Semi-resolved function research on gas-solid two-phase coupling of high-temperature pebble beds
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摘要: 为精确模拟高温球床堆内数万计燃料颗粒的气固两相耦合传热过程，并克服传统CFD-DEM方法因网格粗大导致的精度不足及全解析方法计算成本过高的问题，提出了一种适用于精细流体网格的半解析函数模型。该模型通过引入高斯核函数，对颗粒周围物理属性进行平滑与加权平均，从而实现在亚网格尺度下对颗粒所受流体作用力的精确计算。沃罗单元体分析表明，无量纲扩散时间的最优取值为0.6。超过此值会导致核函数影响域过度扩展，致使空间分布过度平滑而难以捕捉球床局部特征。在HTR-10球床堆的耦合传热仿真中，采用该模型计算得到的温度场分布与经验模型高度吻合。结果表明，本模型能够准确捕获颗粒间的相间作用力，为高温气冷堆热工流体仿真提供了一个兼具精度与效率的解决方案。Abstract:
Background Accurately simulating the gas-solid coupled heat transfer in high-temperature pebble-bed reactors is challenging due to the complex configuration involving tens of thousands of fuel pebbles. Conventional unresolved CFD-DEM methods are limited in accuracy by their requirement for coarse fluid grids, whereas fully resolved simulations are often prohibitively expensive.Purpose This study aims to develop a semi-resolved function model suitable for fine fluid grids to enable accurate and efficient coupled thermal-fluid simulation in pebble beds.Method A Gaussian kernel-based semi-resolved function was introduced to smooth physical properties around particles and compute interphase forces via weighted averaging. The key parameter, the dimensionless diffusion time, was optimized through comparison with Voronoi cell analysis. The model was implemented in an open-source CFD-DEM framework and validated against both a single-particle settling case and a fluidized bed experiment.Results Voronoi cell analysis determined the optimal diffusion time to be 0.6. Exceeding this value over-smoothens the spatial distribution and obscures local bed features. The single particle settling case demonstrated excellent agreement with experimental terminal velocities under various viscosities. The fluidized bed simulation successfully captured porosity distribution and the relationship between fluid velocity and particle density, consistent with experimental data. Application to HTR-10 pebble bed thermal-hydraulics showed temperature distributions aligning well with the SA-VSOP benchmark.Conclusions The proposed semi-resolved function model effectively overcomes the grid size limitation of traditional CFD-DEM, accurately capturing interphase forces in sub-particle-scale grids. It provides a high-precision and computationally viable scheme for detailed thermal-fluid analysis in advanced pebble-bed reactors.-
Key words:
- high-temperature pebble beds /
- semi-resolved function /
- CFD-DEM /
- particle /
- Gaussian kernel function.
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