Research On Flow Field Density Measurement Method Of Two-tracer Planar Laser Induced Fluosrescence

With the continuous development of flow field visualization technology,the study of flow field structure is also deepening.Density,as one of the basic characteristics of gaseous fluid,can reveal the structural characteristics of flow field,so the flow field structure can be analyzed by measuring the fluid density at different locations.At present,most of the methods to measure the density of air flow field are based on the refraction of light passing through the flow field to calculate the density change of air flow field.This method has low spatial and temporal resolution.In recent years,with the continuous development of planar laser-induced fluorescence(PLIF)method,more and more studies have been conducted to measure the structure and density of flow field using PLIF technology,which has the characteristics of high spatial and temporal resolution.However,at present,most studies on PLIF technology rarely apply it to the density measurement of air flow field.Therefore,this paper proposes a method for the density measurement of air flow field based on PLIF technology.Currently,most PLIF techniques use single tracer method to study the flow field,but single tracer can only establish the relationship between the fluorescence intensity and the concentration of the tracer itself.Therefore,in this paper,the double tracer PLIF method was adopted,and acetone and toluene were selected as tracers.According to the oxygen quenching effect of toluene,the tracer can be associated with oxygen,and then the concentration of the double tracer can be associated with the concentration of air,so as to measure the density of the whole air flow field.According to the absorption spectrum and fluorescence spectrum of the double tracer,the excitation wavelength of the double tracer and the filter used to obtain the fluorescence image of the double tracer were determined.Experiments were designed and the oxygen quenching coefficient of toluene was measured at room temperature.The proper mixing ratio and concentration range of the two tracers were obtained through the experiments,and calibration experiments were carried out according to the mixing ratio.According to the determined mixing ratio,the relationship between the fluorescence intensity and the concentration of the tracer was calibrated,and the relationship between the fluorescence intensity and the concentration of the tracer was obtained.The measurement experiment of static air flow field density was conducted according to the fitted expression and the measured oxygen quenching coefficient,and the fluorescence intensity of the fluorescence image of the double tracer was captured.The density of air flow field was calculated through the density measurement theory,and the error between the measured flow field density value and the actual value was less than 20%.The feasibility of double tracer PLIF to measure the density of air flow field is illustrated,but there are some errors in the experiment,and the errors are analyzed.In the future,the theoretical study of the interaction between the two tracers should be improved to provide a theoretical basis for the subsequent measurement of dynamic flow field density.