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On the role of roughness valleys in turbulent Rayleigh–Bénard convection
Journal of Fluid Mechanics ( IF 3.7 ) Pub Date : 2021-07-21 , DOI: 10.1017/jfm.2021.583
Mebarek Belkadi 1 , Anne Sergent 2 , Yann Fraigneau 3 , Bérengère Podvin 3
Affiliation  

Three-dimensional direct numerical simulations are used to characterize turbulent buoyant convection in a box-shaped Rayleigh–Bénard cavity with a rough bottom plate made of a series of square based blocks separated by valleys. The cavity is filled with water. The Rayleigh number varies over five decades up to $10^{10}$ . As mentioned in the literature, three successive heat transfer regimes are identified: from inactive roughness (I) to a regime (III) where the heat transfer increase is larger than that expected from only surface increase due to roughness. The heat transfers of the transitional regime II are particularly intense. After validation against experimental and numerical data from the literature, we highlight the role of the fluid retained within valleys (the inner fluid). It is shown that only the heat transfer across the fluid interface between the cavity bulk and the inner fluid is responsible for changes in the overall heat transfer at the rough plate, with an exponent of the heat transfer scaling law close to $1/2$ in regime II. The valley flow typifies the limits of this regime: the blocks protrude from the thermal boundary layer while remaining within the kinetic boundary layer. As compared with regimes I and III, regime II is characterized by larger temperature fluctuations, especially near the rough plate, and a larger friction coefficient. A fluctuating rough fluid layer overlaying both blocks and valleys appears in regime III, in addition to the classic boundary layers formed along the plate geometry.

中文翻译:

粗糙谷在湍流瑞利-贝纳德对流中的作用

三维直接数值模拟用于表征箱形 Rayleigh-Bénard 腔中的湍流浮力对流,该腔具有由一系列由山谷隔开的方形块组成的粗糙底板。空腔充满水。瑞利数在五个十年内变化直至 $10^{10}$ . 正如文献中提到的,确定了三个连续的传热状态:从非活动粗糙度 (I) 到状态 (III),其中传热增加大于由于粗糙度仅表面增加所预期的传热增加。过渡区 II 的热传递特别强烈。在对文献中的实验和数值数据进行验证后,我们强调了保留在山谷中的流体(内部流体)的作用。结果表明,只有通过腔体和内部流体之间的流体界面的传热是造成粗糙板处整体传热变化的原因,传热比例定律的指数接近 $1/2$ 在制度 II。谷流代表了这种状态的限制:块从热边界层突出,同时保留在动力学边界层内。与状态 I 和 III 相比,状态 II 的特点是温度波动较大,尤其是在粗糙板附近,以及较大的摩擦系数。除了沿板块几何形状形成的经典边界层外,在区域 III 中还出现了覆盖块体和山谷的波动粗糙流体层。
更新日期:2021-07-21
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