bluuebunny/crossref_metadata_2025 huggingface dataset:
In-Situ O2 Sensor Demonstration in a Pressurized Lean Premixed Combustion Rig
Authors: Straub Douglas L. , Thornton Jimmy D. , Richards Geo. A. , Simmers Doug , Shuk Pavel , Monoharan Ramasamy
Published: November 2008

State-of-the-art gas turbines engines continuously strive for higher cycle efficiencies and lower pollutant emissions. The gas turbine combustor is critical for achieving these goals, and operation near the lean extinction limit is necessary. Slight changes in the flow splits (fuel and/or air) can lead to unexpected flame extinction, or other operational issues such as combustion oscillations. Operating these gas turbine combustors near the flame extinction limit could be improved if acceptable in-situ sensors for the combustion section were commercially available. Although exhaust gas oxygen sensors are commonly used in other combustion processes including large utility boilers and automobiles, the use of in-situ oxygen sensors in gas turbine engines has been limited. This paper will describe the results from rig tests in a pressurized lean premixed combustor. The O2 sensor technology used in these tests is commercially available for industrial boiler applications which typically operate near atmospheric pressure and oxygen levels that range from 0–3% of the effluent. In modern gas turbines, however, the amount of excess oxygen is considerably higher. These high levels of excess oxygen result in low level signals from the O2 sensor, which creates concern for in-situ monitoring in gas turbines. The results indicate that this sensor technology will operate at elevated pressure and at high levels of excess oxygen in the process gas suggesting possible application as an operational and diagnostic tool. Data will be presented to show the effects of different operating variables such as pressure, inlet-air temperature, heat-release, and fuel-air ratio.
The Upgraded Power Turbine for the Industrial Gas Turbine THM 1304 Development and First Operational Experience
Authors: Aschenbruck E. , Beukenberg M. , Blaswich M. , Bokelmann Horst
Published: November 2008

The THM 1304 industrial gas turbine is a two shaft machine incorporating a two stage free power turbine suitable for mechanical and generator drive applications (Fig. 1). As part of an ongoing uprating and upgrading program design modifications were made to the power turbine. The aim was not only to increase power output and efficiency but also to improve on the high availability. The latest design incorporates new blades and vanes, increasing the aerodynamic efficiency and improving the high temperature endurance. Additionally, a new single piece casing and a redesigned mechanical turbine discs arrangement and shaft leads to a higher performance and optimized maintainability. The up rated turbine covers the entire nominal design load range from 9 to 14 MW and extends the available speed range compared to its predecessor. Furthermore, compatibility with the existing product range has been considered. A test program was carried out on the MAN TURBO test bed in Oberhausen, Germany to verify the achievement of the design goals. The program covered not only thermodynamic and aerodynamic measurements but also temperature and mechanical measurements. Special emphasis was put on the validation of the vibration characteristics by means of a telemetry system. Examples will highlight the development testing program in detail. The first production engine went into service at the WINGAS pipeline compression station in Reckrod, Germany. Not only the station layout but also the purpose of the station will be described. Service data registered by the installed monitoring system within the first 10,000 service hours will be discussed and the service experience with the new engine will be presented. During the in house test program the entire turbine performance map was covered.
Mathematical Model of SOFC (Solid Oxide Fuel Cell) for Power Plant Simulations
Authors: Milewski Jaroslaw , Miller Andrzej
Published: November 2008

Presentation of concept of SOFC model is given. The SOFC model was built in HYSYS.Plant environment based on its standard libraries. Main elements of SOFC model and chemical reactions are presented. Selected performance characteristics at the design point of stand-alone SOFC are presented. The new equation to define of SOFC voltage, which was obtained based on new assumptions and which can be used instead of the Nernst equation, is given.
Analysis of Optimal Unit Numbers and Sizes for Microturbine Cogeneration Systems
Authors: Gamou Satoshi , Ito Koichi , Yokoyama Ryohei
Published: November 2008

The relationships between unit numbers and capacities to be installed for microturbine cogeneration systems are analyzed from an economic viewpoint. In analyzing, an optimization approach is adopted. Namely, unit numbers and capacities are determined together with maximum contract demands of utilities such as electricity and natural gas so as to minimize the annual total cost in consideration of annual operational strategies corresponding to seasonal and hourly energy demand requirements. This optimization problem is formulated as a large-scale mixed-integer linear programming one. The suboptimal solution of this problem is obtained efficiently by solving several small-scale subproblems. Through numerical studies carried out on systems installed in hotels by changing the electrical generating/exhaust heat recovery efficiencies, the initial capital cost of the microturbine cogeneration unit and maximum energy demands as parameters, the influence of the parameters on the optimal numbers and capacities of the microturbine cogeneration units is clarified.
Large Eddy Simulation of Flow and Heat Transfer in a 90° Ribbed Duct With Rotation: Effect of Coriolis and Centrifugal Buoyancy Forces
Authors: Abdel-Wahab Samer , Tafti Danesh K.
Published: November 2008

