Zhiping Li, Long He, Tianyu Pan, Yao Yin, Shaobin Li, Wei Yuan, Bo Meng
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引用次数: 0
Abstract
Previous studies revealed the skin-friction drag reduction properties induced by transverse grooves. However, the effects of unsteady characteristics of vortices within the grooves on the drag reduction properties have not been investigated. A hypothesis that the unsteady motion of vortices may reduce the friction drag-reduction rate induced by transverse V-grooves is proposed in this paper. To verify this hypothesis, we use the LES (large eddy simulation) method to investigate the flow field in the range of Reynolds number 0.5E5 to 7.5E5 over the different profiles of symmetric V-grooves, whose depths are 0.2 mm and AR’s are 0.5, 1, 2, 5, and 8. The results show that the AR (aspect ratio of a transverse groove) affects the stability of boundary vortices, thus driving the variation of total viscous drag and pressure drag. With the increase of AR, the boundary vortices tend to be stable at first and then gradually become unstable. When AR is 2, the boundary vortices are stable within the grooves, corresponding to optimal drag reduction. In this case, the slip velocities induced by boundary vortices are the largest, and the Reynolds shear stress is the least, suggesting that the grooves have the strongest abilities to reduce the total viscous drag. When the stability of the boundary vortices is broken, a larger area containing high pressure and low pressure is formed in the groove, and the difference also becomes greater between the high pressure and low pressure. The results provide improved understandings of the drag reduction mechanism of transverse grooves.
期刊介绍：
EPJ E publishes papers describing advances in the understanding of physical aspects of Soft, Liquid and Living Systems.
Soft matter is a generic term for a large group of condensed, often heterogeneous systems -- often also called complex fluids -- that display a large response to weak external perturbations and that possess properties governed by slow internal dynamics.
Flowing matter refers to all systems that can actually flow, from simple to multiphase liquids, from foams to granular matter.
Living matter concerns the new physics that emerges from novel insights into the properties and behaviours of living systems. Furthermore, it aims at developing new concepts and quantitative approaches for the study of biological phenomena. Approaches from soft matter physics and statistical physics play a key role in this research.
The journal includes reports of experimental, computational and theoretical studies and appeals to the broad interdisciplinary communities including physics, chemistry, biology, mathematics and materials science.
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