A new simulation method for turbines in wake - Applied to extreme response during operation

The work focuses on prediction of load response for wind turbines operating in wind forms using a newly developed aeroelostic simulation method The traditionally used concept is to adjust the free flow turbulence intensity to account for increased loads in wind farms-a methodology that might be suitable for fatigue load simulation. For extreme response during operation the success of this simplified approach depends significantly on the physical mechanism causing the extremes. If the physical mechanism creating increased loads in wake operation is different from an increased turbulence intensity, the resulting extremes might be erroneous. For blade loads the traditionally used simplified approach works better than for integrated rotor loads-where the instantaneous load gradient across the rotor disc is causing the extreme loads. In the article the new wake simulation approach is illustrated with flapwise blade loads and yaw loads as examples. In this method it is assumed that the wind speed deficit moves transversally depending on the free turbulence transversal components, and it is used as inflow for the actual turbine. It is shown that the new method simultaneously predicts power reduction and load response characteristics for these loads in wake conditions in good agreement with measurements. The results are compared with the traditionally used simplified method, and this approach seems conservative for some loads, e.g. the extreme blade moments, and non-conservative for others, e.g. the extreme yaw moments. Copyright (C) 2004 John Wiley Sons, Ltd.