bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Ruthenium, Rhenium and Yttria Additions on the Microstructure of Wide Gap Brazing of IN738
Authors: Huang Xiao , Yandt Scott , Nagy Doug , Yao Matthew
Published: March 2009

Modern gas and steam turbine components are subject to severe thermomechanical loads and extremely high temperature in order to provide increased performance and efficiency. Most high temperature turbine components are made of superalloys specifically developed for high temperature and high mechanical stress applications but at considerable cost. Defects may occur during manufacturing of superalloy castings as well as after service. Repair of these components, rather than replacement, helps to reduce the life cycle cost. Wide gap brazing is a cost effective and reliable means to repair gas turbine hot section components with defect sizes exceeding 0.3 mm. With proper control of the braze alloy and brazing cycle, the repaired region has been reported to posses mechanical properties approaching that of the parent materials. In order to further improve the mechanical properties of the repaired region and to explore the possibility of employing the wide gap brazing method to repair single crystal components in the future, three alloying additions, Ruthenium (Ru), Rhenium (Re) and yttria (Y2O3), were incorporated into the braze filler metal by mechanical alloying. The microstructures of the wide gap brazed joints with Ru, Re and yttria additions were studied and compared to a braze joint with standard wide gap braze alloys of IN738 and AWS BNi-9. It has been found that two types of borides formed in all braze alloys, namely eutectic γ-Ni-rich and boride phases and discrete boride containing primarily Cr and W (or Ru). The addition of Ru to the filler metal did not seem to modify the microstructural constituents after brazing. However, Ru partitioned strongly to the discrete borides. No isolated elemental Ru region was observed. On the other hand, Re addition was found to change the occurrence and distribution of both types of borides. The eutectic boride constituent was significantly reduced and finer discrete boride particles were observed. The addition of yttria did not change the boride formation but led to the generation of more voids in the brazed joint.
Effects of Deposits on Film Cooling of a Vane Endwall Along the Pressure Side
Authors: Sundaram N. , Barringer M. D. , Thole K. A.
Published: March 2009

Film-cooling is influenced by surface roughness and depositions that occur from contaminants present in the hot gas path, whether that film-cooling occurs on the vane itself or on the endwalls associated with the vanes. Secondary flows in the endwall region also affect the film-cooling performance along the endwall. An experimental investigation was conducted to study the effect of surface deposition on film-cooling along the pressure side of a first-stage turbine vane endwall. A large-scale wind tunnel with a turbine vane cascade was used to perform the experiments. The vane endwall was cooled by an array of film-cooling holes along the pressure side of the airfoil. Deposits having a semi-elliptical shape were placed along the pressure side to simulate individual row and multiple row depositions. Results indicated that the deposits lowered the average adiabatic effectiveness levels downstream of the film-cooling rows by deflecting the coolant jets towards the vane endwall junction on the pressure side. Results also indicated that there was a steady decrease in adiabatic effectiveness with a sequential increase in the number of rows with the deposits.
Aerodynamic Performance Measurement in a Fully Scaled Transient Turbine Test Facility
Authors: Atkins N. R. , Ainsworth R. W. , Harvey N. W.
Published: March 2009

The practical performance, both the efficiency and durability, of a High-Pressure (HP) turbine depends on many interrelated factors, including both the steady and unsteady aerodynamics and the heat transfer characteristics. The aerodynamic performance of new turbine designs has traditionally been tested in large scale steady flow rigs, but the testing is adiabatic, and the measurement of heat transfer is very difficult. This paper presents the results of turbine aerodynamic performance measurements at the Oxford Rotor Facility (ORF). Transient test facilities such as the Oxford Rotor allow the simultaneous study of turbine performance and heat transfer. The transient operation gives engine representative Mach number, Reynolds number and gas-to-wall temperature ratios, which are key to the aerothermodynamics of a highly-loaded, transonic, HP turbine stage. Time resolved experimental results are presented together with numerical CFD predictions over a 3% range of non-dimensional speed. The precision uncertainty of the measurements has been resolved to a level comparable with the state of the art in steady flow testing, in the region of ±0.3%.
Fuel Flexibility Test Campaign on a 10 MW Class Gas Turbine Equipped With a Dry-Low-NOx Combustion System
Authors: Cocchi Stefano , Provenzale Michele , Ceccherini Gianni
Published: March 2009

