Vibrations of wind turbine blades in standstill: Mapping the influence of the inflow angles

Abstract

The present investigation used numerical simulations to study the vibrations of a wind turbine blade in standstill. Such vibrations are presumed to affect horizontal axis wind turbine designs and can jeopardize the structural integrity of the machine. The applied numerical methods relied on a fluid–structure interaction (FSI) approach, coupling a computational fluid dynamics (CFD) solver with a multibody finite-element structural solver. A 96-m-long wind turbine blade was studied for a large parametric space, accounting for the variation of both pitch and inclination. The inclination was defined as the angle between the freestream velocity and the cross-sectional plane at the root, allowing for the introduction of a flow component in the spanwise direction. The pitch variation corresponded to the rotation of the inflow around the spanwise axis, steering the angles of attack seen by the airfoils. Two regimes of vibrations were characterized, depending on the considered range of the inclination angle. For high inclinations, the pitch angles leading to vibrations clustered around a particular region of the parametric space, and the appearance of large oscillations was accompanied by the synchronization of the loading with the frequency of motion. At low inclination angles, the mechanism triggering vibrations was relatively similar, even if the excitation spectrum was richer, and the critical pitch angles seemed to be more scattered. Regardless of the inflow, the problem was highly three-dimensional, and several complex flow phenomena such as oblique shedding and phase dislocations were identified.

Multiple limit cycle amplitudes in high-fidelity predictions of standstill wind turbine blade vibrations

“…5. From earlier work (Horcas et al, 2022;Riva et al, 2022), it is known that, for the low wind speeds experienced here, the structural mode shape obtained in HAWCSTAB2 is very similar to the deflection shape seen in FSI.…”

“…As the computations presented here are computationally heavy, three flow scenarios are picked with basis in the study of Horcas et al (2022). One case which shows high vibrations in the mapping study of Horcas et al (2022) is the P = 100 • , I = 50 • case.…”

Multiple limit cycle amplitudes in high fidelity predictions of standstill wind turbine blade vibrations

“…9 shows the results for the flow case P100-I50. The spanwise power per cycle P cycle is here found as the injected work averaged over the time span of n cycles as presented in Horcas et al (2022). The work w s over n cycles is found as the integration over the time range of the sectional loads F s and the velocity of the considered section us .…”

“…Originally in the work of Horcas et al (2022), cases P90-I50 and P95-I50 were found to not cause VIVs, as found in the neighbouring case P100-I50. However, from the FM amplitude sweeps depicted in Fig.…”

“…I is positive when blade points toward the wind with flow from tip to root, and zero when the wind strikes the blade perpendicularly. In particular, (Horcas et al, 2022).…”