微型矩形凹槽的长方体通道的减阻和传热特性

Features of drag reduction and heat transfer in rectangular channel with miniature cuboid dimples

在长方体通道底面沿展向方向间隔设置了微型矩形凹槽,凹槽的深度与边界层尺度相当。采用大涡模拟方法对长方体通道内的流动及传热特性进行研究。数值计算结果表明:在长方体通道内设置的微矩形凹槽可以诱导“突出效应”及二次涡,二次涡的作用类似于微型空气滚动轴承,因而可减小流阻,并使传热性能略有提高。研究表明:微凹槽导致了速度滑移,从而有效降低了通道底部附近流体速度梯度;造成低速条纹变宽,使高低速流体的混合受到抑制。微凹槽内产生的二次涡增加了黏性底层的厚度,且二次涡与微凹槽上方流体之间的滚动摩擦代替了壁面与流体之间的滑动摩擦。与没有布置微型矩形凹槽的长方体通道相比,布置微凹槽的长方体通道可在不影响传热效果的前提下达到6%以上的减阻率。

Miniature cuboid dimples are arranged on the bottom surface of rectangular channel along spanwise direction.The depth of the dimples is of the same order of magnitude as the boundary layer thickness.The flow and heat transfer characteristics in rectangular channel are studied by large eddy simulation.The numerical results show that the“protrusion effect”and secondary vortexes can be induced by the miniature cuboid dimples.The role of the secondary vortexes is similar to that of miniature air rolling bearings,thus reducing flow resistance and improving heat transfer performance slightly.The results show that the miniature cuboid dimples lead to velocity slip,which effectively reduce the velocity gradient near the channel bottom.The low speed streaky widens and the mixing of high and low speed fluids is inhibited.The secondary vortexes in the miniature cuboid dimples increase the thickness of the viscous sub-layer.Moreover,the rolling friction between the secondary vortexes and the upper fluid replaces the sliding friction between the wall and the fluid.Compared with the rectangular channel without miniature cuboid dimples,the rectangular channel with miniature cuboid dimples can achieve more than 6%drag reduction without affecting the heat transfer effect.