An experimental test campaign, aimed to provide a preliminary assessment of the fuel flexibility of small power gas turbines equipped with Dry Low NOx (DLN) combustion systems, has been carried over a full-scale GE10 prototypical unit, located at the Nuovo-Pignone manufacturing site, in Florence. Such activity is a follow-up of a previous experimental campaign, performed on the same engine, but equipped with a diffusive combustion system. The engine is a single shaft, simple cycle gas turbine designed for power generation applications, rated for 11 MW electrical power and equipped with a DLN silos type combustor. One of the peculiar features of such combustion system is the presence of a device for primary combustion air staging, in order to control flame temperature. A variable composition gaseous fuel mixture has been obtained by mixing natural gas with CO2 up to about 30% vol. inerts concentration. Tests have been carried over without any modification of the default hardware configuration. Tests performed aimed to investigate both ignition limits and combustors’ performances, focusing on hot parts’ temperatures, pollutant emissions and combustion driven pressure oscillations. Results indicate that ignition is possible up to 20% vol. inerts concentration in the fuel, keeping the fuel flow during ignition at moderately low levels. Beyond 20% vol. inerts, ignition is still possible increasing fuel flow and adjusting primary air staging, but more tests are necessary to increase confidence in defining optimal and critical values. Speed ramps and load operation have been successfully tested up to 30% vol. inerts concentration. As far as speed ramps, the only issue evidenced has been risk of flameout, successfully abated by rescheduling combustion air staging. As far as load operation, the combustion system has proven to be almost insensitive to any inerts concentration tested (up to 30% vol.): the only parameter significantly affected by variation in CO2 concentration has been NOx emission. As a complementary activity, a simplified zero-dimensional model for predicting NOx emission has been developed, accounting for fuel dilution with CO2. The model is based on main turbine cycle and DLN combustion system controlling parameters (i.e., compressor pressure ratio, firing temperature, pilot fuel and primary air staging), and has been tuned achieving good agreement with data collected during the test campaign.
An Experimental Study of Combustor Exit Profile Shapes on Endwall Heat Transfer in High Pressure Turbine Vanes
Authors: Barringer M. D. , Polanka M. D. , Thole K. A.
Published: March 2009

The design and development of current and future gas turbine engines for aircraft propulsion have focused on operating the high pressure turbine at increasingly elevated temperatures and pressures. The drive towards thermal operating conditions near theoretical stoichiometric limits as well as increasingly stringent requirements on reducing harmful emissions, both equate to the temperature profiles exiting combustors and entering turbines becoming less peaked than in the past. This drive has placed emphasis on determining how different types of inlet temperature and pressure profiles affect the first stage airfoil endwalls. The goal of the current study was to investigate how different radial profiles of temperature and pressure affect the heat transfer along the vane endwall in a high pressure turbine. Testing was performed in the Turbine Research Facility located at the Air Force Research Laboratory using an inlet profile generator. Results indicate that the convection heat transfer coefficients are influenced by both the inlet pressure profile shape and the location along the endwall. The heat transfer driving temperature for inlet profiles that are non-uniform in temperature is also discussed.
Application of Whole Engine Finite Element Models in Aero-Engine Rotordynamic Simulation Analysis
Authors: Hong Jie , Chen Meng , Liu Shuguo
Published: March 2009

The thrust-to-weight ratio of aero-engine is increasing, the structure stiffness is reducing along with its weight, the mechanical exciting force and aerodynamic force become more and more intricate, for these reasons, dynamic interaction of different structures have to be taken into account in aero-engine vibration analysis. In traditional methods, as transfer matrix method and finite element method based on beam element, the rotor is reduced as mass point and beams, so the true dynamic interaction between the disk and shaft can’t be calculated. In this paper, MSC/NASTRAN was developed by adding the effect of gyroscopic moment to the 8 nodes solid element CHEXA with DMAP (direct matrix abstraction program) language. A rotordynamic analysis of a whole engine model based on three-dimensional (3-D) solid element was performed using the program. Firstly, an unbalance response calculation of the casing was performed to predict the translation function (dynamic stiffness) at the bearing support, as well as their effects on rotor dynamics. In the analysis of solid element models and beam element models, the effects of the coupled disks and shafts vibration as well as the corner stiffness between shafts and disks on rotor dynamics were compared, the results shown that various vibration modes could be accurately calculated using the model based on solid element. A phenomenon of the coupled rotor bending and casing vibration was captured, it was shown the third rotor critical speed of the coupled rotor bending and casing vibration mode was a frequency range. The method to predict critical speeds and mode shapes of the rotor considering dynamic interaction between the rotor and casing was investigated. Finally, a simulation platform for aero-engine dynamic analysis was set up, on which the whole engine model could be found and thermal load or aero force could be considered for different purposes. It was concluded that the true dynamic interaction between the rotor and casing as well as the disk and shaft could be captured using the whole engine model based on solid element. Further more, the foreground of the thermal and tip clearance analysis of turbine blades based on the whole engine model was discussed.
Information Fusion Strategy for Aircraft Engine Health Management
Authors: Yu LiJie , Cleary Dan , Osborn Mark , Rajiv Vrinda
Published: March 2009

