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Efficient prediction of classical flutter stability of turbomachinery blade using the boundary element type numerical method

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ENGINEERING ANALYSIS WITH BOUNDARY ELEMENTS 2020年 113卷 328-345页

作者： Prasad, Chandra Shekhar Pesek, Ludek Inst Thermomech Prague Czech Republic

In this paper classical flutter phenomena in power turbine rotor is studied. A medium fidelity 2D flow solver based on boundary element method is developed for this purpose. The classical flutter parameters in turbomachinery cascades such as aerodynamic damping at different inter-blade phase angle are estimated using flutter stability analysis flow solver. The flow solver is developed using 2D unsteady potential flow based panel method. The unsteady aerodynamic loading on the vibrating cascade is estimated using a traveling-wave mode oscillation. The simulated aerodynamic damping and pressure coefficient using boundary element method are compared against both experimental data and the computational fluid dynamics model's results at different flow conditions. The boundary element based method results demonstrate good agreement with experimental data. The boundary element based flow solver shows significant reduction in computational time compared to computational fluid dynamics model.

关键词： Turbomachinery Aeroelasticity Panel method (PM) Aerodynamic damping (AD) Traveling wave mode (TWM) classical flutter Boundary element method (BEM)

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Parameter sensitivities analysis for classical flutter speed of a horizontal axis wind turbine blade

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Journal of Central South University 2018年第7期25卷 1746-1754页

作者： GAO Qiang CAI Xin GUO Xing-wen MENG Rui College of Mechanics and Materials Hohai UniversityNanjing 210098China Collaborative Innovation Centre for Developing and Protecting Coastal Area Hohai UniversityNanjing 210098China School of Mechanical Engineering Anhui University of TechnologyMaanshan 243002China

The parameter sensitivities affecting the flutter speed of the NREL （National Renewable Energy Laboratory） 5-MW baseline HAWT （horizontal axis wind turbine） blades are analyzed. An aeroelastic model, which comprises an aerodynamic part to calculate the aerodynamic loads and a structural part to determine the structural dynamic responses, is established to describe the classical flutter of the blades. For the aerodynamic part, Theodorsen unsteady aerodynamics model is used. For the structural part, Lagrange’s equation is employed. The flutter speed is determined by introducing “V–g” method to the aeroelastic model, which converts the issue of classical flutter speed determination into an eigenvalue problem. Furthermore, the time domain aeroelastic response of the wind turbine blade section is obtained with employing Runge-Kutta method. The results show that four cases （i.e., reducing the blade torsional stiffness, moving the center of gravity or the elastic axis towards the trailing edge of the section, and placing the turbine in high air density area） will decrease the flutter speed. Therefore, the judicious selection of the four parameters （the torsional stiffness, the chordwise position of the center of gravity, the elastic axis position and air density） can increase the relative inflow speed at the blade section associated with the onset of flutter.

关键词： wind turbine blade aeroelastic model classical flutter parameter sensitivities analysis

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The limit cycle oscillation of divergent instability control based on classical flutter of blade section

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JOURNAL OF VIBROENGINEERING 2017年第7期19卷 5114-5136页

作者： Liu, Tingrui Shandong Univ Sci & Technol Coll Mech & Elect Engn Qingdao Peoples R China

Numerical simulation of a novel fuzzy control and back propagation neural network (BPNN) control for divergent instability based on classical flutter of 5-DOF wind turbine blade section driven by pitch adjustment has been investigated. The work is dedicated to solving destructive flap/lag/twist divergent instability from classical flutter, which might occur during the gust wind action, and might cause fracture failure of the blade itself and tower body. In order to investigate the optimal control method, the parameters of blade section are specially designed so as to simulate the actual situation, which lead to absolutely divergent motions (ADM) under gust wind load. The control of ADM often leads to limit cycle oscillation (LCO), the larger amplitude of which is likely to cause fracture failure of tower body. A novel fuzzy control method with adjustable quantization gain and BPNN control strategy are investigated in order to effectively eliminate LCO (leading to direct convergence of the system) or reduce the amplitude of LCO. The obvious effects of fuzzy control and BPNN control are illustrated by numerical comparisons of vibration suppression from nonlinear time response, amplitude of LCO and frequency spectrum analysis. An experimental platform is built based on hardware-in-the-loop simulation by way of PLC-OPC technology in order to test the real-time performance of the control algorithm. The feasibility of the control algorithm is demonstrated by the experimental results displayed by touch-screen hardware.

