Simulation of transient gusts on the NREL 5 MW wind turbine using the URANS solver THETA

Abstract

A procedure to propagate longitudinal transient gusts through a flow field by using the resolved-gust approach is implemented in the URANS solver THETA. Both the gust strike of a 1-cos() gust and an extreme operating gust following the IEC 61400-1 standard are investigated on the generic NREL 5 MW wind turbine at rated operating conditions. The impact of both gusts on pressure distributions, rotor thrust, rotor torque, and flow states on the blade are examined and quantified. The flow states on the rotor blade before the gust strike at maximum and minimum gust velocity are compared. An increased blade loading is detectable in the pressure coefficients and integrated blade loads. The friction force coefficients indicate the dynamic separation and re-attachment of the flow during the gust. Moreover, a verification of the method is performed by comparing the rotor torque during the extreme operating gust to results of FAST rotor code.