Analyses of Vibration Characteristics of Power Fan for the 4ZTL-1800 Pneumatic Conveying Combine Stripper Harvester

The vibration noise of the fan is a critical weakness of the 4ZTL-1800 pneumatic conveying combine stripper harvester. The objectives of the present study were to ascertain the causes of the fan noise by analyzing its vibration characteristics and to propose some measures to solve the problem. To achieve these aims, we combined finite element modal analysis with experimental modal analysis to obtain the fan’s principal natural frequencies at ten different orders and typical mode shapes to investigate the fan’s natural vibration characteristics. The results indicated that, within the frequency range of 22.13 Hz ≤ f ≤ 141.99 Hz, the vibration mode shapes of the fan were the axis’ mode shapes, which showed torsional and bending vibrations, and the distortion at the higher frequency was greater than that at the lower frequency. The position of maximum distortion on the housing was at the joint with the impeller. The mode shapes of the impeller chassis showed rotating vibration and bending vibration alternately, but the blades’ mode shapes showed only bending vibration. When the fan ran at the rated rotational speed, at a frequency of f = 189.23 Hz, the mode shape of the fan was outward vibration of the fan housing’s inlet plate, and resonance occurred, which was the cause of the fan noise. Experimental tests on the natural frequencies of the fan housing verified the validity of the finite element modal analysis. In order to decrease the vibration noise of the fan, we studied changing the rotational speed of the fan and using a resonant muffler at the outlet of the fan. From the test results, we found that changing the rotational speed of the fan was not feasible for achieving noise reduction of this agricultural fan. The resonant muffler was feasible, and the fan noise was decreased to 79.1 dB. This study will be helpful in decreasing the vibration noise of fans.