The prediction of airflow-generated noise in mechanical ventilation systems.

Buildings located in noisy areas require a high degree of sound insulation. This will usually involve making the building envelope virtually airtight, and as a result losing the possibility of utilising natural ventilation. The solution is to employ a mechanical ventilation system, but such systems can themselves constitute a source of intrusive noise. Discontinuities in ducts result in the generation of flow noise and a loss of static pressure. The greater the discontinuity, the greater is the loss in static pressure and the greater is the sound power generated. This paper describes work carried out at the University of Liverpool which is aimed at providing system designers with more accurate methods of predicting noise from airflow generated in mechanical ventilation systems. We show that for a typical duct discontinuity, it is possible to predict the sound power generated from knowledge of its pressure loss characteristics.