bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nonlinear Harmonic Method Applied to Turbine Conjugate Heat Transfer Analysis for Efficient Simulation of Hot Streak Clocking and Unsteady Heat Transfer
Authors: Mehdizadeh Omid Z. , Vilmin Stéphane , Tartinville Benoît , Hirsch Charles 
Published: August 2017

High pressure turbine (HPT) optimum thermal design is critical in further improving gas turbine efficiency. However, this is a challenging task as it requires accurate simulation of unsteady flows in conjunction with heat transfer simulation of the airfoil solid structure, which in turn requires large computational resources.
In this work, the nonlinear harmonic (NLH) method is applied to conjugate heat transfer (CHT) simulation to provide an effective tool for turbine thermal design and analysis. The NLH method can be seen as a computationally affordable alternative to the traditional time-marching unsteady simulation particularly in turbomachinery applications, where the unsteadiness is mostly periodic. When applied to CHT simulations, it also addresses the difficulty of dealing with large time-scale mismatch between fluid and solid domains by casting the periodic perturbations into the frequency domain. Furthermore, it naturally allows for the study of hot streaks clocking effects by means of space harmonics.
These capabilities are demonstrated on the HPT of the NASA/GE Energy Efficient Engine (E3), where hot streaks clocking effect on the metal temperature of the nozzle guide vane (NGV) is simulated. Also, the time variation of the rotor blade metal temperature as it crosses the hot streaks is simulated. The results confirm that, with only a single NLH solution, different aspects of the thermal design of a multi-stage turbine can be explored with little additional computational effort with respect to the standard steady approach.
CFD Study of a Micro-Combustor Under Variable Operating Conditions
Authors: Cameretti Maria Cristina , De Robbio Roberta , Tuccillo Raffaele 
Published: August 2017

New concepts for power generation are discussed as a response to CO2 emissions from the combustion of fossil fuels. These concepts include low-carbon fuels as well as new fuel supplies will be used, with (biogenic) low-caloric gases such as syngas with an amount of hydrogen, with a share of 50% and even higher. However, hydrogen mixtures have a higher reactivity than natural gas (NG) mixtures, burned mostly in today’s gas turbine combustors.
The authors discuss in this paper the potential of a micro gas turbine (MGT) combustor when operated under unconventional conditions, both in terms of variation in the fuel supplied and concerning the part-load or off-design operation.
In particular, the authors’ methodology relies on an advanced CFD approach that makes use of extended kinetic mechanisms coupled with the turbulent interaction of the reacting species. A preliminary set-up of the combustion model is based on data provided by experimental tests of the micro-turbine.
In the paper, several computational examples are discussed, namely:
- The comparison of combustion stability and efficiency and pollutant production with several fuels.
- The analysis of the combustor response with reduced load.
- The use of the pilot and main injectors for supplying different fuels.
Stress Corrosion Cracking in Steam Turbine: Two Case Studies
Authors: Gowreesan Vamadevan , Grebinnyk Kirill 
Published: August 2017

Stress corrosion cracking in steam turbines had been an old problem though some modern steam turbines have almost eliminated this problem by several methods. The methods include design modification to reduce the stress levels below the threshold stress level for stress corrosion cracking, inducing compressive stress by different means and using pure steam [1, 2]. Some of the older steam turbine discs are prone to stress corrosion cracking. Two cases where such machines experienced stress corrosion cracking in their discs are discussed here.
The row 6 disc of an integral steam turbine rotor developed cracks in the root sections. Some of the cracks were mechanically opened for the evaluation. Evaluation of the fracture surfaces with a scanning electron microscope showed evidence of intergranular mode of cracking. Optical microscopy of a cracked root confirmed intergranular mode of cracking. In addition, it showed branching of cracks. Based on these findings, it was concluded that stress corrosion cracking was the reason for the cracks. In addition, finite element analysis was used to calculate the stress distribution in the blade root of the disc. The location of the maximum equivalent stress coincided perfectly with that of the actual crack location in the disc root section. Unfortunately, redesign of the root geometry to minimize the local stress concentration is very difficult due to the size limitation of the blade roots. Small amount of chlorine was identified on the fracture surface and the chlorine could have come from the steam used. The customer was advised to analyze their steam quality and to improve the quality of the steam if needed. The cracked portion was removed from the disc and weld-build up to machine new root sections with the same type of roots.
Root section of the row 6 disc of another steam turbine developed failure. This disc had radial entry type blades. Portion of the disc root and some blades were liberated from the disc due to the cracking. The fracture surface had heavy oxide layer on it. Evaluation of the fracture surface with a scanning electron microscope revealed intergranular mode of failure. Energy dispersive spectroscopy analysis of the fracture surface found oxides on the fracture surface. Optical microscopy showed secondary cracking and branched cracking. All these evidences confirmed that the failure occurred due to stress corrosion cracking. In addition, it was suspected that forging was not heat treated properly due to measured lower toughness and different microstructure. The lower toughness was believed to be a result of improper heat treatment rather than that of embrittlement. Methods to mitigate the risk of stress corrosion cracking were proposed.
Large Eddy Simulation of Conventional and Bias Flow Acoustic Liners
Authors: Ramdani Soufiane , Yamasaki Nobuhiko , Inokuchi Yuzo , Ishii Tatsuya 
Published: August 2017

