Effects of unstable oblique modes on the acoustic filed in a supersonic plane turbulent jet
Effects of unstable oblique modes on the acoustic filed in a supersonic plane turbulent jet
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不稳定斜模态对超音速平面湍流射流声场的影响
DOI：
10.1299/kikaib.72.2878
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发表时间：
2006
期刊：
影响因子：
--
通讯作者：
Y. Matsuo
中科院分区：
文献类型：
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作者：
Daisuke Watanabe;H. Maekawa;Y. Matsuo
采用高阶紧凑型迎风格式，对三维时相关可压缩Navier-Stokes方程进行了数值求解，研究了超音速飞机射流在高对流马赫数下的声发射机理。空间导数采用Deng和Maekawa(1996,1997)(1)(2)的5阶高阶紧凑格式，时间推进采用4阶龙格-库塔格式。沿流方向和垂直方向采用Navier-Stokes特征边界条件，沿展向采用周期边界条件。给出了对流马赫数Mc=1.17的两种情况。第一种情况是随机强迫射流。第二种情况是受随机扰动和一对具有亚音速相速的线性不稳定斜模的强迫射流。数值结果为研究平面湍流射流的三维结构和声波产生机理提供了新的物理见解。低频辐射的强马赫波是由于射流切变层中以超声速相速度生长的二维辐射模式所致。上游扰动条件对急流切变层的演化起着重要作用。射流剪切层的Λ结构主要由一对斜模的生长引起，剪切层的快速演化导致了中心线速度的快速衰减。因此，在随机强制射流中观测到的强声辐射可以通过施加一对斜模来减小。
The three-dimensional time dependent compressible Navier-Stokes equations are numerically solved to study acoustic emission mechanism in a supersonic plane jet at high convective Mach numbers using high-order compact upwind schemes. High-order compact schemes of 5th order developed by Deng and Maekawa (1996, 1997) (1)(2) are used for spatial derivatives and a 4th order Runge-Kutta scheme is employed for time advancement. Navier-Stokes characteristic boundary conditions are used in the streamwise and vertical directions and periodic boundary conditions in the spanwise direction. Two cases for convective Mach number Mc=1.17 are presented. The first case is the jet flow forced randomly. The second case is the jet forced by random disturbances and a pair of linear unstable oblique modes with a subsonic phase speed. The numerical results provide new physical insights into three-dimensional structures and acoustic wave generation mechanisms in a plane turbulent jet. Intense Mach waves radiating at low-frequencies are attributable to the growth of two-dimensional radiating mode with a supersonic phase speed in the jet shear layers. Upstream disturbance conditions play an important role for the evolution of the jet shear layers. The growth of a pair of oblique modes is responsible for the Λ structure in the jet shear layers, which yields sooner decay of the centerline velocity due to the shear layer rapid evolution. Therefore, the intense sound radiation observed in the randomly forced jet can be reduced by forcing with a pair of oblique modes.