The addition of soluble long-chain polymers to a Newtonian fluid, and the incorporation of aerophilic textures on submerged solid boundaries, have both been successfully employed as independent, stand-alone methods for drag reduction in turbulent aqueous flows. In this work, we explore the possibility of combining the two strategies additively to obtain enhanced frictional drag reduction in wall-bounded turbulence. By means of skin friction measurements in fully turbulent Taylor-Couette flow, we show that dissolved polymer chains act in concert with superhydrophobic walls to yield a net reduction in turbulent drag that is up to greater than that obtainable from either method employed independently. Cooperative drag reduction measurements are presented for various combinations involving one of two common water-soluble polymers (either polyacrylamide or polyethylene oxide) paired with one of two prototype drag-reducing superhydrophobic surfaces—either a regular pattern of streamwise microgrooves, or a scalable random superhydrophobic texture possessing hierarchical multi-scale roughness. The surface activity of polyethylene oxide is observed to adversely influence the wall slip on the randomly textured surface, leading to significant diminution in the overall drag reduction efficacy of this polymer-surface combination. In cases where such interfacial effects are absent, an additive friction law is proposed that yields fairly accurate predictions of the combined drag reduction performance anticipated from a given polymer-surface pair, each possessing known individual drag-reducing characteristics.

中文翻译：

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使用聚合物添加剂和超疏水壁合作减少湍流阻力

向牛顿流体中添加可溶的长链聚合物，并在浸没的固体边界上掺入好气质地，都已成功地用作独立，独立的方法来减少湍流中的水流。在这项工作中，我们探索了将两种策略相结合以在壁面湍流中获得增强的摩擦阻力减小的可能性。通过在完全湍流的泰勒-库埃特流中进行皮肤摩擦测量，我们显示出溶解的聚合物链与超疏水壁协同作用，从而产生的湍流阻力净减少量最大，其降低幅度大于独立使用任一方法获得的阻力。提出了针对各种组合的协同减阻测量，涉及两种常见的水溶性聚合物（聚丙烯酰胺或聚环氧乙烷）之一与两个原型减阻超疏水表面中的一种配对–流式微沟槽的规则图案或可扩展的随机超疏水性具有分级多尺度粗糙度的纹理。观察到聚环氧乙烷的表面活性对无规织构表面上的壁滑产生不利影响，从而导致该聚合物-表面组合的总体减阻效果显着降低。如果不存在这种界面效应，则提出了加性摩擦定律，该定律可以对从给定的聚合物表面对预测的组合减阻性能产生相当准确的预测，