| In order to cope with the increasingly serious loss to tea and orchard production due to frost damage,the frost protection wind machine based on the airflow disturbance technology of near-ground inversion layer has been initially popularized and applied in China,but most of the domestic agricultural development is the economy of individual farmers.Tea and orchards are close to villages,leading to the layout of frost protection wind machine close to villages.And the fans work at night,affecting the sleep of surrounding residents.In this paper,in order to reduce the aerodynamic noise of the arc-plate blade of frost protection wind machine,the aerodynamic noise of the existing fan is firstly analyzed;Secondly,two kinds of noise reduction structures,stripe and sawtooth,were designed respectively,and their noise reduction effects were analyzed,and the better effect of noise reduction structure was selected.Then the comprehensive performance of the noise reduction profile was tested in the tea garden environment.Finally,on the basis of the noise reduction blade,the structural parameters of the impeller are optimized and the integrated noise reduction blade is designed.The main research contents and results are as follows:(1)Analysis of aerodynamic noise of arc-plate blade of frost protection wind machineThe aerodynamic noise of the existing arc-plate blade of frost protection wind machine is tested and simulated.The test results show that: as the distance increases,the sound pressure level(SPL)gradually decreases;The SPL of each monitoring point in front of the fan is higher than that of the right side of the radial direction and the right side of the radial direction,which is 3.49% higher than that of each point on the right side of the radial direction.It was 3.27% higher than the points directly behind.The air supply area of the fan is directly in front,and the air flow causes the noise to be too large,while SPL distribution on the right side and the rear side in the radial direction is similar.The simulation results show that the pressure difference between the suction surface and the pressure surface of the fan is large,which is easy to form the tip vortex,which affects the performance of the fan and increases the aerodynamic noise.The generation and crushing of the shed will also produce aerodynamic noise.(2)Noise reduction structure design and effect analysisThe stripe structure is designed on the pressure surface of the impeller and the sawtooth structure is designed on the trailing edge of the impeller,in order to reduce the aerodynamic noise without changing the motor power and ensuring the aerodynamic performance.Taking the width,height and spacing of the stripes,the length,width,number and position of the sawtooth as the optimization parameters,and taking SPL at 1.0 m directly in front of the impeller axis and the average wind speed at the outlet surface as the evaluation indicators,numerical simulation and response surface test were used.The combined method optimizes the parameters of the two structures respectively.The results show that: the noise reduction effect becomes better with the stripe width of 3.0 mm,the stripe height of 6.3 mm,the stripe spacing of 79.7 mm.At this time,SPL is 88.57 d B and the wind speed is 14.53 m/s;The noise reduction effect becomes better with the sawtooth length of 26.0 mm,the sawtooth width of 11.6 mm,the sawtooth position of 480.0 mm,and the sawtooth number of 16.At this time,SPL is 87.30 d B and the wind speed is 13.20 m/s.Compared with control blade,the SPL of the striped blade is reduced by 5.75%,and the wind speed is increased by 7.49%,but its impeller power exceeds the power of the established motor by 3.0 k W;the SPL of the sawtooth blade is reduced by 7.10%,and the wind speed is only reduced increased by0.68%,and the impeller power has not increased.The sawtooth structure can reduce the noise of the fan more significantly than the fringe structure without changing the motor power and ensuring no obvious change in aerodynamic performance.(3)Experimental study on noise reduction and frost resistance of sawtooth bladeThe field comprehensive performance of sawtooth blade profile was studied,including noise distribution,wind speed distribution and frost resistance test.The noise distribution test results show that the error between the simulated value and the measured value of the SPL at each monitoring point directly in front of the sawtooth blade is less than 3.77%,and the model accuracy is better;compared with control blade,the SPL at the front of the sawtooth blade decreased by 9.65%,the SPL at the back decreased by 8.83%,and the SPL at the right side of the radial blade decreased by 4.66% on average.The wind speed distribution test results show that the experimental wind speed variation trend is similar to the simulation results;there is no significant difference in the wind speed distribution of the two blades,and the maximum wind speed occurs 12.0 m directly in front of the fan,and the airflow range is about 30.0 m.The test results of frost protection performance show that:under the same temperature inversion conditions,the average temperature rise of sawtooth blade at 10.0 m and 15.0 m is 2.8℃ and 3.2℃ respectively;the average temperature rise of control blade at 10.0 m and 15.0 m is 3.0℃ and 3.1℃ respectively.(4)Noise reduction design of arc plate-blade comprehensive structureBased on the sawtooth blade profile,the installation Angle,sweep Angle and section radius of the impeller were taken as test factors,and the sound pressure level and wind speed were also taken as evaluation indexes.Combined with numerical simulation and orthogonal test,the structural parameters were optimized and the integrated noise reduction blade profile was designed.The results show that the significant order of influence on SPL is sweep Angle,installation Angle and section arc radius.The order of influence on wind speed is installation angle,sweep angle and radius of section arc.After optimization,the installation Angle is 25°,the sweep Angle is 87°,and the radius of section arc is 1250 mm.Compared with the sawtooth blade,the SPL decreased by 4.49% and the wind speed increased by 6.52%,and the power did not exceed the set motor power. |
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