对称槽道涡波流场流动特征的POD分析

Analysis on flow characteristics of vortex wave flow field within symmetric channel using proper orthogonal decomposition technology

为深入分析层流状态下对称槽道内涡波流场的流动特性及其变化规律,对流场进行了二维粒子图像测速(2DPIV)测量获取瞬态速度矢量数据,利用本征正交分解(POD)技术进行模态分解以及涡波流场的重构,然后根据重构的流场对对称槽道内涡波流场进行了平均速度剖面、流场脉动强度以及特征点的速度和频谱分布等方面的分析。结果表明:POD的前15阶模态能够表征涡波流场的主导结构,第1,3阶模态主要表现为一对旋向相反的涡对特征,第2阶模态具有涡旋和波状主流的特征;提取了5个涡旋涡核的位置作为流场流动特性的特征点;根据POD重构流场分析发现流向平均速度呈抛物线形状分布,法向平均速度呈对称分布特征;流向脉动强度受壁面的影响较大,法向脉动强度呈现抛物线形状分布;距离中心主流较近的1~#,4~#,5~#特征点的速度脉动程度受主流的脉动强度影响较大,速度的脉动主频0.15 Hz与次频、流场的自然频率0.35 Hz共同影响特征点的速度分布;2~#,3~#特征点的流向速度呈衰减趋势,法向速度在初期幅度变化较大。

The vortex wave flow field of symmetric channel has a wide range of applications in industrial mass transfer and heat transfer.To further analyze the flow characteristics and variation laws of the vortex wave flow field within symmetric channel under laminar flow conditions,2 DPIV measurements was carried out to obtain data of instantaneous flow velocity vector field,then modes were decomposed and vortex wave flow field reconstructed using proper orthogonal decomposition（POD）technology.According to the reconstruction of the flow field,analysis were carried out for mean velocity profile,pulsation intensity of flow field,velocity and spectral distribution of the characteristics points,etc.of the vortex wave flow field within the symmetrical channel.The results show that the first 15 POD modes could characterize the dominant vortex wave flow field structure,the first and the third modes were a pair of vortices with opposite rotating,while the second mode had a vortex and the wavy mainstream feature.Five vortex core positions were extracted as the flow field feature points.Analysis based on POD reconstructed stream field.Analysis shows that the average speed distribution in the flow direction is parabolic,and the normal average speed distribution is symmetrical;flow pulsation intensity is greatly influenced by the wall,the normal fluctuation intensity distribution exhibits aparabolic shape;the speed pulsation features of feature points 1~#,4~#,5~#（closer to the center mainstream）are influenced by mainstream pulsation strength,the velocity distribution of feature points is affected by pulsation speed frequency of 0.15 Hz frequency and the natural frequency of the flow field 0.35 Hz together;the flow velocity of feature points 2~#,3~#has a fading trend,the normal speed variation amplitude is large in the early stage.