bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Simulation of Unsteady Wake/Blade Interactions in Low Pressure Turbine Flows Using an Intermittency Transport Equation
Authors: Suzen Y. B. , Huang P. G.
Published: November 2008

An extensive computational investigation of the effects of unsteady wake/blade interactions on transition and separation in low-pressure turbines has been performed by numerical simulations of two recent sets of experiments using an intermittency transport equation. The experiments considered have been performed by Kaszeta and Simon [1] (Kaszeta et al. [2,3]), and Stieger [4] (Stieger and Hodson [5]) in order to investigate the effects of periodically passing wakes on laminar-to-turbulent transition and separation in low-pressure turbines. The test sections were designed to simulate unsteady wakes in turbine engines for studying their effects on boundary layers and separated flow regions over the suction surface. The numerical simulations of the unsteady wake/blade interaction experiments have been performed using an intermittency transport model. The intermittent behavior of the transitional flows is taken into account and incorporated into computations by modifying the eddy viscosity, with the intermittency factor. Turbulent quantities are predicted by using Menter’s two-equation turbulence model (SST). The intermittency factor is obtained from the transport equation model which can produce both the experimentally observed streamwise variation of intermittency and a realistic profile in the cross stream direction. Computational results are compared to the experiments. Overall, general trends are captured and prediction capabilities of the intermittency transport model for simulations of unsteady wake/blade interaction flowfields are demonstrated.
An Integrated Design System for Fans, Compressors, and Turbines: Part 2 — Interactive Interface
Authors: Sandel Wolfgang A. , Miller Max J.
Published: November 2008

A new, comprehensive, flexible, integrated design system for the aerodynamic design of fans, compressors, and turbines was developed during the past decade. It operates in both batch and interactive modes. The system contains a flow path generator, a through-flow solver, a stacked airfoil geometry generator, and a flank-milled airfoil geometry generator. This paper describes the interactive interface in more detail. In particular, it describes the design considerations, appearance, and functionality of the interactive interface. Top level requirements were established before the interface was designed. These requirements are explained and some of the key reasoning that drove the high level design of the interface is discussed. The four principal windows in the interface are described in detail. The interactive interface that was developed has significantly increased the productivity of fan, compressor and turbine aero designers.
Using Neural Network for Diagnostics of an Industrial Gas Turbine
Authors: Ghoreyshi M. , Singh R.
Published: November 2008

Gas Turbines are being utilized in increasing numbers for industrial applications because of their increasing in efficiency and reliability. However, they become degraded during operation and their associated maintenance costs can become extremely high for the owners. Hence, successful maintenance techniques are those which are able to reduce maintenance costs and down-time. In recent decades industry has started to use predictive maintenance techniques because of their benefits in reducing down-time compared to traditional techniques like breakdown maintenance, as a result different predictive maintenance and diagnostics techniques have been developed during the last fifteen years. This study, in particular, will focus on performance diagnostic techniques based on Neural Networks. The network features and training algorithms will be discussed to develop an appropriate model for gas turbine diagnostics. In addition, it will be shown how training data can affect training performance. This study follows on from previous work carried out at Cranfield University to develop engine health monitoring techniques; however it will attempt to investigate the different abilities of neural networks for use in industrial gas turbine diagnostics, especially in non-standard ambient temperatures and its advantages compared to Gas Path Analysis (GPA) techniques.
Prediction of Velocities and Heat Transfer Coefficients in a Rotor-Stator Cavity
Authors: Evans Justin , Stevens Lon M. , Bodily Clint , Kang Moon-Kyoo Brian
Published: November 2008

The calculation of swirl velocities and convective heat transfer coefficients in a rotor-stator cavity has been mostly based on equations taken from empirical data. However, the validity of these empirical relations is questionable in geometries and environments other than the specific ones for which they were derived. A commercial CFD code, Fluent, has been used to predict the swirl velocities and rotor disk convective heat transfer coefficient distribution for a rig at Arizona State University. The rig was run at several rotational Reynolds numbers (Reφ) varying from 4.6×105 to 8.6×105 and for various mass secondary flows. Several different turbulence models were used and the resulting predictions were compared with data obtained from the rig. Fluent was able to predict the swirl velocities, on average, within 30% and the convective heat transfer coefficients, on average, within 30% and often within 20%. The degree of agreement with the measured data was found to depend on which turbulence model that was used, mesh resolution, as well as the secondary flow and Reφ.
A Critical Evaluation of NOx Modeling in a Model Combustor
Authors: Jiang Lei-Yong , Campbell Ian
Published: November 2008