Modern aircraft engines are equipped with sophisticated sensing instruments to enable proactive condition monitoring and effective health management capability. Development of intelligent systems that efficiently process sensor and operational data both onboard and off-board, to provide maintenance personnel with timely decision support, is the key to minimize flight service disruption and reduce engine ownership cost. The goal of this research is to develop a practical approach and strategy to leverage various available information sources and modeling techniques to streamline the engine health management process and maximize system accuracy and efficiency. This paper demonstrates a flexible fusion architecture that encapsulates the key elements of the engine monitoring and diagnostic process, i.e., sensor trend analysis module for anomaly detection, feature selection and fault isolation module for root cause identification, a decision module for diagnostic model fusion and action determination, and finally, a feedback module for knowledge validation and continuous learning. At the core of this engine health management system is a diagnostic fusion model designed around a common fault hierarchy which captures both a priori probabilities and interactions among various engine faults isolated by different classification models. The fusion model will resolve conflicting assessments from individual diagnostic models and provide a more accurate and comprehensive engine state estimate.
Probabilistic Mission Identification of Aircraft Engine Usage Using Nonparametric Density Estimation Techniques
Authors: Enright M. P. , Hudak S. J.
Published: March 2009

Fatigue life prediction of aircraft gas turbine engine rotating components requires estimates of the applied stress values throughout the life of the component. These values may vary considerably from flight-to-flight, and are highly dependent upon the mission type. However, engine flight data recorders currently do not have the capability to identify the mission type, so an automated mission identification method would greatly improve remaining life predictions. In this paper, a method is presented for predicting the most likely mission type for a given flight history. It is based on volume integration of the joint probability densities that are common to both the flight history and a standard mission. An analytical framework is presented, including a brief description of the adaptive kernel method used to estimate the probability densities of the flight history and standard mission. The effectiveness of the method is illustrated using rainflow stress data associated with actual flight histories. The results can be used to improve fatigue and fracture risk predictions of military gas turbine engines.
The Challenges Facing the Utility Gas Turbine
Authors: Kiesow Hans Juergen , McQuiggan Gerard
Published: March 2009

The object of this paper will be to examine the market place and some of the consequential technical challenges facing large frame utility gas turbines (greater than 100MW’s) over the next decade. The significant and rapid increase in the price of oil and gas and restrictions in fuel and electricity supply are posing many obstacles to the successful application of the gas turbine in the electricity supply market in both North America and worldwide. The paper will examine the historical background leading up to these changes and will discuss the predicted future price levels for gas turbine fuels. Alternative fuels will also be discussed. The paper will also discuss the challenges facing the large frame gas turbine with respect to the technical improvements that will be required to lower emissions and capital costs, while improving efficiency and potentially capturing and sequestering carbon dioxide.
Turbulence Modeling for the Numerical Simulation of Film and Effusion Cooling Flows
Authors: Bacci Alessandro , Facchini Bruno
Published: March 2009

RANS simulations are known to suffer from serious deficiencies in the prediction of jet in a crossflow (JCF) because of the high complexity of this kind of flow. Particularly, the coherent structures resulting from the interaction of the two flow streams are characterized by a highly unsteady and anisotropic behavior which hardly stresses the hypotheses underling common eddy viscosity models (EVMs). Direct numerical simulation (DNS) and large eddy simulation (LES) methodologies are still excessively computationally intensive to be used as ordinary design tools. Therefore, the development of reliable RANS turbulence models for film cooling flows deserved a great deal of attention from the gas turbine community. Computations presented in this work were carried out using a modified k-ε turbulence model specifically designed for film cooling flows. The model, due to Lakehal et al., is based on the usage of an anisotropic eddy viscosity. The model has been implemented in the framework of a CFD commercial package through the user subroutine features. Computational model is developed following the suggestions of Walters and Leylek concerning the correct representation of the problem geometry and the location of the boundary conditions. The predictive capabilities of the model concerning the ability to capture the main flow structures as well as heat transfer features are investigated. Comparison of computed adiabatic effectiveness profiles with experimental measurements is provided in order to quantitatively validate the model. Results obtained with standard EVMs, particularly a two layer standard k-ε model, are also shown in order to reveal the improvements in the predictive capabilities resulting from the modified models.
Performance Analysis On Gas Engine – Gas Turbine Combined Cycle Integrated With Regenerative Gas Turbine
Authors: Tsuji Tadashi
Published: March 2009

The gas engine-gas turbine combined cycle was developed as the ETCS (Engine Turbo Compound System) that has a potential to be a future high performance combined cycle. The reciprocating engine operates with a maximum pressure and temperature in the cylinder, higher than that of the conventional gas turbines. When the gas engine is integrated with a gas turbine instead of a turbocharger, the concept of the ETCS with ERGT (Engine Reheat Gas Turbine) is available. In order to attain a better ETCS performance, a natural gas firing RGT (Regenerative Gas Turbine) was selected as the core gas turbine. For the system integration, the recuperator of RGT was exchanged for a gas engine. Focusing on the effect of engine exhaust temperature, we found that the ETCS cycle with ERGT has the potential to achieve a higher thermal efficiency than that of a re-generative cycle gas turbine with no change of TIT (Turbine Inlet Temperature). The engine exhaust temperature of 900°C increases the system power generation efficiency from 39% of RGT to 45% in ERGT (GT-Gas Engine) and up to 59% in ETCS (GT-Gas Engine-Steam Turbine) (TIT 1200°C).
A Complexity-Based Approach to Robust Design and Structural Assessment of Aero Engine Components
Authors: Lomario D. , De Poli G. P. , Fattore L. , Marczyk J.
Published: March 2009

