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

为了降低超声速射流噪声，研究了多孔塞式喷管和引射喷管的应用。研究了在二维矩形喷管中插入翼型多孔塞对尖厉噪声和激波噪声的影响。当多孔塞被放置在离喷嘴下游稍远时，出现边缘音型机构的声音。当多孔塞的前缘接近喷嘴出口时，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。通过流动显示观察到的多孔塞孔周围的高湍流度是造成这种趋势的主要原因，研究了利用混合器-引射喷嘴快速降低高速射流速度以降低噪声的方法。对引射器壁面脉动压力的测量表明，在引射混合器喷嘴的上游部分，低频成分占主导地位，而在下游部分，高频成分占主导地位，且随着向下游方向的推移，两者的水平逐渐增大。结果表明，在核心流与二次流的混合过程中，超声速核心流经过多次压缩和膨胀，开始形成大尺度的流向涡，并随着流向下游的推进而增强。

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.