Experimental environmental hydraulics: mixing in turbulent flows

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The ocean has long been considered as the ultimate receiving body for water-borne waste products.  The increasingly stringent environmental laws on pollution motivates the study of environmental hydraulics.  Its concern is with the disposal of and accidental spills of effluents from smoke stacks to the atmosphere and through outfalls to surface water bodies like rivers, lakes and oceans, and the prediction of the effluents' subsequent dispersion at the local or regional scale (up to 100 km).  Minimization or mitigation of the detrimental effects of the pollutants is sought though dilution.  One of the remarkable properties of turbulence is its capacity to mix and dilute either a vector (effluent velocity) or a scalar (pollutant) extremely rapidly.  Turbulence can be in either or both the effluent and the receiving water body.  Minimizing or mitigating the effects of the pollutants gives rise to engineering problems such as the calculation of dilution zones, and the estimation of pollutant concentrations and extent of spreading from accidental spills.  The long term research objective is a deeper understanding of turbulent transport and mixing processes, while the short term goals are to investigate the following three topics experimentally.  1) The effect of ambient turbulence on jet hydraulics and dilution when a turbulent jet is released into a turbulent receiving fluid.  The work will continue recent preliminary work indicating that the current assumption, that jet driven dilution and turbulent diffusion can be superimposed, may significantly over-predict dilution rates.  2) The importance of differential diffusion in turbulent flows.  Most environmental flows involve more than one scalar and are at moderate Reynolds numbers where the assumption that differential diffusion is negligible no longer holds.  The work will investigate the degree of differential diffusion in jets over a range of Reynolds numbers and in the presence of ambient turbulence.  3) Lagrangian flow statistics in isotropic homogeneous turbulence.  These will be determined experimentally using 3-D particle tracking velocimetry in a flow created using a synthetic jet array.  The results will be used to improve turbulent dispersion models of environmental flows.