Particle image velocimetry (PIV) experiments on a laminar stirred tank flow with floating particles at just drawdown conditions were performed. Careful refractive index matching of the two phases allowed to resolve the flow around the particles. The maximum solids volume fraction was 4%. The impeller was a pitched blade turbine with upward and downward pumping modes and with different off-bottom clearances, and the impeller-based Reynolds number ranged from about 50 to 120. Computational fluid dynamics (CFD) coupled to a discrete phase model (DPM) and discrete element method (DEM) was used to predict the flow field, with an emphasis on the tangential velocity component. The liquid velocity profiles predicted by the CFD simulations are in good agreement with the PIV experimental data. The drawdown process and local particle accumulation simulated by the DPM-DEM model agrees with the experimental phenomena as well. Tangential velocity and particles collisions around the shaft trigger the onset of the drawdown of the floating particles.

在刚刚降落的条件下，在具有悬浮颗粒的层流搅拌槽流中进行了颗粒图像测速（PIV）实验。两相的仔细的折射率匹配可以解决颗粒周围的流动。最大固体体积分数为4％。叶轮是具有向上和向下泵送模式且具有不同的底部间隙的变桨叶涡轮，基于叶轮的雷诺数范围介于50到120之间。计算流体力学（CFD）与离散相模型（DPM）耦合用离散元法（DEM）预测流场，重点是切向速度分量。CFD模拟预测的液体速度曲线与PIV实验数据非常吻合。DPM-DEM模型模拟的水降过程和局部颗粒堆积也与实验现象相吻合。切线速度和轴周围的粒子碰撞会触发浮动粒子降落的开始。