alternating behavior between turbulent and non-turbulent flows are about 20% in the near-wall region, but are negligible for Y+ > 30. The turbulent part uv values are higher than the fully turbulent and unconditioned values in the inner boundary layer but lower in the outer boundary layer. The mean-step change has negligible effect on unconditioned uv values. As acceleration increases, both u′ and t′ in the turbulent part are suppressed; however, turbulent part u′ is still higher than the unconditioned u′. Acceleration promotes streamwise Reynolds heat flux (ut) transport in both turbulent and non-turbulent parts. A second peak of the turbulent part ut occurs at around Y+ = 120 as acceleration increases. The turbulent part eddy viscosity values are much lower than those in the fully turbulent flow.
Direct Prediction of the Effects of Mistuning on the Forced Response of Bladed Disks
Authors: Mignolet Marc P. , Hu Wei
Published: December 2014

In this paper, a novel approach to determine reliable estimates of the moments of the steady state resonant response of a randomly mistuned bladed disk is presented and the use of these moments to accurately predict the corresponding distribution of the amplitude of blade vibration is described. The estimation of the moments of the response is accomplished first by relying on a “joint cumulant closure” strategy that expresses higher order moments in terms of lower order ones. A simple modeling of the error terms of these approximations is also suggested that allows the determination of an improved, or accelerated, estimate of the required moments. The evaluation of the distribution of the amplitude of blade response is then accomplished by matching the moments computed by the cumulant closure with those derived from a three-parameter model recently derived. A first order approximation of the moments obtained for a simple structural model of a bladed disk yields a new parameter that can be used as a measure of the localization of the forced response. Then, numerical results demonstrate that the method provides extremely accurate estimates of the moments for all levels of structural coupling which in turn lead to a description of the amplitude of blade response that closely matches simulation results. Finally, a comparison with existing perturbation techniques clearly shows the increased accuracy obtained with the proposed joint cumulant closure formulation.
The Evaporative Gas Turbine [EGT] Cycle
Authors: Horlock J. H.
Published: December 2014

Humidification of the flow through a gas turbine has been proposed in a variety of forms. The STIG plant involves the generation of steam by the gas turbine exhaust in a heat recovery steam generator [HRSG], and its injection into or downstream of the combustion chamber. This increases the mass flow through the turbine and the power output from the plant, with a small increase in efficiency. In the evaporative gas turbine [or EGT] cycle, water is injected in the compressor discharge in a regenerative gas turbine cycle [a so-called CBTX plant-compressor [C], burner [B], turbine [T], heat exchanger [X]]; the air is evaporatively cooled before it enters the heat exchanger. While the addition of water increases the turbine mass flow and power output, there is also apparent benefit in reducing the temperature drop in the exhaust stack. In one variation of the basic EGT cycle, water is also added downstream of the evaporative aftercooler, even continuously in the heat exchanger. There are several other variations on the basic cycle [e.g. the cascaded humidified advanced turbine (CHAT)].

The present paper analyses the performance of the EGT cycle. The basic thermodynamics are first discussed, and related to the cycle analysis of a dry regenerative gas turbine plant. Subsequently some detailed calculations of EGT cycles are presented. The main purpose of the work is to seek the optimum pressure ratio in the EGT cycle for given constraints [e.g. fixed maximum to minimum temperature]. It is argued that this optimum has a relatively low value.
Active Stabilization of Rotating Stall and Surge in a Transonic Single Stage Axial Compressor
Authors: Weigl H. J. , Paduano J. D. , Fréchette L. G. , Epstein A. H. , Greitzer E. M. , Bright M. M. , Strazisar A. J.
Published: December 2014

Rotating stall and surge have been stabilized in a transonic single-stage axial compressor using active feedback control. The control strategy is to sense upstream wall static pressure patterns and feed back the signal to an annular array of twelve separately modulated air injectors. At tip relative Mach numbers of 1.0 and 1.5 the control achieved a 11% and 3.5% reduction in stalling mass flow respectively, with injection adding 3.6% of the design compressor mass flow. The aerodynamic effects of the injection have also been examined.

