Determining the Effects of Competing Instabilities in Complex Rotating Boundary Layers

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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.