River Reoxygenation And Its Numerical Simulation

The study on river reaeration is of great importance to the control of riverpollution. Numerical simulation of river reaeration in a 3-D body-fitted coordinatesystem is achieved in this paper Following works have been carried out:1.Oxygen-tusfer theories are reviewed and commented briefly, and numericalsimulation techniques of turbulence are analyzed and evaluated in order to establishand refine the current models for the present research.2.Based on the oxygen-transfer theory this paper derives the expression of1iquid film thickness in the view of the turbulent structure. A 3-D mathematic modelused for river reaeration is established.3.A body-fitted coordinate generated by a Poisson-type equation is employed tosimulate complex boundary. The governing equations in physical space aretransformed into the calculation space, and finite difference equations are obtainedby finite-volume method. Single equation is solved by ADI method, and theSIMPLEC algorithm is used to handle the pressure-velocity coupling. The "nopairing resolution" method is used to so1ve the concentration field. A generalcomputer program is built.4.The present model is applied to the reaeration in an open channel. Thecomputed results agree with the previous experimental values. The model is alsoused to predict the reaeration in a"S"-shaped channel, and numerical results arediscussed.5.The mathematic model of the reaeration in real rivers is discussed by revisingthe reaeration coefficient, analyzing the reaeration of the discharges from hydraulicstructures, and considering biochemical oxygen demand and other factors related tothe dissolved oxygen in rivers.