Study of drag reduction using periodic spanwise grooves on incompressible viscous laminar flows
Study of drag reduction using periodic spanwise grooves on incompressible viscous laminar flows
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DOI：
10.1103/physrevfluids.5.064102
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发表时间：
2020-06-22
影响因子：
2.7
通讯作者：
Hidrovo, Carlos H.
中科院分区：
文献类型：
--
作者：
Tirandazi, Pooyan;Hidrovo, Carlos H.
引入表面波纹来改变边界层流动是减少表面上的流体阻力的经证实的方法。在这项研究中，我们研究了周期性的，无限长的展向槽的层流边界层的整体雷诺数（Re-L）在1000和25 000之间的板。通过在二维域中采用数值模拟，我们调查的表面上的流动和压力的演变包含矩形槽是垂直于流动和无限长的展向方向，并比较它们的平板。我们的特征的槽附近的流动相互作用的基础上，其宽度与深度的纵横比（AR）。在某一纵横比以下，主涡流填充每个凹槽内的空间。这些涡流允许自由流“滑过”凹槽区域，并导致壁面上的表面摩擦较小。然而，流动和凹槽的垂直壁之间的相互作用导致压力阻力。我们研究了在宽展弦比（0.2 < AR < 200）范围内各个阻力分量的行为，并比较了每种情况下的总阻力减少。基于模拟结果，横向槽在层流状态下可以减少总阻力高达10%，与平板相比，尽管增加了板的润湿表面积。相反，在某些纵横比下，凹槽导致总阻力增加超过200%。我们观察到，通过增加纵横比，自由流更多地向凹槽弯曲;最终在一定的纵横比下，由AR* 表示，流动打破了底层循环并到达凹槽的底部。当这种情况发生时，槽底壁上的流动剪切与施加在垂直壁上的高压阻力相结合，可导致阻力的净增加。因此，槽的纵横比是优化横向几何形状中的减阻的关键参数。
Introducing surface corrugations to alter the boundary layer flow is a proven way to reduce the fluid drag on a surface. In this study, we examine the effect of periodic, infinitely long spanwise grooves on the laminar boundary layer over a plate for global Reynolds numbers (Re-L) between 1000 and 25 000. By employing numerical simulations in two-dimensional domains, we investigate the flow and pressure evolution over surfaces containing rectangular grooves that are perpendicular to the flow and infinitely long in the spanwise direction, and compare them to a flat plate. We characterize the flow interactions near the grooves based on their width-to-depth aspect ratio (AR). Below a certain aspect ratio, a primary vortex fills the space inside each groove. These vortices allow the free stream to "slip over" the grooved regions and result in less skin friction on the wall. However, the interaction between the flow and the grooves' vertical walls leads to a pressure drag. We study the behavior of the individual drag components over a wide range of aspect ratios (0.2 < AR < 200) and compare the total drag reduction in each case. Based on the simulation results, the transverse grooves in the laminar regime can reduce the total drag up to 10% in comparison to a flat plate, despite increasing the wetted surface area of the plate. Conversely, at some aspect ratios the grooves cause a total drag increase of more than 200%. We observe that by increasing the aspect ratio, the free stream bends more toward the grooves; ultimately at a certain aspect ratio, denoted by AR*, the flow breaks apart the underlying circulation and reaches the bottom of the grooves. When this happens, the flow shear on the grooves' bottom walls combined with the high-pressure drag exerted on the vertical walls can lead to a net increase in the drag. Therefore, the aspect ratio of the grooves is a critical parameter in optimizing drag reduction in transverse geometries.