bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimization of Large Offshore Wind Farm Layout Considering Reliability and Wake Effect
Authors: Li Xiangyu , Dao Cuong D. , Kazemtabrizi Behzad , Crabtree Christopher J. 
Published: January 2021

Abstract
Nowadays, the increasing demand of electricity and environmental hazards of the greenhouse gas lead to the requirement of renewable energies. The wind energy has been proved as one of the most successful sustainable energies. Recently, the development trend of the wind energy is to build large offshore wind farms (OWFs) with hundreds of wind turbines, which could generates more power in one wind farm. In the large OWF, the wake effect is a very important impact factor to the wind farms, especially for those with close spacing. Therefore, the wind farm layout, the location of the wind turbines (WTs) is very essential to the performance of the whole wind farm, especially for large OWFs. In this research, we focus on the optimization of the large OWF layout by considering performance of the OWF, such as the total output energy. Firstly, the model for wind farm performance evaluation is established by incorporating historical wind speed data and the wake effect which can affect the total wind farm output. Then, by using the metaheuristic algorithms, the genetic algorithm (GA), the OWF layout is optimized. This study can offer useful information to the wind farm manufactures in the large OWF design phase.
The Impact of Exceptional Points on the Reliability of Thermoacoustic Stability Analysis
Authors: Schäfer Felicitas , Guo Shuai , Polifke Wolfgang 
Published: January 2021

Abstract
Exceptional points can be found for specific sets of parameters in thermoacoustic systems. At an exceptional point, two eigenvalues and their corresponding eigenfunctions coalesce. Given that the sensitivity of these eigenvalues to parameter changes becomes infinite at the exceptional point, their occurrence may greatly affect the outcome and reliability of numerical stability analysis. We propose a new method to identify exceptional points in thermoacoustic systems. By iteratively updating the system parameters, two initially selected eigenvalues are shifted towards each other, ultimately colliding and generating the exceptional point. Using this algorithm, we were able to identify for the first time a physically meaningful exceptional point with positive growth rate in a thermoacoustic model. Furthermore, our analysis goes beyond previous studies inasmuch as we employ a more realistic flame transfer function to model flame dynamics. Building on these results, we analyze the effect of exceptional points on the reliability of thermoacoustic stability analysis. In the context of uncertainty quantification, we show that surrogate modeling is not reliable in the vicinity of an exceptional point, even when large sets of training samples are provided. The impact of exceptional points on the propagation of input uncertainties is demonstrated via Monte Carlo computations. The increased sensitivity associated with the exceptional point results in large variances for eigenvalue predictions, which needs to be taken into account for reliable stability analysis.
Experimental Results of Local Shear Stresses and Friction Torque in an Open Rotor-Stator Disc System
Authors: Kuntze Alexander , Odenbach Stefan , Uffrecht Wieland 
Published: January 2021

Abstract
This contribution presents experimental investigations of friction torque in an open rotor-stator disc system by using two different measuring procedures. The first procedure based on a thermo electrical wall shear stress sensor. The sensor is investigated in two different substrates and different measuring parameters. A thermal model consisting of the supplied heating power, the thermal resistance toward the fluid, and into the substrate as well as the over temperature is used to achieve the heat transfer coefficient on the sensor surface. This heat transfer coefficient is attributed by a functional relationship to the wall shear stress. This relationship is firstly calibrated in a rectangular channel and subsequently validated at a fully turbulent flat plat flow.
The second measuring procedure based on the tangential displacement of the stator disc due the friction torque. The disc is attached at a torsion spring. The friction torque is achieved by the torsion spring constant and the tangential displacement of the stator disc. Both measuring procedures are compared and agree well with each other.
The used test rig has the possibility of reaching rotational Reynolds numbers representative for instance of a modern gas turbine. The investigations were carried out by a 0.5 m diameter rotor disc rotating up to 8500 rpm with a gap ratio between 0.008 and 0.04. The friction torque is measured on the stator disc and can be converted into moment coefficient. Moment coefficient on stator as well as measured pressure distributions are presented for different gap ratios and rotational Reynolds number.
Numerical Investigation of Conjugate Heat Transfer in an Effusion and Impingement Cooled Combustor Wall
Authors: Jackowski Thomas , Elfner Maximilian , Bauer Hans-Jörg 
Published: January 2021

