基于实验数据的湍流扩散POD模态分析

POD modal analysis of turbulent diffusion based on experimental data

采用粒子成像测速(PIV)和激光诱导荧光(LIF)技术同时测量了水平通道中湍流扩散过程的流速和荧光剂浓度的瞬时分布,并利用实验数据,通过本征正交分解(POD)模态分析方法,实现了湍流条件下荧光剂扩散过程中浓度分布的数值重构。该方法应用于瞬时浓度分布的特征分析中,得到了瞬时分布的各阶模态,并分析各阶模态空间分布特征及其所含能量。结果表明,浓度分布在距离荧光剂入口较近的区域具有较强的周期性,且低阶POD模态能量占主导地位。应用POD分析得到的模态可以较准确地重构距离荧光剂入口较近区域的浓度分布的基本特征,相对误差主要集中于距离荧光剂入口较远的区域,表明本文提出的基于POD模态分析的湍流条件下浓度场的数值重构更适用于周期性较强的系统,为预测未知时刻的湍流扩散浓度分布提供了基础。

In this paper,velocity and concentration distributions of fluorescent agent in turbulent liquid flow in a horizontal channel were experimentally measured by simultaneous use of particle image velocimetry(PIV)and laser induced fluorescence(LIF)technologies.Then an approach to numerical reconstruction of the concentration distribution by using the proper orthogonal decomposition(POD)analysis based on the experimental data was developed.For doing this,the POD method was applied to analyze instantaneous concentration distribution characteristics,and obtain different modes of the concentration distribution,and the spatial characteristics of the modes and their energy were analyzed.The results show that the concentration distribution in the area close to the phosphor inlet has a strong periodicity,and the low-order POD mode energy is dominant.The modalities obtained by applying POD analysis can more accurately reconstruct the basic characteristics of the concentration distribution in the area closer to the phosphor inlet,and the relative error is mainly concentrated in the area which is far from the injection mouth.This suggests that the POD analysis approach proposed in the present paper is suitable for numerical reconstruction of concentration distribution in the turbulent flow systems with periodicity,and thus lays a foundation for effective prediction of concentration distribution in turbulent diffusion processes.