Advances in Magnetic Resonance Imaging (MRI) of Flow

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Steady fluid flow at low speeds is laminar: layers of fluid slide smoothly past one another in an ordered way. When the flow becomes fast enough or when it happens in a sufficiently large vessel, the flow is turbulent: there is complicated and unpredictable mixing of the fluid. Turbulent fluid flow has fascinated scientists since the time of Leonardo da Vinci, but despite nearly 600 years of study, we are still occasionally surprised by the features of turbulence. This is a frustration for scientists and engineers, because an understanding of turbulent flow is important in the atmosphere, in rivers, through dams and turbines, around fish and submarines, in chemical plants, through rocks and inside the human body. In a quest to improve our understanding, we make measurements of fluid flow. This proposal concerns the development of improved measurements for the study of fluid flows in general, but turbulent fluid flows in particular. We will use magnetic resonance imaging (MRI) equipment, which is in principle identical to those used in hospital scans, to measure turbulent flow. MRI is a fabulous tool for the measurement of flow, because it can look inside opaque fluids like foams or slurries and because it does not disturb the flow at all - no probe or tracer need be inserted. Our particular MRI flow measurement method is unique for two reasons. The measurement time is very short (for MRI), which allows us to measure a much broader range of flow speeds than other MRI methods. The measurement time is constant for all parts of our data acquisition, which eliminates certain artefacts to which other MRI methods are prone, particularly in flows like foams, which contain a mixture of liquid and gas. In this proposal we develop some of the hardware used in our method, we extend the method to measure the character of the turbulent flow in all directions, we refine the techniques that we use to select our region of interest within the flow and we study turbulence in some fluids that no other technique can cope with. All of these developments will afford us new insight into the deceptively complicated phenomenon of turbulence.