Fluid dynamic properties of irregular, multi-scale rough surfaces

在许多工业部门，表面粗糙度会影响能源效率和维护成本。粗糙表面影响透平机械和海洋能源收集系统的性能。污垢引起的表面粗糙度增加了船舶和飞机的阻力。对粗糙度影响的准确预测是设计具有弹性的系统和经济地安排受表面粗糙度积聚(例如由于表面污垢或侵蚀)影响的机械维护周期的先决条件。表面粗糙度增加了流体动力阻力，并导致近壁速度分布向下移动，称为粗糙度函数。流体动力粗糙度效应受粗糙度高度和粗糙度地形的影响。粗糙度高度相同但地形不同的工程粗糙表面可能会产生相差四倍的粗糙度函数值。虽然粗糙度高度和阻力之间的关系已经很清楚，但粗糙度地形和流体动力学性质之间的关系仍然不清楚，这使得准确预测粗糙表面的流体动力学性质是不可能的。在这个项目中，将使用摩擦学的表面模拟方法来生成具有指定地形参数的逼真随机粗糙表面。通过直接数值模拟表面上的湍流槽流来获得其流体动力学特性，目的是建立地形参数与流体动力阻力、粗糙度函数和近壁湍流强度水平之间的关系。这种新的关系将有助于开发更好的湍流模型，用于考虑表面地形影响的典型工业计算流体力学模拟。这将为更准确地预测粗糙度在包括海洋能源领域在内的各种工程系统中的影响提供基础，在这些领域，生物污垢和腐蚀会导致强烈的表面粗糙度效应。

Surfaces roughness affects energy efficiency and maintenance costs in many industrialsectors. Rough surfaces impair the performance of turbomachinery and marine energy harvesting sys-tems. Surface roughness caused by fouling increases the drag of ships and aircraft. An accurate prediction of the impacts of roughness is a prerequisite for the design of resilient systems and the economic scheduling of maintenance cycles for machinery affected by surface roughness built-up e.g. due to surface fouling or erosion. Surface roughness increases fluid dynamic drag and cause a downwards shift in the near-wall velocity profile called the roughness function. The fluid dynamic roughness effect is influenced both by the roughness height and the roughness topography. Engineering rough surfaces with the same roughness height but different topographies can give rise to roughness function values that differ by a factor of four. While the relationship between roughness height and drag is well understood, the relationship between roughness topography and fluid dynamic properties remains unclear, making an accurate prediction of the fluid dynamic properies of a rough surface impossible.In this project, surface simulations methods from tribology will be used to generate realistic randomrough surfaces with specified topographical parameters. Direct numerical simulations of turbulent channelflow over the surfaces will be used to obtain their fluid dynamic properties with the aim to establishrelationships between topographical parameters and quantities such as the fluid dynamic drag, the roughness function and near-wall turbulence intensity levels. The new relationships will enable the development of betterturbulence models for typical industrial computational fluid dynamics simulations that can takesurface topography effects into account. This will provide the basis for a more accurate prediction ofthe impact of roughness in a wide range of engineering systems including the marine energy sector,where bio-fouling and corrosion lead to strong surface roughness effects.