This study deals with the acoustic behavior of acoustic liners and the flow field around the perforated plate by solving numerically the compressible Navier-Stokes equations. The difficulty of visualizing the flow around the small holes of the plate makes the numerical simulations very attractive in order to well understand the acoustic behavior of the liner.
The chosen liner was previously studied by Tam et al. [1] experimentally and using the Direct Numerical Simulation for the case of a conventional acoustic liner under normal sound wave incidence. The results obtained by Tam et al. [1] serve for the validation of the results obtained in the present research. Moreover, in this study, the focus is on the numerical simulation of the influence of bias flow on the absorption performance of a slit liner using the large eddy simulation.
Two different methods are used to calculate the absorption coefficient in the computational aeroacoustics (CAA) simulation of the resonator. The first method is the transfer function method, and it simulates the impedance acoustic tube used in the experiment. The second method is the viscous dissipation method, and it calculates the power at which the acoustic energy is converted in viscous dissipation.
The viscous dissipation method gives good agreement for the calculated absorption coefficients at the sound source pressure level of 150 dB. Shed vortices are developed in this case, and are considered to be the main cause of sound dissipation.
The transfer function and the viscous dissipation methods used to calculate the absorption coefficients give good results for frequencies higher and equal to 2 kHz when the sound source pressure level is set to 130 dB. Only at the frequencies of 1 kHz, the obtained values are different from the values obtained by Tam et al. [1]. Shed vortices are not observed when the resonator is under only normal sound wave incidence of 130 dB.
The introduction of a bias flow passing through the aperture of the resonator is investigated. The acoustic performance of the liner in this case and a comparison of the flow behavior at the aperture with a conventional liner is highlighted. When the sound pressure level is equal to 130 dB, an increase in the absorption is obtained for frequencies above the resonance frequency when the bias flow passing through the aperture is introduced. On the other hand, the absorption is reduced for the resonance frequency. However, when the SPL is equal to 150 dB, the absorption coefficient is higher near the resonance frequency, while for higher frequencies the absorption coefficient is lower.
Cycle Modeling and Optimization of an Integrally Geared sCO2 Compander
Authors: Bennett Jeffrey , Wilkes Jason , Allison Timothy , Pelton Robert , Wygant Karl 
Published: August 2017

This paper presents the selection of a system configuration and off-design control method for an integrally geared compander based on cycle modeling and optimization. The goal of the cycle modeling was to determine a cycle configuration that would reach an efficiency of 50% at design conditions and to optimize off-design control to maintain high efficiencies. The compander is being developed for use in a concentrated solar power supercritical carbon dioxide power plant with expected turbine inlet temperatures of 705°C and utilizing dry cooling leading to compressor inlet temperature varying between 35°C and 55°C. The compander is unique as it consists of eight turbomachinery stages on four pinions all being driven by a single bull gear. The separate stages offer the opportunity to consider a variety of flow splits and cycle configurations including intercooling and multiple stages of reheat.
Cycle modeling was conducted in two stages: on-design and off-design. On-design modeling was simulated with all components operating at their design point. This was used to compare the performance of different cycle configurations and design temperatures. Off-design modeling was then performed to investigate the temperature dependence of the cycle efficiency and power output and to develop a control strategy. Strategies considered and discussed include: turbine bypass, compressor recycle, inlet guide vanes, and inventory control. To determine the best operating conditions for each configuration and control strategy, a genetic algorithm was implemented to optimize the cycle performance across the range of operating temperatures being considered. The final selection of cycle configuration, design temperature and control strategy is also presented.
A Hybrid Approach for 3D Full-Field Measurement on a Closed Slinger Combustor by Hydraulic Simulations
Authors: Jia Lichao , Yang Lili , Yuan Huijing , Jia Yongxia , Wang Yiyang , Feng Yang 
Published: August 2017

