Abstract In this paper, natural convection due to two heated cylinders inside a rhombus enclosure with lower temperature with respect to the cylinders is investigated. Here, Cu-water is the working nanofluid. The numerical algorithm is based on an iterative direct immersed boundary method (IBM). The focus of this article is on stability, instability, symmetry as well as asymmetry of nanofluid flow pattern in three different Rayleigh (Ra) numbers, i.e. 104, 105 and 106. The effects of important parameters such as cylinder diameters, nanoparticle volume fraction and distance between two cylinders are analyzed. The results of this study disclose that at both Ra = 104 and 105, nanofluid flow is symmetric and stable, while at Ra = 106 four different flow regimes including steady-symmetric, steady-asymmetric, unsteady-asymmetric with periodic oscillations and unsteady-asymmetric with irregular oscillations are observed. In addition to geometrical parameters, nanoparticle volume fraction has a considerable impact on the flow regime. Furthermore, the possibility of unsteady-asymmetric flow increases considerably by increasing the distance between two cylinders.

中文翻译：

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充满Cu-水纳米流体的菱形外壳内两个加热圆柱体非定常自然对流的数值分析

摘要 本文研究了菱形外壳内两个加热圆柱体的自然对流，该圆柱体的温度低于圆柱体。在这里，铜水是工作的纳米流体。数值算法基于迭代直接浸入边界法 (IBM)。本文的重点是三种不同瑞利 (Ra) 数（即 104、105 和 106）下纳米流体流动模式的稳定性、不稳定性、对称性和不对称性。 圆柱直径、纳米粒子体积分数和纳米粒子体积分数等重要参数的影响分析两个气缸之间的距离。这项研究的结果表明，在 Ra = 104 和 105 时，纳米流体流动是对称且稳定的，而在 Ra = 106 时，四种不同的流态，包括稳态对称、稳态非对称、观察到具有周期性振荡的不稳定不对称和具有不规则振荡的不稳定不对称。除了几何参数外，纳米颗粒的体积分数对流动状态也有相当大的影响。此外，通过增加两个气缸之间的距离，不稳定非对称流动的可能性大大增加。