Aerodynamic Sound from Centrifugal-Fan Rotors

Abstract

The sound powers of small uncased centrifugal-fan rotors were measured at low-tip Mach numbers. Correlation of the data by use of a similarity relationship derived from theory has shown that the broad-band rotor sound is a result of randomly oriented dipole sources caused by fluctuations in fluid momentum. Deviations of the dependence of sound power on speed from that theoretically predicted were found. Speed dependences less than that predicted can be explained as a nearfield effect; the lack of agreement between theory and the fan law for sound can be explained on the same basis. Observed speed dependences greater than that predicted appear to result from having fixed frequency limits on the measurement system. A sharp wedge placed near the rotor periphery was found to generate discrete-frequency dipole sound. Quadrupole sound appeared to be negligible.

Tunable acoustic vortex generation by a compact rotating disk

“…Near field and far field terms are seen explicitly as 1/r 2 and 1/r terms in the integrals, respectively. Besides, dimensional analysis has been used to show the relationship between the acoustic power of the acoustic dipoles of a rotating object and its parameters, such as diameter and rotation rate 63 .…”

An Application of the Acoustic Similarity Law to the Numerical Analysis of Centrifugal Fan Noise

“…In 1963, Maling proposed a simple equation by the dimensional analysis using Buckingham PI theorem for broadband noise of a centrifugal blower with forward curved blades (8) . Chanaud claimed that the centrifugal fan noise has dipole characteristics by conducting experiments for a fan having forward curved blades (9) . Weidemann initiated researches on acoustic similarity law extensively (10) .…”