bluuebunny/crossref_metadata_2025 huggingface dataset:
Boundary Layer Influence on the Unsteady Horseshoe Vortex Flow and Surface Heat Transfer
Authors: Sabatino D. R. , Smith C. R.
Published: March 2009

The spatial-temporal flow-field and associated surface heat transfer within the leading edge, end-wall region of a bluff body were examined using both particle image velocimetry and thermochromic liquid crystal temperature measurements. The horseshoe vortex system in the end-wall region is mechanistically linked to the upstream boundary layer unsteadiness. Hairpin vortex packets, associated with turbulent boundary layer bursting behavior, amalgamate with the horseshoe vortex resulting in unsteady strengthening and streamwise motion. The horseshoe vortex unsteadiness exhibits two different natural frequencies: one associated with the transient motion of the horseshoe vortex, and the other with the transient surface heat transfer. Comparable unsteadiness occurs in the end-wall region of the more complex airfoil geometry of a linear turbine cascade. To directly compare the horseshoe vortex behavior around a turning airfoil to that of a simple bluff body, a length scale based on the maximum airfoil thickness is proposed.
Spike and Modal Stall Inception in an Advanced Turbocharger Centrifugal Compressor
Authors: Spakovszky Z. S. , Roduner C. H.
Published: March 2009

In turbocharger applications bleed air near the impeller exit is often used for secondary flow systems to seal bearing compartments and to balance the thrust load on the bearings. There is experimental evidence that the performance and operability of highly loaded centrifugal compressor designs can be sensitive to the amount of bleed air. To investigate the underlying mechanisms and to assess the impact of bleed air on the compressor dynamic behavior, a research program was carried out on a pre-production, 5.0 pressure ratio, high-speed centrifugal compressor stage of advanced design. The investigations showed that bleed air can significantly reduce the stable flow range. Compressor rig experiments, using an array of unsteady pressure sensors and a bleed valve to simulate a typical turbocharger environment, suggest that the path into compression system instability is altered by the bleed flow. Without bleed flow, the pre-stall behavior is dominated by short wavelength disturbances, or so called ‘spikes’, in the vaneless space between the impeller and the vaned diffuser. Introducing bleed flow at impeller exit reduces endwall blockage in the vaneless space and destabilizes the highly-loaded vaned diffuser. The impact is a 50% reduction in stable operating range. The altered diffuser characteristic reduces the compression system damping responsible for long wavelength, modal pre-stall behavior. A four-lobed backward traveling rotating stall wave is experimentally measured, in agreement with calculations obtained from a previously developed dynamic compressor model. In addition, a self-contained, endwall blockage control strategy was employed, successfully recovering 75% of the loss in surge-margin due to bleed flow and yielding a 1 point increase in adiabiatic compressor efficiency.
A Comparison of Loss Models Using Different Radial Distribution of Loss in an Axial Turbine Streamline Curvature Program
Authors: de Jesus Genival Sena , Barbosa Joa˜o Roberto , Ramsden Kenneth W.
Published: March 2009

The streamline computer codes published in the open literature and used to analyze the performance of axial flow turbines have employed a particular loss model chosen from a number of existing prediction methods. It is well known that the performance prediction methods developed for one-dimensional models concentrates the losses at the blade mid-height. When used in a streamline curvature model, however it is necessary to distribute these losses along the blade span. However the way to distribute the losses is not unique, as is clear from the open literature. Some methods seem to be an arbitrary procedure, with a shortcoming in representing the real flow behavior within the blade row. In this paper, two different loss distribution models were implemented in a streamline curvature program specially developed for the study of axial flow turbine performance. The study seeks to establish which one best represents the reality of the complex flow physics occurring within a blade row. Three different loss models were also implemented in the program to check their reliability and validity when combined with different loss distribution systems. Performance maps for a single-stage turbine were generated by means of different combinations of loss models and radial loss distributions. The computed result for each case was compared with available experimental data of a single-stage turbine.
Impact of Biodiesel on Fuel Preparation and Emissions for a Liquid Fired Gas Turbine Engine
Authors: Bolszo Christopher , McDonell Vincent , Samuelsen Scott
Published: March 2009

This paper reports the fuel injection, vaporization, and emissions characteristics when running a 30 kW gas turbine engine on biodiesel (B99), and diesel fuel distillate # 2. Compositional analysis is used to assess the distillation of these fuels and a comparison is made with ethanol. The role of the liquid properties on fuel preparation and the subsequent engine performance is also assessed. The results show that while compositionally simple, biodiesel features some properties that result in inferior atomization and longer evaporation times compared to DF2. In addition, the overall spray behavior differs substantially in terms of density and width. The measured NO and CO emissions levels produced by the engine reveal significant increases with the use of biodiesel which is expected given the inferior fuel preparation characteristics. It appears reasonable to modify the fuel injector in order to overcome the deleterious effects observed for biodiesel. The benefits of blending biodiesel and ethanol in order to eliminate duel fuel operation during cold startup are discussed.
A Reynolds-Averaged Navier-Stokes Solver in a Turbomachinery Design System
Authors: Gu Fahua , Anderson Mark R.
Published: March 2009

