Passive control of centrifugal fan noise by employing open-cell metal foam

Experimental and numerical studies were conducted to investigate passive control of a forward-curved centrifugal fan noise by employing the open-cell metal foam (OCMF). The results indicated that a reduction of about 5 dB in overall A-weighted sound pressure level (OASPL) was successfully achieved with a decline of about 200 Pa in total pressure rise (TPR). For the OCMF investigated in the present paper with the pores per inch (PPI) of 20 and the porosity of 97%, the noise control mechanism was to suppress the source strength of tonal noise generated from the periodic impeller–tongue interaction rather than to absorb the broadband acoustic energy. The decline of the aerodynamic performance was mainly caused by reducing the work capacity of the impeller rather than caused by flow loss owing to the flow resistance of the OCMF. An improved design of the OCMF was suggested to achieve more reduction in noise level with less decline of aerodynamic performance.