| In winter,wind resources are rich in China due to the monsoon climate,but the icing problem seriously restricts the development of wind power industry.Ice on blades changes the aerodynamic performance,causing power loss to the wind turbine.Ice adhered to the blade is easily thrown out by centrifugal force in the process of rotation,which is harmful to the crew and staff near turbine.Ice accretion model for wind turbine was mainly on 2-D airfoil,where the 3-D rotating case was transformed into a specific angle of attack by the classical Blade Element Momentum theory(BEM).Besides,most research lacked experimental verification.Considering the vector of spanwise direction of the rotating blade,3-D model is more accurate on describing the process of wind turbine icing.Thereby,3-D numerical calculation model is combined with icing test,and the blade ice prediction model is based on the meteorological parameter.This has important engineering significance and practical value on wind farm warning and optimization of anti-icing and de-icing method in winter.In this paper,firstly,the ice accretion process is experimentally studied.Then,the 3-D ice accretion model is established and contains four parts: air flow computation,water collision efficiency computation,heat and mass transfer and ice shape simulation.The 3-D ice accretion algorithm is improved on the basis of 2-D Messinger model.The influence of turbulence model,the motion of water film on the surface and the ice roughness on the ice accretion are all taken into consideration.The distribution of collision efficiency,heat transfer coefficient,freezing fraction and ice shape and their environmental influences are also studied in this paper.Finally,the ice accretion model is verified with icing tests.The work and achievements are shown as follows:(1)The test platform is built in both the artificial climate chamber and Xuefeng Mountain natural icing test station.The ice distribution on the blade is experimentally studied and the environmental effects on ice load are studied by both microscopic imaging method and rotating multi-cylinder monitoring method.Results show that ice mainly accumulates at the leading edge and increases along the spanwise direction.The increase of wind velocity,liquid water contents(LWC),and temperature decline will all lead to the heavier icing.(2)The blade rotation is performed by multiple reference frame(MRF)method.Based on S-A,standard k-? and k-? SST,the influence of turbulence model on the pressure coefficient of the blade is studied.The local edge velocity is computed by potential flow theory of LEWICE.Numerical results show that k-? SST has higher accuracy,which agrees well with the experiment.S-A shows smaller pressure coefficient at the leading edge of suction side and Standard k-? is not sensitive to the change of pressure coefficient on the suction side.(3)In the case of wings,cylinder and sphere,the supercooled droplet impingement is simulated by both lagrangian and eulerian method.This is applied to calculate the distribution characteristics of collision efficiency of blades and its influence factor.Numerical results show that the collision region mainly accumulates at the leading edge,and collision efficiency increases along the spanwise side.Collision efficiency increases and collision area expands with media volume diameter(MVD).Lower rotor speed and higher wind velocity would both lead to the collision region moving to pressure side of the blade.(4)The influence of blade roughness of clean blades on ice accretion and ice roughness is experimentally studied,and the ice roughness changes with time and its distribution are observed under microscope.The ice roughness model of blades is proposed on the basis of observation.Results show that blade roughness can be ignored during long time icing process.Ice roughness shows strongly functional relationship with time.Based on the images of the ice roughness along the chordwise,the development of ice roughness is divided into three stages: water film,bead and rivulet.(5)By expanding 2-D Messinger model to the 3-D blade and combining the water film motion,the 3-D numerical calculation algorithm is developed.The blade freezing thermodynamic model is established based on mass and heat transfer balance equations.The distribution of heat transfer coefficient and freezing fraction on the blade and environmental effects are numerically studied.Results show that from the root to tip,the heat transfer coefficient increases and freezing fraction decreases.The heat transfer coefficient significantly increases with MVD.The freezing fraction decreases with temperature,MVD and LWC.Wind velocity effect on heat transfer coefficient and freezing fraction is obvious only at the stagnation point.(6)The ice shape calculation is developed by the linear interpolation on the gird node,B-spline smoothing ice boundary and spring grid remesh method.The blade ice prediction model and whole numerical calculation process are proposed.The dynamic change process of blade icing is simulated by multi-step method and the judging method of time step is proposed as well.The ice prediction model is reliable by the verification of FENSAP-ICE simulation and icing test.The influences of grid node number and ice layer number of iterations on numerical calculation model are discussed based on the ice prediction model.The environmental influences on ice shape are numerically studied as well.Results show that more nodes help to improve the calculation accuracy.The time step can be determined by the ice degree and ice growth rate.As temperature reduced,more glaze ice is found at the leading edge,and ice area significantly decreases.Smaller droplets lead to rime and thinner ice at the leading edge.Larger LWC leads to more serious ice,but ice accretion is less affected by wind velocity when wind turbine is on the rated operation. |
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