Large Eddy Simulation of Wind Turbine Wakes during the Evening Transition Period

Abstract

A transient simulation of a two inline wind turbines during the evening transition period is modelled using Large Eddy Simulation with an actuator disc method. Two inline turbines are placed parallel to the stream-wise direction and the distance between the turbines is seven rotor diameters. The wind profiles and turbulence data are produced by a precursor simulation. The simulation was carried out for four physical hours and the surface heat flux varies with time according to the evening period. The wind profile evolves over the transition period and the atmospheric stability gradually changes from unstable in the late afternoon to a stable condition in the evening. The wake recovers more quickly in the afternoon and it recovers more slowly corresponding to the changes in atmospheric stability. This causes a reduction in the power output and the mean thrust load of the downstream turbine over the period. Additionally, the velocity spectrum displays higher fluctuations at the downstream turbine.