Results from large eddy simulations (LES) of fully developed flow in a 90° ribbed duct are presented with rib pitch-to-height ratio P/e = 10 and a rib height-to-hydraulic-diameter ratio e/Dh = 0.1. Three rotation numbers Ro = 0.18, 0.36 and 0.68 are studied at a nominal Reynolds number based on bulk velocity of 20,000. Centrifugal buoyancy effects are included at two Richardson numbers of Ri = 12, 28 (Buoyancy number, Bo = 0.12 and 0.30) for each rotation case. Buoyancy strengthens the secondary flow cells in the duct cross-section which leads to an increase of 20% to 30% in heat transfer augmentation at the smooth walls over and above the effect of Coriolis forces. Buoyancy also accentuates the augmentation of turbulence near the trailing wall of the duct and increases the heat transfer augmentation ratio 10% to 20% over the action of Coriolis forces alone. However, it does not have any significant effect at the leading side of the duct. The overall effect of buoyancy on heat transfer augmentation for the ribbed duct is found to be less than 10% over the effect of Coriolis forces alone. Friction on the other hand is augmented 15% to 20% at the highest buoyancy number studied. Comparison with available experiments in the literature show excellent agreement.
Large Eddy Simulation of Flow and Heat Transfer in a Staggered 45° Ribbed Duct
Authors: Abdel-Wahab Samer , Tafti Danesh K.
Published: November 2008

Results from large eddy simulation (LES) of fully developed flow in a staggered 45° ribbed duct are presented with rib pitch-to-height ratio P/e = 10 and a rib height to hydraulic diameter ratio e/Dh = 0.1. The nominal Reynolds number based on bulk velocity is 47,300. Mean flow and turbulent quantities, together with heat transfer and friction augmentation results are presented. The flow is characterized by a helical vortex behind each rib and a complementary cross-sectional secondary flow, both of which result from the angle of the rib with respect to the mean flow. Averaged velocity profiles at the duct center show excellent agreement with experiments and heat transfer predictions agree well with experiments. Turbulent kinetic energy, shear stress, and heat transfer augmentation ratios show a strong correlation to the rib vortex and the secondary flow. Overall, heat transfer is augmented by a factor of 2.3 compared with a smooth duct and matches experimental data within 2%.
Investigation of Blade and Disc Vibrations on the Upgraded Power Turbine for the THM 1304 Gas Turbine
Authors: Frank D. , Kleinefeldt A. , Orth U. , Cline W.
Published: November 2008

As part of an ongoing uprating and upgrading program of the THM 1304 gas turbine directed towards increasing power output and efficiency as well as further improving the high level of availability, major design modifications were made on the power turbine (PT). New blades and vanes were designed for increased aerodynamic efficiency, improved high temperature capability, higher power output and higher nominal operating speed. This report presents the analytical and experimental investigations made on the vibration modes and frequencies of blades with pre-loaded interlocking tip shrouds. One focus is upon observed families of mode shapes at different nodal diameters. A comparison of finite-element results with test data shows how good predictions are in the case of coupled blade vibrations. The value of testing the vibration behavior of power turbine blades in the actual machine, over the complete speed range, becomes evident as an important addition to the numerical predictions and laboratory tests. Another focus is on the method of testing, including the telemetry system used and the problem of optimum placement of strain gages on the blades. The selected strain gage positions are crucial to the value and meaningfulness of the test results. The observed strain vibration amplitudes were compared with high-cycle-fatigue (HCF) data available for the blade material. It was shown that measured amplitudes were significantly below allowable levels over the complete range of operating power and speed. The analytical and experimental methods employed to determine blade mode shapes and frequencies for a blade system with pre-loaded tip shrouds are presented in detail.
URANS-Modelling of Flame Transfer Functions of Turbulent Premixed Jet Flames
Authors: Hettel Matthias , Habisreuther Peter , Bu¨chner Horst , Bockhorn Henning , Zarzalis Nikolaos
Published: November 2008

The understanding of the formation of self excited pressure oscillations in technical combustion systems depends on the knowledge of the dynamical behaviour of the flame used. As an important mechanism driving these combustion instabilities the formation and reaction of coherent large-scale ring-vortices has been indentified. The phenomenon is investigated with numerical simulations using “Unsteady Reynolds-Averaged Navier-Stokes” (URANS)-methods, applying the k-ε turbulence model and a “Turbulent-Flamespeed-Closure” (TFC) combustion model. Firstly, a premixed turbulent axial methane jet flame with a thermal load of 40 kW was calculated using steady-state flow conditions. The axial distibutions of the measured radiation of OH-radicals and the calculated reaction rate show good agreement, if the turbulent burning velocity is reduced versus the original formulation. The axial positions of the maxima of the curves coincide and are applied to define a characteristic overall time delay. Secondly, a pulsed flame with a forcing frequency of 100 Hz was calculated. An additional transport equation for the residence time of fuel was solved. The analysis of the distribution of the residence time showed, that the characteristic overall time delay of the steady-state flame is a good approximation for the overall time delay of the pulsed flame. Thirdly, the flame frequency response of the pulsed flame was calculated up to frequencies of 200 Hz. For the calculation with reduced burning velocity the phase angle function of the flame coincides with the measurement and shows the typical behaviour of an ideal idle-time model.
A New Method of Calculating Transient Response of Complex Rotors
Authors: Li Lin , Wang Bao Feng
Published: November 2008

