Scalar dispersion in turbulent open channel flows over smooth and rough beds

Study of passive dispersion of a neutral scalar in turbulentflows is highly important due \nto its numerous applications in the areas of turbulent flow visualization, turbulent heat \ntransfer and transport of pollutants and other substances in the environment. Over the past \nfew decades, many analytical, numerical, and experimental studies have been conducted \non this topic to obtain a better understanding of the physical process. In the present work, \nLarge Eddy Simulations (LES) of scalar dispersion in turbulent flow over smooth and rough \nchannels is conducted to contribute to the further understanding of the relation between the \nturbulent velocity field and the concentration field. \nThe LES results from the present work showed good agreement with a recently com-pleted experimental study(Rahman and Webster [2005]). An in-depth comparison of in-stantaneous concentration and velocity fields revealed thecorrelation between scalar dis-persion and coherent structures of the turbulent flow. Also,a three dimensional visual-ization of concentration iso-surfaces at different instants provided a good picture of the \nconcentration structures transported as a result of hairpin vortices of turbulent flow, which \nis quite difficult to accomplish using experimental studies.