This hybrid approach proposed in the present study is a mixture algorithm of the 3D PTV and Tomo-PIV based on a two-camera system, which is able to measure the flow field in a closed system with high refractive without in situ calibration. Knowing the calibration data in the air and refractive indices of different optical media, a simplified multimedia photogrammetry model is established based on the least square method. A new particle matching algorithm using the concept of match probability between the twin image frames has been developed to reconstruct the physical position of the particles. In order to overcome the disadvantage of low particle density, time-resolved PIV is utilized at a sampling rate being 2000 Hz to acquire the instantaneous particle images. Then, the spectrum superposition of the cross-correlation distribution is applied to increase the signal-to-noise ratio in the velocity prediction.
The technique proposed here can be used to overcome the difficulty in conventional calibration method for closed measurement objects. Both the computer simulation and some experiments imaging a calibration target reference field are conducted to show the accuracies of the calibration and reconstruction process. The capability of the technique in real experimental conditions is assessed with the measurement of the flow structure in a closed slinger combustor by hydraulic simulations.
Preliminary Investigation on the Effect of the Modification of the Sweep Angle at the Blade Tip of Forward Swept Axial Fans
Authors: Masi Massimo , Lazzaretto Andrea 
Published: August 2017

The flow path close to the suction side of fan rotor blades mostly affects the overall drag of the blading. The blade lift is affected as well because of the separation of the low energy boundary layer that drives the blade into stall at low fan flow rates.
Forward sweep allows to position the airfoil sections of blades featuring a positive circulation gradient along the span so that they “accompany” the near-wall flow trajectories at the blade suction side. So, rotor efficiency and stall margin of the fan can be improved. On the other hand, blade end effects play a relevant role in high hub-to-tip and low aspect ratio rotors and may compromise the effectiveness of forward sweep. Nevertheless, some authors in the literature stated the beneficial contribution of changing the sweep angle at the ends of the blade both at design and off-design conditions.
The paper studies the end effects on constant-swirl design rotors by means of CFD simulations focusing on the distribution of blade sweep in the near-tip region. In particular, the performance and efficiency calculated for a forward swept tube-axial fan featuring a hub-to-tip ratio equal to 0.4 are compared with those estimated for the corresponding unswept fan at equal duty point. Several modifications of the sweep distribution in the blade tip region are considered in the swept fan to quantify their effect on performance, efficiency and stall margin.
Results show that the addition of up to 6 degrees of local forward sweep at the blade tip to the unswept blading does not affect fan pressure at design operation.
On the other hand, this local increase of the sweep angle allows for a very notable increase of the peak pressure and efficiency at flow rates close to stall inception.
Numerical Analysis of the Impact of Manufacturing Errors on the Structural Stiffness of Foil Bearings
Authors: Fatu Aurelian , Arghir Mihai 
Published: August 2017

The dynamic characteristics of foil bearings operating at high rotation speeds depend very much on the mechanical characteristics of the foil structure. For this reason, the stiffness and damping of the structure of foil bearings is a problem that is the focus of many analyses. The mechanical characteristics of the foil structure (top and bump foil) are analyzed either by using a simple approach obtained for an isolated bump modeled as a beam or with more elaborate ones taking into account the three-dimensional nature of the bumps and their mutual interactions. These two kinds of models give different foil structure stiffness, with lower values for the simplified model. However, the published experimental results of the foil bearing structure tend to validate the simplified model. The present paper explains the differences between the simplified and the elaborate models by taking into account the manufacturing errors of the foil structure.
A three-dimensional model based on the non-linear theory of elasticity is developed. The model offers a unique insight into the way the bearing structure deforms when the rotor is incrementally pushed into the foil structure. Three realistic manufacturing errors, bump height, bump length and radius of the bump foil are analyzed. Bump height and length vary following a normal distribution with a given standard deviation while the radius of the bump foil is given a waviness form with an imposed peak-to-peak amplitude. Three to five cases were calculated for each kind of error. Results show that only the manufacturing errors of the bump height affect the stiffness of the foil structure by diminishing its values. Height errors of 20 μm standard deviation (4% of the average bump height and 60% of the radial clearance) may induce a 40–50% reduction of the stiffness of the foil structure, i.e. in the range of the predictions of the simplified model.
A Physically Based Model for High Temperature Deformation of Inconel 718Plus™
Authors: Ozturk Utkudeniz , Cabrera Jose Maria , Calvo Jessica 
Published: August 2017

