隔板对流系统中影响流动和温度特性的关键几何参数

Influence of geometric parameters on flow and temperature characteristics in partitioned thermal convection

有效提高热对流系统的传热效率是湍流热对流研究的重要目标之一.在对流装置中加入留有狭缝的竖直隔板可以产生传热效率增强现象,并且增强显著.隔板的加入增加了热对流系统的几何参数.本文采用直接数值模拟(DNS)对隔板对流装置的流动和温度特性进行计算研究,讨论隔板几何参数对流动特性的影响.研究结果表明,隔板局部区域几何尺寸相同则流动特性基本相同,装置的宏观宽高比对流动特性影响不大.对Ra=10~8,P_r=5.3的情况,通过大量不同几何参数系列计算数据分析发现,通道宽度b与狭缝高度d在满足b≥4d时,b对流动特性影响很小,狭缝高度d是控制隔板对流系统流动和温度特性的关键几何参数.狭缝水平流动为二维泊肃叶流动,与狭缝中的温度分布解耦.改变狭缝高度d对狭缝中流动速度的变化影响不大,但影响系统的流动流量以及整体温度分布特性,继而影响整体传热特性.

An unprecedented heat-transport enhancement of the Rayleigh-Bénard convection can be leaded by inserting vertical partitions with thin gaps left open between the partition walls and cooling/heating plates. The more geometric parameters appeared in the partitioned thermal convection. The two-dimensional direct numerical simulations（DNS） were performed for partitioned thermal convection with the various aspect ratio Γ, height of gap d and width of channel b, and the influence of geometric parameters on the flow characteristics is discussed. The flow characteristics are mainly reflected by the average velocity of the gaps and the average velocity of the channels, and the temperature distribution is mainly reflected by TD number that characterizing the magnitude of temperature in the channels. The results show that flow characteristics and temperature distribution of different systems are basically the same when the local height of gap d and width of channel b are the same, and the aspect ratio of the whole system has little effect. By analyzing a great deal of results of numerical simulation, we can estimate that d is the critical geometric parameter that controls the flow and temperature characteristics in the case of b≥4 d at Ra=10-8 and P_r=5.3 for the different height of gap d and width of channel b. In addition, the flow in the gaps is two-dimensional Poiseuille flow, and it decouples from the temperature distribution but has function as a transporter of the horizontal heat flow. The height of gap d has little influence on the velocity in the gaps, but affects the flow and temperature characteristics of the whole system.