Turbulent flows over rough walls

流体在粗糙表面上的流动（如大气在地球表面的流动，水在带钩的船体上的流动，或石油在工业管道中的流动）可能会与光滑表面上的流动有所不同。几十年来，人们一直认为，所有的粗糙度都是影响表面阻力的变化（通常是增加），而不会显著改变离开表面的流动结构。越来越多的证据表明，这并不总是正确的，显然，对于足够大的地表隆起，直觉上是最不可能的。对于外部流动（边界层）和内部流动（管道和通道）而言，从来没有一个协调一致的努力来探索这种“经典”观点在什么样的确切情况下是不充分的，以及粗糙表面和光滑表面流动之间的区别是什么。我们的目标就是这样做，从而探索(i)受湍流细节（例如标量色散或传热）影响的过程如何受到影响，以及（ii）预测技术中通常的表面效应建模如何变得不充分以及如何改进。

Fluid flows over surfaces that are rough (like the atmospheric flow over the earth's surface, the water flow over a barnacled ship's hull, or oil flow through industrial pipework) might be expected to differ from those over smooth surfaces. It has for decades been believed that all the roughness does is to effect a change (usually an increase) in the surface drag, without changing significantly the structure of the flow away from the surface. There is increasing evidence that this is not always true and, clearly, for sufficiently large surface protruberances it is intuitively most unlikely. There has never been a concerted effort to explore under what precise circumstances this 'classical' view is inadequate and what are then the distinguishing differences between the rough-surface and smooth-surface flow, for both external flows (boundary layers) and internal flows (pipes & channels). We aim to do just that and thus to explore (i) how processes affected by details of the turbulence (e.g. scalar dispersion or heat transfer) might be influenced and (ii) how the usual modelling of surface effects in prediction techniques becomes inadequate and how it might be improved.