Abstract
In this paper, a numerical investigation of conjugate heat transfer in a double-wall combustor will be presented. The model replicates the cooling air duct, the double wall with impingement and effusion cooling, as well as the hot gas duct. For simplification, the walls are modeled planar, and the test parameters were adapted from an upcoming experiment at the Institute of Thermal Turbomachinery, Karlsruhe Institute of Technology. The geometry was scaled up by a factor of 8 through performing a similarity analysis. Aerodynamic and thermal boundary conditions were scaled to ambient pressure and low temperatures while maintaining dimensionless quantities from realistic operating conditions. The diameter of the cylindrical impingement cooling holes is D = 4mm. The effusion cooling holes are angled with α = 30° to the surface and have a cylindrical entrance diameter of E=2D. The outlet of the effusion cooling hole is fanshaped with an opening of 7° to each side as well as laidback by 7°. Both walls have a staggered pattern in which the rows of holes are repeated every 4th row.
A range of blowing ratios from Meff = 0.5 to 3.0 was set as operating conditions for the calculations. Besides, the distance between the impingement wall and the effusion wall was varied from Hcav = 3D to 7D to investigate the influence on heat transfer and aerodynamic behavior of the setup.
The results show an increase in the overall cooling effectiveness θ while reducing the cavity height Hcav. The overall cooling effectiveness θ increases with higher blowing ratios M but shows an absolute saturation above blowing ratios of approximately M &gt; 2.0. Another significant finding is the aerodynamically unfavorable flow of the coolant into the effusion cooling holes and the identification of the flow path from the coolant.
Life Cycle Analysis for a Powertrain in a Concept for Electric Power Generation in a Hybrid Electric Aircraft
Authors: Schneider Michael , Dickhoff Jens , Kusterer Karsten , Visser Wilfried 
Published: January 2021

Abstract
In the recent decades, civil aviation was growing 4.7% per annum. In order to reduce emissions promoting the global warming process, alternative propulsion systems are needed. Full-electric propulsion systems in aviation might have the potential for emission-free flights using renewable energy. However, several research efforts indicate electric propulsion only seems feasible for small aircraft. Especially due to the low energy density of batteries compared to fossil fuels.
For this reason, hybrid propulsion systems came into focus, combining the benefits of all-electric and conventional propulsion system concepts. It is also considered as bridging technology, system test and basis for component development — and therewith paves the way towards CO2 free aviation. In the ‘HyFly’ project (supported by the German Luftfahrtforschungsprogramm LuFo V-3), the potential of a hybrid electric concept for a short/mid-range 19 PAX aircraft is assessed — not only on system but also on single component basis. In a recent study, the propulsion architecture and the operating mode of the gas turbine and the electric components have been defined [1].
In this paper, the advantages of the hybrid propulsion architecture and a qualitative assessment of component life are presented. Methods for life time prediction for the aircraft engine, the electric motor, the reluctance generator and the battery are discussed. The impact of turbine inlet temperature on life consumption is analyzed. The life cycle of the aircraft engine and the electric components including gradual component deterioration and consequent performance degradation is simulated by using an in-house gas turbine simulation tool (GTPsim). Therefore, various effects on electric propulsion system can be predicted for the entire drivetrain system in less than one hour.
A General-Purpose Test Facility for Evaluating Gas Lubricated Thrust Bearings
Authors: Gary Keith , Ertas Bugra , Delgado Adolfo 
Published: January 2021

Abstract
The design, construction, operational capabilities, and proof of concept results are presented for a test rig used to evaluate gas-lubricated thrust bearings. The following work is motivated by a desire to utilize the working fluid of high-performance turbomachinery, such as gas turbines, for bearing lubricant. Auxiliary equipment required to cool, pump, and clean oil for a typical thrust bearing is eliminated by taking advantage of the turbomachinery’s working fluid as bearing lubricant. The benefit of removing such auxiliary equipment is obvious when considering cost and weight of turbomachines, yet the working fluid of gas turbines typically has very low viscosity compared to oil which introduces load capacity and stability challenges. It is therefore necessary to build a facility capable of testing gas-lubricated thrust bearings to advance the technology. The test rig design in this work allows for 7 to 15 inch (180–380 mm) diameter thrust bearings, static loads up to 30,000 lbf (135 kN), and speeds up to 20 krpm. The test facility also provides up to 500 psig (3.45 MPa) static air pressure to enable testing of hydrostatic and hybrid (hydrodynamic combined with hydrostatic) bearings. This paper describes the test rig operating principle, details experimental procedures to obtain measurements, and provides test results necessary to prove the test rig concept by means of a hybrid gas bearing.
Numerical and Analytical Investigation of Heat Transfer Mechanisms and Flow Phenomena in an IP Steam Turbine Blading During Startup
Authors: Bohn Dieter , Betcher Christian , Kusterer Karsten , Weidtmann Kristof 
Published: January 2021