The design of turbomachinery has been focusing on the improvement of the machine efficiency and the reduction of the design cost. This paper presents an integrated design system to create the machine geometry and to predict the machine performance at different levels of approximation, including one-dimensional design and analysis, quasi-three-dimensional-(blade-to-blade, throughflow) and full-three-dimensional-steady-state CFD analysis. One of the most important components, the Reynolds-averaged Navier-Stokes solver, is described in detail. It originated from the Dawes solver with numerous enhancements. They include the use of the low speed pre-conditioned full Navier-Stokes equations, the addition of the Spalart-Allmaras turbulence model and an improvement of wall functions related with the turbulence model. The latest upwind scheme, AUSM, has been implemented too. The Dawes code has been rewritten into a multi-block solver for O, C, and H grids. This paper provides some examples to evaluate the effect of grid topology on the machine performance prediction.
A Robustness Analysis Tool for Fleetwide Variability and Degradation Assessment in Propulsion Control Systems
Authors: Byington Carl , Roemer Michael , Amin Sanket , Kallappa Pattada , Karlsons Glen
Published: March 2009

The desire to enlarge the flight envelope of tactical aircraft and provide enhanced maneuvering capabilities has led to the use of forces and moments produced by the propulsion system to directly influence aircraft dynamics. This coupling between propulsion and flight dynamics is significant enough that traditional techniques for control system design and analysis are either conservative or inaccurate. An integrated approach is required in order to obtain an overall system that provides stability and performance with minimum pilot workload. The authors propose a solution that integrates existing techniques for linear robustness analysis, nonlinearity analysis, optimization, and robust identification into a software tool that facilitates the analysis of robustness of stability and dynamic performance of propulsion control systems and investigates the system’s ability to meet aggregate performance measures, specifically in the presence of fleet-wide component “variability.” The paper first discusses the motivation for the solution by identifying the variability problem in control system design. Following this, an overview of the proposed solution is presented with highlights of key elements, including a discussion on nonlinearity assessment techniques. The paper next describes the prototype version of the software tool and its initial analytical capabilities. Results of the prototype as applied against a nonlinear, engine control model using two different optimization routines, Genetic Algorithms and Particle Swarm Optimization, are presented to demonstrate the promising performance of both algorithms for finding the worst variability due to operating condition flight dynamics and aerothermal component degradation.
Real-Time Prediction of Incipient Lean Blowout in a Partially Premixed, Liquid-Fueled Gas Turbine Combustor
Authors: Yi Tongxun , Gutmark Ephraim J.
Published: March 2009

The present paper addresses real-time prediction of incipient lean blowout (LBO) in partially premixed, liquid-fueled gas turbine combustors. Near-LBO combustion is characterized by the “intensified” low-frequency combustion oscillations, typically below 30 Hz. Two indices, namely the normalized chemiluminescence RMS and the normalized cumulative duration of LBO precursor events, are recommended for LBO prediction. Both indices are associated with the statistical characteristics of the flame structure, which changes from the normal distribution to the Rayleigh distribution at the approach of LBO. Both indices change little within a large range of equivalence ratios and start to shoot up only when LBO is approached. To use the two indices for LBO prediction, one needs to perform a detailed a priori LBO mapping under simulated engine operating conditions. However, the mapping can be done without running the engines very close to LBO.
The Effects of Fuel Dilution With Steam on Gas Turbine Combustor Performance
Authors: Lei Yu , Cui Yufeng , Xu Gang , Nie Chaoqun , Huang Weiguang
Published: March 2009

The formation of nitrogen oxides (NOx) in combustion systems is a significant pollutant source in the environment, and How to control NOx emission is a worldwide concern as the utilization of fossil fuels continues to increase. Syngas is produced from variety of fossil fuels through a gasification process. Though syngas is regarded as one kind of clean fuel, its NOx emission control techniques in combustion systems still remain many problems for further development. Steam dilution of fuel is an effective method for NOx reduction in practical gas turbine systems. This paper describes the study focusing on the influence about steam dilution of fuel for reducing the NOx emission. Experimental investigations are conducted on a 40MW gas turbine fired with syngas. The pollutant emissions, combustor dynamic pressure, metal temperature distribution of liner and combustion efficiency are analyzed at the base load of gas turbine with different steam injection rate to fuel flow. Three-dimensional CFD numerical simulation of combustor according to experiment parameters is applied to investigate the influence of steam dilution on NOx emission and the combustion liner wall temperature. Comparisons are made between experiment data and CFD simulation results for further understandings about NOx formation characteristics in steam diluted syngas and its influence to gas turbine combustion system. The investigation of this paper’s work shows tha steam dilution is an effective method of NOx emission control technique in practical gas turbine combustion systems fired with syngas. The CFD simulation results show that steam in flame can remarkably reduce temperature of the flame for its high thermal capacity and it can remarkably reduce formation of NOx in gas turbine combustor. Moreover, as the steam flowrate added to fuel increase the wall temperature of some zone of liner may increase because of the convection heat transfer is strengthened and the combustion oscillation will be weaken.
A Novel Concept for Combined Heat and Cooling in Humid Gas Turbine Cycles
Authors: Corradetti Alessandro , Desideri Umberto , Rao Ashok D.
Published: March 2009

