Electro-Thermal De-Icing Process And Its Numerical Simulation Of Wind Turbine

Along with the worldwide rapid development of wind industry,icing problems on wind turbines become more and more noticeable.At present,wind turbine electric-thermal de-icing technology is considered to be the most efficient,realiable,and economically feasible method to deal with icing problems in wind farms.However,due to both the complexity of the ice melting problem on rotating wind turbines and the difficulty of conducting corresponding research,no principal progress has been yet achieved and reported in terms of foundamental technologies.Based on the above research background and combined with many problems faced by the development of wind turbine electro-thermal de-icing system,this paper carried out a systematic study of wind turbine electro-thermal de-icing process to revealed the physical process of ice melting on wind turbine,and thus provided a theoretical basis for the rational de sign and efficient operation of the de-icing system.The main work and achievements of the paper are as follows:(1)Based on the basic physical process and heat conduction process of wind turbine de-icing,both physical model and mathematical blades were established.The dynamic change process of heat exchange among blades,ice layer and environment during the process of ice melting was considered.The generation and growth of air gap,which appears at the bottom of ice layer,was analyzed.The calculation method of ice melting time was given.(2)According to the numerical method which combines the coupled flow and heat transfer calculation method with a two-step sensible heat capacity method,this article established a numerical method for wind turbine de-icing calculation.By applying accurate geometric shapes of iced blade profiles,dynamic simulations of ice melting process were conducted.Meanwhile,wind turbine de-icing facilities were designed and manufactured to conduct verification experiments for the numerical model.The results show that the numerical model of wind turbine de-icing is competent in simulating the dynamic de-icing process of wind turbine.De-icing temperature curves obtained by simulation is in good agreement with the experimental ones,and the error is less than ±5°C,which meets the requirements of engineering application.(3)Based on the analysis of the phenomena and results of the blade de-icing experiments,a natural termination is believed to be existed for wind turbine de-icing process.Via the application of the established numerical model,the velocity and temperature fields in the air gap were investigated.The definition of natural termination condition of blade ice melting is given as: An air gap,which is connected with the outside air at both ends,appears underneath the ice layer,or the temperature field distribution of blade heating area remains stable after triggering of de-icing system.(4)Throught the comprehensive analysis of experimental and numerical results,the complete dynamic de-icing process is analyzed and put forward for the first time.The dynamic deicing process can be divided into five periods: initial temperature rise period,air gap generation period,air gap growth period,natural termination period and ice shedding period.(5)Threshold de-icing heat flux and time-restricted de-icing heat flux were calculated and analyzed via the application of numerical model.The results show that,threshold de-icing heat flux is affected by icing degree,environment temperature,and resultant wind velocity.The time-restricted de-icing heat flux is influenced by de-icing duration,icing degree,environment temperature,and resultant wind velocity.The impact of angle of attack is disordered and negligible for both kinds of heat flux.It is found that the simulated values of threshold and time-restricted de-icing heat flux are in good agreement with the experimental values,and the average errors are 6.6% and 6.9% respectively,which further verified the correctness and accuracy of the numerical model.