NUMERICAL SIMULATION OF ICE-COVER INFLUENCE ON NEARFIELD MIXING

摘要

This paper presents the results of a numerical-simulation investigation of ice-coverrninfluence on the mixing and transport of a neutrally buoyant contaminant released inrna straight reach of a dune-bed channel. The investigation used a three-dimensionalrncomputational fluid dynamics model, validated against flume data for flow distributionrnin the channel and against a simple analytical solution for mixing in the channel.rnThe model was used to simulate contaminant release near the ice-cover undersidernand near the bed. The results show that, for constant water discharge, coverrnpresence reduces near-field mixing because it redistributes the flow, increases flowrndepth, decreases bulk velocity, reduces maximum level of turbulence, and modifiesrndune geometry. For the ice-covered flow, a contaminant released near the bed orrnnear the cover underside remains closer to those boundaries over a longer distancernthan for openwater flow. The simulation shows that cover presence reduces therndepth-averaged diffusivity to about 45% of the corresponding diffusivity forrnopenwater flow. The distance to attain full mixing across the flow depth increases byrna commensurate amount.