Effect of Reynolds Number on Turbulent Drag Reduction by Superhydrophobic Surface Textures
Effect of Reynolds Number on Turbulent Drag Reduction by Superhydrophobic Surface Textures
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DOI：
10.1007/s10494-015-9627-z
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发表时间：
2015-10-01
影响因子：
2.4
通讯作者：
Zaki, Tamer A.
中科院分区：
文献类型：
--
作者：
Lee, Jin;Jelly, Thomas O.;Zaki, Tamer A.
在流向排列的超疏水表面(SHS)结构上的湍流中，减阻百分比取决于雷诺数。在Re(B)=2800、6785和10975这三个散体雷诺数下，对SHS织构上的槽道流动进行了直接数值模拟，验证了这种相关性。为了进行比较，还对相同体积速度下的规则无滑移槽道流动进行了模拟。研究了由于SHS织构引起的流动变化，特别关注了相平均统计和相干湍流运动。随着雷诺数的增加，纹理性能或减阻百分比也会增强。在湍流运动方面，切应力减弱表现为小尺度涡旋结构的减少和大尺度运动的减弱。雷诺数越高，大尺度运动附近随机波动的影响越小。因此，性能的提高是由于小型和大型涡旋结构的强度显著下降。较弱的涡旋运动使雷诺切应力和平均动量输运显著降低。SHS质地引入了性能损失，表现为在防滑自由滑边缘的局部阻力增加。这种不利影响是由近壁流场的不均匀引起的。然而，雷诺数越高，受影响区域的宽度就越窄。因此，减阻百分比接近纹理的气体分数。
In turbulent flows over streamwise-aligned superhydrophobic surface (SHS) textures, the percent drag reduction is dependent on Reynolds number. This dependence is examined using direct numerical simulations of channel flow over SHS texture at three bulk Reynolds numbers, R e (b) = 2800, 6785 and 10975. Simulations of regular no-slip channel flows at the same bulk velocities are also performed for comparison. Changes in the flow due to the SHS texture are examined with particular focus on phase averaged statistics and coherent turbulent motions. As the Reynolds number is increased, the texture performance, or the percent drag reduction, is enhanced. In terms of turbulent motions, the weakened shear stresses are manifest as a decrease in the population of the small-scale vortical structures and a weakening of large-scale motions. The influence of stochastic fluctuations near the large-scale motions diminishes at higher Reynolds number. The enhanced performance is therefore due to a significant drop in the strength of small- and large-scale vortical structures. The weaker vortical motions yield a considerable reduction in the Reynolds shear stress and the transport of mean momentum. The SHS texture introduces a performance penalty in the form of a local increase in drag at the no-slip free-slip edge. This adverse effect is caused by the inhomogeneity of the near-wall flow field. However, the affected region narrows in width at higher Reynolds numbers. As a result, the percent drag reduction approaches the gas fraction of the texture.