This paper presents a complexity-based methodology for the design of aero engine components. Upon a rigorous definition of complex system, a metric for the complexity is introduced as a function of system’s topology and entropy. As a consequence, complexity becomes a measurable and manageable property of systems. Furthermore, a novel definition of robustness is provided, based on the shape of the probability density functions (PDF) of the performances. Complexity and robustness are related together by a simple, qualitative law. Based on these premises, two algorithms are introduced, namely the Stochastic Design Improvement (SDI) and the Complex Systems Analyzer (CSA). The former searches the design space seeking for solutions which meet the design requirements. The latter extracts the fundamental features of the design, previously perturbed by means of Monte Carlo Simulation (MCS). The SDI is proposed as a competitor of the practice of optimization. Though both can be used separately, the combination of SDI and CSA provides a powerful novel method for design. The capabilities of the algorithms are illustrated on three test-cases, namely an LPT Casing, a Turbo-prop bearing retainer and an LPT disk. It is important to point out that response surfaces or other surrogates have never been used.
Thermoeconomic Optimization of Gas Turbine Combined Heat and Power System in a Paper Mill
Authors: Sanaye Sepehr , Ghazinejad Maziar
Published: March 2009

Located in the South of Iran, Jiroft Paper Mill Company requires an integrated combined heat and power plant, which can provide 50 MW of electric power and 100 ton/hr saturated steam at 13 bars, to produce paper from an adjacent eucalyptus forest. The plant is comprised of a gas turbine, air compressor, combustion chamber, and air preheater as well as a heat recovery steam generator (HRSG). The design Parameters of the plant were chosen as: compressor pressure ratio (rc), compressor isentropic efficiency (ηAC), gas turbine isentropic efficiency (ηT), combustion chamber inlet temperature (T3), and turbine inlet temperature (T4). In order to optimally find the design parameters a thermoeconomic approach has been followed. An objective function representing the total cost of the plant in terms of dollar per second, was defined as the sum of the operating cost related to the fuel consumption, and the capital investment which stands for equipment purchase and maintenance costs and the cost, corresponding to the exergy destruction in various components. Subsequently, different parts of the objective function have been expressed in terms of decision variables. Finally, the optimal values of decision variables were obtained by minimizing the objective function using sequential quadratic programming (SQP). The influence of changes in the demanded power and steam on the design parameters have been also studied for 40, 50, 60, and 70 MW of net power output, and 100, 120, 150, ton/hr of saturated steam mass flow rate.
Some Aspects of CFD Modeling in the Analysis of a Low-Pressure Steam Turbine
Authors: Rubechini Filippo , Marconcini Michele , Arnone Andrea , Cecchi Stefano , Dacca` Federico
Published: March 2009

A three-dimensional, multistage, Navier-Stokes solver is applied to the numerical investigation of a four stage low-pressure steam turbine. The thermodynamic behavior of the wet steam is reproduced by adopting a real-gas model, based on the use of gas property tables. Geometrical features and flow-path details consistent with the actual turbine geometry, such as cavity purge flows, shroud leakage flows and partspan snubbers, are accounted for, and their impact on the turbine performance is discussed. These details are included in the analysis using simple models, which prevent a considerable growth of the computational cost and make the overall procedure attractive as a design tool for industrial purposes. Shroud leakage flows are modeled by means of suitable endwall boundary conditions, based on coupled sources and sinks, while body forces are applied to simulate the presence of the damping wires on the blades. In this work a detailed description of these models is provided, and the results of computations are compared with experimental measurements.
An Economic and Risk Analysis Model for Aircrafts and Engines
Authors: Pascovici D. S. , Colmenares F. , Ogaji S. O. T. , Pilidis P.
Published: March 2009

To conceive and assess engines with minimum global warming impact and lowest cost of ownership in a variety of emission legislation scenarios, emissions taxation policies, fiscal and Air Traffic Management environments, a Techno-economic and Environmental Risk Assessment model is needed. This paper presents an approach to estimate the cost of maintenance and the direct operating costs of turbofan engines of equivalent thrust rating, both for long and short range applications, as well as for typical long and short range aircraft. The economic model is composed of three modules: a lifing module, an economic module and a risk module. The lifing module estimates the life of the high pressure turbine disk and blades through the analysis of creep and fatigue over a full working cycle of the engine. The economic module uses the time between overhauls together with the cost of labour and the cost of the engine (needed to determine the cost of spare parts) to estimate the cost of maintenance of the engine. The risk module uses the Monte Carlo method with a Gaussian distribution to study the impact of the variations in some parameters on the net present cost (NPC) of operation. The accuracy of the economic model in DOC estimation is good (within about 15%) and so can be adapted for use in the cost analysis of future types of engines, such as ultra high bypass ratio turbofans, with little modifications. The equations that constitute the economic model are under a confidentiality agreement of the European project VITAL and can not be divulgated.
CM 939 Weldable® Alloy Update
Authors: Wahl Jacqueline B. , Harris Ken
Published: March 2009

