Natural convection in cylindrical containers with isothermal ring-shaped obstacles
Natural convection in cylindrical containers with isothermal ring-shaped obstacles
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DOI：
10.1017/jfm.2019.797
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发表时间：
2020-01-10
影响因子：
3.7
通讯作者：
Shishkina, Olga
中科院分区：
文献类型：
--
作者：
Emran, Mohammad S.;Shishkina, Olga
采用三维直接数值模拟的方法，研究了加热和冷却平板的规则粗糙度对长径比为1的圆柱Rayleigh-Benard对流槽内平均热传递的影响。粗糙度是由一组等温障碍物引入的，这些障碍物附着在平板上，并具有相同宽度的同心环的形式。所考虑的Prandtl数Pr=1，Rayleigh数Ra在10(6)到10(8)之间变化，每个平板上的环数为1、2、4、8或10，环的高度在圆柱体高度的1.5%到49%之间变化，环之间的间隙在单元直径的1.5%到18.8%之间变化。总共分析了135个不同的案例。直接数值模拟表明，与光滑平板的经典Rayleigh-Benard对流相比，在小Ra和宽粗糙度环的情况下，平均热传递(Nusselt数Nu)是可能的，但在大多数情况下，加热和冷却障碍物的存在通常会导致Nu的增加。当环很高，并且环之间的间隙足够宽时，有效平均热流密度可能比光滑情况下的大几倍。对于固定的障碍物几何形状，Nu对Ra标度中的标度指数首先随着Ra的增加而增加，直到大约0.5，但在无障碍的情况下，标度指数向指数平滑地减小。
By means of three-dimensional direct numerical simulations, we investigate the influence of the regular roughness of heated and cooled plates on the mean heat transport in a cylindrical Rayleigh-Benard convection cell of aspect ratio one. The roughness is introduced by a set of isothermal obstacles, which are attached to the plates and have a form of concentric rings of the same width. The considered Prandtl number Pr equals 1, the Rayleigh number Ra varies from 10(6) to 10(8), the number of rings on each plate is 1, 2, 4, 8 or 10, the height of the rings is varied from 1.5% to 49% of the cylinder height and the gap between the rings is varied from 1.5% to 18.8% of the cell diameter. Totally, 135 different cases are analysed. Direct numerical simulations show that with small Ra and wide roughness rings, a small reduction of the mean heat transport (the Nusselt number Nu) is possible, but, in most cases, the presence of the heated and cooled obstacles generally leads to an increase of Nu, compared to the case of classical Rayleigh-Benard convection with smooth plates. When the rings are very tall and the gaps between them are sufficiently wide, the effective mean heat flux can be several times larger than in the smooth case. For a fixed geometry of the obstacles, the scaling exponent in the Nu versus Ra scaling first increases with growing Ra up to approximately 0.5, but then smoothly decreases back towards the exponent in the no-obstacle case.