| At present,there are problems such as low productivity,high power consumption,high noise and easy blockage during the working of forage crushing machine and forage kneading machine,which seriously restrict the development of this kinds of machinery to high quality and low energy consumption.To solve the above problems,improve the crushing performance and reduce the noise on the premise of ensuring no blockage and meeting the crushing quality,a new forage crushing machine was developed.To accurately predict the aerodynamic noise of this kinds of machinery,the influence of straw crushing process on the flow characteristics of the coupled flow field and the aerodynamic noise source was studied by combining theoretical analysis,CFD-DEMBPM coupling simulation and noise test.Based on the acoustic analogy theory and the indirect boundary element method,the aerodynamic noise of the new forage crusher considering the straw crushing process was predicted.And multi-island genetic algorithm was used to optimize the parameters that have significant influence on aerodynamic noise.The results show that :(1)Compared with the original forage crushing machine,the rated productivity of processing green straw of the new forage crushing machine increased from 1056kg/h to1800kg/h,and the power consumption per hour increased from 129kg/(kW·h)to240kg/(kW·h).The rated productivity of processing yellow straw of the new forage crushing machine increased from 646kg/h to 1200kg/h,and the power consumption per hour increased from 85 kg/(kW·h)to 166 kg/(kW·h).(2)Although the material crushing process has little effect on the distribution of the coupled flow field and the maximum airflow velocity in the crushing chamber,the turbulence in the feeding tray and the discharge tube is significantly increased,indicating that the material crushing process has a significant effect on the aerodynamic noise source at the monitoring points of feed inlet and the discharge outlet.(3)Straw crushing process has a noticeable effect on aerodynamic noise.The total sound pressure level at the inlet and outlet is higher than that at no load;the sound pressure level of the load at the feed inlet is higher than that of the no-load except for the fundamental frequency of hammer passing through frequencies and the third harmonic frequency,especially,after the fourth harmonic frequency,the sound pressure level during load is significantly higher than it under no-load;The sound pressure level during load at the discharge outlet after third harmonic frequency is significantly higher than it under no load.Compared with the noise without load,the noise during load of the feed inlet and the discharge outlet have changed the frequency of the sound pressure level that contributes prominently to the total sound pressure level.(4)The aerodynamic noise simulation at the inlet and outlet of the load is basically consistent with the measured sound pressure level spectrum curve,and the frequency of the higher sound pressure level is the same.The total sound pressure level difference between the simulation and the experiment is 2.00 dB(A)at the inlet and 1.49 dB(A)at the outlet.It can be seen that the aerodynamic noise prediction model considering the material crushing process is accurate and the calculation results are credible.(5)After aerodynamic noise optimization,the sound pressure level of aerodynamic noise at the inlet of the new forage crusher is 89.97 dB(A),and the sound pressure level of aerodynamic noise at the outlet is 86.32 dB(A),the sound pressure level of aerodynamic noises at the inlet and outlet are lower than 90 dB(A),which meet the requirements of national standards,therefore,the optimization results are feasible.It provides a method reference for low noise design of forage crushing machine,forage kneading machine and other straw processing machinery. |
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