Experimental environmental hydraulics: entrainment and mixing in turbulent flows

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The increasingly stringent environmental laws on pollution motivate the study of environmental hydraulics. Its concern is with the disposal and accidental spills of effluents to the atmosphere and 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). Turbulent mixing and, hence, dilution minimizes or mitigates the detrimental effects. 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. Prediction or analysis of pollutant dispersion in turbulent flows (effluent and/or receiving water body) gives rise to engineering problems for which an understanding of turbulent mixing processes is required. 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 four topics. 1) The effect of ambient turbulence on jet dynamics and the entrainment mechanisms will be studied using 3-D particle tracking velocimetry (PTV) experiments. Recent work indicating that turbulence in the ambient reduces dilution rates, contrary to the prevailing assumption, will be extended to examine changing entrainment mechanisms. 2) The suppressed mixing mechanisms at river confluences will be studied experimentally using PTV and statistical analysis of the turbulence and will use geomorphological and geographical experience to interpret the results for real environments. 3) Lagrangian flow statistics in isotropic homogeneous turbulence will be determined experimentally using 3-D PTV in an approximately isotropic homogeneous turbulent flow created using a random jet array. The results will improve turbulent dispersion models of environmental flows. 4) SPH-ALE modeling of free surface channel flows with sediment transport will use the mesh-free Lagrangian particle method, SPH, which is suited to problems with deformable boundaries, moving interfaces and large deformations. The ALE adaptation of SPH is more computationally efficient and improves the treatment of the boundary conditions which is important for free surface river flows with sediment transport.