CN114663625A - Surface image flattening method applied to rotating turbine straight blade leading edge and application thereof - Google Patents
Surface image flattening method applied to rotating turbine straight blade leading edge and application thereof Download PDFInfo
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Abstract
一种应用于旋转涡轮直叶片前缘的表面图像展平方法及其应用，包括：选取一待测涡轮直叶片，在其前缘面上设计出等间距分布的标记点结构，通过3D打印加工制作出该涡轮直叶片，用于后续开展的旋转实验；实验中将待测涡轮直叶片放入封闭的涡轮实验段中并保持匀速旋转，固定在涡轮实验段外的相机以某一固定频率透过涡轮实验段上的观测窗口对待测涡轮直叶片的前缘面进行拍摄并保存为灰度图像；基于标记点的图像展平法将涡轮直叶片前缘面灰度图像的待测区域进行展平。本发明解决了现有技术中获得旋转状态下的涡轮直叶片前缘表面展平图像的难题，具有结构简单，设计和加工方便，展开效果好的特点，可应用于各种涡轮直叶片前缘面的图像展开处理。A surface image flattening method applied to the leading edge of a rotating turbine straight blade and its application, comprising: selecting a turbine straight blade to be tested, designing a structure of marking points distributed at equal intervals on its leading edge surface, and processing it by 3D printing The turbine straight blade was produced for subsequent rotation experiments; in the experiment, the turbine straight blade to be tested was placed in a closed turbine experimental section and kept rotating at a constant speed, and the camera fixed outside the turbine experimental section transmitted through a certain fixed frequency. The leading edge surface of the turbine straight blade to be tested is photographed through the observation window on the turbine experimental section and saved as a grayscale image; the grayscale image of the leading edge surface of the turbine straight blade is expanded by the image flattening method based on marker points. flat. The invention solves the problem of obtaining the flattened image of the front edge surface of the turbine straight blade in the rotating state in the prior art, has the characteristics of simple structure, convenient design and processing, and good unfolding effect, and can be applied to the leading edge of various turbine straight blades The image expansion processing of the surface.
Description
Technical Field
The invention belongs to the technical field of variable curvature surface image processing, and particularly relates to a surface image flattening method applied to a rotating turbine straight blade leading edge.
Background
Gas turbine engines are thermodynamic devices based on the brayton cycle, which have been widely used in modern military and industrial applications by virtue of their powerful output power and high thermal efficiency. Experience shows that under the premise that the size of an engine is not changed, the thrust of a gas turbine can be increased by 8-13% and the cycle efficiency can be increased by 2-4% when the temperature of the inlet of the turbine is increased by 56K. The turbine front temperature of the advanced aeroengine exceeds 2000K at present, and the temperature resistance limit of the turbine blade material is far less than the inlet temperature of the turbine, so that an efficient cooling technology must be adopted to ensure the normal operation of the turbine blade material. The front edge of the turbine blade is directly impacted by high-temperature high-speed main flow and is a region with the highest convective heat transfer strength of the blade. Therefore, the leading edge region is a difficult and difficult region for cooling design on the turbine blade, and an efficient cooling technology is very important for reducing the temperature of the leading edge and ensuring the normal operation of the turbine blade.
Film cooling is one of the important cooling methods for the leading edge of a turbine blade. The film cooling is realized by opening discrete holes on the surface of the turbine blade and leading the cooling working medium out of the interior of the turbine blade to the outer wall surface. Under the action of the main flow, the cooling working medium is pressed on the surface of the blade to form an air film, so that the wall surface is separated from the high-temperature main flow fuel gas, and meanwhile, the heat of the wall surface is taken away.
The turbine blade leading edge surface is generally the curved surface, and the curvature change is great, therefore the turbine blade surface in the image is taken for the curved surface for the experiment, and camera shooting still can have the picture distortion simultaneously, consequently in the data processing link after the experiment, need become the rectangle plane with the curved surface flattening in the image, conveniently carry out subsequent data analysis.
