Enhanced Mixing by Vortex Dynamics

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Turbulent mixing is the governing process for a wide variety of phenomena including weather patterns, the dispersion of pollutants from an exhaust stack, convective heat transfer and turbulent combustion. It involves the entrainment and mixing of a foreign species in a turbulent carrier fluid, where the species being mixed may be in the same or different phase from the carrier. The ability to generate, control, and model mixing processes down to the molecular level is of fundamental scientific and technical importance. For example, the development of low-emission combustion technologies for gas turbines depends on the ability to maximise the rate and uniformity of fuel-air mixing. Despite the pressing environmental need for such development due to the threat of global warming, progress in this area is currently hampered by a lack of understanding of how gases, droplets and particles are transported and mixed in turbulent flows.The classical view of mixing treats the species being mixed as a passive scalar within the turbulent carrier fluid, so that the scalar is correlated to the velocity field which is governed by the concepts of the Kolmogorov cascade theory. However, an increasing body of experimental research using advanced laser diagnostics suggests that this traditional conceptual framework for mixing is inadequate. Studies of this kind are typically directed towards understanding fundamental phenomena such as departures from Gaussian behaviour in simple flows, but there is also a need to apply the latest experimental techniques to more complex flows, which are closer to practical mixing devices. This proposal outlines a series of experiments which aim to develop a flow control device for enhanced mixing, known as a vortex generator. The use of vortex generators in the context of mixing enhancement is entirely novel, and their performance as mixers will be evaluated in comparison with jets in cross-flow. By studying both single-and two-phase flows at the smallest possible scales the fundamental aspects of turbulent mixing involving vortex dynamics will be brought to light, which will not only advance the understanding of mixing processes but will also contribute to the future development of mixing technologies.