bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat Transfer and Pressure Drop Evaluation in Thin Wedge-Shaped Trailing Edge
Authors: Carcassi C. , Facchini B. , Innocenti L.
Published: February 2009

In modern high loaded transonic turbines the aerodynamic losses of turbine airfoils are mostly covered by the thickness and the wedge angle of the blade trailing edges. Due to the aerodynamic requirements the thin trailing edges are the life limiting parts of the airfoils. The aerodynamic design requirements lead to trailing edge slots with extreme aspect ratio and huge fillet radius in relation to the internal slot geometry. In most cases, the conventional design tools are not validated for these geometries, therefore an improved knowledge of flow and heat transfer in this area is necessary. This paper discusses the measurements of endwall heat transfer coefficient and pressure drops in a wedge-shaped duct with two different turbulators arrangement. The first one is concerning five different long ribs (pedestals) configurations disposed streamwise while the other one is related to three configurations of staggered pin fins. Pedestals and pin fins stand vertically on the bottom surface of the wedge–shaped duct. This surface, named endwall, is coated with a thin layer of thermochromic liquid crystals and several transient tests are run to obtain detailed heat transfer coefficient distributions. Both for the pedestal and pin fins several parametric studies has been performed, varying both Reynolds number range (from 9000 to 27000) and turbulators configurations while outlet Mach number was set to 0.3 for all tests. Investigated pedestal configurations are different for turbulators spanwise pitch while pin fins geometry have different pin diameter values. In all cases the wedge duct angle is 10°. Results indicate that the smallest long ribs pitch and pin fin diameter are most recommended because of its significant endwall heat transfer and moderate pressure-drop penalty. Long ribs and pin-fins are aluminium made in order to evaluate an average value of the heat transfer coefficient on their side surface. So a valuation of global heat transfer coefficient in the internal trailing edge cooling duct become possible.
Exo-Skeletal Engine: Novel Engine Concept
Authors: Chamis Christos C. , Blankson Isaiah M.
Published: February 2009

The Exo-Skeletal Engine concept represents a new radical engine technology with the potential for a substantial revolution in engine design. It is an all composite drum rotor engine in which conventional heavy shafts and discs are eliminated and are replaced by rotating casings that support the blades in spanwise compression. Thus the rotating blades are in compression rather than in tension. The resulting open channel at the engine centerline has immense potential for jet noise reduction, and can also accommodate an inner combined-cycle thruster such as a ramjet. The Exo-Skeletal Engine is described in some detail with respect to geometry, components and potential benefits. Initial evaluation, results for drum rotors, bearings and weights are summarized. Component configuration, assembly plan and potential fabrication processes are also identified. A finite element model of the assembled engine and its major components are described. Preliminary results obtained thus far show at least 30 percent reduction of engine weight and about 10 db noise reduction, compared to a baseline conventional high bypass-ratio engine. Potential benefits in all aspects of engine technology are identified and tabulated. Quantitative assessments of potential benefits are in progress.
Using Hydrogen as Gas Turbine Fuel
Authors: Chiesa Paolo , Lozza Giovanni , Mazzocchi Luigi
Published: February 2009

This paper addresses the possibility to burn hydrogen in a large size, heavy–duty gas turbine designed to run on natural gas, as a possible short-term measure to reduce greenhouse emissions of the power industry. The process used to produce hydrogen is not discussed here: we mainly focus on the behavior of the gas turbine, by analyzing the main operational aspects related to switching from natural gas to hydrogen. We will consider the effects of variations of volume flow rate and of thermo-physical properties on the matching between turbine and compressor and on the blade cooling of the hot rows of the gas turbine. In the analysis we will keep into account that those effects are largely emphasized by the abundant dilution of the fuel by inert gases (steam or nitrogen), necessary to control the NOx emissions. Three strategies will be considered to adapt the original machine, designed to run on natural gas, to operate properly with diluted hydrogen (VGV operations, increased pressure ratio, re-engineered machine). The performance analysis, carried out by a calculation method including a detailed model the cooled gas turbine expansion, shows that moderate efficiency decays can be predicted with elevated dilution rates (nitrogen is preferable to steam under this point of view). The combined cycle power output substantially increases if not controlled by VGV operations. It represents an opportunity if some moderate re-design is accepted (turbine blade height modifications or HP compressor stages addition).
The Number and Speed of Stall Cells During Rotating Stall
Authors: Levy Y. , Pismenny J.
Published: February 2009