At present, a mature image flattening processing method is available around the leading edge experiment of the turbine blade under a static condition. The test will typically use both reference and test blades. The method comprises the steps that grid paper (a plurality of straight lines are drawn on the surface of the grid paper to form uniformly distributed rectangular grids) is closely attached to the surface of a reference blade, a camera is used for obtaining an image of the surface of the reference blade, an image processing program firstly converts pixel points of the image of the surface of the blade into orthogonal coordinate points, the pixel points where the grid nodes are located also are included, under the condition that the geometric relation of the rectangular grids in a planar state is known, the grid distorted in the image can be re-flattened into the rectangular grids by moving the pixel points, and finally displacement information of each pixel point in an orthogonal coordinate system in the grid flattening process is recorded. The geometric structures of the experimental blade and the reference blade are completely consistent, the surface of the experimental blade is not provided with the mesh paper, and under the condition that the positions of the camera and the blade are the same (namely, the position of the blade in the shot image is unchanged), the curved blade surface image can be directly converted into the flattened blade surface image through a program under the condition that the displacement information of the pixel points of the image flattening is known. As can be seen from the above described process, this method is only applicable to cases where the blade is stationary in the camera field of view, where a flattening program written from a grid of reference blades has reference value to the experimental blade.
At present, the research around air film cooling at home and abroad mainly focuses on the development of static flat plates and static cascade wind tunnels. Film cooling studies taking into account the spinning effect and performed in a spinning state are few, which are mainly limited by experimental conditions and testing techniques. In the rotation experiment, in order not to destroy the flow field structure of the turbine, an image of the surface of the rotating blade is generally obtained from the outside of the turbine by using a lock-up shooting technology. The lock is to the shooting technique and utilize the light sensing element who fixes at rotatory end and static end promptly for the fixed position of every rotation week can stimulate out signal pulse, and control camera shoots, and then when guaranteeing camera shooting at every turn, the fixed position of target experiment blade all can appear in the camera visual field. However, this method of capturing is affected by light sensing errors and delays in signal excitation and transmission, which can cause the captured blade surface image to swing within a certain range in the camera field of view. Therefore, if a method such as a method for flattening a mesh paper image in a static cascade experiment is adopted, the experimental image cannot be superposed with the reference image, and an experimental image flattening program cannot be compiled by using pixel point displacement information obtained by the reference blade. Based on this, image flattening processing needs to be performed on each blade surface image shot under a rotating condition, and therefore, a new method needs to be researched, so that a program can be ensured to recognize and flatten each image.
In summary, how to design a method for flattening the surface image of the front edge of the straight blade of the turbine under the rotation condition, and the method has the characteristics of simple operation and good repeatability of multiple photos, is a problem to be solved in the art.
Disclosure of Invention
The invention aims at the problems and provides a surface image flattening method applied to a rotating turbine straight blade leading edge, which mainly comprises the following steps:
step 1: selecting a turbine straight blade to be tested, designing mark point structures distributed at equal intervals on the front edge surface of the turbine straight blade, manufacturing the turbine straight blade through 3D printing processing, and using the turbine straight blade for a subsequent rotary experiment;
step 2: during the experiment, the turbine straight blade to be tested is placed in a closed turbine experiment section and keeps rotating at a constant speed, and a camera fixed outside the turbine experiment section shoots the front edge surface of the turbine straight blade to be tested through an observation window on the turbine experiment section at a certain fixed frequency and stores the front edge surface as a gray image;
and step 3: and flattening the to-be-measured area of the gray image of the front edge surface of the straight turbine blade by using an image flattening method based on the mark points.
As a further improvement of the above technical solution: the cross section of the straight turbine blade is in an airfoil shape, the cross sections at the blade heights are completely consistent, the surface of the straight turbine blade is a cylindrical surface in a geometric sense, and the airfoil curve of the cross section is a directrix.
