Experimental Study On Icing Shape Scaling Method For Rotating Blade Under Rime Ice Condition

Nowadays,with the reduction of fossil energy and the prominent problem of enviro nmental pollution,wind energy,as a kind of green and no-pollution clean energy,has been widely developed and utilized.Its main useful form is wind power generation.Wind turbine is the basic unit wind power generation.Its development direction is large-scale and intellectualization.The wind farm gradually develops from the traditional "three-north" area to the low wind speed area and the sea area.Throughout most of the traditional "three north" area,low wind speed area and the offshore wind,the wind turbines are all occure icing phenomenon.Especially the blade icing will change the blade surface and aerodynamic properties.The load distribution of the blade will be changed which will which leads to the decrease in the power performance and affect the reliability and safety of rotor.Therefore,the icing research for wind turbine is getting more and more attention.It’s difficult to carry out the full-size blade icing wind tunnel test due to the blade size.Reffering the research mehods of wing icing of aviation,it is an effective method to carry out model test after reducing the large-scale blade by using the scaling method.This paper makes a preliminary study on this method.The theory of wing icing scaling method which is mature and systematic of aviation has been deeply analyzed in this study.Combining with the working characteristics of wind turbine blades,an icing shape scaling method of rotating blade under rime ice conditions has been proposed.This method is suitable for the small scale and small shrinkage ratio conditions.The verification test of this method had been carried out by using a self-built icing wind tunnel test system which has a variable test section.The main works of this study are as follows:(1)In order to formulate a set of scaling method of icing shape of rotating blades,two kinds of aspects has been researched in this paper.The one hand is to deeply analyze the icing mechanism of rotating blade.The icing scaling method for rime ice,glaze ice and mix ice should be studied and established respectively.The rime ice which has simple process and obvious characteristics was identified the basic type of ice in this study.T he rotation effect in the process of rotation should be taken into account in the icing scaling method,and a new rotation scaling parameter,centrifugal tensile stress σ_c was developed.On the other hand,the wing icing sacling method in aviation has been deeply studied.The basic parameters which affecting the icing shape were determined.The parameters including wind speed v,temperature T,liquid water content LWC,medium volum droplets MVD,environmental pressure P,icing time t,etc.The centrifugal tensile stress σ_c was added into the series of basic parameters to form a system of icing scaling parameters.The section principle and order of each parameter had been established based on the weber number which based on the water film thickness.Finally,the icing shape scaling method of rotating blade under rime ice conditions which suitable for the sma ll scale and small shrinkage ratio condition has been established.(2)In order to research the accuracy and applicability of the icing shape scaling method proposed in this study,the icing wind tunnel verification test need to be carried out.Therefore,the icing wind tunnel test with variable test section was established in this study.This system is based on the original icing wind tunnel test system which using natural low temperature.A new type of icing wind tunnel test system is formed by combining the variable test section and the original test system.In order to test the performance and stability of this new system,the wind speed distribution and stability,temperature distribution and stability,liquid water content distribution were tested and calibrated.The results show that the the parameters of the system reach the requirements of the icing wind tunnel.To verify the experiment ability of the system,through the rotating cylinder and rotating blade icing test obtained the icing shapes,and the icing shapes were compared with that of the original system.The results show that the icing shapes of these two systems are similar.It is shown that the icing environment of the two systems is approximately the same,which indicates that the system designed in this study is stable and reliable,and the system can be used for icing wind tunnel test.(3)In order to verify the applicability of the icing shape scaling method of rotating blade under rime ice conditions proposed in this paper,the test scheme which including two scales blades was designed.The airfoils of these two scales blades are all symmetrical airfoils NACA0018.The chord lengths are 200 mm and 100 mm respectively.The material is solid aluminum,the thickness is 20 mm and the surface roughness is 3.2 mm.The icing test was carried based on the icing wind tunnel test system established in this study.The icing shapes of these two scales blade were obtained.The icing shapes with different scales were normalized.The results show that the icing shapes of two scales blades are similar.To quantitively analyze the similarity of icing shapes two scales blades,an evaluation method of icing shape similarity has been developed.The icing shape similarity of these two scales blades is 75.22%~93.01% which obtained by this evaluation method.It indicates that the icing shape scaling method proposed in this study is accurate and applicable,which provides test data and lays a theoretical foundation for the further study on the icing scaling method of rotating blades.