Research On Videogrammetry Of Density Field In High Speed Wind Tunnel Test

The aircraft has been playing an important role in enhancing national defense force.In order to meet the needs of modern complex war environment,many new types of configuration layouts of aircrafts are developed to improve the performance.As a result,the flow around the aircraft becomes much more complex than ever.It is necessary to develop some measurement methods which can be used to investigate the flow mechanism and analyze the aerodynamic characteristics.The method,which obtains flow information by analyzing the variation of density field,has been used in wind tunnel test for several decades due to its robustness and easyuse.Among this kind of methods,the schlieren and the shadow method is easy to use but cannot provide accurate quantitative data;the interferometric method needs expensive facility,complicated installation and is sensitive to measurement environment;the accuracy of the BOS is determined by the window size of cross-correlation calculation of images,which is dependent on individual experience;compared to the methods above,the videogrammetry method has advantages of easy installation,no interference on flow and wind tunnel model.In this thesis,we focus on the measurement of density field based on video.from the three directions of image processing,ray deflection theory and density field reconstruction,the sub-pixel image edge detection and center positioning in wind tunnel test have been studied.Under the field disturbance condition,the formation mechanism of optical deflection displacement measurement error and the measurement error minimization method have been studied.And then the density field solution method based on discrete deflection displacement has been studied.The main research contents include:1.Research on image sub-pixel center positioningFirstly we analyze common edge detection methods such as Robers,Sobel and Canny,then analyze sub-pixel edge detection methods such as moment method,interpolation method and fitting method.The sub-pixel edge detection center positioning method use Canny and partial area effect was propose,which is suitable for the wind tunnel environment.2.Research on calculation method of optical deflection angleWe study the calculation method of the circle center vector displacement in the wind tunnel coordinate system,and analyze the optical path principle of the videogrammetry experiment.According to the calculation method of the deflection angle of BOS,the calculation method of the deflection angle of the non-parallel optical path based on videogrammetry has been derived.3.Research on the method of density field based on discrete light deflection angleAccording to the principle of density field reconstruction,we study the relationship between the optical deflection angle and the density field.Propose a fast solution method for density field reconstruction,which is use the boundary conditions.4.Research on application of density field videogrammetry methodThe density field videogrammetry method has been applicated in wind tunnel test,the flow field around a cavity model with different Mach numbers have been measured,which provides data support for the subsequent flow field analysis.