bluuebunny/crossref_metadata_2025_split huggingface dataset:
Data Selection and Feature Engineering for the Application of Machine Learning to the Prediction of Gas Turbine Trip
Authors: Losi Enzo , Venturini Mauro , Manservigi Lucrezia , Ceschini Giuseppe Fabio , Bechini Giovanni , Cota Giuseppe , Riguzzi Fabrizio 
Published: September 2021

Abstract
A gas turbine trip is an unplanned shutdown, of which the consequences are business interruption and a reduction of equipment remaining useful life. Therefore, detection and identification of symptoms of trips would allow predicting its occurrence, thus avoiding damages and costs.
The development of machine learning models able to predict gas turbine trip requires the definition of a set of target data and a procedure of feature engineering that improves machine learning generalization and effectiveness.
This paper presents a methodology that focuses on the steps that precede the development of a machine learning model, i.e., data selection and feature engineering, which are the key for a successful predictive model.
Data selection is performed by partitioning units into homogeneous groups according to different criteria, e.g., type, region of installation, and operation. A subsequent matching algorithm is applied to rotational speed data of multiple gas turbine units to identify start-ups and shutdowns so that the considered units can be partitioned according to their operation, i.e., base load or peak load.
Feature engineering aims at creating features that improve machine learning model accuracy and reliability. First, the Discrete Fourier Transform is used to identify and remove from the time series the seasonal components, i.e., patterns that repeat with a given periodicity. Then, new features are created based on gas turbine domain knowledge in order to capture the complex interactions among system variables and trip occurrence.
The outcomes of this paper are the definition of a set of target examples and the identification of a meaningful set of features suitable to develop a machine learning model aimed at predicting gas turbine trip.
Prediction of Gas Turbine Trip: a Novel Methodology Based on Random Forest Models
Authors: Losi Enzo , Venturini Mauro , Manservigi Lucrezia , Ceschini Giuseppe Fabio , Bechini Giovanni , Cota Giuseppe , Riguzzi Fabrizio 
Published: September 2021

Abstract
A gas turbine trip is an unplanned shutdown, of which the most relevant consequences are business interruption and a reduction of equipment remaining useful life. Thus, understanding the underlying causes of gas turbine trip would allow predicting its occurrence in order to maximize gas turbine profitability and improve its availability.
In the ever competitive Oil & Gas sector, data mining and machine learning are increasingly being employed to support a deeper insight and improved operation of gas turbines. Among the various machine learning tools, Random Forests are an ensemble learning method consisting of an aggregation of decision tree classifiers.
This paper presents a novel methodology aimed at exploiting information embedded in the data and develops Random Forest models, aimed at predicting gas turbine trip based on information gathered during a timeframe of historical data acquired from multiple sensors. The novel approach exploits time series segmentation to increase the amount of training data, thus reducing overfitting.
First, data are transformed according to a feature engineering methodology developed in a separate work by the same authors. Then, Random Forest models are trained and tested on unseen observations to demonstrate the benefits of the novel approach. The superiority of the novel approach is proved by considering two real-word case-studies, involving filed data taken during three years of operation of two fleets of Siemens gas turbines located in different regions.
The novel methodology allows values of Precision, Recall and Accuracy in the range 75–85 %, thus demonstrating the industrial feasibility of the predictive methodology.
Studying the Effect of Porosity of Porous Layer Coating on the Performance of the Horizontal Tubular Falling Film Evaporator
Authors: Ibrahim Alaa Adel , Elgamal Hassan , Elmekawy Ahmed M. Nagib 
Published: September 2021

