bluuebunny/crossref_metadata_2025_split huggingface dataset:
Identification of Contact Area From Full Field Displacement Surface Measurements
Authors: Chatelet Eric , Nouri Baranger Thouraya , Jacquet-Richardet Georges , Saulot Aurélien 
Published: September 2014

One of the most common failure modes for turbomachinery wheels is associated to high-cycle fatigue of blades. A practical way to extend working life is obtained through the introduction of specific devices that allow a reduction in vibrational magnitudes during resonance. Different kinds of components are used such as shrouds and wires for power industries and under platform dampers for aeronautics. The dry friction phenomenon between those devices and the blades induces nonlinear behaviors and flatten associated frequency response functions. This phenomenon is now well known and different modeling techniques of contact are available within numerical simulation softwares. Nevertheless, it is always difficult to estimate or to measure with sufficient precision the actual contact characteristics needed to run those softwares. Due to practical experimental capabilities, measurements are only possible quite far from the contact zone and major quantities such as the transverse loading for example are often unreachable directly.
In this paper, a new inverse methodology is presented. This method uses surface displacement measurements (obtained usually experimentally from conventional accelerometer and fast camera) in order to identify the characteristics of contact zones within elastic body assemblies. The new methodology is validated and illustrated by a numerical approach based on an academic set up.
CFD Investigation of Hydrodynamic and Acoustic Instabilities of Bluff-Body Stabilized Turbulent Premixed Flames
Authors: Lee C. Y. , Cant R. S. 
Published: September 2014

Combustion instabilities in propulsion systems are often manifested through high amplitude pressure oscillations that can severely compromise performance and even lead to mechanical failure. Such instability arises from the development of large-scale coherent structures and their breakdown into fine scale turbulence that can alter the flame structure and affect turbulent mixing. When in phase with the pressure, the modulated heat release rate fluctuations can drive the system to the point where it reaches a limit cycle.
Using high fidelity CFD, the present investigation describes the occurrence of combustion-driven instability in bluff-body stabilized turbulent premixed flames, in which there is dynamic coupling between the preferred hydrodynamic modes and the acoustics of the duct. A URANS approach is adopted, using a second moment closure to solve for the anisotropic turbulent Reynolds stresses. This is combined with the Bray-Moss-Libby (BML) combustion model with a modified reaction rate closure that aims to capture the changes in the flame surface density due to external flow perturbations. Two different geometries are used for the investigation: the first is a laboratory-scale planar bluff-body flameholder [1]; and the second is the well-known Volvo afterburner experiment [2]. Four different conditions are presented to illustrate the various self-excited instabilities that can appear depending on the coupling mechanisms between the different fluid-mechanical and acoustic phenomena.
For the planar geometry, a self-sustained hydrodynamic instability induced by large-scale coherent structures occurs under fuel-lean conditions. When the equivalence ratio is increased, the flame becomes strongly wrinkled due to velocity perturbations arising from the Kelvin-Helmholtz (K-H) instability of the shear layer. The combustion heat release becomes modulated such that its phase relationship with the pressure fluctuations is sufficient to trigger thermoacoustic instability. For the Volvo experiment, symmetric shedding takes place and an acoustic mode of the duct is excited when the mixture strength is lean. At higher equivalence ratio, the flame is perturbed by the hydrodynamic instabilities of the most amplified mode. Small scale structures can be seen in the vicinity of the flameholder, and larger fluctuations in the flame occur further downstream. No appreciable feedback from the acoustic modes is present to sustain combustion instabilities.
The Effect of Aircraft Integration Design on Gas Turbine Shaft Thermal Bow and the Newkirk Effect
Authors: Smith Evan Oscar , Neely Andrew J. 
Published: September 2014