关键词： fuzzy control BPNN control pitch adjustment classical flutter divergent instability limit cycle oscillation hardware-in-the-loop simulation real-time effect

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Cyber-physical flexible wing for aeroelastic investigations of stall and classical flutter

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JOURNAL OF FLUIDS AND STRUCTURES 2016年 67卷 34-47页

作者： Fagley, Casey Seidel, Jurgen McLaughlin, Thomas US Air Force Acad Dept Aeronaut 2410 Fac Dr Colorado Springs CO 80840 USA

The fluid-structure interactions of a finite aspect ratio, cantilevered, flexible wing were investigated using a cyber-physical system to virtually augment the torsional dynamics of the wing. Cyber-physical systems (CPS), which have recently been pursued by a small number of research groups, have proven to be a very useful mechanism to interrogate the fluid-structure interaction parameter space. The premise of a CPS is to use dynamic feedback control to make a system behave according to desired equations of motion. Systems are composed of embedded hardware and software coupled with real-time computing to give the user the flexibility to quickly explore a range of structural parameters. With the advancement of modern control theory, robotics and embedded systems, CPSs integrate both simulation and physical properties into a smart structure which can be used to push the boundaries of research investigations. The CPS in this work allows for the investigation of dynamic aeroelastic instabilities of a three-dimensional, flexible, rectangular planform wing. Two dynamic instability regimes are observed: first, stall flutter, in which the torsional or pitch mode is excited through the dynamic stall process, and second, coupled (or classical) flutter, in which the pitch mode couples with the bending mode. By varying the torsional stiffness and therefore the frequency of torsional versus bending oscillations of the wing, both of these regimes can be attained at the same aerodynamic conditions using the CPS. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： Dynamic aeroelasticity Stall flutter classical flutter Cyber-physical system

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Wind-tunnel tests on the post-critical response of classical-flutter-based generators 10

Wind-tunnel tests on the post-critical response of classical...

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10th International Conference on Structural Dynamics (EURODYN)

作者： Pigolotti, Luca Mannini, Claudio Bartoli, Gianni Univ Florence CRIACIV Dept Civil & Environm Engn I-50139 Florence Italy

Harvesting energy from two-degree-of-freedom flutter requires large-amplitude steady-state oscillations. Nevertheless, the post critical behaviour of this aeroelasic instability is still an open issue. The present study attempts to improve its scientific understanding and to supply information for the design of more unstable solutions for energy-harvesting applications. In this framework, the energy extraction was simulated through additional damping in the transverse motion component. Then, the influence of some governing parameters was explored through wind-tunnel tests and parametric linear analyses. It was found that a small mass unbalance downstream of the elastic centre is fundamental to anticipate the instability and to obtain unstable systems also in the presence of high damping levels. Moreover, the still-air frequency ratio is the main responsible for the magnitude of the pitching-to-heaving amplitude ratio. An increment of the heaving damping significantly affects the motion amplitude and conditions the optimal position of the elastic axis. Finally, the post-critical response seems to be little affected by the flow turbulence, suggesting the high potentiality of flutter-based generators for applications in real-flow environments. (C) 2017 The Authors. Published by Elsevier Ltd.

