bluuebunny/crossref_metadata_2025 huggingface dataset:
Part Load Performance of Chemically Recuperated Gas Turbine Cycles Compared to Other Advanced Cycles
Authors: Abdallah Hicham , Facchini Bruno , Harvey Simon
Published: December 2014

A number of different innovative gas turbine cycles are currently being developed for future high performance power generation applications. Of particular interest are new cycles such as the Humid Air Turbine (HAT) cycle and the Chemically Recuperated Gas Turbine (CRGT) cycle. The HAT cycle has reached the stage of commercial demonstration, whereas the CRGT cycle is still in the research stage.

Performance predictions for CRGT cycles show cycle performance levels higher than those of the basic Steam Injected (STIG) cycle, but lower than those of state-of-the-art combined cycles. Thus, CRGT cycles are most likely to be of interest for intermediate load operation or cogeneration. For such applications, part load performance is a key performance criterion. Part load operation is generally detrimental to power plant performance, and it is thus important to assess the part load performance of such a plant under various operating conditions. The emphasis of this paper is on the comparison of part load performance of various advanced cycles (STIG, CRGT, Combined Cycle). The results show that the part load performance levels of a CRGT cycle deteriorate less fast than those of a combined cycle, whereas part load behavior is similar to that of a STIG cycle. However, this study also indicates that CRGT part load performance is less attractive than published performance curves of Westinghouse’s innovative CHAT cycle, thus confirming that the key advantage of the CRGT cycle is the projected ultra-low emissions characteristics of the cycle.
Experimental and Numerical Investigation of Flapping Wing Propulsion and its Application for Boundary Layer Control
Authors: Dohring Claus M. , Fottner Leonhard , Platzer Max F.
Published: December 2014

A thrust generating flapping airfoil adds energy to the flow and therefore can be used as a means for active boundary layer control if positioned close to a profile’s surface. This effect is investigated with a small flapping airfoil placed in the flow at varying distances above a flat plate. The experimental data are based on flow visualization using dye injection and Laser Doppler Velocimetry data from a water tunnel. Vortical structures and time averaged velocity profiles are compared with numerical computations from an existing two-dimensional Navier Stokes solver and show good agreement. Even asymmetric wake structures which develop above a critical reduced frequency are obtained numerically. It is found that the boundary layer can be eccelerated both upstream and downstream of the airfoil and that there exists a beneficial ground interference effect if the airfoil is placed close to the surface. Furthermore it is shown that the wake pattern along the wall is dominated by clockwise vortices at low reduced frequencies and counterclockwise vortices at high reduced frequencies. Finally a stationary profile with trailing edge separation is used in the water tunnel and it is demonstrated that flow reattachment can be obtained applying a small flapping airfoil downstream. Parametric studies are performed to determine the influence of plunge frequency, amplitude, airfoil size and airfoil location and considerations to find the optimum parameters are presented.
Validation of a Throughflow Time-Marching Finite-Volume Solver for Transonic Compressors
Authors: Baralon Stephane , Eriksson Lars-Erik , Håll Ulf
Published: December 2014

An improved throughflow method to treat transonic viscous flows with shocks, using a finite-volume time-marching solver, is presented. Effects due to deviation, secondary losses, endwall skin friction and spanwise mixing are modelled. An alternative blade blockage is used to better take into account the effect of the blade on the transonic passage flow. A theoretical and numerical study of the axisymmetric shock showed that it is treated as a normal blade passage shock by the blade row model. Two different techniques to solve the numerical problems associated with the leading edge singularity due to incidence are investigated. The computation of an entire speed-line for a three stage transonic fan has been conducted in order to further calihrate and validate the various models. The validation showed that the solver is capable of giving a reasonable meridional picture of the transonic flow field for different operating points.
Jet Mixing in a Slot
Authors: Wang Ting , Chintalapati Sekhar , Bunker Ronald S. , Lee Ching Pang
Published: December 2014

Jet mixing inside a slot has the potential to be applied for cooling in various components in gas turbines. Based on the premise that more uniform flow at the exit of the slot would achieve more uniform cooling downstream of the slot, an experimental program was conducted to focus on investigating the flow mixing behavior inside the slots. Various parameters including orientation angle, inclination angle, slot width, effect of primary flow and slot depth were systematically examined.

An array of seven jets with a jet-to-jet spacing of five diameters and velocity ratio of unity was used in the experiment. Experiments were performed by changing the orientation angles of the jets with two inclination angles (90° and 30°). The results indicated that the flow distribution at the slot exit becomes more uniform as the orientation angle was increased from 0° to 60°. Wider slot width brought about high non-uniformity and was clearly undesirable. The optimum slot depth was found to range from 2 to 2.8 times the jet diameter for slots perpendicular to the primary flow (i.e. with 90° inclination angle). The flow field was the most uniform where the shear layers of the two adjacent jets met. Regions of low velocity and high pressure caused non-uniform velocity distribution downstream where the jets met, so deeper slots do not necessarily render better uniformity. When the orientation angle increased from 0 to 30° and 60°, the jets bent toward the wall in the inclined direction caused by the Coanda effect. The presence of the primary flow forced the jet to spread faster in the lateral direction and caused some nonuniform flow pockets at the slot exit.

