Mixing and transport

Abstract

The International Symposium on Environmental Hydraulics was held in Hong Kong in December 1991 and produced a two volume proceedings.1 The proceedings include over 200 papers, most related to mixing and transport. Conference sessions cov ered such topics as jets and plumes, ocean outfalls, turbulent mixing, dispersion, sediment transport, stratified flow, and modeling. The annual American Society of Civil Engineers National Conference on Hydraulic Engineering was held in Nashville, Tennessee, in July and August 1991 ? Sessions pertinent to mix ing and transport addressed field measurements of dispersion in rivers, water-sediment interface processes, thermal discharges, estuary modeling, oil spills, sediment transport, and water quality hydraulics. Frankel and Brenner3 extended generalized Taylor dispersion theory to unbounded homogeneous shear flow. Using a coor dinate system that deforms with the shear flow, they derived a convective-dispersion type solution for solute transport. Smith4 analyzed the influence of wind mixing on buoyant and slightly dense particles in shallow water. He found that the concentrating action of downwind movement of buoyant particles was coun teracted by increased mixing, thus explaining the lack of cor relation between onshore winds and shoreline pollution. Komori et al5 considered the mixing dynamics of two reacting species injected at separate points to a turbulent flow field. They used the model to evaluate the "unmixedness" parameter, a measure of the effects of mixing on the mean chemical reaction rate. Borgas and Sawford6 revised previously derived formulations of the statistical properties of oneand two-particle turbulent dis persion. New relations for the one-particle Lagrangian acceler ation correlation and two-particle acceleration covariance were derived for the inertial subrange. Squires and Eaton7 evaluated the dispersion of heavy particles in turbulent flow. Through numerical simulations, they deter mined how drift due to body forces and inertia changes diffusion of a heavy particle from that of a neutral particle. Mei et al* mathematically analyzed the influence of Basset and gravitational forces on dispersion of particles. Basset forces were found to affect the particle movement but not the structure of the fluid velocity fluctuations. Yang et al9 presented a new higher-order numerical technique for solution of the advection-diffusion equation. The method tracked advection by the method of characteristics and inter polated the concentration and its derivatives using higher-order polynomials. Kerstein10 reported on the linear-eddy approach for modeling turbulent diffusion over a wide range of length scales. He modeled molecular diffusion deterministically but su perimposed a stochastic model of turbulence-induced diffusive movements. Pai and Tsang11 proposed a second-order closure turbulence model solved by finite elements. They tested their model against laboratory, wind-tunnel, and large-eddy simula tions and reported on the model's parameter sensitivity. Li12 developed a model to solve the two-dimensional advection-dis persion equations using a split-operator scheme. The advective step was solved by minimizing error in a characteristics solution; the dispersion step was solved by an alternating direction explicit method. Ernest et al13 developed a parameter estimation algorithm for advection-dispersion particle transport. The theory was tested against dye clouds and particles in mixed laboratory columns.