关键词： classical flutter Post-Critical Motion Damping Energy Harvesting Turbulence Wind-Tunnel Tests

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Wind-tunnel tests on the post-critical response of classical-flutter-based generators

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Procedia Engineering 2017年 199卷 3480-3485页

作者： Luca Pigolotti Claudio Mannini Gianni Bartoli CRIACIV/Department of Civil and Environmental Engineering University of Florence Florence 50139 Italy

Harvesting energy from two-degree-of-freedom flutter requires large-amplitude steady-state oscillations. Nevertheless, the post-critical behaviour of this aeroelasic instability is still an open issue. The present study attempts to improve its scientific understanding and to supply information for the design of more unstable solutions for energy-harvesting applications. In this framework, the energy extraction was simulated through additional damping in the transverse motion component. Then, the influence of some governing parameters was explored through wind-tunnel tests and parametric linear analyses. It was found that a small mass unbalance downstream of the elastic centre is fundamental to anticipate the instability and to obtain unstable systems also in the presence of high damping levels. Moreover, the still-air frequency ratio is the main responsible for the magnitude of the pitching-to-heaving amplitude ratio. An increment of the heaving damping significantly affects the motion amplitude and conditions the optimal position of the elastic axis. Finally, the post-critical response seems to be little affected by the flow turbulence, suggesting the high potentiality of flutter-based generators for applications in real-flow environments.

关键词： classical flutter Post-Critical Motion Damping Energy Harvesting Turbulence Wind-Tunnel Tests

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Active flutter control of the wind turbines using double-pitched blades

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RENEWABLE ENERGY 2021年 163卷 2081-2097页

作者： Chen, Bei Hua, Xugang Zhang, Zili Nielsen, Soren R. K. Chen, Zhengqing Hunan Univ Key Lab Wind & Bridge Engn Changsha 410082 Hunan Peoples R China Aarhus Univ Dept Engn DK-8000 Aarhus Denmark Aalborg Univ Dept Civil Engn DK-9220 Aalborg Denmark

classical flutter of a wind turbine blade is a concerned issue to hinder the wind utilization to a large extent. Recent predictions showed a decreasing flutter margin (the ratio of flutter speed to rated rotor speed) with the increase in wind turbine size. To address this issue, a new blade configuration called the double-pitched blade is proposed and analytically investigated for its potential to enhance the flutter suppressing capability of modern large-size wind turbine blades. This new blade comprise an inner part and a tip part, where the tip part can rotate (or pitch) independently with respect to the inner part through a tip actuator commanded by a feedback control law. The aerodynamic loads of blade tip due to the actively controlled rotation of the tip part provide a torque on the inner part, which provides damping for the torsional mode of the wind turbine blade. The effectiveness of this new double-pitched blade for suppressing flutter is verified through a simulation study conducted on a 907-DOF aero-servo-elastic wind turbine model. Parametric studies are performed on two main design parameters, i.e. the length of the tip part and the associated chordwise location of tip shaft with respected to the blade cross section, and flutter control performance are obtained by numerical optimization process. Simulation results show the optimal length of tip part is around 3:3% of blade length, and the associated chordwise location of tip shaft is around 45%of chord length, the flutter amplitude of the conventional blade can be mitigated to around 4%using this double-pitched blade. (c) 2020 Elsevier Ltd. All rights reserved.

关键词： Horizontal axis wind turbines Active vibration control Double-pitched blade classical flutter

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Stochastic Analysis for Wind Turbine Blades Subjected to Aeroelastic Instabilities

Stochastic Analysis for Wind Turbine Blades Subjected to Aer...

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作者： Li, Shaoning Northeastern University