The compound angle configuration (60° jet orientation and 30° slot inclination angles) was discovered as the best choice with four merits: (i) The acceptable uniform flow can be reached as shallow as h/d = 1.0 (slot depth over jet diameter), (ii) The range of the acceptable uniform flow was the broadest (form y/d = 1.0 to y/d = 2.8). (iii) Flow uniformity was the best at the exit, (iv) The total pressure loss was the lowest.
Highly Resolved Distribution of Heat Transfer for Turbine Leading Edge Film Cooling Including Reynolds Number and Blowing Rate Effects
Authors: Jung K. , Hennecke D. K.
Published: December 2014

The effect of leading edge film cooling on heat transfer was experimentally investigated using the naphthalene sublimation technique. The experiments were performed on a symmetrical model of the leading edge suction side region of a high pressure turbine blade with one row of film cooling holes on each side. Two different lateral inclinations of the injection holes were studied: 0° and 45°. In order to build a data base for the validation and improvement of numerical computations, highly resolved distributions of the heat/mass transfer coefficients were measured. Reynolds numbers (based on hole diameter) were varied from 4000 to 8000 and blowing rate from 0.0 to 1.5. For better interpretation, the results were compared with injection-flow visualizations.

Increasing the blowing rate causes more interaction between the jets and the mainstream, which creates higher jet turbulence at the exit of the holes resulting in a higher relative heat transfer. This increase remains constant over quite a long distance dependent on the Reynolds number. Increasing the Reynolds number keeps the jets closer to the wall resulting in higher relative heat transfer. The highly resolved heat/mass transfer distribution shows the influence of the complex flow field in the near hole region on the heat transfer values along the surface.
Evaluation of Acoustic Flutter Suppression for Cascade in Transonic Flow
Authors: Lu Pong-Jeu , Chen Sen-Kuei
Published: December 2014

Flutter suppression via actively excited acoustic waves is a new idea proposed recently. The high flutter frequency (typically 50–500 Hz for a fan blade) and stringent space constraint makes conventional mechanical type flutter suppression devices difficult to implement for turbomachines. Acoustic means arises as a new alternative which avoids the difficulties associated with the mechanical methods. The objective of this work is to evaluate numerically the transonic flutter suppression concept based on the application of sound waves to 2D cascade configuration. This is performed using a high-resolution Euler code based on a dynamic mesh system. The concept has been tested to determine the effectiveness and limitations of this acoustic method. In a generic bending-torsion flutter study, trailing-edge is found to be the optimal forcing location and the control gain phase is crucial for an effective suppression. The P&W fan rig cascade was used as the model to evaluate the acoustic flutter suppression technique. With an appropriate selection of the control logic the flutter margin can be enlarged. Analogous to what were concluded in the isolated airfoil study, for internal excitation, trailing-edge forcing was shown to be optimal since the trailing-edge receptivity still works as the dominant mechanism for generating the acoustically-induced airloads.
Multistage Centrifugal Compressor Surge Analysis: Part I — Experimental Investigation
Authors: Arnulfi G. L. , Giannattasio P. , Giusto C. , Massardo A. F. , Micheli D. , Pinamonti P.
Published: December 2014

This paper reports an experimental investigation on centrifugal compressor surge. The compression system consists of a four-stage blower with vaned diffusers and a large plenum discharging into the atmosphere through a throttle valve. Measurements of unsteady pressure and flow rate in the plant, and of instantaneous velocity in the diffusers of the first and fourth compressor stage are performed during deep surge, at several valve settings and three different rotation speeds. Additional tests have been carried out on a different system configuration, i.e., without plenum, in order to obtain the steady-state compressor characteristics and to collect reference data on stall in surge-free conditions. In this configuration, a fully developed rotating stall was detected in the compressor diffusers, while during surge it affects only a limited part of the surge cycle.