As a further improvement of the above technical solution: the front edge surface and the suction surface of the straight turbine blade are convex surfaces with curvature, and the pressure surface of the straight turbine blade is a concave surface with curvature.
As a further improvement of the above technical solution: 2-5 rows of air film holes are formed in the front edge surface of the straight turbine blade, and the arrangement direction of each row of holes is parallel to the blade height direction.
As a further improvement of the above technical solution: the marking points are arranged in two rows and are respectively positioned at the upper end and the lower end of the front edge surface, and except the leaf height positions, other structural parameters of the two rows of marking points are completely consistent. The mark points are of circular pit structures, the intervals of the adjacent mark points are the same, and the mark points completely surround the area to be measured of the front edge of the straight blade.
As a further improvement of the technical scheme: the diameter of the mark point is d, the depth of the mark point is t, and the distance between adjacent arc lengths of the mark points in the same row is s.
As a further improvement of the above technical solution: the marker diameter d should be such that the marker occupies at least 5 pixels in the captured image to satisfy the requirement of the image processing program to identify the marker in the captured image.
As a further improvement of the technical scheme: the long arc distance s of the adjacent mark points is more than or equal to 2d so as to meet the requirement of an image processing program for distinguishing the adjacent mark points in the shot image;
as a further improvement of the above technical solution: the adjacent mark point arc long distance s should also satisfy the requirement of the unfolding precision sigma
The value of the sigma is determined according to experimental precision, R is the minimum curvature radius of the area to be measured of the front edge surface, and the physical meaning of the unfolding precision is the deviation caused by replacing an arc line with a straight line of adjacent mark points.
As a further improvement of the above technical solution: the image flattening method based on the mark points in the step 3 specifically comprises the following steps:
step 31: firstly, reading a gray level image by using an image processing program to obtain a two-dimensional matrix corresponding to the gray level image
The dimensionality M and the dimensionality N of the matrix A are consistent with the resolution of the gray level image, the number a (i, j) of the matrix A is consistent with the gray level value of a pixel point corresponding to the gray level image, and the i and the j are called as the coordinates of elements in the matrix A;
step 32: the mark points are colored in advance and are distinguished from the surrounding surface, the image processing program can be used for identifying the coordinate P (x, y) of the center position of the mark point in the matrix A, and identifying a connected component WithStats () based on a connected domain analysis function of 0penCV2, wherein the function can identify a connected region in a specific gray value range a (i, j) epsilon [ b, c ] and obtain the coordinate of the center position of the connected region, namely (x, y);
step 33: using the central coordinates P of four adjacent marking points1(x1，y2)～P4(x1，y2) Connecting to form a trapezoid area, transforming the trapezoid area into a rectangle with a specific size by perspective transformation, and designating new vertex coordinates of the rectangle as Q according to the actual geometric structure1(x1，y2)～Q4(x1，y2) The perspective transformation formula is
Wherein i and j are coordinates of corresponding pixels in the trapezoid area, u/w and v/w are coordinates corresponding to the pixels after perspective transformation, and transformation matrix
From the known vertices P of the trapezoid area1(x1，y2)～P4(x1，y2) And the transformed rectangle vertex Q1(x1，y2)～Q4(x1，y2) And (6) calculating. And transforming the coordinates of other pixel points in the irregular rectangular area after the transformation matrix H is obtained. And sequentially transforming the trapezoid areas formed by other mark points according to the perspective transformation process, and finally splicing the rectangular areas together according to the relative position relationship to obtain the flattening result of the area surrounded by the mark points, wherein correspondingly, the gray image of the front edge surface of the straight turbine blade is flattened.
The invention also discloses a method for flattening the surface image of the front edge of the straight blade of the rotating turbine, which is applied to the test of the high-pressure turbine moving blade of the aircraft engine.