In this paper the ‘transfer coefficient-direct integral method’ is developed to analysis of transient response of rotor systems, especially for non-linear rotor systems. The main difference from the classical transfer matrix-direct integral method rests with the introduction of complex modal analysis corresponding to positive and negative whirling frequencies, and after obtaining the critical speed and the corresponding vibration modes by the transfer coefficient method it is no longer necessary to do transfer calculation (but in classical transfer matrix-direct integral method, after every integral step, it is necessary to do a transfer calculation through the whole rotor system). In the transfer coefficient-direct integral method, corresponding every integral step it is only a linear transformation between the real displacements and the modal displacements. It makes the transfer calculation and the direct integral become two independent steps of the calculation. Each step fully takes advantages of the method correspondent. The whole analysis procedure is then greatly simplified. The paper gives, at first, the principle of the transfer coefficient-direct integral method. After this, the transient response of a co-axial double rotor system with a squeeze film damper is calculated by the method. The response history of the system from an initial time to stable state is given.
Analysis of Local Flow Structure and Global Compressor Performance During Rotating Stall
Authors: Palomba Chiara
Published: November 2008

Rotating stall is an instability phenomenon that arises in axial flow compressors when the flow is reduced at constant rotational speed. It is characterised by the onset of rotating perturbations in the flow field accompanied by either an abrupt or gradual decrease of performances. Although the flow field is unsteady and non axisymmetric, the global operating point is stable and a stalled branch of performance curve may be experimentally determined. The number, rotational speed, circumferential extension of the rotating perturbed flow regions named rotating cells may vary from one compressor to another and may depend on the throttle position. The present work focuses on the interaction between local flow parameters and global compressor performance parameters with the aim of reaching a better understanding of the phenomenon. Starting from the Day, Greitzer and Cumpsty [1] model the detailed flow conditions during rotating stall are studied and related to the global performance parameters. This is done both to verify if the compressor under examination fits to the model and if the detailed flow structure may highlight the physics that in the simple model may hide behind the correlation’s used.
A Detailed Analysis of Thermoacoustic Interaction Mechanisms in a Turbulent Premixed Flame
Authors: Schuermans Bruno , Bellucci Valter , Guethe Felix , Meili Franc¸ois , Flohr Peter , Paschereit Christian Oliver
Published: November 2008

A combined theoretical and experimental analysis of thermoacoustic interaction mechanisms of a lean pre-mixed swirl-stabilized gas turbine burner is presented. A full-scale gas turbine burner has been tested in an atmospheric test rig. The test facility was equipped with loudspeakers to excite the acoustic field and with arrays of microphones to measure the response of the acoustic field to the forcing signal. With this set-up transfer matrices relating the acoustic pressure and velocity on both sides of the flame front have been measured. A laser absorption measurement technique allowed for measurement of the fluctuations of fuel concentration in the mixture. Heat release fluctuations were monitored using a photo-multiplier. The measurement of the acoustic field, heat release and equivalence ratio fluctuations have been measured simultaneously. Special attention has been given to the role of fuel concentration fluctuations in the thermoacoustic interaction mechanism. In order to be able to clearly separate this mechanism from other possible mechanisms, all the experiments have been performed in pre-premixing mode as well. In pre-premixing mode the fuel is injected far upstream of the burner in order to avoid fuel concentration fluctuations at the burner location. This is in contrast with premixing mode where fuel and air are mixed in the burner. An acoustic flame model has been derived. The model includes the well-known interaction mechanism of equivalence ratio fluctuations but also includes a novel mechanism that is caused by fluctuations of vorticity. This latter mechanism relates the turbulent flame speed via turbulence intensity fluctuations to the acoustic field. The idea is that periodic acoustic fluctuations cause periodic changes of the turbulence intensity. The turbulence intensity strongly affects the turbulence flame speed. The fluctuations of the turbulent flame speed result in fluctuations of the heat release. This turbulence intensity fluctuation model has been compared with the measured pre-premix transfer functions and shows an excellent agreement. The measured transfer functions in premix mode have been compared with the model that includes fluctuations of fuel concentration and turbulence intensity. Also in this case a very good agreement is found. Moreover, it has been demonstrated that the phase relation between measured equivalence ratio fluctuation and heat release corresponds to the model.
Unsteady Heat Transfer Measurements From Transonic Turbine Blades at Engine Representative Conditions in a Transient Facility
Authors: Allan William , Ainsworth Roger , Thorpe Steven
Published: November 2008

