Research On Electrothermal De-icing Cycle Controlled Method Of Wind Turbine Blades

The icing on turbine blades caused by low temperature seriously restricts the development of wind power industry,Icing blades would cause the decline of aerodynamic performance,the seriously power loss,and even the damages or other safety accidents.Electrothermal method is an effective blade de-icing technique,but there are only few studies on de-icing method,especially the control strategies in China.In this paper,a new electrothermal de-icing cycle controlled method is proposed,and its control strategy is analyzed in depth.Through theoretical analysis,numerical modeling and experimental verification,the controlled strategies suitable for typical icing environments are proposed,and the influence of environmental factors on the de-icing effect is analyzed.This research has important academic significance and practical engineering value for improving the de-icing performance and reducing the damage for wind farms.Based on the electrothermal cycle controlled de-icing method and combined with mass transfer and heat transfer equilibrium theory,blade element theory and turbulence theory,the electrothermal cycle controlled de-icing model framework is established based on CFD(Computational Fluid Dynamics)and NHT(Numerical Heat Transfer)method.Then by taking NACA4412 airfoil as an example,the experimental verification is done in the glaze and rime icing environment.Finally,according to the analysis of the actual icing environment of 300 kW wind turbine generator,the feasible cycle controlled de-icing strategy is put forward,and the influence of various factors is analyzed.The main work and results are as follows:(1)The finite element numerical simulation software-COMSOL Multiphysics is used to establish the electrothermal cycle controlled de-icing model based on the fluid field and thermal field.According to the typical glaze and rime environment,The NACA4412 airfoil cycle controlled de-icing model are established,and the de-icing simulation study found that the peak wind velocity around blades mainly focus on the bulge,and minimum value of the wind velocity is mainly concentrated in pothole of the ice layer and the front/ tail of the airfoil,the higher the icing roughness,the greater the local wind speed.During the heating process,the temperature of the blade shows a cyclic increasing trend of rising and then decreasing.The energy tends to flow and gather at the thinner ice layer,so the temperature rises rapidly in the thinner ice layer while rises slowly in the thicker places.(2)The experimental platform was built in the multi-functional artificial climate chamber,and the two typical icing conditions of NACA4412 airfoil were carried out by cycle controlled de-icing test.The image observation method was used to observe the de-icing change,and temperature of the ice layer were collected and recorded by the data measurement system.It is found that the experimental results are basically the same with the theoretical results,the average error is less than 12% which indicates that the theoretical model can truthfully reflect the real electrothermal de-icing process.(3)A de-icing model is built for the 300 kW wind turbine blades in the Chongqing University Xuefeng mountain natural icing station.According to the three kinds of typical ice environment(glaze/ rime)in Xuefeng mountain,the influence of four main strategy factors including heating power density,zoning mode,single heating time and de-icing time is studied,and based on the principle of energy conservation,the feasible de-icing strategy is determined.The cycle controlled de-icing method can saves 6.5%~25.9% energy than the continuous de-icing method by using this strategy,which shows that the electrothermal cycle controlled de-icing method can effectively save the energy.(4)The specially designed compound heating element is used as the basic unit of de-icing.The influence of various factors on the de-icing effect is analyzed theoretically and numerically.This paper analyses the heat insulation effect of the compound heating unit and provides the theoretical basis for the blade to determine the minimum thickness of the heat insulation layer.The influence of ice thickness on de-icing efficiency is studied,and suggestions for blades' de-icing control mode are put forward.The influence of wind speed on blade de-icing is analyzed.It is found that de-icing time decreases first and then increases with the wind speed from 6 m/s to 20 m/s.The influence of temperature on de-icing is analyzed.It is found that the environmental temperature is linearly proportional to the de-icing time,which provides a theoretical basis for further research and de-icing work.