学位级别：Ph.D., Doctor of Philosophy

Wind energy has been the fastest growing clean energy resource. The use of offshore, horizontal-axis wind turbines has been rapidly expanding in recent years. Larger rotor areas of offshore wind turbines usually result in higher wind power generation. However, long and flexible wind turbine blades are more vulnerable to flow-induced, aeroelastic instabilities. classical flutter is one of the aeroelastic in- stability phenomena, which can cause operational blade failure and, consequently, limit its maximum dimensions. Risk analysis of the blades due to classical flutter is an important engineering problem because of the aleatory nature of both the mechanical system and flow field. Several gaps, such as uncertainty quantification, error propagation, and stochastic modeling of the blade dynamics, currently prevent the successful design of future offshore wind turbines. The main objective of this dissertation is to examine the classical flutter of off- shore wind turbine blades, accounting for main uncertainties sources, by novel aerodynamic and probabilistic theories. A simulation framework is proposed and introduced in this work to study stochastic flutter analysis of offshore wind turbine blades. A benchmark blade model, i.e., the National Renewable Energy Laboratory (NREL) 5MW blade, is used for verification and application of the proposed frame- work throughout this dissertation. The main features of the proposed framework are: numerical prediction of blade flutter onset, examination of random aerodynamic and aeroelastic blade forces through wind tunnel tests, uncertainty quantification for the blades in the context of risk analysis. The simulation component of the dissertation includes the following modules: advanced model for deterministic flutter prediction, stochastic model for risk analysis of blades contaminated by various uncertainty sources, wind tunnel test protocols for experimental error examination and its effects on the aerodynamic and aeroelastic load

关键词： classical flutter flutter derivative Uncertainty quantification Wind tunnel experiment Wind turbine blade

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Structural damping sensitivity affecting the flutter performance of a 10-MW offshore wind turbine

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ADVANCES IN STRUCTURAL ENGINEERING 2020年第14期23卷 3037-3047页

作者： Hua, Xugang Meng, Qingshen Chen, Bei Zhang, Zili Hunan Univ Coll Civil Engn Key Lab Wind & Bridge Engn Hunan Prov Changsha 410082 Hunan Peoples R China Aarhus Univ Dept Engn Aarhus Denmark

classical flutter of wind turbine blades is one of the most destructive instability phenomena of wind turbines especially for several-MW-scale turbines. In the present work, flutter performance of the DTU 10-MW offshore wind turbine is investigated using a 907-degree-of-freedom aero-hydro-servo-elastic wind turbine model. This model involves the couplings between tower, blades and drivetrain vibrations. Furthermore, the three-dimensional aerodynamic effects on wind turbine blade tip have also been considered through the blade element momentum theory with Bak's stall delay model and Shen's tip loss correction model. Numerical simulations have been carried out using data calibrated to the referential DTU 10-MW offshore wind turbine. Comparison of the aeroelastic responses between the onshore and offshore wind turbines is made. Effect of structural damping on the flutter speed of this 10-MW offshore wind turbine is investigated. Results show that the damping in the torsional mode has predominant impact on the flutter limits in comparison with that in the bending mode. Furthermore, for shallow water offshore wind turbines, hydrodynamic loads have small effects on its aeroelastic response.

关键词： classical flutter flutter speed offshore horizontal axis wind turbines structural damping

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Numerical Investigation into flutter and flutter-Buffet Phenomena for a Swept Wing and a Curved Planform Wing

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INTERNATIONAL JOURNAL OF AEROSPACE ENGINEERING 2019年第Pt.1期2019卷 1-19页

作者： Chiarelli, Mario Rosario Bonomo, Salvatore Univ Pisa DICI Largo Lucio Lazzarino 1 I-56122 Pisa Italy

The results of numerical studies carried out on high-aspect-ratio wings with different planforms are discussed: the transonic regime is analysed for a swept wing and a curved planform wing. The wings have similar aspect ratios and similar aerodynamic profiles. The analyses were carried out by CFD and FE techniques, and the reliability of the numerical aerodynamic results was proven by a sensitivity study. Analysing the performances of the two wings demonstrated that in transonic flight conditions, a noticeable drag reduction can be obtained by adopting a curved planform wing. In addition, for such a wing, the aeroelastic instability condition, consisting in a classical flutter, is postponed compared to a conventional swept wing, for which a flutter-buffet instability occurs. In a preliminary manner, the study shows that, for a curved planform wing, the high speed buffet is not an issue and at the same time notable fuel saving can be achieved.

关键词： ASPECT RATIO drag reduction Wings classical flutter swept wings flutter TRANSONIC FLIGHT Curved

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