Compared with the prior art, the invention has the advantages that:
1. the existing flattening method can only be applied to a static condition, and the method provided by the invention can flatten the image with the curvature surface obtained in a rotating state;
2. the existing flattening method is a mesh paper method, the flattening precision of the method depends extremely on the fit degree of mesh paper and a surface to be unfolded, the surface to which the mesh paper is attached can only be used as a reference surface, and other surfaces to be unfolded need to be unfolded according to an unfolding program written by the reference surface, so that the positions of all the surfaces to be unfolded in an image need to be completely consistent with the reference surface. According to the method, the mark point structure is added on the surface of the blade to replace mesh paper, so that the problem of the attaching degree is solved, and the mark points can be manufactured in advance through modeling and 3D printing, so that the flattening operation can be directly carried out by identifying the mark points in the image without adopting a reference surface or keeping the positions of all the surfaces to be unfolded in the image completely consistent.
Drawings
FIG. 1 is an isometric view of a straight turbine blade of the present invention.
Fig. 2 is a front view of the present invention.
Fig. 3 is a cross-sectional view a-a of fig. 2 of the present invention.
Fig. 4 is a partial enlarged view B of fig. 3 according to the present invention.
FIG. 5 is a diagram illustrating an image flattening method based on mark points according to the present invention.
FIG. 6 is a comparison of a flattened image and flattened geometry of the present invention.
Detailed Description
The following detailed description of the present invention is given for the purpose of better understanding technical solutions of the present invention by those skilled in the art, and the present description is only exemplary and explanatory and should not be construed as limiting the scope of the present invention in any way.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, specific embodiments thereof are described in detail below. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, but rather should be construed as broadly as the present invention is capable of modification in various respects, all without departing from the spirit and scope of the present invention.
A surface image flattening method applied to a rotating turbine straight blade leading edge mainly comprises the following steps:
step 1: selecting a straight turbine blade, designing mark point structures distributed at equal intervals on the front edge surface of the straight turbine blade, manufacturing the straight turbine blade through 3D printing processing, and using the straight turbine blade for a rotation experiment to be developed; the front edge surface and the suction surface of the straight turbine blade are convex surfaces with curvature, and the pressure surface of the straight turbine blade is a concave surface with curvature. According to the characteristics of a real turbine blade cooling structure, 2-5 rows of air film holes are formed in the front edge surface of the straight turbine blade, and the arrangement direction of each row of holes is parallel to the blade height direction. The marking points are arranged in two rows and are respectively positioned at the upper end and the lower end of the front edge surface, and except for different leaf height positions, other structural parameters of the two rows of marking points are completely consistent. The mark points are of circular pit structures, the intervals of the adjacent mark points are the same, and the mark points completely surround an area to be measured on the front edge surface of the straight blade. And the region to be measured of the front edge surface surrounded by the mark points is flattened into a rectangular region. The marking points need to be painted and distinguished from surrounding areas. The diameter of the mark point is d, and the depth is t. The distance between the adjacent arc lengths of the same row of mark points is s. The diameter d and the arc length distance s of the mark point meet the following conditions:
1) the diameter d should be such that the marker points occupy at least 5 pixels in the captured image to satisfy the image processing program's requirement for identifying the marker points in the captured image;
2) the arc length distance s is more than or equal to 2d so as to meet the requirement of an image processing program for distinguishing adjacent mark points in a shot image;
3) the arc length distance s should also meet the unfolding accuracy σ requirement, where the unfolding accuracy
The sigma value is determined according to experimental precision, R is the minimum curvature radius of the area to be measured of the front edge surface, and the physical meaning of the unfolding precision is the deviation caused by replacing an arc line with a straight line of adjacent mark points;
4) the mark point depth t is 0.1 d-0.2 d, and the influence on the main flow field is reduced.