Abstract
Through the recent decades, many studies have focused on finding efficient methods to enhance the heat transfer performance in heat exchangers. Therefore, using porous media attracted many researchers, as it is such a simple, efficient, and low-cost technique in enlarging the surface contact area of heat transfer through the fluid pass. Nevertheless, there is little work associated with using porous media to enhance the thermal performance of falling film evaporators. The present study seeks to discuss numerically the liquid flow behaviour over falling film evaporator tubes in the case of bare tubes and tubes with porous layer coating. The two-dimensional multi-phase numerical simulations are also carried out in order to investigate the effect of the porosity ratio of the porous medium added to the tubes in the heat transfer performance. Furthermore, deducing the way to select a decent porosity ratio to be used to get the best thermal performance is demonstrated through the study. Time-averaged results gained from the numerical simulations have been compared to those of bare-tube falling film evaporator to observe much higher heat transfer performance represented in the average surface Nusselt number (Nu) which increased by 3 times.
On the Forced Response Predictions and Life Improvements of an Industrial Axial Compressor Rotor Blade
Authors: Krishnababu Senthil , Bruni Giuseppe , Frach Agnieszka 
Published: September 2021

Abstract
Improvements made to the high cycle fatigue life of an industrial compressor rotor blade for tip active modes through aerodynamic design changes and aero-mechanical assessments are presented in this paper. Typical aero-mechanical computations involved utilising an in-house linear-harmonic solver to compute the aero damping. In parallel, a novel hybrid model with whole-anulus domain for the blade rows of interest followed by a single passage domain for the rest of the compressor was used to compute the modal forcing. In addition to the standard blade passing resonances, low engine order excitations due to vane number differences, were analysed. This was achieved within a time frame consistent with the product design cycle by using TurboStream, a GPU based non-linear time domain unsteady flow solver. The excitation due to low engine order resonance was found to be influenced by a harmonic of upstream blade passing frequency. When considering a design change targeting HCF life, the calculated reserve factors showed significant improvements for the tip modes of interest. The subsequent engine tests carried out with tip timing agreed closely with the predictions thus validating not only the design but also the forced response prediction process.
Investigation on Mode Characteristics of Rotating Instability and Rotating Stall in an Axial Compressor
Authors: Yang Zeyuan , Wu Yadong , Ouyang Hua 
Published: September 2021

Abstract
Rotating instability (RI) and rotating stall (RS) are two types of aerodynamic instability in axial compressors. The former features the side-by-side peaks below the blade passing frequency (BPF) in frequency spectra, and the latter represents one or more stall cells rotating in the compressor. This paper presents an experimental on the nearfield pressure and farfield acoustic characteristics of RI phenomenon in a low-speed axial compressor rotor, which endures both RI and RS at several working conditions. In order to obtain the high-order modes of RI and other aerodynamic instability, a total of 9 or 20 Kulites are circumferentially mounted on the casing wall to measure the nearfield pressure fluctuation using a mode order calibration method. Meantime in the farfield 16 microphones are planted to measure the acoustic mode order using the compressive sensing method. Through calibration the experiments acquire the mode orders generated by RI and the interaction between RI and BPF, which is higher than the number of transducers. As for RS, the mode decomposition shows a mode order of 1, indicating one single stall cell rotating in the compressor. This experiment also shows that amplitude of RI modes is decreased when RS occurs, but RS modes and RI modes will both be enhanced if the flow rate is further reduced. This experiment reveals that RI experiences three stages of “strengthen-weaken-strengthen”, and hence RI may not be regarded only as “prestall” disturbance.
Composite UHBR Fan for Forced Response and Flutter Investigations
Authors: Eggers Torben , Friedrichs Jens , Goessling Jan , Seume Joerg R. , Natale Nunzio , Flüh Jan Peter , Paletta Nicola 
Published: September 2021

Abstract
In the CA3ViAR (Composite fan Aerodynamic, Aeroelastic, and Aeroacoustic Validation Rig) project, a composite low-transonic fan is designed and tested. The aim is a scaled ultra-high bypass ratio (UHBR) fan with state-of-the-art aerodynamic performance and composite rotor blades, which features aeroelastic phenomena, e.g. forced response by inlet distortions and flutter, under certain operating points within the wind tunnel. In this paper, the aerodynamic and aeroelastic design process starting from the overall performance specifications to a threedimensional numerical model is described. A target of eigen-frequency and twist-to-plunge ratio is specified such that flutter occurs at desired operating conditions with a sufficient margin with respect to the working line. Different materials and layups of the composite blade are analyzed to reach the structural target. The fan should serve as an open test case to advance the future research on aerodynamic, aeroelastic, and aeroacoustic performance investigations in a wide range of operating conditions. A preliminary fan stage design is presented in this paper.
Design and Analysis of an Aircraft Thermal Management System Linked to a Low-Bypass Ratio Turbofan Engine
Authors: Clark Robert A. , Shi Mingxuan , Gladin Jonathan , Mavris Dimitri 
Published: September 2021