The number of stall cells and their rotational speed are distinctive features of the rotating stall phenomenon and play an important role in the prediction and analysis of the pressure fields during rotating stall. Various aspects of numbers and speed of stall cells are analyzed using an original interpretation method based on the pressure distribution in the circumference of a specific transverse cross-section at a specific time. This characteristic is similar to that of the pressure variation with time at a certain location on the compressor circumference. In some cases, the number of stall cells in any transverse cross-section may be defined after graphing the phase of pressure oscillation versus sensor positions and their joint analysis with the pressure signal variations in time and space. It is shown that whereas the numbers of stall cells in different transverse cross-sections of a multistage compressor may vary, the pressure field rotational speeds and accordingly the rotation speeds of all stall cells seem to be the same.
Combustion Noise Measurement System for Low Emissions Combustor Performance Optimization and Health Monitoring
Authors: Stuttaford Peter J. , Martling Vince , Green Andrew , Lieuwen Timothy C.
Published: February 2009

The design of modern gas turbine combustors continues to be driven by the demand for lower emissions of NOx and CO. Achieving reduced emissions on dry low emissions combustors necessitates the monitoring of associated, potentially destructive combustion noise. Power Systems Manufacturing (PSM) has developed a Dynamic Data Acquisition System for use in the noise performance optimization and health monitoring of low emissions combustors. Various noise probes and set-ups have been evaluated on test benches, combustion test rigs, and engines operating over their complete load range. The set-up and calibration of the combustion dynamic monitoring system is described here. An application of the dynamic data acquisition system is presented for the PSM combustor retrofit of the 85MW General Electric Frame MS7001EA machine, achieving 6ppm NOx, and 2ppm CO at base load and maintaining single digit emissions down to 50% load. The excellent condition of the combustion hardware following 8,000 hours of base load operation was indicative of operation in a low combustion noise environment. Combustion system noise monitoring ensures the lowest possible emissions, without compromising combustion hardware durability through excessive dynamic loading.
Systematic Numerical Studies on Heat Transfer and Aerodynamic Characteristics of Impingement Cooling Devices Combined With Pins
Authors: Funazaki K. , Hachiya K.
Published: February 2009

This paper deals with extensive numerical studies on heat transfer characteristics and fluid dynamics inside several impingement cooling devices combined with pins. As a numerical analysis tool, a commercial software CFX-4.4, AEA Technology, is used. The purpose of this paper is two-fold. First the validity of the numerical tool and grids adopted in this study is checked through the comparison of the numerical results with the experimental counterparts. Turbulence models available in the software are thoroughly tested so as to screen out a turbulence model among them which can reproduce the experimental heat transfer characteristics best. Consequently, k–ω turbulence model is finally adopted as the turbulence model. Parametric studies, where Reynolds number based on impingement hole diameter, pin height-diameter ratio and pin pitch-diameter ratio vary from 5,000 to 25,000, from 0.75 to 4 and from 2 to 4, respectively, are then executed to clarify effects of important dimensions, such as pin height, pin pitch, upon local and averaged heat transfer characteristics as well as pressure loss generated in the devices.
Influence of Rotor Stagger Angle on Rotating Stall Inception in an Axial-Flow Fan
Authors: Nishioka Takahiro , Kuroda Shuuji , Kozu Tadashi
Published: February 2009

Inception patterns of rotating stall in a low-speed axial flow fan have been investigated experimentally. Experiments have been carried out at two different stagger angle settings for rotor blades. Pressure and velocity fluctuations were measured to elucidate the features of the stall cells and the stall inception patterns. At the design stagger angle setting for the rotor blades, a short length-scale stall cell known as a “spike” and multiple short length-scale stall cells appear when the slope of pressure-rise characteristic is almost zero. These stall cells grow into a long length-scale stall cell as flow rate decreases. The spike and the multiple short length-scale stall cells do not make the slope of the characteristic positive. However, the long length-scale stall cell induces a full-span stall, and makes the slope of the characteristic positive. At the small stagger angle, a long length-scale disturbance known as a “modal oscillation” is observed first, when the slope of the characteristic is positive. Then the spikes appear together with the modal oscillation as flow rate decreases. The long length-scale stall cell is generated by the spikes without change in the size of the modal oscillation. Suction-tip corner stall occurs in the stator passage near the peak of the characteristic at both the design and the small stagger angle settings. At the design stagger angle, however, the corner stall does not induce the modal oscillation and does not make the characteristic positive. In contrast, the corner stall at the small stagger angle induces the modal oscillation and makes the characteristic positive because it is larger than that at the design stagger angle. It is concluded from these results that the rotating stall inception patterns depend on the rotor stagger angle, which influences blade loading and rotor-stator matching.
Compressor Blade Tip Timing Using Capacitance Tip Clearance Probes
Authors: Lawson Craig , Ivey Paul
Published: February 2009

Turbomachinery blade vibrations of sufficient amplitude cause High Cycle Fatigue, which reduces blade life. In order to observe this vibration a non-intrusive monitoring system is sought. The vibration can be detected by measuring blade tip timing since in the presence of vibration the blade timing will differ slightly from the passing time calculated from rotor speed. This paper provides new insights into the ability of a commercially available capacitance probe tip clearance measurement system for application as a non-intrusive turbomachinery blade tip timing measurement device. Initial experimental investigations are reported where a compressor blade with mounted strain gauges is used in a low-speed compressor. Capacitance probe results are correlated with simultaneously measured strain gauge results. Finite Element simulations are also used. The performance of the capacitance system in measuring blade vibration is analysed. Measurements were facilitated by the commissioning of a new instrument dedicated compressor test facility and this test facility is described.
A CAD-Based Blade Geometry Model for Turbomachinery Aero Design Systems
Authors: Merchant Ali , Haimes Robert
Published: February 2009

