Wind power is one of the most pivotal components in the renewable energy infrastructure against global climate and fossil-fuel depletion over the past decade. However, the flat and open terrain cannot fully meet the demand to install the wind turbines, particularly with the rapid development of wind power industry. Consequently, a number of turbines are deployed on the complex terrain, such as mountain ridges. Furthermore, the cut slopes can be formed by the hoisting assembly platforms for the wind turbine installation on complex terrains in engineering practice, leading to the varying topography and vegetation coverage. This terrain modification can significantly alter the turbulence characteristics of the wind fields, severely impairing wind turbine power generation efficiency and operational safety. This study aims to explore the turbulent wind fields characteristics over the slope terrain. A two-dimensional ridge terrain was also utilized as the research object. An atmospheric turbulent wind field was established as the inflow condition using narrow band synthesis random flow generation (NSRFG). Large eddy simulations (LES) were subsequently conducted to determine the wind fields over slope terrains. Five excavation positions and five excavation depths were obtained for the hoisting platform. The results show that the wind speed exhibited the following pattern (first increased, then decreased, increases once more, and finally stabilized) with the increasing height at the excavation sites for the five wind turbine installation platforms. When the installation platform was located on the windward side, the wind speed increased and stabilized at the lowest height (compared with the rest locations). As height above the platform increased, turbulence kinetic energy (TKE) demonstrated an initial increase, followed by a decrease, before ultimately reaching a steady state. The minimum TKE peak was achieved to require the lowest height for the TKE stabilization, when the platform was windward positioned, compared with the rest installation positions. There was the minimal influence of the flow separation caused by embankment topography on the turbulent flow characteristics at wind turbine installation platforms under windward siting configurations. Therefore, the windward ridge slope was recommended for the wind turbine installations in the complex terrain. As the excavation depth of the wind turbine installation platform increased, the wind speed fluctuations were intensified at positions closer to the platform surface. At 0.195 times the ridge height excavation depth (0.195H), the wind speed variation range was 1.67 times greater than that at 0.075 times the ridge height excavation depth (0.075H). Among the five excavation depths, the maximum turbulence kinetic energy (TKE) was obtained at 0.165 times the ridge height excavation depth (0.165H), while the minimum peak TKE occurred at 0.075 times the ridge height excavation depth (0.075H). The turbulent flow characteristics shared the minimal interference from the slope terrain-induced flow separation, when the installation platform was excavated to 0.075 times the ridge height (0.075H). Therefore, the excavation depth was the lower tip of the rotor plane over the summit elevation for the wind turbine installations in sloped terrain. This configuration can be expected to minimize the flow separation disturbances in the incoming airstream.

Icing has posed the significant impact on the aerodynamic performance and power output in wind turbines, particularly on the airfoil at the blade tip position. Therefore, it is particularly important to evaluate the performance of wind turbines before and after icing for real operating. According to the conditions of GW87/1500 wind turbine, this study aims to analyze the icing behavior of the blade tip airfoils and the aerodynamic performance using computational fluid dynamics. The objects were also adopted as the commonly-used DU-96W-180, DU-95W-180, and S810 airfoils at the blade tips of the wind turbine. Three kinds of operating conditions were set as the light, medium and heavy icing. The results show that there were the similar icing mass, thickness and limit of DU95-W-180 and DU96-W-180 airfoils. The smaller icing mass and thickness were found on the S810 airfoils; Under the light icing conditions, the angles of attack corresponding to the maximum lift-to-drag ratios of the three airfoils were the same as those under the un-iced condition, which were about 7°. The angles of attack were advanced from 13° to about 11°, corresponding to the peak lift coefficients of the DU96-W-180 and DU95-W-180 airfoils. While the aerodynamic performance of the S810 airfoil was deteriorated more significantly, where the angle of attack was advanced from 13° to about 9° corresponding to the peak lift coefficient; Under the moderate icing conditions, the angles of attack were still about 7° corresponding to the maximum lift-to-drag ratios of DU95-W-180 and DU96-W-180 airfoils, while those of S810 airfoils were advanced to around 5°. The peak lift coefficients were advanced from 13° to 9° corresponding to the peak lift coefficients of the DU96-W-180 and DU95-W-180 airfoils, while those of the S810 airfoils were advanced from 13° to 5°. Moreover, the lift and drag coefficients varied even more drastically. The aerodynamic performance of the three airfoils decreased more significantly under heavy icing conditions. The pressure distribution and surface flow pattern of the blade tip airfoils were measured under different icing conditions. There was the destroyed distribution of surface pressure on the three icing airfoils. The pressure coefficient at the leading edge of the airfoils was oscillated to reduce the lift, indicating the decreasing difference of pressure. There was the great variation in the flow distribution on the airfoil surface before and after icing of the three blade tip airfoils at 5° angle of attack. There was the increase in the separation vortices between the leading and trailing edge position of the DU95-W-180, DU96-W-180, and S810, when the icing condition was ranged from the light to the heavy. The flow separation was aggravated at the boundary layer of the airfoil surface. The better aerodynamic performance of DU96-W-180 airfoil was achieved before and after icing. The finding can be applied to optimize the airfoils of wind turbine blades in cold regions, in order to improve the energy utilization efficiency of wind turbines.