Ab initio hydrodynamic rough surface characterisation with applications

在自然界和许多技术应用中，粗糙表面上的湍流是常见的，然而用于预测它的方法是基于有限的实验数据库和已知给出相互矛盾的预测的关联式。关于特定的表面特征如何导致某些阻力增加，仍有许多需要了解，人们普遍认为，等效沙粒粗糙度的标准度量不再足够，因为在这种尺度上具有相同粗糙度的表面在过渡粗糙流态中具有不同的行为。我们提出了一个基于数值模拟的研究计划，以研究粗糙表面流动，特别是在高速飞行状态下，我们对政府和工业中的项目合作伙伴有迫切的要求。随着浸没边界条件高阶实现的发展，对规则或随机粗糙表面的流动进行数值模拟将是可行的，解决了与壁面附近湍流相互作用的粗糙度问题。为发展这一能力提出了一项工作方案，最初的基础是需要使用国家超级计算机设施的参数研究和高分辨率研究。然而，随着计算能力成本的迅速下降，我们将用于这项工作的技术被认为是更广泛的有用的，在项目结束时，我们建议开发一种粗糙的表面表征工作流程，其中可以使用例如共焦显微镜扫描样品，将表面数据内插到用于数值模拟的边界条件中，然后模拟在一定范围内(表面尺度相对于流动尺度)运行，以建立表面的流体动力学表征图。

Turbulent flow over rough surfaces is common in nature and in many technological applications, yet the methods used to predict it are based on a limited experimental database and on correlations that are known to give contradictory predictions. There is much still to learn about how particular surface features lead to certain drag increases and it is widely accepted that the standard measure of equivalent sand grain roughness is no longer sufficient, since surfaces with the same roughness on this scale have different behaviour in the transitionally rough flow regime. We propose a research programme based on numerical simulation to study rough surface flow, particularly in the high speed flight regime where we have an immediate requirement from our project partners in government and industry. With the proposed development of high-order implementations of immersed boundary conditions, numerical simulation of flow over regular or random rough surfaces will be feasible, resolving the scales of roughness that interact with turbulent flow near a wall. A programme of work is proposed to develop such a capability, initially based on parameteric studies and high resolution studies requiring the use of national supercomputer facilities. However, with the rapidly decreasing cost of computing power, the technique we will use for this work is believed to be more widely useful, and by the end of the project we propose to develop a rough surface characterisation workflow, whereby samples can be scanned, using for example a confocal microscope, surface data interpolated into a boundary condition for numerical simulation and then simulations run for a range of scales (surface scale relative to flow scale) to build a hydrodynamic characterisation map of the surface.