Research On 3D-deformation Mearmrnt Techlnology Of Aero Engine Blade Based On Digital Image Correlation

Aeroengine is known as the "pearl on the crown of industry",but also considered as the heart of the aircraft.Blade is the core component of aero engine,each level of blade for the engine to provide more than 80% of the thrust.Blade work in complex mechanical environment will lead to the change of blade shape,and the change of blade shape will change the airflow through the engine relative to the design condition,thus affecting the stability,noise level and thrust performance of the engine.It is of great significance to master the deformation law of blades under working conditions,not only for the safe operation of existing aero-engines but also for the optimization design of new blades.In this paper,a three-dimensional deformation measurement method based on binocular vision and digital image correlation method is proposed for the measurement of three-dimensional deformation of blade surface under the working conditions of aeroengine.The image acquisition method of rotating blade surface based on high-speed stroboscopic and the rigid body displacement elimination method were combined to measure the blade surface displacement field and main strain field under the condition of 6000rpm(N1 speed of CFM56-7 engine).The main research contents include:In the aspect of detection point matching before and after deformation,a DIC-based detection point matching model was established.This model starts from the principle of DIC and studies the key technology of digital image correlation method.Considering the anti-interference and calculation efficiency,the correlation function and displacement mode are selected.In terms of initial value search algorithm,an initial value search algorithm based on ORB features is proposed,and compared with traditional methods in terms of accuracy,speed and rotation adaptability.In terms of sub-pixel matching,FA-NR and IC-GN sub-pixel matching models were established,and their matching speed and accuracy were compared through simulation.In the aspect of the positioning of detection points before and after deformation,a 3D reconstruction model based on binocular vision system was established.In this model,the calibration method of binocular camera based on checkerboard and stereo matching method based on second order shape function are used to calculate the spatial coordinates of the detection points before and after deformation.In order to solve the problem that stereo matching is prone to mismatching,a detection method based on RMS window and a correction method based on two-stage sub-pixel iteration were proposed to detect and correct the mismatching points during three-dimensional reconstruction of blade surface.In order to solve the problem of inaccurate calculation of displacement field in a specific coordinate system,a three-dimensional displacement field calculation method for a specific coordinate system was proposed.Based on P3 P theory,the rotation matrix of camera coordinate system relative to measurement coordinate system was solved,and the method was used for displacement correction.The experimental results show that the displacement measurement error of the 3D-DIC system is less than 2μm when the measurement distance is 0.5m.For the displacement measurement in a specific direction,the displacement measurement errors in X,Y and Z directions decreased by 40%,88% and 81%,respectively,compared with those before correction.In the aspect of strain field calculation,the main strain calculation model based on spatial non-orthogonal grid is established.The experimental results show that the principal strain measurement error of the3D-DIC system is less than 50με when the measuring distance is 0.5m.Finally,the matching strategy of 3D-DIC was optimized to reduce the measurement time of the whole process on the premise of ensuring the accuracy.Finally,an experimental platform for deformation measurement of rotating blades was built.The images of rotating blades were collected by high-speed strobography method,and the image quality of the images taken in the rotating state was evaluated by Kblur coefficient to verify the effectiveness of the proposed method.A coordinate registration method based on two-region selection was proposed to solve the problem that the rigid body displacement introduced by the trigger error affected the measurement accuracy.GUI was written according to the3D-DIC principle to measure the blade surface deformation field under the condition of 6000 rpm.