A CAD-centric approach for constructing and managing the blade geometry in turbomachinery aero design systems is presented in this paper. Central to the approach are a flexible CAD-based parametric blade model definition and a set of CAD-neutral interfaces which enable construction and manipulation of the blade solid model directly inside the CAD system’s geometry kernel. A bottleneck of transferring geometry data passively via a file-based method is thus eliminated, and a seamless integration between the CAD system, aero design system, and the larger design environment can be achieved. A single consistent CAD-based blade model is available at all stages of the aero design process, forming the basis for coupling the aero design system to the larger multi-disciplinary design environment. The blade model construction is fully parameterized so that geometry updates can be accurately controlled via parameter changes, and geometric sensitivities of the model can be easily calculated for multidisciplinary interaction and design optimization. A clear separation of the parameters that control the three-dimensional shape of the blade (such as lean and sweep) from the parameters that control the elemental profile shape allows any blade profile family or shape definition to be utilized. The blade model definition, construction interface, and implementation approach are described. Applications illustrating solid model construction, parametric modification and sensitivity calculation, which are key requirements for automated aerodynamic shape design, are presented.
Urban Air Quality Impacts of Distributed Generation
Authors: Medrano Marc , Brouwer Jack , Samuelsen G. S. , Carreras Marc , Dabdub Donald
Published: February 2009

Distributed Energy Resources (DER) have the potential to meet a significant portion of increased power demands of the future. DER applications can potentially provide benefits in electrical reliability and power quality, in addition to reducing total energy costs in combined cooling, heating and power (CHP) applications. However, the shift from a central generation paradigm to distributed generation results in different emissions characteristics and profiles from both a spatial and temporal perspective. Distributed generation is characterized by many sparsely distributed stationary sources within an urban air-shed compared to central generation where emissions sources are much larger, but typically located outside the air-shed in more remote locations. As a result, high market adoption of fuel-driven (non-renewable) distributed generation (DG) technologies, such as reciprocating engines and microturbines, may influence the air quality within a region. The present paper estimates air quality impacts for a representative distributed generation scenario in the South Coast Air Basin (SoCAB) of California. Simulations are based on the year 2010 with comparison to a base case scenario with no DG emissions. The DG scenarios are developed for a reasonable percentage of power met by DG, representative spatial distribution and temporal operation, and a mix of DG technologies and emissions factors. The resultant emissions inventory for each DG scenario is then provided as input to a three-dimensional air quality model including detailed atmospheric chemistry and transport for simulation of the SoCAB. Preliminary air quality results suggest that there will be an air quality impact, that the impacts will not be uniform throughout the air-shed, and that individual criteria pollutant concentrations may either rise or fall with the introduction of DG.
Direct-Transfer Preswirl System: A One Dimensional Modular Characterization of the Flow
Authors: Dittmann M. , Dullenkopf K. , Wittig S.
Published: February 2009

In high-efficiency gas turbine engines, the cooling air for the high pressure turbine stage is expanded through stationary preswirl nozzles, transferred through the preswirl chamber and delivered to the blade feed holes of the rotor. By accelerating the cooling air in the direction of rotation, the total temperature relative to the rotor disk and the pressure losses occurring at the receiver hole inlet can be reduced. The discharge behavior of a direct-transfer preswirl system has been investigated experimentally for different number of receiver holes and different inlet geometries, varying axial gap widths between stator and rotor and for rotational Reynolds numbers up to Reφ = 2:3 × 106. The discharge coefficients of the preswirl nozzles are given in the absolute frame of reference while the definition of the discharge coefficients of the receiver holes is applied to the rotating system in order to consider the work done by the rotor. A momentum balance is used to evaluate the deflection of the preswirled air entering the receiver holes. The flow in the preswirl chamber is characterized by introducing an effective velocity of the cooling air upstream of the rotor disk. The influences of geometrical parameters and operating points are reported and discussed in this paper.
Investigation of Turbulence Models Applied to Premixed Combustion Using a Level-Set Flamelet Library Approach
Authors: Engdar Ulf , Nilsson Per , Klingmann Jens
Published: February 2009