Various gas turbine cycles are known where water is introduced as a liquid or as a vapor into the combustor of the gas turbine. Such cycles include the Humid Air Turbine (HAT) cycle, the Steam Injected (STIG) cycle, and the Regenerated Water Injected gas turbine cycle (RWI). The effect of water vapor is the increasing of net power output and the reduction of NOx formation within the combustor. However the net increase in power output is limited in commercial models of gas turbines, because a large addition of water vapor leads to the mismatch between the compressor and the turbine. In this paper a possible method to solve this problem is proposed: it is based on a novel concept for combining refrigeration and power production in humid gas turbine cycles. In the proposed system a fraction of the air at compressor discharge is extracted, cooled to nearly ambient temperature, dried and expanded in a turbine. At turbine outlet the air is at a very low temperature and can be used for providing refrigeration. A thermodynamic analysis has been carried out to investigate the performance of the system in HAT, STIG and RWI cycles for different operating conditions representing the state of art of commercial gas turbines. In particular the pressure ratio and the turbine inlet temperature have been respectively varied in the range 7–45 and 900–1500°C. Sensitivity analyses have been performed to assess how the amounts of extracted air and injected steam affect the net power output, the electrical efficiency and the cooling. The results show that cryogenic temperatures (lower than −100°C) for refrigeration can be achieved in combination with very high electrical efficiency (over 40%, typical of humid gas turbine cycles).
Techno-Economic Analysis and Comparative Evaluation of the Use of Gas Turbines and Reciprocating Engines in Small Scale Applications of Industrial Cogeneration
Authors: Arcioni Livia , Corradetti Alessandro , Desideri Umberto , Proietti Stefania , Pogliano Paolo , Caspani Giuseppe
Published: March 2009

This paper presents the results of a research made by University of Perugia in collaboration with Energia Spa (now Sorgenia Spa). Various analysis have been carried out to determine the techno-economic feasibility of industrial CHP plants. Due to the particular field of application, the installation of a gas turbine has been considered and compared to the traditional internal combustion engine (ICE), both being characterized by an electrical power lower than 2 MW. The feasibility study has been made in two different way: an analytical study and a simplified approach elaborated to have a first approach formula for the installation of CHP Plant. The results confirmed that IC is more convenient, giving lower payback period for the investment for this typology of installation. We present also the sensitivity analysis to determine the minimum value over that the installation of gas turbine can become convenient.
Model Validation for a Shrouded Rotor-Stator System With Superposed Cooling and Static Protuberances
Authors: Pett Alexander D. W. , Coren Daniel D. , Childs Peter R. N.
Published: March 2009

This paper analyses numerical and experimental data gathered from a shrouded rotor-stator wheelspace supplied with a radial outflow of cooling air introduced along its central axis. Computational Fluid Dynamics (CFD) investigations into plain disc, roughened disc, roughened stator and stator protrusions were carried out and the results compared to previously gathered experimental data in order to validate the CFD code and improve confidence in its ability to model the given situations. Comparisons of cooling air flow enthalpy rises, torques required to drive the disc and one-sided moment coefficients for the disc have been made between the experimental and the computational models and agreement was obtained across the range of nondimensional numbers analysed. For the plain disc analyses this agreement was within 2% to 15% and was from 6% to 20% for the static protrusions on the stator. Results for the roughness on the rotor models corresponded closely with the experimental findings of previous authors. It was also confirmed that increasing roughness on the rotor increased moment coefficient and that increasing roughness from hydrodynamically smooth up to a roughness ratio of 1125 (corresponding to a roughness height of 0.2 mm) caused a doubling of torque at all rotational and throughflow Reynolds numbers. The same magnitude of roughness on stator was also found to double the torque experienced by the stationary casing but this only corresponded to a 5% increase in disc moment coefficient.
Preliminary Analysis of a New Methodology for Flameless Combustion in Gas Turbine Combustors
Authors: Levy Yeshayahou , Rao G. Arvind , Sherbaum Valery
Published: March 2009

