Method for measuring geometric quantity of blade

Abstract

The invention discloses a blade geometric quantity measuring method, which belongs to a blade detection method and comprises the following steps of: planning a to-be-measured point of a blade, extracting geometric quantity dimensions of a chord line and a chord line angle and extracting the maximum thickness of a blade section. According to the method for measuring the geometric quantity of the blade, the to-be-measured point of the blade can be planned, the geometric quantity dimensions of the chord line and the chord line angle and the maximum thickness of the section of the blade can be extracted, the planning of the to-be-measured point of the blade is based on a curve segmentation and vertical distance method, and fitting precision and measurement efficiency requirements are comprehensively considered; the algorithm related to extraction of the chord line, the chord line angle and the maximum thickness of the blade section is relatively simple, the extraction precision is relatively high, writing is easy, the operation speed is high, and the precision and efficiency of geometric quantity measurement of the blade are improved.

Description

Technical Field

[0001] The invention relates to a blade detection method, and in particular to a blade geometric measurement method. Background Art

[0002] The aviation industry, as a vital component of a nation's manufacturing sector and a representative of high-tech industries, represents a country's strength in high-end manufacturing, possessing a high strategic position and technological content. As core components of an engine, the performance of aircraft engine blades impacts engine efficiency, reliability, and safety. Blade manufacturing quality and geometric parameters (dimensional accuracy, form and position tolerances, and surface quality of complex surfaces) directly impact the engine's aerodynamic performance and service life. For example, blade profile error significantly affects the flow field structure near the blade surface. Large blade profile errors can lead to premature boundary layer separation on the blade back. For supersonic blades, large blade profile errors can exacerbate shock waves. Blades deflect airflow, performing work on the airflow. If the chord length is too short, the compressor rotor cannot fully deflect the airflow, leading to a large separation zone on the blade back. This not only increases aerodynamic performance but also prevents the compressor from meeting its design load. If the chord length is too long, boundary layer friction losses increase, reducing compressor efficiency. Therefore, if there are large errors in the blade manufacturing process, the final processing state of the blade will deviate significantly from the design requirements, affecting the actual application performance of the aircraft engine. Therefore, the rapid and accurate measurement of blade geometry is of great significance to blade manufacturing and product qualification evaluation. Summary of the Invention

[0003] In view of the above problems, the present invention aims to provide a blade geometry measurement method to improve the accuracy and efficiency of blade geometry measurement.

[0004] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is as follows:

[0005] A method for measuring blade geometry is provided, comprising the steps of:

[0006] S1. Planning of test points on the blade: For the theoretical model of the blade, based on the curvature characteristics of the blade cross-section curve, the curvature of discrete points on the curve is calculated and the second-order derivative of the curvature is taken to obtain the inflection points. The blade cross-section curve is divided into four parts: the leading edge, the back of the blade, the trailing edge, and the blade basin. For each part of the curve, the characteristic points of each section are obtained using the vertical distance method as the test points.

[0007] S2. Extracting geometric dimensions of the chord and chord angle: Based on the theoretical model of the blade, obtain the blade airfoil cross-sectional curve data, perform least squares linear fitting on the scattered points on the blade airfoil cross-sectional curve to obtain a straight line L1 with a slope of k, find points A and B on the upper and lower parts of the blade airfoil cross-sectional curve, where the scattered points are farthest from the straight line L1, respectively, and connect point A and point B to obtain a straight line L2; obtain a set P of blade profile scattered points that are simultaneously lower than or higher than the straight lines L1 and L2; the point in the blade profile scattered point set P whose slope of the straight line formed by point A is closest to the slope k is the other endpoint C of the desired chord; the angle between the chord and the horizontal plane is the chord angle;

[0008] S3. Extraction of the maximum thickness of the blade cross section: obtaining the maximum inscribed circle within the blade cross section curve, where the diameter of the maximum inscribed circle is the maximum thickness of the blade cross section.