The unsteady heat transfer measurements about a transonic turbine blade at engine representative Mach and Reynolds numbers are presented. High density, fast response thin film gauges are employed at the mid-height streamline. A description of the novel development of gold gauges together with a brief overview of their calibration and signal processing is presented. Detailed time and phase-averaged measurements have been obtained, providing insight into the role of upstream nozzle guide vane wakes and shock features. These heat transfer results compliment recent fast-response aerodynamic results on this and similar transonic profiles, which highlight the dominance of the upstream vane-rotor interaction over convected wake segments, particularly in light of unsteady turbine blade loading. From a heat transfer standpoint however, whilst the periodic shock events contributed to abrupt, localized heat transfer enhancements, the influence of NGV wake segments on the boundary layer could not be discounted when duration of unsteadiness was considered.
Advanced Combustion Modeling in Gas Turbines With ILDM Approach
Authors: Pixner Paul , Krebs Werner , Prade Bernd
Published: November 2008

One of the greatest challenges in modern gas turbine engineering is to optimize the combustion system for the reduction of emissions. For better understanding of combustion systems and hence having the possibility of systematic innovation of gas turbine combustion systems, a permanent improvement of design tools is essential. Demonstrated here is the use of an advanced combustion model — the INTRINSIC LOW DIMENSIONAL MANIFOLD (ILDM) approach — in Computational Flow Dynamics (CFD) analysis. In the past, chemical kinetic models used in CFD-calculations were based on empirical parameters and so called “global mechanisms” which are in fact “local” models and can be used only when modeling one operating point of the gas turbine combustion system. The scope of the integration of the ILDM approach into CFD is the use of a generalized approach for modeling chemical kinetics in CFD. Turbulence-chemistry interaction is considered by a presumed Probability Density Function (PDF) approach. The benefit of this method is a realistic prediction of all relevant flame characteristics e.g. piloting of premixed flames. This offers the possibility to integrate the whole combustion modeling tool in an overall emission prevention strategy. This work here will present the results of applying this new approach to an atmosperic test rig and first validation results.
Moisture Condensation Effect on Turbine Performance Tests
Authors: Roumeliotis I. , Mathioudakis K.
Published: November 2008

Water is always present in the atmospheric air in the form of vapour, affecting the operation of turbomachinery components in gas turbine engines. Due to water presence in the working medium, condensation may occur, which can influence the thermal performance of the component and alter the measurements taken for calculations. This can lead to erroneous evaluation of component performance parameters during development performance tests. Procedures to detect condensation and if possible to correct the measurements during engine or component test should be used to avoid such situations. A method allowing the prediction of condensation and the correction of the measurements for low speed expansion is presented. The method is implemented in turbine testing measurements where condensation occurs and the results show that condensation may be predicted and its effects corrected.
The Effect of Diluents on the Formation Rate of Nitrogen Oxide in a Premixed Laminar Flame
Authors: Hermann Fredrik , Zeuch Thomas , Klingmann Jens
Published: November 2008

New high-efficiency power cycles and environmentally friendly cycles have introduced combustion atmospheres that differ from the traditional hydrocarbon-air mixtures. Wet cycles, solid oxide fuel cell with a gas turbine (SOFC-GT), CO2 separation/capture and biogas combustion are processes that involve high concentrations of inert gases such as H2O, CO2 and N2. These new combustion atmospheres have not been well characterized for premixed flames, hence greater interest is attached how NOx formation is affected. At combustion temperatures above 1800 K, NOx emission is dominated by thermal NOx. The thermal NOx mechanism consists of three elementary reactions. The process is known to be exponential in combustion temperature, but it is also comparably slow and thus dependent on the residence time and the temperature in the post-flame zone. To model the flame, code for a one-dimensional flame with detailed chemistry was used. The flame code solves the combustion evolvement for a one-dimensional, premixed laminar flame. Detailed chemistry was used to model the chemical kinetics. NOx production was described by a NOx mechanism, including thermal, prompt and N2O intermediate. Altogether, the mechanisms consisted of 116 species and 713 reactions. The cases investigated were all premixed flames, diluted with either H2O, CO2, N2 or Ar. The cases used a constant combustion temperature of 2000 K and different pressure levels. All cases were investigated at constant inlet air-fuel temperature and varying equivalence ratio. The rate of formation of NO was investigated for both natural gas and hydrogen flames. The rate of formation of NO is reduced by the addition of any diluents at constant combustion temperature if the O-atom concentration is reduced in the high temperature post-flame zone. The computations show equilibrium between O and O2, and the reduced rates of formation of NO (at constant temperature) are thus simply the result of reduction in the product [O2]0.5[N2] in the post-flame zone.
An Approach to Integrated Multi-Disciplinary Turbomachinery Design
Authors: Jarrett Jerome P. , Dawes William N. , Clarkson P. John
Published: November 2008

