Flow-Generated Noise Radiated by the Interaction of Two Strip Spoilers in Low Speed Flow Ducts

A theory has been developed for prediction of flow-generated noise due to the interaction of two strip spoilers in a low Mach number airflow duct in a ventilation system. In this paper, the concept of partially coherent fields is applied to formulate the sound powers radiated at frequencies below and above the cut-on frequency of the first transverse duct mode. An interaction factor is defined as a result of a simple relationship between the sound power level due to the interaction of two flow spoilers and that due to a single flow spoiler in an air duct. The present investigation therefore indicates that it is possible to predict the level and spectral distribution of the additional acoustic energy produced by the interaction of two similar strip spoilers. The proposed prediction method can form a basis of a generalised prediction method for flow-generated noise radiated by in-duct elements in a ventilation system.