Most of the common modeling approaches to premixed combustion in engineering applications are either based on the assumption of infinitely fast chemistry or the flamelet assumption with simple chemistry. The level-set flamelet library approach (FLA) has shown great potential in predicting major species and heat release, as well as intermediate and minor species, where more simple models often fail. In this approach, the mean flame surface is tracked by a level-set equation. The flamelet libraries are generated by an external code, which employs a detailed chemical mechanism. However, a model for the turbulent flame speed is required, which, amongst other considerations, depends on the turbulence intensity, i.e. these models may show sensitivity to turbulence modeling. In this paper, the FLA model was implemented in the commercial CFD program Star-CD, and applied to a lean premixed flame stabilized by a triangular prism (bluff body). The objective of this paper has been to investigate the impact on the mean flame position, and hence on the temperature and species distribution, using three different turbulent flame speed models in combination with four different turbulence models. The turbulence models investigated are: the standard k-ε model, a cubic non-linear k-ε model, the standard k-ω model and the Shear Stress Transport (SST) k-ω model. In general, the computed results agree well with experimental data for all computed cases, although the turbulence intensity is strongly underestimated at the downstream position. The use of the non-linear k-ε model offers no advantage over the standard model, regardless of flame speed model. The k-ω based turbulence models predict the highest turbulence intensity with the shortest flame lengths as a consequence. The Mu¨ller flame speed model shows the least sensitivity to the choice of turbulence model.
Effect of Rotation on Heat Transfer in Narrow Rectangular Cooling Channels (AR = 8:1 and 4:1) With Pin-Fins
Authors: Wright Lesley M. , Lee Eungsuk , Han Je-Chin
Published: February 2009

The effect of rotation on smooth narrow rectangular channels and narrow rectangular channels with pin-fins is investigated in this study. Pin-fins are commonly used in the narrow sections within the trailing edge of the turbine blade; the pin-fins act as turbulators to enhance internal cooling while providing structural support in this narrow section of the blade. The rectangular channel is oriented at 150° with respect to the plane of rotation, and the focus of the study involves narrow channels with aspect ratios of 4:1 and 8:1. The enhancement due to both conducting (copper) pin-fins and non-conducting (plexi-glass) pins is investigated. Due to the varying aspect ratio of the channel, the height-to-diameter ratio (hp/Dp) of the pins varies from two, for an aspect ratio of 4:1, to unity, for an aspect ratio of 8:1. A staggered array of pins with uniform streamwise and spanwise spacing (xp/Dp = sp/Dp = 2.0) is studied. With this array, 42 pin-fins are used, giving a projected surface density of 3.5 pins/in2 (0.543 pins/cm2), for the leading or trailing surfaces. The range of flow parameters include Reynolds number (ReDh = 5000–20000), rotation number (Ro = 0.0–0.302), and inlet coolant-to-wall density ratio (Δρ/ρ = 0.12). Heat transfer in a stationary pin-fin channel can be enhanced up to 3.8 times that of a smooth channel. Rotation enhances the heat transferred from the pin-fin channels 1.5 times that of the stationary pin-fin channels. Overall, rotation enhances the heat transfer from all surfaces in both the smooth and pin-fin channels. Finally, as the rotation number increases, spanwise variation increases in all channels.
A Review of Rotary Pressure-Gain Combustion Systems for Gas Turbine Applications
Authors: Nalim M. Razi , Pekkan Kerem
Published: February 2009

In the last two decades, jet engines and gas turbines attempting constant-volume combustion without positive–displacement mechanisms have regained attention, mainly due to their theoretical high efficiency, potential low emissions, and compact design features. The idea can be traced back to experiments in the 1930’s and production of devices like the V1 missile motor and the Comprex® supercharger. Both for power generation and for aerospace applications, specific hardware and ingenious cycle designs are being developed to address known technological challenges. Different thermodynamic approaches and design methods are proposed to predict the performance potential of these periodic-unsteady wave machines. There have been experimental studies and successfully operated test-rigs that were sometimes shelved due to immediate economic concerns. These “lost” previous studies and experiences are worth reviewing amidst the increased attention to pulse detonation engine and wave-rotor applications proposed for gas turbine cycles by engine makers and government laboratories. In this review paper, our aim is to summarize the status and important efforts in this field. Recent research is highlighted by specific research groups worldwide attempting diverse applications. A compilation of promising applications is presented, to help focus efforts on future work needed.
Robust Optimal Design in Multistage Expansion of a Gas Turbine Cogeneration Plant Under Uncertain Energy Demands
Authors: Yokoyama Ryohei , Ito Koichi , Murata Tatsuhiro
Published: February 2009

In designing cogeneration plants, the estimation of energy demands is an important work. However, many conditions under which energy demands are estimated have some uncertainty at the design stage. Therefore, designers should consider that energy demands have some uncertainty, evaluate the robustness in the performance under uncertain energy demands, and design plants rationally in consideration of the robustness. The authors have developed a robust optimal design method based on the minimax regret criterion for the single-stage planning of energy supply plants. In this paper, the method is extended for the multistage expansion planning. Under uncertain energy demands increasing stepwise, equipment capacities and utility contract demands as well as energy flow rates for each expansion period are determined in consideration of their sequential relationships to minimize the maximum regret in the annual total cost and satisfy all the possible energy demands for all the expansion periods. Through a case study on a gas turbine cogeneration plant for district energy supply, features of the economic robustness and the robust optimal design are clarified in relation to the uncertainty in energy demands and the numbers of years for the expansion periods.
3D-LDA Measurements in an Aero-Engine Bearing Chamber
Authors: Gorse Ph. , Willenborg K. , Busam S. , Ebner J. , Dullenkopf K. , Wittig S.
Published: February 2009