Aeroengines are designed using fractured processes. Complexity has driven the design of such machines to be subdivided by specialism, customer and function. While this approach has worked well in the past, with component efficiencies, current material performance and the possibilities presented by scaling existing designs for future needs becoming progressively exhausted it is necessary to reverse this process of disintegration. Our research addresses this aim. The strategy we use has two symbiotic arms. The first is an open data architecture from which existing disparate design codes all derive their input and to which all send their output. The second is a dynamic design process management system known as “SignPosting”. Both the design codes and parameters are arranged into complementary multiple level hierarchies: fundamental to the successful implementation of our strategy is the robustness of the mechanisms we have developed to ensure consistency in this environment as the design develops over time. One of the key benefits of adopting a hierarchical structure is that it confers not only the ability to use mean-line, throughflow and fully 3D CFD techniques in the same environment but also to cross specialism boundaries and insert mechanical, material, thermal, electrical and structural codes, enabling exploration of the design space for multi-disciplinary non-linear responses to design changes and their exploitation. We present results from trials of an early version of the system applied to the redesign of a generic civil aeroengine core compressor. SignPosting has allowed us to examine the hardness of design constraints across disciplines which has shown that it is far more profitable not to strive for even higher aerodynamic performance, but rather improve the commercial performance by maintaining design and part speed pressure ratios stability and efficiency while increasing rotor blade creep life by up to 70%.
Influence of Fuel Composition on Solid Oxide Fuel Cell Hybrid System Layout and Performance
Authors: Marsano Francesco , Magistri Loredana , Bozzolo Michele , Tarnowski Olivier
Published: November 2008

The design of Solid Oxide Fuel Cell (SOFC) Hybrid Systems (HS) is usually based on the use of natural gas as fuel. However, the possibility of using other fuels such as biomass gasification, pyrolysis, fermentation, and coal gasification could potentially increase the market for SOFC Hybrid Systems. In this paper, the influence of fuel composition on both HS layout and performance is investigated. The analysis is based on a layout and a detailed simulation model of a Hybrid System based on Rolls-Royce Integrated Planar SOFC (IP-SOFC) technology fed with natural gas, previously developed by the authors. Particular attention has been given to the thermal management of the stack, the anode flow recirculation design and the turbine-compressor redesign, including safe surge margin operation conditions.
Assessment of the Effectiveness of Gas Path Diagnostic Schemes
Authors: Mathioudakis K. , Kamboukos Ph.
Published: November 2008

A variety of methods can be used for the diagnosis of faults in gas path components of gas turbines. Problems that are common for diagnostic method implementation are the choice of measured quantities, choice of health parameters and choice of operating conditions for data retrieval. The present paper introduces some general principles for evaluation of the effectiveness of different diagnostic schemes. They encompass criteria proposed in past publications, while they offer additional possibilities for assessment of diagnostic effectiveness in various situations. The method is based on the evaluation of the behavior of linear systems, which are a good approximation of the non-linear ones for small deviations and employs the concept of system condition number to formulate criteria. The determination of limits for this number for establishing system condition criteria and quantification of observability is examined, on the basis of uncertainty propagation. Sample problems evaluated are: maximizing effectiveness of individual component identification from a multiplicity of available measurements, selection of individual operating points for multi-point applications.
Fluid Dynamics and Performance of Partially and Fully Shrouded Axial Turbines
Authors: Porreca L. , Behr T. , Schlienger J. , Kalfas A. I. , Abhari R. S. , Ehrhard J. , Janke E.
Published: November 2008

A unique comparative experimental and numerical investigation carried out on two test cases with shroud configurations differing only in the labyrinth seal path, is presented in this paper. The blade geometry and tip clearance is identical in the two test cases. The geometries under investigation are representative of an axial turbine with a full and partial shroud, respectively. Global performance and flow field data were acquired and analyzed. Computational simulations were carried out to complement the investigation and to facilitate the analysis of the steady and unsteady flow measurements. A detailed comparison between the two test cases is presented in terms of flow field analysis and performance evaluation. The analysis focuses on the flow effects reflected on the overall performance in a multi-stage environment. Strong interaction between the cavity flow and the blade tip region of the rotor blades is observed up to the blade mid span. A marked effect of this interaction can be seen in the downstream second stator where different vortex structures are observed. Moreover, in the partial shroud test case, a strong tip leakage vortex is developed from the first rotor and transported through the downstream blade row. A measurable change in the second stage efficiency was observed between the two test cases. In low aspect ratio blades within a multistage environment, small changes in the cavity geometry can have a significant effect on the mainstream flow. The present analysis has shown that an integrated and matched blade-shroud aerodynamic design has to be adopted to reach optimal performances. The additional losses resulting from small variations of the sealing geometry could result in a gain of up to one point in the overall stage efficiency.
Intentional Mistuning Design Space Reduction Based on Vibration Energy Flow in Bladed Disks
Authors: Lim Sang-Ho , Castanier Matthew P. , Pierre Christophe
Published: November 2008

