Numerical assessment of a deformable trailing-edge flap on aerodynamic load control of a pitching S809 airfoil using OpenFOAM

2019 ◽  
Vol 233 (7) ◽  
pp. 890-900
Author(s):  
Mahbod Seyednia ◽  
Mehran Masdari ◽  
Shidvash Vakilipour
Keyword(s):  
Phase Shift ◽  
Flow Control ◽  
Hysteresis Loops ◽  
Aerodynamic Characteristics ◽  
Aerodynamic Load ◽  
Trailing Edge ◽  
Numerical Work ◽  
Pitching Motion ◽  
Trailing Edge Flap ◽  
Fatigue Loads

Due to the unsteady nature of the flow around horizontal-axis wind turbines, the blades are subjected to severe unsteady and fatigue loads. This necessitates an in-depth aerodynamic analysis of flow control techniques to enhance the performance of a wind turbine as well as the lifetime of its components. Using OpenFOAM package in this study, a series of two-dimensional incompressible simulations are performed to present a deeper insight into the aerodynamic characteristics of an oscillating deformable trailing-edge flap, as a promising flow control device, in a sinusoidal pitching motion of an S809 airfoil. Herein, it is of particular interest to investigate the effects of deformable trailing-edge flap size, oscillation frequency, and the phase shift with reference to airfoil motion on lift and drag hysteresis loops. For this purpose, a pure-pitching motion of an S809 airfoil without flap deflection is considered as the benchmark problem in which the airfoil oscillates in the near-stall region at [Formula: see text]. After validation and verification of our simulations through comparison against the corresponding experimental and numerical work, a comprehensive investigation is conducted to study the effects of the aforementioned parameters on the aerodynamic loads. Our results reveal the fact that an out-of-phase deflection of the deformable trailing-edge flap with a frequency equal to the airfoil frequency can significantly mitigate the fatigue load. Under these circumstances, an increase in the deformable trailing-edge flap size can also help the airfoil experience less-severe loads in a cycle of motion. Furthermore, higher values of deformable trailing-edge flap frequency or other values of phase shift except the out-of-phase oscillation cannot alleviate fatigue loads. An airfoil under these conditions can, however, enhance the resultant load required for a blade rotation in the case of low wind periods.

New combinational active control strategy for improving aerodynamic characteristics of airfoil and rotor

2019 ◽  
Vol 234 (4) ◽  
pp. 977-996
Author(s):  
Yi-yang Ma ◽  
Qi-jun Zhao ◽  
Guo-qing Zhao
Keyword(s):  
Flow Control ◽  
Control Strategy ◽  
Active Flow Control ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Synthetic Jet ◽  
Dynamic Stall ◽  
Trailing Edge ◽  
Trailing Edge Flap ◽  
Cfd Method

In order to improve the aerodynamic characteristics of rotor, a new active flow control strategy by combining a synthetic jet actuator and a variable droop leading-edge or a trailing-edge flap has been proposed. Their control effects are numerically investigated by computational fluid dynamics (CFD) method. The validated results indicate that variable droop leading-edge and synthetic jet can suppress the formation of dynamic stall vortex and delay flow separation over rotor airfoil. Compared with the baseline state, Cdmax and Cmmax are significantly reduced. Furthermore, parametric analyses on dynamic stall control of airfoil by the combinational method are conducted, and it indicates that the aerodynamic characteristics of the oscillating rotor airfoil can be significantly improved when the non-dimensional frequency ( k*) of variable droop leading-edge is about 1.0. At last, simulations are conducted for the flow control of rotor by the combinational method. The numerical results indicate that large droop angle of variable droop leading-edge can better reduce the torque coefficient of rotor and the trailing-edge flap has the capability of increasing the thrust of rotor. Also, the synthetic jet could further improve the aerodynamic characteristics of rotor.

