The reason why wind tunnel testing is so important in the tracking support design process is that local regulations do not include all the parameters that define the tracking support structure. In addition, the increase in module size reduces the aerodynamic stability of the tracking bracket, and it is necessary to redesign the tracking bracket according to these new conditions. Through the wind tunnel test, more realistic wind pressure coefficient and other data can be obtained, and the aerodynamic stability of the tracking bracket can be evaluated.
The hazards of wind-induced failure
Local standards are mainly applicable to more rigid and heavier structures. For more flexible tracking brackets, the local standards do not provide for the stability of them. In addition, these specifications do not consider the variable torsional stiffness of the torque tube along the tracking bracket. In terms of structural stability, these specifications do not consider the fact that different critical speeds depend on different protection positions.
Since the local regulations do not involve the wind-induced vibration effects of flexible structures, it is necessary to conduct a comprehensive aeroelasticity test on the tracking bracket to investigate the aerodynamic stability of the bracket array under different factors such as incoming flow conditions, tracking angles, and arrangement methods. The flexible scale model of the bracket array is placed in different wind speeds and wind directions, which simulates the natural frequency, damping ratio and other parameters of the tracking support in the manufacturing process, and can obtain the lowest critical wind speed of the tracking support under different conditions.
In addition, the module industry has experienced some substantive changes. Nowadays, large-size modules are more and more used in the photovoltaic industry.
Therefore, upgrading the tracking support to adapt to large-size modules requires many changes in the structural design to ensure the reliability and optimal power generation performance of the system at all wind speeds.
The size and weight of these modules have increased, which affects the stability of the tracking support, so they need to be considered in the wind tunnel test.
An increase in the assembly length means a corresponding increase in the chord length of the tracking support, which in turn increases the torque. The length of the tracking bracket increases with the increase of the module width. Longer support length and longer chord will reduce the natural frequency of the support, thus increasing the wind-induced vibration response and aeroelastic effect.
As the module length increases, the height of the tracking support needs to be increased, which means that the reaction force of the pile foundation increases, so the calculation needs to be corrected.
The R&D team needs to consider these factors when designing the tracking support, and conducted a complete wind tunnel test on the premise of considering the static and aeroelastic effects. Aeroelastic effect is very important to the stability and reliability of tracking support, including flutter, vortex induced resonance and torsional divergence.
● Vortex induced resonance is caused by Karman Vortex Street phenomenon. At the same time, the shedding vortex generated by the first row of the array will also lead to the wake resonance effect of the subsequent rows
●Flutter is a self-excited aerodynamic instability phenomenon, and the aerodynamic self-excited force it receives depends on the movement of the structure itself. Flutter can cause large vibrations in the torsion or vertical bending direction, causing structural damage
●For a highly flexible central torque tube system, the torque applied to the row during its rotation may exceed the torque tube’s bearing capacity, resulting in the so-called torsional divergence effect
Analyzing these effects in different stages of wind tunnel test is helpful to optimize the design of the system and key modules of the tracking support, and improve the stability and reliability of the tracking system in the whole life cycle.
