Relating Cutoff Pressure Distribution and Acoustic Signature of Centrifugal Fans Through Experimental Correlation

Abstract Potential noise sources of rotating machinery are diverse and complex. This includes the acoustic signature of the impeller itself and the design of the fan casing. This is especially true for centrifugal fans with an asymmetric spiral casing. Here, a nonuniform and unsteady pressure field interacts with the volute cutoff, thus resulting in broadband noise radiation and, under given geometric circumstances, significant tonal noise effects. The current study investigates the relation between the local pressure distribution at the volute cutoff and the acoustic far-field signature of the fan. A low-speed centrifugal fan, placed in an anechoic environment, is equipped with pressure sensors to gather information on the mean pressure distribution and the unsteady wall pressure field at selected spots. Correlating the captured signature with the radiated far-field noise reveals significant common spectral components and helps identify relevant noise sources, affected by the volute cutoff. In the long term, the definition of transfer functions between the near-field wall pressure and the radiated noise into the far-field is expected to enhance the geometric optimisation of the volute cutoff in both experimental and numerical environments. The test rig, in close agreement with ISO 5801, allows for simultaneous capture of the aerodynamic performance, allowing for an analysis of the pressure correlation along the entire characteristic curve.