The application claims priority under 35 U.S.C. 119(a-d) to CN 202110394021.6, filed Apr. 13, 2021.
The present invention relates to a technical field of aero-engine turbine blade strain measurement and its data processing, which is for full-field strain measurement of turbine blades and strain field reconstruction.
The strain state of turbine rotor blades during working of an aero-engine is one of the key parameters for studying the mechanical properties of the engine turbine blades, evaluating the working state of the blades, and improving the blade structure. Blade strain measurement and strain field reconstruction are the key and difficulty in the field of aero-engine turbine blade testing. The conventional high-temperature strain gauge method is a point-to-point contact measurement method, which is complicated in installation and wiring, difficult to reconstruct the strain field, and low in upper limit of application temperature. Such issues have seriously hindered the study of the stress and strain state of the turbine rotor blades under high temperature and high pressure.
To solve such issues, the present invention provides a full-field reconstruction method for a turbine blade strain field based on dual-mode fusion, which is based on optical non-contact measurement. With a combination of infrared acquisition and imaging technology, strain measurement is performed at edges and surfaces of turbine blades. Then data of the two modes are combined according to surface characteristics of the blades to reconstruct the full-field strain of the blade.
The present invention combines imaging technology and infrared photoelectric strain measurement technology, and uses the same optical path and non-contact measurement of the same probe to realize measurement and reconstruction of an entire strain field of the same target blade, which solves problem that conventional turbine rotor blade strain measurement has too few data points to form field measurement.
The present invention integrates two measurement methods, providing an imaging measurement mode and an infrared measurement mode. The present invention uses one probe to realize simultaneous collection of digital image signals and infrared signals, and centrally processes the signals in a host computer system. The probe has two functions: telescoping and rotating. The telescoping function means that during collecting blade optical information, the probe will move up and down in a reserved hole on an engine casing. During movement, a light hole of the probe can radially cover multiple target areas of the blade. The rotating function refers to adjustment of the probe based on preliminary relative positional relationship between the light hole and the target blade before the telescoping process of the probe, so as to satisfy arc-shaped focal length adjustment of different blade areas. The imaging measurement mode of the probe is based on a charge-coupled device CCD connected to a rear end of a bi-telecentric optical system. The charge-coupled device CCD works outside the engine casing. Because of limitations of the light hole and the view field of the probe imaging system, a view field of the imaging measurement mode is not enough to directly record the entire blade area. Therefore, the same blade area is imaged multiple times through the telescoping function of the probe cooperating with a blade rotation speed sensor. It is difficult to make feature points at blade edges, so strain calculation accuracy is not high in the imaging mode. Therefore, the infrared mode is used for the blade edge. During the telescoping and rotating processes of the probe, the infrared mode can continuously record. After one telescoping displacement of the probe, an infrared radiation signal of the blade is transmitted to the infrared photodetector at the rear end through the probe, so as to record a converted voltage signal. The infrared radiation signal is collected based on rotation of the blade. After the probe reaches a certain height, the rotation of the blade and the infrared radiation difference between the blade and the surrounding environment will cause periodic changes of a collected voltage signal. A width of a periodic signal of the blade can be determined through accurate identification of the infrared radiation difference, which means that an axial displacement change of the blade can be calculated according to a recorded time difference together with steady-state rotation of the blade.
