Experimental Study On Time-varying Structural Performance Of Wind Turbines Based On Aero-optimization Model

Wind energy,as a clean and sustainable energy,plays an increasingly important role in the energy mix of the world today.Monopile foundation is the most common and widely used turbine foundation.During the service period of the turbine for 20-30 years,the mechanical behavior of soil around the pile will change with time,which leads to time-varying dynamic performance of turbine structure,affecting structural safety and service life.In view of this phenomenon,a series of model tests are designed to study the effect of pile-soil effect on the dynamic performance of monopile turbine structure.The main contents are as follows:For accurately simulating the load and boundary conditions of the turbine,the scale scheme of the turbine model is systematically proposed,and the similarity criterion combining aerodynamic characteristics and structural dynamic characteristics is established with the similarity of the Strouhal number.A model blade optimization design method of aerodynamic similarity is proposed to overcome the problem of the reduction of thrust coefficient caused by scale effect.Based on the prototype of NREL 5MW turbine,the 1:100 scale model of turbine including blades,engine room,tower and monopile foundation is designed and manufactured.Based on the newly designed turbine model and the existing wind-structure-soil coupling test platform,the aerodynamic and dynamic performance of the turbine model is tested and verified;The dynamic behavior of turbine model with rigid foundation and monopile foundation under different load conditions are compared and analyzed.It is found that the fundamental frequency of the turbine of running state is larger than that of static state,and it decreases with increasing rotational speed;The peak value and amplitude of the acceleration at the top of the tower decrease to a certain extent due to the pile-soil effect,which indicates that the pile-soil damping has a weakening effect on the structural vibration.Because of the plastic deformation of soil around the monopile,the upwind displacement increment and displacement standard deviation in the engine room of the turbine are greatly increased with the increase of load.The time-varying law of dynamic performance of turbine structure is further studied.By controlling the wind speed of wind tunnel and the rotational speed of turbine,the influence of vary pile diameter and load intensity on the vibration modal and dynamic response of turbine is studied.It is found that with the increase of loading cycle,the fundamental frequency of turbine structure increases to a certain extent,and the damping ratio has no obvious change rule,and the initial value and amplitude of both are greatly affected by the pile diameter;The dynamic response amplitude of the turbine structure is reduced by time-varying dynamic behavior;The amplitude of the dynamic response of the turbine is obviously affected by the pile diameter,and the smaller the pile diameter,the greater the amplitude of the decrease;In the design of turbine structure,the time-varying law of structural modal and dynamic response should be fully considered to avoid fatigue failure of the structure or affecting its normal use due to excessive cumulative rotation angle.