关键词: 相干时间尺度, 相位随机因子, 相干结构

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