STUDY ON TIME-SPATIAL CHARACTERISTICS OF HEAT TRANSFER BY VISUALIZATION OF INFRARED IMAGES AND DYE FLOW

通过对染料流动和红外图像的观测，研究了大尺度旋涡对时空换热特性的影响。纵向涡是由管内单个小翼涡生成器人工产生的。等速、静压、摩擦因数和换热系数的变化规律与主涡向下游螺旋流动的现象具有很好的一致性。证实了换热与剪应力之间的定量类比，但在某些区域，二次流的下洗或吹扫的影响是由于主涡在壁面上绕自己的轴旋转造成的。当钝体位于风道高度中心时，侧涡与卡门涡在壁面上发生连锁运动。这些周期性的侧涡增长现象对换热的增加起到了一定的作用。在窄间隙条件下，卡门涡没有脱落，最大换热出现在气流通过间隙后的分离点附近。当物体附着在管道表面时，剪切层中的旋涡有序地向下游流动，然后在下游区域相互结合，之后较大的旋涡附着在管道表面。在再附着点附近，温度呈现高低值交替变化。表面附着涡导致表面温度降低，低温区根据涡系向下游移动。再附着点保持较高的温度，直到下一个旋涡相继附着在那里。大尺度旋涡的再附着和脱离强化了换热。

The effect on time-spatial heat transfer characteristics of large-scale vortices was investigated by means of observing both dye flow and infrared images. Longitudinal vortices were artificially generated by a single winglet vortex generator in a pipe. The patterns of iso-velocity, static pressure, friction factor, and heat transfer coefficients show good correspondences to phenomena of the main vortex spirally flowing downstream. The quantitative analogy between the heat transfer and the shear stress is confirmed except for some regions, where the effects of the down-wash or blowaway of the secondary flows is caused by the main vortex rotating on its own axis on the surface at the wall. When the blunt body placed at the center of the duct height, the side vortex is observed to occur at the wall in an interlocking motion with a Karman vortex. These periodical phenomena of growing side vortices play a role in the increase of heat transfer. At narrow clearances, Karman vortex was not shedding, the maximum heat transfer is near the separation point of flow after it has passed the clearance space. When the body was attached to the duct surface, the vortices in the shear layer flow in good order to downstream direction, then combine with each other in downstream region, and after that large vortex attaches the surface. Near the reattachment point, the temperature shows high and low values alternatively. Attaching vortices to the surface caused to decrease the temperature on there, and the low temperature region moves downstream according to the vortices. The reattachment point was kept a high temperature until next vortex attaches to there successively. The heat transfer was augmented by the reattachment and detachment of large-scale vortices.