Turbulent Boundary Layers over Heterogeneous Rough Surfaces

在自然界中，经常会遇到表面粗糙度沿流向变化的湍流（例如海洋和陆地、农村和城市地区之间的界面，森林和草原）以及各种工程应用（例如，由于生物结垢或磨损/腐蚀效应，涡轮机叶片和船舶船体）对流体的空气动力/流体动力性能和寿命有直接影响，流动系统以及城市地区空气污染和风模式的分散。然而，在这一领域的研究是有限的，因此，行为/预测的湍流和相关的表面摩擦阻力发展仍然不清楚这些类型的粗糙表面。本研究旨在通过先进的基于激光的光流诊断（即PIV，PTV和DIC）的尖端实验研究来填补这一空白。我们特别感兴趣的是解决和预测流动动力学和相关的表面摩擦阻力改变表面粗糙度的变化（在流向），以及新形成的内部边界层（剪切层）与自由表面的相互作用。后者对于理解和控制CO2和O2的传输机制也很重要（考虑到全球变暖的严重和不可逆转的影响以及未来几十年的环境目标）。

Turbulent flows over surfaces that have roughness variation in the streamwise direction are frequently encountered in nature (e.g. interfaces between ocean and landmasses, rural and urban areas, forest and grasslands) and in various engineering applications (e.g. turbine blades and ship hull due to bio-fouling or abrasive/corrosive effects) having a direct impact on aero/hydrodynamic performance and lifespan of fluid-flow systems as well as on dispersion of air pollution and wind patterns over urban areas. However, there is limited research in this field, hence the behaviour/prediction of turbulent flows and associated skin-friction drag development remain unclear over these types of rough surfaces. This study aims to fill this gap through cutting-edge experimental research with advanced laser-based optical flow diagnostics (i.e, PIV, PTV and DIC). We are particularly interested in resolving and predicting flow dynamics and associated skin-friction drag altered by a change in surface roughness (in the streamwise direction), as well as the interaction of a newly formed internal boundary layer (a shear layer) with the free surface. The latter is also important to understand and control transport mechanisms for CO2 and O2 (considering the severe and irreversible effects of global warming and the environmental targets for the next decades).