Wind inflow observation from load harmonics: wind tunnel validation of the rotationally symmetric formulation

Abstract

Abstract. The present paper further develops and experimentally validates the previously published idea of estimating the wind inflow at a turbine rotor disk from the machine response. A linear model is formulated that relates one per revolution (1P) harmonics of the in- and out-of-plane blade root bending moments to four wind parameters, representing vertical and horizontal shears and misalignment angles. Improving on this concept, the present work exploits the rotationally symmetric behaviour of the rotor in the formulation of the load-wind model. In a nutshell, this means that the effects on the loads of the vertical shear and misalignment are the same as those of the horizontal quantities, simply shifted by π / 2. This results in a simpler identification of the model, which needs a reduced set of observations. The performance of the proposed method is first tested in a simulation environment and then validated with an experimental data set obtained with an aeroelastically scaled turbine model in a boundary layer wind tunnel.

Wind inflow observation from load harmonics: initial steps towards a field validation

“…The model coefficients F are not all independent, because of the rotational symmetry of the rotor (Bertelè et al, 2019). In a nutshell, the effects on loads caused by the horizontal shear are the same as the ones caused by the vertical shear after a rotation of π/2; the same holds true for the wind misalignment angles.…”

“…This is in fact an intrinsic limit of field testing, where an exact ground truth is in general difficult if not impossible to obtain. Realistic simulations and wind tunnel studies as the ones reported in Bertelè et al (2017Bertelè et al ( , 2018Bertelè et al ( , 2019 -where the ground truth is known-may help in this sense.…”

“…The method based on load harmonics was first proposed by Bottasso and Riboldi (2014), and then further elaborated and improved by Bottasso and Riboldi (2015); Cacciola et al (2016a); Bertelè et al (2017Bertelè et al ( , 2018Bertelè et al ( , 2019. In a nutshell, this method is based on the fact that some characteristics of the inflow (horizontal and vertical shear, lateral and vertical misalignment angles) generate a specific response of the rotor at the 1P (once per revolution) frequency.…”

“…Even when a model is available, it might not have been fully validated, so that a purely data-driven approach has a significant appeal. Thanks to the rotational symmetry of the rotor (Bertelè et al, 2019), the measured wind conditions that are necessary for training can be limited to the vertical shear and the horizontal (or yaw) misalignment; based on these quantities, the effects caused by horizontal shear and vertical (upflow) misalignment can be reconstructed. After training, the method can estimate the four wind parameters online during turbine operation simply from measured rotor loads.…”

Detection of wakes in the inflow of turbines using nacelle lidars

“…A wind state observer for vertical and horizontal shear, yaw misalignment and flow inclination based on flap-and edgewise blade bending moment measurements was formulated and tested through simulations in Bertelè et al (2017) and validated on a scaled experimental turbine in Bertelè et al (2018). In Bottasso et al (2018) a similar observer using flapwise blade bending moments was developed to estimate the average wind speed over four azimuthal sector of the rotor plane.…”