Academic literature on the topic 'Active blade pitching'
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Journal articles on the topic "Active blade pitching"
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Delafin, Pierre-Luc, François Deniset, Jacques André Astolfi, and Frédéric Hauville. "Performance Improvement of a Darrieus Tidal Turbine with Active Variable Pitch." Energies 14, no. 3 (January 28, 2021): 667. http://dx.doi.org/10.3390/en14030667.
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Vertical axis turbines, also called Darrieus turbines, present interesting characteristics for offshore wind and tidal applications but suffer from vibrations and a lower efficiency than the more conventional horizontal axis turbines. The use of variable pitch, in order to control the angle of attack of the blades continuously during their rotation, is considered in this study to overcome these problems. 2D blade-resolved unsteady Reynolds-Averaged Navier–Stokes (RANS) simulations are employed to evaluate the performance improvement that pitching blades can bring to the optimal performance of a three-straight-blade vertical axis tidal turbine. Three pitching laws are defined and tested. They aim to reduce the angle of attack of the blades in the upstream half of the turbine. No pitching motion is used in the downstream half. The streamwise velocity, monitored at the center of the turbine, together with the measurement of the blades’ angle of attack help show the effectiveness of the proposed pitching laws. The decrease in the angle of attack in the upstream half of a revolution leads to a significant increase in the power coefficient (+40%) and to a better balance of the torque generated in the upstream and downstream halves. Both torque and thrust ripples are therefore significantly reduced.
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Roy, Lalit, Kellis Kincaid, Roohany Mahmud, and David W. MacPhee. "Double-Multiple Streamtube Analysis of a Flexible Vertical Axis Wind Turbine." Fluids 6, no. 3 (March 13, 2021): 118. http://dx.doi.org/10.3390/fluids6030118.
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Vertical-axis wind turbines (VAWTs) have drawn increased attention for off-grid and off-shore power generation due to inherent advantages over the more popular horizontal-axis wind turbines (HAWTs). Among these advantages are generator locale, omni-directionality and simplistic design. However, one major disadvantage is lower efficiency, which can be alleviated through blade pitching. Since each blade must transit both up- and down-stream each revolution, VAWT blade pitching techniques are not yet commonplace due to increased complexity and cost. Utilizing passively-morphing flexible blades can offer similar results as active pitching, requiring no sensors or actuators, and has shown promise in increasing VAWT performance in select cases. In this study, wind tunnel tests have been conducted with flexible and rigid-bladed NACA 0012 airfoils, in order to provide necessary input data for a Double-Multiple Stream-Tube (DMST) model. The results from this study indicate that a passively-morphing VAWT can achieve a maximum power coefficient (Cp) far exceeding that for a rigid-bladed VAWT CP (18.9% vs. 10%) with reduced normal force fluctuations as much as 6.9%. Operational range of tip-speed ratio also is observed to increase by a maximum of 40.3%.
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Bottasso, Carlo L., Alessandro Croce, Federico Gualdoni, Pierluigi Montinari, and Carlo E. D. Riboldi. "Articulated blade tip devices for load alleviation on wind turbines." Wind Energy Science 1, no. 2 (December 1, 2016): 297–310. http://dx.doi.org/10.5194/wes-1-297-2016.
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Abstract. This paper investigates the load alleviation capabilities of an articulated tip device, where the outermost portion of the blade can rotate with respect to the rest of the blade. Passive, semi-passive and active solutions are developed for the tip rotation. In the passive and semi-passive configurations tip pitching is mainly driven by aerodynamic loads, while for the active case the rotation is obtained with an actuator commanded by a feedback control law. Each configuration is analyzed and tested using a high-fidelity aeroservoelastic simulation environment, by considering standard operative conditions as well as fault situations. The potential benefits of the proposed blade tip concepts are discussed in terms of performance and robustness.
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Wijewardana, S., M. H. Shaheed, and R. Vepa. "Optimum Power Output Control of a Wind Turbine Rotor." International Journal of Rotating Machinery 2016 (2016): 1–8. http://dx.doi.org/10.1155/2016/6935164.
