| As one of the important renewable energy sources,wind energy has the characteristics of large reserves and green pollution-free.It is widely used in the field of wind power generation,and plays an important role in promoting China’s peak carbon dioxide emissions,carbon neutralization and improving the global climate environment.However,when the wind turbine works in cold and humid environment,icing will occur on the blade surface,which will lead to the change of blade aerodynamic shape,the deterioration of aerodynamic performance,the decrease of wind energy utilization rate and the decrease of power generation efficiency.In addition,the icing on the blade surface will increase its weight,destroy the dynamic balance of the wind turbine,increase the load of the transmission system,shorten the service life of the wind turbine,and seriously affect the safe and stable operation of the wind turbine.Therefore,the research on icing characteristics of wind turbine blade has important scientific significance and engineering application value.At present,icing research methods mainly include theoretical analysis,numerical simulation and wind tunnel test.However,the wind turbine blades are large in scale and work in the wild,and the climatic conditions are complex,so it is difficult to study by theoretical analysis and numerical simulation.It is an important means to explore the icing law through icing wind tunnel test at present.Limited to the size of the wind tunnel,whether the test results conform to the actual working conditions of the wind turbine needs to meet certain similarity,at present,there is no in-depth study at home and abroad.In addition,the adhesion between ice and object surface is an important factor to study icing characteristics and anti-icing technology,and adhesive force is an important index to describe the adhesive characteristics of icing interface.However,at present,the research on the adhesiveadhesive characteristics of icing is not in-depth,especially on the surface adhesiveadhesive force of dynamic icing.Therefore,this paper mainly conducts wind tunnel test research on the icing similarity and icing adhesiveadhesive characteristics of wind turbine blades,and combines theoretical analysis and numerical simulation to provide theoretical and experimental basis for the research on icing characteristics and anti-icing technology of wind turbine blades.The main research work and results of this paper are as follows:(1)On the basis of airplane airfoil icing similarity criterion,combined with the working characteristics of wind turbine and airfoil blade icing theory,considering the influence of rotating centrifugal force on icing characteristics,and adding the similarity parameters of rotating dynamics,a research method for icing similarity of rotating blades of wind turbine is proposed.Based on this method,the selection principles of similar icing parameters of wind turbine blades under static and rotating conditions were determined,including the correction of inertia parameters,aggregation factor,freezing ratio coefficient,relative heat factor,air energy transfer potential,water droplet energy transfer potential,Weber number based on water film thickness and centrifugal tensile stress.On this basis,in order to quantitatively analyze the similarity of icing shape of wind turbine blades,dimensionless icing area,dimensionless icing stagnation point thickness,dimensionless icing upper limit and dimensionless icing lower limit are selected as evaluation parameters.(2)In order to study the icing similarity and adhesiveadhesive characteristics of wind turbine blades,a small reflux low-speed icing wind tunnel test system was developed.The wind tunnel consists of three parts:reflux air duct,refrigeration system and spray system.Among them,the cross-section size of the test section of the reflux airway is 250 mm×200 mm,which can be extended to variable cross-section structure for the study of dynamic icing similarity and adhesiveadhesive characteristics of wind turbine blade sections.The working parameters and their distribution in wind tunnel test section were measured,including wind speed,temperature,liquid water content(LWC)and water droplet particle diameter(MVD).The results are as follows:The wind speed in the test section is 1 m/s～20 m/s,the temperature is-20℃～0℃,the liquid water content(LWC)is 0.1 g/m~3～5 g/m~3,and the water droplet particle diameter(MVD)is 20μm～100μm,the above parameters meet the test requirements.In order to verify the icing performance of wind tunnel,the icing tests of cylinder,symmetric airfoil blade section(NACA0018)and asymmetric airfoil blade section(S809)were carried out under static and low-speed rotation conditions,and the results were compared with the numerical simulation results of FENSAP icing software.The test results show that under static and low-speed rotation conditions,the rime ice shape on the surface of the three icing model has the highest coincidence degree with the numerical simulation results,and the coincidence degree of glaze ice is the lowest.Under each ice type condition,the coincidence degree of frozen ice shapes on the cylindrical surface is the highest,and the coincidence degree of asymmetric airfoil(S809)blade segments is the lowest.Under rime condition,the maximum coincidence degree of ice shape is 90.1%,and the minimum coincidence degree is 80.9%.The influence of variable cross-section test section on ice shape is small,and this method can be used to expand the experimental ability of icing wind tunnel.(3)Icing similarity test of cylinder and wind turbine blade(using symmetrical airfoil NACA0018)was carried out.Three diameter cylinders(with scaling factors of 1.5 and 2)and five chord length blade segments(with scaling factors of 0.5,0.75,1.25 and 1.5)were selected,the static and rotating icing shapes of test samples under the conditions of glaze ice,mixed ice and rime ice were studied,The typical characteristic quantities of scaling models under each icing condition are quantitatively analyzed,including icing area,dimensionless icing area,icing thickness,dimensionless icing thickness,upper and lower limits of icing and upper and lower limits of dimensionless icing.The research results show that:under the condition of static icing,when the scale factor of the model is in the range of 0.5～2,the similarity of frozen ice shape of cylinder is 80.1%～96.4%,and that of symmetrical airfoil blade segment is 62.4%～93.6%;Under the condition of rotating icing,when the scale factor of the model is in the range of 0.75～2,the similarity of the frozen ice shape of rotating cylinder is 76.8%～83.2%,and that of rotating airfoil is 78.9%～92.7%.Within the above scale range,the ice shape similarity of cylinder and blade is high.(4)On the basis of similarity test,the icing similarity of the 1.5 MW horizontal axis wind turbine blades is studied by numerical simulation,the ice shapes at the tip of blade models with scaling factors of 0.2 and 0.5 were calculated.When the scaling factor is in the range of 0.2-1,the ice shape coincidence degree is high,and the contour change trend of three-dimensional icing ice shape is consistent.(5)In order to study the icing adhesive characteristics and anti-icing technology on the blade surface of large wind turbine,the experimental study on icing adhesive characteristics of cylinder and block surface was carried out.The non-impact and impact icing adhesion of the sample surface with and without hydrophobic coating was tested and analyzed by shear method and centrifugal method.The results show that environmental temperature and hydrophobicity of surface coating are important factors affecting the adhesive strength of static state and dynamic state icing,and the increase of temperature and hydrophobicity of coating will reduce the adhesive strength between icing and objects.Under the uncoated condition,the adhesive force of impact icing is less than that of static state icing.For non-impact ice,the effect of hydrophobic coating and temperature on the adhesive strength of ice layer is significant.When the temperature increases,the adhesive strength of ice layer decreases significantly.When the sample surface has hydrophobic coating,the adhesive strength of ice layer decreases significantly with the increase of hydrophobic ability of coating.For impact icing,the ability of hydrophobic coating to reduce ice adhesive force is reduced. |
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