A study of planar jet flow control and perforated fairings for the reduction of the flow-induced noise of tandem rods in a cross-flow

摘要

Recent research has investigated the use of a planar jet in a cross flow, referred to as an air curtain, as an alternative noise reduction technology to solid fairings. The air curtain can achieve significant noise reduction from the original bluff body source through deflection of the main flow but the noise emission of the planar jet is a limiting factor on the performance of the technology. This paper investigates alternative air curtain geometries in an attempt to minimise the noise of the planar jet and further enhance the achieved noise reduction. The work considers a pair of tandem cylinders as a representative aerodynamic noise source and begins by investigating the effectiveness of a single stream air curtain in reducing the noise emission. The noise emission of the single stream planar jet was identified as a significant noise source under certain conditions. In order to reduce the noise emission of the jet a dual stream air curtain was investigated. It was found that upstream secondary air-curtain, which had a lower jet velocity, serves to reduce the primary air curtain jet noise and slot exit noise. The air curtains were also tested in combination with a perforated fairing. This combination of flow deflection through both air curtains and perforated fairings further reduced the flow velocity impinging on the dual cylinders. It was found that the air curtain reduced noise emission from the perforated fairing edge. Results of a flow field survey using PIV are presented as well as the results of microphone array measurements. The ability of the approaches to provide noise reduction is also quantified through their effective shielding height.