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

Abstract

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.

A Numerical Study of Wind Turbine Airfoil Combined Oscillations Considering Phase Difference under Yaw Loads

“…They studied the aerodynamics of NACA0012 airfoil at h=0.4~0.7, Reynolds number Re=1×10 6 , and reduced frequency k=0.8. Reference [16] studied the DS characteristics of S809 airfoil at relative flapwise and…”

“…However, compared with the static airfoil, the reattachment of the dynamic airfoil boundary layer will occur at a lower angle of incidence, resulting in a hysteresis of the aerodynamic coefficient. On the other hand, the periodic load due to DS and the unstable wind turbine wake have a negative impact on the rotor performance of the wind turbine [6][7], leading to fatigue failure [8][9]. In the 1990s, Ramsay et al [10] systematically studied the aerodynamic performance of the airfoil under pitching oscillation motions through wind tunnel tests of the airfoil dedicated to wind turbines.…”

Analysis of dynamic stall control on a pitching airfoil using dynamic mode decomposition

“…Flow control technologies are mainly divided into two categories: active and passive control technologies. Active control technologies require an external energy source to add energy into the boundary layer or auxiliary structure, such as deformable flap, 4 synthetic jets, 5 and plasma actuator. 6,7 Passive control technologies do not consume additional energy or require any auxiliary control system.…”

Investigation on hydrodynamic characteristics of a hydrofoil based on γ-Reθt transition model

“…If the transition effect is not considered in the design or optimization process, the error in energy conversion caused by laminar separation bubbles is as high as 20%. Seyednia [7] found that the inaccuracy of the pressure distribution of the S809 aerofoil at an angle of attack of 5.13º was also solved when the transition was taken into account in the calculation. In the hydraulic machinery investigations, Rijpkema [8] studied the scaling effect of marine propellers and found that the predicted efficiency errors ranged from 15% to 35% at different Reynolds numbers, and the analysis suggested that the performance differences could be related to the incorrect capture of transition on the blades.…”