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An active and optimum controller is applied to regulate the power output from a wind turbine rotor. The controller is synthesized in two steps. The first step defines the equilibrium operation point and ensures that the desired equilibrium point is stable. The stability of the equilibrium point is guaranteed by a control law that is synthesized by applying the methodology of model predictive control (MPC). The method of controlling the turbine involves pitching the turbine blades. In the second step the blade pitch angle demand is defined. This involves minimizing the mean square error between the actual and desired power coefficient. The actual power coefficient of the wind turbine rotor is evaluated assuming that the blade is capable of stalling, using blade element momentum theory. This ensures that the power output of the rotor can be reduced to any desired value which is generally not possible unless a nonlinear stall model is introduced to evaluate the blade profile coefficients of lift and drag. The relatively simple and systematic nonlinear modelling and MPC controller synthesis approach adopted in this paper clearly highlights the main features on the controller that is capable of regulating the power output of the wind turbine rotor.
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Glaz, Bryan, Li Liu, Peretz P. Friedmann, Jeremy Bain, and Lakshmi N. Sankar. "A Surrogate-Based Approach to Reduced-Order Dynamic Stall Modeling." Journal of the American Helicopter Society 57, no. 2 (April 1, 2012): 1–9. http://dx.doi.org/10.4050/jahs.57.022002.
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The surrogate-based recurrence framework (SBRF) approach to reduced-order dynamic stall modeling associated with pitching/plunging airfoils subject to fixed or time-varying freestream Mach numbers is described. The SBRF is shown to effectively mimic full-order two-dimensional computational fluid dynamics solutions for unsteady lift, moment, and drag, but at a fraction of the computational cost. In addition to accounting for realistic helicopter rotor blade dynamics, it is shown that the SBRF can model advancing rotor shock induced separation as well as retreating blade stall associated with excessive angles of attack. Therefore, the SBRF is ideally suited for a variety of rotary-wing aeroelasticity and active/passive design optimization studies that require high-fidelity aerodynamic response solutions with minimal computational expense.
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Guevara, Pablo, Phillip Rochester, and Krishna Vijayaraghavan. "Optimization of active blade pitching of a vertical axis wind turbine using analytical and CFD based metamodel." Journal of Renewable and Sustainable Energy 13, no. 2 (March 2021): 023305. http://dx.doi.org/10.1063/5.0026591.
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Maldonado, Victor, and Soham Gupta. "Active Flow Control of a Low Reynolds Number S809 Wind Turbine Blade Model under Dynamic Pitching Maneuvers." Open Journal of Fluid Dynamics 07, no. 02 (2017): 178–93. http://dx.doi.org/10.4236/ojfd.2017.72012.
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Bin Mohamad Saifuddin, Muhammad Ramadan, Thaiyal Naayagi Ramasamy, and Wesley Poh Qi Tong. "Design and Control of a DC Collection System for Modular-Based Direct Electromechanical Drive Turbines in High Voltage Direct Current Transmission." Electronics 9, no. 3 (March 16, 2020): 493. http://dx.doi.org/10.3390/electronics9030493.
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In response to an increasing demand for offshore turbine-based technology installations, this paper proposes to design a DC collection system for multi-connected direct drive turbines. Using tidal stream farm as the testbed model, inverter design and turbine control features were modelled in compliance with high voltage ride-through capabilities that operate in isochronous mode suggested by IEEE1547-2018. The aim of the paper is twofold. Firstly, operation analyses in engaging a single-stage impedance source inverter as an AC-link busbar aggregator to pilot a parallel-connected electromechanical drive system. It uses a closed-loop voltage controller to secure voltage-active power (Volt/Watt) dynamics in correspondence with turbine’s arbitrary output voltage level. It also aspires to truncate active rectification stages at generation-side as opposed to a traditional back-to-back converter. Secondly, a proposition for a torque-controlled blade pitching system is modelled to render a close to maximum power point tracking using blade elevation and mechanical speed manipulations. The reserve active power generation aids with compensating an over-voltage crisis as a substitute for typical reactive power absorption. The proposed Testbed system was modelled in PSCAD, adopting industrial related specifications and real-time ocean current profiles for HVDC transmission operations. Analytical results have shown a positive performance index and transient responses at respective tidal steam turbine clusters that observe fault ride-through criterion despite assertive operating conditions.
