论文标题

朝着卵石床系统的近壁区域开发改进的摩擦相关性

Toward Development of an Improved Friction Correlation for the Near-Wall Region of Pebble Bed Systems

论文作者

Reger, David, Merzari, Elia, Balestra, Paolo, Schunert, Sebastian, Hassan, Yassin, Yuan, Haomin

论文摘要

利用卵石燃料的核反应堆的发展已大大提高了改善模拟这些反应器中填充床的能力的需求。在卵石床中发现的复杂流场使计算流体动力学(CFD)模拟耗时且昂贵。但是,中级多孔媒体模型能够以更高的计算有效方式近似这些流场。这些模型需要使用闭合来捕获复杂流现象的影响,而无需明确对其进行建模。该研究采用了从卵石床的高保真CFD模拟获得的数据,以改善床近壁区域中多孔介质模型中使用的阻力封闭。具体而言,启用GPU的光谱元素CFD代码NEKR用于模拟以多个雷诺数数字的1,568个卵石的床。该病例分为五个同心子域,以提取每个子域中平均孔隙率,速度和壁剪切的径向轮廓。在爱达荷州国家实验室的Pronghorn多孔媒体代码中创建了与高保真模型一致的模型,并选择了KTA相关性作为比较的阻力封闭。发现KTA相关性高估了近壁区域的速度。对两个代码之间的阻力系数的研究表明,KTA相关性低估了最外层区域的形状,同时高估了它在内部四个区域。这项工作中的这项分析揭示了KTA相关的近壁区域中的潜在不准确性,并为使用高保真模拟来预测先验的更准确的阻力系数,而不是使用手动匹配速度匹配的方法来预测更准确的阻力系数。此过程将允许开发改进的阻力闭合,以用于多孔媒体模型。

The development of nuclear reactors that utilize pebble fuel has drastically increased the demand for improving the capabilities to simulate the packed beds found in these reactors. The complex flow fields found in a pebble bed make computational fluid dynamics (CFD) simulations time consuming and costly. Intermediate fidelity porous media models, however, are capable of approximating these flow fields in a much more computationally efficient manner. These models require the use of closures to capture the effects of complex flow phenomena without modeling them explicitly. This research employs data obtained from high-fidelity CFD simulations of a pebble bed to improve the drag closures used in porous media models in the near-wall region of the bed. Specifically, NekRS, a GPU-enabled spectral element CFD code, was used to simulate a bed of 1,568 pebbles at multiple Reynolds numbers. The case was divided into five concentric subdomains to extract radial profiles of the average porosity, velocity, and wall shear in each subdomain. A model consistent with the high-fidelity model was created in Idaho National Laboratory's Pronghorn porous media code and the KTA correlation was chosen as the drag closure of comparison. It was found that the KTA correlation overestimates the velocity in the near-wall region. An investigation of the drag coefficients between the two codes revealed that the KTA correlation underestimated the form factor in the outermost region while overestimating it in the inner four regions. This analysis in this work has revealed the underlying inaccuracy in the near-wall region of the KTA correlation and has set up the process for using high-fidelity simulation to predict more accurate drag coefficients a priori, rather than with a manual velocity-matching approach. This process will allow for the development of an improved drag closure for use in porous media models.

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