Flameless combustion is one of the most promising technologies that can meet the stringent demands of reduced pollution and increased reliability in future gas turbine engines. Although this new combustion technology has been successfully applied to industrial furnaces, there are inherent problems that prevent application of this promising technology in a gas turbine combustor. One of the main problems is the need for recirculating large amount of burnt gases with low oxygen content, within limited volume, and over a wide range of operating conditions. In the present paper, thermodynamic analysis of a novel combustion methodology operating in the flameless combustion regime for a gas turbine combustor is carried out from the first principles, with an objective to reduce oxygen concentration and temperature in the primary combustion zone. The present analysis shows that unlike in the conventional gas turbine combustor, transferring heat from primary combustion zone to secondary (annulus) cooling air can substantially reduce oxygen concentration in reactants and the combustion temperature, thus reducing NOx formation by a large margin. In addition, to reduce the peak temperature, the proposed methodology is conceptualised / designed such that energy from fuel is released in two steps, hence reducing the peak flame temperature substantially. The new proposed methodology with internal conjugate heat transfer is compared vis-a`-vis to other existing schemes and the benefits are brought out explicitly. It is found that transferring heat from the combustion zone reduces oxygen concentration and increases carbon-dioxide concentration in the combustor, thus creating an environment conducive for flameless combustion. In addition, a schematic of a practical engineering design working on the new proposed methodology is presented. This new methodology, which calls for transfer of heat from the primary combustion zone to alternative air streams, is expected to change the way gas turbine combustors will be designed in the future.
Expert Decision Support System for Costing of Aircraft Gas Turbine Engine
Authors: Tammineni S. V. , Scanlan J. P. , Reed P. A. S.
Published: March 2009

This paper presents the role of performance parameters for an aircraft gas turbine engine in influencing the configuration of systems/sub-systems and related costs at the preliminary design phase. An expert decision support system is provided that employs a hybrid decision tree inference mechanism to provide cost estimates for configurations of a system/sub-system based on the specifications of the performance parameters by the user. The inference mechanism provides a way of dealing with certain and uncertain knowledge extracted from experts for decision making. This assists the designer in the preliminary phase of design in evaluating decisions on the specification of performance parameters by considering their cost influence. The designer can optimize the system/sub-system configuration and performance parameters based on cost. A case study demonstrating the research applied to an exemplar turbojet engine compressor sub-system is presented.
Dynamics of Pulsed Jet in Crossflow
Authors: Arienti M. , Soteriou M. C.
Published: March 2009

We examine the effect of time-dependent forcing on jet-in-crossflow atomization in the case of pulsed liquid injection and uniform crossflow. The dynamics of the jet is captured by a numerical approach that blends interface tracking of the liquid surface with an empirical description of the atomization process. The unsteady Reynolds-Averaged Navier-Stokes equations for the gas and the continuous (i.e., preceding breakup) liquid phase are solved simultaneously with the Lagrangian equations for the droplet trajectories. This approach captures the near field transient due to the opening (closing) of the fuel valve, as well as the convective delay of the spray in the far field. Validation is carried out with Phase Doppler Interferometry (PDI) and Mie scattering measurements at standard conditions for pulsed jets of water and ethanol in crossflow air. The discussion is focused on the shape of the convecting spray pulse and on the trends due to variations in crossflow and jet velocities.
Endwall Boundary Layer Development in an Engine Representative Four-Stage Low Pressure Turbine Rig
Authors: Vera Maria , de la Rosa Blanco Elena , Hodson Howard , Vazquez Raul
Published: March 2009

In a linear cascade of low pressure turbine, LPT, blades, the position and strength of the vortices forming the endwall flows depends on the state of the inlet endwall boundary layer, i.e., whether it is laminar or turbulent. The latter will determine, amongst other effects, the location where the inlet boundary layer rolls up into a passage vortex, the amount of fluid that gets swept up by the passage vortex and the interaction with the pressure side separation bubble, de la Rosa Blanco et al. [1]. As a consequence, the mass-averaged stagnation pressure loss and therefore the design of a low-pressure turbine are influenced by the state of the inlet endwall boundary layer. The paragraph above highlights the importance of determining the state of the boundary layer along the endwalls if an understanding of the endwall flows in a LPT at realistic engine conditions is sought. The results presented in this paper are taken from hot film measurements performed on the endwalls of selected nozzle guide vanes from the fourth stage of the Affordable Near Term Low Emission, ANTLE, LPT rig. These results are compared with those from a low speed linear cascade of similar LPT blades. In the cold flow four-stage LPT rig, a transitional boundary layer has been found on the platforms upstream of the leading edge of the blades. The boundary layer is more turbulent nearer the leading edge of the blade and for higher Reynolds numbers. As for the passage, for both the cold flow four-stage rig and the low speed linear cascade, the new inlet boundary layer formed behind the pressure leg of the horseshoe vortex is a transitional boundary layer. The transition process progresses from the pressure to the suction surface of the passage in the direction of the secondary flow.
Comparison of a Few Fault Diagnosis Methods on Sparse Variable Length Time Series Sequences
Authors: Sambasivan Lokesh Kumar , Kini Venkataramana Bantwal , Ryali Srikanth , Mukherjee Joydeb , Mylaraswamy Dinkar
Published: March 2009

