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首页> 外文期刊>International Journal of Heat and Mass Transfer >Contribution of vortex structures and flow separation to local and overall pressure and heat transfer characteristics in an ultralightweight lattice material
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Contribution of vortex structures and flow separation to local and overall pressure and heat transfer characteristics in an ultralightweight lattice material

机译：超轻晶格材料中涡旋结构和流分离对局部和整体压力与传热特性的贡献

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摘要

Ultralightweight lattice-frame materials (LFMs) with open, periodic microstructures are attractive multifunctional systems that can perform structural, thermal, actuation, power storage and other functions [A.G. Evans, J.W. Hutch-inson, M.F. Ashby, Multifunctionality of cellular metal systems, Prog. Mater. Sci. 43 (1999) 171-221]. This paper presents experimental and numerical studies of local fluid flow behaviour and its contribution to local and overall pressure and heat transfer characteristics of such a lattice material with tetrahedral unit cells. A single layer of the LFM with porosity of 0.938 is sandwiched between impermeable endwalls that receive uniform heat flux and the heat transfer is subjected to forced air convection. Experimental measurements with particle image velocity (PIV) and thermochromic liquid crystal (TLC), backed by computational fluid mechanics (CFD) simulations, revealed two dominant local flow features in the LFM. Distinctive vortex structures near the vertices where the LFM meets the endwalls and flow separation on the surface of LFM struts were observed. The vortex structures formed around the vertices include horseshoe vortices and arch-shaped vortices. The horseshoe vortex increases local heat transfer on the endwall region up to 180% more than that in regions where the least influence of the horseshoe vortex is present. The arch-shaped vortex behind the vertices creates regions of flow recirculation and reattachment, leading to relatively high heat transfer. The location of flow separation along the struts varies with the spanwise position due to the presence of vertices (or endwalls). The regions on the strut surface before flow separation contribute approximately 40% of the total heat transfer in the LFM. The delay of the flow separation leads to an increase in the overall heat transfer. Comparisons with foams and other heat dissipation media such as packed beds, louvered fins and microtruss materials suggest that the LFMs compete favourably with the best available heat dissipation media.
机译：具有开放的周期性微结构的超轻晶格框架材料（LFM）是有吸引力的多功能系统，可以执行结构，热，致动，蓄电和其他功能[AG。埃文斯（J.W.） Hutch-inson，M.F. Ashby，多孔金属系统的多功能性，编。母校科学43（1999）171-221]。本文介绍了局部流体流动行为及其对这种具有四面体晶胞材料的局部和整体压力以及传热特性的贡献的实验和数值研究。孔隙率为0.938的LFM的单层夹在不渗透的端壁之间，该端壁接收均匀的热通量，并且热传递经过强制空气对流。在计算流体力学（CFD）模拟的支持下，用粒子图像速度（PIV）和热致变色液晶（TLC）进行的实验测量揭示了LFM中两个主要的局部流动特征。在LFM与端壁相遇的顶点附近有明显的涡旋结构，并观察到LFM支杆表面的流动分离。围绕顶点形成的漩涡结构包括马蹄形漩涡和弓形漩涡。与在马蹄涡流影响最小的区域相比，马蹄涡流在端壁区域的局部传热增加了多达180％。顶点后面的弧形漩涡形成了流动再循环和重新附着的区域，从而导致相对较高的热传递。由于存在顶点（或端壁），沿支柱的流分离位置随翼展方向位置而变化。流动分离之前，支杆表面上的区域约占LFM总传热的40％。流动分离的延迟导致整体热传递的增加。与泡沫和其他散热介质（如填充床，百叶窗式散热片和微桁架材料）的比较表明，LFM与最佳的散热介质竞争良好。

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