| Frost has become a major factor restricting tea production and tea quality.As a mechanized anti-frost equipment based on inversion airflow disturbance,the frost protection wind machine has the advantages of significant anti-frost effect and easy automatic control compared with traditional anti-frost measures.It has been applied and promoted on a small scale in China.Existing blade-type frost protection wind machines such as small arc plates or large airfoils have poor adaptability to the hilly and mountainous terrain where the tea orchard in our country is located,especially the lack of a medium-sized frost protection wind machine with a medium-sized anti-frost area.Under the conditions of a given power,this study intends to design a fan airfoil with good aerodynamic performance and a large air supply distance(anti-frost area).First,the airfoil design software Profili was selected to analyze the influence of airfoil geometric parameters on aerodynamic performance based on the gray correlation method and the new concave-convex airfoil was optimized through orthogonal experimental design;Then,the air-flow field model simulation of the airfoil action process and use air volume and wind speed as indicators to optimize the blade profile parameters through response surface analysis;Design the small similar fan of the above optimization model,simulate its action process and perform characteristic test verification;Finally,analyze and optimize the pressure and wind speed of the airfoil frost protection wind machine Distribution and other characteristics.This research provides a new design method for optimizing the design of frost protection wind machine blades.The main research contents and research results are as follows:(1)Optimal design of airfoil for frost protection wind machineBy comparing the aerodynamic performance of NACA5412 airfoil,NACA4409 airfoil and MH114 airfoil,MH114 airfoil was selected as the initial airfoil.According to the grey correlation analysis,four factors that have the greatest influence on the aerodynamic performance of airfoil are obtained: maximum thickness and its thickness position,maximum camber and its position;By analyzing the influence of four geometric parameters on the lift coefficient and lift-drag ratio at continuous angle of attack,the results show that: reducing the maximum thickness,moving the maximum thickness position forward,increasing the maximum camber can improve the aerodynamic performance of the airfoil;The optimum range of maximum camber is 7～9% of chord length.The maximum camber position is located at 40～70% of chord length and the lift-drag ratio curve span of the rearward moving airfoil at the maximum camber position decreases.Profili is used to carry out multi-objective optimization design through orthogonal test with lift coefficient and lift-drag ratio of airfoil as indicators.It was obtained that when the maximum thickness was 11% of the chord length,the maximum camber was 8.5% of the chord length,the maximum thickness position was 31% of the chord length,and the maximum camber position was 49% of the chord length,the aerodynamic performance of the airfoil is optimal.After optimization,the lift-to-drag ratio of the airfoil is increased by 6.9%,the lift coefficient is improved and the stall characteristics were improved.The performance analysis of the optimized airfoil showed that the pressure difference between the front and rear airfoil decreases and the boundary layer separation does not occur,which can play a role in protecting the blade.Analyzing the performance of the optimized airfoil,the pressure difference between the front and rear of the airfoil is reduced,without boundary layer separation,which can protect the blade;the area formed by the pressure coefficient is positively correlated with the angle of attack.The pressure of the airfoil gradually increases as the angle of attack increases.(2)Optimal design of Concave-convex Wing Shape Parameters of wind machineBased on the optimized concave-convex airfoil,the air-flow field model simulation was carried out on the action process of the airfoil and the air volume and wind speed were used as indicators.Under the condition of a given power,the airfoil parameters were optimized through response surface analysis and the air volume was analyzed.Power and the relationship between the wind speed in the 90 m canopy directly in front of the fan and the blade profile parameters.The results show that: the blade diameter has the most significant impact on each index;appropriately increasing the installation angle,blade chord length and blade diameter can increase the air volume and wind speed;the maximum value of the air volume and wind speed was set as the goal.The power was not more than 11 k W as the limit.The optimal combination of frost-proof fan blade profile parameters was obtained: the installation angle was 16°,the blade chord length was 190 mm and the blade diameter was1620 mm.When the speed is 500 rpm,the air volume is 1402.45 m3/min,the power is10770.20 W,and the wind speed of the canopy 1 m from the ground 90 m in front of the fan is 1.01 m/s to meet the design requirements,which meets the design requirements.(3)Model fan test verification and performance analysis of optimized wind machineAccording to the similarity theory,the model fan was designed with a scale factor of0.25.Through simulation analysis,it was concluded that the wind speed distribution and change trend of the model fan and the designed anti-frost fan are the same.The errors of pressure,power and flow rate of the model fan are respectively 8.53%,7.22%,and 6.56% of the theoretical value;the model fan was tested and simulated under two working conditions of 500 rpm and 700 rpm and the results were as follows: The change trend of the measured wind speed with distance was the same as the simulation analysis.The maximum wind speed error was 4.48% and 9.19% respectively.The closer the distance to the center of the disturbing airflow,the smaller the gap between the measured wind speed and the simulated wind speed;under the working condition of 500 rpm,the maximum wind speed measured on the horizontal plane was 2.13 m/s.There was still a wind speed of 0.50 m/s at a straight line distance of 5.4 m from the center of rotation of the fan.The pressure distribution of the optimized concave and convex airfoil of the frost protection wind machine was analyzed.It was concluded that the dynamic pressure on the surface of the blade was less than the safety strength of the material used in the actual blade,so there will be no damage during the operation of the protection wind machine.Analyze the wind speed distribution of the optimized frost protection wind machine.The range of 0～24 m was the blind zone of protection wind machine.The wind speed within the frost protection range increases first and then decreases gradually with the increase of the distance;the maximum wind speed at different heights and horizontal planes gradually increases as the height rises and the average wind speed decreases as the height rises. |
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