The Significance of Bypass Transition on the Annual Energy Production of an Offshore Wind Turbine

Abstract

Awareness of Leading-Edge Erosion (LEE) on wind turbine blades, and the impacts it can have on Annual Energy Production (AEP) have increased significantly over recent years. This is especially important in offshore environments, where a combination of more extreme weather and higher tip speeds result in higher rates of erosion. In this paper the impact of LEE on AEP has been quantified and the derived method validated. The DTU 10 MW Reference Wind Turbine (RWT) is used to demonstrate the method. An equivalent sand grain roughness approach in CFD is used to simulate clean and roughened aerofoil performance. These CFD results are applied to a Blade Element Momentum (BEM) model of the turbine to generate clean and eroded power curves. Finally, a wind distribution from Anholt offshore wind farm is used to estimate the AEP for the clean and eroded cases. An AEP loss of 0.7% was computed for the specific case considered in this study. This result is benchmarked against those from previously published studies. Most research into LEE has thus far focussed on either estimating the impacts on AEP or mitigating against them, with less emphasis on understanding the physical aerodynamic changes that result in reduced energy output. In this paper the significance of bypass transition on the AEP loss caused by roughness, specifically as it relates to the operational angles of attack of the blade, is examined and found to impact turbine efficiency in this case for over 56% of the total operating time.