Cannon-Muskegon has developed a proprietary chemistry modified version of IN 939 designated CM 939 Weldable®. As presented in 2004, emphasis was placed on optimizing aim chemistry, utilizing Cannon-Muskegon ultra high purity manufacture technology, and obtaining superior casting microstructure for improved weldability and mechanical properties. This paper will review the unique properties that make this alloy desirable, with particular attention to production experience and ongoing developments. Significant market interest has resulted in extensive vacuum casting experience throughout the gas turbine industry. In the 2–3 years since introduction, CM 939 Weldable alloy has accumulated substantial engine performance experience in industrial gas turbine vane applications. New application programs, including vane rings and turbine containment ring components, advances in weldability using CM 939 Weldable filler wire and special application alloy modifications (DT1 & DT2) will also be presented.
Development of Engine Intake Anti-Icing Systems for LCAC
Authors: Dvornak Michael
Published: March 2009

US Navy ships operating in cold weather require the protection of an engine intake air anti-ice system to prevent blockage of combustion airflow during snow and icing conditions. This requirement does not present any unusual design demands on large displacement type ships because there is more available space, an abundance of usable thermal energy, and lastly their design allows engine weather intakes to be placed in relatively protected locations. However on small craft such as the Navy’s Landing Craft Air Cushion (LCAC), intake air anti-icing presents a unique design challenge. This is due to the spray generated by venting of the craft’s pressurized air cushion during normal over-water operations that results in significant carry-over of this spray onto the cargo deck, from which it is subsequently ingested into the engine intakes. LCAC is also powered by gas turbines that require large quantities of inlet combustion air for power generation. Because of these considerations the thermal energy required for intake anti-icing on LCAC are significantly higher than for large displacement type ships. Adding to this challenge are the facts that on-board space in an air cushion vehicle is at a premium, and power for thermal energy must be obtained from existing sources whose primary function is other than anti-icing. This paper will trace the development and evolution of LCAC’s engine intake anti-ice systems from the craft’s initial design, through to the present systems used in the fleet. It will present the tradeoff issues that effected selection of the anti-ice systems, such as energy availability, cold weather criteria, and craft design constraints.
Numerical Investigation of Low Solidity Vaned Diffuser Performance in a High-Pressure Centrifugal Compressor: Part I — Influence of Vane Solidity
Authors: Oh JongSik , Agrawal Giri L.
Published: March 2009

The LSD (Low Solidity Diffuser) is becoming popular in most industrial centrifugal compressor designs because it is found to offer a wide operating flow range while maintaining a similar level of efficiency as in case of conventional vaned diffusers. Most related studies have been for low or moderate pressure ratio machines providing a limited range of design information for high-pressure ratio compressors. As a first step forward information of design parameters, a numerical CFD investigation was applied to a high-pressure industrial centrifugal compressor of design total-to-static pressure ratio of 4.0 with LSDs of NACA65-series profiles whose solidity varies from 0.452 to 0.968 in 5 cases with all the other design parameters fixed. Near design flow, the case of 0.839 solidity has the highest isentropic total-to-static efficiency. Other performance changes are accordingly investigated.
Optimal Performance of Combined Cycles With Chemical Looping Combustion for CO2 Capture
Authors: Naqvi Rehan , Bolland Olav
Published: March 2009

Chemical Looping Combustion (CLC) is an ingenious concept of CO2 capture from fossil fuels combustion. CLC is closely related to oxy-fuel combustion as the chemically bound oxygen reacts in a stoichiometric ratio with the fuel. In CLC, the overall combustion takes place in two steps while air and fuel are kept away from each other in two separate reactors. The necessary oxygen is supplied to the fuel by a certain metal oxide (Me/MeO). In a fuel reactor, the fuel reacts with the metal oxide and reduces it to metal (Me). The reduced metal oxide (Me) circulates to a separate air reactor where it reacts with oxygen in the air and gets oxidised back to metal oxide. The metal oxide keeps circulating between the two reactors in a loop while taking part in the successive chemical reactions. CLC can be applied in conventional circulating fluidised bed reactors. The air reactor product is hot oxygen-depleted air and the fuel reactor exhaust ideally consists of hot CO2/steam mixture. The exhaust can be condensed to separate steam and CO2 is compressed. Hence, energy penalty for CO2 capture is lower as compared to pre- and post-combustion capture methods. When the reactors are pressurised, CLC can be applied in combined cycles. This paper addresses optimal performance of two CLC-combined cycle configurations. In order to obtain optimal efficiency at base-load, thermodynamic analysis has been carried out and design point established. Further, the cycles’ performance at different load conditions has been analysed. The cycles are also compared with two conventional combined cycles including post-combustion CO2 capture in amine solution. The results show that the CLC-combined cycles exhibit higher net plant efficiencies at base-load as well as at part-load with close to 100% CO2 capture as compared to conventional combined cycles with post-combustion CO2 capture. Also, the CLC-combined cycles have better relative net plant efficiencies at part-load compared to conventional combined cycles. This work concludes that the CLC-combined cycles have high potential of efficient power generation with high degree of CO2 capture at base-load as well as part-load. The challenges with respect to cycles control have also been identified and control strategies discussed.
Numerical Study of the Precessing Vortex Core in a Confined Partially Premixed Swirl Combustion System
Authors: Schneider Elena , Sadiki Amsini , Maltsev Alexander , Janicka Johannes
Published: March 2009

