bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modelling of Partially Wetting Liquid Film Using an Enhanced Thin Film Model for Aero-Engine Bearing Chamber Applications
Authors: Singh K. , Sharabi M. , Jefferson-Loveday R. , Ambrose S. , Eastwick C. , Cao J. , Jacobs A. 
Published: January 2021

Abstract
In the case of aero-engine, thin lubricating film servers dual purpose of lubrication and cooling. Prediction of dry patches or lubricant starved region in bearing or bearing chambers are required for safe operation of these components. In the present work thin liquid film flow is numerically investigated using the framework of the Eulerian thin film model (ETFM) for conditions which exhibit partial wetting phenomenon. This model includes a parameter that requires adjustment to account for the dynamic contact angle. Two different experimental data sets have been used for comparisons against simulations, which cover a wide range of operating conditions including varying the flow rate, inclination angle, contact angle, and liquid-gas surface tension coefficient. A new expression for the model parameter has been proposed and calibrated based on the simulated cases. This is employed to predict film thickness on a bearing chamber which is subjected to a complex multiphase flow. From this study, it is observed that the proposed approach shows good quantitative comparisons of the film thickness of flow down an inclined plate and for the representative bearing chamber. A comparison of model predictions with and without wetting and drying capabilities is also presented on the bearing chamber for shaft speed in the range of 2,500 RPM to 10,000 RPM and flow rate in the range of 0.5 liter per minute (LPM) to 2.5 LPM.
Machine Learning for the Development of Data Driven Turbulence Closures in Coolant Systems
Authors: Hammond James , Montomoli Francesco , Pietropaoli Marco , Sandberg Richard D. , Michelassi Vittorio 
Published: January 2021

Abstract
This work shows the application of Gene Expression Programming to augment RANS turbulence closure modelling for flows through complex geometry, designed for additive manufacturing. Specifically, for the design of optimised internal cooling channels in turbine blades. One of the challenges in internal cooling design is the heat transfer accuracy of the RANS formulation in comparison to higher fidelity methods, which are still not used in design on account of their computational cost. However, high fidelity data can be extremely valuable for improving current lower fidelity models and this work shows the application of data driven approaches to develop turbulence closures for an internally ribbed duct. Different approaches are compared and the results of the improved model are illustrated; first on the same geometry, and then for an unseen predictive case.
The work shows the potential of using data driven models for accurate heat transfer predictions even in non-conventional configurations.
Study on Flow and Heat Transfer Characteristics of a New-Proposed Alternating Elliptical U-Channel
Authors: Xiao Kun , He Juan , Feng Zhenping 
Published: January 2021

Abstract
This paper proposed an alternating elliptical U-shaped internal cooling channel and investigated the flow and heat transfer characteristics, based on the optimal flow field structure deduced from the Field Synergy Principle. The channel consisted of the straight sections and the transition sections. In the straight sections, the cross section of the channel is ellipse, and in the transition sections, the long axis gradually shortened into the short axis, and the short axis gradually expanded to the long axis. However, the cross-section area of the channel remained unchanged.
Numerical simulations were performed to solve 3D steady Reynolds-averaged Navier-Stokes equations (RANS) with the standard k-ε turbulence model. The influence of alternating of the cross section on heat transfer and pressure drop of the channel was studied by comparing with the smooth elliptical U-shaped channel, and all the cases were conducted with the Re numbers from 10,000 to 40,000. On this basis, the investigation on alternating elliptical U-shaped internal cooling channel performance was made mainly into two parts. One was the effect of aspect ratio which was set as from 1.1 to 2.0, while the other was the effect of alternating angle θ which was set as from 10° to 90°.
The results showed that for the flow field, there was no vortex in the first pass of the smooth elliptical U-shaped channel. On the contrary, in the first pass of the alternating elliptical U-shaped channel, after the transition section, for different Re numbers, four or eight longitudinal vortices were generated. In the second pass, the flow separation in smooth elliptical U-shaped channel was serious because of the centrifugal force at the elbow, while the alternating elliptical channel restrained the flow separation to a certain extent and formed a double-vortex structure just like the vortex cooling. The average Nusselt number of the alternating elliptical U-shaped channel was significantly higher than that of the straight channel, but the pressure loss increased slightly. In addition, with the increase of aspect ratio, the thermal performance of the channel increased in the study range, and when the alternating angle is between 40° to 90°, the thermal performance nearly kept constant and the best.
Exploring the Presence of Pressure Waves in Axial Compressor Cascades
Authors: Leggett John , Sandberg Richard 
Published: January 2021

