Noise characteristics of the asymmetric combined step under passive control

Exposed sizeable mechanical equipment, their cooling and exhaust systems generate much noise during operation. Steps are prevalent in these systems, so their study is significant for mechanical noise control. This paper conducted controlled experiments on combined backward-facing and forward-facing steps (BFS and FFS) in a small acoustic wind tunnel, and data acquisition was performed using a far-field microphone array. In the paper, passive control is carried out by changing the model's shape, and the control results are obtained by comparison with the base model. The experimental results show that chamfered, chamfered rounded, and rounded polygons can reduce the noise. However, there is a marginal decreasing effect of efficacy. Forward perforation increases the model noise at small perforation rates, while significant perforation rates reduce the model noise, and backward perforation has little effect on the model noise.