Nonlinear mechanisms of sound generation in a perturbed parallel jet flow
Nonlinear mechanisms of sound generation in a perturbed parallel jet flow
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DOI：
10.1017/s0022112006001315
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发表时间：
2006-09
影响因子：
3.7
通讯作者：
N. Sandham;C. Morfey;Zhiwei Hu
中科院分区：
文献类型：
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作者：
N. Sandham;C. Morfey;Zhiwei Hu
研究了与喷流噪声有关的初值问题。平面平行射流受到空间局部化的初始扰动，然后根据二维可压缩Navier-Stokes方程进行演化。水动力响应的形式是对流涡包。Ffowcs Williams-Hawkings方法在时域中制定，并用于从模拟的近场外推到声学远场。主要的下游声辐射来自涡包非线性发展的早期阶段。两个简化的模型来解释辐射，基于非线性模式的相互作用在一个规定的基流。第一个使用两套线性化的欧拉方程，耦合通过无粘Lilley-Goldstein声学类比。该公式将线性声场与非线性相互作用驱动的声场分离;后者与Navier-Stokes计算的定性一致性表明了非线性相互作用的重要性。第二个模型使用线性无粘本征模的组合来驱动声场，这允许提取负责所观察到的辐射图案的主导模式相互作用。结果表明，差波数非线性相互作用机制主导了剪切流中亚音速不稳定模态的声辐射。
An initial value problem with relevance to jet noise is investigated. A plane parallel jet flow is subjected to a spatially localized initial disturbance and is then left to evolve according to the two-dimensional compressible Navier–Stokes equations. The hydrodynamic response is in the form of a convecting vortex packet. The Ffowcs Williams–Hawkings approach is formulated in the time domain and used to extrapolate from the simulated near field to the acoustic far field. The predominant downstream sound radiation comes from an early stage of nonlinear development of the vortex packet. Two simplified models to account for the radiation are introduced, based on nonlinear mode interactions on a prescribed base flow. The first uses two sets of linearized Euler equations, coupled via the inviscid Lilley–Goldstein acoustic analogy. This formulation separates the linear sound field from the sound field driven by nonlinear interactions; qualitative agreement of the latter with the Navier–Stokes computations demonstrates the importance of nonlinear interactions. The second model uses combinations of linear inviscid eigenmodes to drive the sound field, which allows extraction of the dominant mode interactions responsible for the observed radiation pattern. The results indicate that a difference-wavenumber nonlinear interaction mechanism dominates sound radiation from subsonic instability modes in shear flows.