bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigations on the Fatigue Load Reduction Potential of Advanced Control Strategies for Multi-MW Wind Turbines Using a Free Vortex Wake Model
Authors: Perez-Becker Sebastian , Saverin Joseph , Marten David , Alber Jörg , Pechlivanoglou George , Paschereit C. O. 
Published: August 2018

This paper presents the results of a fatigue load evaluation from aeroelastic simulations of a multi-megawatt wind turbine. Both the Blade Element Momentum (BEM) and the Lifting Line Free Vortex Wake (LLFVW) methods were used to compute the aerodynamic forces. The loads in selected turbine components, calculated from NREL’s FAST v8 using the aerodynamic solver AeroDyn, are compared to the loads obtained using the LLFVW aerodynamics formulation in QBlade.
The DTU 10 MW Reference Wind Turbine is simulated in power production load cases at several wind speeds under idealized conditions. The aerodynamic forces and turbine loads are evaluated in detail, showing very good agreement between both codes. Additionally, the turbine is simulated under realistic conditions according to the current design standards. Fatigue loads derived from load calculations using both codes are compared when the turbine is controlled with a basic pitch and torque controller. It is found that the simulations performed with the BEM method generally predict higher fatigue loading in the turbine components. A higher pitch activity is also predicted with the BEM simulations. The differences are larger for wind speeds around rated wind speed. Furthermore, the fatigue reduction potential of the individual pitch control (IPC) strategy is examined and compared when using the two different codes. The IPC strategy shows a higher load reduction of the out-of-plane blade root bending moments when simulated with the LLFVW method. This is accompanied with higher pitch activity at the actuation frequency of the IPC strategy.
Effects of Upstream Step Geometry on Axisymmetric Converging Vane Endwall Secondary Flow and Heat Transfer at Transonic Conditions
Authors: Li Zhigang , Liu Luxuan , Li Jun , Sibold Ridge A. , Ng Wing F. , Xu Hongzhou , Fox Michael 
Published: August 2018

This paper presents a detailed experimental and numerical study on the effects of upstream step geometry on the endwall secondary flow and heat transfer in a transonic linear turbine vane passage with axisymmetric converging endwalls. The upstream step geometry represents the misalignment between the combustor exit and the nozzle guide vane endwall. The experimental measurements were performed in a blowdown wind tunnel with an exit Mach number of 0.85 and an exit Re of 1.5 × 106. A high freestream turbulence level of 16% was set at the inlet, which represents the typical turbulence conditions in a gas turbine engine. Two upstream step geometries were tested for the same vane profile: a baseline configuration with a gap located 0.88Cx (43.8 mm) upstream of the vane leading edge (upstream step height = 0 mm) and a misaligned configuration with a backward facing step located just before the gap at 0.88Cx (43.8 mm) upstream of the vane leading edge (step height = 4.45% span). The endwall temperature history was measured using transient infrared thermography, from which the endwall thermal load distribution, namely Nusselt number, were derived. This paper also presents a comparison with CFD predictions performed by solving the steady-state Reynolds Averaged Navier Stokes (RANS) with Reynolds Stress Model using the commercial CFD solver ANSYS Fluent v.15. The CFD simulations were conducted at a range of different upstream step geometries: three forward-facing (upstream step geometries with step heights from −5.25 to 0% span), and five backward-facing, upstream step geometries (step heights from 0 to 6.56% span). These CFD results were used to highlight the link between heat transfer patterns and the secondary flow structures, and explain the effects of upstream step geometry.
Experimental and numerical results indicate that the backward-facing upstream step geometry will significantly enlarge the high thermal load region and result in an obvious increase (up to 140%) in the heat transfer coefficient level, especially for arched regions around the vane leading edge. However, the forward-facing upstream geometry will modestly shrink the high thermal load region and reduce the heat transfer coefficient (by ∼10%–40% decrease), especially for the suction side regions near the vane leading edge. The aerodynamic loss appears to have a slight increase (0.3%–1.3%) as a result of the forward-facing upstream step geometry, but is slightly reduced (by 0.1%–0.3%) by the presence of the backward upstream step geometry.
Fuel Interchangeability Effects on the Lean Blowout for a Lean Premixed Swirl Stabilized Fuel Nozzle
Authors: Gadiraju Siddhartha , Park Suhyeon , Singh Prashant , Pandit Jaideep , Ekkad Srinath V. , Liberatore Federico , Srinivasan Ram , Ho Yin-hsiang 
Published: August 2018