At a tip Mach number, Mtip, of 1.0, the stall inception dynamics and effective active control strategies are similar to results for low-speed axial compressors. The range extension was achieved by individually damping the first and second spatial harmonics of the pre-stall perturbations using constant gain feedback.

At a Mtip of 1.5 (design rotor speed), the pre-stall dynamics are different than at the lower speed. Both one-dimensional (surge) and two-dimensional (rotating stall) perturbations needed to be stabilized to increase the compressor operating range. At design speed, the instability was initiated by approximately 10 rotor revolutions of rotating stall followed by classic surge cycles. In accord with the results from a compressible stall inception analysis, the zeroth, first, and second spatial harmonics each include more than one lightly damped mode which can grow into the large amplitude instability. Forced response testing identified several modes traveling up to 150% of rotor speed for the first three spatial harmonics; simple constant gain control cannot damp all of these modes and thus cannot stabilize the compressor at this speed. A dynamic, model-based robust controller was therefore used to stabilize the multiple modes which comprise the first three harmonic perturbations in this transonic region of operation.
Design, Optimization, and Analysis of a High-Turning Transonic Tandem Compressor Cascade
Authors: Weber Anton , Steinert Wolfgang
Published: December 2014

As a feasibility study for a stator guide vane a highly loaded transonic compressor stator blade row was designed, optimized, and tested in a transonic cascade facility.

The flow entering the turning device with an inlet Mach number of 1.06 has to be turned by more than 60° and diffused extremely to leave the blade row without swirl. Therefore, the basic question was: Is it feasible to gain such a high amount of flow turning with an acceptable level of total pressure losses?

The geometric concept chosen is a tandem cascade consisting of a transonic blade row with a flow turning of 10° followed by a subsequent high-turning subsonic cascade. The blade number ratio of the two blade rows was selected to be 1:2 (transonic: subsonic).

Design and optimization have been performed using a modern Navier-Stokes flow solver under 2D assumptions by neglecting side wall boundary-layer effects. In the design process it was found to be necessary to guide the wake of the low turning transonic blade near the suction surface of the subsonic blade. Furthermore, it is advantageous to enlarge the blade spacing of the ‘wake’ passage in relation to the neighbouring one of the high turning part.

The optimized design geometry of the tandem cascade was tested in the transonic cascade windtunnel of the DLR in Cologne. At design flow conditions the experiments confirmed the design target in every aspect. A flow turning of more than 60°, a static pressure ratio of 1.75, and a total pressure loss coefficient of 0.15 was measured. The working range at design inlet Mach number of 1.06 is about 3.5° in terms of the inlet flow angle. A viscous analysis of various operating points showed excellent agreement with the experimental results.
Development of Ultra High Temperature Ceramic Composites for Gas Turbine Combustors
Authors: Holmquist Magnus , Lundberg Robert , Razzell Tony , Sudre Olivier , Molliex Ludovic , Adlerborn Jan
Published: December 2014

All-oxide ceramic composites as a material with potential for long life-time applications at temperatures in the 1400–1600°C range in combustion environments were studied. The properties of available polycrystalline and single crystal oxide fibres were summarised. The literature on stable weak interfaces in all-oxide composites was reviewed. Composites with single crystal fibres, a polycrystalline matrix of the same material as the fibres, and a compatible high temperature stable weak oxide interphase was suggested to be the most promising approach. Recent progress in an ongoing European project aiming at development, scale-up and property evaluation of all-oxide composites is reported. The composite will be applied to a simple prototype combustor tile and tested in a combustor rig.
Viscous Throughflow Modelling of Axial Compressor Bladerows Using a Tangential Blade Force Hypothesis
Authors: Gallimore Simon J.
Published: December 2014

