Experimental Investigation On Torsional Aerodynamic Instability Characteristics Of Single-axis PV Trackers

With the increasing demand for photovoltaic power generation,tracking photovoltaic brackets have been widely used.Among them,the single-axis PV tracker is the most common form of tracking photovoltaic brackets.Due to its large span,flexible structure and low damping,this kind of photovoltaic brackets often cause torsional wind-induced vibration and aerodynamic instability in windy weather.Due to the excessive amplitude,The single-axis PV trackers are destroyed,resulting in significant economic losses.In this thesis,the aerodynamic instability of the singleaxis PV tracker is studied by the vibration test and pressure test of the segment model.The influence of turbulence,torsional stiffness,damping ratio,component chord length,tilt angle and wind speed on the aerodynamic stability of the single-axis PV tracker is clarified,and the mechanism of aerodynamic instability of the single-axis PV tracker is analyzed.The specific work is as follows:(1)The effects of turbulence intensity,tilt angle and wind speed on the torsional aerodynamic stability of the single-axis PV tracker were studied by the sectional model vibration wind tunnel test.The results show that with the increase of turbulence intensity,the critical wind speed of the support with the same tilt angle does not change greatly,but the turbulence intensity will affect the tilt angle range of the single-axis PV tracker aerodynamic instability.Under the larger turbulence intensity,the tilt angle range of the aerodynamic instability of the support is larger.When the turbulence intensity is 20%,the tilt angle range of the large amplitude vibration of the support is-30°～25°.When the turbulence intensity is 0.5%,the tilt angle range of the large amplitude vibration of the support is-15°～15°.In this range,the smaller the tilt angle,the higher the critical wind speed.(2)The effects of natural frequency,damping ratio,component chord length,tilt angle and wind speed on the torsional aerodynamic stability of single-axis photovoltaic support are studied by wind tunnel test.The results show that increasing the torsional stiffness can effectively improve the critical wind speed of aerodynamic instability.With the increase of damping ratio,the aerodynamic instability of 15°angle bracket is effectively suppressed,and the control effect of 0° and 5° angle bracket is very limited.Increasing the chord length of the photovoltaic module will reduce the critical wind speed of the structure.(3)Through the static pressure test of the segment model,the wind pressure coefficient and torque coefficient of the model under different tilt angles are studied,and the most unfavorable working conditions are analyzed,which provides suggestions for the wind protection of the flat single-axis photovoltaic support.The results show that the average value and pulsation value of wind pressure coefficient and torque coefficient at 0° tilt angle are small,and the critical wind speed of torsional aerodynamic instability is higher than that of other tilt angles.The 0° tilt angle can be used as the wind protection tilt angle of the single-axis PV tracker.(4)The aerodynamic damping and aerodynamic stiffness of the photovoltaic module test model under different tilt angles and wind speeds were obtained by the free vibration test of the segment model.The aerodynamic instability mechanism of the single-axis PV tracker was discussed based on the wind-induced vibration theory and mechanism of the structure.The research shows that the torsional aerodynamic instability process of the single-axis PV tracker has obvious separation and reattachment phenomenon,showing obvious aerodynamic coupling effect,and the self-excited force is very significant.The natural vibration characteristics of the structure change greatly with the increase of wind speed,which belongs to the type of self-excited vibration.Compared with torsional relaxation,it is more like nonlinear torsional flutter.