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Ward, Dawn, Maurizio Collu, and Joy Sumner. "Reducing Tower Fatigue through Blade Back Twist and Active Pitch-to-Stall Control Strategy for a Semi-Submersible Floating Offshore Wind Turbine." Energies 12, no. 10 (May 18, 2019): 1897. http://dx.doi.org/10.3390/en12101897.
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The necessity of producing more electricity from renewable sources has been driven predominantly by the need to prevent irreversible climate chance. Currently, industry is looking towards floating offshore wind turbine solutions to form part of their future renewable portfolio. However, wind turbine loads are often increased when mounted on a floating rather than fixed platform. Negative damping must also be avoided to prevent tower oscillations. By presenting a turbine actively pitching-to-stall, the impact on the tower fore–aft bending moment of a blade with back twist towards feather as it approaches the tip was explored, utilizing the time domain FAST v8 simulation tool. The turbine was coupled to a floating semisubmersible platform, as this type of floater suffers from increased fore–aft oscillations of the tower, and therefore could benefit from this alternative control approach. Correlation between the responses of the blade’s flapwise bending moment and the tower base’s fore–aft moment was observed with this back-twisted pitch-to-stall blade. Negative damping was also avoided by utilizing a pitch-to-stall control strategy. At 13 and 18 m/s mean turbulent winds, a 20% and 5.8% increase in the tower axial fatigue life was achieved, respectively. Overall, it was shown that the proposed approach seems to be effective in diminishing detrimental oscillations of the power output and in enhancing the tower axial fatigue life.
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Dehaeze, F., K. D. Baverstock, and G. N. Barakos. "CFD simulation of flapped rotors." Aeronautical Journal 119, no. 1222 (December 2015): 1561–83. http://dx.doi.org/10.1017/s0001924000011404.
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AbstractThe use of active trailing edge flaps on rotors may lead to performance benefits as well as noise and vibration reduction. In this work, computational fluid dynamics, using the HMB2 solver, is used to assess the effect of the trailing edge flaps on the whole flight domain of a modern main rotor. Starting from a baseline blade design, multiple techniques are demonstrated. The flap is first assessed using 2D pitching aerofoil simulations, followed by dMdt simulations, that account for the simultaneous variations of pitch and Mach around the azimuth. It was shown that enhanced lift was obtained while inspection of the moment coefficient showed negative damping for the flap for a limited set of conditions. Due to the 2D formulation, dMdt computations are fast to perform and can be used to inform codes predicting the rotor performance. The flap was then assessed in hover, and only allowed for limited improvement in blade performance at high thrust. In forward flight, the flap was actuated at a frequency of 1 per revolution, and was found to have a strong effect on the loads on the retreating side. The effect on the moments was even stronger. The flight envelope of the blade was explored, and clean and flapped cases were compared. The most noticeable changes occur at high and medium thrust. The CFD method was found to be efficient and robust, without any substantial penalties in CPU time, due to the flap modelling, over the tested conditions.
Dissertations / Theses on the topic "Active blade pitching"
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Melani, Pier Francesco. "Power augmentation of Darrieus-type turbines by means of novel solutions and multi-fidelity simulations." Doctoral thesis, 2022. http://hdl.handle.net/2158/1276840.
