Abstract
Abstract. This paper investigates the aerodynamic impact of Gurney flaps on a research wind turbine of the Hermann-Föttinger Institute at the Technische Universität Berlin. The rotor radius is 1.5 m, and the blade configurations consist of the clean and the tripped baseline cases, emulating the effects of forced leading-edge transition. The wind tunnel experiments include three operation points based on tip speed ratios of 3.0, 4.3, and 5.6, reaching Reynolds numbers of approximately 2.5×105. The measurements are taken by means of three different methods: ultrasonic anemometry in the wake, surface pressure taps in the midspan blade region, and strain gauges at the blade root. The retrofit applications consist of two Gurney flap heights of 0.5 % and 1.0 % in relation to the chord length, which are implemented perpendicular to the pressure side at the trailing edge. As a result, the Gurney flap configurations lead to performance improvements in terms of the axial wake velocities, the angles of attack and the lift coefficients. The enhancement of the root bending moments implies an increase in both the rotor torque and the thrust. Furthermore, the aerodynamic impact appears to be more pronounced in the tripped case compared to the clean case. Gurney flaps are considered a passive flow-control device worth investigating for the use on horizontal-axis wind turbines.
Highlights
The energy yield of modern horizontal-axis wind turbines (HAWTs) is supposed to be optimal while keeping the maintenance costs as low as possible over a lifetime of around 20 years
This paper investigates the retrofit application of Gurney flaps (GFs) in order to improve the aerodynamic performance of rotor blades
According to the steady-state blade element momentum (BEM) method, the optimum axial wake velocity is supposed to be around one-third of the inflow (Burton et al, 2011)
Summary
The energy yield of modern horizontal-axis wind turbines (HAWTs) is supposed to be optimal while keeping the maintenance costs as low as possible over a lifetime of around 20 years. Separation is a problem especially in the inner blade region towards the root, where the angles of attack (AoAs) are elevated due to structural constraints, such as limited chord length and twist angles (see Fig. 1a). The resulting dynamic loads contribute to the material fatigue of the blade (Mueller-Vahl et al, 2012). For this reason, passive flow-control (PFC) devices, such as vortex generators (VGs), are implemented in the inner blade region of different-size HAWTs aiming at stall delay (Pechlivanoglou et al, 2013). The long-standing surface erosion causes roughness effects, especially close to the leading edge (LE; see Fig. 1b). The energy yield of HAWTs is often found to be lower than predicted or regressing over time (Wilcox et al, 2017)
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