Study On Quantitative Schlieren Techniques For Density Measurement Of Flow Field

The basic principle and method of traditional schlieren technique are described in this paper.Then,the relevant application in the research fields of combustion,shock wave and wind-tunnels are introduced.Besides,the advantages and disadvantages of existing different types of schlieren techniques are analysed.In order to solve the problem of schlieren quantitative measurement method is not perfect,a new method for density quantitative measurement of schlieren was proposed in this paper.The main works are followed:1.An experimental device is developed,and it is mainly composed of transmission-type schlieren optical path,knife edge control circuit and the quantitative analysis software of flow field.2.The auto-focusing algorithm of the schlieren knife edge,calibration curve of schlieren image and density quantitative measurement algorithm are studied.The auto-focusing algorithm of the schlieren knife edge is based on analyzing image features during the process of seeking focal point,and it makes the position of schlieren edge device automatically searches the position of second schlieren mirror focus by comparing homogeneity of image gray.The density quantitative analysis algorithm is based on the principle of quantitative schlieren technique measures,and the density value of flow filed is calculated.3.The experimental device is set up,it takes the heating air above the rectangular electric heating platform as the test object and combines with three core contents including the auto-focusing algorithm of the schlieren knife edge,calibration curve of schlieren image and density quantitative measurement algorithm,Meanwhile,it is carried on the flow density measurement.Comparing the measurement results with the density measured by standard devices.The experimental results show that under the condition of temperature is 20 ?,the precision of auto-focusing algorithm is 0.3-0.5mm,and the relative error of flow density measurement is less than 5%.The measurement experiment of density field of heated air above the rectangular electric heating platform is completed in this subject.The research contents of this paper provide a new thought for project application and measurement experiment of the flow density field.