During the cooling process after shutdown, gas turbines can suffer from differential thermal expansion due to buoyant convection. This process can result in asymmetric cooling of the shaft, which can in turn lead to differential thermal expansion, causing deformation of the shaft, known as thermal bow. Attempts to start a gas turbine in this bowed condition can lead to rotor-to-stator contact, triggering further heating, and subsequently further bow. This phenomenon, known as the Newkirk Effect, can result in severe damage to the engine, representing a risk to both airworthiness and logistics.
This study utilises a technique previously developed by the authors for modelling shaft thermal bow in gas turbines using a combination of 3D conjugate heat transfer (CHT) computational fluid dynamics (CFD) and finite element analysis (FEA). A baseline model comprises a simple hollow shaft supported at each end, enveloped inside a simple case. Body temperatures obtained through 3D CHT CFD at set time intervals are transferred to FEA, where the physical distortion associated with the application of an asymmetric thermal load is measured. The baseline model was allowed to cool down from representative operational temperatures, with the shaft thermal bow measured for 90 minutes of flow time. Simple modifications were then made to the baseline model including the addition of representative helicopter and fast jet inlet and exhaust analogues, and the use of porosity to simulate the presence of blades, to analyse their influence on the onset time, duration, and severity of the shaft deformation.
While the geometries used in this initial study are basic, the results indicate that these aspects of gas turbine design do have an appreciable effect on the onset time, severity, and duration, as well as the axial distribution of the shaft thermal bow. This also indicates the importance of further work in this area using more realistic geometries.
Heat Transfer in a Vane Trailing Edge Passage With Conical Pins and Pin-Turbulator Integrated Configurations
Authors: Kruekels J. , Naik S. , Lerch A. , Sedlov A. 
Published: September 2014

The trailing edge sections of gas turbine vanes and blades are generally subjected to extremely high heat loads due to the combined effects of high external accelerating Mach numbers and gas temperatures. In order to maintain the metal temperatures of these trailing edges to a level, which fulfills the mechanical integrity of the parts, highly efficient cooling of the trailing edges is required without increasing the coolant consumption, as the latter has a detrimental effect on the overall gas turbine performance.
In this paper the characteristics of the heat transfer and pressure drop of two novel integrated pin bank configurations were investigated. These include a pin bank with conical pins and a pin bank consisting of cylindrical pins and intersecting broken turbulators. As baseline case, a pin bank with cylindrical pins was studied as well. All investigations were done in a converging channel in order to be consistent with the real part.
The heat transfer and pressure drop of all the pin banks were investigated initially with the use of numerical predictions and subsequently in a scaled experimental wind tunnel. The experimental study was conducted for a range of operational Reynolds numbers. The TLC (thermochromic liquid crystal) method was used to measure the detailed heat transfer coefficients in scaled Perspex models representing the various pin bank configurations. Pressure taps were located at several positions within the test sections. Both local and average heat transfer coefficients and pressure loss coefficients were determined.
The measured and predicted results showed that the local internal heat transfer coefficient increases in the flow direction. This was due to the flow acceleration in the converging channel. Furthermore, both the broken ribs and the conical pin banks resulted in higher heat transfer coefficients compared with the baseline cylindrical pins. The conical pins produced the highest average internal heat transfer coefficients in contrast to the pins with the broken ribs, though this was also associated with a higher pressure drop.
Analysis of the Scatter of the Elastic Properties in Conventionally Cast Nickel Base Superalloys: Quantification, Modeling and Evaluation of the Impact on Gas Turbine Blade Design
Authors: Riva Andrea , Bessone Andrea 
Published: September 2014

Cast nickel-base superalloys elastic properties have a very large scatter, mainly because of the coarse grain microstructure and in-grain anisotropy.
This high dispersion must be taken into account in the design of gas turbine blades, in particular when evaluating phenomena directly linked to the elastic behavior, such as blades vibration. This source of elastic properties scatter becomes even more important on specimens for material characterization because of their inferior size, which entails a lesser number of grains (i.e. a larger scatter).
In this paper a model aimed to quantify such scatter is proposed. The performances of the model in predicting the standard deviation of the Young’s modulus (and consequently of the eigenfrequencies) are also shown, both for tested specimens and blades excited on clamps.
Finally, a sensitivity FEM modal analysis is performed in order to evaluate how the elastic property dispersion might affect the blade eigenfrequencies and the relative mode shapes, with particular emphasis on the case of a specific region of a geometrically complex component affected by an anomalous Young’s modulus. Besides, the influence of the blade mass is evaluated through both experimental clamp impact tests and FEM analyses. The effect on blades of such source of scatter is then compared to the effect of the elastic properties dispersion. ANSYS program has been used for the simulations.
Fuel Switchover at High Load, Integration Into an Engine Operation Concept
Authors: Schell Susanne , Singla Ghislain 
Published: September 2014