Accurate gas turbine engine Fault Detection and Diagnosis (FDD) is essential to improving aircraft safety as well as in reducing airline costs associated with delays and cancellations. This paper compares broadly three methods of fault detection and diagnosis (FDD) dealing with variable length time sequences. Chosen methods are based on Dynamic Time Warping (DTW), k-Nearest Neighbor method, Hidden Markov Model (HMM) and a Support Vector Machine (SVM) which makes use of DTW ingeniously as its kernel. The time sequences are obtained from Turbo Propulsion Engines in their nominal conditions and two faulty conditions. Typically there is paucity of faulty exemplars and the challenge is to come up with algorithms which work reasonably well under such circumstances. Also, normalization of data plays a significant role in determining the performance of the classifiers used for FDD in terms of their detection rate and false positives. In particular spherical normalization has been explored considering the advantage of its superior normalization properties. Given sparse training data how well each of these algorithms performs is shown by means of tests performed on time series data collected at normal and faulty modes from a turbofan gas turbine propulsion engine and the results are presented.
Design of an Air-Launched Tactical Missile for Three Different Propulsion Systems: ATR, Rocket and Turbojet
Authors: Edefur Henrik , Haglind Fredrik , Olsson Stefan
Published: March 2009

The objective of this paper is to assess the feasibility of a solid propellant Air Turbo Rocket (ATR), in comparison with a conventional turbojet engine or a solid rocket motor, as power source for a medium range tactical air-launched missile from an overall system point of view. A sizing method for missiles is developed, which together with flight performance calculations and engine performance data determines the final size and weight of the missile and its engine. The results suggest that an ATR engine is more favourable than a jet engine when the ratio between maximum (manoeuvre) thrust and minimum (cruise) thrust is large; for example for a mission including a cruise segment and a high load factor manoeuvre made at constant speed. For the missile range investigated in this paper no breakpoint in distance has been found beyond which the ATR engine becomes impractical. The rocket motor can produce a huge amount of thrust, thus giving it a very large maximum to minimum thrust ratio. However, it has a disadvantage in its low fuel efficiency and high combustion temperature, making it impracticable for missions requiring any longer duration. Altogether the choice of propulsion system has a large impact on maximum take-off weight, size and performance of the missile.
Vane Endwall Heat Transfer for Smooth and Stepped Inlet Using Streamwise and Cross Stream Film Injection
Authors: Wu Pey-Shey , Chang Shun-Fu
Published: March 2009

Cross film injection is employed in this study to generate a shear-induced secondary flow having the same sense of rotation as that of the passage vortex. Local heat transfer coefficient and film cooling effectiveness on the endwall surface are measured using liquid crystal techniques. The Reynolds number of the main flow based on the vane inlet velocity was fixed at ReC = 1.24×105. The blowing ratio was 0.5, 1.0, or 2.0. The investigated endwall conditions before the vane entrance include a smooth endwall, an endwall with a forward-facing step, and an endwall with a backward-facing step. Cooling performance of the cross injection scheme is compared to that of streamwise, parallel injection, under the same coolant flow rate, endwall entrance condition, and the blowing ratio. The heat transfer results show that both cooling scheme have similar magnitude of overall heat transfer coefficient. In the film cooling results, cross injection shows a better attachment along the endwall. Also, the protected region is shifted towards the suction wall which may also help the cooling of the suction wall near the trailing edge. The cross injection is more advantageous than the streamwise parallel injection, regardless of the blowing ratio and the endwall conditions.
Constitutive Behaviour of IN738LC Under TMF Cycling With and Without Intermediate Ageing
Authors: Hasselqvist Magnus , Moverare Johan
Published: March 2009

Out of Phase Thermo Mechanical Fatigue (OP TMF) 100–950°C tests with 5 min hold time, some including intermediate ageing for 4000h at 950°C after 25 cycles, have been performed on IN738LC at Siemens Industrial Turbomachinery (SIT) AB. In the standard tests, the variation in stress range during the tests was neutral. When tests with intermediate ageing were added to the analysis, the combination of test data strongly suggest that the neutral response above was because of a fairly even competition between softening due to degradation (particle coarsening etc.) and work hardening. We have concluded that the work hardening occuring for a lab hold time of 5 min. will be insignificant under more realistic, i.e. component-near, hold times. Based on this, we have devised a method for reduction of lab TMF test results, with their too short hold times, to handle actual, i.e. significantly longer, component hold times.
Real Time Health Estimation and Automated Fault Accommodation for Propulsion Systems
Authors: Tang Liang , Roemer Michael J. , Kacprzynski Gregory J.
Published: March 2009

