翼型涡发生器对半圆形螺旋通道的换热强化机理

为考察不同形状和布置方式的翼型涡发生器强化半圆形截面螺旋通道的换热特性,对单一以及安装了jxjs、jxjk、sjjs和sjjk 4种涡发生器的螺旋通道内流动与换热特性进行了数值研究,数值模拟结果与实验结果吻合较好。结果表明,研究范围内涡发生器前后180°范围内的换热壁面平均Nusselt数与单一通道的相应值之比的平均值在1.044～1.074之间,流动阻力系数f/f₀在1.105～1.188之间。对传热效果而言,矩形翼优于三角形翼,对翼渐缩布置优于渐扩布置。涡发生器产生的纵向脱落涡旋改变了原有的二次流场结构,改善了速度场和温度场的协同性,强化了传热。安装jxjs和sjjs型涡发生器的复合二次流场分别为4涡和2个大涡结构,Re=8000时两者在通道内强化换热作用范围分别可达10.47和12.56倍翼高的距离。

Enhanced heat transfer mechanism of winglet vortex generator in helical channel with semicircular cross section

The purpose of this paper is to obtain the enhanced heat transfer characteristic of the winglet vortex generator (VG) in the helical channel with semicircular cross section. The shape and layout of the VG are concerned. CFD software is adopted to simulate the fluid flow and heat transfer characteristic in the smooth helical channel and that installed with four kinds of winglet vortex generator. The four styles of vortex generator are characterized as jxjs, jxjk, sjjs and sjjk VG, respectively. The simulated data coincide well with the experimental data. The results based on the current research show that after installing the vortex generator, the average ratio of Nu_m to Nu₀ is in the range of 1.044—1.074 where Nu_m is the surface average Nusselt number of helical channel within the scope of ±180o away from the vortex generator and Nu₀ is the corresponding value of smooth helical channel. However, the specific value between the flow resistance coefficient of helical channel with VG and the corresponding value of smooth channel, i.e. f/f₀ is in the range of 1.105—1.188. The rectangular winglet VG is superior to the triangular winglet VG only in terms of heat transfer enhanced. Along with the flow direction, the convergent layout of VG is superior to the divergent layout for heat transferring. Based on the field synergy principle, the secondary flow field structure would be changed by the vortices shedding from the VG. Thus, the cooperativity of flow and temperature fields would be better and the heat transfer would be improved. For the helical channel with rectangular and triangular winglet VG, the compound secondary flow fields are four vortices and two large vortices, respectively, and the length of heat transfer effect is 10.47 and 12.56 times of winglet height, respectively.