The goal of the present experimental work was to get a deeper insight into unstable operating conditions of multi-stage centrifugal compressors and to validate a theoretical model of the system instability to be used for the design of dynamic control systems.
Design and Testing of Swept and Leaned Outlet Guide Vanes to Reduce Stator-Strut-Splitter Aerodynamic Flow Interactions
Authors: Wadia A. R. , Szucs P. N. , Gundy-Burlet K. L.
Published: December 2014

Large circumferential varying pressure levels produced by aerodynamic flow interactions between downstream stators and struts present a potential noise and stability margin liability in a compression component. These interactions are presently controlled by tailoring the camber and/or stagger angles of vanes neighboring the fan frame struts. This paper reports on the design and testing of a unique set of swept and leaned fan outlet guide vanes (OGVs) that do not require this local tailoring even though the OGVs are closely coupled with the fan frame struts and splitter to reduce engine length. The swept and leaned OGVs not only reduce core-duct diffusion, but they also reduce the potential flow interaction between the stator and the strut relative to that produced by conventional radial OGVs. First, the design of the outlet guide vanes using a single bladerow three-dimensional viscous flow analysis is outlined. Next, a two-dimensional potential flow analysis was used for the coupled OGV-frame system to obtain a circumferentially non-uniform stator stagger angle distribution to further reduce the upstream static pressure disturbance. Recognizing the limitations of the two-dimensional potential flow analysis for this highly three-dimensional set of leaned OGVs, as a final evaluation of the OGV-strut system design, a full three-dimensional viscous analysis of a periodic circumferential sector of the OGVs, including the fan frame struts and splitter, was performed. The computer model was derived from a NASA-developed code used in simulating the flow field for external aerodynamic applications with complex geometries. The three-dimensional coupled OGV-frame analysis included the uniformly-staggered OGVs configuration and the variably-staggered OGVs configuration determined by the two-dimensional potential flow analysis. Contrary to the two-dimensional calculations, the three-dimensional analysis revealed significant flow problems with the variably-staggered OGVs configuration and showed less upstream flow non-uniformity with the uniformly-staggered OGVs configuration. The flow redistribution in both the radial and tangential directions, captured fully only in the three-dimensional analysis, was identified as the prime contributor to the lower flow non-uniformity with the uniformly-staggered OGVs configuration. The coupled three-dimensional analysis was also used to validate the design at off-design conditions. Engine test performance and stability measurements with both uniformly- and variably-staggered OGVs configurations with and without the presence of inlet distortion confirmed the conclusions from the three-dimensional analysis.
The Influence of Endwall Contouring on the Performance of a Turbine Nozzle Guide Vane
Authors: Dossena Vincenzo , Perdichizzi Antonio , Savini Marco
Published: December 2014

The paper presents the results of a detailed investigation of the flow field in a gas turbine linear cascade. A comparison between a contoured and a planar configuration of the same cascade has been performed, and differences in the three-dimensional flow field are here analyzed and discussed. The flow evolution downstream of the trailing edge was surveyed by means of probe traversing while a 3-D Navier-Stokes solver was employed to obtain information on flow structures inside the vaned passages. The experimental measurements and the numerical simulation of the three-dimensional flow field has been performed for two cascades; one with planar endwalls, and the other with one planar and one profiled endwall, so as to present a reduction of the nozzle height. The investigation was carried out at an isentropic downstream Mach number of 0.6. Airfoils of both cascades were scaled from the same high pressure gas turbine inlet guide vane. Measurements of the three-dimensional flow field have been performed on five planes downstream of the cascades by means of a miniaturized five-hole pressure probe. The presence of endwall contouring strongly influences the secondary effects; the vortex generation and their development is inhibited by the stronger acceleration taking place throughout the cascade. The results show that the secondary effects on the contoured side of the passage are confined in the endwall region, while on the flat side the secondary vortices display characteristics similar to the ones occurring downstream of the planar cascade. The spanwise outlet angle distribution presents a linear variation for most of the nozzle height, with quite low values approaching the contoured endwall. The analysis of mass averaged losses shows a significant performance improvement in the contoured cascade. This has to be ascribed not only to lower secondary losses but also to a reduction of the profile losses.
Experimental and Numerical Studies of NOx Formation in Two-Stage Methane-Air Flames
Authors: Li S. C. , Williams F. A.
Published: December 2014

To help understand how staged combustion aids in reducing emissions of oxide of nitrogen from gas turbines, measurements and computations are made of structures of two-stage counterflow methane-air flames at nomal atmospheric pressure and a feed-stream temperature of about 300 K. The fuel stream is partially premixed, with equivalence ratios from 1.5 to 3.0. To the air stream is added up to 10% by mass of water spray, carbon dioxide, or nitrogen. Flame structures, including formation of species containing two carbon atoms, are measured by gas chromatography of samples withdrawn by fine quartz probes and are calculated by numerical integrations of the conservation equations employing an updated elementary chemical-kinetic data base. The same sampling system is employed with a low-flow-rate NOx analyzer to obtain profiles of nitric oxide and nitrogen dioxide, which are also calculated in the numerical integrations. The two-stage flame exhibits a green fuel-rich premixed flame and a blue diffusion flame with the maximum NOx concentrations found near the blue flame. At an air-side strain rate of 50 s−1, for fuel-side equivalence ratios of 1.5, 2.0, 2.5 and 3.0, respectively, measured peak NOx concentrations were about 70, 90, 100 and 90 ppm, reduced to 60, 70, 50, and 40 ppm, respectively, when 5% water by mass was added to the air stream. Results of the numerical integrations were in reasonable agreement with these experimental results when suitable selections were made of certain critical elementary reaction-rate constants. These new NOx measurements and computations help to increase understanding of influences of staging and diluent addition, identify important reactions for pollutant formation and suggest means to reduce emissions.
IGV-Rotor Interactions in a 4-Stage Axial Compressor
Authors: Puetz O. , Eikelmann J. , Stoff H.
Published: December 2014

Detailed experiments have been made in a 4-stage axial compressor of industrial design. The exit flow field of the rotor of the first stage was measured by hot-wire anemometry and fast-response pressure probes under design operating conditions. Tandem inlet guide vanes (IGV) are situated upstream of the first rotor.