Dynamic Stall Flow Control via a Trailing-Edge Flap

AIAA Journal ◽  
2006 ◽  
Vol 44 (3) ◽  
pp. 469-480 ◽  
Author(s):  
P. Gerontakos ◽  
T. Lee
Keyword(s):  
Flow Control ◽  
Dynamic Stall ◽  
Trailing Edge ◽  
Trailing Edge Flap

Alleviation of Airfoil Dynamic Stall Moments via Trailing-Edge Flap Flow Control

AIAA Journal ◽  
10.2514/1.853 ◽  
2004 ◽  
Vol 42 (1) ◽  
pp. 17-25 ◽  
Author(s):  
Daniel Feszty ◽  
Eric A. Gillies ◽  
Marco Vezza
Keyword(s):  
Flow Control ◽  
Dynamic Stall ◽  
Trailing Edge ◽  
Trailing Edge Flap

Dynamic Aeroelastic Response of Wind Turbine Rotors Under Active Flow Control

2019 ◽  
Author(s):  
Muraleekrishnan Menon ◽  
Fernando L. Ponta
Keyword(s):  
Flow Control ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Active Flow Control ◽  
Load Control ◽  
Aerodynamic Load ◽  
Trailing Edge ◽  
Trailing Edge Flaps ◽  
Utility Scale ◽  
Active Flow

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.

Wind Tunnel Testing of a Helicopter Rotor Trailing Edge Flap Actuated via Pneumatic Artificial Muscles

2010 ◽  
Author(s):  
Benjamin K. S. Woods ◽  
Norman M. Wereley ◽  
Curt S. Kothera
Keyword(s):  
Wind Tunnel ◽  
Aerodynamic Load ◽  
Artificial Muscles ◽  
Specific Work ◽  
Test Model ◽  
Trailing Edge ◽  
Actuation System ◽  
Wide Range ◽  
Pneumatic Artificial Muscles ◽  
Trailing Edge Flap

A novel active trailing edge flap actuation system is under development. This system differs significantly from previous trailing edge flap systems in that it is driven by a pneumatic actuator technology. Pneumatic Artificial Muscles (PAMs) were chosen because of several attractive properties, including high specific work and power output, an expendable operating fluid, and robustness. The actuation system is sized for a full scale active rotor system for a Bell 407 scale helicopter. This system is designed to produce large flap deflections (±20°) at the main rotor rotation frequency (1/rev) to create large amplitude thrust variation for primary control of the helicopter. Additionally, it is designed to produce smaller magnitude deflections at higher frequencies, up to 5/rev (N+1/rev), to provide vibration mitigation capability. The basic configuration has a pair of Pneumatic Artificial Muscles mounted antagonistically in the root of each blade. A bellcrank and linkage system transfers the force and motion of these actuators to a trailing edge flap on the outboard portion of the rotor. A reduced span wind tunnel test model of this system has been built and tested in the Glenn L. Martin Wind Tunnel at the University of Maryland at wind speeds up to M = 0.3. The test article consisted of a 5-ft long tip section of a Bell 407 rotor blade cantilevered from the base of the tunnel with a 34 in, 15% chord plain flap that was driven by the PAM actuation system. Testing over a wide range of aerodynamic conditions and actuation parameters established the considerable control authority and bandwidth of the system at the aerodynamic load levels available in the tunnel. Comparison of quasi-static experimental results shows good agreement with predictions made using a simple system model.

scholarly journals Deep dynamic stall and active aerodynamic modification on a S833 airfoil using pitching trailing edge flap

2020 ◽  
pp. 0309524X2093885
Author(s):  
Farid Samara ◽  
David A Johnson
Keyword(s):  
Wind Turbine ◽  
Turbine Blades ◽  
Hysteresis Loops ◽  
Bending Moment ◽  
Dynamic Stall ◽  
Wind Turbine Blades ◽  
Trailing Edge ◽  
Load Fluctuation ◽  
Trailing Edge Flaps ◽  
Trailing Edge Flap

Due to the dynamic nature of the wind resource, wind turbine blades are subjected to significant variation in flow parameters, such as the angle of attack ([Formula: see text]). In some cases, the occurrence of dynamic stall on wind turbine blades causes load fluctuation which leads to material fatigue that tends to decrease the life span of the blades. In this study, the influence of a trailing edge flap on dynamic stall effects is investigated at high [Formula: see text] typical of wind turbines but atypical elsewhere. Pitching of the trailing edge flap was found to have a significant impact on the dynamic stall hysteresis loops responsible for the load fluctuation. Frequency analysis showed that the trailing edge flap was capable of reducing the cyclic fluctuation in the coefficient of lift and root bending moment by at least 26% and 24%, respectively. These results are a significant contribution toward understanding the advantages of using trailing edge flaps and how implementing them will reduce wind turbine blade load fluctuations.

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