中文摘要：

采用粒子图像测速技术（PIV）对三层组合桨（HEDT＋2WHU）搅拌槽（槽径0.476m）内的流动特性进行了研究,在搅拌转速、顶桨浸没深度和顶层桨高度不变的情况下,得到了中层桨位置的变化对搅拌槽内的流型、相位解析速度场和湍流动能的影响规律。结果表明,中层桨位置的改变对搅拌槽上部区域流体的流动特性影响显著,而对搅拌槽下部区域流体的流动特性产生影响较小;随中层桨位置降低,槽上部液面处反向回流区逐步缩小直至消失,中、顶层桨合并轴向流断裂,底桨上涡环作用范围不断压缩;对于相位解析速度场,较之中层桨尾涡几乎没有变化,顶桨尾涡的发展由极其微弱逐渐清晰,底桨尾涡则提前了10°相位出现;对于湍流动能分布,中、上层桨逐渐趋向于类似两层桨单独作用,底、中层桨间整体湍流动能增大。

英文摘要：

The flow fields in a triple-impeller stirred tank with diameter of 0.476 m have been measured by using particle image velocimetry （PIV）. A deep hollow blade （semi-ellipse） disk turbine （HEDT） was used as the lower impeller and two upward-pumping 4-wide-blade hydrofoil impellers （WHU） were used as middle and upper impellers. The effect of the location of middle impeller on the flow pattern,trailing vortex and turbulent kinetic energy distributions was investigated while keeping the rotational speed and the submergence of the upper impeller constant. The results show that the position of the middle impeller has more influence on the flow characteristics of the upper region than on those of the lower region in the stirred tank. As the middle impeller was moved down： （i） the reverse flow near the liquid surface gradually disappeared,and the axial flow between the middle and upper impellers finally became separated from each other,while the upper circulation region of the lower impeller became smaller; （ii） In phase-resolved plots of velocity,there was no distinct change in the trailing vortex generated by the middle impeller,but the trailing vortex of the upper impeller became more and more clear,and that of the lower impeller appeared earlier at an angle of 10°; （iii） In the distribution of the turbulent kinetic energy,the interactions between the upper and middle impellers decreased,but the values for the middle and lower impeller increased. The results are of importance for the design and optimization of industrial multi-impeller stirred tanks.