翼片诱导纵向涡强化层流对流传热数值模拟

利用三维数值模拟,分析了圆管内添加翼片后流体的流动结构和对流传热特性。模拟中,翼片与壁面呈45°倾斜放置,选取包含1个翼片的1／6通道进行研究。结果表明,翼片可在下游诱导产生2个旋转方向相反的纵向涡,形成对称的涡偶,涡偶外侧为背壁流,内侧为向壁流。纵向涡结构提高了流体在径向上的速度波动,在翼片下游靠近管壁处,最大速度可达到主流平均速度的80％,增强了对速度边界层的扰动。流场的改善使通道内的温度场分布更加均匀,与光滑通道相比,壁面附近的温度梯度可提高接近1个数量级。流体对壁面的冲刷作用使对流传热得到强化,相对于光滑通道,壁面局部Nu数可提高近50倍。纵向涡对通道内流体的强化传热作用随Re的增加而显著提高。

Numerical simulations on convective heat transfer characteristics of laminar flow with longitudinal vortex induced by winglets

3-D numerical simulations were presented for studying the flow structures and convective heat transfer characteristics in a cylinder tube embedded with wing-finned vortex generators. In the numerical simulation, the winglet was upstream placed at an angle of 45 to the tube wall and 1／6 of channel was selected for studying due to symmetry. The results showed that two counter-rotating longitudinal vortices were induced downstream the winglet, forming a symmetric vortex pair. The flow inner vortex pair was towards the wall while the flow outer vortex pair was backwards the wall. The longitudinal vortex could improve the magnitude of velocity in the radial direction, and the maximum value in near wall region reached 80％ of the average mainstream velocity downstream the winglet. As a result, the winglet booted the disturbance of the velocity boundary layer. The improved velocity field could make the temperature field in the tube more uniform. Compared with the smooth tube, the temperature gradient near the wall could improve approximately an order of magnitude. The flow induced by the longitudinal vortex rushed to the wall, which strengthened the convective heat transfer significantly. The maximum value of the local Nu on the wall surface could reach 50 times of the smooth tube. The improved convective heat transfer performance lead by longitudinal vortex enhanced with the Reynolds numbers increasing.