搅拌槽流场特性的大涡模拟研究

摘要

The gas-liquid two-phase flow equations were solved by the large eddy model to numerically simulate the flow field characteristics in a stirred tank equipped with six-bladed Rushton turbine .The free fluid surface was simulated by the VOF method .The equations were solved by the Simplec method . The complex double vortex flow structures in the stirred tank ,the trailing vortex development near the impellers’ tips and the flow velocity distribution were obtained .The comparisons of the large eddy simu-lation and RNGκ-εmodel calculated results show that the large eddy model is able to simulate the deve-lopment process of instantaneous vortex flow field ,and that the presence of the baffles destroys the flow field in the round stirred tank to improve the mixing efficiency near the blades ,and that the turbulence near the blades shows significant anisotropy ,and mean velocity shows obvious fluctuations .Thus the reliability of large eddy simulation to explore turbulence phenomena and flow structures in a stirred tank is proved .%采用大涡模型结合气液两相流时均方程，对六直叶圆盘涡轮搅拌槽内的流场特性进行了数值模拟。自由水面的捕捉用VOF（Volume of Fluid）法，用Simplec方法求解控制方程。通过模拟得到了搅拌槽内复杂的双涡旋流场结构、转轮叶端尾涡的发展变化情况以及轴向流速的分布规律。通过对比大涡模拟与RNGκ-ε的计算结果，得知大涡模型能模拟出流场内瞬时旋涡的发展变化过程，反映出挡板的存在破坏了圆形搅拌槽的流通模式，提高了叶片附近的混合效率；桨叶区域湍流呈现明显的各向异性，时均流速存在明显的波动性。从而证明了用大涡模拟探讨搅拌槽内湍流现象及流场结构的可靠性。