For future efficient and light aero-engines it is essential to develop optimized lubrication systems. These systems require increased temperature and pressure levels in combination with high rotational speeds without compromising the high level of safety and reliability. This applies especially to the bearing chamber as one of the most challenging components of the oil system. Due to the mixing of the sealing airflow and the lubrication oil a complex air- / oilflow is formed inside the chamber. In order to gain a deeper insight into the physical phenomena of the flow inside the bearing chamber a multiyear fundamental study has been initiated. This study focuses for the first time on detailed measurements of the local air- / oilflow field. In the first phase of the project experiments have been carried out to determine the rotating and swirling pure airflow. Hence a specially adapted three dimensional Laser Doppler Anemometry (LDA) system was used to resolve the complex flow. The results revealed that different flow patterns occurred depending on the ratio between the shaft speed and the airflow rate. In the near future it is aimed to resolve the droplet flow also to provide a complete knowledge of the air- / oilflow in bearing chambers.
A New-Conception, Electromagnetically Controlled, Diaphragmless Shock Tube
Authors: Ferrara Giovanni , Ferrari Lorenzo , De Lucia Maurizio
Published: February 2009

A new conception, electro-magnetically controlled, diaphragmless shock tube was realized and tested in the laboratories of University of Florence. A piston separates the co-axial driver and driven sections. The piston is kept in position by a force of an electromagnet acting on an iron disc linked to its rod. In order to obtain very short opening time, light materials were tested for moving devices: aluminum, ergal, titanium and iron. Opening time was measured using contact sensors. Several different dimensionless driven section lengths were tested by changing the driven section length and by reducing the driven section diameter. The influence of the two factors on shock presence and shock formation was analyzed separately. Tests were carried out for driver-to-driven pressure ratios of up to 22, obtaining shock waves at Mach number of up to 1.70 with a difference from the theoretical value for a straight shock tube of 9%. A configuration for increasing the useful test time after the shock passage is also proposed and tested. The system realized is simple, easy-to-use, quite cheap and can be a very useful way of obtaining a reproducible shock wave. The shock tube details and the test results are reported below.
The Use of Helmholtz Resonators in a Practical Combustor
Authors: Dupe`re Iain D. J. , Dowling Ann P.
Published: February 2009

The drive to reduce emissions has led to the development of lean premixed combustors. However lean premixed combustion is often associated with combustion oscillations which can be so severe that they can cause structural damage to the engine. Since the associated frequencies are typically of the order of hundreds of Hertz, there is a need for a compact device to absorb the noise which drives the oscillation. Helmholtz resonators are commonly used as absorbers of incident acoustic power. In addition they are relatively compact. However, their use in combustors creates practical issues, such as placement within the chamber, neck length and cooling, which need to be addressed. In this paper we consider these practical problems and describe how to overcome them in a real combustor.
On the Three-Dimensional Structure of Turbulent Spots
Authors: Chong T. P. , Zhong S.
Published: February 2009

A detailed measurement of turbulent spots propagating in a laminar boundary layer over a flat plate was made at a zero pressure gradient and three favourable pressure gradients. Data were recorded across the span of turbulent spots at a number of streamwise locations along the plate using a hot-wire probe and surface-mounted hot films. This work aims at extending the existing studies that are largely based upon measurements made in the plane of symmetry of the spots and away from the wall and investigating the three-dimensional structure of turbulent spots and its dependence on streamwise pressure gradients. The results from the present experiment reveal some interesting aspects of the overall structure of the spots and the role that regions with negative velocity perturbations play in spanwise growth of turbulent spots. The presence of a spanwise overhang is also confirmed which is believed to be responsible for the smaller spreading angle of spots measured at the wall. This finding is expected to have important implications to the development of improved transition models which are used to predict heat transfer and skin friction for turbine blades.
A Numerical Investigation of Aeroacoustic Fan Blade Flutter
Authors: Wu X. , Vahdati M. , Sayma A. I. , Imregun M.
Published: February 2009