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Vertical-axis wind turbines (VAWTs) represent a valuable alternative to horizontal- axis ones for non-conventional installations like highly turbulent environments and off- shore floating. Due to their inherently complex aerodynamics, nonetheless, characterized by a continuous oscillation of the angle of attack on the blade, often above the static stall limit, their development has fallen behind. The nature of this technological gap is twofold. On the one hand, new strategies for increasing their performance and stabilizing their operation must be developed. In this perspective, one can work both on improving the airfoils' performance with passive flow control devices and on controlling the angle of attack (e.g., with active blade pitching). On the other hand, analysis tools with a fidelity higher than the ubiquitous Blade Element Momentum (BEM) method are needed. Blade- resolved Computational Fluid Dynamics (CFD) has shown its potential for this application, but its elevated computational cost makes it suitable only for analyses of few cases. In between the two, interest is being devoted at developing hybrid approaches, able to conjugate the accuracy of CFD and the calculation cost reduction coming from a lumped-parameter modeling of airfoil aerodynamics. Among the different methodologies available, the Actuator Line Method (ALM) is particularly promising. Several shortcomings of this approach have not been solved by the scientific community yet, in particular: the spreading of aerodynamic forces in the domain, the sampling of the angle of attack from the resolved flow field, and a robust dynamic stall modelling. Moving from this background, this thesis presents a comprehensive approach to the power augmentation of vertical-axis rotos. Two strategies have been investigated, i.e., Gurney Flaps and active blade pitching. To this end, high-fidelity, blade-resolved CFD simulations were sided by a new generation ALM tool, here developed within the commercial solver ANSYS® FLUENT®. In the effort of tailoring the ALM to this type of machines, different features have been implemented and discussed in the present study, including a novel strategy for sampling of the angle of attack from the resolved flow field, a sensitivity analysis on the force spreading within the domain and several sub-models to account for secondary aerodynamic effects. Particular attention has been given to dynamic stall and to tip effects modelling. Validation on selected test cases, for which high-fidelity blade forces and wake field data were available from wind tunnel tests and blade-resolved simulations, has proved the reliability of the developed ALM tool. Effectiveness of the proposed power augmentation strategies has been demonstrated also via their application to a hydrokinetic rotor (HVAT - hydrokinetic vertical-axis turbine), designed in collaboration with an industrial partner. Both ALM and blade-resolved CFD simulations showed a simultaneous increase in the turbine aerodynamic efficiency and a reduction in fatigue loading.
Conference papers on the topic "Active blade pitching"
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MacPhee, David, and Asfaw Beyene. "The Straight-Bladed Morphing Vertical Axis Wind Turbine." In ASME 2016 Power Conference collocated with the ASME 2016 10th International Conference on Energy Sustainability and the ASME 2016 14th International Conference on Fuel Cell Science, Engineering and Technology. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/power2016-59192.
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Blade pitch control has been extremely important for the development of Horizontal-Axis Wind Turbines (HAWTs), allowing for greater efficiency over a wider range of operational regimes when compared to rigid-bladed designs. For Vertical-Axis Wind Turbines (VAWTs), blade pitching is inherently more difficult due to a dependence of attack angle on turbine armature location, shaft speed, and wind speed. As a result, there have been very few practical pitch control schemes put forward for VAWTs, which may be a major reason why this wind turbine type enjoys a much lower market share as compared to HAWTs. To alleviate this issue, the flexible, straight-bladed vertical-axis turbine is presented, which can passively adapt its geometry to local aerodynamic loadings and serves as a low-cost blade pitch control strategy increasing efficiency and startup capabilities. Using two-dimensional fluid-structure action simulations, this novel concept is compared to an identical rigid one and is proven to be superior in terms of power coefficient due to decreased torque minima. Moreover, due to the flexible nature of the blades, the morphing turbine achieves less severe oscillatory loadings. As a result, the morphing blade design is expected to not only increase efficiency but also system longevity without additional system costs usually associated with active pitch control schemes.
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Menon, Muraleekrishnan, and Fernando L. Ponta. "Dynamic Aeroelastic Response of Wind Turbine Rotors Under Active Flow Control." In ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/ajkfluids2019-4731.
