Large Eddy Simulation Study on Flow and Heat Transfer in Narrow Channel with a Semi-ellipsoid Blockage
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摘要: 为研究半椭球堵流结构对窄通道内冷却剂流动传热特性的影响，针对高度为窄边宽1/2的半椭球堵流结构开展了大涡模拟，分析了堵流结构下游的时均速度场、湍动能和温度分布，研究了堵流结构附近的流动传热特征。半椭球堵流结构下游流场有显著的三维特性，存在绕流及边界层分离形成的回流区、剪切层、主流区和再发展区等特征区域。结合时均温度场及局部努塞尔数（Nu）的变化规律，研究了堵流结构对窄通道传热的影响机制。分析发现，半椭球底面侧壁面附近回流区及其顶部壁面再发展区内，由于热流体聚集，缺乏主流低温流体冲扫，出现局部Nu极小值和局部高温。总体上看，半椭球堵流结构对窄通道速度场和温度场的展向影响范围为5倍半椭球长半轴范围。Abstract: In order to study the influence of semi-ellipsoid blockage on the flow and heat transfer characteristics of coolant in narrow channels, large eddy simulation was carried out for a semi-ellipsoid blockage with a height of 1/2 of the narrow side width. The time-average velocity field, turbulent kinetic energy and temperature distribution downstream of the blockage are analyzed, and the characteristics of flow and heat transfer near the blockage are studied. The downstream flow field of semi-ellipsoid blockage has obvious three-dimensional characteristics, and there are characteristic regions such as recirculation region brought by the flow around the blockage and the boundary layer separation, shearing layer, main flow region and recovery region. Combined with the time-averaged temperature field and the local Nusselt number (Nu), the influence mechanism of the blockage on the heat transfer in narrow channels is studied. It is found that the local minimum Nu and local high temperature appear in the recirculation region near the side wall of the semi-ellipsoid bottom and the recovery region of the top wall due to the accumulation of hot fluid and the lack of mainstream low temperature fluid. In general, the spanwise influence range of the semi-ellipsoid blockage on the velocity field and temperature field in the narrow channel is 5 times of the semi-diameter range.
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Key words:
- Narrow channel /
- Semi-ellipsoid blockage /
- Flow structure /
- Heat transfer inhomogeneity
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图 2 LES与实验结果对比
W—流向流速，m/s；Wmax—最大流向流速，m/s
Figure 2. Comparison between LES and the Experiment
图 4 中心平面时均流向流速和时均湍动能分布
Figure 4. Time-averaged Streamwise Velocity and Turbulent Kinetic Energy Contour of Central Plane
图 5 不同平面时均流向流速分布
Figure 5. Time-averaged Streamwise Velocity Contour of Different Planes
图 6 不同位置时均湍动能分布
Figure 6. Time-averaged Turbulent Kinetic Energy Contour of Different Locations
图 11 堵流结构下游湍动能分布规律
Figure 11. Turbulent Kinetic Energy Distribution Downstream the Semi-ellipsoid Blockage
图 12 半椭球底面侧壁温和Nu分布
Figure 12. Temperature and Nu Distribution on the Side Wall of Semi-ellipsoid Blockage Bottom
图 13 半椭球底面侧壁温和Nu沿流向的变化
Figure 13. Evolution of Temperature and Nu in the Streamwise Direction on the Side Wall of Semi-ellipsoid Blockage Bottom
图 14 半椭球顶部侧壁温和Nu分布
Figure 14. Temperature and Nu Distribution on the Side Wall of Semi-ellipsoid Blockage Top
图 15 半椭球顶部侧壁温和Nu沿流向的变化
Figure 15. Evolution of Temperature and Nu in the Streamwise Direction on the Side Wall of Semi-ellipsoid Blockage Top
表 1 15.5 MPa，280℃下水的物性参数
Table 1. Physical Properties of Water under 15.5 MPa and 280℃
密度/
(kg·m−3)定压比热容/
(kJ·kg−1·K−1)动力粘度/
(Pa·s)导热系数/
(W·m−1·K−1)764.28 5.73 9.64×10−5 0.59 
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