Abstract
The design of an aircraft thermal management system (TMS) that is capable of rejecting heat loads into the bypass stream of a typical low-bypass ratio turbofan engine, or a ram-air stream, is investigated. The TMS consists of an air cycle system (ACS), which is similar to the typical air cycle machines (ACMs) used on current aircraft, both military and commercial. This system turbocharges compressor bleed air and uses heat exchangers in a ram air stream or the engine bypass stream to cool the engine bleed air prior to expanding it to low temperatures suitable for heat rejection. In this study, a simple low-bypass ratio afterburning turbofan engine was modeled in NPSS to provide boundary conditions to the TMS system throughout the flight envelope of a typical military fighter aircraft. The engine was sized to produce sea level static (SLS) thrust roughly equivalent to that of an F-35-class engine. Two different variations of the TMS system, a ram air cooled and a bypass air cooled, were sized to handle a given demanded aircraft heat load, which might include environmental control system (ECS) loads, avionics cooling loads, weapons system loads, or other miscellaneous loads. The architecture and modeling of the TMS is described in detail, and the ability of the sized TMS to reject these demanded aircraft loads throughout several key off-design points was analyzed, along with the impact of ACS engine bleeds on engine thrust and fuel consumption. A comparison is made between the cooling capabilities of the ram-air stream versus the engine bypass stream, along with the benefits and drawbacks of each cooling stream. It is observed that the maximum load dissipation capability of the TMS is tied directly to the amount of engine bleed flow, while the level of bleed flow required is set by the temperature conditions imposed by the aircraft cooling system and the heat transfer fluid used in the ACS thermal transport bus. Furthermore, the higher bypass stream temperatures significantly limit the thermodynamic viability and capability of a TMS designed with bypass air as the ultimate heat sink.
The results demonstrate the advantage that adaptive, variable cycle engines (VCEs) may have for future military aircraft designs, as they combine the best features of the two TMS architectures that were studied here.
Low-Order Modeling of Can-Annular Combustors
Authors: Fournier Guillaume J. J. , Meindl Max , Silva Camilo F. , Ghirardo Giulio , Bothien Mirko R. , Polifke Wolfgang 
Published: September 2021

Abstract
Heavy-duty land-based gas turbines are often designed with can-annular combustors, which consist of a set of identical cans, acoustically connected on the upstream side via the compressor plenum, and, downstream, with a small annular gap located at the transition with the first turbine stage. The modeling of this cross-talk area is crucial to predict the thermo-acoustic modes of the system. Thanks to the discrete rotational symmetry, Bloch wave theory can be exploited to reduce the system to a longitudinal combustor with a complex-valued equivalent outlet reflection coefficient, which models the annular gap. The present study reviews existing low-order models based purely on geometrical parameters and compares them to 2D Helmholtz simulations. We demonstrate that the modeling of the gap as a thin annulus is not suited for can-annular combustors and that the Rayleigh conductivity model only gives qualitative agreement. We then propose an extension for the equivalent reflection coefficient that accounts not only for geometrical but also flow parameters, by means of a characteristic length. The proposed model is in excellent agreement with 2D simulations and is able to correctly capture the eigenfrequencies of the system. We then perform a Design of Experiments study that allows us to explore various configurations and build correlations for the characteristic length. Finally, we discuss the validity limits of the proposed low-order modeling approach.
Numerical Investigation of Air-Oil Two-Phase Flow Pattern Transition in the Scavenge Line of an Aeroengine
Authors: Sekrani Ghofrane , Dick Jean-Sebastien , Poncet Sébastien , Nallamothu Sravankumar 
Published: September 2021

