多孔形低騒音弁の減音の効率化に関する研究 : 第2報,孔出口形状による減音効果

概要

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The noise characteristics and flow behavior of supersonic jet flow discharged through a hole with a modified-shape exit have been investigated experimentally over a range of ratios up to 7 in order to reduce noise from each jet of multiple supersonic jets. Two types of holes are used: one is a step hole with an abrupt enlarged exit, the other is a tapered hole with a conical diffuser. Substantial reductions in both peak and broadband sound pressure are obtained over the range of operating pressure ratios in both types of holes. Schlieren photographs recorded at these operating conditions reveal the appearance of a characteristic pattern of shock structure which effectively eliminates the usual repetitive shock cells associated with supersonic jet flows. The dependence of the noise reduction on the observed flow changes is discussed form the point of view that the flow velocity at the exit is reduced through the so-called λ-type strong shock wave heading into the jet flow. For multiple supersonic jets discharged through the multiple-step holes, the same noise reductions are also achieved.
一般社団法人日本機械学会の論文
1989-12-25