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The Validity of Approximate Boundary Conditions for Natural Convection With Thermal Radiation in Open Cavities

机译:开腔热辐射自然对流近似边界条件的有效性

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The use of approximate boundary conditions at the opening of the cavities leads to restriction of the computational domain and, hence, the reduction in computational effort. However, the accuracy of the restricted domain approach (RDA) had been evaluated only for the natural convection inside open cavities and that too only for one aspect ratio (AR). The validity of the approach had not been evaluated for inclined, as well as, shallow cavities. This study focuses on the analysis of the accuracy of RDA against extended domain approach (EDA) in open cavities of different ARs, at different inclinations and different Rayleigh numbers (Ra). The results show that the difference between the approaches is only significant in very shallow cavities (AR is defined as the height of the hot wall divided by the depth of the cavity) at low Ra. For Ra higher than 106 and an AR greater than 0.2, the maximum difference between the two approaches is around 5% and hence RDA can be recommended in these ranges, resulting in increased computational efficiency without significant loss in the accuracy. Moreover, the maximum difference in the results for the two methods is for intermediate inclinations. Even there, an increase in the difference is more pronounced at lower Ra. Furthermore, distribution of the exit velocity and temperature at the opening as well as the distribution of the Nusselt number at the hot wall is compared for RDA and EDA to explain the behavior of error at different ARs and inclinations.
机译:在腔开口处使用近似边界条件导致计算领域的限制,从而降低计算工作。然而,已经仅针对开口腔内的自然对流评估了限制域方法(RDA)的准确性,并且仅为一个纵横比(AR)。该方法的有效性尚未评估倾斜,以及浅腔。本研究侧重于分析不同ARS的开放空腔中RDA对扩展域方法(EDA)的准确性,不同倾斜和不同的瑞利数(RA)。结果表明,该方法之间的差异在非常浅的腔中仅在非常浅的空腔中仅为显着(AR被定义为低RA在腔中除以腔深的热壁的高度)。对于高于106的RA和大于0.2的RA,两种方法之间的最大差异约为5%,因此可以在这些范围内推荐RDA,从而提高计算效率而无需显着损失。此外,两种方法的结果的最大差异是用于中间倾斜。即使存在,差异的增加也更明显。此外,对开口的出口速度和温度的分布以及RDA和EDA对热壁进行的喷射数分布,以解释不同AR和倾斜的误差的行为。

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