平流式沉淀池二维数值模拟--数学模型及计算方法的验证

2D Modeling of Rectangular Primary Settling Tanks——Verification of Mathematical Model and Numerical Method

建立描述沉淀池内的水流流动、混合与沉淀特性的k-ε双层模型及传质沉降模型,速度与压力解耦时使用了SIMPLE算法,采用交错网格技术布置变量,利用混合有限分析格式来离散求解所建立的数学模型。结合文献中经典的实验结果进行数学模型及计算方法的验证:首先检验了不同雷诺数范围内水流由池底进入时模型的预测能力,与Imam等的速度场(Re=10900)及挡板后方回流涡长度(雷诺数从2500~25000)进行了比较,验证了模型的有效性;与Imam等的实验及计算所得过流曲线进行了比较,结果表明本文预测的结果精度更高;低浓度污染物<150~200 mg/L时,固相对液相的影响可以忽略,所建立的沉降模型可以预测沉淀池内污染物的去除率,计算结果与其它文献值吻合良好;水流入口从池子中部进入时流场发生了变化,入口处出现了两个旋涡,预测结果也得到了验证。因此作者所建立的数学模型及求解方法可以用来预测沉淀池内低悬浮物固体浓度污水的流场,传质与沉降特性。

The two-layer turbulence model combining mass transfer model and settling model was used to establish a mathematical model describing flowing, mixing and settling characteristics in rectangular primary settling tanks. The Semi-Implicit Method for the Pressure-Linked Equations （SIMPLE） method was used on pressure correction. The hybrid finite analytic method with staggered grid was used to solve this model. The simulation results obtained using the mathematical model were compared with the experimental data and simulation results available in literatures, and the results of comparison indicate that the profiles of the velocity field at Re = 10900 and the recirculation length increasing with Reynolds number range from 2500 to 25000 in case of incoming flow coming from the bottom are in agreements with the experimental results and simulation results of Imam ; the Flow-Through Curve （I^C） obtained using the mathematical model are in good agreement with the curves based on experimental data and simulation results of Imam, and the accuracy of predicted FCT is higher than Imam＇ s results. Under the low Suspended Solids （ SS 〈 150 - 200 mg/L） concentration, the influence of solid phase to the fluid phase could be ignored, the mathematical model could be used to predict the remove efficiency, and the results are in good agreements with other predicted values available in literatures. The flow field changes when the incoming flow coming from the middle part of the inlet, there are two vortices in the inlet region in this case, and the predicted results were verified by comparing with Adams and Rodi＇ s work. It is therefore concluded that the mathematical model and HFAM approach can be used to simulate the turbulent flow, mass transfer and settling process in rectangular primary settling tanks with low SS concentration wastewater.