Test analysis and numerical simulation of noise from forage crushers

Abstract

To identify the exact noise source and accurately predict the coupled noise from forage crushers, the multipoint synchronous measurement method based on sensor arrays is used, and the collected data are analyzed using auto-spectrum and wavelet analysis. The vibration transmission characteristics of the unbalanced rotor, the airflow–material coupling flow field, and the shell are calculated and analyzed based on the analysis results. The acoustic-solid coupling method is then used to numerically predict the coupled noise of the forage crusher's air noise and mechanical noise. The primary source of noise in forage crushers is aerodynamic noise. Mechanical noise from unbalanced rotor excitation, as well as material and mechanical structure collisions, play important roles in coupled noise distribution. The noise energy around the excitation fundamental frequency generated by the rotor hammer disturbing the airflow accounts for 58.32% of the total energy, the noise energy around the third harmonic frequency accounts for 9.15%, the noise energy caused by the unbalanced rotor excitation accounts for 7.05%, and the noise energy around the second harmonic frequency accounts for 4.34%. The overall change trends of the simulated sound pressure levels (SPLs) are similar to those of the measured values, and the maximum SPLs of the measured and simulated results appear at the same location near the inlet. The total SPLs of the measured values are slightly higher than those of the simulated values, and the maximum difference is 1.6 dB(A). The numerical prediction method for the coupled noise of forage crushers is feasible, and the prediction results are credible. This study provides the basis for the low-noise design of forage crushers.