湍流边界层多尺度相干结构的子波自相关辨识

采用热线风速仪测量平板湍流边界层的流向速度信号,运用连续子波变换的自相关分析,研究边界层相 干结构的变化规律,提出了子波尺度与涡时间尺度关系的计算式．结果显示,相干结构在时空中呈多尺度分布,在 对数区集中在较大尺度,在缓冲区扩展到较小尺度,越靠近黏性底层,拟序运动越明显,并向更小尺度发展;广泛存 在的相关性很弱的小尺度涡成为数量巨大、含能很少的背景湍流．子波变换的自相关分析可以定性,也可定量显示 涡的时空特性,是研究湍流多尺度相干结构的有效方法．

Wavelet Auto-Correlated Identification of Multi-Scale Coherent Structures in Turbulent Boundary Layer

The velocity time sequence in a turbulent boundary layer was measured with IFA300 constant-temperature anemometer. Continuous wavelet auto-correlation was analyzed to study the coherent structures of turbulent boundary layer. A formula was proposed to represent the relationship between time and wavelet scales. The result showed that coherent structures in space-time were of multiple scales. Besides, in the logarithmic layer coherent structures focused on larger scales while in the buffer layer they extended to smaller ones. With their measured position nearer to the wall, quasi-ordered motions became more obvious and extended to smaller scales. Many small scales with feeble correlation and little energy became turbulent background. The wavelet auto-correlation analysis can be used to determine the characters of coherent structures in space-time in terms of quantity and quality, which proved to be effective for multi-scale coherent turbulent structure study.