Centrifugal compressors are noisy and require noise control. Just as a pump raises the pressure on a liquid, a compressor raises air or gas pressure. Centrifugal compressor noise is produced primarily by blade-tip turbulence which is a function of horse power, speed, discharge pressure, piping velocities, number of stages of compression, type and number of blades etc. The high speed rotation of vanes or impellers generates noise which primarily consists of discrete tones inter dispersed over a broad-band frequency spectrum of lesser intensity. The maximum amplitude occurs at the blade passing frequency and its second harmonic. The high frequency noise generated is in the audible range and requires treatment for achieving noise control.
The importance of proper sizing of intake and discharge piping cannot be overemphasized. Both intake and discharge silencing is normally required. These silencers are absorptive type silencers which are essentially a high frequency, low pressure drop attenuate. It depends on sound absorbing material to dissipate the acoustical energy and are usually straight thru designs. All silencers should be coupled as close as possible to the compressor to prevent excessive pipe radiated noise.