完全发展的非对称槽道湍流的分形维数研究

湍流的分形维数刻画了湍流的统计正则性 ,本文利用正交子波变换对完全发展的非对称槽道湍流脉动速度的实验数据进行了分析研究。文中首先将脉动速度信号分解到各个尺度 ,然后利用正则法和盒子法两种方法计算了不同尺度信号的分形维数 ,着重于考虑分形维数的变化趋势。研究结果表明 :(1 )随着信号分解尺度的增加 ,速度信号的低频部分和高频部分的维数都逐渐减小 ;(2 )逆输运现象对速度信号的分形维数没有本质的影响 ;(3)正则法计算得到的分形维数要略大于盒子法得到的分形维数

Fractal Dimensions of Velocity Signals in Fully Developed Asymmetric Channel Flow

The fractal dimensions can describe the statistical regularity of turbulence. In this paper, orthogonal wavelet transform was applied to analyze the experimental fluctuating velocity signals (measured by LDV) of the full developed asymmetric turbulent channel flow. The experimental data was firstly decomposed into multiple scales, then fractional dimensions of different scales were calculated by regulation method and box method, and the different results between the two methods were compared each other, what we focus on most is to consider the variation trend of the fractal dimensions. The results show that: (1) the low frequency part of signal (approximation part) and the high frequency part (detailed part) decrease when the level of decomposition is increased; (2) counter gradient transport phenomena have no distinct effect on the fractional dimensions of simultaneous velocity; (3) the fractional dimensions estimated by regulation method are larger than those by box method.