一个模拟密度分层流特征的改进三维数值模型

An improved 3-D numerical model for simulating characteristics of density stratified flow

为实现对强密度分层流的数值模拟,本文对Boussinesq近似及静压假设进行了讨论。并根据密度分层流的特点,在质量流量守恒条件下对通用POM模型的连续方程、动量方程及湍流模型方程进行了必要的改进。应用改进的三维数值模型,对两组盐度差下的分层流动进行了模拟。结果表明:在环境水体垂向密度变化不明显的情况下,采用静压假设是可取的。但对于环境水体存在明显密度分层的情况,由于垂向密度变化较大,静压假设并不适宜。相对原模型,改进模型得到的盐度等值线更加平稳,盐度垂向变化的梯度更大,计算结果更符合密度分层流的特征。

This paper discusses the Boussinesq and hydrostatic approximation for stratified flows, and some improvements on the density-uneven flow are introduced into the general POM model. First, based on the concept of mass conservation, the volume-conservation continuity equation is revised. Second, according to the characteristics of density-stratlfied flows, the approximate condition of the momentum equation is revised and the density variation is included in the equation. Third, in the turbulence closure model, a local density rather than an average one is used to calculate the pressure. A series of numerical simulation on the density stratified flows are conducted by means of both the original POM and the improved model, and the vertical distribution of salinity and the salinity contour are obtained. It is shown that the results of the simulation by the improved model agree with the field data much better than what from POM model.