曝气-搅拌反应器内环流流场的PIV测量和POD分析

PIV measurement and POD analysis of circulating flow field in aeration stirred reactor

该文采用二维粒子图像测速技术(PIV)对曝气-搅拌反应器内环流流场进行测量,获得不同搅拌转速下流场的流速和涡量分布。应用本征正交分解(POD)方法提取流场主要相干结构,系统地研究了能量贡献和POD模式。结果表明:搅拌转速对环流流场的影响体现在环流速度和涡量分布上,对流场的流型影响较小,高搅拌转速有利于提高混合效果和区域间的物质交换作用。前3阶模态表征环流流场最主要的相干结构,呈现层次化三尺度流动结构,第一个尺度主要与反应器的主流流动有关,通常由1阶模态表示;第二个尺度主要由大尺度的涡对来表示,体现在2阶和3阶模态中;第三个尺度表现为更均匀的小尺度涡,主要分布在搅拌区内和转速为1200r/min的2阶和3阶模态中。因此,增强低转速下的大尺度结构将有利于环流流动,提高反应器的混合效果。

Two-dimensional particle image velocimetry(PIV)was used to measure the annular flow field in an aeration stirred reactor,and the velocity and vorticity distributions were obtained at different stirring speeds.The main coherent structures of the flow field are extracted by the method of intrinsic orthogonal decomposition(POD),and the energy contribution and POD mode are systematically studied.The results show that the influence of stirring speed on the circulation flow field is reflected in the distribution of circulation velocity and vorticity,which has little influence on the flow pattern.High stirring speed is beneficial to improve mixing effect and material exchange between regions.The first three modes represent the main coherent structure of the circulation flow field,showing a hierarchical three-scale flow structure.The first scale is mainly related to the mainstream flow in the reactor,which is usually represented by the first-order mode.The second scale is mainly represented by large-scale vortex pairs,which are reflected in the second and third-order modes.The third scale is more uniform small-scale vortex,which is mostly distributed in the mixing zone and the second and third-orde r modes with the rotating speed of 1200 r/min.Enhancing the large-scale structure at low rotational speed will be beneficial to the c irculation flow and improve the mixing effect of the reactor.