Swirl flows play an important role in modern combustion systems such as gas turbines, aero propulsion systems etc. Next to desirable effects such as enhanced mixing such flows often exhibit aerodynamical instabilities called precessing vortex core. The configuration under study here represents a model Gas Turbine(GT) combustion chamber and features the main properties of real gas turbine combustors: a confined swirled flow with multiple recirculation zones and reattachment points, resulting in reacting case in a partially premixed methane/air aerodynamically stabilised flame. This flame exibits also precessing vortex core (PVC). The present study especially concentrates on an evaluation of the performance of different URANS-based model-combinations in predicting this confined swirling reacting flow exhibiting such aerodynamic instabilities. For this purpose an extended Bray-Moss-Libby model and a G-equation based approach, both coupled to the mixture fraction transport equation to account for partially premixed effects, are applied. Their prediction potential in capturing partially premixed combustion properties is appraised by comparison with LDV, Raman and PLIF measurements. It turns out that the influence of the combustion model on simulation results of the flame front stabilisation or mean flow field is not obvious. Nevertheless it could be mentioned that the computation time with G-equation was approximately three times longer than with BML model due to the reinitialization needed in steady case calculations and 2 times longer in case of unsteady calculations.
Effects of Reynolds Number and Freestream Turbulence Intensity on the Unsteady Boundary Layer Development on an Ultra-High-Lift LPT Airfoil
Authors: Zhang Xue Feng , Hodson Howard
Published: March 2009

The effects of Reynolds numbers and the freestream turbulence intensities (FSTI) on the unsteady boundary layer development on an ultra-high-lift low-pressure (LP) turbine airfoil, so-called T106C, are investigated. The measurements were carried out at both Tu = 0.5% and 4.0% within a range of Reynolds numbers, based on the blade chord and the isentropic exit velocity, between 100,000 and 260,000. The interaction between the unsteady wake and the boundary layer depends on both the strength of the wake and the status of the boundary layer. At Tu = 0.5%, both the wake’s high turbulence and the negative jet behaviour of the wake dominate the interaction between the unsteady wake and the separated boundary layer on the suction surface of the airfoil. Since the wake turbulence cannot induce transition before separation on this ultra-high-lift blade, the negative jet of the wake has the opportunity to induce a rollup vortex. At Tu = 4.0%, the time-mean separation on the suction surface is much smaller. With elevated FSTI, the turbulence in the wake just above the boundary layer is no longer distinguishable from the background turbulence level. The unsteady boundary layer transition is dominated by the wake’s negative jet induced boundary layer variation.
Exergy Analysis for the Performance Evaluation of Different Setups of the Secondary Air System of Aircraft Gas Turbines
Authors: Zeller Philipp W. , Staudacher Stephan
Published: March 2009

Secondary Air System related losses in aircraft gas turbines cannot be directly assessed and quantified as possible for other sub-systems of the engine. If a particular setup is to be evaluated and compared to other, competing designs, it is required to have a distinct understanding of the loss mechanisms and the way these losses appear in the cycle. The relevant loss phenomena are therefore discussed in detail and are quantified with regard to the respective specific entropy increase. The exergy method is found to be the method of choice, since it holds some important advantages compared to other loss accounting methods like gas horsepower or thrust work potential. An exergy analysis is carried out for a high TET, two shaft engine of the medium thrust range. A comparison of setups with different compressor offtake positions is performed. It is found that the contribution of Air System related losses to overall engine efficiency deficits is significant, but may be reduced by careful design.
A Fast Gas Turbine Engine Performance Analysis Tool Able to Capture Three Dimensional Effects
Authors: Templalexis Ioannis , Pilidis Pericles , Pachidis Vassilios , Kotsiopoulos Petros
Published: March 2009

