图2. (a) 运用泰勒冻结假设,计算当地下游位置 $x\pm 0.2$mm 处的 $D_{ii}$ 与尺度 $r$ 的关系. 不同的颜色 代表对应的距离栅格的距离 $x/M$. 两台相机一次的拍摄视野只有 $ 100{\rm mm}=20 M$. 为获得距离栅格更宽范围 的统计特性,本文通过移动栅格使相机距离栅格 $S/M=12$, 20, 30 和 50,分 4 次实验完成. (b) $-\langle \delta u_i \delta a_i \rangle$ 与尺度 $r$ 的关系,在正向级串区表现出 $r^{1.5}$ 的幂次律. 图中的各 颜色代表不同的空间位置,同 (a) 中一致. 本图和上图的竖直实线为尺度 $r=0.35 M$,其与各种颜色线的交点即为各 下游位置在 $r=0.35 M$ 上的 $-\langle \delta u_i \delta a_i \rangle$ 和 $D_{ii}$

Fig.2. (a) Using Taylor frozen flow hypothesis, we calculate the relationship between $D_{ii}$ and $r$ in local downstream location $x\pm 0.2$mm. Different colors correspond to different separation below the comb $x/M$. The capture window of two cameras is 100mm =20M in each time. To obtain a wider regions statistics, we set the relative separation between camera and comb as $S/M=12$, 20, 30 and 50. (b) The relationship between $-\langle \delta u_i \delta a_i \rangle$ and $r$, which shows $r^{1.5}$ power law in direct enstrophy range. The colors mean different downstream locations which are the same with (a). The vertical solid line lies in $r=0.35 M$, whose cross points with different colorful lines are $-\langle \delta u_i \delta a_i \rangle$ and $D_{ii}$ in $r=0.35 M$