涡轮桨搅拌槽内流场的数字PIV测量

Digital PIV measurements of flow fields in a tank stirred by a Ruston turbine

为研究机械搅拌槽内的流场特性,用数字粒子图像测速仪对桨叶直径与搅拌槽直径比约为0.5的涡轮桨搅拌槽内流场进行了测量。实验发现测量值随时间的随机脉动非常剧烈,为准确获取时均速度场,确立了多采样点平均的实验方法并进而找出了最佳采样点数。在获取的时均速度场的基础上计算了流量准数、涡量和湍动能的分布,考察了转速和测量面位置对流场的影响。结果表明:湍动能分布不均匀,在叶轮区较高,而在主体区较小;由于自由液面的作用,湍动能在高度方向上呈非对称性分布,并且这种非对称性随转速的变化而变化。

The velocity fields in mechanically agitated vessels were investigated using digital particle image velocimetry (DPIV) to measure the flow field within a baffled tank stirred by a Ruston turbine impeller with a large impeller-tank diameter ratio. The measurement errors due to the random fluctuations of the near-instantaneous velocity field obtained from the DPIV were minimized by using time-averaged velocity measurements with an optimum sample number. The time-averaged velocity fields were used to calculate the pumping number, vorticity, and dimension one turbulent kinetic energy. The effects of rotational speed and measuring plane position on the velocity field were also investigated. The results show that the kinetic energy in the impeller region is higher than in the bulk flow. The kinetic energy is distributed asymmetrically in the axial direction, and the asymmetry variation is a function of the rotational speed due to the influence of the free surface.