Reliable NOx modeling depends on the accurate prediction of both velocity and temperature fields. The velocity and temperature fields of a propane diffusion flame combustor, with interior and exterior conjugate heat transfers, were first numerically studied. The results from three combustion models, together with the re-normalization group (RNG) k-ε turbulence model and the discrete ordinates radiation model are discussed, and compared with comprehensive experimental measurements. The flow patterns and the recirculation zone length in the combustion chamber are excellently predicted, and the mean axial velocities are in fairly good agreement with the experimental data for all three combustion models. The mean temperature profiles are fairly well captured by the probability density function (PDF) and eddy dissipation (EDS) combustion models. However, the EDS-finite-rate combustion model fails to provide an acceptable temperature field. Based on the acceptable velocity and temperature fields, a number of NO modeling approaches were evaluated in a post-processing mode. The partial-equilibrium approach of O and OH radical concentrations shows a significant effect on the thermal NO formation rate. In contrast, the prompt NO, the NO re-burn mechanism and the third reaction of the extended Zeldovich mechanism have negligible effects on the overall NO formation in the present study. This study indicates that the semi-empirical, post-processing NO model can provide valuable NO simulations as long as the velocity and temperature fields are adequately predicted.
Testing of a Small Turbocharger/Turbojet Sized Simulator Rotor Supported on Foil Bearings
Authors: Walton James F. , Heshmat Hooshang , Tomaszewski Michael J.
Published: November 2008

A small rotor designed to simulate a miniature turbojet engine or turbocharger rotor mounted on compliant foil bearings was tested at speeds in excess of 150,000 rpm and temperatures above 260C (500F). The simulator rotor-bearing system was operated while positioned in various orientations and was subjected to transient shock impacts exceeding 35-Gs. Subsequent testing was completed to demonstrate the capabilities of miniature thrust foil bearings as well. The tested rotor weighed approximately 400 grams, used 15 mm diameter foil journal bearings and a multi-pad 25 mm diameter double acting thrust foil bearing. Results of the rotor bearing system dynamics are presented along with experimentally measured natural frequencies, rotor displacements and thrust load carrying ability. Good correlation between measurement and analysis is observed. Very short rotor acceleration times from rest to maximum speed were also measured. A parallel test simulator has been used to accumulate over 1,000 start-stop cycles to demonstrate the life of the bearing and coating. Based on this successful testing it is expected that the goal of developing oil-free turbochargers and small turbojet engines that operate at high speeds with long life will be achieved.
A Comparative Aerodynamic and Performance Study of a Three-Stage High Pressure Turbine With 3-D Bowed Blades and Cylindrical Blades
Authors: Schobeiri M. T. , Suryanarayanan A. , Jermann C. , Neuenschwander T.
Published: November 2008

To investigate the effect of the blade geometry on blade total pressure loss coefficient, efficiency, and performance, a comparative study is presented that deals with the aerodynamic and performance behavior of three-stage high pressure research turbine utilizing two different blade types. Keeping the initial conditions and the pressure ratio the same, two different rotors with the same hub and tip diameters are experimentally investigated. The first rotor incorporates 3-D convexly bowed blades, where as the second one utilizes a set of fully cylindrical blades. Using shrouded rotors and stators, the stator rings are correspondingly configured. The research turbine incorporates six rows beginning with a stator row. Interstage aerodynamic measurements are performed at design speeds at three stations, namely downstream of the first rotor row, the second stator row, and the second rotor row. For both rotors, the interstage radial and circumferential traversing present detailed flow pictures of the middle stage. Aerodynamic measurements were carried out at the turbine design speed. The experimental investigations have been carried out on a HP 3-stage gas turbine research facility at the Turbomachinery Performance and Flow Research Laboratory of Texas A&M University.
Dynamic Simulation of Carbonate Fuel Cell-Gas Turbine Hybrid Systems
Authors: Roberts Rory A. , Brouwer Jack , Liese Eric , Gemmen Randall S.
Published: November 2008

Hybrid fuel cell/gas turbine systems provide an efficient means of producing electricity from fossil fuels with ultra low emissions. However, there are many significant challenges involved in integrating the fuel cell with the gas turbine and other components of this type of system. The fuel cell and the gas turbine must maintain efficient operation and electricity production while protecting equipment during perturbations that may occur when the system is connected to the utility grid or in stand-alone mode. This paper presents recent dynamic simulation results from two laboratories focused on developing tools to aid in the design and dynamic analyses of hybrid fuel cell systems. The simulation results present the response of a carbonate fuel cell/gas turbine, or molten carbonate fuel cell/gas turbine, (MCFC/GT) hybrid system to a load demand perturbation. Initial results suggest that creative control strategies will be needed to ensure a flexible system with wide turndown and robust dynamic operation.
Full Annulus Simulation of a High-Speed Centrifugal Compressor Using an Unstructured RANS Flow Solver
Authors: Sheng Chunhua
Published: November 2008

This paper presents numerical simulations for a high-speed centrifugal compressor using an unstructured Reynolds averaged Naiver-Stokes flow solver U2NCLE. It solves three-dimensional compressible governing equations using an arbitrary Mach number solution algorithm. The stability enhancement for a centrifugal compressor was achieved by injecting air streams into the vaneless region of the diffuser. Numerical prediction of the stabilizing effect of air injection in the centrifugal compressor requires full annulus simulations of the compressor system. This work presents numerical procedures for simulating full annulus centrifugal compressor, including air injection modeling. A sliding technique is employed to handle relative motion grids for impeller and diffuser interactions. Computed results for the centrifugal compressor are analyzed and assessed with the experiment.
Computation of Flow and Heat Transfer in Two-Pass Rotating Rectangular Channels (AR=1:1, AR=1:2, AR=1:4) With 45-deg. Angled Ribs by Reynolds Stress Turbulence Model
Authors: Su Guoguang , Chen Hamn-Ching , Han Je-Chin , Heidmann James D.
Published: November 2008

