凹槽表面的流动与传热特性

Flow and heat transfer characteristics of groove surface

采用大涡模拟对底面为凹槽的矩形通道内湍流流动与传热特性进行了研究,为验证所采用数值方法的准确性与可靠性,将平直矩形通道内模拟结果与文献中的直接数值模拟结果进行了比较,换热面Nusselt数与采用Dittus-Boelter公式计算所得Nu进行了比较,计算误差小于5%。以凹槽表面为底面的矩形通道的数值模拟结果表明:通道底面的凹槽结构改变了凹槽表面处流动结构,不同的凹槽高度和长度对流动阻力和换热效果的影响不同,在特定的几何参数下,与平直矩形通道相比,凹槽表面时均Nusselt数提高了近50.5%,时均摩擦阻力系数减小了近35.17%,综合系数增加了73.89%。通道内的流动结构显示:凹槽表面附近存在流体垂直流向壁面区域,在垂直流动区域内流体出现前、后分流,分流位置处Nusselt数增加明显,摩擦阻力系数没有明显增加,其综合流动特性最好。

The turbulent flow and heat transfer characteristics of rectangular channel with groove bottom surface are investigated by use of large eddy simulation. To validate the accuracy and reliability of the simulation method, the simulation results for plate channel are compared with the direct numerical simulation results of reference. The heat transfer surface Nusselt number is compared to that calculated by Dittus-Boelter equation. The differences are less than 5%. From the simulation results for rectangular channel with groove bottom surface, it is found that the groove structure of the channel bottom surface changes the flow structure near the groove surface. Groove heights and lengths influence the flow resistance and heat transfer effect. Compared with the plate rectangular channel with specific geometric parameters, the time-averaged Nusselt number of groove surface is increased nearly by 50.5%, and the time-averaged friction drag coefficient decreases by 35.17 %, and the comprehensive coefficient is increased by 73.89%. The flow structure in the channel shows that there is a region near the groove surface, in which the flow is perpendicular to the wall. The fluid flows forward and backward in the vertical flow region. Since the friction drag coefficient does not increase significantly and the Nusselt number is obviously enhanced, the comprehensive flow characteristic is the best.