[0009] Furthermore, in step S1, the perpendicular distance method is a threshold-controlled method for finding characteristic points of a curve. For an ordered curve, a chord is continuously connected with subsequent points starting from the starting point, and then the distance from the point set between the starting point and the end point to the chord is calculated as the perpendicular distance, until the maximum perpendicular distance is greater than a given threshold, the point meets the requirements and is output as a characteristic point, and then the end point is used as the starting point to continue to find the next characteristic point until the point set on the curve is calculated.

[0010] Furthermore, in the perpendicular distance method, the maximum perpendicular distance is to use the line connecting the starting point and the final point of the feature point curve to be sought as the chord, and then calculate the distance from the point set between the starting point and the final point to the chord, where the maximum distance is the maximum perpendicular distance; the minimum perpendicular distance is to calculate the distance from each point in the point set between the starting point and the final point of the feature point curve to the chord formed by connecting its left and right points, where the minimum value of all distances is the minimum perpendicular distance, and the given threshold is half of the sum of the maximum perpendicular distance and the minimum perpendicular distance.

[0011] Furthermore, in step S2, the calculation formula of the other endpoint C is:

[0012]

[0013] Among them, x i and y i are the horizontal and vertical coordinate points of the other endpoint C respectively; A and x A are the horizontal and vertical coordinate points of point A, k is the slope of straight line L1; P is the scattered point set of the blade surface.

[0014] Preferably, when the scattered points on the blade body cross-section curve are densely distributed, the calculation formula of the other endpoint C is:

[0015]

[0016] Among them, x i and y i are the horizontal and vertical coordinate points of the other endpoint C respectively; A and x A are the horizontal and vertical coordinate points of point A, k is the slope of line L1; P is the scattered point set of the blade surface; sigmod is the activation function, that is:

[0017]

[0018] When the scattered points on the blade cross-section curve are densely distributed, the solution is often disturbed by the point set near point A and an incorrect chord is obtained. Therefore, an activation function sigmoid function is added, where The distance d-[(y A -y i ) 2 +(x A -x i ) 2 ] is introduced into the activation function as an independent variable to reduce the interference of points near point A in the point set P. When (x A ,y A ) is a point near point A, d is approximately 0, and the activation function is used as a classification function, and its value change near x = 0 is more sensitive. Therefore, in the process of solving the chord, the interference of the points near A can be eliminated without affecting other points. This can specifically prevent the misunderstanding of the solution of the chord by the points near point A when the surface point set is too dense.

[0019] Furthermore, in step S3, the method for obtaining the maximum inscribed circle within the blade cross-section curve includes:

[0020] Step S3.1, obtain the blade's mean camber line: uniformly draw straight lines parallel to the y-axis within the x-axis range of the curve, then find the maximum inscribed circle of the blade's cross-sectional curve on each straight line. Then, fit all the obtained circle center points to a curve using a cubic equation, i.e., the blade's mean camber line.

[0021] Step S3.2: Set the initial value x0 and the step size Δx. The calculation formula for the initial value x0 is:

[0022]

[0023] Among them, x min and x max are the horizontal coordinates of the two end points of the arc line in the blade profile;

[0024] Step S3.3, find the maximum inscribed circle within the blade cross-section curve at the arc point x=x0 in the blade profile, then move the step size Δx to find the maximum inscribed circle at the arc point x=x0+Δx in the blade profile, and compare the two maximum inscribed circle diameters. If the diameter becomes larger, continue moving until it becomes smaller. The maximum inscribed circle diameter before the diameter becomes smaller is the maximum thickness. Otherwise, if the diameter becomes smaller, reverse the direction.

[0025] The beneficial effects of the present invention are as follows: a blade geometry measurement method of the present invention can plan the blade points to be measured, extract the geometric dimensions of the chord and the chord angle, and extract the maximum thickness of the blade section, wherein the planning of the blade points to be measured is based on the curve segmentation and perpendicular distance method, and comprehensively considers the fitting accuracy and measurement efficiency requirements; the algorithm involved in extracting the geometric dimensions of the chord and the chord angle and the maximum thickness of the blade section is relatively simple, has high extraction accuracy, is easy to write, and has a fast running speed, thereby improving the accuracy and efficiency of blade geometry measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The figure is a flow chart of a blade geometry measurement method.

