四斜叶桨搅拌槽内的流动特性

采用粒子图像测速技术(PIV),在直径为0.5m的平底搅拌槽内,对单层、双层平行布置和双层交错布置等三种条件下直径为0.2m的四斜叶桨(PBT)的流场进行测量,并利用标准k-ε模型对相应的流动特性进行计算流体动力学数值模拟。实验结果表明：三种流型下PBT叶片后方均存在单一的尾涡结构，其在径向方向的移动距离较轴向方向小。高湍流动能区与尾涡一起运动，实现能量自桨叶向搅拌槽内主体流动区的传递。模拟结果表明：标准k-ε模型对单层PBT搅拌槽内流场的预测与PIV实验吻合较好，而双层PBT的模拟结果与实验偏差较大，两层桨间径向速度被低估而轴向速度被高估是标准k-ε模型产生误差的主要原因，但是标准k-ε模型计算得到的功率准数与实验基本一致。

Flow characteristics in a stirred vessel with a four-pitched-blade turbine

The flow characteristics in a stirred vessel of diameter 05?m agitated by one four pitched blade turbine (PBT) of diameter 02?m and two PBTs with parallel or cross arrangement have been experimentally investiga ted by particle image velocimetry (PIV) and numerically simulated by computational fluid dynamics (CFD) using the standard k-εmodel. The PIV results show that a single trailing vortex only exists behind the impeller of the PBT for all three conditions. The radial distance of the trailing vortex is less than that of the axial. The region with high turbulent kinetic energy moves with the trailing vortex, such that the energy is transferred from the impeller to the bulk fluid in the vessel. The CFD results show that the flow field estimated by the standard k-εmodel in a single PBT stirred vessel is in agreement with PIV data, but the flow field predicted in the vessel stirred by two PBTs is not consistent with the PIV results. The radial velocities are underestimated between the two PBTs and the axial velocities are overestimated, these being the main reasons why the prediction of the standard k-ε model is inaccurate. The power number predicted by the standard k-ε model is in agreement with the experimental data.