The capability to switch online from a main to a back-up fuel is a necessity for dual fuel gas turbines. The switching procedure is itself challenging; fuel gas, fuel oil and supporting systems need to be operated in parallel, with the safe start-up and shut-down of each system having to be ensured. Additionally, the requirements of gas turbine and combined cycle have to be considered; with the target to provide fast reliable fuel switching, without a major effect on the power output.
Alstom’s GT26/GT24 High Load Fuel Switchover (HLFSW) fulfils these requirements. HLFSW is a concept which allows switching back and forth between fuel gas and fuel oil in the load range of base load down to 60 % relative GT load. A key feature of the HLFSW is the stable load during the complete duration of the fuel switchover process, ensuring nearly constant power output in combined cycle mode from the moment the fuel switchover is triggered until standard operation is achieved on the secondary fuel.
In this paper the integration of the HLFSW into the engine operation concept is presented. It is shown, how the sequential combustion of the Alstom GT26/GT24 is transferred from primary to secondary fuel by sequential fuel switchover. The focus is on how the high load fuel switchover concept is embedded into the gas turbine’s engine operation concept, allowing a smooth transfer between the fuel gas standard operation concept and the fuel oil standard operation concept and vice-versa, resulting in a fuel switchover concept without any significant disturbances to the heat recovery steam generator (HRSG).
Stress Corrosion Cracking and Corrosion Fatigue Analysis of Nuclear Steam Turbine Rotor
Authors: Chen Gang , Jiang Puning , Ye Xingzhu , Zhang Junhui , Hu Yifeng , Hao Zhenzhen 
Published: September 2014

Although stress corrosion cracking (SCC) and corrosion fatigue cracking can occur in many locations of nuclear steam turbines, most of them initiate at low pressure disc rim, rotor groove and keyway of the shrunk-on disc. For nuclear steam turbine components, long life endurance and high availability are very important factors in the operation. Usually nuclear power plants operating more than sixty years are susceptible to this failure mechanism. If SCC or corrosion fatigue happens, especially in rotor groove or keyway, it has a major influence on nuclear steam turbine life.
In this paper, established methods for the SCC and corrosion fatigue-controlled life prediction of steam turbine components were applied to evaluating a new shrunk-on disc that had suffered local keyway surface damage during manufacture and loss of residual compressive stress.
Evaluation of FEM Based Methods to Predict Temperature Distributions of a Convection Cooled Gas Turbine Blade
Authors: Woerz B. , Mick Y. , Findeisen E. , Jeschke P. , Rabs M. 
Published: September 2014

This paper presents different numerical methods to predict the thermal load of a convection cooled gas turbine blade under realistic operating temperature conditions. The subject of the investigation is a gas turbine rotor blade which is equipped with a state-of-the-art convection cooling system.
Firstly, two FEM based methods are introduced. One method, referred to as FEM1D method, uses empirical correlations from the open literature to obtain one dimensional heat transfer coefficients along one flow line inside the cooling channels while in the hot gas path a three dimensional CFD simulation is used. The second method (FEM2D) uses three dimensional CFD simulations to obtain two dimensional heat transfer coefficient distributions for both, the inner cooling channels and the hot gas path. The results from both numerical methods are compared with each other and are validated with experimental data, quantifying also their accuracy limits.
In total this paper gives an evaluation of two different FEM methods to predict temperature distribution in convection cooled gas turbines. Their accuracy, numerical cost and limitations are evaluated. It turns out that the temperature profiles gained by both methods are generally in good agreement with the experiments. However, while causing higher numerical costs the more detailed FEM2D method achieves more accurate results.
NOx Reduction in Gas Turbine Combustors With Compact Non-Premixed Flame Front
Authors: Tsatiashvili V. V. , Avgustinovich V. G. 
Published: September 2014

This paper represents results of R&D efforts towards reducing a bypass turbofan engine NOx emission by 45 % compared with CAEP/6 to meet the ICAO NOx emission goal of 2020.
To achieve ICAO NOx technology goal, a new approach is used based on the NOx emission reduction in combustors with non-premixed combustion well proved in operation. The new approach is represented by structured system of low emission combustion principles — a concept of combustor featuring compact non-premixed flame (CNPF). The essence of CNPF concept is in suppression of volume and surface NOx formation sources by flame front blocking in liner primary zone and by increasing of fuel effective burning rate. The paper represents the development of concept up to and including the 4th technology maturity level. It demonstrates CNPF concept independence and interaction with other up-to-date gas turbine low emission concepts. The paper indicates comparison of rig test results between in-service combustor and CNPF adopted combustors carried out on a single liner. A CNPF adopted combustor shows NOx emission index reduction by 35 …47 % at take-off engine conditions. Preliminary estimation shows that it is possible to reach the ICAO goal for NOx emission level of 2020.
Design, Validation and Verification of Film Cooling on Gas Turbine Rotor Endwall
Authors: Abba L. , Abram R. , Barigozzi G. , Perdichizzi A. 
Published: September 2014

