基于数字全息干涉术测量液相云微物理起伏的湍流参数表征

Investigation of Turbulence Parameters Based on Liquid-phase Cloud Microphysics Fluctuation Measured by Digital Holography

针对云降水物理研究中湍流的测量需求,提出了一种基于数字全息干涉术测量液相云微物理起伏的湍流参数表征方法。该方法无需假设云滴谱分布函数及调整相关参数即可获得实际湍流影响的液相云微物理起伏。利用定常湍流影响的雾滴模拟液相云滴,采用像元尺寸1.67μm的相机时序记录雾滴谱,获得含水量与雾滴平均半径的起伏。根据湍流理论,计算了湍流的方差,时间相关系数,协方差和互相关系数。最终,通过分析不同间隔时间含水量的时间相关系数,获得湍流场的时间尺度为100 ms;在固定采样间隔71 ms的条件下,分析不同起始时间含水量的时间相关系数,其起伏量与平均值的最大偏差为23%,证明了测量区域流场为定常湍流。该方法可为研究液相云微物理与湍流特性及相互作用机理提供有效的测量手段。

In response to the measurement requirements of turbulence in the study of cloud precipitation physics,a turbulence parameter characterization method based on digital holographic interferometry to measure the microphysical fluctuation of liquid cloud is proposed.Since there is no need to assume the distribution function of the cloud droplet spectrum and adjust related parameters,digital holographic interferometry can obtain the microphysical fluctuations of the liquid phase cloud affected by the actual turbulence.The fog droplets affected by steady turbulence are used to simulate liquid phase cloud droplets,and the droplet spectrum is recorded by a camera with a pixel size of 1.67μm,and then the fluctuations of the water content and the average radius of the droplets are obtained.According to the theory of turbulence,the variance,time correlation coefficient,covariance and cross-correlation coefficient of turbulence are obtained.Finally,by analyzing the time correlation coefficients of water content at different intervals,the time scale of the turbulent field is 100 ms.Under the condition of a fixed sampling interval of 71 ms,the time correlation coefficient of water content at different initial times is analyzed,and the maximum deviation of the fluctuation from the average value is 23%,which proves that the flow field in the measurement area is steady turbulence.This method can provide an effective measurement method for studying the characteristics of liquid cloud microphysics and turbulence and the mechanism of their mutual influence.