Vortex Shedding Lock-In due to Stream-Wise Oscillation of a 2-D Wind Turbine Blade Section at High Angles of Attack

Abstract

The unsteady, incompressible flow around a translating two-dimensional wind turbine blade section (NREL S809) in the stream-wise direction has been simulated using unsteady RANS with the transition SST turbulence model. The Reynolds number is Re = 106 referred to a chord length of 1 m. A prescribed sinusoidal stream-wise motion has been applied at a fixed amplitude of 0.25 m for a range of high angles of attack [30° < α < 150°]. At these incidences, the airfoil will behave more like a bluff body and may experience periodic vortex shedding. It is well known that oscillations can lead to a synchronization (lock-in) of the vortex shedding frequency, fv, with the body’s motion frequency, fs, in bluff body flows. In order to investigate the susceptibility of the wind turbine blade section to lock-in, a parametric study has been conducted varying the frequency ratio r, (r = fs/fv0), in a range around r = 1 and r = 0.5. The lock-in region boundaries have been proposed and an analysis of the effect of the oscillation amplitude has been conducted. The synchronization map obtained suggests that, for the vibration amplitude considered, the risk of vortex-induced vibration is more significant in the regions of α = 35° and α = 145°. Furthermore, it has been found that for some stream-wise amplitudes, increasing the oscillation amplitude, lock-in appears to be unexpectedly suppressed in the vicinity of r = 1.

Vortex Shedding Lock-In due to Pitching Oscillation of a Wind Turbine Blade Section at High Angles of Attack

“…Lind and Jones [22] have reported experimentally determined Strouhal numbers and aerodynamic loads for a static NACA0012 at Reynolds numbers of up to 6 6 × 10 5 and they note that the behavior of thicker sections is qualitatively similar. Pellegrino and Meskell [23] have examined the effect of streamwise translational oscillation on vortex shedding from the S809 airfoil section. The goal of the first part of the current work is to determine the extent of lock-in, for a pitching cambered airfoil (NREL S809) at a given oscillation amplitude for different positive high angles of attack, using uRANS.…”

“…The domain, shown in Figure 2, extends to 10 c (airfoil chord) length from the body in the upstream direction, 40 c in the downstream direction, and 20 c in the cross-flow direction. The reference chord length is 1 m. The model is similar to that which was implemented by Pellegrino and Meskell [23] for the case of vortex shedding from a translating S809 airfoil.…”

Vortex induced vibrations of wind turbine blades: Influence of the tip geometry

“…Even if the proneness of standstill wind turbine blades to experience flow induced vibrations was predicted in several works based on airfoils Pellegrino and Meskell, 2014;Zou et al, 2015;and Meskell and Pellegrino, 2019), the first research that studied a representative blade geometry was carried out by Heinz et al (2016b). The authors presented a computational study of a 86 m long wind turbine blade, corresponding to the reference wind turbine (RWT) developed by the Technical University of Denmark (DTU) known as DTU 10MW RWT (Bak et al, 2013).…”