Abstract: Rational design of impellers in stirred vessels for strengthening the fluid flow and mixing is an important way to achieve efficient and energy-saving mixing. Rigid-flexible coupling impeller can be designed by combination of flexible body and rigid body, possessing multiple-body motion behavior. In this study, CFD simulation and PIV flow visualization were comparatively employed to analyze the difference between rigid impeller and rigid-flexible coupling impeller for fluid flow structure and mixing performance. Results showed that, compared with rigid impeller system, velocity decaying rate was reduced by 25% with rigid-flexible coupling impeller system, because it had the ability to intensify the input energy transportation by flexible part and distribute the input energy in flow field structure effectively. The streamline of the fluid stirred by rigid PBT-6 impeller and rigid RDT-6 impeller had obviously periodic attractor with fractal dimension 1.9046 and 1.9138 respectively. Rigid-flexible coupling impellers could intensify chaotic mixing of fluid and regulate the fractal dimension of flow field structure. The streamline of fluid stirred by flexible RDT-6 impeller had quasi-periodic attractors with fractal dimension of 1.9337, while the fractal dimension of chaotic attractor was 1.9545 with flexible PBT-6 impeller. It suggests that the flexible impeller could regulate multi-scale structure of the flow field by changing streamline attractor to intensify the chaotic mixing and achieve energy efficient operation.

Key words: mixing, chaos, stirred vessel, rigid-flexible coupling impeller, fractal dimension, CFD simulation, attractor

摘要： 合理设计搅拌反应器的桨叶，强化流体流动与混合行为，是实现流体高效、节能混合的重要手段。柔性体与刚性体组合，可设计出具有多体运动行为的刚-柔组合搅拌桨。结合PIV流场观测和CFD模拟，对比分析了刚性桨和刚-柔组合桨对流场结构及流体混沌混合行为的影响。结果表明，与刚性搅拌桨相比，刚-柔组合桨的柔性端强化能量传递，流体流速衰减速率降低25%，有利于搅拌桨输入能量在流场结构内的有效分配。传统刚性六凹叶和六直叶涡轮桨搅拌反应器内流体形成的流线结构具有明显的周期吸引子，其时均流场的分形维数分别为1.9046和1.9138。刚-柔组合六直叶涡轮桨搅拌反应器内流体流线呈明显的准周期性吸引子性质，其流场分形维数为1.9337，而刚-柔组合六凹叶涡轮桨搅拌反应器内流体流线具有典型的混沌吸引子性质，其流场分形维数为1.9545。刚-柔组合搅拌桨可改变流体流线的吸引子来调控流场的多尺度结构，强化流体混沌混合，实现高效节能操作。

关键词: 混合, 混沌, 搅拌槽, 刚-柔组合搅拌桨, 分形维数, CFD模拟, 吸引子