Determining the Effects of Competing Instabilities in Complex Rotating Boundary Layers

流体力学具有根本的重要性，并支撑着一系列学科的关键发展，包括航空航天，国防，能源和环境研究。例如，有效使用燃料已成为民航业日益重要的因素，国际航空运输协会（IATA）承诺“到2020年将燃料消耗和二氧化碳排放量与2005年相比至少减少25%”。同时，飞机发动机噪声已经成为一个真实的和日益严重的环境问题，特别是在世界各地的机场附近。鉴于全球对航空旅行的需求增加，节能和更安静的航空发动机是航空和航天工业的重要目标。空气动力学的改进有可能有助于设计下一代节能航空发动机和涡轮机械。具体而言，通过主动流动控制增加对基础物理的理解可以减少气动阻力并延迟向非结构化湍流的过渡，这两者都已知对燃料消耗和噪声排放具有负面影响。通过详细的数值模拟，而不是相对昂贵的实验研究，可以以具有成本效益的方式实现延迟被动过渡的目标。该项目将通过应用一种新的计算方法来帮助实现这一目标，该方法可以模拟复杂旋转几何形状上的边界层内的流动。边界层是一层薄薄的流体，其粘性限制在边界面附近，可以深刻而重要地影响流体流动的空气动力学和阻力特性。历史上，由于它们的速度剖面之间的相似性，旋转盘上的边界层流动被用于模拟后掠翼上的空气流动。今天，在航空发动机，涡轮增压器，旋转射弹和最近的电化学应用的持续发展，创造了需要了解旋转物体，如磁盘，球体和圆锥体上的边界层流动。事实上，旋转三维边界层流动现在已知表现出许多流动特性，由高度复杂且经常竞争的机制控制，这些机制导致流动不稳定并最终分解为湍流。对于一系列旋转锥，实验观察到随着控制流动参数的改变，流动特性连续变化。申请人已经表明，这种变化是由控制边界层内流动的各种力之间的相互作用引起的。然而，这种竞争性相互作用的性质在很大程度上仍然未知。考虑到这一点，本研究项目将开发一个复杂的计算建模代码，能够提供强大的和准确的定量预测的竞争流动不稳定机制之间的相互作用，在顺磁过渡过程。这种预测有助于加速空气动力学研究，并为创新的流量控制策略提供信息或形成其一部分，以减少阻力，从而改善燃油消耗，并减少有害噪音和二氧化碳排放。

Fluid mechanics is of fundamental importance and underpins key developments in a range of disciplines, including aerospace, defence, energy and environmental research. For example, the efficient use of fuel has become an increasingly important factor in civil aviation, with the International Air Transport Association (IATA) committed to "reducing fuel consumption and CO2 emissions by at least 25% by 2020, compared with 2005 levels". Concurrently, aircraft engine noise has become a real and growing environmental issue, especially in the vicinity of airports around the world. Given the global demand for increased air travel, energy efficient and quieter aeroengines are important targets for the aviation and aerospace industries. Aerodynamic improvements have the potential to contribute to the design of the next generation of energy-efficient aeroengines and tubomachinery. Specifically, an increased understanding of the underlying physics through active flow control can reduce aerodynamic drag and delay the transition to unstructured, turbulent flow, both of which are known to have negative implications for fuel consumption and noise emissions. The goal of delaying turbulent-transition can be achieved in a cost-effective way through detailed numerical simulations, as opposed to comparatively expensive experimental investigations. This project will help to achieve that goal by applying a novel computational approach that can model flow within the boundary layer over complex rotating geometries.The boundary layer, a thin layer of fluid confining its viscosity close to a bounding surface, can influence the aerodynamics and drag characteristics of a fluid flow in a profound and significant way. Historically, the boundary layer flow over a rotating disk was used to model air flow over a swept-wing due to the similarity between their velocity profiles. Today, continuing developments in aeroengines, turbomachinery, spinning projectiles and, more recently, electrochemical applications, has created the need to understand boundary-layer flows over rotating bodies, such as disks, spheres and cones. Indeed, rotating 3D boundary-layer flows are now known to exhibit numerous flow characteristics, governed by highly complex and often competing mechanisms that cause flow instability and eventual breakdown to turbulent flow. For a family of rotating cones, experiments have observed a continuous change of flow characteristics as the governing flow parameters are altered. The applicant has shown that this change arises from an interaction between various forces governing flow within the boundary layer. However, the nature of this competing interaction remains largely unknown. With this in mind, this research project will develop a complex computational modelling code capable of providing robust and accurate quantitative predictions of the interaction between competing flow instability mechanisms in the turbulent-transition process. Such predictions can help to accelerate aerodynamics research, and inform or form part of innovative flow control strategies to reduce drag, thereby improving fuel consumption, as well as decreasing harmful noise and CO2 emissions.