Numerical predictions of three-dimensional flow and heat transfer are presented for rotating two-pass rectangular channel with 45-deg rib turbulators. Three channels with different aspect ratios (AR=1:1; AR=1:2; AR=1:4) were investigated. Detailed predictions of mean velocity, mean temperature, and Nusselt number for two Reynolds numbers (Re = 10,000 and Re = 100,000) were carried out. The rib height is fixed as constant and the rib-pitch-to-height ratio (P/e) is 10, but the rib height-to-hydraulic diameter ratios (e/Dh) are 0.125, 0.094, and 0.078, for AR=1:1, AR=1:2, and AR=1:4 channel, respectively. The channel orientations are set at 90 deg, corresponding to the cooling passages between mid-portion and the leading edge of a turbine blade. The rotation number varies from 0.0 to 0.28 and the inlet coolant-to-wall density ratio varies from 0.13 to 0.40, respectively. The primary focus of this study is the effect of the channel aspect ratio on the nature of the flow and heat transfer enhancement in a rectangular ribbed channel under rotating conditions. A multi-block Reynolds-averaged Navier-Stokes (RANS) method was employed in conjunction with a near-wall second-moment turbulence closure to provide detailed resolution of the Reynolds stresses and turbulent heat fluxes induced by the rib turbulators under both the stationary and rotating conditions.
Development of Management Support System for Gas Turbine Hot Gas Path Parts
Authors: Fujii Tomoharu , Fujioka Terutaka , Morinaga Masahiko , Takahashi Toshihiko , Tokoro Ken-Ichi , Takahashi Takeshi
Published: November 2008

The combined cycle power plants operating in Japan are normally provided with two or more gas turbines and spare parts in quantities as required by the number of gas turbine units in operation. Since the quantity of hot gas path parts installed in a gas turbine is massive, the parts required for a gas turbine are arranged in groups so as to simplify the control of parts inventory. These parts groups are replaced and repaired at each inspection. Furthermore, since the costs of hot gas path parts are very high, using the parts efficiently and implementing measuring to prolong the life of the parts are very important. Detailed parts rotation schedules are prepared to properly rotate the spare parts groups. In doing so, the length of service life, quantity of spare parts, schedules for using the parts for several years to come, and time required for maintenance and repairs must be taken into consideration. Special characteristics of respective power plants such as plans for prolonging the service life of parts and various costs must be taken into consideration. Since it is difficult to prepare the schedules for rotating parts automatically, skilled workers are carrying out most of work manually at present. Against such a backdrop, the authors have developed the “Management Support System for Gas Turbine Hot Gas Path Parts”. This system can be used to reduce the maintenance and repair costs by optimizing parts rotation schedules. The basic concepts of the development are as follows. 1) Some parts can be shared among plural number of power plants with the gas turbines of the same model. A user freely sets models of the gas turbines, categorization of parts, and numbers of the parts dealt with. 2) The unit of the part management is done based on not groups but serial numbers. Moreover, replacing parts is enabled. 3) The program is modulated according to the functions. Addition, change, and deletion of these functions are facilitated. The total system is developed platform-free.
Experimental Investigation of a High Pressure Ratio Aspirated Fan Stage
Authors: Merchant Ali , Kerrebrock Jack L. , Adamczyk John J. , Braunsheidel Edward
Published: November 2008

The experimental investigation of an aspirated fan stage designed to achieve a pressure ratio of 3.4:1 at 1500 feet/sec is presented in this paper. The low-energy viscous flow is aspirated from diffusion-limiting locations on the blades and flowpath surfaces of the stage, enabling a very high pressure ratio to be achieved in a single stage. The fan stage performance was mapped at various operating speeds from choke to stall in a compressor facility at fully simulated engine conditions. The experimentally determined stage performance, in terms of pressure ratio and corresponding inlet mass flow rate, was found to be in good agreement with the 3D viscous computational prediction, and in turn close to the design intent. Stage pressure ratios exceeding 3:1 were achieved at design speed, with an aspiration flow fraction of 3.5% of the stage inlet mass flow. The experimental performance of the stage at various operating conditions, including detailed flowfield measurements, are presented and discussed in the context of the computational analyses. The sensitivity of the stage performance and operability to reduced aspiration flow rates at design and off-design conditions are also discussed.
Development of Multi Cluster Burner for Fuel Grade DME
Authors: Saitou Takeo , Inoue Hiroshi , Kobayashi Nariyoshi , Watanabe Tomoko
Published: November 2008