The present invention provides is a full-field measurement and reconstruction method for a turbine blade strain field based on dual-mode fusion. The full-field measurement and reconstruction method uses a probe, which can simultaneously collect optical information and infrared information, to collect turbine blade data. The probe has telescoping and rotating functions, and a telescoping direction is consistent with a turbine radial direction. The full-field measurement and reconstruction method comprises steps of:
Step 1: dividing a surface of a turbine blade into several rectangular areas, and pre-calculating acquisition angles and telescoping amounts of a probe when collecting optical information of the rectangular areas;
Step 2: when a turbine works, using the probe to collect the optical information of the rectangular areas of the turbine blade according to the acquisition angles and the telescoping amounts pre-calculated in the Step 1;
Step 3: splicing the obtained optical information of each area of the turbine blade to obtain a complete turbine blade image;
Step 4: fixing the telescoping amount of the probe, and collecting infrared information changes of the blade surface and blade gaps of the turbine blade at a certain speed and a certain height; converting an infrared signal into a continuous voltage signal based on a photoelectric converter, then outputting and storing the continuous voltage signal; obtaining edge information of the same turbine blade under different telescoping amounts of the probe with the same method;
Step 5: using the Steps 1-4 to obtain accurate turbine blade images at different temperatures;
Step 6: processing data, wherein first, the blade optical image spliced in the Step 3 is subjected to grayscale conversion, Gaussian high-pass filtering, and histogram equalization based on MATLAB software for image enhancement, so as to increase contrast between blade surface feature points and background in the image;
second, image sub-areas are matched; a normal temperature image is used as a reference image, marked as ƒ(x, y), and a high temperature image is used as a target image, marked as g(x′,y′); x, y are coordinates of a feature point, ƒ(x,y) and g(x′,y′) are gray values of corresponding feature points; a correlation function is used to find a position and a shape of a target sub-area with a highest similarity to the a reference sub-area, in which a cross-correlation function is specifically used to take maximum value between the target sub-area and the reference sub-area; at the same time, a search process of a target image sub-region uses a Newton-Rapshon algorithm combined with bicubic interpolation to achieve sub-pixel level matching accuracy; full-field displacement field changes are obtained based on the high-accuracy matching of a target image and a reference image, and a local least squares fitting method is used to preform full-field strain measurement; third, blade edge information is processed; through reasonable path planning and infrared signal scanning, a continuous signal curve of the voltage converted from the infrared signal of the blade at different temperatures and different heights is obtained; a blade width can be detected by the infrared intensity difference between the blades and the blade gaps with a slope threshold value of a setting voltage signal; blade edge strain change can be calculated by comparing blade width changes at different temperatures but same height; and
Step 7: fusing the blade full-field strain information of the obtained by the image mode with the blade edge information based on continuity of the blade strain changes together with a spline interpolation algorithm, thereby reconstructing complete strain field information of the blade.
Beneficial effects of the present invention are as follows: the present invention combines digital image technology with infrared photoelectric measurement technology, which not only realizes the strain measurement of the turbine rotor blade at harsh high temperature and high pressure environment of the aeroengine, but also reconstructs the blade strain field based on methods such as data processing and image splicing. Compared with conventional reconstruction methods based on limited point data and software simulation, the method of the present invention performs interpolation reconstruction based on actual measurement results, and the reconstructed strain field has more engineering significance.
Element reference: 1. Dual-mode probe; 2. Dual-mode optical path; 3. Engine casing wall; 4. Engine shaft; 5. Turbine blade; 6. Probe telescoping function; 7. Imaging sub-area; 8. Imaging optical path; 9. Blade sub-area; 10. Probe rotating function; 11. Blade sub-area feature image; 12. Infrared optical path; 13. Infrared radiation scanning; 14. Infrared photoelectric scanning signal; 15. Feature image strain calculation; 16. Reference sub-area; 17. Target sub-area; 18. Dual-mode data fusion; 19. Strain field reconstruction.
Referring to
Aero-engine turbine blades work in an extreme environment with high temperature and high pressure. However, during steady-state operation of the engine, the turbine blades can be considered as in a steady state due to an overall steady state of gas temperature, pressure, and the engine, wherein load and strain are in dynamic balance. That is to say, during measurement, a strain field of the turbine blades does not change rapidly with rotation. Referring to
Blade edge strain measurement is shown in
At the same height of the blade, the infrared photoelectric scanning signal 14 is collected at different temperatures, as shown in
The blade edge displacement value calculated in the infrared mode is combined with the blade surface displacement vector diagram obtained in the imaging mode through an interpolation method, so as to obtain a blade surface displacement vector diagram in the steady-state operation, as shown in
as shown in
Number | Date | Country | Kind |
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202110394021.6 | Apr 2021 | CN | national |