Numerical Simulation Of Downburst And Its Induced Wind Load On Wind Turbine

In recent years,the wind power market in many countries around the world has been growing rapidly.As the number of wind turbines increases,more attention is paid to the operational safety of wind turbines.In 2001,the United States developed and analyzed a database for assessing long-term thunderstorm fluctuations.The data show that thunderstorm strong winds play a leading role in the extreme wind events leading to major damage.Downburst is a kind of small-scale local strong wind with strong outburst.The wind speed near the ground can reach 75m/ s,and the load caused by downburst is quite different from the atmospheric boundary layer wind,which seriously threatens the safety of near ground structures such as wind turbines,transmission line towers,etc.Because of the hazards of downburst and the limitation of code guidance,it is of great value to study the wind characteristics of downburst and its wind load,which can provide basis for the wind resistance design of structure.In this paper,based on the RANS and LES,CFD numerical simulations are conducted to study the wind field characteristics of downburst and the wind load on wind turbine under downburst.Firstly,the three-dimensional steady numerical simulation of the static downburst is carried out by using the impinging jet model,and the simulation results are compared with those of other scholars.The data are in good agreement,which confirms that the model and simulation method selected in this paper are reliable and effective.This paper analyzes the velocity cloud map of the formation,sinking and diffusion process of the downburst,and gives the radial profile,vertical profile and the correlation of the wind speed of the downburst.It can be seen that there are great differences between downburst and atmospheric boundary layer wind.Secondly,in addition to quantifying the complex flow characteristics of downburst wind,the wind turbine model in shutdown status is mounted at different radial positions from the jet port to explore the influence of radial distance on the downburst-induced wind load acting on the wind turbine model.Then,the wind turbine is fixed at the radial position where the maximum wind speed is(r(28)1.0D),and the effect of the downburst acting on the wind turbine is simulated in detail.The results show that the pressure coefficient of the windward side of the wind turbine is positive under the impact of downburst,and the distribution is symmetrical.At the same vertical height,the pressure coefficient on the center line is the largest.With the increase of the height from the ground,the pressure coefficient of the center line of the windward face of the tower increases first and then decreases gradually,reaching the maximum value near the ground.The pressure coefficient on the side and leeward side of the wind turbine is negative.At the same vertical height,the absolute value of the wind pressure coefficient at the intersection with the side of the model is greater than that at the center of the back.Finally,with the help of multiple reference frame MRF model,the numerical simulation is carried out to explore the aerodynamics of the wind turbine blades in the rotating state.And also,the aerodynamic forces of wind turbine blades in two different states under the action of downburst are compared in detail.The results show that the aerodynamic force change trend of the wind turbine blades in the two states under the downburst is consistent at different radial positions,and the peak value is reached when the radial distance r(28)0.5D.The wind turbine blades experience much larger force for the case with its blades stationary than those with the blades in rotation.But the fluctuation of load on the rotating blade is greater.The research results in this paper give the characteristics of the downwind wind field and the law of wind load,which can help to further understand the potential damage of downburst acting on the wind turbine and improve the safety of the wind turbine in thunderstorm-prone areas.