This paper describes the modelling of axial compressor blade rows in an axisymmetric viscous throughflow method. The basic method, which has been reported before, includes the effects of spanwise mixing, using a turbulent diffusion model, and endwall shear within the throughflow calculation. The blades are modelled using a combination of existing two-dimensional blade performance predictions for loss and deviation away from the annulus walls and a novel approach using tangential blade forces in the endwall regions. Relatively simple assumptions about the behaviour of the tangential static pressure force imposed by the blades allow the secondary deviations produced by tip clearance flows and the boundary layer flows at fixed blade ends to be calculated in the axisymmetric model. Additional losses are assigned in these regions based on the calculated deviations. The resulting method gives realistic radial distributions of loss and deviation across the whole span at both design and off-design operating conditions providing a quick method of estimating the magnitudes of these effects in the preliminary design process. Results from the method are compared to measured data in low and high speed compressors and multistage three-dimensional viscous CFD predictions.
A Navier-Stokes Inverse Method Based on a Moving Blade Wall Strategy
Authors: Léonard Olivier , Demeulenaere Alain
Published: December 2014

A two-dimensional viscous inverse method for the design of compressor and turbine blades is presented. An initial geometry is modified iteratively to reach a target pressure distribution imposed on the blade surfaces. The Navier-Stokes equations are solved in a numerical domain of which some boundaries (the blade walls) move during the transient part of the computation. The blade modifications are based on the transpiration principle. The transpiration flux is computed from the difference between the actual and the prescribed pressure distributions.

A high-resolution Navier-Stokes solver has been developed for this purpose, based on a Finite-Volume formulation. Multi-block structured grids allow for a selective concentration of discretization points in the zones of higher gradients. Both explicit (Runge-Kutta) and implicit (Newton-Krylov) time integration schemes have been implemented.

Applications to turbine and compressor blade design illustrate the accuracy of the flow computation, and the efficiency of the inverse method.
Three-Dimensional Navier-Stokes Analysis of Turbine Rotor and Tip-Leakage Flowfield
Authors: Luo J. , Lakshminarayana B.
Published: December 2014

The 3-D viscous flowfield in the rotor passage of a single-stage turbine, including the tip-leakage flow, is computed using a Navier-Stokes procedure. A grid-generation code has been developed to obtain embedded H grids inside the rotor tip gap. The blade tip geometry is accurately modeled without any “pinching”. Chien’s low-Reynolds-number k-ε model is employed for turbulence closure. Both the mean-flow and turbulence transport equations are integrated in time using a four-stage Runge-Kutta scheme. The computational results for the entire turbine rotor flow, particularly the tip-leakage flow and the secondary flows, are interpreted and compared with available data. The predictions for major features of the flowfield are found to be in good agreement with the data. Complicated interactions between the tip-clearance flows and the secondary flows are examined in detail. The effects of endwall rotation on the development and interaction of secondary and tip-leakage vortices are also analyzed.
Influence of 3D Hot Streaks on Turbine Heat Transfer
Authors: Gundy-Burlet Karen L. , Dorney Daniel J.
Published: December 2014

Experimental data have shown that combustor temperature non-uniformities can lead to pressure side burning on first-stage turbine rotor blades. Although most modern turbines operate in an environment with significant heat transfer, the majority of hot streak experiments and simulations during the last decade have assumed adiabatic flow. This assumption can cause errors in the prediction of turbine cooling requirements. In the present investigation, three-dimensional unsteady Navier-Stokes simulations have been performed for a 1-1/2 stage high-pressure turbine geometry operating in subsonic flow. Combustor hot streaks and heat transfer effects at the airfoil surfaces were included in the simulations. The predicted aerodynamic (pressure) data shows close agreement with the available experimental data. The predicted heat flux results agree with experimental observations.
Development of a Corrosion Resistant Directionally Solidified Material for Land Based Turbine Blades
Authors: Cheruvu N. S.
Published: December 2014

Advanced turbines with improved efficiency require materials that can operate at higher temperatures. Availability of these materials would minimize cooling flow requirements and thus, improve the efficiency of a turbine. Advanced processing such as directional solidification (DS), can improve temperature capability of the majority of Ni based superalloys. However, results of earlier work on IN-738 reveal that the DS process does not significantly improve temperature capability of this alloy. A research program was initiated to develop a corrosion resistant Ni-based DS blade material for land-based turbines.

