Centrifugal blower noise studies: literature survey and noise measurements

A review of the existing literature on the subject of centrifugal fan and blower noise studies is presented in this report to establish further areas of research needed to aid in the development of a quiet blower. Noise measurements on a wide variety of blowers used in the laboratory, ranging from 1/3 to 700 horsepower are described, with the...

Far field radiation of rotor-stator interactions tones from an annular duct

An expression is derived to calculate the directivity of the far field sound pressure levels radiated from an annular duct based on Tyler and Sofrin's approach for a circular duet. Both radial and circumferential variations in the acoustic pressure field inside the duct are considered in the derivation. A computer programme to calculate the...

Sound adsorption tests on polyurethane and liquid soap foams for anechoic enclosures

An investigation was made of the normal and random incidence absorption of samples of 2-in thick polyurethane foam selected for use in the construction of an anechoic enclosure for lifting-fan noise studies. Impedance tube measurements gave normal incidence absorption coefficients ranging from 0.38 at 500 c/s to 0.91 at 1500 c/s. Reverberation...

Noise studies from the fan-in-wing model

Some preliminary measurements of noise from a highly loaded fan-in-wing configuration are reported. Measurements of the spectra are presented for fan speeds of 7500, 9750, and 13,125 rpm (corresponding to tip Machnumber 0.35, 0.45, and 0.62) at an angle of 20º from the axis of the fan and at 5 feet from the inlet and efflux (aces of the fan. The...