Reducing the aerodynamic noise of the axial flow fan with perforated surface

In this study, the effect of utilizing a perforated surface as an innovative flow control method to reduce fan noise is numerically investigated. The case study consists of a shrouded axial flow fan with a perforated surface placed on its shroud behind the trailing edge. Using the LES model and FW-H analogy, the fan noise is determined in the frequency domain at a nominated location by performing computational aero-acoustic (CAA) simulations. In order to evaluate the penalty imposed on the aerodynamic performance by this control method, an aerodynamic simulation is performed using RANS equations and the k-ω SST turbulence model. The mentioned numerical models are experimentally validated. The results show that the coherent structures of the flow are disrupted, and the fan noise is reduced in the trailing edge area - an extremely noise-prone zone - thanks to the passive control method. The noise reduction values could potentially reach 6 dB specifically at the critical blade pass frequency, which significantly contributes to the overall noise produced by the fan. Moreover, it is shown that there are strong relationships between the Proudman, turbulence kinetic energy, and entropy indexes with the total aeroacoustic performance of the fan. In contradistinction to other applied methodologies, this control method does not impose any aerodynamic performance penalty, though it could be improved by around 1.5 % at the operating point.