Effect of passive control cylinder on the acoustic generation of a rectangular impinging jet on a slotted plate

Abstract

Impinging jets are encountered in ventilation systems in order to ensure air mixing and thermal comfort such as in residential buildings. These jets represent, under certain configuration, a source of noise which degrades the acoustic comfort. This source can be reinforced by the presence of self-sustaining tones which occurs when the impinged wall has a slot or other abrupt geometry. In order to reduce the acoustic level, many techniques of passive or active control could be adapted. In this work a cylinder is introduced between the exit nozzle and the impinged wall. This aims to disturb the vortex dynamics of the flow and to break the self-sustaining tones loop what will drastically decrease the acoustic generation as it is shown in this study. Thus, in this paper we present the influence of the introduced cylinder on the acoustic field generated by a flow impinging on a slotted plate for a Reynolds number Re=4600. An acoustic cartographic is illustrated to present of the noise level with respect to the cylinder position between the nozzle and the impinged wall. A total number of 1085 spatial positions for the cylinder with a step of 1 mm were experimentally investigated to find out the optimal position to adapt for the best noise attenuation.