The Performance of Jet Noise Suppression Devices for Industrial Applications

Commercially available jet noise suppression devices were tested to determine their noise reducing characteristics compared to an open pipe. Both exhaust silencers and ejector nozzles were measured for sound power level and mass flow rate. In addition for ejector nozzles, the added noise from a jet impinging on a flat plate was measured. The primary noise generating mechanism for both the open pipe and the silencing devices was due to turbulent mixing, which is dependent upon the velocity. In light of jet noise theory, it will be shown that these devices reduce turbulent noise levels by restricting the flow and creating interactions between small jets. The amount of noise reduction depended upon the design of the silencing device. A large flow reduction was not found to be a necessary criterion for a large noise reduction.