k-ε双方程水库水温模型浮力模拟分析

The buoyance simulation analysis of k-ε double equation reservoir water temperature model

在比较国内外常用水库水温紊流模型的基础上,针对采用k-ε双方程紊流模型的宽度平均立面二维水库水温模型,从理论分析和数值模拟两方面讨论了k-ε紊流模型在模拟温差异重流时紊动动能生成项和浮力项的作用机理。分析了紊动动能生成项和浮力项对紊动动能和耗散率各自的影响程度,对水温垂向梯度与紊动动能的相互制约关系进行了探讨,研究了紊动动能浮力项和生成项在水库垂向的分布规律。W2模型根据实测数据率定的涡黏系数或混合长度在通用性上存在一定不足,但在使用者经验丰富的条件下仍能得到足够精确的预测结果。k-ε模型紊动动能生成项和浮力项引起的耗散率改变对紊动动能的影响作为小量可予忽略;k-ε模型可通过紊动动能生成项和浮力项计算与垂向流速和温度分布相适应的涡黏系数,将温差浮力影响反映在垂向动量方程中;浮力项主要受垂向温度梯度控制,紊动动能与垂向温度梯度的相互制约关系是k-ε紊流模型模拟温差异重流的关键因素。

Based on a comparative study of the reservoir water temperature turbulence models commonly used,a reservoir water temperature model with averaged width and 2-D elevation adopting k-ε double equation turbulence model is used to simulate thermal density flow.In the view of theoretical analysis and numerical simulation,this paper discussed the mechanism of turbulent kinetic energy's buoyancy term and production term.It investigated the buoyancy term's and production term's impacts on turbulent kinetic energy and energy dissipation,respectively.This paper explored the inter restricted relationship between water temperature vertical gradient and turbulent kinetic energy,and studied the vertical distribution law of turbulent kinetic energy's buoyancy term and production term in reservoir.The eddy viscosity coefficient or mixing length in W2 model was lack of generality,which was rated by measured data,but a sufficient precise prediction result can be obtained by a veteran.The effect of the energy dissipation caused by the buoyancy term and production term on turbulent kinetic energy can be ignored as a small factor in k-ε turbulence model.This model can calculate eddy viscosity corresponding to the vertical velocity and temperature distribution by turbulent kinetic energy's buoyancy term and production term.Therefore,the influence of thermal buoyancy was reflected in vertical momentum equation.The buoyancy term was mainly controlled by temperature vertical gradient.The inter restricted relationship of water temperature vertical gradient and turbulent kinetic energy was the key factor in a simulation of thermal density flow with the k-ε turbulence model.