In this program, eight heats with varied Cr, Al, Ti, Ta, and W contents were selected for evaluation. Screening tests performed on these heats in the DS condition include tensile, creep, and corrosion. The results of experimental heats were compared with those of IN-738 in the equiaxed condition. From these results, two chemistries offering approximately 100°F temperature advantage at typical row 1 turbine blade operating stress, were selected for castability and further mechanical property evaluation. Several row 1 solid and cored turbine blades were successfully cast. The blades were evaluated for grain structure and mechanical properties. Tests were also conducted to evaluate the effects of withdrawal rates on properties. These results are summarized in this paper.
Corrosion Resistant Single Crystal Superalloys for Industrial Gas Turbine Application
Authors: Erickson G. L.
Published: December 2014

Two different, non-Re containing single crystal (SX) superalloys are defined primarily for industrial turbine application. The alloys, CMSX®-11B and CMSX-®-11C, contain respective chromium levels of about 12.5% and 14.5%. Both materials develop unique and extremely good blends of hot corrosion and oxidation resistance. They exhibit extremely good testability, employ relatively simple solution heat treatments and provide creep strength which is as good or better in comparison to other first generation SX materials such as CMSX-2/3, PWA 1480 and René N4. Moreover, at certain engine-pertinent temperature/stress conditions, and particularly in long-term tests (greater than 1,000 hours duration), the alloys appear to exhibit density corrected rupture strengths which are similar or better than CMSX-4® and other second generation SX casting superalloys.
Extensive Industrial Gas Turbine Experience With Second Generation Single Crystal Alloy Turbine Blades
Authors: Brentnall W. D. , Aurrecoechea J. M. , Rimlinger C. M. , Harris K. , Erickson G. L. , Wahl J. B.
Published: December 2014

The rhenium containing second generation single crystal alloy CMSX-4® was introduced for turbine blading in the Solar® Turbines Incorporated Mars® T-14000 engine in 1990. Based on the initial success with the first 4,000 hour engine test, the alloy was confirmed as bill of material for the stage 1 turbine blades in the T-14000 engine. Field experience has been excellent and there are now about 1,500,000 hours total accumulated engine time with several engines having completed their first overhaul cycle (Typically 30,000 hours). Use of this alloy is now being considered by Solar for other turbine airfoil components.

This update provides the results of metallurgical evaluations on high time blades. A detailed analysis of the substrate and coating, microstructure following the 25,000 hours field exposure was conducted and the results reported herein. A brief discussion of the effect of PtAl coatings on fatigue properties is also included.
Application of the Shell DeNOx System on Gas Turbine-Heat Recovery Steam Generators
Authors: Croce Gregory P. , Yistra Wessef , Kinsfather Richard , Hamilton David
Published: December 2014

The Shell DeNOx System (SDS) is an innovative selective catalytic reduction (SCR) system in which NOx emission reduction efficiencies greater than 90% can be achieved from fluegas streams at temperatures as low as 163 °C (325 °F).

The low temperature capability allows the SDS to be positioned at the tail-end of a furnace convection section or gas turbine HRSG. This feature permits the installation of SDS without the extensive retrofit costs associated with the implementation of conventional (medium or high) temperature SCRs which require a 288–385 °C (550–725 °F) or 427–593 °C (800–1100 °F) temperature window, respectively.

This paper will discuss the application and operating experience of the SDS on gas turbines heat recovery steam generators (GT-HRSG).
Systemic Approach Applied to Dual Pressure HRSG
Authors: Leide B. , Gicquel R.
Published: December 2014

Starting from a traditionally designed heat exchanger arrangement, a dual pressure and supplementary fired heat recovery steam generator (HRSG) has been examined according to a novel thermal design approach which features thermodynamic loss analyses being separately applied to individual components and to the thermal system as a whole. Basic Process Integration tools are employed in order to unveil the utility target. In addition recently developed analysis tools which are especially adapted to heat recovery equipment are introduced and then applied to the HRSG. Design modifications are identified which lead to an encouraging −8% reduction of heat exchange surface with respect to initial design while steam load and utility heat supply (by means of post-combustion) are kept unchanged. The design options are commented step by step and reflected against engineering feasibility as well as their overall economic impact.
Development of Ceramic Gas Turbine Combustor for 300kW-Class(CGT301)
Authors: Saitou Tsukasa , Sato Jun’ichi
Published: December 2014