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Abstract The significance of wind power and the associated relevance of utility-scale wind turbines are becoming more prominent in tapping renewable sources for power. Operational wind turbines today rated at 8 MW have rotor diameters of 164 m. Economies-of-scale factor suggest a sustained growth in rotor size, forecasting the use of longer and heavier blades. This has led to an increased emphasis on studies related to improvements and innovations in aerodynamic load-control methodologies. Among several approaches to controlling the stochastic aerodynamics loads on wind turbine rotors, most popular is the pitch control. Widely used in operational wind turbines, conventional pitch control is an effective approach for long-term load variations. However, their application to mitigate short-term fluctuations have limitations that present a bottleneck for growth in rotor size. Sporadic changes occurring within short time scales near the turbine rotor have significant impact on the aeroelastic behavior of the blades, power generation, with long-term effects on the rotor life-span. Cyclic variations occurring within few seconds emphasize the need for swift response of control methods that counter the resulting adverse effects. Current study revolves around the need to evaluate innovative active load control techniques that can swiftly handle high frequency oscillations in dynamic loading of turbine rotors. This may result from sudden changes in wind conditions due to gusts, environmental effects like atmospheric boundary layer and uneven terrain, or from turbine design features and operating conditions such as tower shadow effects. The upward surge in rotor size is linked with a down-side for existing techniques in rotor control that now need to account for heavier blades and the associated inertia. For example, the pitching operation rotates the entire blade around its longitudinal axis to regulate angle of wind at specific blade sections, involving huge inertial loads associated with the entire blade. On the other hand, active flow-control devices (FCDs) have the potential to alleviate load variations through rapid aerodynamic trimming. Trailing-edge flaps are light weight attachments on blades that have gradually gained relevance in studies focused on wind turbine aerodynamics and active load control. This computational study presents an aeroelastic assessment of a benchmark wind turbine based on the NREL 5-MW Reference Wind Turbine (RWT), with added trailing-edge flaps for rapid load control. The standard blades used on the NREL 5-MW RWT rotor are aerodynamically modified to equip them with actively controllable fractional-chord trailing-edge flaps, along a selected span. The numerical code used in the study handles the complex multi-physics dynamics of a wind turbine based on a self-adaptive ODE algorithm that integrates the dynamics of the control system in to the coupled response of aerodynamics and structural deformations of the rotor. Using the 5-MW RWT as a reference, the blades are modified to add trailing-edge flaps with Clark Y profile and constant chord. Attached at chosen sections of the blade, these devices have a specific range of operational actuation angles. Numerical experiments cover scenarios relevant to the aeroelastic response of a rotor with such adapted blades under operating conditions observed in utility-scale wind turbines. These fractional-chord devices attached along short spans of the blades make them light weight devices that can be easily controlled using low power of actuation. This overcomes the bottleneck in active aerodynamic load control, giving flexibility to study a wider ranged of control strategies for utility-scale wind turbines of the future. Preliminary outcomes suggest that rapid active flow control has high potential in shaping the future of aerodynamic load control in wind turbines.
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Kröger, G., U. Siller, and J. Dabrowski. "Aerodynamic Design and Optimization of a Small Scale Wind Turbine." In ASME Turbo Expo 2014: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/gt2014-26937.
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Small scale wind turbines can meet a substantial part of the electricity demand of residential buildings and facilities in isolated areas. It is a curious fact, however, that for many of these systems the actual power output has been dramatically overestimated. This can be partially explained by the very high rated wind speeds at which the design power output applies. The current work depicts the pathway to an aerodynamically optimized design of a small scale horizontal axis wind turbine in the 1kW class, optimized for wind speeds between 3.5 m/s and 5.5 m/s, a typical range of the energetic average of urban wind speeds. The aerodynamic stability of the blade has been a particular focus leading to a nearly constant efficiency over a range of wind speeds. The rotating speed of the system is adjusted to the optimal tip speed ratio at wind speeds up to maximum power via active control of the aerodynamic torque of the rotor blades. This is realized by adapting the generator torque to the current wind speed guaranteeing optimal efficiency and power output. The rotor blade optimization has been conducted unconventionally, in a turbomachinery-inspired 3D-blade design optimization campaign, using high-fidelity compressible CFD. This approach is described in detail, focussing on geometry parametrization and the numerical model with reasonable boundary conditions. Finally, the aerodynamic performance of the rotor blade is assessed at different wind speeds and pitching angles.
