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，研究了大尺度涡旋对其时空换热特性的影响。纵向涡旋是由管内单个小翼涡发生器人工产生的。等速、静压、摩擦系数和换热系数的分布规律与主涡下游螺旋流动的现象有较好的对应关系。除部分区域外，二次流的下洗或吹散作用是由主涡在壁面上沿自身轴向旋转引起的，证实了传热与剪应力之间的定量类比。当钝体放置在管道高度的中心时，观察到侧涡与卡门涡联锁运动发生在壁面上。这些侧涡生长的周期性现象对传热的增加起作用。在窄间隙处，卡门涡不脱落，最大换热发生在气流通过间隙后的分离点附近。当阀体附着在风管表面时，剪切层内的涡依次向下游方向流动，然后在下游区域相互结合，之后大涡附着在风管表面。在再附着点附近，温度交替显示高、低值。在表面附着涡旋使表面温度降低，低温区域根据涡旋向下游移动。再附着点保持高温，直到下一个涡旋相继附着在那里。大尺度涡旋的重新附着和分离增加了换热。

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.