This work is motivated by an interest in understanding the fuel interchangeability of a fuel nozzle to operate under extreme lean operating conditions. A lean premixed, swirl-stabilized fuel nozzle designed with central pilot hub was used to test various fuel blends for combustion characteristics. Current gas turbine combustion technology primarily focuses on burning natural gas for industrial systems. However, interest in utilizing additional options due to environmental regulations as well as concerns about energy security have motivated interest in using fuel gases that have blends of Methane, Propane, H2, CO, CO2, and N2. For example, fuel blends of 35%/60% to 55%/35% of CH4/CO2 are typically seen in Landfill gases. Syngas fuels are typically composed primarily of H2, CO, and N2. CH4/N2 fuel blend mixtures can be derived from biomass gasification.
Stringent emission requirements for gas turbines stipulate operating at extreme lean conditions, which can reduce NOx emissions. However, lean operating conditions pose the problem of potential blowout resulting in loss of performance and downtime. Therefore, it is important to understand the Lean Blowout (LBO) limits and involved mechanisms that lead to a blowout. While a significant amount of research has been performed to understand lean blowout limits and mechanisms for natural gas, research on LBO limits and mechanisms for fuel blends has only been concentrated on fuel blends of CH4 and H2 such as syngas. This paper studies the lean blowout limits with fuel blends CH4-C3H8, CH4-CO2, and CH4-N2 and also their effect on the stability limits as the pilot fuel percentage was varied. Experimental results demonstrate that the addition of propane, nitrogen and carbon dioxide has minimal effect on the adiabatic flame temperature when the flame becomes unstable under lean operating conditions. On the other hand, the addition of diluent gas showed a potential blowout at higher adiabatic temperatures.
Thermal Management System for the MEE and Engine Embedded Electric Machine
Authors: Morioka Noriko , Oyori Hitoshi , Seki Naoki , Fukuda Tsuyoshi , Suzuki Fuminori 
Published: August 2018

The MEE (More Electric Engine) is a concept for engine system electrification and is an evolutionary step in engine system design that contributes to the reduction of aviation CO2 emissions. Mifee (Metering and integrated fuel feeding electrification) and the E3M (Engine Embedded Electric Machine) are the key technologies of the MEE. The purpose of engine thermal management is maintaining the balance between heat generation by the engine system and heat dissipation to the outside of the engine. In recent engine system designs, thermal system design has become an issue because of increased heat generation within the system. For example, a recently developed turbo-fan engine system increases the heat generation by introduction of a fan drive gear system that produces a large amount of heat in addition to the conventional heat source, such as engine main bearings and gears. The MEE will have further heat sources within its system, like the E3M, which is a high-power electric machine. In this paper, an investigation approach and the result of a feasibility study of the MEE thermal management system is described.
In addition, the perspective of the technology trend from the MEE toward future hybrid propulsion is also discussed. The global requirements for climate protection strongly demand game-changing technology that significantly improves the aircraft’s overall efficiency. A series/parallel partial hybrid propulsion system, in which both a turbo-fan engine and electrical motor-driven fans generate propulsive power, is considered to be one of the most promising approaches for the future commercial aircraft hybrid propulsion system. The MEE and E3M technology evolves until it will be applied in hybrid propulsion system.
Direct Integration of Axial Turbomachinery Preliminary Aerodynamic Design Calculations in Engine Performance Component Models
Authors: Kolias Ioannis , Alexiou Alexios , Aretakis Nikolaos , Mathioudakis Konstantinos 
Published: August 2018

