Linear and nonlinear mechanisms of sound radiation by instability waves in subsonic jets
Linear and nonlinear mechanisms of sound radiation by instability waves in subsonic jets
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DOI：
10.1017/s0022112010002375
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发表时间：
2010-06
影响因子：
3.7
通讯作者：
V. Suponitsky;N. Sandham;C. Morfey
中科院分区：
文献类型：
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作者：
V. Suponitsky;N. Sandham;C. Morfey
通过对可压缩Navier-Stokes方程的数值模拟，研究了亚音速射流中的线性和非线性发声机理。主要目的是证明在亚音速喷流中，由初级、高度放大、不稳定波之间的非线性相互作用产生的低频波可以成为有效的声辐射体。目前的方法允许区分线性、弱非线性和高度非线性机制。结果表明，与线性不稳定波在相同频率下直接辐射相比，由非线性相互作用产生的低频波具有更高的辐射效率。结果表明，在模拟中可以观察到低频声主要在下游方向辐射，并具有ST=0.2附近的宽带谱峰特征，并可用非线性相互作用模型来描述。结果还表明，在较大角度(θ=60°-70 7°)下辐射的相干低频声可能来自方位波数n=±1的两个螺旋模之间的相互作用。下游和侧线方向的高频噪声似乎来自于射流分解成较小的结构。
Linear and nonlinear mechanisms of sound generation in subsonic jets are investigated by numerical simulations of the compressible Navier–Stokes equations. The main goal is to demonstrate that low-frequency waves resulting from nonlinear interaction between primary, highly amplified, instability waves can be efficient sound radiators in subsonic jets. The current approach allows linear, weakly nonlinear and highly nonlinear mechanisms to be distinguished. It is demonstrated that low-frequency waves resulting from nonlinear interaction are more efficient in radiating sound when compared to linear instability waves radiating directly at the same frequencies. The results show that low-frequency sound radiated predominantly in the downstream direction and characterized by a broadband spectral peak near St = 0.2 can be observed in the simulations and described in terms of the nonlinear interaction model. It is also shown that coherent low-frequency sound radiated at higher angles to the jet axis (θ = 60°–707°) is likely to come from the interaction between two helical modes with azimuthal wavenumbers n = ±1. High-frequency noise in both downstream and side-line directions seems to originate from the breakdown of the jet into smaller structures.