Noise attenuation and performance study of a small-sized contra-rotating fan with microperforated casing treatments

•Acoustic interaction between the microperforated-panel (MPP) treatment and the rotor behaves like stator-rotor interaction, which can be suppressed by optimizing the row numbers of holes of the treatment to increase the interaction mode and frequency.•The MPP treatments over the front rotor are superior to the treatments over the rear rotor in terms of controlling CR fan intake noise without imposing aerodynamic penalties on fan performance.•An enlarged back cavity is beneficial to noise attenuation when using the MPP treatment over the front rotor. A 3.5 dBA reduction in overall noise can be achieved, and interaction tones and rotor-alone tones above 35 dBA are all attenuated.