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Transient laminar heat transfer simulations in periodic zigzag channels

机译:周期性锯齿形通道中的瞬态层流传热模拟

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摘要

At sufficiently high Reynolds numbers, laminar flows in tortuous channels become unsteady. A computational fluid dynamics methodology is developed to study transient, laminar flow and heat transfer in a periodic zigzag channel with a semi-circular cross-section. The computational domain consists of seven repeating zigzag units with smoothly joined inlet and outlet sections. Reynolds numbers ranging from 400 to 800 and Prandtl numbers ranging from 0.7 to 20 are examined for constant wall heat flux and constant temperature thermal boundary conditions. Simulation results show that the flow reaches a "developed" state after around three units, where the local velocities fluctuate with time but give well defined average heat transfer rates and pressure loss. The power spectra of the velocity at monitor points located periodically along the channel also become very similar. Significant heat transfer enhancement is observed in the transient regime studied, which is accompanied by a modest pressure-drop penalty, both of which increase with increasing Reynolds number. Vortex structures are visualized at different simulation times and Reynolds numbers and it is found that with increasing Reynolds number, vortices with smaller length-scale are generated, which contribute largely to the enhancement of heat transfer. The results for different Prandtl numbers show that the heat transfer enhancement is proportional to Pr1'3. The Nusselt number for the T boundary condition is found to be always higher than that for the H2 boundary condition.
机译:在足够高的雷诺数下,曲折通道中的层流变得不稳定。开发了一种计算流体动力学方法,以研究具有半圆形横截面的周期性之字形通道中的瞬态,层流和传热。计算域由七个重复的曲折单元组成,入口和出口部分平滑连接。对于恒定的壁热通量和恒定的温度热边界条件,检查范围为400至800的雷诺数和范围为0.7至20的普兰特数。仿真结果表明,在大约三个单位后,流动达到“发展”状态,其中局部速度随时间波动,但给出了明确的平均传热速率和压力损失。沿通道周期性放置的监视点处的速度功率谱也变得非常相似。在研究的过渡态中观察到显着的传热增强,伴随有适度的压降损失,两者都随着雷诺数的增加而增加。在不同的模拟时间和雷诺数下可以看到涡旋结构,发现随着雷诺数的增加,会生成长度尺度较小的旋涡,这在很大程度上促进了传热。不同普朗特数的结果表明,传热增强与Pr1'3成正比。发现T边界条件的Nusselt数始终高于H2边界条件的Nusselt数。

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