Prediction of radiation characteristic of intermittent exhaust noise generated via pneumatic value

A mechanism for intermittent exhaust noise (IEN) generation mechanism, and the existing pressure shockwave with the standing-wave variation resulting in the impulse characteristic sound source that sequentially develops the airflow-induced IEN with the much high-frequencies content, is proposed. The shockwave impulse acoustic source (SIAS) describes the impulse sound source caused by the shockwave, conceptually and aerodynamically. Upon analysis of the exhaust noise source distribution in the pneumatic exhaust system via the pneumatic valve, this paper proposes that the SIAS with the maximum amplitude is located at the exhaust outlet; a relation of the noise source and both mass flux and flow speed is set up. With the piston acoustic source approximating the SIAS radiation at the outlet, formulae for calculating the sound pressure (SP) and sound pressure level (SPL) are given. Experiments support the proposed IEN-generation mechanism. The analytical results are in a good agreement with the experimental results in the octave bands, with the difference between the measured and calculated overall A-weighted sound level less than 3 dB. Especially for the octave bands from 250 Hz to 16 kHz, the differences between the measured and calculated A-weighted sound level are less than 3.5 dB. (C) 2009 Institute of Noise Control Engineering.