Recently, DME (dimethyl ether: CH3OCH3) has attracted attention as a clean next-generation fuel, but it has the possibility of spontaneous ignition in gas turbine use. To avoid spontaneous ignition or flash-back, a coaxial jet cluster nozzle burner configuration was proposed previously, which can mix air and fuel effectively within a short distance. In this research, the full size multi cluster burner composed of coaxial jet cluster nozzle burners was designed, and combustion tests for gaseous fuel grade DME were carried out. (Fuel grade DME includes minor amounts of methanol and water as impurities.) In making the configuration tests of the multi cluster burner, the robust design method was applied. Characteristics of NOx emission, combustion efficiency, combustion stability, etc. were evaluated, and the optimal configuration of the combustor was determined. Also, the influences of impurities of fuel grade DME on the combustion performance were evaluated. With the optimal combustor, the prospects were good for achieving the targets, NOx < 20 ppm (16% O2), combustion efficiency > 99.9%, and pressure oscillation < 3.5 kPa. Regarding the influences of impurities of fuel grade DME, there was no great difference in combustion efficiency and pressure oscillation with addition of impurities in this test range.
CFD Simulation of the Losses in an Inlet Guide Vane of a Transonic Test Turbine
Authors: Sanz W. , Pieringer P. , Baumgartner W. , Edelbauer W. , Pilz C. , Neumayer F. , Rossi E.
Published: November 2008

In this work the flow through a pre-swirl turbine guide vane was calculated using two different flow solvers and compared with total pressure measurements in a downstream plane. The flow is transonic and strongly influenced by secondary flows. A special feature of this cascade is that the gap height at the hub is varying. Flow separation and leakage vortex flow dominate the loss generation. The flow is simulated using an in-house CFD code as well as the commercially available code FLUENT. The flow is carefully analysed and the loss generation mechanisms are presented in detail. The comparison with the measured total pressure distribution shows that the overall loss scheme is well predicted by both codes, but there are still large deficiencies in the quantitative results. The commercial code FLUENT is closer to the measurement data. Further investigations are performed to find out the differences between both codes.
Compressor Transient Behaviour
Authors: Tveit Gisle B. , Bakken Lars E. , Bjo̸rge Tor
Published: November 2008

An important issue related to compressor and driver integration is the behaviour during driver trip. Field tests at Troll Kollsnes gas treatment plant have shown that under a short power outage and within certain operating scenarios, the compressor enters the surge- and rotating stall area. These problems lead to a reduced flexibility in the operation of the pipeline compressors. The 40 MW variable speed electric motor driven compressors have therefore been subjected to dynamic simulation analyses to reveal the transient response. Dynamic simulations based on earlier trip tests have been performed so as to understand what parameters affect the severity and duration of a surge under power outage. An elaborate plant model has been created with the dynamic simulation tool OTISS™ by AspenTech and tuned to represent the plant. The model is validated against actual plant tests and operating data. The paper reports experience from analyses of the compressor and driver behaviour during run down. It is based on earlier tests and dynamic simulations performed for the Troll Kollsnes gas treatment plant. The main objective has been to study the compressor system sensitivity related to variation in polar inertia, driver power decay and trip signal delay on the transient rundown behaviour.
An Average-Passage Empirical Closure Model for Centrifugal Compressors
Authors: Gao Limin , Xi Guang , Wang Shangjin
Published: November 2008

Applying the novel time- and passage-averaging operators, a reduced average-passage equation system is derived to remove the bodyforce and the blockage factor in Adamczyk’s average-passage equations. Like the Reynolds-averaged Navier-Stokes equations the average-passage flow model does not contain sufficient information to determine its solution. Based on the rich throughflow analysis for axial-flow turbomachinery and numerous studies for centrifugal compressors, a semi-empirical model of the deterministic stress is developed for centrifugal compressors in the present study. Finally, the empirical model coupled with the interface approach is applied to predict the time-averaged flow field in a tested centrifugal compressor stage and the results are compared with experimental data. Using the same computational grids, the computational cost with the empirical model is slightly more than that with the mixing plane model, and a good agreement was obtained between the numerical results and experimental data.
Forced Response of Shrouded Bladed Disc Assemblies: A Jointed Experimental Numerical Approach
Authors: D’Ambrosio F. , Chatelet E. , Ravoux J. , Jacquet-Richardet G.
Published: November 2008

The objective of the proposed study is to progress towards a better modeling of bladed assemblies dynamic. Coupling devices are introduced in bladed stages to increase frequencies of resonance above the range of possible excitations. Commonly they are not only used to stiffen flexible structures but also to increase damping by dry friction, reducing the amplitude of vibration. Consequently, the resulting dynamic behavior is complex and highly non linear. In order to improve numerical capabilities used for the design of part span shrouds and to gain a better understanding of the dynamic behavior of shrouded assemblies, a jointed experimental and numerical approach has been conducted. A first experimental test based on a cantilever beam is considered. The beam, excited by a controlled electrodynamic shaker, is associated to a dry friction damper at its free end. A numerical finite element analysis and a macroslip model of contact has been developed. The solution method in time domain allows accurate computations of response levels and gives the main harmonics of the steady state response. Comparison between numerical and experimental results is very good. A second experimental set up is constituted by an assembly of 13 beams, cyclically mounted around a common disk and linked by geometrically simplified shrouds. The set up allows controlling the resultant forces in the contact and is able to exhibit all states of contact from fully slipping to fully stuck. The first results obtained are associated to a single couple of blades brought into contact.
Prediction of Turbulence and Transition in Turbomachinery Flows Using an Innovative Second Moment Closure Modeling
Authors: Borello Domenico , Rispoli Franco , Hanjalic Kemal
Published: November 2008

