The noise produced by a contra-rotating ventilator can cause injury to humans.Therefore, it is important to reduce noise caused\nby ventilators. In this study, the FfowcsWilliams and Hawkings (FW-H) model was used to simulate the acoustics of four different\naxial impeller spacing points based on the unsteady flow field through a FBD No. 8.0 contra-rotating ventilator. Experiments were\nconducted to verify the correctness of the numericalmodel.Meanwhile, the Variable FrequencyDrive (VFD) drives the two motors\nof 55kW to give the impellers different speeds to distinguish different conditions. The results showed that the main noise source\nof the ventilator was the two rotating impellers and the area between them. For the same axial space, the noise decreased with the\nincrease of flow rate and then decreased. And the amplitude of the discrete pulse increased gradually. It can be concluded that the\nvortex acoustics decreased gradually with the increase of flow rate and the rotating acoustics were the major contributor.With the\naxial distance increasing, the noise caused by the two impellers was weak, and the frequencies of sound pressure level moved toward\nmedium- and low-frequency bands gradually. The suitable axial space could reduce noise and improve the working environment.
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