On the effects of wind shear and veer on the power of a downstream turbine

Abstract. Understanding flow behavior within wind farms remains one of the central challenges in wind energy research, where wakes play a prominent role by coupling individual machines together. In fact, turbines are frequently operated under waked conditions, with wake effects on power production further modulated by atmospheric stability at the site. This paper investigates the influence of wind shear and veer on the power output of a waked wind turbine. The analysis is based on field measurements from two aligned wind turbines operating under inflow conditions that are often strongly sheared and veered. The results demonstrate that both shear and veer significantly affect wake characteristics and trajectory. Because isolating their individual contributions from field data alone is challenging, dedicated computational fluid dynamics (CFD) simulations were performed, confirming the experimental observations and enabling the effects of shear and veer to be disentangled.

The performance of several wake models was evaluated against experimental data, showing that prediction accuracy can be improved by explicitly accounting for shear and veer effects. This improved accuracy could be leveraged to support various applications. To explore the potential benefits in one exemplary use case, we consider shear- and veer-enhanced models in the context of wake-steering wind farm control. This application, however, requires real-time estimates of wind gradients, which are not available from standard onboard anemometry. To overcome this limitation, a wind sensing technique based on blade load measurements is employed to estimate shear and veer during operation. Furthermore, the strong correlation between these two quantities observed at the test site is exploited to simplify practical implementation. Wake-steering simulations indicate that incorporating shear and veer into the control strategy can lead to improved power capture.