An experimental and theoretical investigation into ice ribbing instabilities

飞机机翼或风力涡轮机上的冰形成都会降低性能并存在重大危险。在典型的英国条件下，温度很少低于冰点，冰通常形成坚硬，光滑的釉冰，水存在于机翼或叶片上的气流剪切的薄片中。在风力涡轮机上，径向水流的冻结可以在尖端形成几米长的碎片，这些碎片在脱落时代表致命的抛射物。由于冰罩而引起的几何形状的变化也会引起空气动力学的不稳定性。在机翼上，剪切水膜本身可能是不稳定的，并冻结为肋，改变表面粗糙度和性能。然而，结冰在这些过渡制度的机制没有得到很好的研究，没有这种理解，它仍然是具有挑战性的结构，以保障性能和safety.This项目旨在发展之间的复杂的相互作用的理解流体力学和热力学过程冻结水片与相关的风力涡轮机叶片和翼型的几何形状。通过这种理解，我们可以确定可以延迟冰肋形成的干预措施，或者通过例如智能涂层消除涡轮机尖端形成的可能性。该项目将首先探索在旋转盘上加速的水膜的稳定性，模拟翼型或风力涡轮机叶片上的剪切边界层，使用控制方程的线性稳定性分析，并通过实验室实验进行验证。在第二阶段，冻结通过釉冰边界条件将被纳入稳定性分析，以深入了解冻结肋的起源，以及它们的生长成三维冰的形成。实验室实验将与该理论一起开发，以验证严格控制的流体力学和热力学边界条件下的预测。

Ice formations on aircraft wings or wind turbines both reduce performance and present significant hazard. In typical UK conditions, where temperatures rarely go much below freezing, ice usually forms as hard, smooth glaze ice with water present in sheets sheared by the airflow over the wing or blade. On a wind turbine the freezing of the radial water flow can form shards some metres long at the tips, which represent lethal projectiles when dislodged. The change in geometric presentation due to the glaze ice can also cause aerodynamic instabilities. On an aerofoil, the sheared water film can itself be unstable and freeze as ribs that change the surface roughness and performance. However, the mechanics of icing in these transitional regimes is not well studied, and without this understanding it remains challenging to develop effective anti- and de-icing strategies for structures to safeguard performance and safety.This project seeks to develop that understanding of the complex interplay between the fluid mechanic and thermodynamic processes in freezing water sheets with geometries relevant to wind turbine blades and aerofoils. Through this understanding we can identify interventions that could delay the formation of ice ribs, or remove the possibility of turbine tip formations through e.g. smart coatings.The project will first explore the stability of water films accelerated on a spinning disk, mimicking the sheared boundary layer over an aerofoil or wind turbine blade, using linear stability analysis of the governing equations and verified though laboratory experiments. In the second phase, freezing through a glaze ice boundary condition will be incorporated into the stability analysis to gain insight into the origin of frozen ribs, and their growth into three-dimensional ice formations. The laboratory experiment will be developed alongside this theory, to verify the predictions under tightly controlled fluid mechanic and thermodynamic boundary conditions.