On the mechanism of turbulent heat transfer in composite porous-fluid systems with finite length porous blocks: Effect of porosity and Reynolds number
On the mechanism of turbulent heat transfer in composite porous-fluid systems with finite length porous blocks: Effect of porosity and Reynolds number
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有限长度多孔块复合多孔流体系统中的湍流传热机理：孔隙率和雷诺数的影响
DOI：
10.1016/j.ijheatmasstransfer.2023.124006
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发表时间：
2023
影响因子：
5.2
通讯作者：
Jadidi M
中科院分区：
文献类型：
--
作者：
Jadidi M
大多数关于复合多孔流体系统的文献研究涉及充分发展的多孔通道流动，其中多孔介质覆盖通道的整个长度。这些研究利用了入口和出口处的周期性边界条件。在这些系统中，在多孔块的正面的停滞，在多孔流体界面上的湍流分离气泡，和从多孔到非多孔区域的流动泄漏不存在。这些流动特征的存在，在一个有限的多孔块浸入在一个通道流的情况下修改整个多孔流体界面的湍流相互作用。与以往的研究不同，本文研究了含有限长多孔块的槽道湍流的流动和传热特性。为此，孔隙尺度的大涡模拟在复合多孔流体系统中进行两个孔隙率（53%和91%）在三个雷诺数为3600，7200和14400。流动可视化显示，在低孔隙率情况下，在界面上形成两个不同的区域：靠近前缘的区域#1，具有有组织的发夹结构和高流动泄漏;远离前缘的区域#2，具有无组织的发夹结构和较低的流动泄漏。在区域#1中，最大湍流波动发生在远离界面的地方，而在区域#2中它们接近界面。结果表明，随着雷诺数或多孔长度的增加，最大湍流统计量的位置接近界面。这一观察结果支持了早期的研究结果，充分发展的多孔通道流，这是唯一有效的区域#2。然而，在低雷诺数或短孔长度下，湍流统计峰值远离界面，与区域1中的观察结果一致。此外，有人发现，增加孔隙率和雷诺数减少流动泄漏（从多孔区域到非多孔区域）分别高达50%和10%，这反过来又破坏了轮廓旋转涡对和发夹结构的模式在界面上。进一步发现，对于一个固定的雷诺数，高孔隙率的情况下的总努塞尔数是2.6倍，比低孔隙率的情况下。低孔隙率情况下的压降是高孔隙率情况下的1.8倍。
The majority of literature studies on composite porous-fluid systems involve fully-developed porous channel flows where the porous media covers the whole length of the channel. These studies utilized periodic boundary conditions at the inlet and outlet. In these systems, the stagnation at the frontal face of the porous block, turbulent separation bubble over the porous-fluid interface, and flow leakage from the porous to non-porous regions do not exist. The existence of these flow features in the case of a finite porous block immersed in a channel flow modifies turbulent interactions across the porous-fluid interface. In contrast to the previous studies, this paper investigates the flow and thermal characteristics of turbulent channel flow containing a porous block with a finite length. To this end, pore-scale large eddy simulations are performed in composite porous-fluid systems with two porosities (53% and 91%) at three Reynolds numbers of 3600, 7200 and 14400. Flow visualization shows that two distinct regions are formed over the interface in low-porosity cases: Region#1 near the leading edge with organised hairpin structures and high flow leakage; Region#2 away from the leading edge with unorganised hairpin structures and lower flow leakage. In region#1, maximum turbulent fluctuations occur far away from the interface while they approach the interface in region#2. The results showed that by increasing either the Reynolds number or porous length, the location of maximum turbulence statistics approaches the interface. This observation supports earlier findings for fully-developed porous channel flows which are only valid in region#2. Whereas, with a low Reynolds number or a short porous length, the turbulent statistics peak far from the interface, consistent with the observations in region#1. Besides, it was found that increasing the porosity and Reynolds number reduces the flow leakage (from the porous region to the non-porous region) up to 50% and 10%, respectively, which in turn disrupts the patterns of contour-rotating vortex pairs and hairpin structures over the interface. It is further found that for a fixed Reynolds number, the overall Nusselt number for the high-porosity case is 2.6 times higher than that of the low-porosity case. The pressure drop for the low-porosity cases is 1.8 times more than that for the high-porosity cases.