Noise Generation in Ventilation Systems by the Interaction of Airflow with Duct Discontinuities: Part 1 Bends

Discontinuities in air duct systems give rise to turbulence and some of this turbulence results in airflow generated noise. One potential source of flow generated noise in ducts is the presence of a bend. Various strategies are employed to reduce turbulence by smoothing the flow around a bend, such as the use of turning vanes, large radius of curvature and the associated use of splitters, and these will also affect the noise generated. Recent work on the prediction of airflow generated noise in ducts based upon pressure loss characteristics is applied to a range of bends including mitred bends, with and without turning vanes, and radiussed bends, with and without splitters. The effect of bends with different aspect ratios is also examined. An excellent collapse of measured data onto a single characteristic curve is reported for each configuration based upon standard values of pressure loss coefficients. It is suggested that these characteristic curves might form the basis for a practical prediction method.