Flow field results are presented for total pressure, massflux and swirl angle over a closely-spaced grid of probe locations in radial and circumferential directions in the absolute and rotating frame of reference. The tandem inlet guide vane row and stage 1 vane row are positioned peripherally for various settings (clocking).

Depending on the peripherical position of IGV and stator 1 the mean values for one rotor pitch varies by 1.5% for mass flow, 1.3° for swirl angle and 8.7% for total pressure.

Loss in total pressure at the rotor exit is a minimum, when the IGV row wakes enter the downstream rotor passage at about 1/4 pitch from the suction-side. Blade and vane channels have similar pitchwise spacing.
Secondary Flow Decay Downstream of Turbine Inlet Guide Vane With End-Wall Contouring
Authors: Michelassi V. , Martelli F. , Corradini U.
Published: December 2014

The secondary flows development downstream of a turbine stator blade with non-symmetric endwall contours is measured and analyzed. Measurements are carried out in a subsonic linear cascade with a large test section. The measurements are carried out using micro-pneumatic five hole probes which allow a detailed description of the vortical structures. The effect of secondary flows on the blade load is discussed. The passage vortices are found to collide and produce two pairs of counter-rotating vortices. The collision is caused by the mutual influence of the endwall contours and the pressure distribution on the blade. The measurements in 13 planes downstream of the trailing edge also show the presence of an extra vortex which appears because of sudden channel expansion. The 13 measurement planes orthogonal to the mean flow allow a detailed description of the secondary flow decay. The large flow distortion in terms of pitch and yaw angles is analyzed and discussed.
Isothermal Fatigue Behavior and Damage Modeling of a High Temperature Woven PMC
Authors: Gyekenyesi Andrew L.
Published: December 2014

This study focuses on the fully reversed fatigue behavior exhibited by a carbon fiber/polyimide resin woven laminate at room and elevated temperatures. Nondestructive video edge view microscopy and destructive sectioning techniques were used to study the microscopic damage mechanisms that evolved. The elastic stiffness was monitored and recorded throughout the fatigue life of the coupon. In addition, residual compressive strength tests were conducted on fatigue coupons with various degrees of damage as quantified by stiffness reduction. Experimental results indicated that the monotonic tensile properties were only minimally influenced by temperature, while the monotonic compressive and fully reversed fatigue properties displayed greater reductions due to the elevated temperature. The stiffness degradation, as a function of cycles, consisted of three stages; a short-lived high degradation period, a constant degradation rate segment covering the majority of the life, and a final stage demonstrating an increasing rate of degradation up to failure. Concerning the residual compressive strength tests at room and elevated temperatures, the elevated temperature coupons appeared much more sensitive to damage. At elevated temperatures, coupons experienced a much larger loss in compressive strength when compared to room temperature coupons with equivalent damage. The fatigue damage accumulation law proposed for the model incorporates a scalar representation for damage, but admits a multiaxial, anisotropic evolutionary law. The model predicts the current damage (as quantified by residual stiffness) and remnant life of a composite that has undergone a known load at temperature. The damage/life model is dependent on the applied multiaxial stress state as well as temperature. Comparisons between the model and data showed good predictive capabilities concerning stiffness degradation and cycles to failure.
Experimental and 3D CFD Investigation in a Gas Turbine Exhaust System
Authors: Sultanian Bijay K. , Nagao Shinichiro , Sakamoto Taro
Published: December 2014

Both experimental and 3D CFD investigations are carried out in a scale model of an industrial gas turbine exhaust system to better understand its complex flow field and to validate CFD prediction capabilities for improved design applications. The model consists of an annular diffuser passage with struts, followed by turning vanes and a rectangular plenum with side exhaust. Precise measurements of total/static pressure and flow velocity distributions at the model inlet, strut outlet and model outlet are made using aerodynamic probes and locally a Laser Doppler Velocimeter (LDV). Numerical analyses of the model internal flow field are performed utilizing a three-dimensional Navier-Stokes (N-S) calculation method with the industry standard k-ε turbulence model. Both the experiments and computations are carried out for three load conditions: full speed no load (FSNL), full speed mid load (FSML, 57% load), and full speed full load (FSFL). Based on the overall comparison between the measurements and CFD predictions, this study concludes that the applied N-S method is capable of predicting complicated gas turbine exhaust system flows for design applications.
Thermodynamic Performance Analyses of Mixed Gas-Steam Cycle (1): Performance Prediction Method
Authors: Hanawa Kirk
Published: December 2014

