Impact Of The Dynamic Frequency And Stress Characteristics Of Wind Wheel On The Variation Of Flow Field Under Yaw

Wind energy is a kind of available energy that is provided to humans by air flow,it belongs to renewable energy and has broad prospects for development.Different wind speeds,different speeds and different yaw angles will affect the flow field and strain characteristics of wind turbines and the characteristics of vibration frequency,but there is little research on the system at present for the relationship between them.This paper research on a new type of 1.4m diameter wood small horizontal axis through the combined method of experiment and Numerical Simulation.The velocity distribution?the development of tip vortex?the distribution of turbulent kinetic energy and other flow parameters were obtained by using the high-frequency PIV device near the wake,the distribution of velocity field and vorticity field behind the wind turbine is obtained through numerical simulation,and get the surface pressure of the blade.The strain is obtained by the TST5925 C rotating stress strain device and the vibration frequency on the nose tower is obtained by the BK vibration and noise testing system.To obtain the variation of them with different working conditions,the inner relation between the flow field behind the wind turbine and the dynamic frequency characteristics as well as stress characteristics are explored using the wake field as an intermediate variable.First,the wind turbine near wake is analyzed.Extraction of axial velocity and radial velocity behind the blade,the axial velocity decreases and the radial velocity increases with the increase of yaw angle.The pulsating speed root mean square of 30 mm rear of the wind wheel is further extracted and the variation rule under different wind speeds,different speeds and different yaw angles is obtained.We analyze the turbulent kinetic energy of the shooting area under different conditions in order to know more about the flow field in the shooting area.The velocity and vorticity distribution at different yaw angles are obtained in the far wake analysis and the velocity and vorticity are analyzed for the typical rear position of the wind turbine at the time of not yaw.The evolution rule and strength of velocity and vorticity of rear wind field of wind turbines are described at different position.And found,the length of the whole wake of the wind turbine will decrease correspondingly when the speed of the blade becomes larger.Secondly,the strain of the blade is analyzed.The strain values of blades are obtained by two different experimental methods(different speeds and different loads).It is found that the strain value will increase with the increase of load and speed.The increase in strain is larger and smaller under different loads,the increase in strain is approximately equal under different speeds.Determine the load and speed,we obviously see the increase of strain under the constant load is greater with the increase of the incoming wind speed.The load and rotation speed were determined again,and the variation of the strain at different yaw angles was analyzed.In order to understand the correlation between strain and flow field,take the tip point as an example,and compare it with the turbulent energy value at 30 mm behind the tip of the wind wheel in the flow field.It is found that the strain value is basically consistent with the change law of turbulent kinetic energy with the change of different working conditions.To investigate the reason,the distribution of pressure on the surface of the blade at different wind speeds and at different rotational speeds was obtained.It was found that the reason for the increase in strain was due to the difference in surface pressure,but the causes of the larger pressure difference caused by different wind speeds and different rotation speeds were different.Finally,we analyze the changes in the vibration frequency at the top of the nose(closest to the blades)under different conditions,it is found that the yaw angle has little effect on the frequency and acceleration of each mode.Different wind speeds have less influence on the frequency of each mode,but can significantly change the acceleration of some modes.Different rotational speeds can change the rotational basic frequency of the wind turbine.When the rotating fundamental frequency or multiple fundamental frequency is close to some natural frequency of the wind turbine,the vibration acceleration value will be greatly increased,it will severe damage to the structure of the wind turbine.Extract the energy spectrum in the flow field,there are several vibration modes in the energy spectrum,and the frequency value of each mode shape is basically similar to that of the vibration mode in the vibration spectrum.Established the relationship between flow field and vibration frequency with frequency as the link.