Rotating machinery, such as centrifugal compressors, is widely used in different industries for a variety of applications involving the compression of a gas. A typical compressor, however, generates a significant amount of noise which is an obvious nuisance to those in the vicinity of the device. This noise generated can also cause vibrations in the compressor which can lead to inefficiencies and even structural failure.
The dominant noise source in a centrifugal compressor is typically generated at the impeller exit or diffuser inlet, due to the high velocity of the fluid passing through these regions. The noise level becomes higher when discharge vanes are installed in the diffuser to improve pressure recovery, due to the aerodynamic interaction between the impeller and the diffuser vanes.
Various external noise control measures such as enclosures and wrappings have been used to reduce the noise generated by compressors and other rotating machinery. These external noise reduction techniques, however, can be relatively expensive, especially when offered as an add-on product after the device is manufactured. Internal noise control devices, usually in the form of acoustic liners, have also been used for controlling noise inside the gas flow paths of compressors and other rotating machinery. Some liners are based on Helmholtz resonators and include a three-piece sandwich structure consisting of honeycomb cells sandwiched between a perforated facing sheet and back plate. Although these three-piece designs efficiently suppress noise in aircraft engines, their performance declines in rotating machinery, such as centrifugal compressors. For example, the perforated facing sheet can break off its bond with the honeycomb under extreme operating conditions and thereby cause increased aerodynamic losses, and even the possibility of mechanical, catastrophic failure.
Other internal acoustic liners include steel, annular plates having a plurality of holes formed therein to provide an array of resonators, and an array of cavities defined beneath the holes to capture and cancel the sound waves. While these acoustic liners successfully overcome the drawbacks to conventional Helmholtz resonators, they also present various drawbacks. For instance, the holes and cavities of the acoustic liners are drilled into the metal base plates in a labor intensive and costly process which requires long periods of machining time and frequent tooling rehabilitation and/or replacement. Also, because the acoustic liners are made of metal, extensive manufacturing processes are required to create unique and diverse structural arrays to fit varying applications.
What is needed, therefore, is an internal acoustic liner system and method that reduces or eliminates the various drawbacks described above of current acoustic liners.