Intentional mistuning is the deliberate incorporation of blade-to-blade parameter variations in the nominal design of a bladed disk. Previous studies have shown that this is a promising strategy for mitigating the damaging effects of unintended, random mistuning. In this paper, the mechanisms of intentional mistuning are studied by investigating the relation between blade response and vibration energy flow in lumped parameter models. Based on key observations from the energy flow analysis, a few design guidelines are proposed that drastically reduce the design space for intentional mistuning patterns. Thus, an optimization may be performed on the reduced design space or skipped altogether, yielding dramatic reductions in computational costs. The guidelines are validated by extensive Monte Carlo simulations for the lumped parameter models as well as for a finite-element-based reduced-order model of an industrial rotor. It is shown that the reduced design space includes optimal or near-optimal intentional mistuning patterns.
Aerothermodynamics of Micro-Turbomachinery
Authors: Gong Y. , Sirakov B. T. , Epstein A. H. , Tan C. S.
Published: November 2008

Engineering foundation for micro-turbomachinery aerothermal design, as an enabling element of the MIT micro-gas turbine technology, is developed. Fundamental differences between conventional, large scale and micro turbomachinery operation are delineated and the implications on design are discussed. These differences are largely a consequence of low operating Reynolds number, hence a relatively higher skin friction and heat transfer rate. While the size of the micro-gas turbine engine is ∼ a few mm, several order of magnitude smaller than conventional gas turbine, the required compressor stage pressure ratio (∼3–4) and impeller tip Mach number (∼1 and greater) are comparable; however, the disparity in the size implies that the operating Reynolds number of the micro-turbomachiery components is correspondingly several order of magnitudes smaller. Thus the design and operating requirements for micro-turbomachinery are distinctly different from those of conventional turbomachinery used for propulsion and power generation. Important distinctions are summarized in the following. 1. The high surface-to-flow rate ratio has the consequence that the flow in micro-compressor flow path can no longer be taken as adiabatic; the performance penalty associated with heat addition to compressor flow path from turbine is a primary performance limiting factor. 2. Endwall torque on the flow can be significant compared to that from the impeller blade surfaces so that direct use of Euler Turbine Equation is no longer appropriate. 3. Losses in turbine nozzle guide vanes (NGVs) can be one order of magnitude higher than those in conventional sized nozzle guide vanes. 4. The high level of kinetic energy in the flow exiting the turbine rotor is a source of performance penalty, largely a consequence of geometrical constraints. It can be inferred from these distinctions that standard preliminary design procedures based on the Euler equation, the adiabatic assumption, the loss correlations for large Reynolds numbers, and the three-dimensional geometry, are inapplicable to micro-turbomachinery. The preliminary design procedure, therefore, must account for these important differences. Characterization of the effects of heat addition on compressor performance, modification of Euler turbine equation for casing torque, characterization of turbine NGV performance and turbine exhaust effects are presented.
Strategic Management of Technology for Power Generation Equipment: A System Dynamics Approach
Authors: Franco Flavio J.
Published: November 2008

There is a large number of studies about energy long term trends and policies, published by national and international government organisations. Commercial companies, particularly manufacturers of power generation equipment, can take benefit of these studies to test the robustness of long term technology development strategies. Scenario Planning and System Dynamics have been used by the government organisations to study energy policies. In this paper an application of this methodology is proposed for manufacturers of power generation equipment, in particular gas turbine manufacturers. A generic company is used as an illustrative example, against scenarios produced by the International Institute for Applied System Analysis. A System Dynamics model is proposed, simplifications and assumptions are discussed, the type of results that can be obtained is shown and some recommendations are suggested for the construction of more realistic models.
Method for Analysis of Nonlinear Multiharmonic Vibrations of Mistuned Bladed Discs With Scatter of Contact Interface Characteristics
Authors: Petrov E. P. , Ewins D. J.
Published: November 2008

An efficient method for analysis of nonlinear vibrations of mistuned bladed disc assemblies has been developed. As a result, this development has facilitated the use of large-scale finite element models for realistic bladed discs, as used hitherto in analysis of linear vibration, to be extended for the analysis of nonlinear multiharmonic vibration. The new method is based on a technique for the exact condensation of nonlinear finite element models of mistuned bladed discs. The model condensation allows the size of the nonlinear equations to be reduced to the number of degrees of freedom where nonlinear interation forces are applied. The analysis of nonlinear forced response for simplified and realistic models of mistuned bladed discs has been performed. For a practical high-pressure bladed turbine disc, several types of nonlinear forced response have been considered including: (i) mistuning by scatter of underplatform dampers; (ii) mistuning by shroud gap scatter; (iii) mistuning by blade frequency scatter in the presence of nonlinear shroud interactions.
Method for Direct Parametric Analysis of Nonlinear Forced Response of Bladed Discs With Friction Contact Interfaces
Authors: Petrov E. P.
Published: November 2008