Abstract
As a result of an ever-increasing share of volatile renewable energies on the world wide power generation, conventional thermal power plants face high technical challenges in terms of operational flexibility. Consequently, the number of startups and shutdowns grows, causing high thermal stresses in the thick-walled components and thus reduces lifetime and increases product costs. To fulfill the lifetime requirements, an accurate prediction and determination of the metal temperature distribution inside these components is crucial. Therefore, boundary conditions in terms of local fluid temperatures as well as heat transfer coefficients with sufficient accuracy are required. As modern numerical modeling approaches, like 3D-Conjugate-Heat-Transfer (CHT), provide these thermal conditions with a huge calculation expense for multistage turbines, simplified methods are inevitable. Analytical heat transfer correlations are thus the state-of-the-art approach to capture the heat transport phenomena and to optimize and design high efficient startup curves for flexible power market.
The objective of this paper is to understand the predominant basic heat transfer mechanisms such as conduction, convection and radiation during a startup of an IP steam turbine stage. Convective heat transport is described by means of heat transfer coefficients as a function of the most relevant dimensionless, aero-thermal operating parameters, considering predominant flow structures. Based on steady-state and transient CHT-simulations the heat transfer coefficients are derived during startup procedure and compared to analytical correlations from the literature, which allow the calculation of the heat exchange for a whole multistage in an economic and time-saving way.
The simulations point out that the local convective heat transfer coefficient generally increases with increasing axial and circumferential Reynolds’ number and is mostly influenced by vortex systems such as passage and horseshoe vortices. The heat transfer coefficients at vane, blade, hub and labyrinth-sealing surfaces can be modeled with a high accuracy using a linear relation with respect to the total Reynolds’ number. The comparison illustrates that the analytical correlations underestimate the convective heat transfer by approx. 40% on average. Results show that special correlation-based approaches from the literature are a particularly suitable and efficient procedure to predict the heat transfer within steam turbines in the thermal design process. Overall, the computational effort can be significantly reduced by applying analytical correlations while maintaining a satisfactory accuracy.
The Effect of Thermal Barrier Coating Surface Temperature on the Adhesion Behavior of CMAS Deposits
Authors: Clark Robert A. , Plewacki Nicholas , Gnanaselvam Pritheesh , Bons Jeffrey P. , Viswanathan Vaishak 
Published: January 2021

Abstract
The interaction of thermal barrier coating’s surface temperature with CMAS (calcium magnesium aluminosilicate) like deposits in gas turbine hot flowpath hardware is investigated. Small Hastelloy X coupons were coated in TBC using the air plasma spray (APS) method and then subjected to a thermal gradient via back-side impingement cooling and front-side impingement heating using the High Temperature Deposition Facility (HTDF) at The Ohio State University (OSU). A 1-D heat transfer model was used to estimate TBC surface temperatures and correlate them to intensity values taken from infrared (IR) images of the TBC surface. TBC frontside surface temperatures were varied by changing back-side mass flow (kept at a constant temperature), while maintaining a constant hot-side gas temperature and jet velocity representative of modern commercial turbofan high-pressure turbine (HPT) inlet conditions (approximately 1600K and 200 m/s, or Mach 0.25). In this study, Arizona Road Dust (ARD) was utilized to mimic the behavior of CMAS attack on TBCs. To identify the minimum temperature at which particles adhere, the back-side cooling mass flow was set to the maximum amount allowed by the test setup, and trace amounts of 0–10 μm ARD particles were injected into the hot-side flow to impinge on the TBC surface. The TBC surface temperature was increased through coolant reduction until noticeable deposits formed, as evaluated through an IR camera. Accelerated deposition tests were then performed where approximately 1 gram of ARD was injected into the hot side flow while the TBC surface temperature was held at various points above the minimum observed deposition temperature. Surface deposition on the TBC coupons was evaluated using an infrared camera and a backside thermocouple. Coupon cross sections were also evaluated under a scanning electron microscope for any potential CMAS ingress into the TBC. Experimental results of the impact of surface temperature on CMAS deposition and deposit evolution and morphology are presented. In addition, an Eulerian-Lagrangian solver was used to model the hot-side impinging jet with particles at four TBC surface temperatures and deposition was predicted using the OSU Deposition model. Comparisons to experimental results highlight the need for more sophisticated modeling of deposit development through conjugate heat transfer and mesh morphing of the target surface. These results can be used to improve physics-based deposition models by providing valuable data relative to CMAS deposition characteristics on TBC surfaces, which modern commercial turbofan high pressure turbines use almost exclusively.
Low Fidelity, Numerical Simulation of Gas Turbine Propulsion Across Off Design Conditions
Authors: De Luca Mark John , Taylor Ian J. 
Published: January 2021