This paper presents the development of innovative realtime health estimation and automated fault accommodation techniques for advanced propulsion systems within a Dynamic Decision Support (D2S) framework. The proposed approach uses dynamic models in a real-time computing environment to not only diagnose system degradation and faults, but also to determine “on the fly” how to accommodate for them. The realtime health estimation modules enhance on-board PHM (Prognosis & Health Management) capabilities with a dynamic system identification algorithm that is capable of detecting faults with a continuously updated dynamic model. In addition, a real-time, self-tuning Kalman filter and fault classification algorithm are combined to provide accurate health estimation. Based on the inferred health condition, mission requirements and flight regime information, the automated fault accommodation module automatically makes decisions regarding control reconfiguration and change of control strategies. The presented techniques have been applied to a generic turbofan engine model with simulated engine component faults and degradation and simulation results are presented. To further raise the technological readiness level, select algorithms have been implemented and evaluated on a PC104 embedded platform. The dynamic modeling capabilities, techniques and tools sets will not only improve the reliability of the propulsion systems, but also greatly enhance maintenance decision support and contingency planning concepts.
Compressor/Diffuser/Combustor Aerodynamic Interactions in Lean Module Combustors
Authors: Walker A. Duncan , Carrotte Jon F. , McGuirk James J.
Published: March 2009

The paper reports an experimental investigation into the possibility of increased interactions between combustor external aerodynamics and upstream components e.g. pre-diffuser, compressor OGV and even the compressor rotor, caused by the trend in lean module fuel injectors to larger mass flows entering the combustor cowl. To explore these component interaction effects, measurements were made on a fully annular rig comprising a single stage compressor, an advanced integrated OGV/pre-diffuser, followed by a dump diffuser and a generic combustor flametube with metered cowl and inner/outer annulus flows. The flow split entering the cowl was increased from 30% to 70%. The results demonstrate that, with fixed geometry, as the injector flow increases, the performance of the pre-diffuser and feed annuli suffer. Pre-diffuser losses increase and at high injector flow rates the diffuser moves close to separation. The substantial circumferential variation in cowl flow can feed upstream and cause rotor forcing. Notable differences in performance were observed inline and between injectors at OGV exit, suggesting that geometry changes such as an increased dump gap or non axisymmetric pre-diffuser designs may be beneficial.
Investigation of Soot Formation and Oxidation in a High-Pressure Gas Turbine Model Combustor by Laser Techniques
Authors: Lammel Oliver , Geigle Klaus Peter , Lu¨ckerath Rainer , Meier Wolfgang , Aigner Manfred
Published: March 2009

Swirl-stabilized, non-premixed C2H4/air flames were investigated at pressures up to 9 bar in order to contribute to a better understanding of soot formation and oxidation under gas turbine like conditions. The flames had a thermal power of up to 45 kW and were confined by a squared combustion chamber with quartz windows. Secondary air could be injected into the post-flame zone to study the influence of cooling air on the oxidation of soot. The good optical access to the flame enabled the application of optical and laser measuring techniques. Temperatures were measured by coherent anti-Stokes Raman scattering (CARS) and soot concentrations by 2D laser induced incandescence (LII). The influence of the flow field characteristics, known from previous measurements in similar configurations, on the soot distributions is discussed. Furthermore, the effects of pressure, equivalence ratio and secondary oxidation air on the instantaneous and mean soot distributions were studied. All measurements were performed under well-defined and documented conditions, so that the data sets are suitable for the validation of numerical simulations.
Comparison of Flow Characteristics in Axial-Gap Seals for Close- and Wide-Spaced Turbine Stages
Authors: Wang Cheng-Zhang , Johnson Bruce V. , De Jong Frederick , Vashist T. K. , Dutta Rajib
Published: March 2009

3D unsteady computational fluid dynamics analyses were performed for both close-spaced and wide-spaced turbine stages with axial gap seals and a cavity. Turbine stages, with airfoil configurations similar to those previously studied at United Technologies Research Center (UTRC) and Arizona State University (ASU), were simulated for vane-blade spacing at 34 percent and 70 percent of the vane axial chord length, L. Three configurations were investigated, with the first one placing an axial gap rim seal at 17 percent L upstream of the blade for close-spaced stage, and the other two placing the axial gap seal at either 17 or 34 percent L upstream of the blade for the wide-spaced stage. The seal velocity ingestion characteristics were strongly dependent on axial location for the wide-spaced stage. The seals placed at equal distances upstream of the blade leading edge for the wide- and close-spaced stages had approximately the same average ingestion velocity characteristics. However, the ingestion velocity profiles for the wide-spaced stage were less influenced by vane wakes than for the close-spaced stage. The calculated variation of radial velocity in all gaps was consistent with previous tangential and radial velocity measurements in the seal gap measurements at the University of Aachen.
Measurements in Film Cooling Flows With Periodic Wakes
Authors: Womack Kristofer M. , Volino Ralph J. , Schultz Michael P.
Published: March 2009

