Comparison of methods for load simulation for wind turbines operating in wake

Abstract

For simulation of load response for a wind turbine operating in wake conditions, two different approaches exist. One method - the equivalent turbulence method - is based on the assumption that all load generating mechanisms causing increased loads in wake operation can be merged into an equivalent value of increased turbulence intensity. This method is specified in the IEC61400-1 safety standard. The other method (the new dynamic wake meandering model) is a recently developed more physical approach, taking into account the transversal and vertical dynamics of the wake (i.e. wake meandering). The objective of the work is to compare these two methods for a specific turbine in a specific wind farm environment. Both fatigue loads and ultimate loads are considered. The turbine is a 2.0 MW variable speed/pitch controlled turbine. The aeroelastic model HAWC has been used for the investigation. A number of fatigue load cases are analyzed using the Rainflow counting method, and the combined life time fatigue loads are compared for the two different wake simulation methods at mean wind speeds 10m/s and 20m/s, respectively. The difference in fatigue load is within 20% for most load sensors. Concerning the extreme loads, no differences are expected for the stand still/idling 50-year load case; however, for extreme loads occurring during normal operation the wake method applied influences the results significantly. The main differences between the two wake simulations methods are seen for the extreme yaw loads during operation. © 2007 IOP Publishing Ltd.