Given the current level of computational resources that are readily available, three dimensional (3-D) gas turbine engine performance simulation remains extremely time consuming. The current paper presents a synthesis of existing flow simulation methods coupled together in the form of a new software package. The software is able to assess the impact of a 3-D flow profile at the intake inlet on engine performance, demanding relatively low computational resources. More precisely four flow simulation techniques are employed, represented respectively by four individual stand alone software sub-modules. 3-D Vortex Lattice Method (VLM) is used to simulate the intake flow. Subsequently the intake outlet 3-D flow profile is decomposed into a radial and a circumferential component. For the compressor performance simulation, that receives those components as inlet boundary conditions, a two dimensional (2-D) Streamline Curvature (SLC) simulation method coupled with an extended parallel compressor model is used. SLC addresses the impact of the radial flow distortion, whereas the extended parallel compressor model examines the impact of circumferential flow distortion on engine performance. The results of the above analysis are stored into an intake-compressor performance characteristic map, which is then fed into a zero dimensional (0-D) performance simulation tool in order to evaluate the overall impact of the intake inlet distorted flow on engine performance. The paper is divided into two major sections. The first one presents the individual flow simulation techniques, together with the corresponding software modules. A short summary of each method is given first and then the software module is described, followed by brief comments on the validation results that have been already published. The section in concluded by the description of the synthesized software. The second major section deals with the application of the synthesized simulation method on a turbojet engine. A generic turbojet engine has been chosen mounted behind a generic intake, given the lack of relevant experimental results. The engine has a four stage axial flow compressor driven by a single stage axial flow turbine, followed by a converging nozzle. 3-D total pressure profiles were imposed at the intake inlet and several comparative graphs of engine’s performance parameters between “clean” and distorted inlet flow conditions are given. The paper is concluded with a discussion on software’s abilities and weaknesses as well as on its potential future expansion.
Life Remaining Prognostics for Structural Components
Authors: Rideout Curtis A. , Ritchie Scott J.
Published: March 2009

Retirement criteria for many structural components and particularly landing gear structural parts, are generally based on analytical fatigue methods because the current means of detecting actual component damage cannot detect sufficiently small levels of damage such that safe operation for a useful interval can be confidently determined; limiting the capability to apply damage tolerance methods. The testing completed in these projects demonstrated that Induced Positron Analysis (IPA) technologies are sensitive to the tensile plastic strain damage induced in aerospace material specimens and components. The IPA process has shown that IPA methods can reliably detect and quantify plastic strain and plastic deformation under simulated and operational conditions. A preliminary functional relationship between total strain and the normalized IPA S parameter has been developed for several aerospace materials. The fatigue testing has demonstrated the IPA technologies have potential to detect fatigue damage induced in specimens and operational components when the loads are large enough to cause plastic deformation.
The Effects of Fuel Composition on Flame Structure and Combustion Dynamics in a Lean Premixed Combustor
Authors: Figura Lorenzo , Lee Jong Guen , Quay Bryan D. , Santavicca Domenic A.
Published: March 2009

The stability characteristics of a laboratory-scale lean premixed combustor operating on natural gas - hydrogen fuel mixtures have been studied in a variable length combustor facility. The fuel and air were mixed upstream of the choked inlet to the combustor to eliminate equivalence ratio fluctuations and thereby ensure that the dominant instability driving mechanism was flame-vortex interaction. The inlet velocity, inlet temperature, equivalence ratio and percent hydrogen in the fuel were systematically varied, and at each operating condition the combustor pressure fluctuations were measured as a function of the combustor length. The results are presented in the form of two-dimensional stability maps, which are plots of the normalized rms pressure fluctuation versus the equivalence ratio and the combustor length, for a given inlet temperature, inlet velocity, and fuel mixture. In order to understand the effects of operating conditions and fuel composition on the observed stability characteristics, two-dimensional chemiluminescence images of the flame structure were recorded at all operating conditions and for all fuel mixtures under stable conditions. Changes in the stable flame structure, as characterized by the location of the flame’s “center of heat release”, were found to be consistent with the observed instability characteristics. The location of the flame’s “center of heat release” was found to lie along a single path for all operating conditions and fuel mixtures. It was also observed that there were regions of stable and unstable combustion as one moved along this path. Furthermore it was found that flames having the same “center of heat release” location, but different operating conditions and fuel composition, have very nearly the same flame shape. These results will be useful for developing phenomenological models for predicting unstable combustion.
Experimental Studies on Cooling Effectiveness of the Double-Decker Air Jet Impingement With Film Outflow
Authors: Mao Junkui , Guo Wen , Liu Zhenxiong , Zeng Jun
Published: March 2009

Experiments were carried out to investigate the cooling effectiveness of a lamellar double-decker impingement/effusion structure. Infrared radiation (I.R.) thermal camera was used to measure the temperature on the outside surface of the lamellar double-decker. Experimental results were obtained for a wide range of governing parameters (blowing rate M (0.0017∼0.0066), the ratio of the jet impingement distance to the diameter of film hole H/D (0.5∼1.25), the ratio of the distance between the jet hole and film hole to the diameter of the film hole P/D (0, 3, 4), and the material of double-decker (Steel and Copper)). It was observed that the local cooling effectiveness η varies with all these parameters in a complicated way. All the results show that higher cooling effectiveness η is achieved in larger blowing rate cases. A certain range of H/D and P/D can be designed to result in the maximum cooling effectiveness η. And η is less sensitive to the material type compared with those parameters such as H/D, M and P/D.
Impacts of Hydrogen Addition on Near-Lean Blowout Dynamics in a Swirling Combustor
Authors: Zhang Qingguo , Noble David R. , Shanbhogue Santosh J. , Lieuwen Tim
Published: March 2009