An effective method for direct parametric analysis of periodic nonlinear forced response of bladed discs with friction contact interfaces has been developed. The method allows, for the first time, forced response levels to be calculated directly as a function of contact interface parameters such as the friction coefficient, contact surface stiffness (normal and tangential coefficients), clearances, interferences, and the normal stresses at the contact interfaces. The method is based on exact expressions for sensitivities of the multiharmonic interaction forces with respect to variation of all parameters of the friction contact interfaces. These novel expressions are derived in the paper for a friction contact model, accounting for the normal load variation and the possibility of separation-contact transitions. Numerical analysis of effects of the contact parameters on forced response levels has been performed using large-scale finite element models of a practical bladed turbine disc with underplatform dampers and with shroud contacts.
Development of the Unsteady Flow on a Turbine Rotor Platform Downstream of a Rim Seal
Authors: Gallier Kirk D. , Lawless Patrick B. , Fleeter Sanford
Published: November 2008

In high temperature turbines, air from disk cavities is forced through the vane-rotor seal to prevent hot gas ingress into these cavities. This emergent seal air can play a significant role in the formation of secondary flows which emanate from the hub region near the rotor blade leading edge. The formation of these structures is also dependent on the inherently unsteady flow field driven by the vane-rotor interaction. As these secondary flows play an important role in both blade performance and heat transfer, the physics that governs them is of significant interest in turbine aero and thermal design. This work investigates and characterizes the aerodynamic signature of the interaction between an emergent seal flow and the hub flow approaching the downstream rotor including the effects of vane-rotor interaction. This is accomplished by means of an experimental investigation performed on the first stage of the Purdue Research Turbine using Particle Image Velocimetry (PIV). The flow field is interrogated in the near-hub region of the intra-stage space, downstream of the first vane row. Purge air is introduced through a planar seal at two different flow rates which characterize typical high and low boundaries for the range of dimensionless seal flow rates encountered in practice. Two-dimensional (radial and axial) velocity data from four measurement planes spaced from vane pressure side to mid-passage are acquired. These data are phase-locked to rotor position. The ensemble-averaged vorticity data from each of ten rotor positions provide a characterization of the effect of the rotor potential field on the emergent seal flow. Vane wake affects on purge strength and downstream flow development are captured at each of two seal flow rates.
Combined Heat and Power Technologies: Application Studies of Options Including Micro Gas Turbines
Authors: Gonza´lez Miguel Angel , Padilla Ro´ger , Willinger Reinhard
Published: November 2008

Recently, several methods have been developed to select and optimize energy systems with the purpose of finding the most economical solution that supplies the required energy demand. This paper presents a theoretical study of cogeneration technolgies, which includes a qualitative survey, and technical and economical arguments to define which combinations of supply technologies can be expected to serve six different demand cases. The comparison from economical viewpoint, based on annualized capital and operatinal costs of the system, shows a trend to use backpressure steam turbine for small cases (power demand ≤ 5MW) and industrial gas turbine for big cases (power demand ≥ 5MW).
Foreign Object Damage Behavior of a SiC/SiC Composite at Ambient and Elevated Temperatures
Authors: Choi Sung R. , Bhatt Ramakrishna T. , Pereira J. Michael , Gyekenyesi John P.
Published: November 2008

Foreign object damage (FOD) behavior of a gas-turbine grade SiC/SiC ceramic matrix composite (CMC) was determined at 25 and 1316°C, employing impact velocities from 115 to 440 m/s by 1.59-mm diameter steel-ball projectiles. Two different types of specimen support were used at each temperature: fully supported and partially supported. For a given temperature, the degree of post-impact strength degradation increased with increasing impact velocity, and was greater in a partially supported configuration than in a fully supported one. The elevated-temperature FOD resistance of the composite, particularly under partially supported loading at higher impact velocities ≥ 350 m/s, was significantly less than the ambient-temperature counterpart, attributed to a weakening effect of the composite. For fully supported loading, frontal contact stress played a major role in generating composite damage; whereas, for partially supported loading, both frontal contact and backside bending stresses were combined sources of damage generation. The SiC/SiC composite was able to survive higher energy impacts without complete structural failure but suffered more strength affecting damage from low energy impacts than AS800 and SN282 silicon nitrides.
A Computational Study of Tip Desensitization in Axial Flow Turbines: Part 1 — Baseline Turbine Computations and Comparisons With Measurement
Authors: Tallman James A.
Published: November 2008