The microstructural evolution of Inconel 718Plus during hot forming operations is modeled through a physically based model which includes the effects of precipitating particles.
Inconel 718Plus has been a successful alloy since its introduction in 2003 owing to its moderate cost, good formability and weldability, and its higher maximum service temperature compared to its ancestor, Inconel 718.
It is well known that the service performance and hot-flow characteristics of this alloy are strongly dependent on the microstructure, particularly the grain size. Thus, comprehension of the microstructural evolution and its modeling is an important task.
In precipitation hardening superalloys and microalloyed steels, it is particularly more challenging to model the microstructural evolution in the processing windows where material softening and precipitation processes take place concurrently. The model presented in this work is based on dislocation density evolution which is considered as a result of the competition between dislocation generation and dynamic recovery at the early stages of deformation.
In the hardening region, recovery through climb is described by the diffusion of vacancies and glide is assumed to be proportional to the strain rate in accordance with the models proposed by Bergstrom. Since the deformation is assumed to be controlled by glide and climb, the peak stress is modeled based on a modified hyperbolic-sine model which takes into account the temperature dependence of self-diffusion of Nickel and elastic modulus.
It is known that under high temperature deformation conditions Inconel 718Plus may undergo dynamic precipitation. Second-phase particles in the material may impede the grain boundary motion and contribute to an increase in flow-stress due to Orowan looping. To account for the dynamic precipitation, the present model combines previously obtained experimental results and precipitation models to predict volume fraction and particle radius. For the peak stress modeling, the effect of precipitation is expressed as an extra stress term.
The flow stress is calculated for the deformed and the recrystallized material separately and the total flow stress for the material is calculated using a law of mixtures considering the fraction of recrystallized material, while recrystallization is described as a nucleation-growth process via Avrami formalism.
Cylindrical compression tests were employed to observe the hot flow behavior and validate the model. The predictions are compared with the experimental findings and good agreement is observed.
Design of Fault Detection System for a Heavy Duty Gas Turbine With State Observer and Tracking Filter
Authors: Liu Yongwen 
Published: August 2017

There exist many approaches for gas turbine engine condition monitoring and fault diagnosis. Among them, gas path analysis depends on the relations between deviations of performance parameters and deviations of measurements, such as pressure, temperature, at some positions in the flow path. A dynamic tracking filter combined with a nonlinear gas turbine model can be used to implement a fault detection system. The dynamic tracking filter is composed with multiple feedback loops in which the residuals between model output and measurement are driven to zero by adjusting the performance parameters. In many cases, the number of measurement parameters is less than that of performance parameters, which impose a limit on the application of tracking filter in practical situations. In the present study, the tracking filter is retrofitted to be driven by the error between state of the model and the estimated state reconstructed from the engine measurement. For the time being, only linear time-invariant (LTI) state observer is considered. A nonlinear simulation model of the heavy-duty gas turbine under study is used to derive the linear system model needed for the design of LTI state observer. Input vector and output vector are chosen according to the practical situations. The linear system model obtained around the nominal operating point is observable, so a state observer can be designed. With 6 state variables observable from the engine, 6 performance parameters can be tracked with the proper design of tracking filter. The structure of the tracking filter consists of a static decoupling matrix DM and in series with 6 PI controllers.
Deviations of performance parameters are implanted into the gas turbine model by scaling the performance maps used; and then simulation results are taken as measurements needed for the tracking filter to run. Tracking results of performance parameters in different cases are given to show the tracking capability for isolated performance deviations and concurrent performance deviations.
High-Loaded Compressor Blisk-Type Impeller Multidisciplinary Optimization
Authors: Buyukli Tatiana , Salnikov Anton , Fedorchenko Yury 
Published: August 2017

The current work concerns the approach to the problem of the optimal design of experimental HPC blisk-type impellers. This approach is based on the use of modern optimization methods and a unified parameterized multidisciplinary 3D model, which was specially developed for the problem-solving method, which was formulated. The model included the HPC air-gas channel and the finite-element model of the HPC first stage impeller sector with one blade.
At each optimization iteration a consecutive call to different parts of the unified model takes place and as a result the impeller sector and air-gas channel sector solid models, and the 3D strength and aerodynamic analysis computational grids are modified, and then the necessary characteristics are performed.
This approach allows us to solve the problem of the agreement between the different requirements and the different impeller characteristics (aerodynamic, strength, weight, etc.), because these characteristics are carried out within unified computational space at each optimization iteration. During the process, according to the optimization problem statement, the characteristics of aerodynamics, strength, and weight are taken into account either as criterions or as restrictions.
As an additional restriction, the design and technological requirements are used. The improvement in the structure characteristics is carried out by searching the optimal combination of dimensions using the optimizer IOSO.
The approach described is applied for the improvement of HPC blisk-type first stage impeller characteristics. As an optimization criterion mass minimizing is used, as a restriction — the requirements are the static strength of the blade and disk, the condition of the blade in terms of dangerous resonance detuning, and the requirements for the conservation of stage and HPC pressure ratio, efficiency and flow rate.
As a result of the optimization, when the first four natural resonance frequency detuning of the blade is carried out, the total impeller mass is reduced by approximately 10% and the aerodynamic characteristics remain unchanged. In addition, the disk weight is reduced by about 12%.
At the same time, all the formulated restrictions on aerodynamic and strength characteristics are not broken.
The total optimization process is automated and takes place without user participation.