Turbulence in the wake increases fatigue damage of downstream wind turbines compared with ambient wind turbines. The current international specification published by International Electrotechnical Commission (IEC61400-1 Ed3.1) assumes uniform turbulence intensity in the wake due to the upstream turbines. The objective of this research is to investigate the effects of turbulence intensity distribution on downstream wind turbine fatigue damage. A previous study suggested that actual turbulence intensity distribution is approximately represented as a bell shaped from the measurement data. We then assumed that the bell shape is approximated by applying a simple Gaussian distribution. In this proposed model, turbulence intensity at the wake center is calculated using IEC recommended model, and wake width is calculated using the Park model which is one of the widely used wake model. In addition, mean wind speed is assumed as constant inside the wake. Calculation results using the proposed model were compared with measurement data based on damage equivalent load (DEL). Strains are measured to calculate DEL by using strain gauges at the tower base and the blade root of Hitachi HTW2.0-80. As a result of comparing DEL calculated using the wake model and the measurement data, the IEC model was shown to overestimate fatigue damage of the wind turbine in this research whereas the proposed Gauss model showed similar trends with the field test data.
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