There are various papers relevant to the improvement ideas of gas turbine cycles, which in general discuss only optimum one-point cycle analysis.*1,*2,*6 It is, accordingly, unclear whether such improvement concepts can be applied into existing gas turbines or not. It might be difficult to incorporate such ideas, in the case of yielding significant changes for operation modes. And it may be essential to assess improvement ideas, from view points of applicability to existing gas turbine models.*3 This paper introduces the performance analysis method of simplified small perturbation procedure, showing thermodynamic behaviors based upon the component characteristics, and resultant influences due to settled operation parameters, like ambient temperature & pressure, turbine inlet temperature, etc. The established method might be used as a rule of thumb for the performance prediction when introducing water and/or steam injection into GTs, where operational parameters’ changes are defined under multi-linear differential equations. This is easy to compile in the computer as Lotus 1-2-3 or Exel to evaluate whether every parameter is within the limit or not, offering very helpful performance evaluation tool for the conceptual design stage.
Modular Simulation of Coolant Internal Network and Rotating Cavity Analysis
Authors: Carcasci Carlo , Carnevale Ennio , Facchini Bruno , Ferrara Giovanni
Published: December 2014

The increase in gas turbine performance requires very high total inlet temperatures even in heavy-duty applications. Therefore, an accurate design of both the blade cooling and the cooling network from the compressor to the blade is very important. In previous works, the authors have studied the cooling blade problems for both the stator and the rotor case. The present paper presents a simple and fast procedure to study the cooling network: a modular code has been developed for this purpose and particular attention has been focused on the study o the rotating cavities between the stator and the rotating disks.

The results we have obtained are good and the code developed is at present used in industry.
Italian Navy Application, Operation and Maintenance of Fiat - GE LM2500 Gas Turbine Propulsion Systems
Authors: Maggini Massimo , Tonelli Roberto
Published: December 2014

The LM2500 gas turbine has been used in Italian Navy (ITN) ships for more than twenty years, as the first engines were installed on board the “Lupo” class Frigates during the second half of the 1970s.

The LM2500 during its service has proven to be reliable in both the “Combined Diesel or Gas” (CODOG) and the “Combined Gas and Gas” (COGAG) propulsion plant, with Controllable Pitch Propeller (CPP) and Fixed Pitch Propeller (FPP) as the ITN marine operational experience demonstrates. The last application was in the DURAND DE LA PENNE Class DDG with a CODOG arrangement and two shaft lines with Feathered Controllable Pitch Propellers (FCPP), produced by FINCANTIERI shipyard, which may range from a forward to an astern direction till the blades reach a flag position. This type of propeller allows a considerable drop in the absorbed power and therefore in fuel consumption and noise when using a single shaft.

Based on the ITN experience with the DDG class, the use of FCPP achieves remarkable fuel savings with the gas turbine since, due to the high specific consumption of the engine at low speeds, it is cheaper to have a single shaft running.

The maintenance approach to the engines installed on board ITN ships, based on the “on condition” concept, has been developed by the ITN and Fiat Avio to maximise the availability of the vessels. This covers both on-board corrective maintenance (inspection, special maintenance and / or introduction of improvements) and the substitution maintenance, with successive overhaul and application of decided updating of gas generators and power turbines.
A Novel Optimisation Method for Variable Cycle Jet Engines
Authors: Oggero Lorenzo , Pilidis Pericles
Published: December 2014

A variable cycle engine (VCE) is a very complex concept. Extensive variable geometry features are required to ensure safe handling characteristics in the two or more operating modes that are envisaged. These may include variable compressor staters, variable nozzle areas and variable bypass valves.

In this paper a method for assessing the optimum setting of control variables is described. The starting point of the analysis is one of the operating modes of the engine, and an optimisation is carried out to decide the new values of the control variables within that operating mode or when changing to another.

The sensitivity of the cycle, in the initial mode, is assessed and an influence coefficient vector is created. This is then employed to decide what setting changes should be implemented to the control variables to achieve the desired result, respecting operating constraints such as surge margins, gas temperatures and rotor speeds.

The engine selected for analysis is the selective bleed engine, although the method could be used for other engine geometries after suitable adaptation. There are two very useful features of this method. The first is that it can give a view of the variable cycle capabilities of an engine with variable geometry features. The second is that it identifies the constraints, enabling the designer to focus the development effort where it is most needed.
CHAT Technology: An Alternative Approach to Achieve Advanced Turbine Systems Efficiencies With Present Combustion Turbine Technology
Authors: Nakhamkin Michael , Swensen Eric C. , Scheibel John R. , Cohn Arthur
Published: December 2014

This paper describes the current status and anticipated improvements in the Cascaded Humidified Advanced Turbine (CHAT) technology. With these improvements, CHAT will provide an alternative approach to achieving the goals of the Department of Energy’s Advanced Turbine Systems (ATS) project of a 60% thermal cycle efficiency for natural gas fired combined cycle power plants.

