Conditional and unconditional second-order structure functions in bubbly channel flows of power-law fluids
Conditional and unconditional second-order structure functions in bubbly channel flows of power-law fluids
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DOI：
10.1063/5.0049799
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发表时间：
2021-05
影响因子：
4.6
通讯作者：
E. Trautner;M. Klein;F. Bräuer;J. Hasslberger
中科院分区：
文献类型：
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作者：
E. Trautner;M. Klein;F. Bräuer;J. Hasslberger
在摩擦雷诺数为127.3的条件下，通过一系列直接数值模拟，研究了非牛顿流体行为和Eotvos数对泡状槽道流的条件和无条件二阶结构函数的影响.已经考虑了两个Eotvos数（Eo = 0.3125和Eo = 3.75）以及代表剪切稀化（n = 0.7）、牛顿（n = 1.0）和剪切增稠（n = 1.3）流体行为的三个不同的幂律指数。二阶结构函数的标度可以转化为湍流动能谱的惯性范围标度。然而，由于泡状流中流体性质的不连续性，SFs比基于傅立叶变换的湍流谱更容易获得。已经发现，不同的参数（即，E0，n）对能量含量以及补偿的二阶SF的峰值位置（即，大尺度的尺度）。然而，在适当缩放后，曲线几乎塌陷。为了证实和进一步解释上述发现，方向长度尺度进行了详细的评估和讨论。最后，雷诺应力张量和耗散张量的各向异性已被分析的Lumley三角形，显示泡状通道流是各向同性比他们的单相对应，虽然他们是更均匀的通道中心。虽然耗散张量比通道流的体区域中的雷诺应力张量略微各向同性，但总体上观察到非常相似的行为。
The influence of non-Newtonian fluid behavior and the Eotvos number on conditional and unconditional second-order structure functions of bubbly channel flows has been investigated by conducting a series of direct numerical simulations at a friction Reynolds number of 127.3. Two Eotvos numbers have been considered (Eo = 0.3125 and Eo = 3.75) together with three different power-law indexes representing shear-thinning (n = 0.7), Newtonian (n = 1.0), and shear-thickening (n = 1.3) fluid behavior. The scaling of the second-order structure functions (SFs) can be translated into an inertial range scaling of the turbulent kinetic energy spectrum. However, because of the discontinuous character of the fluid properties in bubbly flows, SFs are more easily accessible than turbulence spectra, which are based on Fourier transform. It has been found that the different parameters (i.e., Eo, n) have an influence on the energy content as well as the peak location of the compensated second-order SFs (i.e., the dimensions of the large scales). However, after appropriate scaling, the curves nearly collapse. To confirm and further explain the above findings, directional length scales have been evaluated and discussed in detail. Finally, the anisotropy of the Reynolds stress tensor and dissipation tensor has been analyzed in terms of the Lumley triangle, showing that bubbly channel flows are less isotropic than their single-phase counterpart, although they are more homogeneous in the channel center. While the dissipation tensor is slightly more isotropic than the Reynolds stress tensor in the bulk region of the channel flow, overall, a very similar behavior is observed.