Forced Convective Heat Transfer Enhancement by the Turbulent Promoter Generating Streamwise Vortices

许多作者已经报道了这种管的流动特性和传热性能，但是所有这些报道都处理了肋垂直于管轴线设置的重复肋粗糙度。由于带有这种促进剂的管道中的流动在促进剂的前部被大大加速，所以压力损失也增加。从降低压力损失和提高传热性能的角度出发，本文提出了倾斜式重复肋粗糙度，即肋的设置不垂直于管轴线，而是倾斜于管轴线。具有这种类型的促进剂的管道被认为具有两种优点。一个优点是较小的流动收缩率的横截面积由于促进剂，与正常的重复肋粗糙度相比。另一种是倾斜的重复肋在管内产生了二次流，提高了管内的传热性能，并考虑了N.S.对流项的贡献，从测量的速度分布定量地研究了二次流的产生机理。方程二次流的强度与雷诺数无关，在雷诺数3500 ~ 20000的范围内，二次流的最大速度超过管道平均轴向速度的45%。利用LDV对管内流动的详细结构进行了表征，结果表明，雷诺应力的测量值与流速梯度的关系较为精确，涡扩散率假设也是适用的，粗糙度函数计算结果表明，倾斜多肋粗糙度管道的流动阻力比普通多肋粗糙度管道的流动阻力小，这意味着倾斜重复肋粗糙度在实际使用中具有很大的优势。

The flow characteristics and the heat transfer performances of such pipes have been reported by many authors, but all of these reports treated the repeated-rib roughness where the ribs were set perpendicular to the pipe axis. Since the flow in the pipe with this promoter is greatly accelerated in the front part of the promoter, the pressure loss also increases. In the light of reducing the pressure loss and getting higher heat transfer performance, the inclined repeated-rib roughness are proposed in this paper, namely the ribs are set not perpendicular but inclined to the pipe axis. The pipe with this type of promoter is considered to have two kinds of advantages. One advantage is smaller flow contraction ratio of the cross sectional area due to the promoter, compared with that of the normal repeated-rib roughness. The other is that the inclined repeated-rib produces the secondary flow in the pipe which enhances the heat transfer performance of the pipe.The mechanism of the generation of secondary flow was quantitatively investigated from the measured velocity profile by considering the contribution of the advection terms of the N.S. equation. The intensity of the secondary flow did not depend on the Reynolds number and the maximum velocity of the secondary motion was over 45 percent of the mean axial velocity of the pipe in the Reynolds nember region from 3500 to 20000. The detailed structure of the flow was claified by the LDV, and it is concluded that the measured Reynolds stress is accurately correspond to the velocity gradient and the eddy diffusivity assumption is applicale.The flow resistance of the pipe with the inclined repeated-rib roughness evaluated by the roughness fuction was lower than that with normal repeated-rib, which means that the inclined repeated-rib roughness has great adavatage in a practical usage.