湍流多尺度相干结构间歇性的PIV实验研究

利用粒子成像测速(PIV)系统测量了湍流边界层中流向速度平面,并对湍流多尺度相干结构统计特性进行了实验研究.利用连续子波变换,计算了不同尺度、不同法向位置的子波系数概率密度函数.结果发现缓冲区有着更强的间歇性.利用子波系数量化湍流间歇性的方法,应用推广的自相似律(ESS),计算了子波系数结构函数的标度指数.研究表明:当多尺度相干结构被提取出后,利用子波系数计算的ESS标度律就符合科尔莫戈罗夫提出的线性标度律,验证了多尺度相干结构是湍流边界层产生奇异标度律的原因.此外,利用PIV系统测量的数据,给出了流向平面内的以子波系数表达的能量分布.这种方法有利于进一步对多尺度相干结构在空间平面内的辨识与特性进行研究.

PIV experimental investigation of multi-scale coherent structures' intermittency in turbulent flow

Turbulent boundary layers were obtained and the statistical properties of multi-scale coherent structures studied experimentally via particle image velocimetry(PIV) measurements in streamwise-wall-normal planes.The probability density function(PDF) of wavelet coefficients at different vertical locations and scale were calculated by a continuous wavelet transform,and the results indicated a more intermittent process in the buffer region.Furthermore,the extended self-similarity(ESS) was applied to compute the scaling exponents of the wavelet coefficients structure function by using the method with a qualitative analysis of intermittency.In this way,after excluding multi-scale coherent structures,intermittency anomalies were no longer observed and the scaling exponents in accordance with the Kolmogorov linear scaling prediction,which demonstrated that multi-scale coherent structures were responsible for the anomalous scaling law in turbulent boundary layer.Moreover,local energy were displayed by using wavelet coefficients in streamwise-wall-normal planes,which provided a method to identify coherent structure from wavelet analysis of PIV data.