[0027] Figure 2 This is a flow chart of the principle of dividing the blade cross-section curve in a blade geometry measurement method.

[0028] Figure 3 Schematic diagram of the principle of the vertical distance method.

[0029] Figure 4 This is the algorithm flow chart of the vertical distance method.

[0030] Figure 5 Schematic diagram of the principle of extracting the geometric dimensions of the chord line and chord angle in a blade geometry measurement method.

[0031] Figure 6 Schematic diagram of the blade's median arc.

[0032] Figure 7 Schematic diagram of the principle of extracting the maximum thickness of a blade cross section in a blade geometry measurement method. DETAILED DESCRIPTION

[0033] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concepts of the present invention are protected.

[0034] like Figure 1As shown, the present invention provides a blade geometry measurement method, characterized in that it includes the steps of:

[0035] S1. Planning of the test points of the blade: For the theoretical model of the blade, according to the curvature characteristics of the blade cross-section curve, the curvature of the discrete points on the curve is calculated and the second-order derivative of the curvature is obtained to obtain the inflection point, and the blade cross-section curve is divided into four parts: the leading edge, the back of the blade, the trailing edge, and the blade basin. Specifically, in the process of planning the test points of the blade cross-section curve of the theoretical model of the blade, first, the first-order and second-order derivatives of the theoretical cross-section curve equation f(x, y) = 0 are taken: f x +f y y′=0,f xx +2f xy y′+f yy ·(y′) 2 +f y y″=0

[0036] Solve for y′ and y″, and then find the curvature The second-order derivative is set to zero to obtain segmentation points to divide the blade cross-section curve into the leading edge, blade back, trailing edge, and blade basin.

[0037] For each part of the curve, the characteristic points of each curve segment are obtained as the test points by the vertical distance method. Specifically, Figures 2 to 4 As shown, the perpendicular distance method is a threshold-controlled method for finding characteristic points of a curve. For an ordered curve, a chord is formed by continuously connecting the subsequent points from the starting point, and then the distance from the point set between the starting point and the end point to the chord is calculated as the perpendicular distance. When the maximum perpendicular distance is greater than a given threshold, the point meets the requirement and is output as a characteristic point. Then, the end point is used as the starting point to continue to find the next characteristic point until the point set on the curve is calculated.

[0038] In the vertical distance method, the maximum vertical distance dmax is to use the line connecting the starting point and the final point of the feature point curve as the chord, and then calculate the distance between the point set between the starting point and the final point and the chord, where the maximum distance is the maximum vertical distance dmax; the given threshold d T It is half of the sum of the maximum perpendicular distance dmax and the minimum perpendicular distance dmin; the minimum perpendicular distance dmin is the distance from each point in the point set between the starting point and the final point of the characteristic point curve to the chord formed by connecting the two points on its left and right, where the minimum value of all distances is the minimum perpendicular distance dmin.

[0039] S2. Extraction of geometric dimensions of chord and chord angle: Figure 5As shown, according to the theoretical model of the blade, the blade airfoil cross-sectional curve data is obtained, and the scattered points on the blade airfoil cross-sectional curve are fitted with the least squares straight line to obtain the straight line L1 with a slope of k. Points A and B, where the scattered points are farthest from the straight line L1, are found in the upper and lower parts of the blade airfoil cross-sectional curve respectively. Points A and B are connected to obtain the straight line L2. A blade profile scattered point set P that is simultaneously lower than or higher than the straight lines L1 and L2 is obtained. The point in the blade profile scattered point set P whose slope of the straight line formed by point A is closest to the slope k is the other endpoint C of the desired chord. The angle between the chord and the horizontal plane is the chord angle.