This paper reports the results of an ongoing research effort to explain the underlying mechanisms for aeroacoustic fan blade flutter. Using a 3D integrated aeroelasticity method and a single passage blade model that included a representation of the intake duct, the pressure rise vs. mass flow characteristic of a fan assembly was obtained for the 60%–80% speed range. A novel feature was the use of a downstream variable-area nozzle, an approach that allowed the determination of the stall boundary with good accuracy. The flutter stability was predicted for the 2 nodal diameter assembly mode arising from the first blade flap mode. The flutter margin at 64% speed was predicted to drop sharply and the instability was found to be independent of stall effects. On the other hand, the flutter instability at 74% speed was found to be driven by flow separation. Further post-processing of the results at 64% speed indicated significant unsteady pressure amplitude build-up inside the intake at the flutter condition, thus highlighting the link between the acoustic properties of the intake duct and fan blade flutter.
Optimization of Operating Conditions and Compressor Cleaning Time Intervals of Combined Cycles in a Liberalized Market
Authors: Silva Paolo , Campanari Stefano , Macchi Ennio
Published: February 2009

The paper addresses the optimization of the managing strategy of a combined cycle power plant in a liberalized market characterized by great time variability of the electricity sale price. Besides electric tariffs, a variety of other factors affect the selection of the plant operating mode, such as environmental conditions, O&M costs, range of plant output regulation capability, performance deterioration of the components and compressor fouling rate. All calculations refer to a real combined cycle power plant owned by an Italian utility, for which are available detailed performance data, in “new and clean” conditions as well as in real operation. The optimum plant operating schedule is found with reference to three different tariff scenarios: (i) the present Italian situation, characterized by the primary role of oil and gas fired steam power stations, (ii) the Italian situation foreseen after the massive repowering program of existing steam power plants is completed, and (iii) a situation where the base-load electricity is generated by coal-fired power stations. The comparison indicates the utmost importance of the reference tariff scenario on the actual energy ad economic budget of the power station.
Managing Maintenance and Operational Availability of Gas Turbine Propelled Naval Ships Through Advanced Engine Fault Diagnostics
Authors: Sampath Suresh , Singh Riti
Published: February 2009

A marine engineer is often confronted with the problem of repairs/maintenance at sea. However, an advance warning of the impending problem can greatly help in scheduling maintenance more efficiently by storing appropriate spares and positioning suitable expertise. The ability to predict the remaining operational life of marine gas turbine engines is considered as an essential requirement for future generation diagnostic systems. Engine deterioration modeling provides the means to estimate economic implications of engine degradation, essential for operational and logistics planning. This paper presents the development of a performance analysis and advanced engine fault diagnostics model for the Rolls-Royce Intercooled-Recuperated WR-21 gas turbine using Artificial Intelligence techniques. It also shows how these innovative solutions have the potential to influence the maintenance philosophy and optimal composition of crew.
Rotordynamic Performance of Finite Length Squeeze Film Dampers
Authors: El-Shafei A. , El-Kabbany A. S.
Published: February 2009

A recently developed finite length model of squeeze film dampers is extended and used in predicting the behavior of a rigid rotor supported by squeeze film dampers (SFDs). The model is based on a perturbation solution of Reynolds’ equation. The finite length SFD damping coefficients are presented for various L/R ratios. The effect of damper finite length is studied. Simulations of the behavior of a rigid rotor with the finite length SFDs illustrate the response of the roto-rbearing system. The accuracy of the finite damper model is shown for cases comparable to short and long dampers models. The short damper and long damper models are generally accepted to be valid for L/D < 1/4, and for L/D > 4, respectively. The capability of the finite length damper model to capture the main essence of the L/R ratio on the rotor response at resonance is illustrated. Analytical formulae for damping estimates are provided for finite length dampers. It is shown that the finite length damper actually provides less damping than either the short or the long damper models, which means that current design practices actually overestimate the SFD damping capabilities.
Application of Conjugate CFD to the Internal Cooling Air Flow System of Gas Turbines
Authors: Brillert D. , Dohmen H. J. , Benra F.-K. , Schneider O. , Mirzamoghadam A. V.
Published: February 2009

Continuous improvements of the secondary air system are basic elements to increase efficiency and power of heavy duty gas turbines. It is becoming more important to perform a precise calculation of the heat transfer characteristics and to produce accurate predictions of the air/metal temperature in the internal cooling air system. Thermal effects influences the cooling behavior and consequently the cooling efficiency and the material temperature. The material temperature influences the stresses and the creep behavior that is important for life prediction and the reliability of the engine. Furthermore, the material temperature influences the clearances and therefore, the cooling mass-flow. This paper deals with a complex internal blade feed system comprising a forced radially-inward jet-flow into a large rotating cavity and the numerical coupling of different cooling air flow passages with component heat transfer, i.e. conjugate CFD. A calculation procedure was adopted to reproduce the measured rotating main shaft temperatures from the Siemens Model V84.3A gas turbine prototype. Based on this procedure, flow and heat transfer throughout the sub-cavities were discussed and the shaft temperature distribution was obtained. Results indicate a strong interaction between the thermal effects of the cooler radial jet-flow and the hotter seal gap regions. Moreover, the deficiencies in the adopted calculation procedure were identified.
A Method for Use of Cyclic Symmetry Properties in Analysis of Nonlinear Multiharmonic Vibrations of Bladed Discs
Authors: Petrov E. P.
Published: February 2009

