子波分析检测壁湍流多尺度相干结构及间歇性

Wavelet analysis of detecting multi-scale coherent structures and intermittency in wall turbulence

用热线风速仪精细测量了风洞中平板湍流边界层不同法向位置的流向速度分量的时间序列信号,用子波分析对湍流脉动速度信号进行多尺度分解,提出了用子波系数的瞬时强度因子和平坦因子检测多尺度相干结构的条件采样方法,提取了不同尺度相干结构的条件相位平均波形,研究了多尺度相干结构的统计特征.计算了子波系数的概率密度函数,研究了多尺度相干结构对其的影响.研究发现,提取出的各尺度相干结构是子波系数的概率密度在小概率位置是非Gauss分布的原因.当这些相干结构被分离出后,概率密度函数就回到Guass正态分布.

The velocity time sequence at different vertical locations were finely measured by hot wire anemometer. A conditional sampling technique for detecting multi-scale coherent structures was developed using instantaneous intensity factor and flatness factor of wavelet coefficients. Multi-scale coherent structures for different scales were extracted by this technique. The probability density function (PDF) was calculated using wavelet coefficients, and the influence of multi-scale coherent structures on PDF was also studied. Multi-scale coherent structure evolution shapes detected at different scales were found to be similar. They are responsible for the anomalous scaling law. When such events are eliminated, intermittency anomalies are no longer observed and the Gauss normal distribution is achieved on the PDF of wavelet coefficients.