Abstract In the work presented in this paper, a section of convergent-divergent (C-D) riblets is applied upstream of a backward-facing rounded ramp in a fully developed laminar channel flow at a Reynolds number based on the channel height of 400. Numerical simulations are undertaken to examine the effects of riblet geometry and yaw angle on the strength of secondary flow produced by the riblets and the extent of flow separation zone. It is found that, in comparison with the baseline case with no riblets, flow separation is delayed and the reattachment occurs earlier leading to a smaller separation zone around the diverging line. The opposite phenomenon occurs around the converging line. Our results also show that for riblets with a given height a maximum strength of the secondary flow motion upstream of the ramp and a maximum reduction in the spanwise-averaged length of separation are obtained at s / h = 4 . At a given s / h = 4 , as the riblet height increases, the strength of the secondary flow motion generated by C-D riblets increases and a minimum riblet height of 3.75% of the channel height is required to produce a net reduction in the spanwise-averaged length of separation. For riblets with a given height and spacing, as yaw angle increases both the strength of secondary flow and net reduction of separation zone exhibit a parabolic trend and both of them peak at γ = 45 ° . Overall, with the riblet setting tested here the benefit of suppressing the laminar separation bubble has not resulted in a net reduction in the total pressure losses compared to that in the baseline case. Nevertheless, an examination of the pressure losses from three different sections along the channel separately has produced some insights about the loss mechanisms and pointed to the possible ways by which the pressure losses could be reduced.

中文翻译：

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在带有 CD 肋条的后向圆形坡道上控制层流分离——肋条高度、间距和偏航角的影响

摘要 在本文介绍的工作中，基于 400 的通道高度，在雷诺数的完全发展的层流通道流中，在向后圆形坡道上游应用了一段收敛-发散 (CD) 肋条。 数值模拟进行了检查肋条几何形状和偏航角对肋条产生的二次流强度和流动分离区范围的影响。发现，与没有棱纹的基线情况相比，流动分离被延迟并且重新附着发生得更早，导致围绕发散线的分离区域更小。相反的现象发生在会聚线周围。我们的结果还表明，对于具有给定高度的肋，在 s/h = 4 时获得了斜坡上游二次流运动的最大强度和展向平均分离长度的最大减少。在给定的 s / h = 4 时，随着肋高度的增加，由 CD 肋产生的二次流动运动的强度增加，并且需要通道高度的 3.75% 的最小肋高度来产生展向的净减少 -平均分离长度。对于具有给定高度和间距的肋条，随着偏航角的增加，二次流的强度和分离区的净减少都呈现抛物线趋势，并且它们都在 γ = 45° 处达到峰值。全面的，在这里测试的肋条设置与基线情况相比，抑制层流分离气泡的好处并未导致总压力损失的净减少。尽管如此，对沿通道三个不同部分的压力损失分别进行的检查已经产生了一些关于损失机制的见解，并指出了可以减少压力损失的可能方法。