An effective method for analysis of periodic forced response of nonlinear cyclically symmetric structures has been developed. The method allows multiharmonic forced response to be calculated for a whole bladed disc using a periodic sector model without any loss of accuracy in calculations and modelling. A rigorous proof of the validity of the reduction of the whole nonlinear structure to a sector is provided. Types of bladed disc forcing for which the method may be applied are formulated. A multiharmonic formulation and a solution technique for equations of motion have been derived for two cases of description for a linear part of the bladed disc model: (i) using sector finite element matrices; (ii) using sector mode shapes and frequencies. Calculations validating the developed method and a numerical investigation of a realistic high-pressure turbine bladed disc with shrouds have demonstrated the high efficiency of the method.
Aerodynamic Analysis of a Multistage Centrifugal Compressor
Authors: Bonaiuti Duccio , Arnone Andrea , Milani Alberto , Baldassarre Leonardo
Published: February 2009

The aerodynamic analysis of a four–stage centrifugal compressor was performed by means of a three–dimensional multi stage CFD code. The whole operating range of the compressor was investigated and the critical elements affecting the choke and stall limit were identified. The isolated impellers were also analyzed separately and the flow field was compared to the one coming from the multistage analysis. This allowed us to study the effect of the interactions between components and quantify the impact of the multistage environment on the impellers’ performance.
Measurement and Prediction of Heat Transfer Distributions on an Aft Loaded Vane Subjected to the Influence of Catalytic and Dry Low NOx Combustor Turbulence
Authors: Ames F. E. , Argenziano M. , Wang C.
Published: February 2009

This paper documents heat transfer rates on an aft loaded vane subject to turbulence generated by mock combustion configurations representative of recently developed catalytic and dry low NOx (DLN) combustors. New combustion systems developed for low emissions have produced substantial changes to the characteristics of inlet turbulence entering nozzle guide vanes. Aft loaded vane designs can have an impact on surface heat transfer distributions by accelerating boundary layers for a greater portion of the suction surface. Four different inlet turbulence conditions with intensities ranging up to 21 percent are documented in this study and vane heat transfer rates are acquired at vane exit chord Reynolds numbers ranging from 500,000 to 2,000,000. Heat transfer distributions show the influence of the turbulence conditions on heat transfer augmentation and transition. Cascade aerodynamics are well documented and match pressure distributions predicted by a commercial CFD code for this large scale low speed facility. The aft loaded vane pressure distribution exhibits a minimum value at about 50 percent arc on the suction surface. Laminar heat transfer augmentation in the stagnation region and on the pressure surface have scaled well on theoretical parameters based on turbulence intensity, Reynolds number, and energy scale. Predictive comparisons are shown based on a two-dimensional boundary layer code using an algebraic turbulence model for augmentation as well as a transition model. This comprehensive vane heat transfer data set is expected to represent an excellent test case for vane heat transfer predictive methods.
A New Multiaxial Fatigue Testing Method for Variable-Amplitude Loading and Stress Ratio
Authors: George Tommy J. , Shen M.-H. Herman , Nicholas Theodore , Cross Charles J.
Published: February 2009

A new vibration-based multiaxial fatigue testing methodology for assessing high cycle turbine engine material fatigue strength at various stress ratios is presented. The idea is to accumulate fatigue energy on a base-excited plate specimen at high frequency resonant modes and to complete a fatigue test in a much more efficient way at very low cost. The methodology consists of: (1) a topological design procedure, incorporating a finite element model, to characterize the shape of the specimens for ensuring the required stress state/pattern, (2) a vibration feedback empirical procedure for achieving the high cycle fatigue experiments with variable-amplitude loading, and finally (3) a yielding procedure for achieving various uniaxial stress ratios. The performance of the methodology is demonstrated by the experimental results from mild steel, 6061-T6 aluminum, and Ti-6Al-4V plate specimens subjected to fully reversed bending for both uniaxial and biaxial stress states. Results are compared with those produced using traditional fatigue test machines.
Numerical Investigation on the Formation of Jet-Wake Flow Pattern in Centrifugal Compressor Impeller
Authors: Zheng Qun , Liu Shunlong
Published: February 2009

Numerical investigations of internal flow field in centrifugal compressor impeller channel are carried out in this paper. Topological analyses of limit streamline pattern are used to interpret the Jet-Wake formation. With such a technique, it can give a clearly description of the wake. And the shape of the wake, the wake onset and wake developing process are depicted in detail. The numerical results also present the internal vortices, secondary flows and their effects on the Jet-Wake pattern formation. The influences of Coriolis force on flow field of the centrifugal impeller are also discussed.
The Effects of High Mainstream Turbulence and Turbine Vane Film Cooling on the Dispersion of a Simulated Hot Streak
Authors: Jenkins Sean , Varadarajam Krishnakumar , Bogard David G.
Published: February 2009