Abstract
The presence of pressure waves in an axial compressor cascade are ubiquitous and have been known and investigated for some time. Much of the work to date focuses on compressor acoustics and vibration, which is largely due to wake blade interactions and trailing edge shedding. However, it has been shown on free aerofoils that pressure waves can be produced from volume sources, such as separation, at non-negligible amplitudes. The work presented here highlights the presence of pressure waves emanating from the suction surface transition of a NACA 65 axial compressor cascade, and briefly investigates and details the influence different free-stream disturbances have on the frequency of the pressure waves produced.
Creation of Models of Fan Blades According to Airfoil Measurements
Authors: Arkhipov Alexandr N. , Ravikovich Yury A. , Kholobtsev Dmitry P. 
Published: January 2021

Abstract
One of the main parts of the engine for the regional aircraft, affecting its efficiency and reliability, is the fan blade, which is designed based on aerodynamic and mechanical integrity (MI) optimization and has a complex geometry of the airfoil. At some operating modes, the aerodynamic and MI characteristics of the blades may deteriorate due to geometric deviations from the nominal airfoil at manufacture. Thus, to increase the robustness of the fan blades, it is necessary to solve the problem of creation of the fan blade models and the arrangement of the blades in the wheel, taking into account the actual geometric parameters.
Aerodynamic and MI calculations of blades with real geometric deviations of the airfoil should be carried out using numerical three-dimensional (3D) methods. In this case, it is important to create 3D models of blades and to carry out their subsequent calculation at minimal costs.
The method of automated creation of a model of finished blades with real production deviations of the airfoil according to the data of measurement in the CAD system is presented.
Since more than 1000 measured points are used in the construction of the model of the measured blade, it is more convenient to reduce the number of initial points (parameters) for robust optimization of the fan blades.
A program has been developed, which is a macro written in the programming language PHYTON, working together with the selected CAD-system Siemens NX, which significantly reduces the time to prepare models for aerodynamic and MI calculations.
Full Flight Envelope Transient Main Control Loop Design Based on LMI Optimization
Authors: Miao Keqiang , Wang Xi , Zhu Meiyin 
Published: January 2021

Abstract
To solve the problem of full flight envelope transient main control loop design of turbofan engine, a design method based on linear matrix inequality (LMI) is proposed. Robust stability of the closed-loop turbofan engine system in all conditions is proved by using Lyapunov inequalities. The robust performance is ensured by gain-schedule and pole-placement. Reduced order multivariable gain-schedule and minimum trace optimization algorithm are presented to guarantee the feasibility of the design method. Full flight envelope simulations based on a nonlinear turbofan engine model were done. The results show that the maximum settling time of N1cor is 4.3s and the maximum overshoot is 1.7%. The maximum settling time of N2cor is 4.5s and the maximum overshoot is 0.1%. The robust stability and consistent performance in full flight envelope are also shown in the results.
Elimination of Numerical Damping in the Stability Analysis of Non-Compact Thermoacoustic Systems With Linearized Euler Equations
Authors: Hofmeister Thomas , Hummel Tobias , Berger Frederik , Klarmann Noah , Sattelmayer Thomas 
Published: January 2021

Abstract
The hybrid Computational Fluid Dynamics/Computational AeroAcoustics (CFD/CAA) approach represents an effective method to assess the stability of non-compact thermoacoustic systems. This paper summarizes the state-of-the-art of this method, which is currently applied for the stability prediction of a lab-scale configuration of a perfectly-premixed, swirl-stabilized gas turbine combustion chamber at the Thermodynamics institute of the Technical University of Munich. Specifically, 80 operational points, for which experimentally observed stability information is readily available, are numerically investigated concerning their susceptibility to develop thermoacoustically unstable oscillations at the first transversal eigenmode of the combustor. Three contributions are considered in this work: (1) flame driving due the deformation and displacement of the flame, (2) visco-thermal losses in the acoustic boundary layer and (3) damping due to acoustically induced vortex shedding. The analysis is based on eigenfrequency computations of the Linearized Euler Equations with the stabilized Finite Element Method (sFEM). One main advancement presented in this study is the elimination of the non-physical impact of artificial diffusion schemes, which is necessary to produce numerically stable solutions, but falsifies the computed stability results.
Improvement of the Inverse Finite Element Analysis Approach for Tensile and Toughness Predictions by Means of Small Punch Technique
Authors: Kulawinski Dirk , Iding Kevin , Schornstein Robin , Özdemir-Weingart Dasgin , Dumstorff Peter 
Published: January 2021

