Wind turbines are often clustered within wind farms. A consequence is that some wind turbines may be exposed to the wakes of other turbines, which reduces their lifetime due to the wake turbulence. Knowledge of the wake is thus important, and we carried out wind tunnel experiments to investigate the wakes. We show how models that describe wakes of bluff bodies can help to improve the understanding of wind turbine wakes and wind turbine wake models, particularly by including a virtual origin.

We analyse the non-stationarity in Pearson correlation matrices for high frequency wind turbine data. Applying a hierarchichal k-means clustering to a time series of matrices, we distinguish different states, which exhibit distinct correlation structures. These arise from the turbine control system reacting to the current wind speed. We model boundary wind speeds between the different states. Our method enables accounting for the non-stationarity when predicting or analysing turbine failures.

This paper presents two methods on how to estimate the lift force that is created by a wing. These methods were experimentally assessed in a wind tunnel. Furthermore, an active trailing-edge flap, as seen on airplanes for example, is used to alleviate fluctuating loads that are created within the employed wind tunnel. Thereby, an active flow control device that can potentially serve on wind turbines to lower fatigue or lower the material used for the blades is examined.

When ice forms on wind turbine blades, the smooth surface of the blade becomes rough which changes its aerodynamic performance. So, it is very important to know how to simulate this rough surface since most CFD simulations depend on assuming a smooth surface. This article compares different mathematical models specialized in simulating rough surfaces with results of real ice profiles. The study presents the most accurate model and recommends using it in future airflow simulation of iced blades.