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

许多作者已经报道了这种管道的流动特性和传热性能，但所有这些报告都处理了垂直于管道轴的重复肋粗糙度。由于该促进剂在管道内的流动在促进剂前部被大大加速，因此压力损失也增加了。为了降低压力损失，获得更高的换热性能，本文提出了倾斜重复肋的粗糙度，即肋的设置不垂直于管轴，而是倾斜于管轴。使用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，与普通的重复肋粗糙度相比，由于促进剂的存在，横截面积的流动收缩比更小。二是斜肋在管道内产生二次流，提高了管道的传热性能。通过考虑nss方程平流项的贡献，从测量的速度剖面定量研究了二次流的产生机理。二次流强度与雷诺数无关，在3500 ~ 20000雷诺数范围内，二次运动的最大速度超过了管道平均轴向速度的45%。通过LDV对流动的详细结构进行了验证，得出了测量的雷诺应力与速度梯度的精确对应和涡流扩散假设的适用性。用粗糙度函数计算得到的倾斜重复肋粗糙度管道的流动阻力低于正常重复肋，说明倾斜重复肋粗糙度在实际应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.