Turbulent flows over rough walls

流体在粗糙表面上的流动(如地球表面上的大气流动、藤壶状船体上的水流或工业管道中的石油流动)可能会与在光滑表面上的流动有所不同。几十年来，人们一直认为，粗糙度所起的作用只是影响表面阻力的变化(通常是增加)，而不会显著改变远离表面的流动结构。越来越多的证据表明，这并不总是正确的，显然，对于足够大的地表突起来说，直觉上这是最不可能的。对于外部流动(边界层)和内部流动(管道和渠道)，从来没有协调一致的努力来探索这种经典的观点在什么情况下是不充分的，那么粗糙表面流动和光滑表面流动之间的区别是什么。我们的目标就是做到这一点，从而探索(I)受湍流细节(例如标量弥散或热传递)影响的过程可能会受到影响，以及(Ii)预报技术中通常的地面效应模型如何变得不够充分以及如何改进。

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.