Step 2: in the experimental process, a turbine straight blade to be tested is placed in a closed turbine experimental section and keeps rotating at a constant speed, an observation window made of transparent materials is arranged on a shell of the turbine experimental section, a camera fixed outside the turbine experimental section shoots a front edge surface of the turbine straight blade to be tested through the observation window at a certain fixed frequency and stores the front edge surface as a gray image, and the gray image is transmitted to a computer through a data line;
and step 3: the method comprises the following steps of flattening a gray image of the front edge surface of the straight turbine blade by using an image flattening method based on mark points, wherein the image flattening method adopts a self-written image processing program as a tool, and comprises the following specific steps:
step 31: firstly, reading a gray level image by using an image processing program to obtain a two-dimensional matrix corresponding to the gray level image
The dimensionality M and the dimensionality N of the matrix A are consistent with the resolution ratio of the gray image, the number a (i, j) in the matrix A is consistent with the gray value of a pixel point corresponding to the gray image, and the i and the j are called as the coordinates of elements in the matrix A;
step 32: the mark points are painted black in advance and distinguished from the surrounding surface, the image processing program can be used for identifying the coordinate P (x, y) of the center position of the mark points in the matrix A, identifying a connected component WithStats () based on a connected domain analysis function of 0penCV2, and the function can identify a connected region in a specific gray value range a (i, j) epsilon [ b, c ] and obtain the coordinate of the center position of the connected region, namely (x, y);
step 33: using the central coordinates P of four adjacent mark points1(x1，y2)～P4(x1，y2) Connected to form a trapezoid area, and the trapezoid area is transformed by perspectiveThe region is transformed into a rectangle of specific dimensions, the new vertex coordinates of which are specified according to the actual geometry, denoted Q1(x1，y2)～Q4(x1，y2) The perspective transformation formula is
Wherein i and j are coordinates of corresponding pixels in the trapezoid area, u/w and v/w are coordinates corresponding to the pixels after perspective transformation, and transformation matrix
From the known vertices P of the trapezoid area1(x1，y2)～P4(x1，y2) And the transformed rectangle vertex Q1(x1，y2)～Q4(x1，y2) And (6) calculating. And transforming the coordinates of other pixel points in the irregular rectangular area after the transformation matrix H is obtained. And sequentially transforming the trapezoid areas formed by other mark points according to the perspective transformation process, and finally splicing the rectangular areas together according to the relative position relationship to obtain the flattening result of the area surrounded by the mark points, wherein correspondingly, the gray image of the front edge surface of the straight turbine blade is flattened.
As a further improvement of the above technical solution: the cross section of the straight turbine blade is in an airfoil shape, the cross sections at the blade heights are completely consistent, the surface of the straight turbine blade is a cylindrical surface in a geometric sense, and the airfoil curve of the cross section is a directrix.
With reference to fig. 1 to 5, the present embodiment provides a surface image flattening method applied to a leading edge of a straight blade of a rotating turbine, which includes the following main steps: firstly, selecting a turbine straight blade 1 to be tested, designing mark points 7 distributed at equal intervals on the front edge surface 3 of the turbine straight blade, and manufacturing the turbine straight blade 1 through 3D printing, wherein the turbine straight blade to be tested rotates around a shaft at a constant speed in a closed turbine experimental section at a certain constant rotating speed in the experimental process, a camera fixed outside the turbine experimental section shoots the front edge surface 3 of the turbine straight blade to be tested through an observation window on the turbine experimental section at a certain fixed frequency and stores the front edge surface as a gray image, and the gray image is transmitted to a computer through a data line and then shoots a gray image of the front edge surface 3 of the turbine straight blade in a rotating state from the outside of the turbine through the camera; and finally, flattening the area 4 to be measured in the gray image of the front edge surface 3 of the straight blade of the turbine by using an image flattening method based on the mark points 7.
The cross section of the straight turbine blade 1 is in an airfoil shape, the cross sections at the blade heights are completely consistent, the surface of the straight turbine blade is a cylindrical surface in a geometric sense, and the airfoil curve of the cross section is a directrix. The front edge surface 3 and the suction surface 5 of the straight turbine blade are convex surfaces with curvatures, the pressure surface 4 of the straight turbine blade is a concave surface with curvatures, 2-5 rows of air film holes 6 are formed in the front edge surface 3 of the straight turbine blade 1, and the arrangement direction of each row of holes is parallel to the blade height direction.