The paper reports on the assessment of two low-Reynolds-number second-moment turbulence closures (Low-Re SMC) in predicting turbulence and laminar-to-turbulent transition in turbomachinery flows. The model under consideration are the one by Hanjalic and Jakirlic (1998) (HJ) and an innovative topology-free Elliptic Blending Model, EBM, (Manceau and Hanjalic, 2002) here presented in a revised formulation. An in-house finite element code based on a parallel Multi-Grid technique for the solution phase (Borello et al., 2003a) is used. The finite element method is applied on mixed Q2-Q1 element shape functions formulation coupled with an innovative Petrov-Galerkin stabilization technique (Corsini et al., 2003). The test-cases under scrutiny are the transitional flow on a flat plate with circular leading edge (T3L ERCOFTAC-TSIG), and the flow around a DCA compressor cascade in quasi off-design condition (i = −1.5°) (Zierke and Deutch, 1989). The comparison between computations and experiments shows a satisfactory performance of the HJ model in predicting complex turbomachinery flows. The EBM also exhibits a fair level of accuracy, though it is less satisfactory in transition prediction. In view of its robustness, relative insensitivity to the grid refinement and the absence of topology-dependent parameters, the EBM is identified as an attractive second-moment closure option for computation of complex 3D turbulent flows in realistic turbomachinery configurations.
Measurement and Simulation of a Transonic Innovative Cooling System (ICS) for High-Temperature Transonic Gas Turbine Stages
Authors: Go¨ttlich E. , Innocenti L. , Vacca A. , Sanz W. , Woisetschla¨ger J. , Facchini B. , Jericha H. , Rossi E.
Published: November 2008

Gas turbine design technology requires the development of transonic turbine stages capable of carrying high stage load and of handling hot gas temperatures at turbine inlet. A reliable cooling system is necessary to cope with shocks emanating from preceding blade rows and impinging on the blade especially in the leading edge region. In order to fulfill these requirements researchers at Graz University of Technology have been working on an Innovative Cooling System (ICS) since 1995. The ICS is able to cover large areas of the blade surface with an effective cooling film and to reduce the metal temperature without a shower head cooling arrangement at the leading edge and any trailing edge cooling air ejection. In this paper the authors present a numerical comparison of the ICS to a conventional modern film cooling system both implemented in the same industrial transonic gas turbine blade. An experimental determination of the adiabatic film cooling effectiveness distribution around the blades surface was necessary for the ICS because of its uncommon design. The measurements were done on a cylindrical blade in a linear cascade arrangement. An infrared camera system was used to determine the effectiveness of this newly designed cooling system by measuring the temperature distribution on the blade surface. Then a numerical simulation of heat transfer and of internal and external cooling for the turbine blade at test rig conditions was performed. The ICS showed a lower outer wall temperature distribution of the blade compared to a standard film cooling system. The heavily loaded leading edge as well as the trailing edge are well cooled. Further conclusions on the advantages and disadvantages of the ICS are drawn.
Heat Recovery Steam Generator Design for a Graz Cycle Prototype Power Plant for CO2 Capture
Authors: Giglmayr I. , Paul J. , Sanz W.
Published: November 2008

The introduction of closed cycle gas turbines with their capability of retaining combustion generated CO2 can offer a valuable contribution to the Kyoto goal and to future power generation. Therefore, research and development at Graz University of Technology has lead to the GRAZ CYCLE, a zero emission power cycle of highest efficiency. The GRAZ CYCLE is still on a theoretical level, first tests with the turbo-machinery equipment were performed. In the GRAZ CYCLE fossil fuels are burned with pure oxygen which enables a cost-effective separation of the combustion generated CO2 by condensation. Cycle efficiencies as high as 63% can be reached. Taking the efforts for the oxygen supply into account the efficiency is reduced to 55% [1]. This work presents a further step towards a GRAZ CYCLE prototype plant, with special emphasis on the layout and design of the heat recovery steam generator (HRSG). The hot exhaust gas of the turbine consists mainly of CO2 and H2O. This exhaust gas causes higher demands on the HRSG. A faster corrosion of the heat exchangers and the recirculation of the cycle fluid have to be considered. Based on the design of conventional HRSGs, the necessary adaptations are discussed and economically evaluated.
Experimental Results of an Ammonia-Water Mixture Turbine System: Effectiveness With a Low Temperature Heat Source
Authors: Takeshita Keisuke , Morimoto Kouji , Amano Yoshiharu , Hashizume Takumi
Published: November 2008

