Abstract Direct numerical simulations (DNS) of flow over triangular and rectangular riblets in a wide range of size and Reynolds number have been carried out. The flow within the grooves is directly resolved by exploiting the immersed-boundary method. It is found that the drag reduction property is primarily associated with the capability of inhibiting vertical velocity fluctuations at the plane of the crests, as in liquid-infused surfaces (LIS) devices. This is mimicked in DNS through artificial suppression of the vertical velocity component, which yields large drag decrease, proportionate to the riblets size. A parametrization of the drag reduction effect in terms of the vertical velocity variance is found to be quite successful in accounting for variation of the controlling parameters. A Moody-like friction diagram is thus introduced which incorporates the effect of slip velocity and a single, geometry-dependent parameter. Reduced drag-reduction efficiency of LIS-like riblets is found as compared to cases with artificially imposed slip velocity. Last, we find that simple wall models of riblets and LIS-like devices are unlikely to provide accurate prediction of the flow phenomenon, and direct resolution of flow within the grooves in necessary.

中文翻译：

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关于流过槽纹和液体注入表面的阻力和垂直速度波动之间的关系

摘要 已经对各种尺寸和雷诺数的三角形和矩形肋条上的流动进行了直接数值模拟 (DNS)。凹槽内的流动是通过利用浸入边界方法直接解决的。发现减阻特性主要与抑制波峰平面垂直速度波动的能力有关，如在液体注入表面 (LIS) 设备中。这在 DNS 中通过对垂直速度分量的人工抑制进行模拟，这会产生与肋条尺寸成比例的大阻力降低。发现根据垂直速度变化对减阻效果的参数化在解释控制参数的变化方面非常成功。因此引入了一个类似穆迪的摩擦图，它结合了滑动速度的影响和一个单一的、几何相关的参数。与人为施加滑动速度的情况相比，发现类 LIS 肋条的减阻效率降低。最后，我们发现槽纹和类似 LIS 装置的简单壁模型不太可能提供对流动现象的准确预测，并且在必要时无法直接解析凹槽内的流动。