bluuebunny/crossref_metadata_2025_split huggingface dataset:
Circumferential Propagation Characteristic of Unsteady Flow in a Subsonic Axial Flow Compressor Rotor at Different Reynolds Numbers
Authors: Chen Zhiyang , Wu Yanhui , Zhang Yanwen , Gan Junwen , An Jinhuaiyuan 
Published: November 2019

Abstract
This paper studies the circumferential propagation characteristic of unsteady flow that occurs close to stall in a subsonic axial compressor rotor at different Reynolds number (Re). Experimental measurements are first conducted at high Re on the ground, and numerical investigations are carried out at two altitudes to explore the mechanism of circumferential propagation characteristic at different Re. The stability operating range of the compressor rotor gets small with the decrease of Re. Rotating instability (RI) is observed in the blade passage near the stall limit of the test rotor at high Re on the ground, which is characterized by a hump frequency band in the spectrum. Characteristic frequencies of numerical pressure signals at fixed frame are limited in the frequency band of RI at high Re. The cross power spectrums of numerical pressure signals detected in the neighboring passages suggest that circumferential disturbances rotates in the flow fields at different Re. Characteristic frequencies of the flow unsteadiness change with the decrease of Re. At high Re, the circumferential propagation of tip leakage flow unsteadiness is controlled by the interaction of the tip leakage flow and incoming flow, which is linked to RI. When the Re is reduced, the tip leakage flow gets weak and the radial flow from the hub to tip induced by the suction surface flow separation is dominant in the tip region. Thereafter, both the tip leakage flow and radial flow are associated with the blade tip loading, which changes the flow mechanism of RI.
A Prognostics and Health Management Framework for Wind
Authors: Sheng Shuangwen , Guo Yi 
Published: November 2019

Abstract
Operation and maintenance costs are a major driver for levelized cost of energy of wind power plants and can be reduced through optimized operation and maintenance practices accomplishable by various prognostics and health management (PHM) technologies. In recent years, the wind industry has become more open to adopting PHM solutions, especially those focusing on diagnostics. However, prognostics activities are, in general, still at the research and development stage. On the other hand, the industry has a request to estimate a component’s remaining useful life (RUL) when it has faulted, and this is a key output of prognostics. Systematically presenting PHM technologies to the wind industry by highlighting the RUL prediction need potentially helps speed up its acceptance and provides more benefits from PHM to the industry. In this paper, we introduce a PHM for wind framework. It highlights specifics unique to wind turbines and features integration of data and physics domain information and models. The output of the framework focuses on RUL prediction. To demonstrate its application, a data domain method for wind turbine gearbox fault diagnostics is presented. It uses supervisory control and data acquisition system time series data, normalizes gearbox temperature measurements with reference to environmental temperature and turbine power, and leverages big data analytics and machine-learning techniques to make the model scalable and the diagnostics process automatic. Another physics-domain modeling method for RUL prediction of wind turbine gearbox high-speed-stage bearings failed by axial cracks is also discussed. Bearing axial cracking has been shown to be the prevalent wind turbine gearbox failure mode experienced in the field and is different from rolling contact fatigue, which is targeted during the bearing design stage. The method uses probability of failure as a component reliability assessment and RUL prediction metric, which can be expanded to other drivetrain components or failure modes. The presented PHM for wind framework is generic and applicable to both land-based and offshore wind turbines.
Numerical Investigation of NOx Emissions Characteristics of a Natural Gas Premixed Burner Based on Chemical Reactor Network Model
Authors: Mu Bin , Lei Fulin , Shao Weiwei , Liu Xunwei , Zhang Zhedian , Xiao Yunhan 
Published: November 2019

Abstract
Numerical optimization of nitrogen oxides (NOx) formation is an essential factor during developing low pollution combustor of gas turbine. The Computational Fluid Dynamics-Chemical Reactor Network (CFD-CRN) hybrid method has a great advantage in fast and accurate prediction of combustor NOx emissions. In this work, a hybrid CFD-CRN approach is established to predict pollutant emissions of a lean premixed model burner for gas turbine applications. Several criteria are compared for separating the combustor into chemically and physically homogeneous zones, and the crucial parameters such as residence time and flue gas recirculation ratio are calculated. The CRN model is preliminarily verified with experimental data. The effects of pressure and fuel-air unmixedness on NOx formation are subsequently investigated. In addition, the effects of changes in fuel/air flow distribution and crucial parameters of CRN model on NOx emissions are also estimated under different pressures and fuel-air unmixedness. The combustor is divided into several zones including reaction preheating region, flame front region, flame transition region, post flame region, main recirculation region and corner recirculation region based on CFD results of fuel-air mixing characteristics, velocity field, temperature field, distribution of OH mass fraction and Damkohler number. The complex CRN model has the advantage of predicting NOx emission characteristics under higher Tad conditions compared with the simple model, and its prediction of NOx emission shows good agreement with experimental data under various equivalence ratio conditions. The structure and distribution of several regions of CRN model are analogous but not significant when Reynolds number exceeds 105 under high pressure. The pathway analysis shows that the NOx emission gradually decreases through N2O and NNH mechanisms, resulted from the decreasing concentration of O radical under low Tad and high pressure. However, the pressure could significantly promote thermal NOx formation resulting form increase of temperature. The fuel-air unmixedness results in the increase of maximum flame temperature, which has significant effect on change of the CRN regions-separating. The fuel-air unmixedness causes the significant increasing of thermal NOx formation.
Numerical Study of Radiation Heat Transfer for a Supercritical CO2 Turbine Linear Cascade
Authors: Khadse Akshay , Curbelo Andres , Kapat Jayanta S. 
Published: November 2019