Abstract
This paper presents the first section of work carried out as part of a larger research investigation into the feasibility of engine type architecture for specific mission profiles, pertaining to next generational concepts of spacecraft propulsion. Significant work has been undertaken to improve the capability of an existing simulation code, HyPro, used to model all aspects of propulsion technologies, with a focus being given to developing gas turbine type components. The paper explores the implementation of an approach that circumvents the requirements for detailed component mapping and eliminates the need for a fixed, specified design point, presenting early stage validation data of the methodology selected for the modelling, which will go towards justifying its inclusion to the code library.
Nozzle Passage Endwall Effectiveness Values With Various Combustor Coolant Flow Rates: Part 1 — Flowfield Velocity and Coolant Concentration Measurements
Authors: Nawathe Kedar P. , Zhu Rui , Lin Enci , Kim Yong W. , Simon Terrence W. 
Published: January 2021

Abstract
The stators of the first stage of a gas turbine are exposed to severe temperatures. The coolant streams introduced to prevent the stators from thermal damage further complicate the highly three-dimensional flow in the vane passage. Recent results have shown that, in addition to these coolant streams, the coolant streams injected for cooling the combustor also influence the flow physics and the cooling effectiveness in the first-stage stator vanes passage. However, the effects of changing the mass flow rate of these combustor coolant streams on the passage flowfield have not been studied. As understanding the coolant transport is necessary for analyzing changes in cooling effectiveness in the vane passage, detailed aerodynamic and thermal measurements along the whole vane passage are required. This two-part paper presents such measurements taken in a first-stage nozzle guide vane cascade for a variety of combustor coolant and endwall film coolant flow rates. The experiments were conducted in a low-Mach-number facility with engine-representative Reynolds numbers and large-scale high-level turbulence. The objective of the first part of the paper is to describe the flow that influences endwall and vane surface cooling effectiveness distributions, which are presented in the second part of this paper. The measurements show changes in the passage flowfield due to changes in both combustor coolant and endwall film coolant flow rates. Overall, the flow-physics remains largely unaffected by changes in coolant flow rates except in the endwall-vane surfaces region where the combustor coolant flow rate dominates changes in coolant transport. This is shown to have a high impact on endwall and vane surface cooling.
Fretting Wear of T800 Coating in Aero-Engine Applications
Authors: Lavella Mario , Botto Daniele 
Published: January 2021

Abstract
High cycle fatigue in blades is triggered by oscillating forces. Devices such as shrouds, that exploit dry friction, are commonly introduced in the blade assembly to reduce the blade vibrations. If severe wear occurs, the effectiveness of the dry friction damping decreases, vibrations increase, and the number of cycles to failure of the blade diminishes. Mating surfaces in shrouds undergo high loads combined with relative displacement of low amplitude. This is the typical condition known as fretting. Coatings are commonly applied on damping surfaces of turbine blades to mitigate wear.
This study investigates the wear mechanism of contact interfaces coated by Tribaloy® T-800, a coating greatly used in aeroengines. The experimental campaign was performed with a point contact test rig. The investigation was carried out using as test parameters temperature, normal load and fretting amplitude. Nine sets of parameters were analyzed at different test durations. Friction coefficients were computed using the hysteresis loops measured during the fretting tests. The worn surfaces were measured by an optical equipment based on focus variation and the volume losses were accurately measured. The wear region was observed by scanning electron microscopy at the end of each test.
At room temperature, the friction coefficient was found substantially independent of the normal load. The wear rates at room temperature were higher than at high temperature. Observation of the worn surfaces by scanning electron microscopy revealed several brittle cracks. The damage mechanism changes from brittle (at room temperature) to ductile (at high temperature). The volume loss as a function of the dissipated energy was found independent of the normal load, showing that dissipated energy is a better variable rather than the number of wear cycles to show results of wear tests.
Effect of Altitude on Turbomachinery Vibration in an Aircraft Compression-Ignition Engine
Authors: McGowan Ryan C. , Fellows David W. , Bodony Daniel J. , Mojica Jovany R. , Pieri James J. , Kweon Chol-Bum M. , Gibson Joseph A. , Meininger Rik D. , Musser Marshall R. 
Published: January 2021

Abstract
To investigate the effect of altitude on vibrations in a turbocharger, an aircraft compression-ignition engine was operated in both a sea level cell and an altitude chamber up to 25,000 ft (7620 m). The turbocharger was instrumented with a nonintrusive stress measurement system to analyze the frequencies, magnitudes, and critical speeds of the blade bending modes as the ambient pressure, ambient temperature, and engine power varied. The measurements were also compared to data from accelerometers mounted on the compressor housing. At sea level conditions, the largest deflection amplitudes were associated with excitations of the first blade bending mode. These deflections grew in amplitude as the altitude increased and the turbocharger/engine worked harder to produce the required pressure rise and power. There was also evidence of a higher-order mode being excited at elevated altitudes. By understanding the factors contributing to resonance and flutter in aircraft turbomachinery, modeling and prediction tools can be improved to update operating envelopes for current designs and minimize these phenomena in future, aviation-specific designs.