Bidirectional wakes over complex terrain using SCADA data and wake models

Abstract. We investigate bidirectional wake effects between two identical wind turbines in a hill region of northern Japan using Supervisory Control and Data Acquisition (SCADA) data and validate the performance of 12 wake models. The two turbines are located 3.7 times a rotor diameter apart with a different elevation of half of a rotor diameter. We identify the wake effects in terms of wind speed ratio, which is defined as a ratio of wind speed at the downstream wind turbine to that at the upstream wind turbine. By comparing the conditions according to the operating state of the upstream wind turbine, the wakes are clearly detected as minimum wind speed ratios for northeasterly and southwesterly winds. The wind speed ratio decreases with inflow wind speed below the rated wind speed. Increase in turbulence intensity and decrease in power output are greater for southwesterly wind than for northeasterly wind because of the combined effects of the turbine-induced wake and the terrain-induced reduction in wind speed. Then, we compare the simulated wakes from the validate the wake models implemented in PyWake software by using simulated wind fields derived from Wind Atlas Analysis and Application Program (WAsP) Computational Fluid Dynamics (CFD). The wind speed ratios derived from the models show strong dependence on inflow wind speed, reflecting the thrust curve used in the engineering wake models. The wake models commonly overestimate the reduction in wind speed for northeasterly wind and underestimate it for southwesterly wind. Thus, this study demonstrates that additional topographic effects alter the wake effects.