Turbulent Flows Over Rough Surfaces

在能源和运输行业中，对粗糙壁边界湍流流动阻力的可靠预测仍然是一个挑战。目前，预测阻力的唯一准确方法是计算成本高昂的直接数值模拟(DNS)或定制的实验装置，它们实现了感兴趣的准确墙面。这些解决方案不切实际。我攻读博士学位的目的是研究潜在的物理学，为预测模型奠定基础。当表面略粗糙时，远离壁面的速度分布为光滑的壁面，阻力增量可以用虚拟原点的概念来计算和模拟。然而，当壁面非常粗糙时，速度分布相对于光滑壁面的情况有所改变。因此，虚拟原点的概念不足以模拟阻力增加。绕单个粗糙度单元的时间平均流动看起来像绕过钝体的流动。由单个粗糙度元素引起的这种流动的影响会传播到远离壁面的地方。对于我的博士学位，我想调查这个时间平均的流动是否可以用来预测相对于光滑壁情况的速度剖面的变化。这不仅将改变我们对粗糙壁面边界流动的看法，而且还将显著减少阻力预测的计算时间。

Reliable prediction of drag due to rough wall-bounded turbulent fluid flow remains a challenge in the energy and transportation industry. At the moment, the only accurate methods that predict drag are computationally expensive direct numerical simulations (DNS) or customised experimental rigs that implement the exact wall surface of interest. These solutions are not practical. The aim of my PhD is to investigate the underlying physics to lay the foundations for a predictive model. When the surface is only slightly rough, the velocity profiles away from the wall are smooth wall like and the drag increase can be calculated and modelled using the concept of virtual origins. However, when the wall is very rough, the velocity profiles are altered relative to the smooth-wall case. Therefore, the concept of virtual origins is not sufficient to model the drag increase. The time-averaged flow around an individual roughness element looks like the flow around a bluff body. The effect of this flow caused by the individual roughness elements propagates away from the wall. For my PhD, I want to investigate whether this time-averaged flow can be used to predict the change in the velocity profiles relative to the smooth-wall case. Not only would this change the way we think about rough wall-bounded flows, but it would also reduce the computation time of drag prediction significantly.