[0040] Specifically, when the scattered points on the blade body cross-section curve are not densely distributed, the calculation formula of the other endpoint C is:

[0041]

[0042] Among them, x i and y i are the horizontal and vertical coordinate points of the other endpoint C respectively; A and x A are the horizontal and vertical coordinate points of point A, k is the slope of straight line L1; P is the scattered point set of the blade surface.

[0043] When the scattered points on the blade section curve are densely distributed, the calculation formula of the other endpoint C is:

[0044]

[0045] Among them, x i and y i are the horizontal and vertical coordinate points of the other endpoint C respectively; A and x A are the horizontal and vertical coordinate points of point A, k is the slope of line L1; P is the scattered point set of the blade surface; sigmod is the activation function, that is:

[0046]

[0047] When the scattered points on the blade cross-section curve are densely distributed, the solution is often disturbed by the point set near point A and an incorrect chord is obtained. Therefore, an activation function sigmoid function is added, where The distance d-[(y A -y l ) 2 +(x A -x l ) 2 ] is introduced into the activation function as an independent variable to reduce the interference of points near point A in the point set P. When (x A ,y A) is a point near point A, d is approximately 0, and the activation function is a common classification function, and its value change near x = 0 is more sensitive. Therefore, in the process of solving the chord, the interference of the points near A can be excluded without affecting other points. This can specifically prevent the misunderstanding of the solution of the chord by the points near point A when the surface point set is too dense.

[0048] S3. Extraction of the maximum thickness of the blade cross section: Obtain the maximum inscribed circle Cmax within the blade cross section curve. The diameter of the maximum inscribed circle Cmax is the maximum thickness of the blade cross section. Specifically, Figure 6 and Figure 7 As shown, the method for obtaining the maximum inscribed circle within the blade cross-section curve includes:

[0049] Step S3.1, obtain the blade's mean camber line: uniformly draw straight lines parallel to the y-axis within the x-axis range of the curve, then find the maximum inscribed circle Cmax of the blade's cross-sectional curve on each straight line. Then, fit all the obtained circle center points to a curve using a cubic equation, i.e., the blade's mean camber line.

[0050] Step S3.2: Set the initial value x0 and the step size Δx. The calculation formula for the initial value x0 is:

[0051]

[0052] Among them, x min and x max are the horizontal coordinates of the two end points of the arc line in the blade profile;

[0053] Step S3.3, find the maximum inscribed circle Cmax within the blade cross-section curve at the arc point x=x0 in the blade profile, then move the step size Δx to find the maximum inscribed circle at the arc point x=x0+Δx in the blade profile, and compare the two maximum inscribed circle diameters. If the diameter becomes larger, continue moving until it becomes smaller. The maximum inscribed circle diameter Cmax before the diameter becomes smaller is the maximum thickness. Otherwise, if the diameter becomes smaller, reverse the process.

[0054] In summary, the blade geometry measurement method of the present invention can plan the blade points to be measured, extract the geometric dimensions of the chord and the chord angle, and extract the maximum thickness of the blade section, wherein the planning of the blade points to be measured is based on the curve segmentation and perpendicular distance method, and comprehensively considers the fitting accuracy and measurement efficiency requirements; the algorithm involved in extracting the geometric dimensions of the chord and the chord angle and the maximum thickness of the blade section is relatively simple, has high extraction accuracy, is easy to write, and runs fast, thereby improving the accuracy and efficiency of blade geometry measurement.

