Research On Flow Field Diagnosis And Fringe Information Processing Based On Moiré Tomography Technolog

The full-field display and three-dimensional quantitative measurement of complex flow field with high temperature are of great significance to modern aviation,aerospace and industrial combustion emission reduction.OCT(Optical Computerized Tomography),which combines optical method with computerized tomography,has the characteristics of real-time,stable and non-contact.And it could also realize three-dimensional quantitative measurement of key parameters in high temperature flow field.As an important branch of OCT,the moirétomography has the advantages of simple and stable optical path,wide measuring area,and could adapt to harsh experimental environment.When the technique is used in flow field diagnosis,the accurate extraction of projection information directly affects the quality of refractive index reconstruction of the field to be measured.Thus,this paper focuses on the extraction of moiré fringes’ projection data,respectively exploring the impact of the location of the flow field to be measured on the extraction of fringe information,proposing the use of Gabor wavelet transform to extract moiré projection data,and focusing on the impact of different grating periods on fringe results.The main work is as follows:1.The theoretical and experimental studies are executed to figure out whether the flow field placement positions could impact on the retrieval of fringes’ information.Theoretical analysis shows that when the measured object is placed in front of two gratings,the offset and phase mainly depend on the distance between two gratings,while the deflection angle is determined by quotient of the phase disturbance divided by the distance of the two gratings.However,when the measured object is placed between two gratings,the offset and phase mainly depend on the distance from the measured object to the next grating,and the deflection angle is determined by quotient of the phase disturbance divided by the distance from the measured object to the next grating.In order to verify the correctness and rationality of the theoretical results,a candle flame is taken as an example for experiments.Furthermore,it is found that as long as the corresponding parameters are chosen properly,it doesn’t make any difference to the extraction of information.2.To solve the problem that the existed methods for extracting moiré fringes’ information have the disadvantage of large noise and necessity of selecting proper frequency,Gabor wavelet transform method is proposed to extract phase information of moiré fringes.The light intensity of first-ordered moiré fringes is selected to derive the phase based on the Gabor wavelet transform method.In order to prove that this method is feasible,three flow fields are adopted for experiment,under which the phase information is successfully extracted.The phase information results above are compared with those extracted by Fourier transform method,which proves that the Gabor wavelet transform method has an advantage in reducing noise and gets higher accuracy.3.The characteristic of moiré fringes with two different grating periods is deduced based on the scalar diffraction theory,and the intensity distribution of moiré fringes with the zeroorder and first-order filtering are mainly discussed.Furthermore,due to consideration of two gratings with different periods,the specific Talbot distances which are available for different grating periods are applied to obtain the moiré fringes’ equations.In addition,some experiments are also done to verify our theoretical deduction,mainly from the perspective of the slope and width of moiré fringes.Finally,the phase of flow field with two different grating periods is successfully extracted,furthermore,the potential application of this study is also proposed and discussed.In a word,the involved results will be useful for expanding the possible application of moiré deflectometry in various fields.