The dynamic yaw significantly affects the aerodynamic load distribution of wind turbines, and the aerodynamic load is one of the main influencing factors of wind turbine structural stress variation. Taking the NACA4415 horizontal axis wind turbine designed by the research group as the research object, the numerical simulation was used to analyze the distribution characteristics of blade stress, surface thrust coefficient, and the wind turbine power output under periodic dynamic yaw conditions. The results show that the blade stress, blade axial thrust, and wind turbine output power were presented as a cosine distribution with yaw fluctuations. The distribution trend of blade stress showed an increase followed by a decrease from the inside out along the span direction. In addition, due to the influence of dynamic yaw and aerodynamic loads, the stress values near the blade root exhibited significant fluctuations. With the increase in tip speed ratio, the stress values of dynamic windward yaw gradually exceeded those of leeward yaw. Within the range of a 10° to 30° yaw variation period, the stress value with positive yaw was larger than that with negative yaw, and the highest stress value occurred in the range of −5° to 15°. The results can be provided as a theoretical basis for the structural design and yaw control strategies of wind turbines, considering dynamic yaw operation.

A time-resolved particle image velocity (TR-PIV) system was used to test the wake flow of a small horizontal-axis wind turbine at tip speed ratios (TSRs) in the range of 4–6 under uniform inflow and turbulent inflow in order to study the impact of turbulence intensity on wind turbine wake characteristics. The impact of incoming turbulence on the wake structure of a wind turbine and its mechanism was examined by comparing and analyzing the turbulence properties of the wake flow, including velocity field, vortex structure, additional turbulence intensity, and energy distribution coefficient. It was found that tip vortex structure remained intact in the range of 9 R under uniform inflow, and the longitudinal distribution of turbulent intensity had double peaks, indicating that it was in the near wake zone. Under turbulent inflow, the three vortex systems could not be distinguished at the position of 5 R, and the longitudinal distribution of turbulent intensity did not have peaks, the wake vortex system was broken and the wake transitioned to the far wake zone. With the increase in the turbulence intensity and tip speed ratio, the contribution of the longitudinal component of turbulence intensity to the turbulent kinetic energy increases, which is also the reason for the rapid wake recovery. Additionally, the recovery of the wake velocity was sped up in the range of 3 R and gradually decreased after 3 R.

Through the self-researched and manufactured dynamic rotating platform and model wind turbine, experiments were carried out at the open end of the wind tunnel, and the wind direction angle change and the yaw versus wind process were simulated. The influence of two variables (yaw speed and yaw delay time) on wind turbine power and blade stress is studied. The results are: During the dynamic yaw process, blade stress decreases from the root to the tip. Among the 4 yaw speeds (0.5°/s, 1.0°/s, 1.5°/s, 2.0°/s), the stress and power increase the fastest at 0.5°/s yaw speed, and the slowest increase at 2.0°/s. The rate of increase is inversely proportional to the yaw speed. It is found that in the dynamic yaw process, the yaw angle range of 20° to 0° is the main area of stress increase and power increase. In addition, the yaw delay time is investigated. It is found that if there is a delay time of 30S, when the yaw angle is 30°, the stress value decreases by 0.73711MPa, when the yaw angle is 60°, it decreases by 0.02965MPa, and when the yaw angle is 90°, it decreases by 0.0065MPa. It can be known that as the yaw angle increases, the effect of the delay time gradually decreases, so the delay time can be controlled in stages, that is, when the yaw angle is larger, a smaller delay time is used. We also introduce a dimensionless coefficient, which represents the ratio of power to blade stress. It is pointed out that a yaw speed of 0.5°/s is used at a yaw angle of 30°, a yaw speed of 1.0°/s at 60°, and a yaw speed of 2.0°/s at 90°. The results show that the staged control of the yaw speed can avoid power loss and improve the reliability of the wind turbine during operation.

Wind tunnel experiments at a model scale have been carried out to investigate the flow characteristics in the near wake of a wind turbine. Time resolved particle image velocimetry (TRPIV) measurements are applied to visualize the wind turbine wake flow. The instantaneous vorticity, average velocities, turbulence kinetic energy, and Reynolds stresses in the near wake have been measured when the wind turbine is operated at tip speed ratios (TSRs) in the range of 3–5. It was found that wind turbine near the wake flow field can be divided into a velocity increased region, a velocity unchanged region, and a velocity deficit region in the radial direction, and the axial average velocities at different TSRs in the wake reach inflow velocity almost at the same radial location. The rotor wake turbulent kinetic energy appears in two peaks at approximately 0.3R and 0.9R regions in the radial direction. The Reynolds shear stress is less than the Reynolds normal stresses, the axial Reynolds normal stress is larger than the Reynolds shear stress and radial Reynolds normal stress in the blade root region, while the radial Reynolds normal stress is larger than the Reynolds shear stress and axial Reynolds normal stress in the blade tip region. The experimental data may also serve as a benchmark for validation of relevant computational fluid dynamics (CFD) models.

The computational fluid dynamics method was used to simulate the flow field around a wind turbine at the yaw angles of 0°, 15°, 30°, and 45°. The angle of attack and the relative velocity of the spanwise sections of the blade were extracted with the reference points method. By analyzing the pressure distribution and the flow characteristics of the blade surface, the flow mechanism of the blade surface in the yawed condition was discussed. The results showed that the variations of the angle of attack and the relative velocity were related to the azimuth angle and the radius in the yawed condition. The larger the yaw angle was, the larger the variation was. The pressure distribution in the spanwise sections was affected by both the angle of attack and the relative velocity. The angle of attack was more influential than the relative velocity. At the same yaw angle, when the angle of attack decreased, the cp∼x/c curve shrunk inward and the lift force decreased. The larger the yaw angle was, the more obvious the shrink was. The effect of the yaw on the blade root region was higher than its effect on the blade tip region.