This paper addresses the impact of H2 addition on lean blowout in premixed swirling flames. Previous work shows that the manner in which the flame blows off varies with percentage of H2 [1,2]. The objective of this paper is to follow up on these observations and systematically characterize the blowoff phenomenology as a function of the H2 levels in the fuel. This is accomplished through high speed visualizations of the flame emission and velocity field measurements. Near blowoff, a variety of highly dynamic flow features are observed, which vary substantially with the H2 levels in the fuel. These features involve complex interactions between the vortex breakdown bubble, outer recirculation zone of the rapid expansion, and flame extinction/reignition phenomenon. Key questions for future studies are the relative roles of fluid mechanics and chemical kinetics in causing the phenomenological variations in near blowoff dynamics, and which features are geometry specific and which are generic to near blowoff flame dynamics.
Analysis of Stator-Stator Clocking in a Transonic Turbine
Authors: Billiard N. , Jerez Fidalgo V. , De´nos R. , Paniagua G.
Published: March 2009

Clocking, i.e. the relative pitch-wise positioning between two successive vanes with the same amount of airfoils, has been demonstrated to bring potential aero-thermal benefits in several recent studies. Indeed, across a vane pitch, a variation of both time-averaged and time-resolved quantities is induced. In order to advance the knowledge on clocking, this 2D numerical investigation proposes a complete description of the unsteady flow field at midspan in a one and half stage turbine at four clocking positions. Mechanisms of migration across the rotor of the first vane wake and its interaction with the second vane has been put into evidence. Additionally, the behavior of the shock system between the rotor and the second stator is assessed indicating effects due to the clocking, like the similar the shape of the shock system when rotor/2nd stator are in the same relative positions.
A Sensor-Fault-Tolerant Diagnosis Tool Based on a Quadratic Programming Approach
Authors: Borguet S. , Le´onard O.
Published: March 2009

Kalman filters are widely used in the turbine engine community for health monitoring purpose. This algorithm gives a good estimate of the engine condition provided that the discrepancies between the model prediction and the measurements are zero-mean, white random variables. However, this assumption is not verified when instrumentation (sensor) faults occur. As a result, the identified health parameters tend to diverge from their actual values which strongly deteriorates the diagnosis. The purpose of this contribution is to blend robustness against sensor faults into a tool for performance monitoring of jet engines. To this end, a robust estimation approach is considered and a Sensor Fault Detection and Isolation module is derived. It relies on a quadratic program to estimate the sensor faults and is integrated easily with the original diagnosis tool. The improvements brought by this robust estimation approach are highlighted through a series of typical test-cases that may be encountered on current turbine engines.
Brazing and Wide Gap Repair of X-40 Using Ni-Base Alloys
Authors: Schoonbaert Stephen , Huang Xiao , Yandt Scott , Au Peter
Published: March 2009

Co-base superalloys are commonly used for vanes and parts of the combustion chamber in gas turbine engines. The Co-base superalloys are primarily solid solution strengthened and have good resistance to hot corrosion, creep and thermal fatigue. In particular, Co-base alloy X-40 was used to fabricate the first stage NGV airfoils of T56 series engines; inspections after service have revealed that X-40 airfoils suffered from severe thermal fatigue damages. In this study, a new braze repair scheme is proposed; in which Ni-base alloys are used to repair the X-40 substrate in both narrow and wide gap configurations. Metallographic examination, X-ray mapping and EDS semi-quantitative compositional analyses were carried out to study the microstructures in the braze joint in the asbrazed condition and after thermal exposure at 950°C. The results obtained so far suggest the formation of Cr-rich borides, eutectic phases and various carbides in the joint. No TCP phases were found in the brazed joint and base metals adjacent to the joint. The high carbon content in the alloy X-40 may have played an important role in preventing the formation of TCP phases during brazing and subsequent thermal exposure.
A Study of a Centrifugal Compressor Using Mixing Plane Implementations
Authors: Yan Jin , Stuckert Greg
Published: March 2009

A study has been conducted to evaluate a mixing plane implementation on a centrifugal compressor with 4:1 compression ratio. The compressor performance and flow field are modeled using a steady state CFD solver at three different operating points. The importance of the mixing plane location in the solution process is discussed. A new initialization method to speed-up the convergence significantly is described and utilized in the study. The compressor performance calculated by the CFD code compares well with the values from laser anemometry and pneumatic probes measurements. The flow structure inside the compressor is illustrated by comparing the results from the experiments to those from the computation. Good agreement on the detailed flow structure is obtained between the CFD and the experimental values. The computational mesh and the location of the mixing plane are discussed.