Abstract
Since most research investments in aeroengines have been targeted at the hot and cold sections, the oil system has remained an area poorly understood. Optimum sizing of the oil system can directly reduce the engine’s weight and specific fuel consumption while maximizing service life. The understanding of air/oil interaction in scavenge lines is required to influence the design of the oil systems and achieve those objectives.
The challenge is in the existence of numerous possible flow regimes and phase interactions. In scavenge lines, a complex two-phase flow results from the interaction of sealing airflow and lubrication oil. Scavenge lines can have bends, junctions and sudden area changes which complicates their modeling by amplifying pressure gradients and turbulence generation, and causing the flow to change morphology (annular, slug, stratified, bubbly, mist, etc.).
Several multiphase flow approaches have been developed to model two-phase flow in straight scavenge lines. However, up until now, no methodology is preferred by the community for simulating two-phase flow in such application. There are still many unknowns regarding the modeling of turbulence, phase interaction and the compressibility of immiscible mixtures such as air and oil.
The present study compares the performance of two numerical models: Volume of Fluid (VOF) and Algebraic Interfacial Area Density (AIAD), for simulating the air/oil flow in a suddenly expanding scavenge line against the experimental data of Ahmed et al. [1–2]. The AIAD model is a two-fluid Eulerian approach newly implemented on Ansys Fluent. Discrepancies between the two models for predicting pressure loss and void fraction are evaluated and discussed into details. The flow regime before and after the sudden expansion is identified using iso-surfaces of the void-fraction and compared against visual data. Based on the results presented, recommendations are formulated for further work regarding the calibration of AIAD modeling parameters.
Rubbing Of a Bladed Disk Considering Coriolis Effect: A Reduced Model Based on Complex Modal Analysis
Authors: Chen Dawei , Zhang Jiguo , Xiao Jiaguangyi , Chen Yong 
Published: September 2021

Abstract
Due to the high demands of aerodynamic efficiency in modern aero-engines, tip clearances between blades and casings are becoming smaller. This increases the possibility of rubbing between rotating bladed disks and their surrounding casings. Rotational effects exhibit increased significance in the latest generation of fans, which currently have relatively long blade and elongated cantilevered shaft. Previous studies on the rotor dynamics during rub impact have mainly focused on simplified models. However, it is necessary to take both realistic blades and Coriolis effect into account. Based on an open-source bladed disk model, the impact of the Coriolis effect on rub-induced responses is investigated. A two-step model reduction method is adopted by combining the fixed interface reduction and cyclic symmetry reduction. Both centrifugal and gyroscopic effects are incorporated in the numerical model. Complex modal analysis, based on classical Craig-Bampton method, is used to improve the model reduction of the gyroscopic system. The response of a flexible bladed disk to a simplified pulse rubbing force is investigated. With the time and space Fourier transform, a Coriolis-induced frequency split is observed on some nodal diameter lines, which indicates the significance of the Coriolis effect in rub-induced responses. A complex model reduction has been successfully applied to the rub-impact problem of cyclic symmetric bladed disks. Compared with the classical model reduction, the numerical results obtained by complex modal analysis are more reasonable. This lays a solid foundation for further rub-impact research considering rotor dynamics.
Effect of Accelerating Convergence in Adjoining 1D Domains Having Large Difference in Thermal Time Scales
Authors: Kaushik Tanvi , Wang Liangyu , Basani Jaydeep , Xu Fang 
Published: September 2021

