Abstract

The backward-facing step flow is seen in applications in our daily life: the high attack angle at airfoil, the separation flow behind a vehicle, the flow in a gas turbine, and the flow around a boat or building. In view of increasing the heat and mass transfer, control of the backward step region is important. In this study, the heat transfer and flow structures with turbulence of step corner structures with a chamfer h/2 and h long and without chamfer were numerically examined with GO (Graphene Oxide)-distilled water (DW) solutions of volumetric concentrations of 0.01% and 0.02% in comparison with distilled water in a vertically positioned backward-facing step flow geometry. The results of the study were obtained via solving conservation equations of a three dimensional and steady k-\(\varepsilon \) turbulence model with the Boussinesq approach using the ANSYS-FLUENT-18.0 computer program. The nanofluids used in the study were considered as single-phase ones, and experimentally obtained thermophysical values were used. The study was carried out for Reynolds numbers of 5000 and 7500. The findings of present study were compared with the numerical results of a work found in the literature. The outcomes were found to be compatible and acceptable. The results were presented as variations of the Nu number, fluid temperature, turbulence kinetic energy, and pressure. In addition, the contours of the temperature and velocity and streamline distributions were visualized for a backward-facing step flow geometry. For Re = 7500 and the step geometry with an h-long chamfer, the average Nu number values for the 0.01% and 0.02% GO-DW nanofluids were determined to be higher by 11.7% and 14.33%, respectively, than those for distilled water.

中文翻译：

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考虑传热和流动结构的氧化石墨烯-蒸馏水纳米流体研究后向阶梯流

摘要

在我们日常生活中的应用中可以看到反向阶梯流：机翼的高迎角、车辆后面的分离流、燃气轮机中的流以及船或建筑物周围的流。考虑到增加传热和传质，后退区的控制很重要。在这项研究中，使用体积浓度为 0.01% 的 GO（氧化石墨烯）-蒸馏水（DW）溶液对具有倒角 h/2 和 h 长且无倒角的阶梯角结构的湍流传热和流动结构进行了数值研究与垂直定位的后向阶梯流几何结构中的蒸馏水相比，0.02%。研究结果是通过求解三维稳态 k- \(\varepsilon \) 使用 ANSYS-FLUENT-18.0 计算机程序通过 Boussinesq 方法建立湍流模型。研究中使用的纳米流体被视为单相流体，并使用实验获得的热物理值。该研究是针对 5000 和 7500 的雷诺数进行的。将本研究的结果与文献中的一项工作的数值结果进行了比较。结果被发现是兼容和可接受的。结果表示为 Nu 数、流体温度、湍流动能和压力的变化。此外，温度、速度和流线分布的轮廓对于后向阶梯流几何形状进行了可视化。对于 Re = 7500 和具有 h 长倒角的阶梯几何形状，0.01% 和 0 的平均 Nu 数值。