基于DFT的水射流红外热像频域时空分析

Temporal and spatial analysis of infrared images from water jet in frequency domain based on DFT

基于二维离散傅里叶变换及空间频谱分析,对水射流湍流脉动的空间尺度进行了研究,得到了由红外辐射温度表征的被动标量湍流场在对流区、耗散区、惯性子区的特征空间尺度及其时间演化规律.对射流不同区域的关心点重新采样,得到湍流场中关心点的时间序列,利用一维离散傅里叶变换,分析了对流区大尺度涡中心、惯性子区小尺度涡中心、耗散区及射流轴心线上各关心点的湍流波动特征.计算了时间序列频谱的分形维数,研究了自由湍流不同尺度区间上述各关心点湍流脉动的分形特征.

Based on 2-D discrete Fourier transforms （DFT） of infrared images from water jet and the analyses of its 2-D spatial spectrum, investigations were made on the spatial scales of passive scalars turbulent flow in high pressure water jet fields, which are represented by infrared images. The characteristic length scales and the law of their temporal evolution process were obtained in the energy （or convection） range, the dissipation range and the inertial range in between. Based on 1-D DFT, the turbulent temporal fluctuation characteristics were obtained for the interest points at large scale eddy center in convection range, sub-scale eddy center in inertial range, dissipation range, as well as in the axis of the jetting flow. In addition, the frac- tal dimensions were also calculated upon the 1-D spectrum, which was then used for fractal characterization of temporal fluctuations of the interest points in different scale regions of the scalars turbulent flow.