LES study of topographical effects of simplified 3D hills with different slopes on ABL flows considering terrain exposure conditions

The oncoming turbulence is of particular importance with respect to the investigation of the turbulent flow fields over hilly terrain, which plays an essential role regarding the optimization of micro-siting of the wind farm and reasonable structural design of wind turbines. In this study, large-eddy simulations (LES) are performed to elucidate the effects of wind shear coefficients (WSCs) and upstream turbulence intensities (TIs) on the complex wind flow fields over the simplified 3-D hills. Systematical analysis of the wind turbulence properties related to the micro-siting and fatigue loads of wind turbines, including fractional speed-up ratio (SUR), terrain-induced TI, velocity spectrum and wind speed probability density function, is performed in a quantitative manner. Stronger non-Gaussianity is identified in the wake of gentle-sloped and moderate-sloped hills, which is weakened by increased WSC and enhanced TI. In addition, remarkable SURs are observed mostly at the summit of a steep-sloped hill near the hill surface, and the fractional speed-up factor is found to increase significantly under higher WSC and larger TI. Furthermore, the influence of topography on the wind direction field is also examined, which shows little dependence on the WSCs and TIs.

Automated summary

In this study, large-eddy simulations (LES) were used to investigate the turbulent flow fields over hilly terrain, revealing significant effects of wind shear coefficients (WSCs) and upstream turbulence intensities (TIs) on the turbulence properties. Non-Gaussianity was stronger in the wake of gentle-sloped and moderate-sloped hills, and the topography had little influence on the wind direction field.