This study used Computational Fluid Dynamics (CFD) to investigate modified turbine blade tip shapes as a means of reducing the leakage flow and vortex. The subject of this study was the single-stage experimental turbine facility at Penn State University, with scaled three-dimensional geometry representative of a modern high-pressure stage. To validate the numerical procedure, the rotor flowfield was first computed with no modification to the tip, and the results compared with measurements of the flowfield. The flow was then predicted for a variety of different tip shapes: first with coarse grids for screening purposes and then with more refined grids for final verification of preferred tip geometries. Part 1 of this two-part paper focuses on the turbine case description, numerical procedure, baseline flat-tip computations, and comparison of the baseline results with measurement. A Runge-Kutta time-marching CFD solver (ADPAC) was used to solve the Reynolds-Averaged Navier-Stokes equations. Two-equation turbulence modeling with low Reynolds number adjustments was used for closure. The baseline rotor flowfield was computed twice: with a moderately sized mesh (720,000 nodes) and also with a much more refined mesh (7.2 million nodes). Both solutions showed good agreement with previously taken measurements of the rotor flowfield, including five-hole probe measurements of the velocity and total pressure inside the passage, as well as pressure measurements on the blade and casing surfaces.
A Transonic Compressor Stage: Part 1 — Experimental Results
Authors: Gannon A. J. , Hobson G. V. , Shreeve R. P.
Published: November 2008

The results of an experimental program to test a transonic compressor stage are presented. The stage was designed using computational fluid dynamic (CFD) techniques to minimize the use of empirical methods. The main performance characteristics of the stage are presented along with a description of the test rig. Some of the technical difficulties and solutions implemented in sustained testing of a transonic stage are outlined. Equations used to mass average the pressure and temperature ratio, to derive the isentropic efficiency and a method of measuring losses due to the case-wall are presented. Results from the experimental program for 70, 80, 90 and 100% speeds for rig open throttle to near stall are presented. Stall occurred at all speeds except 100%, where it was avoided due to rotor stress concerns. Quantitative performance maps of stage total-to-total pressure ratio and isentropic efficiency were determined. In addition, a map showing the losses due to the case-wall is presented. The total-to-total stagnation pressure and temperature profiles at the exit to the stage over the entire test range were measured and used to calculate the isentropic efficiencies. Static pressure measurements along the case-wall and hub-wall through the stage are presented. The experimental program has yielded data from a transonic compressor stage that can be used in the validation of CFD [1] codes and evaluation of the original design methods.
Large Eddy Simulations of Flow and Heat Transfer in Rotating Ribbed Duct Flows
Authors: Tyagi Mayank , Acharya Sumanta
Published: November 2008

Large eddy simulations are performed in a periodic domain of a rotating square duct with normal rib turbulators. Both the Coriolis force as well as the centrifugal buoyancy force are included in this study. A direct approach is presented for the unsteady calculation of the non-dimensional temperature field in the periodic domain. The calculations are performed at a Reynolds number (Re) of 12, 500, a Rotation number (Ro) of 0.12 and an inlet coolant-to-wall density ratio (Δρ/ρ) of 0.13. The time-averaged Nusselt numbers compare satisfactorily with the data of Wagner et al. (J. Turbomachinery, Vol. 114, pp. 847–857). Time-sequences of the vorticity components and the temperature fields are presented to understand the flow physics and the unsteady heat transfer processes. Large scale coherent structures are seen to play an important role in the mixing and heat transfer. The temperature field appears to contain a low frequency mode that extends beyond a single inter-rib geometric module, and indicates the necessity of using at least two inter-rib modules for streamwise periodicity to be satisfied. Proper orthogonal decomposition (POD) of 200 snapshots indicates a low dimensionality of this system with almost 99% of turbulent energy in the first 80 POD modes.
Heat/Mass Transfer in a 4:1 AR Smooth and Ribbed Coolant Passage With Rotation in 90-Degree and 45-Degree Orientations
Authors: Acharya S. , Agarwal P. , Nikitopoulos D. E.
Published: November 2008

The paper presents an experimental study of heat/mass transfer coefficient in 4:1 aspect ratio rectangular channel with smooth or ribbed walls for Reynolds number in the range of 5,000 to 30,000, rotation numbers in the range of 0–0.12 and for two different orientations of the test-section (90-degree and 45-degree relative to the plane of rotation). Such passages are encountered close to the trailing sections of the turbine blade. Inline normal tips (e/Dh = 0.15625 and p/e = 11.2) are used and placed on the leading and the trailing sides. The experiments are conducted in a rotating two-pass coolant channel facility using the naphthalene sublimation technique. It is observed that for the 45-degree orientation of the test-section, all the walls show an increase in the heat transfer with rotation as opposed to the 90-degree orientation where the stabilized wall shows reduction and the destabilized wall shows enhancement. The spanwise mass transfer distributions in the smooth and the ribbed cases are also presented, and show significant variations in the spanwise direction for the smooth channel.