脉动流下棒束通道内流场与湍流特性的PIV实验研究

事故条件下路基核反应堆以及受到海洋条件附加惯性力影响的浮动核反应堆一回路冷却剂会处于非稳定流动状态，进而改变冷却剂的流动和传热特性，影响反应堆的安全运行。本文应用锁相粒子图像测速（PIV）以及折射率匹配技术分别对脉动流条件下有无定位格架棒束通道内瞬时速度进行了测量。实验结果表明：对于不带定位格架的棒束通道，加速使得靠近通道壁面附近流体速度变大，而靠近中心区域流体速度变小。此外湍流强度分量随流体加速而逐渐变小，随流体减速而逐渐增加。对于流向压力梯度驱动的周期性脉动流，横向脉动速度均方根分量u′滞后于流向脉动速度均方根分量v′，且二者都滞后于流速的变化；对于带定位格架的棒束通道，带有搅浑翼的定位格架强烈的交混作用极大地减小了流体加速度对棒束通道内速度分布和湍流强度带来的影响。实验结果有助于更加清晰地揭示脉动流在棒束通道中的作用机理。

Experimental Study of Flow Field and Turbulence in Rod Bundle Channel under Pulsating Flow Using PIV

The flow rate of the primary coolant in a nuclear reactor will fluctuate during accident conditions or in floating reactors that are influenced by inertial forces in the ocean. These fluctuations may have a substantial impact on the heat transfer by the primary coolant of the reactor. In this study, combined with phase-locked PIV technology and matching index refractive (MIR) technology, the instantaneous velocity in the rod bundle channel with and without spacer grid was measured under the pulsating flow. In addition, the phase averaged velocity and RMS component distribution of different phases were analyzed. The experimental results demonstrate that for the bare rod bundle the acceleration increases the fluid velocity near the channel wall. And RMS decreases as the fluid accelerates and increases as the flow rate decelerates. For pulsation flow driven by axial pressure gradient, the u′ lags behind the v′, and both of them lag behind the change of flow rate. The strong mixing effect on the spacer grid with mixing vane greatly reduces the influence of fluid acceleration on the velocity distribution and turbulence intensity in the rod bundle channel. The experimental results are helpful to understand the mechanism of pulsating flow in the rod bundle channel more clearly.