Abstract
The fundamental research and technology development for supercritical CO2 (sCO2) power cycles is gaining worldwide popularity. This is due to their promise of high efficiency, compactness, wide-range-applicability and eco-friendliness. One of the active research areas in the sCO2 power cycle field is to increase cycle efficiency by utilizing a higher turbine inlet temperature. At high temperatures within turbines, radiation may contribute a significant portion of overall heat transfer. The purpose of this paper is to investigate and quantify the effects of radiation heat transfer within a first stage sCO2 turbine linear cascade. This particular topic has not been explored by researchers yet. The correct estimation of radiation heat transfer can prove to be critical for the design of turbine blade cooling system. The aerodynamic and heat transfer analysis of a turbine cascade is carried out using a commercial computational code, STAR-CCM+. Spectral absorption coefficient for CO2 is derived using HITRAN database at required temperature and pressure. Broadening and shifting of intensity lines due to high pressure and temperature are taken into consideration. A second approach utilizes Planck mean absorption coefficient as a function of temperature. Although the data can be extrapolated for the required higher pressure, accuracy of that extrapolated data cannot be verified. Hence the secondary purpose of this study is to encourage researchers to fill the fundamental gaps in the knowledge of CO2 radiation. Findings presented here suggest that radiation can be neglected for cooling system design of the sCO2 turbine stage 1 vane for both inlet temperatures of 1350K and 1775K.
Manufacture, Characterization and Stability Limits of an AM Prefilming Air-Blast Atomizer
Authors: Crayford Andrew P. , Lacan Franck , Runyon Jon , Bowen Philip J. , Balwadkar Shrinivas , Harper Joseph , Pugh Daniel G. 
Published: November 2019

Abstract
With the recent advancement of metallic additive manufacturing (AM), it is perceived that future gas turbines will be manufactured with significantly fewer parts, leading to both financial and safety improvements achieved from reductions in weight, assembly processes and failure modes associated with welded parts. In addition the design and manufacture of highly intricate parts such as fuel atomizers become free from the constraints of tooling, facilitating more complex internal flow geometries to be conceived which afford improved atomization, flame stability and hence combustion efficiency. However, it is noted that increased dimensional tolerances and surface roughness resulting from this manufacturing technique can detrimentally impact internal air and fuel flow paths and hence warrant further investigation. In this study a small-scale (200kW) pre-filming airblast atomizer, based on the Parker Hannifin commercial concept, and typical of injectors utilized in RQL aviation combustors, was manufactured by Cardiff School of Engineering’s High Value Manufacturing Laboratories. Direct metal laser sintering, was utilized to produce a fully operational single component part, manufactured in 316-grade stainless steel using a Renishaw AM250 system, providing a part with measured surface roughness (Ra) values of 12–26 μm in agreement with expected values reported in the literature. Operation of the injector as a single fluid atomizer demonstrated that the fuel channel and integrated swirlers were sufficiently accurate and concentric to result in a uniform spray pattern, displaying global liquid sheet structures which were in agreement with those previously reported. However, the effective area of the atomizer’s air-flow path, when evaluated using differential pressure measurements, was shown to be smaller than predicted, resulting in an increased pressure drop. Laser diffraction droplet sizing was utilized to evaluate the global SMD of the prefilming airblast water spray at atmospheric conditions, across a range of air to liquid ratios. SMD’s between 4.2–115μm were measured at corresponding air-flow rates of 3–25 g/s, with droplet sizes observed to decrease exponentially at higher air-flow rates. This data is again in excellent agreement with SMD correlations previously proposed. Flame stability experiments conducted at ambient pressure and elevated air temperature, demonstrated the stability of a conventional (JET A-1) fuel flame across a range of air and fuel flow rates, representative of pressure drops and AFRs in commercial operation. Further post-processing of the internal flow path walls and swirl vanes to reduce surface roughness is anticipated to result in a lower pressure drop across the air-path geometry, highlighting the potential for further improvements in AM injector performance.
Life Assessment of Large Gas Turbine Blades
Authors: Narasimhachary Santosh B. , Smith Kyle , Shinde Sachin R. , Amann Christian , Kadau Kai , Iyer Saiganesh 
Published: November 2019

