Calibration Scheme Of Planar Laser Induced Fluorescence Measurement Of Water Scalar Field And Its Relative Uncertainty Research

Planar laser-induced fluorescence(PLIF)is a new non-invasive two-dimensional flow visualization and flow measurement method that can reproduce the real flow of the flow field.Coupled with the appropriate calibration scheme,PLIF can perform quantitative measurement accurately,which can be used for the basic research of hydrodynamics,further revealing the mechanism of complex physical and chemical processes such as diffusion of water pollutants,liquid mixing process,flame combustion and so on.The application prospect of PLIF is bright.A new planar laser induced fluorescence calibration scheme for quantitative measurement of water scalar field is developed based on the principles of LIF measurement,which is simple and of some degree of precision.The scheme is helpful for PLIF quantitative measurement.The main contents are as follows:(1)An on-site and real-time calibration model was constructed after fully considering the the principles of PLIF,main factors that affect the quantitative measurement of PLIF,the information conversion process in the measurement process,and the photoelectric conversion characteristics of the CCD camera.On the basis of taking unequal spatial distribution of light intensity,the attenuation of the light intensity,and the divergence of the light beam along the path in the collimated light field and the fan-shaped light field into account,a correction model is constructed to determine the incident laser light intensity in each area of the planar field.In addition,a new image processing algorithm was developed for determining the calibration coefficient,which can determine the center position of the laser beam,avoiding the error to some extent,introduced by the assumption that the photo center coincides with the center of the laser beam.(2)The calibration model was applied to measure the uniform concentration field under the fan-shaped light field.Compared with the real values,it can be found that the distribution of measured concentration values in the central area is consistent with the actual situation,but that of the edge is not.(3)The Monte Carlo method uncertainty evaluation model was established to evaluate the relative uncertainty of the scheme established in this paper.It can be found that the relative uncertainty is mainly distributed in the range of 3.3%~3.4% in the collimated light field and the fan-shaped light field.However,the distribution in the collimated light field is more concentrated.The shape of the light field can affect the relative uncertainty of the measurement of the scalar field.The relative uncertainty of measurement shows a good linearity relationship with the fluctuation of laser power,and a good power function relationship with the camera's signal-to-noise ratio(SNR).