The traditional approach to increasing the efficiency of simple cycle and combined cycle power plants was to increase the firing temperature and pressure of the basic Brayton cycle. However, every increase in the CT firing temperature required progressively higher development cost, associated with new materials and cooling techniques, and increased NOx control challenges.

CHAT is a gas turbine based cycle with intercooling, reheat, recuperation and humidification. It is based upon the integration of an existing design heavy duty combustion turbine with an additional high pressure shaft comprised of industrial compressors and expander. The current CHAT plant design includes an HP expander inlet temperature of 871 C (1600 F), which represents the level of the combustion turbine technology of the late 1960’s – early 1970’s. The expander on the power generation shaft (LP) is based upon current combustion turbine technology with turbine inlet temperature of 1400 C (2550 F). One of the most effective ways to increase the CHAT plant efficiency is to increase the HP expander inlet temperature. By increasing this temperature to a relatively low 1150 C (2100 F), and maintaining the current inlet temperatures on the LP expander, the CHAT plant could achieve the ATS program target efficiency.

The paper presents the current CHAT plant’s performance and cost characteristics, and the initial findings of a project co-sponsored by the Electric Power Research Institute (EPRI) and Energy Storage and Power Consultants, (ESPC) for the development of an HP expander with increased inlet temperatures.
Exergy Analysis of Two Second-Generation SCGT Plant Proposals
Authors: Corti A. , Failli L. , Fiaschi D. , Manfrida G.
Published: December 2014

Two different power plant configurations based on a Semi-Closed Gas Turbine (SCGT) are analyzed and compared in terms of First and Second Law analysis. SCGT plant configurations allow the application of CO2 separation techniques to gas-turbine based plants and several further potential advantages with respect to present, open-cycle solutions. The first configuration is a second-generation SCGT/CC (Combined Cycle) plant, which includes inter-cooling (IC) between the two compression stages, achieved using spray injection of water condensed in a separation process removing vapor from the flue gases. The second configuration (SCGT/RE) combines compressor inter-cooling with the suppression of the heat recovery steam generator and of the whole bottoming cycle; the heat at gas turbine exhaust is directly used for gas turbine regeneration.

The SCGT/CC-IC solution provides good efficiency (about 55%) and specific power output figures, on account of the spray inter-cooling; however, with this configuration the cycle is not able to self-sustain the CO2 removal reactions and amine regeneration process, and needs a substantial external heat input for this purpose.

The SCGT/RE solution is mainly attractive from the environmental point of view: in fact, it combines the performance of an advanced gas turbine regenerative cycle (efficiency of about 49%) with the possibility of a self-sustained CO2 removal process. Moreover, the cycle configuration is simplified because the HRSG and the whole bottoming cycle are suppressed, and a potential is left for cogeneration of heat and power.
A Comparison of Experimental With Computational Results in an Annular Turbine Cascade With Emphasis on Losses
Authors: Casciaro C. , Treiber M. , Sell M. , Saxer A. P. , Gyarmathy G.
Published: December 2014

Recent discussions in the industrial CFD community have identified a need for guidelines covering the accurate and efficient computation of a range of flow field classes. This paper addresses some of these issues for a standard turbomachinery test case, by investigating the flow through on annular blade row of a generic turbine profile, operating at an exit Mach number of 0.5.

The joint experimental and CFD works have focused upon identifying and quantifying the loss sources and loss development. This has been achieved by the acquisition of dense data sets of a known, high and repeatable experimental accuracy, where, concentrating primarily upon the investigation of the secondary flow phenomena, optimised experimental methods have been employed to measure the pressure distributions in the annuls and the development of the flow field, particularly the loss structures, downstream of the trailing edge.

On the CFD side, the flow field has been computed using commercial codes. Adopting the loss distribution as a primary marker for the quality of the CFD results, the performance and efficacy of the codes and the implemented viscous models can be assessed. The flow has been computed both 2D and 3D, from inviscid to laminar to turbulent with different turbulence models, with and without transition. According to the model, the flow has been investigated considering a wide range of parameters influencing its turbulent state.