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Prasad Rao, Jubilee, Arturo Villegas, and F. Javier Diez. "Theoretical Analysis of a Cyclic Pitch Turbine." In ASME 2016 Fluids Engineering Division Summer Meeting collocated with the ASME 2016 Heat Transfer Summer Conference and the ASME 2016 14th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/fedsm2016-7878.
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Theoretical analysis of a drag based vertical axis wind turbine is presented. This builds on previous work where we introduced a novel turbine (Cyclic pitch turbine, CPT) with a tilting mechanism. It allows for cyclic pitch variations of the blades while they rotate about an axis perpendicular to the fluid flow direction. The pitching mechanism changes the angle of attack of the blades from 90 degrees while in the drive stroke to 0 degrees while in the recovery stroke and then back to 90 degrees so that the blades are active during the drive stroke and passive during the recovery stroke. The tilting of the blades takes place while the blades are transitioning from one stroke to the other stroke. In this configuration, the blades present maximum frontal area during the drive stroke and minimum frontal area during the recovery stroke. The drag force on a simple shaped bodies is directly proportional to the effective frontal area with respect to the flow direction of the fluid and hence it is expected that the drag force is maximum during the drive stroke while the blades are perpendicular to the flow and that it is minimum during the recovery stroke as the blades are parallel to the fluid flow direction. Comparison of static torque coefficients of a flat plate to that of a bucket blade typical in a Savonius turbine is performed. It is shown that this new turbine has higher and more consistent starting torque. It is also shown that the positive difference in the torque coefficient would only increase as the turbine starts to rotate and increase in rpm. As a consequence, the relative velocity between the blades and the fluid flow negatively affects the Savonius configuration more than a CPT turbine. As a result, this turbine is expected to be more efficient than the Savonius turbine. Optimization has been performed for this formulation for tip speed ratio (TSR) and active blade angle. To perform the tilting motion of the blades, the turbine uses a novel hybrid mechanism combining the workings of cams and swashplates. A prototype has been developed which integrates ball bearings into the mechanism instead of sliding components used in our first generation turbine that change sliding motion into lower friction rolling motion. This increased the efficiency of the turbine. The mathematical formulations developed compares the static characteristics of the developed CPT turbine to Savonius turbines and help understand its dynamic characteristics.
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Jiang, Zhiyu, Torgeir Moan, Zhen Gao, and Madjid Karimirad. "Effect of Shut-Down Procedures on the Dynamic Responses of a Spar-Type Floating Wind Turbine." In ASME 2013 32nd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/omae2013-10214.
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The design standards (IEC, DNV and GL) define a minimum set of combinations of external conditions and design situations as load cases. Like other design load conditions, the design situations relating to fault and shut-down events shall be addressed. Emergency shut down occurs in the presence of severe faults to prevent turbine damage. For pitch-regulated turbines, blade pitching to feather provides an effective means of aerodynamic braking. The blades are pitched to feather at the maximum pitch rate. This action exerts huge loading on the turbine and may challenge the structural safety. In this paper a 5-MW spar-type wind turbine is used as a case study. By using the HAWC2 code, the turbine pitch actuator fault and shut-down scenarios are simulated through external Dynamic Link Libraries. The shut-down scenarios are: normal shut down with blade pitching, emergency shut down with blade pitching, and emergency shut down with blade pitching and mechanical brake. Due to the occurrence of fault, the pitch angle of one blade is fixed from a specific occurrence time. The supervisory controller reacts by pitching the remaining two blades to the maximum pitch set. The maximum yaw motion value is observed after the first revolution of the rotor during which the tower-top torsion experiences a change of direction. Negative platform pitch motion as well as tower-bottom bending moment are induced due to the pitching activity of the two blades. The response extremes of the main shaft bending moment and the yaw motion exhibit clear variation with the blade azimuth when emergency shut down is initiated. The tower-bottom bending moment and nacelle acceleration are relatively more affected by the wave loads. For a given blade azimuth, larger response variation is observed under harsher environmental conditions. Under the fault scenario, the effects of different shut-down procedures on the response extremes are investigated. It is found that the response extremes are affected significantly by the rotor speed. Among the three procedures, normal shut down, which is associated with the slowest decaying aerodynamic excitations and the highest rotor speed, usually leads to the largest response extremes near the rated wind speed. The employment of mechanical brake reduces rotor speed, motion responses and structural responses effectively. During shut down, the responses of yaw motion, nacelle fore-aft acceleration, main shaft bending moment, and tower-bottom side-to-side moment may be of concern for the floating wind turbine studied.