Abstract
This paper focuses on the inverse FEA to calculate the SPT tests and the prediction of the tensile and fracture toughness behavior. For the description of the SPT tests via FEA the hardening rule of Ramberg-Osgood and the damage model of Gursson-Tvergaard-Needleman (GTN) were used. The inverse FEA optimization process cannot provide a unique solution for the 12 parameters included in the material model. This results from a dependency between some parameters, which leads to the same solution in the optimization. Hence a novel description of the dependent parameters was developed and implemented within the optimization process. Therefore, an enhanced inverse FEA approach was proposed which provides a fast converging solution for determination of the material model parameters. Within this study the forged turbine shaft material EN: 27NiCrMoV15-6 was investigated. For comparison purposes SPT tests as well as tensile tests and fracture toughness tests were carried out. In the case of the tensile properties the test and simulation show coincidence in the curve as well as the characteristic values. For the toughness behavior the characteristic value of the test was met by the simulation.
Model-Based Analysis of a Combined Heat and Power System Featuring a Hydrogen-Fired Gas Turbine With On-Site Hydrogen Production and Storage
Authors: Bexten Thomas , Wirsum Manfred , Roscher Björn , Schelenz Ralf , Jacobs Georg 
Published: January 2021

Abstract
Hydrogen-fired gas turbines have the potential to play an important role in decarbonized energy sectors. However, a demand-oriented supply of CO2-neutral hydrogen for the operation of gas turbines is technically and economically challenging. These challenges mainly arise due to various interdependencies between the volatility of renewable power generation, available hydrogen production capacities, available hydrogen storage capacities and the operational demands to be met by gas turbines. The present study aims to quantify these interdependencies by conducting a detailed model-based analysis of an exemplary combined heat and power system featuring a hydrogen-fired industrial gas turbine with on-site hydrogen production via electrolysis and on-site hydrogen storage in pressure vessels. In order to identify the sought-after interdependencies, simulation runs featuring various combinations of available hydrogen production and storage capacities are analyzed. If only local power surpluses are utilized for the electrolysis, the obtained results reveal a strong non-linear impact of both the hydrogen production capacity and the storage capacity on the ability to provide hydrogen for the gas turbine. Furthermore, the results indicate that an exclusive utilization of local power surpluses leads to very limited periods of hydrogen-based gas turbine operation and low utilization rates of the available hydrogen production and storage capacities. If additional power for the operation of electrolyzers is supplied by the grid, increased utilization rates and prolonged periods of hydrogen-based gas turbine operation can be achieved. However, in order to realize an overall reduction of CO2 emissions, this mode of operation requires the supply of large quantities of renewable power by the grid. Furthermore, the results of an additional economic analysis reveal that both investigated operational modes are currently not economically viable within the considered economic framework.
Detection of Unit of Measure Inconsistency by Means of a Machine Learning Model
Authors: Manservigi Lucrezia , Murray Daniel , de la Iglesia Javier Artal , Ceschini Giuseppe Fabio , Bechini Giovanni , Losi Enzo , Venturini Mauro 
Published: January 2021

Abstract
The evaluation of sensor reliability is fundamental for all types of energy systems. Regardless of the environment in which a sensor is installed, only a reliable measurement can lead to optimal decisions about system operation and health state. In fact, a faulty sensor may provide misleading information for decision making, at the expense of business interruption and maintenance-related costs.
In the literature, several checks are performed in order to detect sensor faults, such as out of range, stuck signal, dithering, standard deviation, trend coherence, spike and bias.
However, process anomalies have been rarely investigated, though they often introduce errors whereby the unit of measure of a sensor is wrongly assumed. In this paper such a situation is named Unit of Measure Inconsistency (UMI).
To this aim, the authors exploit a Machine Learning model, namely a Support Vector Machine, by considering four different approaches for UMI detection and analyzing two field datasets acquired from Siemens gas turbines.
Among all tested approaches, the Radial Basis Function with One-vs-One decomposition proved to be the most effective approach, since it demonstrated its effectiveness and robustness in the majority of the analyses.
Thanks to the selected approach, the actual information regarding sensor unit of measure can be provided and further sensor and engine diagnoses can be safely performed.
Methodology for Simulation of Soak-Back in a Helicopter Engine Bay Using Lattice Boltzmann Method
Authors: Bonnal Benoît , Vanoli Emmanuel , Placko Amélie , Combébias Sébastien 
Published: January 2021

Abstract
Soak-back conditions are a crucial challenge for engine manufacturers to reduce the turnaround time between flights and improve engine durability and security. The natural convection conditions at stake make the numerical predictions of the flow and thermal behaviors rather difficult, when not prohibitively expensive. Consequently, the topic is still assessed with tests which can only be performed at a very late stage of the engine development and do not provide a good overview of the physics behind. Failures discovered so late are extremely expensive and complex to solve.
This paper presents the first phase of a methodology development to tackle the soak-back of an engine with the SIMULIA PowerFLOW Suite Computational Fluid Dynamics code. Comparisons for validation are made with the tests on one hand, and with ANSYS Fluent RANS (Reynolds Averaged Navier-Stokes) simulations whenever possible. The work conducted so far focuses on the engine bay only with coupled fluid-thermal simulations while the core flow is simplified into a 1D fluid nodes network.
A first simplified approach has proved to recover some of the phenomena observed in both the tests and RANS simulations. It failed however to match the initial temperatures of the soak phase, which is consistent with the choice of modelization made. Improvements to the model were therefore brought by adding more complexity and fidelity to the geometry, environment and tests scenario. The new results significantly improve the comparisons with the tests and RANS simulations. Some differences on absolute temperature levels and evolution rates remain here and there and highlight the necessity to improve the core flow modelization, which is what the next phase of the methodology development will focus on.
Operation and Maintenance Improvements of Steam Turbines Subject to Frequent Start by Rotor Stress Monitoring
Authors: Bucciarelli Federico , Checcacci Damaso , Girezzi Gabriele , Signorini Annamaria 
Published: January 2021

