Nolle A W
Department of Physics, University of Texas at Austin 78712, USA.
J Acoust Soc Am. 1998 Jun;103(6):3690-705. doi: 10.1121/1.423089.
The sinuous instability wave of a planar air jet is excited by localized acoustic flow across the nozzle. Phase velocity and the growth exponent are found from synchronous hot-wire measurements made beyond the excited region, where the profile is approximately sech-squared. In the observed range of scaled radian frequency, 0.02-1.33 (the stability limit), results agree with real-frequency (spatially growing) analysis but not with complex-frequency (temporally growing) analysis. The latter predicts smaller phase velocity at low frequencies and has been questioned in edgetone analysis. In further tests, the acoustic driving signal is made independent of downstream distance, as in an organ pipe. The jet deflection is then the sum of acoustic convection and of the instability wave, summing to zero at the nozzle, as proposed by Fletcher, Elder, and others. The instability-wave theory applies to linear behavior in the inviscid limit and therefore to a hypothetical nonspreading jet. The local velocity profile width must be considered in relating to a physical jet. In a flue organ pipe oscillating at equilibrium amplitude the stability-wave theory is not applicable near the lip, where the laminar flow assumed in the theory disappears and the jet deflection exceeds the range of linear behavior. Direct sound generation by the jet is investigated briefly.
平面空气射流的蜿蜒不稳定波由穿过喷嘴的局部声流激发。相速度和增长指数是通过在激发区域之外进行的同步热线测量得到的，在该区域轮廓近似为双曲正割平方。在观测到的标度角频率范围0.02 - 1.33（稳定极限）内，结果与实频（空间增长）分析一致，但与复频（时间增长）分析不一致。后者预测低频时相速度较小，并且在边音分析中受到质疑。在进一步的测试中，使声驱动信号与下游距离无关，就像在风琴管中一样。然后射流偏转是声对流和不稳定波的总和，如弗莱彻、埃尔德等人所提出的，在喷嘴处总和为零。不稳定波理论适用于无粘极限下的线性行为，因此适用于假设的非扩散射流。在与实际射流相关时必须考虑局部速度剖面宽度。在以平衡振幅振荡的烟道风琴管中，稳定波理论在唇部附近不适用，在该理论中假设的层流消失，射流偏转超出线性行为范围。简要研究了射流直接产生声音的情况。