Through this study, guidelines concerning numerical smoothing and free-stream turbulence parameters are proposed for the computation of such flows. The need of a transition model within 3D schemes, rather than an improvement of the turbulence model, to predict accurate loss levels has been recognized. However, through the cross analysis of the different computational results, a good estimate of the loss magnitude and distribution is feasible with the currently used models.
Oscillator Fin as a Novel Heat Transfer Augmentation Device for Gas Turbine Cooling Applications
Authors: Uzol Oguz , Camci Cengiz
Published: December 2014

A new concept for enhanced turbulent transport of heat in internal coolant passages of gas turbine blades is introduced. The new heat transfer augmentation component called “oscillator fin” is based on an unsteady flow system using the interaction of multiple unsteady jets and wakes generated downstream of a fluidic oscillator. Incompressible, unsteady and two dimensional solutions of Reynolds Averaged Navier-Stokes equations are obtained both for an oscillator fin and for an equivalent cylindrical pin fin and the results are compared. Preliminary results show that a significant increase in the turbulent kinetic energy level occur in the wake region of the oscillator fin with respect to the cylinder with similar level of aerodynamic penalty. The new concept does not require additional components or power to sustain its oscillations and its manufacturing is as easy as a conventional pin fin. The present study makes use of an unsteady numerical simulation of mass, momentum, turbulent kinetic energy and dissipation rate conservation equations for flow visualization downstream of the new oscillator fin and an equivalent cylinder. Relative enhancements of turbulent kinetic energy and comparisons of the total pressure field from transient simulations qualitatively suggest that the oscillator fin has excellent potential in enhancing local heat transfer in internal cooling passages without significant aerodynamic penalty.
Aerodynamic Performance of an Axial Compressor Stage With Variable Rotor Blades and Variable Inlet Guide Vanes
Authors: Cyrus Václav
Published: December 2014

Experimental investigations of flow fields and losses in an axial flow compressor stage were carried out. The stage has hub/tip ratio of 0.7. The design values of flow coefficient and pressure coefficient are 0.6 and 0.81, respectively. Aerodynamic performance was investigated for two principal configurations: i) axial flow stage with variable rotor blades, ii) axial flow stage with variable inlet guide and stator vanes. The most efficient volume flow rate regulation of the stage was with the application of variable rotor blades.

On the basis of experimental data an analysis of the origin of flow separation on the suction and pressure surfaces of rotor and stator blades was made with the use of simple design criteria. The unsteady flow of rotating stall type in the tested stage appeared after simultaneous occurence of large stall regions in both rotor and stator blade rows. The existence of large stall regions in the IGV did not affect the rotating stall onset. At high values of the IGV stagger angle change (50 deg) pressure pulsations appeared due to the occurence of stall.
Performance Analysis in a Subsonic Radial Diffuser
Authors: Casartelli E. , Saxer A. P. , Gyarmathy G.
Published: December 2014

Steady-state numerical investigations in a subsonic vaned radial diffuser are presented. The 3D flow field has been computed with a commercial Navier-Stokes code (TASCflow), using two different types of axially variable but circumferentially uniform inlet flow conditions, one based on realistic (measured) time-averaged impeller outflow, the other on an idealized distribution. Two different vane leading-edge shapes were investigated. The leading edge redesign is based on the 2D analysis and inverse-design software package MISES.

For a complete operating speed line a detailed analysis of the flow structure and loss distribution within the diffuser is presented and the results obtained for the different inlet flow conditions and geometries are critically compared. The performance of the diffuser and its subcomponents is evaluated in terms of dimensionless quantities such as blockage, total-pressure-loss and pressure-recovery coefficients. Based on the comparisons and the cross performance analysis of the various effects due to leading edge redesign and different inlet velocity profiles, several design guidelines are postulated.
Catalytic Indirectly Heated Gasification of Bagasse
Authors: Peres Sérgio , Green Alex
Published: December 2014

The catalytic indirectly heated gasification of bagasse was investigated in this study. The quality of the gaseous fuel was assessed using the total energy analysis of the gas, in which both heat content and total yields of the gas produced from the gasification of bagasse are analyzed at temperatures ranging from 700 to 1000°C. Untreated bagasse gasification was used as a baseline for the investigation of the effect of catalysts on the gasification process. The total energy analysis showed a significant improvement of gas quality due to increase of temperature and due to the use of alumina-zinc based catalysts at temperatures below 900°C. The presence of these catalysts in the gasification process affected the quality of the gases formed, mainly by increasing the hydrogen production, reduction of the gas dilution by carbon dioxide and a slightly higher production of carbon monoxide. Above 900°C, temperature dominates the gasification reaction mechanisms causing the catalysts to have little or no significant effect. Thermal cracking of tar is of major importance on the gasification process, as the tar yields reduce from 42.1 to 24.7% of the bagasse original weight with the increase of the gasifier temperature from 700 to 1000°C. However, the solid residue reduced only from 16 to 13.3%. Hence, the increase in the gaseous yields at high temperature appeared to be due to the gasification of tar with some contribution from secondary reactions involving char. The result was the production of a medium heat content gaseous fuel.
Co-Pyrolysis and Co-Gasification of Coal and Biomass in a Pressurized Fixed-Bed Reactor
Authors: Collot Anne-Gaëlle , Megaritis Athanasios , Herod Alan A. , Dugwell Denis R. , Kandiyoti Raphael
Published: December 2014