Abstract
Steam Turbines operating in Concentrated Solar Plants and Peaking Combined Cycles are subjected to daily thermal stresses, induced by start-ups and load variations, deeply affecting allowed production per day. The extent and number of such thermal stresses is largely depending on the capability, of both plant and operators, to smooth the variations in steam temperature and load resulting from both weather conditions (in CSPs) and grid demand. In this operating scenario, conservative simplified rules are normally applied to determine daily warm-up times duration at starts, to preserve critical components from Low Cycle Fatigue damage; the planned maintenance intervals, as well, have been typically defined on the basis of a specified number of starts and running hours.
In this article, the application of an online Rotor Stress Monitoring (RSM) technology, installed in the Steam Turbine User Control Panel, is used to directly determine the fatigue damage cumulated by each Start-Up and variation in operating condition. The results of application of this technology, with respect to standard formulations, are shown for a specific Concentrated Solar Plant across an operating period of four years. It is shown how, using the RSM as a basis for either startup or maintenance scheduling, can result in optimization of start-up times and maintenance intervals both for new units and retro-fit.
The applicability of rotor stress direct monitoring and life analysis to higher temperature services is also introduced.
Rolling Bearing Parametric Excitation of a Jeffcott Rotor System
Authors: Ghannad Tehrani Ghasem , Gastaldi Chiara , Berruti Teresa Maria 
Published: January 2021

Abstract
Rolling bearings are still widely used in aeroengines. Whenever rotors are modeled, rolling bearing components are typically modeled using springs. In simpler models, this spring is considered to have a constant mean value. However, the rolling bearing stiffness changes with time due to the positions of the balls with respect to the load on the bearing, thus giving rise to an internal excitation known as Parametric Excitation. Due to this parametric excitation, the rotor-bearings system may become unstable for specific combinations of boundary conditions (e.g. rotational speed) and system characteristics (rotor flexibility etc.). Being able to identify these instability regions at a glance is an important tool for the designer, as it allows to discard since the early design stages those configurations which may lead to catastrophic failures.
In this paper, a Jeffcott rotor supported and excited by such rolling bearings is used as a demonstrator. In the first step, the expression for the time–varying stiffness of the bearings is analytically derived by applying the Hertzian Contact Theory. Then, the equations of motion of the complete system are provided. In this study, the Harmonic Balance Method (HBM) is used to as an approximate procedure to draw a stability map, thus dividing the input parameter space, i.e. rotational speed and rotor physical characteristics, into stable and unstable regions.
Experimental Investigation of Inlet Distortion in a 4.5-Stage Axial Compressor
Authors: Reutter Oliver , Enders Gerd , Dabrock Theo , Peters Andreas 
Published: January 2021

Abstract
Inlet distortion is a subject of increasing interest in compressors over the last years. Circumferential inhomogeneities can significantly influence the behavior and the aeroelastic response of transonic compressors in gas turbines in the field of airplane propulsion as well as power generation. The circumferential inhomogeneities can result from boundary layer ingestion as planned in many future airplane concepts or from restrictions of the space available leading to short aerodynamically unfavorable intakes. As modern front rows of axial compressors react more and more sensitive to inhomogeneities because of the thinner profiles in the transonic flow regime, understanding the behavior is vital. Therefore, an experimental investigation of the inlet distortion effects on a 4.5 stage axial transonic compressor, Rig250, which is representative of the front stages of a modern high pressure compressor, has been investigated at DLR Cologne.
The inhomogeneity is a total pressure distortion which is applied to the inflow upstream of the strut and the swan neck. The distortion is achieved by a perforated metal plate which can be rotated by 360° at its position. Thereby traverse measurements are possible, which allow a better understanding of the effects of the flow as the sensor positions on the casing and on the blades and vanes are fixed. As these traverses take longer time for measuring only some points are measured with traverses. The compressor has been tested with and without this inlet distortion to get a direct comparison. On the compressor map the 100 % speed line up to surge has been investigated. The inlet distortion shows only a small influence on the surge margin.