Pressure-based lift estimation and its application to feedforward load control employing trailing-edge flaps

This experimental load control study presents results of an active trailing-edge flap feedforward controller for wind turbine applications. The controller input is derived from pressure-based lift estimation methods that rely either on a quasi-steady method, based on a three-hole probe, or on an unsteady method that is based on three selected surface pressure ports. Furthermore, a standard feedback controller, based on force balance measurements, is compared to the feedforward control. A Clark-Y airfoil is employed for the wing that is equipped with a trailing-edge flap of inline-formula $M1inlinescrollmathmlx/c=\mathrm{normal\; 30}\mathrm{italic\; \%}$ 57pt14ptsvg-formulamathimg01fd0c478569bd3d0f7dbe2b29970009 wes-6-221-2021-ie00001.svg57pt14ptwes-6-221-2021-ie00001.png chordwise extension. Inflow disturbances are created by a two-dimensional active grid. The Reynolds number is inline-formulaRe=290 000, and reduced frequencies of inline-formulak=0.07 up to inline-formulak=0.32 are analyzed. Within the first part of the paper, the lift estimation methods are compared. The surface-pressure-based method shows generally more accurate results, whereas the three-hole probe estimate overpredicts the lift amplitudes with increasing frequencies. Nonetheless, employing the latter as input to the feedforward controller is more promising as a beneficial phase lead is introduced by this method. A successful load alleviation was achieved up to reduced frequencies of inline-formulak=0.192.