Film cooling flows subject to periodic wakes were studied experimentally. The wakes were generated with a spoked wheel upstream of a flat plate. Cases with a single row of cylindrical film cooling holes inclined at 35 degrees to the surface were considered at blowing ratios of 0.25, 0.50, and 1.0 with a steady freestream and with wake Strouhal numbers of 0.15, 0.30, and 0.60. Temperature measurements were made using an infrared camera, thermocouples, and constant current (cold wire) anemometry. Hot wire anemometry was used for velocity measurements. The local film cooling effectiveness and heat transfer coefficient were determined from the measured temperatures. Phase locked flow temperature fields were determined from cold wire surveys. Wakes decreased the film cooling effectiveness for blowing ratios of 0.25 and 0.50 when compared to steady freestream cases. In contrast, effectiveness increased with Strouhal number for the 1.0 blowing ratio cases, as the wakes helped mitigate the effects of jet liftoff. Heat transfer coefficients increased with wake passing frequency, with nearly the same percentage increase in cases with and without film cooling. The time resolved flow measurements show the interaction of the wakes with the film cooling jets. Near-wall flow measurements are used to infer the instantaneous film cooling effectiveness as it changes during the wake passing cycle.
Whole Turbine CFD Modelling
Authors: Hills N. J.
Published: March 2009

The level of efficiency of modern turbines means that traditional blade design methods, based on steady state CFD in an idealised annulus, are no longer able to yield the efficiency improvements needed to develop a competitive turbine. Future design improvements will come from understanding and control of the parasitic effects of real geometry, such as cavities, gaps and leakages; and the unsteady interactions between neighbouring components. This paper describes ongoing work to carry out a simulation of a full turbine including both the main annulus and the secondary air system geometry to investigate these effects. A multistage steady-state mixing plane model of an idealised whole turbine was run to provide a baseline solution. Interaction effects between the components were considered by running unsteady models. Firstly the HP stage was modelled as unsteady, with the IP and LP stages continuing to be included as a steady state mixing plane model, but still using the idealised annulus geometry. The idealised geometry for the HP stage was then replaced by the real engine geometry, including the under platform cavity, with similar unsteady calculations being carried out. The feasibility of carrying out these large scale unsteady calculations of a whole turbine with real engine geometry has been demonstrated.
Thermal Aging Failure Analysis of a EBC/CMC Combustor Outer Liner
Authors: Bhattacharya Arun K. , Abdi Frank , Su Xiaofeng
Published: March 2009

Ceramic Matrix Composite (CMC) combustor liners allow higher temperature operation with an industrial gas turbine engine, thereby, increasing its efficiency. They also improve its environmental performance by lowering emissions. Application of an EBC (Environmental Barrier Coating) on the combustor liner hot surface significantly reduces the environmental degradation of these CMC liners and it also improves the thermal gradient through the liner wall. This study focused on the effect of the EBC on the thermal aging life of a SiC/SiC CMC combustor outer liner using a progressive failure numerical procedure. The simulation results are compared with Solar Turbines’ field test observation. Both test and simulation show the liner survived the long-term thermal aging process. There is no obvious damage occurring in the liner during the 13,000 test aging hours. These data are useful for optimizing design of the EBC/CMC liner.
Mechanisms of the Nonlinear Response of a Swirl Flame to Harmonic Excitation
Authors: Thumuluru Sai Kumar , Bobba Mohan K. , Lieuwen Tim
Published: March 2009

This paper describes an experimental investigation of the amplitude dependent processes controlling the response of a swirling flame to harmonic excitation. Simultaneous measurements of the acoustic pressure, velocity, and CH* and OH* radical chemiluminescence were obtained over a range of forcing frequencies, amplitudes, and nozzle exit velocities. These were supplemented with OH planar laser induced fluorescence (PLIF) measurements at several representative conditions. The results presented show that there exist substantial nonlinearities in the flame response to forced oscillations. Furthermore, while the flame response monotonically and linearly increases with perturbation amplitude for low forcing levels, its behavior becomes much more complex at higher levels — this includes saturation as well as more complex, non-monotonic behaviors. Analysis of the OH PLIF images show that the observed dynamics result from a superposition of at least five flame/flow processes — (1) the oscillating velocity of the annular jet, oscillations in (2) position and (3) strength of the vortex breakdown bubble and separation bubble, (4) unsteady liftoff of the flame, and (5) an oscillating turbulent flame speed. These processes generally occur simultaneously, with non-monotonic dependencies upon forcing amplitude. This sheds some light on the complex overall flame heat release response measurements and suggests a fruitful area for detailed computational studies that can better elucidate the underlying physics controlling the phenomenon.
Generation Schedule Optimisation for Gas Turbine Power Systems
Authors: Gomes E. E. B. , Pilidis P. , Polizakis A. L.
Published: March 2009

In the last decades, the approach to dispatch and manage electricity in power generation plants has been one of the most difficult problems in the electricity market. Despite of all the benefits of distributed poly-generation and combined heat and power systems, their penetration in the power market worldwide is quite modest and one of the barriers against their increasing participation is the high fees for back-up supplies, which is one of the problems addressed in this investigation. This paper introduces a hybrid dynamic programming adapted priority list technique to solve the multi unit generation schedule optimization problem of a pool of independent gas turbines based power generation units. The combination of the traditional Dynamic Programming algorithm and the proposed heuristic Adapted Priority List technique allowed a significant reduction on the complexity of the original problem without rejecting the optimal solution. Despite of the power generation optimization studies available in the technical literature, none of them have been modeled for such pool of independent power generators trading electricity in the competitive market. This approach shows that the proposed concept can result in a significant saving to generators/end-users trading electricity in a competitive market.
Safety Loops Identification and Targeting Method Compliant With IEC61511 Requirements
Authors: Cozzarin Philippe , Brooks Robert , Dalton Bret , Kaufman Eric , Leary Kenneth
Published: March 2009

