An Experimental Investigation of The Coupled Aerodynamic-Acoustic Response of an Isolated Rotor to Foam Metal Casing Treatment

This paper presents a systematic experimental study of foam metal casing treatment (FMCT) on an isolated low -speed axial fan rotor. The investigation varies both the Pores Per Inch (PPI: 35, 50, 65) and its axial position to assess impacts on aerodynamic stability and aeroacoustics, independent of stator interactions. Results show that FMCT can significantly enhance stall margin (over 40% SMI) with a minimal efficiency penalty (all < 1.5%). A critical design trade -off is identified: the optimal axial location for stability (overlapping the blade leading edge) does not coincide with the optimal location for noise reduction (further upstream). Mechanistically, a lower PPI proves most effective for stability by suppressing stall precursors and partially unloading the blade tip. Conversely, a higher PPI demonstrates superior broadband noise reduction, particularly at high frequencies.