In the context of an engine design calculation, isentropic or polytropic efficiencies of turbomachinery components are assumed at the outset of the cycle analysis and their values are updated or validated following the aerodynamic design of the components. In the present paper, aerodynamic design calculations of axial-flow compressors and turbines are directly integrated into the corresponding performance component models. This creates a consistent, single-step preliminary design and performance modelling process using a relatively small number of physical and geometric inputs.
The aerodynamic design for establishing a component’s overall efficiency is accomplished through a mean-line, stage-by-stage approach where the stagewise isentropic efficiency is calculated employing either loss or semi-empirical correlations. From this process, the stagewise flow annulus radii are also obtained and are used to axially size the component stages assuming the blade aspect ratio and axial gapping distributions. The component flowpath geometry is then produced by simply “stacking” axially the component stages.
The developed method is validated against publicly available data for a high-pressure compressor and a low-pressure turbine. Finally, the effectiveness of the method is demonstrated by considering the multi-point design of a High Bypass Ratio Geared Turbofan Engine with bypass Variable Area Nozzle.
Analysis of Unsteady Flow Structures in a Radial Turbomachine by Using Proper Orthogonal Decomposition
Authors: Witte Matthias , Torner Benjamin , Wurm Frank-Hendrik 
Published: August 2018

Tonalities in hydro and airborne noise emission are a known problem of turbomachines, wherein the tonalities in the noise spectrum are associated with the different orders of the blade passing frequency (BPF). The proper orthogonal decomposition (POD) method was utilized to find the relationship between the fluctuations in the pressure field at the BPF orders which are the origin of the noise emission and the correlated fluctuations in the turbulent velocity field in terms of coherent, periodic flow structures. In order the provide the input data for the POD analysis, a URANS k-ω-SST scale adaptive simulation (SAS) of the turbulent flow field in a single stage radial pump under part load conditions was performed. Compared to traditional two equation turbulence models this approach is less dissipative and allows the development of small scale turbulence structures and is therefore an appropriate method for this study. In order to compute the POD correlation matrix Sirovich’s “Methods of Snapshots” was applied to the unsteady pressure and velocity fields from the CFD simulation.
The discrimination of coherent, periodic flow structures and the incoherent, chaotic turbulence was carried out by analyzing the POD eigenvalue distributions, the POD mode shapes and the spectral properties of the POD time coefficients. Five coupled POD mode pairs were identified in total, which were strictly correlated with the 1st, 2nd, 3rd, 4th and 5th order of the BPF and therefore responsible for the noise emission at these discrete frequencies. The coherent structures were explored on the basis of the spatial POD velocity und pressure mode shapes and in terms of vortical structures after an additional phase averaging. The scope of this study is to introduce an enhanced collection of post processing techniques which are capable of analyzing highly unsteady flow fields from numerical simulations in a better way than is possible by just using traditional techniques like the evaluation of integral or time averaged quantities. The identified coherent flow structures and their associated pressure fluctuations are key elements for a proper comprehension of the internal dynamics of the turbulent flow field in a turbomachine and therefore essential for the understanding of the noise generation processes and the optimization of such machines.
On the Simulation of Unsteady Turbulence and Transition Effects in a Multistage Low Pressure Turbine: Part I — Verification and Validation
Authors: Ashcroft Graham , Frey Christian , Kersken Hans-Peter , Kügeler Edmund , Wolfrum Nina 
Published: August 2018