The combustor for 300kW class ceramic gas turbine (CGT301) has been developed to achieve high thermal efficiency of 42%. The combustor inlet air temperature and the turbine inlet temperature(TIT) are higher compared with the conventional same class gas turbine. The “pilot” CGT system, with a recuperator to recover the waste heat in the exhaust gas, can heat combustor inlet air up to 1013K(740°C) at TIT of 1623K(1350°C). Low NOx emission is one of the important problems for the CGT combustor. To solve the problem, the lean premixed combustion method was applied. Stable combustion is another important problem for the lean premixed combustor. To solve the problem, this combustor employed the variable geometory system and the fuel staging system. The former controlled the temperature in the combustion zone. The latter optimized the distribution of air/fuel concentration in the mixing zone. The CGT system has achieved both stable combustion and low NOx emission. NOx emission was reduced to 17.6 ppm against the “primary type” CGT target of 70 ppm under the full load condition at TIT of 1200°C in combustor rig test. The engine tests of “primary type” CGT with a ceramic combustor, which did not employ the variable geometry system and the fuel staging system, were conducted successfully for a total of 32 hours without any damage of the ceramic combustor under the full load condition.
LNG Receiving Terminal Associated With Gas Cycle Power Plants
Authors: Chiesa Paolo
Published: December 2014

LNG regasification process needs a considerable quantity of thermal energy that is usually obtained by cooling sea water or by burning a fraction of the evaporated natural gas. These systems, though offering low cost and high reliability, are thermodynamically inefficient: they require energy for water pumping or fuel to provide heat and do not exploit the physical exergy related to the initial conditions of LNG to produce mechanical work.

The present paper aims to assess the performances of various gas turbine based cycles which use the LNG regasification process as a low temperature heat sink for power cycles. In particular it will focus on the following configurations:

• Closed loop gas cycles

• Gas-gas combined cycles

• Combined gas-organic Rankine cycles

Two different sendout pressure (70 and 30 bar, corresponding respectively to the supply of long-distance pipelines or power plants based on heavy-duty gas turbines) are considered. Their performances are calculated and proper effectiveness indexes (e.g. thermal and exergetic efficiency) are introduced to carry out a comprehensive comparison among the systems considered. A simple economical analysis completes the discussion.
Use of Artificial Neural Networks for the Simulation of Combined Cycle Transients
Authors: Desideri Umberto , Fantozzi Francesco , Bidini Gianni , Mathieu Philippe
Published: December 2014

Due to techno-economic assets, the demand of combined cycles (CC) is currently growing. Nowadays, in a diversified electricity mix, these plants are often used on a load cycling duty or in the intermediate load range. The ability to start quickly and reliably may be a decisional criterion for the selection of the plant, in addition to the design performance, the cost and the pollutant emissions. Therefore, together with the simulation of CC transients, a proper monitoring system aimed at keeping high plant performance during the transients is required.

With the help of advanced measurement and monitoring devices, artificial intelligence (AI) techniques as expert systems (ES) and neural networks (NN) can fulfill this duty.

The goal of this paper is to show that a NN technique can be used reliably to obtain the response of a complex energetic system, such as CCs, during a slow transient and consequently as part of an on-line monitoring system.

In this work, a CC power plant is simulated by dividing it into three blocks, which are representative of the three main elements of the CC: namely the gas turbine (GT), the heat recovery steam generator (HRSG) and the steam turbine (ST). To each of them a NN is associated. Once the training and testing of the NNs is carried out, the blocks are then arranged in a series cascade, the output of a block being the input of the subsequent one. With this solution, the NN-based system is able to produce the transient response of a CC plant when the input information are the GT inlet parameters.

The transient data, not easy to obtain from measurements on existing plants, are provided by the CCDYN simulator (Dechamps, 1995). The performance obtained by the NN based system are observed to be in good agreement with those given by CCDYN, the latter being validated on the basis of measurements in an existing plant. The NN code, providing the departures of the measured data from the predicted ones, can be considered as a proper system for on-line monitoring and diagnosis.