Study of the flow fields over simplified topographies with different roughness conditions using large eddy simulations

Abstract

The parameters influencing the wind turbine fatigue load calculations, such as two-point correlations Ruu, power spectrum density Su, turbulent length scale Lu, skewness Sku, and kurtosis Kuu of the wind are examined. Four simplified topographies, i.e., a 3D hill with smooth ground (3Ds), a 3D hill with rough ground (3Dr), a 2D ridge with smooth ground (2Ds), and a 2D ridge with rough ground (2Dr) are considered to investigate the influence from the shape of the topography and the ground roughness conditions. Ruu was found to vary considerably for different hill shapes and ground roughness conditions. Sku and Kuu peaked in the shear layer region in the smooth cases, but not in the rough cases. Su exhibited concentration in the wake in the 3Ds, 3Dr, and 2Ds cases, but not in the 2Dr case. In addition, a prominent increase in Lux was observed just above the summit of the smooth 3D hill. The flow fields were further visualized using the enstrophy and Q-criteria. Coherent turbulent structures were observed to exist in the wake in the 3Ds, 3Dr, and 2Ds cases, whereas the flow was highly mixed in the wake in the 2Dr case.