具有截面自然对流通道内湍流换热的直接数值模拟

对矩形管道内具有稳定自然对流的充分发展湍流换热进行了直接数值模拟，湍流雷诺数如和普朗特数Pr分别为400和0．71，格拉晓夫数Gr为10^4、10^5、10^6和10^7．分析了管道截面上雷诺应力对主流平均速度、截面流速以及截面平均温度的影响．结果表明：在Gr较小时，湍流雷诺应力的作用使截面的平均换热系数增大；在Gr为10^7时，浮升力的作用增强，但湍流产生的雷诺应力使自然对流的作用减弱．因此，与层流相比，在Gr相同时，湍流的管道截面平均换热系数反而减小．

Direct Numerical Simulation of Turbulent Flow and Heat Transfer in Square Duct with Steady Natural Convection in Cross Section

A direct numerical simulation of a fully developed turbulent flow and heat transfer was conducted in a square duct with a steady natural convection.The flow field was simulated at a turbulent Reynolds number of 400 based on the mean friction velocity and the hydraulic diameter,and a Prandtl number of 0.71.Four different Grashof numbers(Gr is 104,105,106 and 107,respectively) were considered.The influence of Reynolds stress on the streamwise velocity,crosswise velocity and mean temperature was investigated.The results show that the Reynolds stress has more effect than buoyancy body force at the lower Gr number,leading to an increase of the mean heat transfer.However,for the higher Grashof number cases(Gr is 107),the buoyancy body force becomes dominant,the natural convection is somewhat weakened by the Reynolds stress,and the mean heat transfer coefficient is even less than that at the same Gr number in laminar case.