This paper presents an experimental investigation of the effectiveness of an AWM (Ammonia-Water Mixture) turbine system with low temperature heat sources. The AWM turbine system (AWMTS) features Kalina cycle technology, namely, it employs an ammonia-water mixture as the working fluid and includes a separation / absorption process of NH3-H2O. Since AWM is a non-azeotropic mixture, its temperature changes during evaporation and condensation. This behavior gives AWMTS the advantage of heat recovery from a sensible heat source such as exhaust gas. It is known that an AWMTS can generate more power than a Rankine cycle system from 250–650°C sensible heat sources. The authors constructed a 70 KW-experimental facility and investigated the practical applications of AWMTS. It is located at the bottoming stage below a conventional combined cycle composed of a gas turbine and a steam turbine. Its heat source is the exhaust steam from a back pressure steam turbine at the middle stage of the system. The experiment was carried out with changing the back pressure of the steam turbine. The experimental results show that power generation is possible from 138 to 162 °C heat source steam.
Optimisation of HAT-Cycles – With and Without CO2 Capture
Authors: Mo¨ller Bjo¨rn Fredriksson , Obana Mitsuru , Assadi Mohsen , Mitakakis Athanasios
Published: November 2008

In a world where distributed power generation and deregulation of energy markets are on everyone’s agenda, the need for highly efficient power plants with short lead times is greater than ever. Although at present combined cycles provide a solution, development of ever more advanced machines to increase efficiency and lower the environmental impact has led to high maintenance costs and a decrease in availability. The Humid Air Turbine (HAT) represents a different approach, suitable for distributed power generation in the medium power range. The HAT cycle, and other wet gas turbine cycles, which have been extensively studied during the last ten years, show as high an efficiency as that of combined cycles, but at a lower specific cost and, with inherently low emissions of NOx. Despite all research done no full-scale plant has been built as yet. CO2 capture is another concept widely studied in recent years. In the present study three HAT cycle configurations are investigated, two of them connected to a post-combustion CO2-capture plant. Thermodynamic and thermoeconomic optimisation of the plants was performed using genetic algorithms (GA), a robust optimisation technique based on Darwinian evolution theories. The three configurations studied were 1) a standard inter-cooled HAT cycle, referred to as the reference cycle, 2) the reference cycle together with an integrated CO2-capture plant taking the energy needed for the CO2 separation from the exhaust heat of the turbine, and 3) the reference cycle together with a CO2 capture plant, in which the energy is supplied by a separate bio-fuelled boiler. This third configuration enables all fossil-based CO2 to be separated. All power cycles were modelled using IPSEpro, a heat- and mass-balance software, employing advanced component models developed by the authors. It has an interface for optimisation and the possibility of employing user-defined objective functions. The impact of CO2 taxation was studied to determine showing which configuration is the most economical at the current fuel-price and tax-level.
CFD Modelling of Thermoacoustic Oscillations Inside an Atmospheric Test Rig Generated by a DLN Burner
Authors: Tiribuzi Stefano
Published: November 2008

The ENEL Produzione Research Centre of Pisa is deeply involved in the study of flame instabilities which could arise in particular operating conditions in the gas turbine equipped with Dry Low NOx (DLN) lean premixed combustors. An atmospheric pressure test facility, named TAO (Turbogas ad Accesso Ottico), is presently used to test, under scaled conditions, the onset of self-sustained thermoacoustic instabilities during the operation of a typical DLN burner. To support this activity, Computation Fluid Dynamic (CFD) analyses are carried out by means of KIEN, an in-house Reynold Averaged Navier Stokes (RANS) code, for simulating 3D instationary reactive flows. A 3D geometrical model, extending from the air plenum upstream the burner up to the end of the long exhaust tube, is adopted. The great extension of the calculation domain, coupled with the long real time required for the spontaneous onset of oscillations, could became computationally very onerous for Large Eddy Simulation (LES) codes, which require a strong control on the cell maximum size throughout the entire domain, while it can be acceptable for an instationary RANS code, which could use a coarser grid. This allows the simulation of long real transients with overnight runs. Starting from uniform no-motion conditions, the same fluctuating behaviour, detected during TAO experiments, spontaneously onsets in the numerical simulations too. The experimental and numerical frequencies are nearly the same and the amplitude of the pressure oscillations is very close. Supported by the congruence with experimental available data, computed results are utilized to get a more detailed description of the evolution of many thermofluiddynamics quantities during these instabilities. A wide sample of information that can be derived directly from the output of the instationary RANS code or by postprocessing of its results is provided.
Numerical Study of Axial Turbine Flow With Variable Gas Property
Authors: Yao Yufeng , Amos Ian G.
Published: November 2008

