姚强 郭雪岩 杨帆

摘要：采用大涡模拟（LES ）方法研究了低雷诺数（Re =1015）下热浮力对球床面心立方（FCC ）单元内的局部流动和传热的影响。为了精确求解燃料球接触面附近的流场，球间接触点表达为面接触，采用结构化网格处理。研究结果表明：热浮力的存在会抑制球床各层平均速度的波动;靠近燃料球表面处的相对时均速度和相对时均温度受热浮力影响变化较大;在中心流场区域，热浮力的存在会减小流场中速度分布的不对称性，使速度最大降低约10%，时均温度至少升高约20%;球表面上尤其在顶部及接触面附近受热浮力影响明显，努塞尔数 Nu最大降低约6%。

关键词：热浮力;球床反应堆;大涡模拟;面心立方;面接触

中图分类号： TK11+2    文献标志码： A

Effect of thermal buoyancy on the convective heat transfer on the surface of fuel pebbles in a pebble bed reactor

YAO Qiang，GUO Xueyan，YANG Fan

（School of Energy and Power Engineering， University of Shanghai for Science and Technology， Shanghai 200093， China）

Abstract：In this paper， large eddy simulation （LES） method was adopted to study the influence of thermal buoyancy at low Reynolds number （Re =1015） on local flow and heat transfer in a face- centered cubic （FCC） of a pebble bed. The plane-plane contact among the pebbles and structured grid were adopted to accurately solve the flow field near the interface of fuel pebbles. It is found that the existence of thermal buoyancy could restrain the fluctuation of averaged velocity at each layer. The influence of thermal buoyancy on relative time-averaged velocity and relative time-

averaged temperature near the surface of fuel pebbles was great. In the center of flow field， the existence of thermal buoyancy could reduce the asymmetry of velocity distribution. The velocity decreased by 10% at most and the time-averaged temperature increased by 20% at least. On the spherical  surface，  especially  at  the  top  and  near  the  interface，  obvious  influence  of thermalbuoyancy was observed. And the Nusselt number Nu number decreased by 6% at most.

Keywords：thermal buoyancy; pebble bed reactor; large eddy simulation; face-centered cubic; plane-plane contact

球床式高溫气冷堆是第四代核反应堆类型之一。在球床反应堆中，氦气作为冷却剂，核燃料嵌在石墨慢化剂中并可以维持很高的温度。这种结构可以保证燃料不会熔化，使反应堆具有良好的固有安全性[1–4]。该堆型具有结构简单、燃料元件适合批量生产以及燃料球装卸方便等特点。

目前，很多学者对球床中的流动和换热特点进行了研究。孟现柯等[5]用由碳钢球堆积成球床，以蒸馏水为工质，采用电磁感应加热方式研究了球床通道内部的换热特性; Jia 等[6]用黑色玻璃球堆积成球床，以水为工质研究了不同床型对内部工质流动情况的影响。考虑到实验成本和复杂性，多数实验结果很难为球床反应堆提供可靠的参考依据。……