A Comparative Study of the Dynamic Wind Loads and Wake Flow Characteristics of a Turbine Sited in Onshore and Offshore Wind Farms

An experimental study was conducted to compare the characteristics of the dynamic wind loads and evolution of the unsteady vortex and turbulent flow structures in the wake of a wind turbine sited in onshore and offshore wind farms. A scaled three-blade Horizontal Axial Wind Turbine (HAWT) model was placed in Atmospheric Boundary Layer (ABL) winds with different mean and turbulence characteristics to simulate the wind conditions in onshore and offshore wind farms. In addition to measuring dynamic wind loads acting on the wind turbine model by using a high-sensitive force-moment sensor unit, a high-resolution digital Particle Image Velocimetry (PIV) system was used to achieve flow field measurements to quantify the characteristics of the turbulent flow in the wake of the wind turbine model. Besides conducting “free-run” PIV measurements to determine the ensemble-averaged statistics of the flow quantities such as mean velocity, Reynolds stress, and Turbulence Kinetic Energy (TKE) distributions in the wake, “phase-locked” PIV measurements were also performed to elucidate further details about evolution of the unsteady vortex structures in the wake flow in relation to the position of the rotating turbine blades. The detailed flow field measurements are correlated with the dynamic wind loads measurements to elucidate underlying physics in order to gain further insight into changes of the dynamic wind loads and wake characteristics behind the wind turbine operating in either onshore or offshore wind farms.