轴流桨搅拌槽三维流场数值模拟

利用k -ε湍流模型预测了搅拌槽在不同操作条件下宏观速度场 ,模型成功预测了搅拌槽内速度分布 ,计算结果与实验结果吻合较好 .模型预测结果表明 ,搅拌槽内宏观流动场受搅拌桨槽径比影响较大 .对单层搅拌桨 -槽体系 ,挡板前后宏观流动场差别很大 ,在挡板以前区域 ,轴向流动较强 ,在整个r -z断面上形成一个整体循环 ;而在挡板后面区域 ,流体在桨叶安装位置高度附近转向轴心流动 ,槽体上半部区域形成二次循环区域 ,且二次循环区域内流体以向下流动为主 .

NUMERICAL SIMULATION OF TURBULENT FLOW IN STIRRED TANK AGITATED BY AXIAL IMPELLER

In this paper a standard k-ε model is used to predict the turbulent flow generated by an axial impeller in a cylindrical baffled vessel. The model predictions successfully reproduce the three dimensional characteristics of flow, and are in good agreement with those obtained by PDA measurement.The simulation results show that the ratio of impeller diameter to tank diameter ( D/T )has a great effect on the flow pattern in a stirred tank.For the small diameter impeller,such as D =0 35 T ,the primary circulation loop is smaller than the whole vessel size,a weak secondary circulation loop is formed in the upper region of the tank.With increasing impeller diameter,axial flow is enforced and the primary circulation loop is extended to the tank top and the secondary circulation in the upper region of tank disappears.The simulation results also demonstrate that the flow in front of baffles is different from the flow behind baffles for the impeller D/T =0 55.In front of baffles, axial flow dominates and only one circulation loop is formed.The flow pattern is approximately the same.Behind baffles,axial flow becomes weaker,and the fluid turns inward just above the impeller level.A small second recirculation loop is formed in the upper part of the vessel,and is directed downwards rather than upwards.