Claims

1. A blade geometry measurement method, characterized in that: Including steps: S1. Planning of test points on the blade: For the theoretical model of the blade, based on the curvature characteristics of the blade cross-section curve, the curvature of discrete points on the curve is calculated and the second-order derivative of the curvature is taken to obtain the inflection points. The blade cross-section curve is divided into four parts: the leading edge, the back of the blade, the trailing edge, and the blade basin. For each part of the curve, the characteristic points of each section are obtained using the vertical distance method as the test points. S2. Extracting geometric dimensions of the chord and chord angle: Based on the theoretical model of the blade, obtain the blade airfoil cross-sectional curve data, perform least squares linear fitting on the scattered points on the blade airfoil cross-sectional curve to obtain a straight line L1 with a slope of k, find points A and B on the upper and lower parts of the blade airfoil cross-sectional curve, where the scattered points are farthest from the straight line L1, respectively, and connect point A and point B to obtain a straight line L2; obtain a set P of blade profile scattered points that are simultaneously lower than or higher than the straight lines L1 and L2; the point in the blade profile scattered point set P whose slope of the straight line formed by point A is closest to the slope k is the other endpoint C of the desired chord; the angle between the chord and the horizontal plane is the chord angle; S3. Extraction of the maximum thickness of the blade cross section: obtaining the maximum inscribed circle within the blade cross section curve, where the diameter of the maximum inscribed circle is the maximum thickness of the blade cross section.

2. The blade geometry measurement method according to claim 1, characterized in that: In step S1, the perpendicular distance method is a threshold-controlled method for finding characteristic points of a curve. For an ordered curve, a chord is formed by continuously connecting the subsequent points starting from the starting point, and then the distance from the point set between the starting point and the end point to the chord is calculated as the perpendicular distance. When the maximum perpendicular distance is greater than a given threshold, the point meets the requirement and is output as a characteristic point. Then, the end point is used as the starting point to continue to find the next characteristic point until the point set on the curve is calculated.

3. The blade geometry measurement method according to claim 2, characterized in that: In the perpendicular distance method, the maximum perpendicular distance is to use the line connecting the starting point and the final point of the characteristic point curve as the chord, and then calculate the distance between the point set between the starting point and the final point and the chord, where the maximum distance is the maximum perpendicular distance; The minimum perpendicular distance is the distance from each point in the point set between the starting point and the final point of the feature point curve to the chord formed by connecting the two points on its left and right, where the minimum value of all distances is the minimum perpendicular distance; the given threshold is half of the sum of the maximum perpendicular distance and the minimum perpendicular distance.

4. The blade geometry measurement method according to claim 1, characterized in that: In step S2, the calculation formula of the other endpoint C is: Among them, x i and y i are the horizontal and vertical coordinate points of the other endpoint C respectively; A and x A are the horizontal and vertical coordinate points of point A, k is the slope of straight line L1; P is the scattered point set of the blade surface.

5. The blade geometry measurement method according to claim 1, characterized in that: In step S2, when the scattered points on the blade body cross-section curve are densely distributed, the calculation formula of the other endpoint C is: Among them, x i and y i are the horizontal and vertical coordinate points of the other endpoint C respectively; A and x A are the horizontal and vertical coordinate points of point A, k is the slope of line L1; P is the scattered point set of the blade surface; sigmod is the activation function.

6. The blade geometry measurement method according to claim 1, characterized in that: In step S3, the method for obtaining the maximum inscribed circle within the blade cross-section curve includes: Step S3.1, obtain the blade's mean camber line: uniformly draw straight lines parallel to the y-axis within the x-axis range of the curve, then find the maximum inscribed circle of the blade's cross-sectional curve on each straight line. Then, fit all the obtained circle center points to a curve using a cubic equation, i.e., the blade's mean camber line. Step S3.2: Set the initial value x0 and the step size Δx. The calculation formula for the initial value x0 is: Among them, x min and x max are the horizontal coordinates of the two end points of the arc line in the blade profile; Step S3.3, find the maximum inscribed circle within the blade cross-section curve at the arc point x=x0 in the blade profile, then move the step size Δx to find the maximum inscribed circle at the arc point x=x0+Δx in the blade profile, and compare the two maximum inscribed circle diameters. If the diameter becomes larger, continue moving until it becomes smaller. The maximum inscribed circle diameter before the diameter becomes smaller is the maximum thickness. Otherwise, if the diameter becomes smaller, reverse the direction.

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