This is the first part of a series of three papers on the simulation of turbulence and transition effects in a multistage low pressure turbine. In this first part, the extension, verification and validation of a Harmonic Balance (HB) method recently proposed by the authors to fully include established turbulence and transition models in the method is presented. As an alternating frequency/time-domain type method the implemented HB solver has the advantage of being able to utilize models (e.g. boundary conditions or residual functions) formulated in either the frequency- or time-domain. On the one hand this allows highly accurate nonreflecting boundary conditions formulated in the frequency-domain to be used along entry, exit or interface boundaries, and on the other hand complex nonlinear terms formulated in the time-domain to be used to describe nonlinear effects. Nevertheless, the wish to minimize the number of harmonics used to describe a given time-periodic unsteady flow, coupled with the often highly nonlinear nature of turbulence and transition models makes the full inclusion of such models in the HB method challenging.
In this work the integration of Menter’s SST two-equation k–ω turbulence model along with Menter and Langtry’s two-equation γ–Reθ transition model in the context of a general framework for transport equations in the CFD solver TRACE is described in detail. Following the basic verification of the underlying transport equation framework, the implemented models are used to compute the well known high lift, low pressure turbine airfoil T106C and results are compared with the available experimental data as well as results from more conventional time-domain simulations. Alongside the basic validation of the models this testcase is furthermore used to investigate the importance of including higher harmonics, as opposed to only the zeroth harmonic, of the turbulence and transition models for the accurate prediction of the time-mean flow.
Optimization of a 900 mm Tilting-Pad Journal Bearing in Large Steam Turbines by Advanced Modeling and Validation
Authors: Mermertas Ümit , Hagemann Thomas , Brichart Clément 
Published: August 2018

Modernization of steam turbine components can extend the life of a power plant, decrease maintenance costs, increase service intervals and improve operational flexibility. However, this can also lead to challenging demands for existing components such as bearings, e.g., due to increased rotor weights. Therefore, a careful design and evaluation process of bearings is of major importance. This paper describes the advanced modeling methods applied for the optimization of a novel 900 mm three-pad tilting pad journal bearing followed by validation results that showed a high bearing temperature sensitivity to the fresh oil supply temperature during operation. The bearing was especially developed to cope with increased rotor weights within the framework of low pressure steam turbine modernizations at two similar 1000 MW nuclear power plants. With a static bearing load of approximately 2.7 MN at a rotor speed of 1500 rpm, it represents one of the highest loaded applications for tilting pad journal bearings in turbomachinery worldwide. After identification of the reasons for the sensitivity, advanced modeling methods were applied to optimize the bearing. For this purpose, a more comprehensive bearing model was developed taking into account the direct lubrication at the leading edge of the pads and the thermo-mechanical pad deformation. For the latter, a co-simulation between the bearing computation code and structural mechanics software was performed. The results of the entire analyses indicated modifications of bearing and pad clearance, pad pivot position, circumferential and axial pad length as well as pad thickness. Furthermore, the oil distribution into the pads was optimized by modifying the orifices within the bearing.
The optimized bearing was then implemented on both units and proved its excellent operational behavior at increased fresh oil supply temperatures of up to 55°C. In addition, inspections during scheduled outages after 18 months of operation and subsequent restarts with reproducible bearing behavior confirmed the robustness of the optimized bearing. In conclusion, the application of advanced modeling methods proved to be the key success factor in the optimization of this bearing, which represents an optimal solution for large steam turbine and generator rotor train applications.
Methodology for Evaluating Efficiency Benefits of Hydrophobic Coatings in Steam Turbine Applications
Authors: Melas Mauro , Sigg Roland , Bühlmann Stefan , Limacher Daniela , Manyoky Thomas 
Published: August 2018

