Entrainment at multi-scales across the turbulent/non-turbulent interface in an axisymmetric jet
Entrainment at multi-scales across the turbulent/non-turbulent interface in an axisymmetric jet
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DOI：
10.1017/jfm.2016.474
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发表时间：
2016-08
影响因子：
3.7
通讯作者：
Dhiren Mistry;J. Philip;J. Dawson;I. Marusic
中科院分区：
文献类型：
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作者：
Dhiren Mistry;J. Philip;J. Dawson;I. Marusic
本文研究了高雷诺数下轴对称射流远场湍流/非湍流界面质量通量和卷吸速度的标度性。采用时间分辨、同步多尺度粒子图像测速技术（PIV）和平面激光诱导荧光（PLIF）来识别和跟踪TNTI，并直接测量沿TNTI的局部卷吸速度沿着。应用盒计数和空间滤波方法，滤波器尺寸$\unicode[STIX]{x1 D 6 E5}$跨越20年的长度，表明，TNTI的平均长度表现出幂律行为的分形维数$D\approximat0.31 {-}0.33$。更重要的是，我们调用一个多尺度的方法来确认的平均质量通量，这是等于产品的夹带速度和表面积，保持恒定的过滤器尺寸的范围内。在实验不确定性范围内的结果还表明，夹带速度沿着TNTI呈现幂律行为与$\unicode[STIX]{x1 D 6 E5}$，使得夹带速度随着$\unicode[STIX]{x1 D 6 E5}$的增加而增加。事实上，平均夹带速度以平衡TNTI长度的缩放的速率缩放，使得质量通量保持独立于粗颗粒过滤器尺寸，如Meneveau和Sreenivasan（Phys.Rev.A，第41卷，第4期，1990年，第100页）首次提出的。2246-2248）。因此，在最小尺度下，夹带速度较小，但通过存在非常大的表面积来平衡，而在最大尺度下，夹带速度较大，但通过较小（更平滑）的表面积来平衡。
We consider the scaling of the mass flux and entrainment velocity across the turbulent/non-turbulent interface (TNTI) in the far field of an axisymmetric jet at high Reynolds number. Time-resolved, simultaneous multi-scale particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) are used to identify and track the TNTI, and directly measure the local entrainment velocity along it. Application of box-counting and spatial-filtering methods, with filter sizes $\unicode[STIX]{x1D6E5}$ spanning over two decades in length, show that the mean length of the TNTI exhibits a power-law behaviour with a fractal dimension $D\approx 0.31{-}0.33$ . More importantly, we invoke a multi-scale methodology to confirm that the mean mass flux, which is equal to the product of the entrainment velocity and the surface area, remains constant across the range of filter sizes. The results, within experimental uncertainty, also show that the entrainment velocity along the TNTI exhibits a power-law behaviour with $\unicode[STIX]{x1D6E5}$ , such that the entrainment velocity increases with increasing $\unicode[STIX]{x1D6E5}$ . In fact, the mean entrainment velocity scales at a rate that balances the scaling of the TNTI length such that the mass flux remains independent of the coarse-grain filter size, as first suggested by Meneveau & Sreenivasan (Phys. Rev. A, vol. 41, no. 4, 1990, pp. 2246–2248). Hence, at the smallest scales the entrainment velocity is small but is balanced by the presence of a very large surface area, whilst at the largest scales the entrainment velocity is large but is balanced by a smaller (smoother) surface area.