The marking points 7 on the front edge surface 3 are arranged in two rows and are respectively positioned at the upper end and the lower end of the front edge surface 3, and the other structural parameters of the two rows of marking points 7 are completely consistent except for different leaf height positions. The mark points 7 are of circular pit structures, the intervals between every two adjacent mark points 7 are the same, and the mark points completely surround the area 4 to be measured on the front edge surface 3 of the straight blade. The distance between adjacent arc lengths of the same row of mark points 7 is s, the diameter of each mark point is d, and the depth is t.
In the present embodiment, there are 3 rows of film holes 6 on the leading edge surface 3 of the turbine bucket, 10 film holes in each row, and a total of 22 marking points 7 surrounding the leading edge region to be measured 4, where the arc length distance s is 3d, and t is 0.1 d.
FIG. 5 shows the flattening method for the front edge surface image of the rotating straight turbine blade, which includes the steps of firstly reading the gray image of the front edge surface by an image processing program, then identifying mark points 7, fitting a plurality of straight lines by using adjacent mark points 7, dividing the front edge region to be measured 4 into a plurality of trapezoid regions, flattening the trapezoid regions into rectangular regions with the same size by means of perspective transformation, splicing the rectangular regions together according to the relative position relationship to obtain the flattening result of the region surrounded by the mark points, and correspondingly, flattening the gray image of the front edge surface of the straight turbine blade.
Fig. 6 shows the image flattening result of the leading edge pending area 4 of the present example compared with the theoretical flattening geometry, and it can be seen from the figure that the positions and sizes of the air film holes 6 of the flattened image and the theoretical flattening geometry are substantially matched, thus illustrating the effectiveness of the method.
It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
The principles and embodiments of the present invention are explained herein using specific examples, which are presented only to assist in understanding the method and its core concepts of the present invention. It should be noted that there are no specific structures but rather a few limitations to the preferred embodiments of the present invention, and that many modifications, adaptations, and variations are possible and can be made by one skilled in the art without departing from the principles of the present invention; such modifications, variations, combinations, or adaptations of the invention using its spirit and scope, as defined by the claims, may be directed to other uses and embodiments.
Claims (10)
1. A surface image flattening method applied to the front edge of a straight blade of a rotating turbine is characterized by comprising the following steps: the method comprises the following steps:
step 1: selecting a turbine straight blade to be tested, designing mark point structures distributed at equal intervals on the front edge surface of the turbine straight blade, manufacturing the turbine straight blade through 3D printing processing, and using the turbine straight blade for a subsequent rotary experiment;
step 2: in the experiment process, the turbine straight blade to be tested is placed in a closed turbine experiment section and keeps rotating at a constant speed, and a camera fixed outside the turbine experiment section shoots the front edge surface of the turbine straight blade to be tested through an observation window on the turbine experiment section at a certain fixed frequency and stores the front edge surface as a gray image;
and step 3: and flattening the to-be-measured area of the gray image of the front edge surface of the straight turbine blade by using an image flattening method based on the mark points.
2. The method for flattening the surface image of the leading edge of the straight blade of the rotating turbine as claimed in claim 1, wherein: the front edge surface and the suction surface of the straight turbine blade are convex surfaces with curvatures, and the pressure surface of the straight turbine blade is a concave surface with curvatures.
3. The method for flattening the surface image of the leading edge of the straight blade of the rotating turbine as claimed in claim 1, wherein: the front edge surface of the straight turbine blade is provided with 2-5 rows of air film holes, and the arrangement direction of each row of holes is parallel to the blade height direction.