Aerodynamic performance characteristics and flow details of industrial gas turbines have been evaluated by using a computational fluid dynamics code with a variable gas property model. Systematic simulations have been carried out first to study numerical effects, notably grid resolution and domain size dependency, followed by applications on a warm air turbine rig and an industrial engine. Studies of the turbine rig are focused on the stage performance characteristics and the results agree with the test data fairly well. It is also found that the variable gas property has little influence on the flow half a chord downstream of the rotor trailing edge, where the conditions of the next turbine stage are determined. Further studies on a 3-stage turbine reveal the influence of the variable gas property model. When the gas properties are made constant with respect to the first blade row conditions, the mass flow rate is the same as when using the variable gas property model, however the exit total temperature is over-predicted by about 15 Kelvin. There is also an over-prediction of turbine power output of 0.6%. Simulations using a constant gas property of averaged value or at the last blade row over-predict the mass flow rate by 0.5% and 1% respectively. Downstream on the blade surface and near the exit, they under-predict the temperature and the power output. The predicted efficiency from the various simulations is found to be less influenced than the parameters discussed above, with a difference of about 0.25%. As a conclusion, it is necessary to include the variable gas property effect in 3D calculations of industrial gas turbine flow to achieve an accurate analysis of the flow and performance.
Damage Analysis of Gas Turbine Vanes Using a Thermal Fluid Dynamic and Mechanical Approach
Authors: Marchegiano Enrico , Benelli Giancarlo , Gheri Paolo , Aquaro Donato
Published: November 2008

Gas turbine combined–cycle systems work with high inlet temperatures, requiring the use of components made of advanced high temperature resistant materials and coatings. These components must be controlled to avoid serious damage to the plants. The durability of these materials and coatings is of great concern to equipment users. This paper deals with a procedure based on thermal fluid dynamic and mechanical integrated analyses of high temperature loaded components. The methodology is applied to uncooled last stator stages vanes of an industrial 165 Mw gas turbine. Several cracks were revealed on these vanes during periodical inspection and mechanical and metallographic investigations were performed. These analyses were used to identify the critical areas of the vanes, from which the component residual life depends on. The procedure was applied to study the damage undergone by gas turbine vanes to discover the causes of crack nucleation and the nucleation mechanism connected to load histories. It has a diagnostic scope, not a predictive one, but it can be considered as the first step of a residual life evaluation and, consequently, of a load cycle optimization: by modifying the future load histories, it could be possible evaluate the best operating conditions to extend component life. The numerical results of these analyses were compared with the damage to vane rows determined during periodical inspections. A good agreement between the analyses results and the inspection data was obtained in terms of critical points and crack locations. The implemented methodology seems to be a powerful tool for increasing the reliability of critical components of gas turbine combined–cycle systems.
Inlet Air Cooling Methods for Gas Turbine Based Power Plants
Authors: Kakaras E. , Doukelis A. , Prelipceanu A. , Karellas S.
Published: November 2008

Power generation from gas turbines is penalised by a substantial power output loss with increased ambient temperature. By cooling down the gas turbine intake air, the power output penalty can be mitigated. The purpose of this paper is to review the state of the art in applications for reducing the gas turbine intake air temperature and examine the merits from integration of the different air-cooling methods in gas turbine based power plants. Three different intake air-cooling methods (evaporative cooling, refrigeration cooling and evaporative cooling of pre-compressed air) have been applied in two combined cycle power plants and two gas turbine plants. The calculations were performed on a yearly basis of operation, taking into account the time-varying climatic conditions. The economics from integration of the different cooling systems were calculated and compared.
Passive Control of Combustion Instability in a Low Emissions Aeroderivative Gas Turbine
Authors: Scarinci Tomas , Freeman Christopher , Day Ivor
Published: November 2008

This paper describes the conceptual ideas, the theoretical validation, the laboratory testing and the field trials of a recently patented fuel-air mixing device for use in high-pressure ratio, low emissions, gaseous-fueled gas turbines. By making the fuel-air mixing process insensitive to pressure fluctuations in the combustion chamber, it is possible to avoid the common problem of positive feedback between mixture strength and the unsteady combustion process. More specifically, a mixing duct has been designed such that fuel-air ratio fluctuations over a wide range of frequencies can be damped out by passive design means. By scaling the design in such a way that the range of damped frequencies covers the frequency spectrum of the acoustic modes in the combustor, the instability mechanism can be removed. After systematic development, this design philosophy was successfully applied to a 35:1 pressure ratio aeroderivative gas turbine yielding very low noise levels and very competitive NOx and CO measurements. The development of the new premixer is described from conceptual origins through analytic and CFD evaluation to laboratory testing and final field trials. Also included in this paper are comments about the practical issues of mixing, flashback resistance and autoignition.
Investigation of a High Lift LP Turbine Blade Submitted to Passing Wakes: Part 1 — Profile Loss and Heat Transfer
Authors: Coton Thomas , Arts Tony
Published: November 2008

