非能动冷却系统上升通道中湍流自然对流的直接数值模拟

Direct Numerical Simulation of Turbulent Natural Convection in Riser of Passive Cooling System

湍流直接数值模拟形成的数据库可以为开发功能更完善的湍流模型提供数据支撑。本文采用直接数值模拟方法研究了在不同普朗特数(Pr)下竖直通道中湍流自然对流的平均速度、平均温度、速度和温度脉动强度、雷诺应力、湍流热通量和湍流结构的分布特性。研究结果表明:(1)湍流自然对流的平均速度和平均温度分布关于通道中心线反对称,最大速度和温度梯度出现在壁面附近区域,Pr数增加,最大速度值减小,而壁面处温度梯度增加;(2)湍流自然对流的速度脉动强度、温度脉动强度、雷诺应力和湍流热通量随Pr数增加而降低,热通量在高温壁面侧会出现负值;(3)湍流自然对流的脉动速度和温度分布没有特别规则的结构,但主流脉动速度与壁面呈一定夹角。

The database of turbulent flow by using direct numerical simulation can support the development of more powerful turbulent models. In the paper, the characteristics of averaged velocity, averaged temperature, intensities of fluctuating velocity and temperature, Reynolds stress, turbulent heat fluxes and turbulent structures of natural convection for different Prandtl numbers are studied by using direct numerical simulation. The results show that： （1） The profiles of averaged velocity and averaged temperature of turbulent natural convection are anti-symmetrical to the center- line of the vertical channel, and the locations of the maximum value of averaged velocity and temperature are near the heated wall. With the Prandtl number, the velocity decrease but the temperature gradient increase near the wall. （2） The intensities of fluctuating velocity and temperature, Reynolds stress, turbulent heat fluxes are all decrease with the increase of Prandtl number, moreover, turbulent heat fluxes are negative near the heated wall. （3） There are no regular structures for fluctuating velocity and temperature fields in turbulent natural convection, but the turbulent structures of mainstream velocity keep at constant angle to the wall.