4. The method for flattening the surface image of the leading edge of the straight blade of the rotating turbine as claimed in claim 1, wherein: the straight blade front edge measuring device is characterized in that the number of the marking points is two, the marking points are respectively positioned at the upper end and the lower end of the front edge surface, the two rows of marking points are completely consistent in structural parameters except for the blade height position, the marking points are of circular pit structures, the intervals between adjacent marking points are the same, and the marking points completely surround the area to be measured of the straight blade front edge.
5. The method for flattening the surface image of the leading edge of the straight blade of the rotating turbine as claimed in claim 4, wherein: the cross section of the straight turbine blade is in an airfoil shape, the cross sections at the blade heights are completely consistent, the surface of the straight turbine blade is a cylindrical surface in a geometric sense, and the airfoil curve of the cross section is a directrix; the diameter of the mark point is d, the depth of the mark point is t, and the distance between adjacent arc lengths of the mark points in the same row is s.
6. The method for flattening the surface image of the leading edge of the straight blade of the rotating turbine as claimed in claim 5, wherein: the marker diameter d should be such that the marker occupies at least 5 pixels in the captured image to satisfy the requirement of the image processing program to identify the marker in the captured image.
7. The method for flattening the surface image of the leading edge of the straight blade of the rotating turbine as claimed in claim 5, wherein: the long arc distance s of the adjacent mark points is more than or equal to 2d, so that the requirement of an image processing program for distinguishing the adjacent mark points in the shot image is met.
8. The method for flattening the surface image of the leading edge of the straight blade of the rotating turbine as claimed in claim 5, wherein: the adjacent mark point arc long distance s should also satisfy the requirement of the unfolding precision sigma
And determining the value of the sigma according to the experimental precision, wherein R is the minimum curvature radius of the region to be measured of the front edge surface.
9. The method for flattening the surface image of the leading edge of the straight blade of the rotating turbine as claimed in claim 1, wherein: the step 3 further comprises the following steps:
step 31: firstly, reading a gray level image by using an image processing program to obtain a two-dimensional matrix corresponding to the gray level image
The dimensionality M and the dimensionality N of the matrix A are consistent with the resolution of the gray level image, the number a (i, j) of the matrix A is consistent with the gray level value of a pixel point corresponding to the gray level image, and the i and the j are called as the coordinates of elements in the matrix A;
step 32: the mark points are colored in advance and are distinguished from the surrounding surface, the image processing program is utilized to identify the coordinates P (x, y) of the center positions of the mark points in the matrix A, and a connected component within the connected domain analysis function () based on OpenCV2 is identified, the function identifies the connected region in a specific gray value range a (i, j) E [ b, c ] and obtains the coordinates, namely (x, y), of the center positions of the connected regions;
step 33: using the central coordinates P of four adjacent mark points1(x1，y2)～P4(x1，y2) Connecting to form a trapezoid area, transforming the trapezoid area into a rectangle with a specific size by perspective transformation, and designating new vertex coordinates of the rectangle as Q according to the actual geometric structure1(x1，y2)～Q4(x1，y2) The perspective transformation formula is
Wherein i and j are coordinates of corresponding pixels in the trapezoid area, u/w and v/w are coordinates corresponding to the pixels after perspective transformation, and transformation matrix
From the known vertices P of the trapezoid area1(x1，y2)～P4(x1，y2) And the transformed rectangle vertex Q1(x1，y2)～Q4(x1，y2) Calculating to obtain; after the transformation matrix H is obtained, the coordinates of other pixel points in the irregular rectangular area can be transformed; and sequentially transforming the trapezoid areas formed by other mark points according to the perspective transformation process, and finally splicing the rectangular areas together according to the relative position relationship to obtain the flattening result of the area surrounded by the mark points, wherein correspondingly, the gray image of the front edge surface of the straight turbine blade is flattened.
10. The method of flattening the surface image applied to the leading edge of a straight blade of a rotating turbine according to any one of claims 1 to 9 was applied to the test of the moving blade of a high-pressure turbine of an aircraft engine.
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