Abstract
Large gas turbine nickel based superalloys blades are typically manufactured using an investment casting process. In spite of superior processing and quality control, large turbine blades may contain manufacturing induced discontinuities such as porosities, segregation, chemical inhomogeneities, particles, etc in few of the manufactured parts. These manufacturing discontinuities can significantly influence the reliable component life if they are under a load condition where they will form a crack. A typical engineering approach is to treat these discontinuities as a crack from the beginning of the part life. This leads to a conservative life prediction, as crack nucleation and influencing geometrical details of the discontinuities are neglected. This paper presents a framework and path forward for a comprehensive life assessment. It includes computer tomography (CT) analysis, metallographic analysis, local stress analysis, crack formation, as well as state of the art fracture mechanics analysis. For instance, CT and destructive tests reveal details of the geometry of a porous region and thereby enabling the calculation of crack formation life. A subsequent fracture mechanics analysis by engineering tool, FRANC3D can then yield a comprehensive life assessment for comparisons to experimental findings and fleet experience. This approach enables Siemens to diligently ensure that comprehensive life predication assessment has been performed for the components for robust and reliable operation.
Flame Edge Dynamics and Interaction in a Multi-Nozzle Can Combustor With Fuel Staging
Authors: Doleiden Daniel , Culler Wyatt , Tyagi Ankit , Peluso Stephen , O’Connor Jacqueline 
Published: November 2019

Abstract
The characterization and mitigation of thermoacoustic combustion instabilities in gas turbine engines is necessary to reduce pollutant emissions, premature wear, and component failure associated with unstable flames. Fuel staging, a technique in which the fuel flow to a multi-nozzle combustor is unevenly distributed between the nozzles, has been shown to mitigate the intensity of self-excited combustion instabilities in multiple nozzle combustors. In our previous work, we hypothesized that staging suppresses instability through a phase-cancellation effect in which the heat release rate from the staged nozzle oscillates out of phase with that of the other nozzles, leading to destructive interference that suppresses the instability. This previous theory, however, was based on chemiluminescence imaging, which is a line-of-sight integrated technique. In this work, we use high-speed laser-induced fluorescence to further investigate instability suppression in two staging configurations: center-nozzle and outer-nozzle staging. An edge-tracking algorithm is used to compute local flame edge displacement as a function of time, allowing instability-driven edge oscillation phase coherence and other instantaneous flame dynamics to be spectrally and spatially resolved. Analysis of flame edge oscillations shows the presence of convecting coherent fluctuations of the flame edge caused by periodic vortex shedding. When the system is unstable, these two flame edges oscillate together as a result of high-intensity longitudinal-mode acoustic oscillations in the combustor that drive periodic vortex shedding at each of the nozzle exits. In the stable cases, however, the phase between the oscillations of the center and outer flame edges is greater than 90 degrees (∼114 degrees), suggesting that the phase-cancellation hypothesis may be valid. This analysis allows a better understanding of the instantaneous flame dynamics behind flame edge oscillation phase offset and fuel staging-based instability suppression.
CFD and Experimental Analysis of Centrifugal Fans With Forward Curved Blades Used in Electric Motors
Authors: Borges S. S. 
Published: November 2019

Abstract
This work presents an analysis of the aerodynamic performance of a centrifugal fan with forward curved blades (Sirocco) applied to electric motors. In this analysis were carried out computational fluid dynamics (CFD) simulations and experimental tests for comparison of results.
The focus of this analysis is the performance comparison among three different models of general connection interface that are required for the connection between the grids of the rotating and stationary domains of CFD simulation, considering the method adopted by the Ansys CFX, software used as computational tool. Thereby, Frozen Rotor, Stage, and Transient Rotor-Stator were the interface models evaluated.
For comparison reference, the experimental data were used to evaluate the performance of each interface models for overall operating range of the fan.
Constitutive Modeling of TMF and Creep-Fatigue of a Ni-Base Alloy
Authors: O’Nora Nathan , Bouchenot Thomas , Geiger Grant , Gordon Ali P. 
Published: November 2019

