Utilising a Naturally Occurring Drag Reduction Method

It is now evident that the global climate is changing. In October of 2018, the United Nations (UN) Intercontinental Panel on Climate Change issued a special report on the impacts of global warming. The report notes that "rapid and far-reaching" changes will be required in order to achieve "net-zero" CO2 emissions by 2050. At present, one of the largest sources of CO2 emissions stems directly from the burning of fossil fuels for transportation purposes. Maritime transport alone emits around 940 million tonnes of CO2 annually and is responsible for around 2.5% of the total global greenhouse gas emissions. It is well understood that a major contributing factor to this worldwide fuel consumption (and, by proxy, greenhouse gas emissions) is skin-friction drag. This force is associated with the drag that all bodies experience as they move through a fluid. Whether that fluid be air, water or otherwise, skin-friction drag will always be present and energy is required to overcome its effect. This includes human energy input in competitive swimming and cycling.

Given the tangible detrimental effects and related societal consequences of global warming, research into techniques that act to reduce skin-friction drag in cars, aeroplanes, ships has intensified in recent decades. One source of inspiration for these drag reduction techniques has come from the study of fliers and swimmers. For the purposes of survival, birds and fish have been adapting for many millennia. It is these adaptations that have most interested scientists. More specifically, the research community has focused on the idea that evolution has ensured that these species move incredibility efficiently through their fluid-centred habitats. A relatively recent example that has garnered a great deal of attention from fluid mechanists is the reduction of skin-friction drag via the introduction of shark-skin-like rough surfaces when attached to flexible membranes, in particular.

A boundary-layer flow is the flow of a thin layer of fluid above or below a bounding surface. These types of flow are pervasive and can be directly affected by skin-friction drag. This project will investigate, theoretically, the idea that boundary-layer flows can be actively controlled via biologically-inspired drag reduction techniques observed operating in the natural world. The goal of the investigation will be to develop mathematical techniques that can be used to model the control of such flows with a specific focus on the ability to delay the onset of turbulent transition. Turbulent flows play a significant role in reducing fuel efficiency and, in the case of fossil-fuel burning engines, have an associated impact in increasing harmful CO2 emissions. In relation to the increasing number of electrical vehicles the road and the associated UK Government's advancement of the cessation of diesel and petrol vehicle production, improved drag reduction techniques would produce improved range performance, that at present to the public is a perceived reason for not readily adopting the technology. The results that stem from this study will provide new insights into active flow control methods which can then be utilised to reduce the effects of drag and improve global fuel consumption with resultant economic benefits.