Abstract
Combustor liners are subjected to high operating temperatures and high temperature gradients, which have an adverse effect on the durability of liners. Accurate prediction of liner wall temperature distribution can provide better insight into the design of effective cooling systems that have the potential to improve liner structure life.
When compared to RANS (Reynolds averaged Navier Stokes), LES (Large eddy simulation) framework provides better accuracy in resolving the large range of temporal and spatial scales of turbulent flow inside combustors. In simulations in which an unsteady LES fluid solver is interacting with an unsteady solid thermal solver, it would be impractical to advance and synchronize fluid and solid domains in physical time, due to a large difference between small fluid time scales set by turbulence and large solid time scales set by the thermal inertia of the solid. By advancing the fluid and solid solvers with different time step sizes, or by loosely coupling fluid and solid solvers such that they communicate at a defined frequency, convergence can be artificially accelerated. The convergence of the predicted temperature field solution is dependent on the implementation methodology of the acceleration techniques.
A combustor liner is subjected to hot turbulent gases on one side of its boundary and relatively colder air on the other side. This scenario is analyzed to understand the effect of accelerating convergence on the temperature field in a simplified 1D linear framework. A representative polychromatic temperature wave that a combustor liner is subjected to, is used in defining the boundary condition of a 1D implicit unsteady heat conduction solver.
Ignition Delay Time Correlation of C1 – C5 Natural Gas Blends for Intermediate and High Temperature Regime
Authors: Mohamed A. Abd El-Sabor , Sahu Amrit Bikram , Panigrahy Snehasish , Bourque Gilles , Curran Henry 
Published: September 2021

Abstract
New ignition delay time (IDT) data for stoichiometric natural gas (NG) blends composed of C1 – C5 n-alkanes with methane as the major component were recorded using a high pressure shock tube (ST) at reflected shock pressures (p5) and temperatures (T5) in the range 20–30 bar and 1000–1500 K, respectively. The good agreement of the new IDT experimental data with literature data shows the reliability of the new data at the conditions investigated. Comparisons of simulations using the NUI Galway mechanism (NUIGMech1.0) show very good agreement with the new experimental results and with the existing data available in the literature. Empirical IDT correlation equations have been developed through multiple linear regression analyses for these C1 – C5 n-alkane/air mixtures using constant volume IDT simulations in the pressure range pC = 10–50 bar, at temperatures TC = 950–2000 K and in the equivalence ratio (φ) range 0.3–3.0. Moreover, a global correlation equation is developed using NUIGMech1.0, to predict the IDTs for these NG mixtures and other relevant data available in the literature. The correlation expression utilized in this study employs a traditional Arrhenius rate form including dependencies on the individual fuel fraction, TC, φ and pC.
Coupling of Endwall and Aerofoil Optimisation on a Low-Speed Compressor Tandem Stator
Authors: Straccia Mattia , Gümmer Volker 
Published: September 2021

Abstract
The scope of this paper is to provide clarity over fundamental effects of non-axisymmetric endwall contouring in a highly-loaded compressor tandem stator. Specifically, the focus of the research will be the influence that aerofoil optimization and end-wall contouring have on each other, and how a combined optimization of the two simultaneously affects the final design of the optimized geometry. The reference geometry used in this research is a standard tandem vane arrangement with smooth axi-symmetric endwalls and designed to represent a datum stage configuration for future investigations of such blade geometries, experimental work on a low-speed research compressor being a next step. The optimization was performed using an in-house developed routine coupled with Auto-Opti, an automated optimizer based on an evolutionary strategy algorithm, developed by the DLR Institute of Propulsion Technology. The entire optimization was conducted solely on the stator, modeled as an annular cascade. This paper reports about a thorough flow field analysis of the optimized geometry in order to understand local mechanisms occurring with non-axisymmetric contouring in the tandem stator passage flow field and its overall performance. Furthermore, it describes and explains the effect that the aerofoil optimization has on the contoured hub surface shape, compared to an optimization process, which is only applied to the hub contouring. In particular, the results clarify how endwall flow field improvements reduce the degree of required aerofoil deformation, and show that the new blade shape is better adapted to the contoured endwall. The 3D endwall flow field has been investigated in order to understand how the optimized geometry modifies the magnitude of the cross-passage flow and reduces the size of the trailing edge corner vortex of the front and rear tandem vane. The paper concludes with some guidelines on how endwall contouring and near endwall aerofoil section design and optimization can be applied most effectively.