Attenuation of sound in a low Mach Number nozzle flow
Attenuation of sound in a low Mach Number nozzle flow
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DOI：
10.1017/s0022112079000124
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发表时间：
1979-02
影响因子：
3.7
通讯作者：
M. S. Howe
中科院分区：
文献类型：
--
作者：
M. S. Howe
本文研究了在低马赫数喷嘴流动情况下，任意喷嘴收缩比的轴对称射流管内低频声发射的能量转换机理。从喷嘴逸出的入射声能被分配给外部流体中的两个不同的扰动。第一种是自由空间辐射，其方向性相当于单极子和偶极子源产生的辐射。第二，本质上不可压缩的涡旋波是由喷嘴嘴唇的涡量脱落激发的，并可能与喷流的大尺度不稳定性有关。讨论了两种线性化的理论模型。其中之一是一种精确的线性理论，在该理论中，喷流边界被视为不稳定的涡片。第二种假定真实射流的平均剪切层的有限宽度不能被忽略。分析结果表明，与最近的衰减测量结果相比，具有较好的可比性。
This paper examines the energy conversion mechanisms which govern the emission of low frequency sound from an axisymmetric jet pipe of arbitrary nozzle contraction ratio in the case of low Mach number nozzle flow. The incident acoustic energy which escapes from the nozzle is partitioned between two distinct disturbances in the exterior fluid. The first of these is the free-space radiation, whose directivity is equivalent to that produced by monopole and dipole sources. Second, essentially incompressible vortex waves are excited by the shedding of vorticity from the nozzle lip, and may be associated with the large-scale instabilities of the jet. Two linearized theoretical models are discussed. One of these is an exact linear theory in which the boundary of the jet is treated as an unstable vortex sheet. The second assumes that the finite width of the mean shear layer of the real jet cannot be neglected. The analytical results are shown to compare favourably with recent attenuation measurements.