The co-processing of coal-biomass mixtures under inert and reducing atmospheres has been studied in a bench scale fixed-bed (‘hot-rod’) reactor. The aim was to look for evidence of synergistic effects during the co-gasification of coal and biomass. Total volatile release, tar and char yields from mixtures of Daw Mill coal and Silver Birch wood (alone and in mixtures of 25, 50 and 75 % by weight), have been determined as a function of temperature (850 and 1000 °C) and pressures (up to 25 bar) under He-pyrolysis and CO2-gasification conditions. The total volatile yields of mixtures have been found to match those calculated theoretically from pure coal and biomass values under all conditions attempted, thus suggesting a lack of synergy in the amount of char produced. However, char reactivity measurements in an atmospheric thermogravimetric analyser (isothermal combustion in air at 500 °C) indicate that chars of coal-biomass mixtures have higher combustion reactivities than would be expected from the reactivities of the raw fuels alone. Similarly, the tar yields from mixtures are also somewhat higher than those predicted from the individual contributions of coal and biomass.
Elevated Temperature Exposure of Gas Turbine Materials to a Bio-Fuel Combustion Environment
Authors: Patnaik P. C. , Adams C. , Fuleki D. , Thamburaj R.
Published: December 2014

The use of biomass fuels in gas turbine engines requires an examination of the effect of the fuel on the engine materials. While the fuel may be more environmentally friendly than conventional fuels, it has the potential to produce serious life limiting corrosion within gas turbine engines. The effects of the high alkali and low sulphur content of the fuel on its corrosive properties needs to be examined. To determine the extent and type of corrosion typical material systems were exposed to bio-fuel combustion products in a flame tunnel and furnace under conditions designed to promote high temperature corrosion. The preliminary results indicate that type I hot corrosion is certainly occurring with some signs of type II hot corrosion in certain material systems.
FADEC Computer Systems for Safety Critical Application
Authors: Schwamm Friedrich
Published: December 2014

One of the main requirements for modern FADEC systems is to implement great computing power with many interfaces and to keep the FADEC hardware effort to a minimum. On the other side the criticality potential of computer failures is considered as ‘hazardous’. The trend in FADEC development is to implement even more complex functions into the control software which consequently increases the authority and therefore the criticality potential of computer failures. In the mid 80’s a double computer system was used to performed a parallel execution of the control software with identical input parameters to output identical results. A difference in any one of these computer results causes the comparator hardware to output a failure indication. This was considered to have a 100% coverage of computer failures. The problem with this system was certainly the relatively large hardware overhead and the limited intelligence of the comparator logic. Some other FADEC systems have implemented only a Watch Dog Timer and Bus Access Supervisory hardware to detect computer malfunctions. With this method the proof for the achievements of the safety requirements have become almost impossible since adequate fault models of the computer components are difficult to establish due to their increasing functional complexity. This paper describes how to develop the safety features for the Computer Design from the Engine Control System Safety Requirements to achieve a full coverage of the potentially critical failure effects with fault tolerant failure recovery functions and a minimum of hardware overhead.
Heat Transfer Contributions of Pins and Endwall in Pin-Fin Arrays: Effects of Thermal Boundary Condition Modeling
Authors: Chyu M. K. , Hsing Y. C. , Shih T. I.-P. , Natarajan V.
Published: December 2014

Short pin-fin arrays are often used for cooling turbine airfoils, particularly near the trailing edge. An accurate heat transfer estimation from a pin-fin array should account for the total heat transfer over the entire wetted surface which includes the pin surfaces and uncovered end walls. One design question frequently raised is the actual magnitudes of heat transfer coefficients on both pins and endwalls. Results from earlier studies have led to different and often contradicting conclusions. This variation, in part, is caused by imperfect or unrealistic thermal boundary conditions prescribed in the individual test models. Either pins or endwalls, but generally not both, were heated in those previous studies. Using a mass transfer analogy based on the naphthalene sublimation technique, the present experiment is capable of revealing the individual heat transfer contributions from pins and endwalls with the entire wetted surface thermally active. The particular pin-fin geometry investigated, S/D = X/D = 2.5 and H/D = 1.0, is considered to be one of the optimal array arrangement for turbine airfoil cooling. Both inline and staggered arrays with the identical geometric parameters are studied for 5,000 ≤ Re ≤ 25,000. The present results reveal that the general trends of the row-resolved heat transfer coefficients on either pins or endwalls are somewhat insensitive to the nature of thermal boundary conditions prescribed on the test surface. However, the actual magnitudes of heat transfer coefficients can be substantially different, due to variations in the flow bulk temperature. The present study also concludes that the pins have consistently 10 to 20% higher heat transfer coefficient than the endwalls. However, such a difference in heat transfer coefficient imposes very insignificant influence on the overall array-averaged heat transfer, since the wetted area of the uncovered endwalls is nearly four times greater than that of the pins.