Lightnin静态混合器内瞬态流场POD分析及混合特性研究

为了研究Lightnin静态混合器（LSM）内的瞬态流场结构和混合特性，以水为工质采用ANSYS FLUENT V16.1中的大涡模拟（large eddy simulation，LES）湍流模型对不同长径比和雷诺数下LSM内的湍流流动进行数值模拟，并用本征正交分解（POD）方法对流场结构进行模态分解以提取流场相干结构。结果表明：当采样数量达到2 000时，低阶模态蕴含流场主要的旋涡结构信息；混合段内横截面平均涡量分布呈正弦状周期性变化，在z/l=5.0~6.0范围内，Re=3 981、5 971和7 962时的平均涡量相较于Re=1 990时增长148.5%~322.7%，拉伸率提高11.5%~18.9%；小长径比的LSM中流体被拉伸的概率更大。

Proper orthogonal decomposition (POD) analysis of the transient flow field and mixing characteristics in a Lightnin static mixer

We report a study of the transient flow field structure and mixing characteristics in a Lightnin static mixer (LSM). Numerical simulation using ANSYS FLUENT V16.1 software was employed to study the turbulent flow in LSM with different aspect ratios and Reynolds numbers. Distilled water was employed as the working fluid. The flow field structures were decomposed modally by an proper orthogonal decomposition (POD) method and coherent structures were extracted. The results show that the low order mode carries the vortex structure information of the main flow field when the number of samples reaches 2 000. The distribution of the average vorticity for different axial sections shows a sinusoidal periodic change. Compared with Re=1 990 in the range z/l=5.0~6.0, the average vorticity increased by 148.5%, 297.6%, and 322.7% when the Re was increased to 3 981, 5 971 and 7 962, respectively. At the same time, the stretching rates in the LSM increased by 11.5%, 15.1% and 18.9%, respectively. The fluid in an LSM with small aspect ratio is more likely to be stretched.