Abstract: Experimental researches on coherent characteristics of sound generated by instability waves in the mixing layer of a planar jet under acoustic excitation are proceeded through the measurement of the coherent time scale. It demonstrates that the coherent time scale keeps a high level in the growing stage of coherent structures under the motivation of instability waves and then turning down abruptly at the breaking point where the large-scale eddies begin to shed downstream. It provides a criterion whether the instability wave or convective eddy becomes dominant in the contour map of the fluctuating velocity amplitude distribution with their particular expression of Lighthill stress.

Key words: coherent time scale, phase randomness factor, coherent structure

摘要： 通过二维射流混合层中相干时间尺度的测量，对声激励不稳定波增长过程及破碎点后的相干特性进行研究。实验结果表明，相干时间尺度在基波和第一亚谐波增长区较大，在破碎点后突然下降并在下游呈逐渐减小趋势。增加声激励强度可使不稳定波增长区的相干时间尺度增大，并对下游的流动结构有明显影响。

关键词: 相干时间尺度, 相位随机因子, 相干结构