Abstract
Engineering materials are often subjected to high temperatures and varying mechanical load, making them display both creep and fatigue. Viscoplastic models have been an attractive way to simulate the behavior of materials under these conditions due to their ability to capture the hysteresis, load rate, and stress relaxation effect exhibited by materials. Nickel-base alloys experience widespread use throughout pressure vessels and turbomachinery due to their ability to retain high strength at high temperature. In this study, the low-cycle fatigue (LCF), thermo-mechanical fatigue (TMF), and creep-fatigue (CF) of candidate material IN617 is modeled using the Chaboche viscoplasticity model. The Chaboche model is implemented using three non-linear kinematic hardening terms with static recovery included as well as nonlinear isotropic hardening. Methods for finding the kinematic and isotropic hardening from Ramberg-Osgood constants are presented to allow for model development to encompass all available data instead of fitting to specific data sets. A novel method for fitting the static recovery portion of the model from creep data is presented, allowing for the capture of complex loadings such as CF from standard creep tests. New temperature-dependent formulations of the Chaboche constants are presented for IN617. The model is compared to available test data and simulations are presented to show future experiments that could be run to further validate or improve the model.
Lagrangian Saddle Point Analysis in the Flow-Field of a Bluff-Body Stabilized Combustor
Authors: Premchand C. P. , George Nitin B. , Raghunathan Manikandan , Unni Vishnu R. , Sujith R. I. , Nair Vineeth 
Published: November 2019

Abstract
Experiments are performed in a partially-premixed bluff-body stabilized turbulent combustor by varying the mean flow velocity. Simultaneous measurements obtained for unsteady pressure, velocity and heat release rate are used to investigate the dynamic regimes of intermittency (10.1 m/s) and thermoacoustic instability (12.3 m/s). Using wavelet analysis, we show that during intermittency, modulation of heat release rate occurring at the acoustic frequency fa by the heat release rate occurring at the hydrodynamic frequency fh results in epochs of heat release rate fluctuations where the heat release is phase locked with the acoustic pressure. We also show that the flame position during intermittency and thermoacoustic instability are essentially dictated by saddle point dynamics in the dump plane and the leading edge of the bluff-body.
Effect of Blade Profile on Four-Passage Serpentine Configuration Designed to Negate Coriolis Effect on Heat and Fluid Flow
Authors: Sarja Ajay , Madhavan Srivatsan , Singh Prashant , Ekkad Srinath V. 
Published: November 2019

Abstract
Gas turbine blades are equipped with serpentine internal cooling channels with 180-degree bends, through which relatively colder air is routed to cool the internal walls. It has been established that under the influence of rotation, pressure and suction side internal wall heat transfer characteristics are very different, which leads to non-uniform metal temperatures, and hence higher levels of thermal stresses. Present study addresses this non-uniformity in heat transfer using parallel rotation to negate Coriolis effect. Further, the blade curvature does not allow rectangular or trapezoidal passages, which are typically studied. In this paper, we have numerically investigated a realistic design for the four-passage channel, where the cooling design can actually be incorporated in a blade. Four-passage configuration also features 90-degree square shaped rib turbulators, and the corresponding baseline case is smooth channel. Numerical simulations have been carried out at Reynolds numbers of 5000, 10000 and 25000 and Rotation numbers were varied between 0 and 0.25. For smooth case, heat transfer enhancement was found to be higher on suction (leading) side compared to pressure (trailing) side under both stationary and rotating conditions. The enhancement levels between stationary and rotation conditions varied marginally in these designs, indicating that buoyancy effects were insignificant. For ribbed case, the effect of 90-degree rib turbulators on local heat transfer was more pronounced on the suction side when compared to smooth case. Under rotating conditions, it was found that the cooling levels were similar to the stationary condition for both pressure and suction side internal walls.
A Non-Dimensional Approach for Generalizing the Particle Impact Behavior of Gas Turbine Fouling
Authors: Suman Alessio , Casari Nicola , Fabbri Elettra , Pinelli Michele , di Mare Luca , Montomoli Francesco 
Published: November 2019

Abstract
The consequences of particle deposition on gas turbine blade surface are studied since the first gas turbine application. The effects generated by particle adhesion range from performance deterioration to life reduction to complete loss of power. Even if, the effects generated by fouled blade surface are well known, the mechanisms responsible for the particle adhesion are still less clear. The variability related to the nature of materials, the impact conditions and the presence of promoting substances (such as water, oil, glue agents, etc.) imply several difficulties for comparing the results and for extracting general trends and rules useful for generating up-to-date predictive models.
In the present work, an attempt to realize a general comparison among several different particle deposition tests is carried out. Starting from the previous review work, which has collected experimental tests carried out over thirty years, in the present study, an original elaboration data is proposed. Over seventy adhesion tests realized with particle composition, size, velocity, and temperature similar to those characterize gas turbine fouling are collected and post-processed. After a dimensional analysis, the data are then classified using non-dimensional groups such as Reynolds, Weber, and Ohnesorge numbers. In this way, general threshold values for the transitions between erosion, deposition, and splashing are identified according to the literature data. This general tool allows the a priori identification of the driving phenomena (such as inertia, viscous/capillary forces), based on the knowledge of basic inputs (such as impact and particle characteristics). The general approach adopted in this work gives the opportunity to increase the gas turbine fouling knowledge based on an interdisciplinary approach.