Research On Optimization of Two-Dimensional Supersonic Jet Noise Reduction.

为了降低超音速喷流噪声，研究了多孔塞式喷管和喷射式喷管的应用。在二维矩形喷管中插入翼型多孔塞，研究了其对尖叫和冲击相关噪声的影响。当多孔塞放置在距离喷嘴下游稍远的位置时，出现了边音型机构的声音。当多孔塞前缘靠近喷嘴出口时，边缘音消失，但出现尖叫声。此外，当多孔塞的前缘插入喷嘴时，尖叫声也消失了。这种趋势可归因于流动显示所观察到的多孔塞孔周围的高度湍流流动。研究了利用混合器-喷射器喷嘴快速降低高速射流速度以降低噪声的方法。喷射器壁面脉动压力的测量表明，混合器-喷嘴上游部分以低频成分为主，下游部分以高频成分为主，且两种成分的水平都随着下游的增加而增加。结果表明，在核心流和二次流混合过程中，超音速核心流经过多次压缩和膨胀后，开始形成大尺度的流向涡卷曲，并随着向下游流动的推进而增强。

For the purpose of reducing supersonic jet noise, application of porous plug nozzle as well as ejector nozzle was investigated. In the case where an airfoil shaped porous plug was inserted into two dimensional rectangular nozzle, its effect on screech and shock associate noise was studied. When the porous plug was placed a little far downstream from the jet nozzle, sound of the edge-tone type mechanism appeared. When the leading edge of the porous plug approached the jet nozzle exit, edge tone disappeared but screech appeared. Further, when the leading edge of the porous plug was inserted into the jet nozzle, screech also vanished. Such tendency was considered to be ascribable to the highly turbulent flow around the porous plug though holes which was observed by flow visualization.The method to reduce noise by rapidly reducing the velocity of high speed jet by use of mixer-ejector nozzle was studied. Measurement of fluctuating pressures on ejector wall showed that in the upstream part of the mixer-ejector nozzle the lower frequency component was dominant while the higher frequency component became dominant in the downstream part, and further, the level of both components increased as we went downstream.The flow field showing the mixing process in the mixer-ejector nozzle was simulated by the computational fluid dynamics. It was revealed that in the mixing process of core and secondary flows, the supersonic core flow repeats compression and expansion several times, then the rolling up of a large scale streamwise vortex starts which is strengthened as the flow proceeds downstream.