加/减速流动下棒束通道内速度分布和湍流特性研究

事故工况及海洋条件下反应堆处于非稳态工况，堆芯燃料组件内热工水力行为复杂多变，对反应堆安全提出了更高挑战，因此有必要对非稳态下燃料组件内流动换热特性开展研究。基于粒子图像测速（PIV）技术，结合远心镜头和脉冲控制器，实现对燃料组件内复杂流场的高时空分辨率、长时间的连续测量，获得了流量波动下燃料组件内时空演变的流场结构，分析了棒束通道内速度分布、湍流强度、雷诺应力等瞬时流场信息的空间演变特性。以定常流动下流场分布特性为基准，对比分析了加速度对燃料组件内空间流场分布的贡献特点。实验结果表明：加速流动提高了棒束通道内流层之间的速度梯度，抑制了横向速度和湍流强度；减速流动减弱了棒束通道内流层之间的速度梯度，提高了横向速度和湍流强度。实验结果有助于揭示燃料组件在非稳态条件下的瞬态特性，并为燃料组件的设计和优化奠定基础。

Velocity Distribution and Turbulence Characteristic in Rod Bundle under Accelerating and Decelerating Flows

The thermal-hydraulic behaviors in fuel assemblies of the reactor core are quite complicated when the reactor is under accident conditions and ocean conditions, which raises a higher challenge to the reactor safety. Therefore, it is necessary to study the transient flow and heat transfer characteristics in fuel assemblies. Based on particle image velocimetry (PIV) technique, combining with telecentric lens and a transistor-transistor logic (TTL), a long-term and high-resolution measurement for the complex flow field in fuel assemblies was achieved, the detailed flow field in fuel assemblies was obtained under the flow fluctuation, such as velocity distribution, turbulent intensity and Reynolds stress. The steady-state flow field was used as a reference, and the influence of acceleration for the spatial flow field in the rod bundle was analyzed. The results show that the accelerating flow improves the velocity gradient between flow layers in the rod bundle and weakens the lateral velocity and lateral turbulent intensity. In the contrary, the decelerating flow weakens the velocity gradient between flow layers in rod bundles and improves lateral velocity and lateral turbulent intensity. The experimental results are helpful to reveal the transient characteristics of the fuel assembly under unsteady conditions and provide a foundation for the design and optimization of the fuel assembly.