Performance of steam turbines operating under wet steam is known to worsen proportionally to the increase in wetness at turbine exhaust. Numerous strategies have been attempted in the past to minimize the efficiency loss and mechanical damage associated with liquid phase formation, mostly with limited success and poor commercial viability due to increased complexity.
The application of hydrophobic coatings is a simple economically favorable strategy and is expected to partially inhibit the formation of water films on blade surfaces and associated consequences.
This paper addresses a need of turbine manufacturers: the development of a methodology to test, rapidly and economically, performance impact and endurance of coatings to allow a systematic selection. The resulting methodology employs specialized equipment to measure the fog rejection effectiveness of coatings and to generate droplet impingement and thermal loads comparable to real applications, all under laboratory conditions. Measurement results indicated that different materials cause different wetness losses and turbine efficiency can be improved with the coating of blades. Transfer functions used to generate the correspondence between laboratory and representative turbine conditions enabled the coating selection for turbine application. Finally, tests in a model turbine allowed validating the prediction of efficiency improvement, confirming the suitability of the developed methodology.
This work demonstrates that this technology delivers an important improvement in turbine efficiency.
Scale Adaptive Simulation of Transient Behavior in a Transonic Centrifugal Compressor With a Vaned Diffuser
Authors: Zamiri Ali , Chung Jin Taek 
Published: August 2018

Three-dimensional, compressible, unsteady Navier-Stokes equations are solved to investigate the unsteady flow behavior in a transonic centrifugal compressor. The computational model is a high compression ratio centrifugal compressor (4:1) consisted of an inlet duct, an impeller (15 main blades and 15 splitters) and a diffuser vane with 24 two-dimensional wedge vanes.
The aim of this study is to conduct a comprehensive assessment of the ability of a hybrid scale-adaptive simulation (SAS) turbulent model to characterize the transient flow structures within the compressor passages. The main idea of SAS approach, an improved URANS (unsteady Reynold-averaged Navier-Stokes) model, is based on the introduction of von Karman length scale into the turbulent scale equation which results in LES-like behavior in unsteady regions of the flow field. A numerical sensitivity test is performed to validate the computational results in terms of pressure ratio and compressor efficiency. Instantaneous and mean flow field analyses are presented in the impeller and the vaned diffuser. Applying transient simulations, it is shown that the interaction between the pressure waves and the surface pressure of the diffuser blades leads to a pulsating behavior within the diffuser. Moreover, spectral analysis is evaluated to analyze the BPF tonal noise as the main noise source of centrifugal compressors. In addition, the current SAS results are compared with those of the URANS-SST (shear stress transport) approach to show the ability of SAS approach in the prediction of the turbulent structures where the SAS model leads to a much better resolution of the unsteady fluctuations.
This study shows that the current SAS approach, as an alternative to the existing hybrid RANS/LES methods, is promising in terms of prediction of transient phenomena like LES, but with a substantially reduced turn-around time.
Exploring the Impact of Manufacturing Geometric Uncertainties on the Aerodynamic Performance of a Small Scale Compressor
Authors: Manohara Selvan Kailash , Kowalczyk Lukasz 
Published: August 2018

The performance of small scale compressors mass-produced for domestic appliances is influenced by geometric manufacturing uncertainty which affects overall product performance and reliability. Precise manufacturing processes through tighter tolerances ensure high geometric accuracy and lower compressor performance spread, but it challenges high volume production capabilities and cost. Good understanding of geometric sensitivities is necessary for robust design and tolerance definition.
This paper presents the application of geometric Sensitivity Analysis (SA), Uncertainty Quantification (UQ) and robust optimization method to a small scale compressor. Geometric SA was carried out on parametric blade geometry and the key influential parameters were identified. The tip clearance was found to be the most influential parameter followed by a blade surface thickness. The tip section of the blade was more influential than hub section and the suction surface was found to be more important than the pressure surface. Findings from the SA were used to define parameters that were measured and controlled to ensure impeller quality during production. Within the parametric bounds studied, impeller chord did not feature as a critical parameter. The machining tool path was optimized accordingly and a 12% reduction in cutting time was achieved. The numerical sensitivities were also compared with experimental data and a trend-level agreement was seen. Meta-models for aerodynamic performance were built using DoE generated geometries which were used to perform manufacturing UQ using a Monte Carlo estimator. Robust design optimization was carried out using stochastic optimization algorithm coupled with the meta-model based Monte-Carlo simulator. This framework was used to choose a robust nominal shape that achieved 18% lower standard deviation in stage pressure rise. The predicted performance spread was compared with production data and a satisfactory agreement was seen.