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Riyad, Iftekhar A., and Uttam K. Chakravarty. "An Analysis of Harmonic Airloads Acting on Helicopter Rotor Blades." In ASME 2018 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/imece2018-86625.
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Rotary wing aircrafts in any flight conditions suffer from excessive vibration which makes the passengers feel uncomfortable and causes fatigue failure in the structure. The main sources of vibration are the rotor harmonic airloads which originate primarily from the rapid variation of flow around the blade due to the vortex wake. Unlike fixed wing aircrafts, helicopter wake consists of helical vortex sheets trailed behind each blade and remains under the rotor disk which induces vertical downwash velocities at chordwise and spanwise stations of the blade. In this study, a mathematical model is developed for rotor blades to compute the harmonic loads induced velocity at rotor blades for two flight conditions-vertical takeoff and landing, and forward flight. This method is useful for the performance analysis of rotor blade and selection of airfoils for the blade. The sectional lift, drag, and pitching moment are computed at a radial blade station for both flight conditions. The numerical integration of Biot-Savart relation are done for all the trailing and shed vortices to calculate the downwash through the rotor disc. The airloads are calculated using the relation between harmonic and inflow coefficients. The lift at a particular radial station is computed considering trailing and shed vortices and summing over each blade. Lifting-surface and lifting-line theories are applied to near wake and far wake, respectively, to calculate the downwash and inflow through the rotor disc. The results for lift are compared to the experimental flight-test data.
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Hennings, H., and J. Belz. "Experimental Investigation of the Aerodynamic Stability of an Annular Compressor Cascade Performing Tuned Pitching Oscillations in Transonic Flow." In ASME 1999 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/99-gt-407.
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A prerequisite for aeroelastic stability investigations on vibrating compressor cascades is the detailed knowledge of the unsteady aerodynamic loads acting on the blades. In order to obtain precise insight into the aerodynamic damping of a vibrating blade assembly, a basic experiment was performed where unsteady pressure distributions were measured for subsonic and transonic flow conditions. The experiments were performed on a non-rotating, two-dimensional section of a compressor cascade in an annular test facility. The cascade consists of 20 blades (NACA3506 profile) mounted on elastic spring suspensions. In order to measure the unsteady pressure distribution, the cascade was set to tuned pitching oscillations (traveling wave modes). Each blade was driven to controlled harmonic torsional motions around midchord by a magnetic excitation system and by inductive displacement probes which measure the feedback signal of the motion. Steady and unsteady pressures were measured by steady pressure taps and piezo-electric pressure transducers, respectively. The measurement of the unsteady aerodynamic response to a shock vibrating on the suction side of the blades was enabled by a dense spacing of transducers in this region. The global aerodynamic stability is assessed by a damping coefficient evaluated from the out-of-phase parts of the unsteady moment coefficients and by the contributions from the local work coefficient, using the measured pressure data.
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Aotsuka, Mizuho, Toshinori Watanabe, and Yasuo Machina. "Role of Shock and Boundary Layer Separation on Unsteady Aerodynamic Characteristics of Oscillating Transonic Cascade." In ASME Turbo Expo 2003, collocated with the 2003 International Joint Power Generation Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/gt2003-38425.
