半圆管曲面涡轮搅拌槽内混合特性的数值模拟

CFD simulation of mixing characteristics in stirred tank by Smith turbine

在商业化软件ANSYSCFX10.0平台上,采用多重参考系法来解决挡板与桨叶之间的相对转动问题,由标准k-ε模型对半圆管曲面涡轮搅拌槽内流动和混合过程进行了详细的数值模拟,本模拟所得的功率准数和设计值以及相关文献值吻合良好。结果表明:当搅拌桨离底距离由搅拌槽直径的1/2处变为1/3处时,搅拌槽内的流型均为典型的'双循环流型',而当搅拌桨离底距离由搅拌槽直径的1/3处降低至1/6处时,槽内流型由典型的'双循环流型'转变为'单循环流型';通过对不同时刻不同桨叶离底距离下的示踪剂浓度分布图分析表明槽内的混合过程与流动场密切相关;加料点位置对于最终的流场混合效果有着显著影响,对于混合时间数据的采集应注意不同加料位置时监测点的选取。CFD模拟结果表明本文所采用的模型可以很好的预测半圆管曲面涡轮搅拌槽内的混合特性,为进一步改进和优化半圆管曲面涡轮的设计提供了一定的参考。

Standard k-ε turbulence model is used to simulate the fluid field and mixing characteristics in a tank stirred by a Smith turbine in a platform of commercial CFD software package,CFX10.0.The relative rotation between baffles and the impeller is numerically simulated by a Multiple Reference Frame approach.The numerical results indicate that when the impeller off-bottom clearance decreases from 1/2 to 1/3 of the impeller diameter,flow pattern is always the ＂typical two loops＂;however,when the impeller off-bottom clearance decreases from 1/3 to 1/6 of the impeller diameter,flow pattern changes from the ＂typical two loops＂ into a ＂single loop＂.Power number predicted by this work is in good agreement with design value and predicted value by other researchers.The snapshots of concentration distribution of tracer indicate that mixing time depends heavily on the flow field in the stirred tank.Both feeding and monitoring points have significant influence on the mixing results.It is important to choose appreciate monitoring points when collecting the mixing time data in practical industrial or experimental work.The above CFD simulation results indicate that the model employed in this paper can predict the mixing characteristics in the stirred tank with a Smith turbine,which provides helpful information for optimization and improvement in the future design of the Smith turbine.