The noise signatures of two identical small axial-flow cooling fans installed in series with a flow straightener between them are experimentally measured and analyzed. A technique of noise source component decomposition is used to decompose the raw sound signals into tonal and broadband
components, both further attributed to either the upstream or the downstream fan. Two major inlet flow conditions (unobstructed inlet and a distorted inlet flow case by the simplified circuit board) and a range of operating conditions under which the tested fan works are investigated. The
tonal and broadband noises radiated by the upstream fan are greatly increased by inlet flow distortion, especially in the low workload region, while the two noise components radiated by downstream fan are hardly affected. The upstream fan and the flow straightener flush mounted between the
two fans both play a significant role in keeping the downstream fan free from the influence of inlet flow distortion. Themagnitude relations among all the noise source components under different inlet flow and operating conditions are compared, which would definitely offermuch help in designing
a quiet two-stage or even multiple-stage fan and adopting an appropriate method to efficient fan noise control and reduction.
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