Safety Instrumented Systems are used in gas turbine (GT) systems design to mitigate potential hazardous situations that can arise from process deviations. International standard IEC61511, (released in 2003) sets out an approach for establishing the relative safety integrity of a safety-instrumented system to perform its prescribed action over the product life cycle (design, installation, and operation of safety instrumented systems). This unified approach is currently being adopted as an industry standard (e.g. UK HSE Guidance Note PM84 and ISO DIS 21789 dedicated to Gas Turbine Safety). Using this approach, each Safety Instrumented Function (SIF) must be evaluated to determine the level of risk reduction required for safe operation of the plant. Properly targeting the necessary level of risk reduction is critical. Underestimating the target risk reduction level can result in exceeding the plant tolerable risk threshold. Over-estimating the target risk reduction level can result in increased life cycle cost of the system design. This paper describes a scientific-numeric approach for targeting the safety integrity requirements that comply with IEC 61511. An Accident Scenario Review (ASR) for each major hazard identified is used to identify the SIF and associated maximum probability of failure on demand (for demand mode) or maximum probability of dangerous failure per hour (for continuous mode). This method can be used for systems previously designed or in operation. The process integrates field experience to validate and justify model assumptions.
A Data Fusion Approach for Aircraft Engine Fault Diagnostics
Authors: Hu Xiao , Eklund Neil , Goebel Kai
Published: March 2009

Accurate and timely detection and identification of aircraft engine faults is critical to keeping the engine and aircraft in a healthy operating state. Early detection of faults increases the window of opportunity to schedule maintenance actions both at a convenient time and before the fault progresses and causes equipment downtime and secondary damage to the system. Typically, diagnostic models are built using parametric sensor data to infer the state of the system. However, recording and collecting this data is costly, and it is generally limited to a few snapshots over the course of a flight for commercial aircraft. Another way to recognize faults is through the use of built-in tests that produce error log messages. These tests produce data that is less information rich, but provide insight over the course of the entire flight. Each data source provides a different perspective of the state of the system. Therefore, it may be advantageous to combine information from parametric and nonparametric sources to improve fault diagnosis in terms of accuracy and timeliness of diagnosis. In this paper, we investigate integrating parametric sensor data and nonparametric information in fault diagnosis, specifically the way to parameterize nonparametric information for use in diagnostic models that accept only parametric data (e.g., most machine learning techniques). Results from high bypass commercial engines are presented.
A Framework of Prognosis and Health Management: A Multidisciplinary Approach
Authors: Bird Jeff , Wu Xijia , Patnaik Prakash , Dadouche Azzedine , Le´tourneau Sylvain , Mrad Nezih
Published: March 2009

A multi-disciplinary team covering mechanical, materials and information technologies are investigating and developing appropriate technologies for aircraft prognostics and health management (PHM) applications. To integrate the efforts, a framework for PHM has been developed with three major functional blocks: Life Prediction, State Awareness, and Information Management. This framework provides a hierarchy for development and implementation. Achievements and future plans within this framework are presented with specific applications to military legacy systems and future acquisitions. Opportunities are described within some new initiatives for development and implementation.
Part Data Mining for Information Re-Use in a PLM Context
Authors: Msaaf Omar , Maranzana Roland , Rivest Louis
Published: March 2009

Difficulty in locating existing information in order to reuse it constitutes a major challenge to productivity. The use of PLM systems (Product Lifecycle Management) aims in particular to reduce the time and cost of developing a product by facilitating the re-use of existing parts or related information (process plans, tools, FEM, estimates, etc.). When information is alphanumerical, using search engines, such as those made popular on the internet, is efficient. However, a significant portion of information used in engineering rests within CAD (Computer Aided Design) models, making such search tools irrelevant. To aid in the re-use of information, two problems must be resolved: it is first necessary to be able to locate similar parts in the electronic database of the company, and then be able to systematically identify their differences. This article presents some of the results from our work on part, product and process data mining (P3DM). It focuses on tools developed to search similar 3D geometric models and to identify their differences. The PartFinder application locates similar parts by comparing signatures extracted from their solid representations. The 3DComparator aims to identify the differences in terms of Form and Fit between the identified parts. In both cases, the recommended approach is independent of the CAD system, and can also deal with parts represented by IGES or STEP files. Moreover, the approach does not require that the parts occupy the same position and have the same orientation in space. These two points, CAD and position independence, are the main benefits of our approach compared to other existing applications. Lastly, if the comparison takes place between two evolutions of the same geometrical representation of a part, a third tool allows the comparison of the specification trees. The SpecComparator is also presented briefly. An example based on industrial data illustrates the benefit that could be generated.