感潮河段盐水入侵的水质模型

盐潮入侵严重影响内河水质。盐度的纵向分布受制于上游径流和海洋潮汐，其水动力学特性非常复杂。数值求解不恒定盐度入侵，主要困难在于对流占优时对纯对流算子的恰当处理，否则将会产生严重的数值耗散和伪振荡等非物理效应。考虑到强混合型河口潮汐的特点，本文采用同步不同格式对盐潮入侵问题的流场及浓度场进行了数值计算。采用欧拉—拉格朗日混合解法（ELM），将对流—扩散方程中的扩散项和对流项分裂求解，应用高精度时间序列插值的特征差分隐格式求解对流项，扩散项采用传统的有限差分法。在汊口处，将描述河网汊口水质变化的三维对流扩散方程在汊口控制体积积分，变量间的插值分布采用Panankar提出的幂函数，得到新的汊口离散方程。计算与实测结果比较表明，本文提出的方法有效可行。

The simulation of water quality in tidal networks due to unsteady salt-water intrusion

Salt-water intrusion seriously affects the water quality of inland river. The longitudinal distribution of is subjected to both the upstream runoff and ocean tides, which makes the hydrodynamics features very complicated. The main difficulty of numerical simulation of the unsteady salt-water intrusion is how to treat the convective operator appropriately when the advection is predominant. Otherwise, the non-physical effects such as serious numerical diffusion and fake oscillation will happen. Considering the characteristics of strong-mixing type of estuarine tides, this paper used different numerical schemes to simultaneously simulate the velocity field and concentration field of salt-water intrusion. By using the Eulerian-Lagrangian combined method (ELM), the convection-diffusion equation is spitted into the diffusion terms and convection terms. For convection terms, the implicit method of characteristics using time-line interpolation with high accuracy is adopted. While for the diffusion terms the conventional finite difference method is used. at junctions, the three-dimensional convection-diffusion equation is integrated within the junction control volume. The power function proposed by Patankar is used to describe the interpolation distribution of the variables, resulting in a new difference equation. The computation results and experimental data are compared. The agreement shows that the method proposed in this paper is feasible and effective.