This paper presents the combined effects of high turbulence and film cooling on the dispersion of a simulated hot streak as it passes over a scaled-up nozzle guide vane. Experimental data demonstrates a considerable decay in the strength of a hot streak due to turbulence effects alone. Film cooling further reduces the peak temperature values resulting in a reduction of the peak temperature in the hot streak on the order of 75% relative to the upstream peak temperature in the hot streak. Comparisons are made between high turbulence (Tu = 20%) and moderate turbulence (Tu = 3.5%) as well as between different blowing conditions for the suction side, showerhead, and pressure side film cooling holes on a simulated nozzle guide vane.
Average Passage Flow Field and Deterministic Stresses in the Tip and Hub Regions of a Multi-Stage Turbomachine
Authors: Uzol Oguz , Chow Yi-Chih , Katz Joseph , Meneveau Charles
Published: February 2009

This paper continues our effort to study the dynamics of deterministic stresses in a multistage turbomachine using experimental data. Here we focus on the tip and hub regions and compare them to mid span data obtained in previous studies. The analysis is based on data obtained in PIV measurements performed in the second stage of a two-stage turbomachine. A complete data set is obtained using blades and fluid with matched optical index of refraction. Previous measurements at mid span have shown that at mid span and close to design conditions, the deterministic kinetic energy is smaller than the turbulent kinetic energy. The primary contributor to the deterministic stresses at mid span is the interaction of a blade with the upstream wakes. Conversely, we find that the tip vortex is the dominant source of phase-dependent unsteadiness and deterministic stresses in the tip region. Along the trajectory of the tip vortex, the deterministic kinetic energy levels are more than one order of magnitude higher than the levels measured in the hub and mid-span, and are of the same order of magnitude as the turbulent kinetic energy levels. Reasons for this trend are explained using a sample distribution of phase-averaged flow variables. Outside of the region affected by tip vortex transport, within the rotor-stator gap and within the stator passages, the turbulent kinetic energy is still 3–4 times higher than the deterministic kinetic energy. The deterministic and turbulent shear stress levels are comparable in all spanwise locations, except for the wakes of the stator blades, where the turbulent stresses are higher. However, along the direction of tip vortex transport, the deterministic shear stresses are about an order of magnitude higher than the turbulent shear stresses. The decay rates of deterministic kinetic energy in the hub and mid-span regions are comparable to each other, whereas at the tip, the decay rate is higher. The decay rates of turbulent kinetic energy are much smaller than those of the deterministic kinetic energy. The paper also examines terms in the deterministic kinetic energy transport equation. The data indicate that “Deterministic Production” and a new term, called here “Dissipation due to Turbulence” are the dominant source/sink terms. Regions with alternating signs of Deterministic Production indicate that the energy transfer between the phase-averaged and average-passage flow fields can occur in both directions. The divergence of the Pressure-Velocity correlation, obtained from a balance of all the other terms, is dominant and appears to be much larger than the deterministic production (source/sink) term. This trend indicates that there are substantial deterministic pressure fluctuations in the flow field, especially within the rotor-stator gap and within the stator passage.
Study of Near-Zero CO2 Emission Thermal Cycles With LNG Cryogenic Exergy Utilization
Authors: Zhang Na , Cai Ruixian , Wang Wei
Published: February 2009

Compared with other fossil fuels, liquefied natural gas (LNG) supplies relatively clean energy because its low contribution to environmental pollution. Furthermore, while 10% of the gas energy was required for its liquefaction, the valuable high cryogenic (at ∼110 K) exergy of the LNG is wasted in many LNG receiving terminals worldwide, by uselessly cooling the seawater used for its re-vaporization. This cryogenic exergy is, however, as an excellent power source. In addition, due to the increasing concern about global climate change, the development of power system which minimizes CO2 emission is of great interest. In this paper, new cycles are proposed which integrate LNG cryogenic exergy utilization and CO2 recovery. The cycles employ both the fuel chemical exergy and LNG cryogenic exergy for power generation, they use no cooling water, and on the contrary, allow the easy removal and recovery of water and CO2 generated from combustion to thereby offer both energy saving and greenhouse gas emission mitigation. The cycles employ CO2 as the main working medium. Oxygen and fuel methane are introduced at stoichiometric ratio, and thus the turbine exhaust is merely a mixture of carbon dioxide and water steam. The LNG coldness is used to improve the power generation efficiency by (1) serving as a low temperature heat sink of the power cycle, and (2) cooling the working fluid prior to compression, to reduce compressor power consumption. Without consuming additional power, the water and extra carbon dioxide generated from combustion can be easily separated from the main stream during the exothermic process when integrated with the LNG evaporation process. Internal combustion and recuperation are adopted to increase the average heat absorption temperature. The proposed cycles are simulated using the commercial ASPEN PLUS code, and their performance is computed. The results indicate that the proposed cycles indeed reduce CO2 emissions significantly with very attractive thermal performances, able to attain thermal and exergy efficiencies of 60∼65% and 45∼53% respectively.