A new test case for very high lift LP turbines has been investigated. The interaction with incoming wakes has been experimentally assessed at two Reynolds number values (13 and 30 × 104) and two inlet turbulence levels (0.8 and 3.5%) for an exit Mach number equal to 0.7. The wakes were generated by bars mounted on a rotating disk. Their features were varied in terms of diameter, rotational speed and number. In part 1 of the paper, the blade performance is discussed. Its evolution with the flow and wake parameters is mainly related to the variations of the boundary layer transition along the suction side. The beneficial effect of the wakes in suppressing the separation bubble could lead to a loss reduction of 36%. Distributions of the heat transfer coefficient and of higher order statistical variables support the discussion and constitute a quantitative database for LP turbines. The boundary layer behavior and its transitional aspects are particularly investigated in part 2.
A Study of Advanced High Loaded Transonic Turbine Airfoils
Authors: Sonoda Toyotaka , Arima Toshiyuki , Olhofer Markus , Sendhoff Bernhard , Kost Friedrich T. , Giess P. A.
Published: November 2008

The development of high performance turbine airfoils has been investigated under the condition of a supersonic exit Mach number. In order to obtain a new aerodynamic design concept for a high loaded turbine rotor blade, we employed an evolutionary algorithm for numerical optimization. The target of the optimization method, which is called evolution strategy (ES), was the minimization of the total pressure loss and the deviation angle. The optimization process includes the representation of the airfoil geometry, the generation of the grid for a blade-to-blade CFD analysis, and a 2D Navier-Stokes solver with a low-Re k-ε turbulence model in order to evaluate the performance. Some interesting aspects, for example, a double shock system, an early transition and a re-distribution of aerodynamic loading on blade surface, observed in the optimized airfoil, are discussed. The increased performance of the optimized blade has been confirmed by detailed experimental investigation, using conventional probes, hot-films and L2F system.
On the Feasibility of Nuclear Versus Combustion Gas Turbine Propulsion for High-Speed Cargo Ships
Authors: Boonstra H. , Groot A. C. , Prins C. A.
Published: November 2008

This paper presents the outcome of a study on the feasibility of a nuclear powered High-Speed Pentamaran, initiated by Nigel Gee and Associates and the Delft University of Technology. It explores the competitiveness of a nuclear power plant for the critical characteristics of a marine propulsion plant. Three nuclear reactor types are selected: the Pressurized Water Reactor (PWR), the Pebble-bed and Prismatic-block HTGR. Their characteristics are estimated for a power range from 100 MWth to 1000 MWth in a parametric design, providing a level base for comparison with conventional gas turbine technology. The reactor scaling is based on reference reactors with an emphasis on marine application. This implies that preference is given to passive safety and simplicity, as they are key-factors for a marine power plant. A case study for a 60-knot Pentamaran shows the impact of a nuclear power plant on a ship designed with combustion gas turbine propulsion. The Prismatic-block HTGR is chosen as most suitable because of its low weight compared to the PWR, in spite of the proven technology of a PWR. The Pebble-bed HTGR is considered too voluminous for High-Speed craft. Conservative data and priority to simple systems and high safety leads to an unfavorable high weight of the nuclear plant in competition with the original gas turbine driven Pentamaran. The nuclear powered ship has some clear advantages at high sailing ranges.
Experimental Investigation of the Rotor-Stator Interactions Within a High-Speed, Multi-Stage, Axial Compressor: Part 2 — Modal Analysis of the Interactions
Authors: Arnaud David , Ottavy Xavier , Vouillarmet Andre´
Published: November 2008

The second part of this paper deals with the analysis of the 2D LDA measurements carried out within the high-speed multistage axial compressor CREATE. First the interactions correlations are quantified using the deterministic stresses introduced by Adamczyk. Secondly, a modal decomposition shows that the interactions are characterized by the presence of spatial harmonics (spinning lobes) given by a linear combination of the blades numbers. An original measurement of the rotating speed of the spinning lobes has been carried out allowing to identify almost all the spinning lobes in the first inter row region resulting from the R1-S1 interactions. For the first stage, where the influence of the downstream rows is low, the measured flow field is well reproduced by the model of Tyler and Sofrin. Spatial DFT of the flow field calculated for each time of the compressor time period show that there is a pulsation of the spatial harmonics with the period associated to the minimum elapsed time to recover the same relative positions of the rotor and stator rows.
Model Adaptation and Nonlinear Model Predictive Control of an Aircraft Engine
Authors: Brunell Brent J. , Viassolo Daniel E. , Prasanth Ravi
Published: November 2008

The performance improvement of constrained nonlinear model predictive control (NMPC) with state and parameter estimation over traditional control architectures is investigated and applied to a model turbofan aircraft engine. Strong nonlinearities are present in turbofan aircraft engines due to the large range of operating conditions and power levels experienced during a typical mission. Also, turbine operation is restricted due to mechanical, aerodynamic, thermal, and flow limitations. Current control methodologies rely strictly on a priori information; therefore they fail to utilize current engine state or health information for reducing conservatism and improving engine performance. NMPC is selected because it depends on a model that can be adapted to the current engine conditions, it can explicitly handle the nonlinearities, both input and output constraints of many variables, and determine the optimal control that will meet the requirements for any engine condition all in a single control formulation. A physics based component level model is developed as the heart of the architecture. The state or health of the engine is determined using a joint state and parameter estimator utilizing extended Kalman filter (EKF) techniques. With the necessary engine information in hand, a constrained NMPC is used to determine the optimal actuator commands. Results regarding steady state performance improvements are presented.