Force Analysis Of Wind Wheel Under Uniform Velocity Change Of Wind Direction

Due to the complexity and changeability of natural wind,the wind turbine is often in a dynamic yaw state during operation.In the study of yaw conditions,different fixed yaw angles are usually changed to explore the influence of yaw on the aerodynamic performance of wind turbines,while the effect of variability of wind direction and wind speed is often ignored.The change of wind direction makes the wind wheel have three-dimensional unsteady characteristics during the rotation process,changing the overall performance of the wind turbine.Therefore,it is of more important practical significance to study the aerodynamic performance of the wind turbine considering the change of wind direction.In this paper,S standard airfoil wind turbines with three-blade horizontal axis independently developed by the research group was taken as the research object,and the method of combining numerical simulation with experiment was adopted for research.In the aspect of numerical simulation,the slip grid and UDF custom program were used in the Fluent solver to carry out research on the aerodynamic performance of wind wheel under uniform wind direction change.In the experimental aspect,the variation of the maximum principal stress and the maximum shear stress along the blade spanwise direction on the blade aerodynamic center line and the output power of the wind turbine under different working conditions are quantitatively analyzed in the opening section of the B1/K1 low-speed wind tunnel.The main research contents and conclusions of this paper are as follows:Firstly,when the yaw angles were 10°,20°and 30°respectively,through comparing the blade gauge pressure distribution of wind turbine under different yaw conditions under rated conditions,we discovered a new rule: the maximum pressure difference between the pressure surface and the suction surface of the wind turbine during dynamic yaw is smaller than that during static yaw,and both these maximum pressure differences were located at the blade tip in the reverse incoming direction,but the static pressure distribution of the three blades under dynamic yaw was more uniform and the overall wind pressure was larger than that under static yaw.This showed that under the same working conditions,the output power of the wind turbine under the dynamic yaw of the wind turbine was less than that under the static yaw,but the overall pressure on the blades was larger and the blades were more easilydamaged.Secondly,the operating parameters such as yaw angle,incoming wind speed,sharp speed ratio and angular velocity of wind direction change were changed in turn,and the aerodynamic performance of wind turbine under different operating conditions at seven yaw positions of 0°,5°,10°,15°,20°,25°and 30°were compared and analyzed.Then it was found that under the same yaw angle,the wind pressure of the wind wheel increased with the increase of the angular velocity of the wind direction change,but it had certain fluctuation.In the process of dynamic yaw,the tip speed ratio had the greatest influence on the blade pressure coefficient,while the incoming wind speed had the smallest influence on the blade surface pressure coefficient,and the influence of wind direction change angular velocity was between the above two.The flow characteristics on the blade surface showed that at 0.35 R from the blade root,the separation vortex would only appear on the blade suction surface when the wind direction changed and the angular velocity was 10 °/s.At 0.55 R and 0.75 R under the angular velocity of other wind direction changes,the diameter of separation vortex increased with the increase of wind speed and increased with the increase of angular velocity under wind direction change.Under the same working condition and at the same yaw position,the difference of the maximum pressure coefficient at the leading edge of the blade increased with the increase of the radial distance,however,the tendency of pressure coefficient decreasing was more obvious with the increase of yaw angle.Finally,we tried a new research method — correlation analysis of the simulated velocity flow field and the experimental structure field.By comparing the simulation and experimental data,we found that under the same working condition,the variation of pressure coefficient at three radial positions(0.35 R,0.55 R,0.75R)in the numerical simulation was consistent with the variation of maximum principal stress and maximum shear stress at the corresponding cross-sectional positions in the experiment.All of them showed that the stress decreased from the blade root to the blade tip,and the stress decreased rapidly at the blade root and the blade tip.This indirectly showed that there was a certain correlation between the structural field and the flow field.In addition,the study also found that the larger the yaw angle under the same working condition,the greater the variation amplitude of the spanwise maximum principal stress value and the maximum shear stress value of the blade were.By comparing the numerical calculation results with the experimental results under the same workingcondition,it was found that the error was the largest when the yaw angle was 30,but it was still below 15%,and the simulation results were reliable.