A calibration method for downwind wake models accounting for the unsteady behaviour of the wind turbine tower shadow behind monopile and truss towers

摘要

Traditionally wind turbines are built in the upwind configuration, but the alternative of a downwind rotor has distinct advantages. A main issue with such a configuration is the tower shadow effect. The presence of the tower generates a complex wind field, consisting of an averaged velocity deficit, unsteady fluctuations from vortex shedding processes and turbulence. Since this tower shadow is commonly implemented using parametric steady wake models, the dynamic behaviour of the wake is not directly accounted for. The present paper introduces a general method for calibrating the parametric steady wake models and an effective turbulence intensity (accounting both for the velocity profile and the unsteady effects) from computational fluid dynamic simulations of the unsteady structural shadow.To demonstrate its potential the method is used in a blade fatigue comparison study. A 15 percent more flexible and lighter blade for the downwind mounted rotors showed a decrease in blade fatigue loads of three, four, and two percent compared to the conventional upwind mounted rotor on a monopile tower for the monopile tower and truss towers at 0 and 22.5 degrees, respectively. This example shows that the truss tower at 0 degree angle seems to result in the lowest blade fatigue loads.The proposed calibration method is completely general and can be used to obtain efficient, effective engineering models for the aerodynamic flow behind complex, multi-membered structures.