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The unsteady aerodynamic characteristics of an oscillating compressor cascade composed of Double-Circular-Arc airfoil blades were both experimentally and numerically studied under transonic flow conditions. The study aimed at clarifying the role of shock waves and boundary layer separation due to the shock boundary layer interaction on the vibration characteristics of the blades. The measurement of the unsteady aerodynamic moment on the blades was conducted in a transonic linear cascade tunnel using an influence coefficient method. The cascade was composed of seven DCA blades, the central one of which was an oscillating blade in a pitching mode. The unsteady moment was measured on the central blade as well as the two neighboring blades. The behavior of the shock waves was visualized through a schlieren technique. A quasi-three dimensional Navier-Stokes code was developed for the present numerical simulation of the unsteady flow fields around the oscillating blades. A k-ε turbulence model was utilized to adequately simulate the flow separation phenomena caused by the shock-boundary layer interaction. The experimental and numerical results complemented each other and enabled a detailed understanding of the unsteady aerodynamic behavior of the cascade. It was found that the surface pressure fluctuations induced by the shock oscillation were the governing factor for the unsteady aerodynamic moment acting on the blades. Such pressure fluctuations were primarily induced by the movement of impingement point of the shock on the blade surface. During the shock oscillation the separated region caused by the shock boundary layer interaction also oscillated along the blade surface, and induced additional pressure fluctuations. The shock oscillation and the movement of the separated region were found to play the principal role in the unsteady aerodynamic and vibration characteristics of the transonic compressor cascade.
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Asgari, Ehsan, Armin Sheidani, and Mehran Tadjfar. "Study on the Effects of Active Flow Control on Aerodynamic Performance of Two Airfoils in Tandem Configuration." In ASME 2017 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/fedsm2017-69461.
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Aerodynamic investigation of tandem airfoil configuration has so many applications in different industries that has become a topic of scientific interest since many years ago. One can name a lot of applications in this field such as the aerodynamic interaction between a wing and a tail or a wing and a flap of an aircraft, blades of a rotor and a stator in a compressor or turbine, the tandem blades in the rotor of a compressor, wings of an MAV, to name but a few. The primary objective of this research is to investigate the effect of active flow control (AFC) on two airfoils in tandem configuration, in which the upstream airfoil undergo pitching motion and the downstream airfoil is stationary. In the first place, the aerodynamic characteristics of airfoils in tandem configuration such as lift and drag coefficient is obtained when there is no flow control on the airfoils (clean case). Following this, the mentioned quantities are calculated for the airfoils when AFC has been applied on the forefoil. In order to analyze the effect of AFC and tandem configuration aerodynamic characteristics, the lift and drag coefficient of clean case is compared to those of the controlled case. The result suggests that AFC has caused the amount of CL to grow significantly. It was also observed that the tandem configuration had little influence on the forefoil. On the other hand, the vortices coming from the upstream airfoil generated thrust on the hindfoil. In case of AFC, our results suggest that fluctuations of both lift and drag forces decrease in the hindfoil. It is worth mentioning that this research is among the firsts studying the effect of AFC on tandem airfoils and will pave the way for those who are interested in this field.
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Camporeale, S. M., M. Torresi, G. Pascazio, and B. Fortunato. "A 3D Unsteady Analysis of a Wells Turbine in a Sea-Wave Energy Conversion Device." In ASME Turbo Expo 2003, collocated with the 2003 International Joint Power Generation Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/gt2003-38715.
Full textAbstract:
A Wells turbine designed for power generation in an innovative OWC (Oscillating Water Column) device for sea-wave energy conversion is investigated. This work aims to predict the turbine performance under a continuously variable reciprocating flow due to the action of the sea waves. When the amplitude of the oscillating flow reaches high values, stall occurs around the blades with a drop in the turbine performance. CFD simulation has been carried out aiming to provide an insight of flow behavior over the blades approaching these large amplitude flow conditions. Three test cases, preliminarily examined in order to assess the capability of the numerical methods, are presented and discussed: the first test-case concerns the 2D unsteady turbulent flow past a symmetrical airfoil undergoing oscillating pitching motion; the second test case concerns the 3D analysis of a high solidity Wells turbine in presence of different constant axial fluxes; the third test case concerns the 3D analysis of a high solidity Wells turbine in presence of an oscillating axial flux. Finally the flow past the low solidity Wells turbine rotor is simulated. The analysis has been performed by considering the flow to be unsteady, incompressible and viscous, while turbulence was modeled using the one-equation Spalart Allmaras model or the two-equations k-ω model.