This paper describes the design process carried out to introduce film cooling coverage on the hub platform of a first turbine blade in order to protect from hot gas corrosion the trailing edge platform region.
The different steps described consist in a design phase, a validation by experimental tests, the production follow up and verification feedbacks.
The first stage endwall is a critical region due to secondary flows overheating; critical areas have been identified by 3D thermal analysis and confirmed through damage reports.
A design phase has been carried out to determine the cooling holes configuration in terms of position, number, inclination and diameter.
A CFD analysis allowed to define the hot gas streamlines near the pressure side fillet region in order to identify the best holes arrangement to ensure a proper thermal coverage; the thermal effectiveness and coverage length has been subsequently verified by means of an experimental activity developed by University of Bergamo.
On the basis of the experimental results a 3D thermal analysis of the new holes configuration has highlighted the improvement in terms of local wall temperature reduction.
Finally the new film holes have been introduced in the machining cycle of the blade and realized by electrochemical drilling. During a maintenance inspection after 20000 operating hours an endoscope investigation has confirmed the improvement obtained, showing no substantial signs of overheating.
Rotating Stall Observations in a High Speed Compressor: Part 2 — Numerical Study
Authors: Dodds J. , Vahdati M. 
Published: September 2014

In this two part paper the phenomenon of part span rotating stall is studied. The objective is to improve understanding of the physics by which stable and persistent rotating stall occurs within high speed axial flow compressors. This phenomenon is studied both experimentally (part 1) and numerically (part 2).
The experimental observations reported in Part 1 are now explored through the use of 3D unsteady RANS simulation. The objective is to both to validate the computational model and, where possible, explore some physical aspects of the phenomena.
Unsteady simulations are presented, performed at a fixed speed with the three rows of variable stator stagger vanes adjusted to deliberately mismatch the front stages and provoke stall. Two families of rotating stall are identified by the model, consistent with experimental observations from Part 1.
The first family of rotating stall originates from hub corner separations developing on the stage 1 stator vanes. These gradually coalesce into a multi-cell rotating stall pattern confined to the hub region of the stator and its downstream rotor. The second family originates from regions of blockage associated with tip clearance flow over the stage 1 rotor blade. These also coalesce into a multi-cell rotating stall pattern of shorter length scale confined to the leading edge tip region. Some features of each of these two patterns are then explored as the variable stator vanes are mismatched further, pushing each region deeper into stall.
The numerical predictions show a credible match with the experimental findings of Part 1. This suggests that a RANS modelling approach is sufficient to capture some important aspects of part span rotating stall behavior.
Electro-Assist Turbo for Marine Turbocharged Diesel Engines
Authors: Shiraishi Keiichi , Krishnan Venky 
Published: September 2014

Turbocharged diesel engines are widely used in the marine industry and have a significant impact on global CO2 and NOx emissions. Turbochargers are an integral component of any diesel engine and they play a critical role in their performance. Mitsubishi Heavy Industries (MHI) and Calnetix Technologies have developed a unique technology called the “Electro-Assist Turbo” (EAT). The EAT unit consists of a specially designed high speed permanent magnet motor directly mounted to the turbocharger rotating assembly. The high speed motor applies torque to the turbocharger rotor enabling it maintain or vary rotor speed at low engine exhaust flow rates in order to supply sufficient charge air to maximize engine performance. Turbocharged diesel engines suffer from inherent deficiencies at low engine speeds; there is not enough energy in the exhaust to produce an optimum and readily available level of boost for the engine intake air system at off-design points. This technology proves even more important as the majority of large marine vessels are now operating in a “slow steaming” part throttle mode. To date the majority of marine diesel engines use auxiliary air blowers (AAB) to supply additional air to the engine intake during off design point operation. These AABs are inefficient and not intended nor designed to be used in constant operation. The EAT unit can provide a higher discharge pressure at the same electrical power consumption as an AAB. This more efficient design with higher discharge pressure further improves fuel efficiency and eliminates the need to run an external piece of machinery during operation, thus lowering maintenance costs.
This paper will provide an overview of the design, integration and initial testing of the 100kW Electro-Assist Turbo into a Mitsubishi Exhaust-gas Turbocharger (MET)-83 marine diesel turbocharger. In addition this paper will go over the custom designed aerodynamic motor housing structure that holds the non-rotating components without penalizing performance of the turbocharger, special software developed for the variable frequency drive system that enables the flexible operation of the high speed motor, and features of the high speed permanent magnet motor that allows for operation without any active cooling. Also, this paper will provide and discuss the initial test results of the EAT integrated into the MET-83 turbocharger along with engine testing results provided by MHI. Low cost designs will be discussed that enable turbochargers currently in operation to be retrofitted and the further improvements taking place to commercialize.