Generalized flow-generated noise prediction method for multiple elements in air ducts

Unavoidable discontinuities due to in-duct elements in a ventilation ductwork system result in the generation of localized turbulence. Some of the turbulence energy is converted into noise. The flow-generated noise problem caused by in-duct elements is due to the complicated acoustic and turbulent interactions of multiple in-duct flow noise sources. Prediction of the flow-generated noise at the design stage is important in engineering, since it is almost impossible to solve the problem after the installation of a ventilation ductwork system. The measurement and computational fluid dynamics simulation can provide an accurate prediction but are expensive in terms of resources. There is an urgent need for developing a practical prediction method for the flow-generated noise in air ducts. Current design guides only provide a prediction method for aerodynamic sound produced by a single in-duct element in the ventilation system, which is usually not in accord with actual systems. An interaction factor β _m is therefore proposed to take account of the interaction effects of multiple in-duct elements. Experimental measurements were conducted to verify the proposed prediction results. The predicted results show an acceptable agreement with the measurements. The proposed method provides engineers a practical generalized technique for predicting noise produced by multiple in-duct elements.