CN109726462B - Attack angle quick identification method suitable for wing profile - Google Patents
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- CN109726462B CN109726462B CN201811579375.2A CN201811579375A CN109726462B CN 109726462 B CN109726462 B CN 109726462B CN 201811579375 A CN201811579375 A CN 201811579375A CN 109726462 B CN109726462 B CN 109726462B
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Abstract
The invention discloses a method for quickly identifying an attack angle suitable for an airfoil, and belongs to the technical field of fluid mechanics experiments. The invention comprises the following steps: acquiring a flow field picture through a high-speed camera, performing gray level binarization processing on the flow field picture to acquire a gray level picture, establishing a coordinate system for the gray level picture, and establishing a data matrix for coordinates and gray levels of all pixel points in the gray level picture; identifying leading edge pixel points and trailing edge pixel points in the gray-scale picture according to wing-shaped leading edge and trailing edge judgment criteria, and respectively recording the leading edge pixel points and the trailing edge pixel points as A (x)1,y1)、B(x2,y2) (ii) a And calculating the airfoil attack angle according to the coordinates of the leading edge pixel points and the trailing edge pixel points. The airfoil angle of attack parameter identified by the steps refers to flow analysis and structural design in the field of water dynamics. The method can reduce the workload of identifying the airfoil attack angle and improve the accuracy of identifying the airfoil attack angle.
Description
Technical Field
The invention relates to a method for quickly identifying an attack angle suitable for an airfoil, and belongs to the technical field of hydrodynamics experiments.
Background
In the aerospace field, the dynamic characteristics of oscillating airfoils are receiving more and more attention in order to avoid dynamic stall, structural flutter and resonance. In the research of hydraulic machinery, the additional acting force generated by rotation and the disturbance of a moving part and a static part have important influences on the turbulent flow process, the development of a boundary layer and the space-time distribution of a flow structure, and the physical mechanism of mutual interference of flow fields of non-rotating/rotating parts is always the key point and the difficulty of research. In the transient processes of starting and stopping of a propeller, a turbine pump and a water turbine, runaway, load increase and decrease and the like, the effective attack angle of a lifting surface is changed due to transient flow in the transient process, and the internal flow is complex and changeable and presents strong instability. Therefore, the method has important significance for knowing the unsteady hydrodynamic load and the vibration change of the object under the dynamic change, knowing the unsteady flow mechanism and the dynamic characteristic in the transient process of the hydraulic machine, optimizing the design of the hydraulic machine and improving the hydraulic performance.
Hydrofoils are used as basic units of hydraulic mechanical structures, and research on the problem of flowing around a moving boundary is often used as a basic object. Experimental research is a basic method for searching physical mechanism, wherein the high-speed full flow field display technology is widely applied to the experimental measurement research of fluid. The working principle of the high-speed full-flow-field display technology is mainly to shoot the flow phenomenon by using a high-speed camera and perform qualitative and quantitative analysis on shot pictures. The previous research work on the flow around the hydrofoil is mostly carried out based on a static object, namely the attack angle of the airfoil profile is fixed and invariable; however, the problem that the hydrofoil attack angle changes at any moment in the high-speed full flow field of the moving boundary circumfluence is shown, and the determination of the hydrofoil attack angle is very important in order to analyze the unsteady flow field and the change of hydrodynamic load under dynamic change. However, at present, no mature technical method exists for accurately identifying the attack angle of the hydrofoil, and a rough measurement method is mostly adopted for pictures manually, so that the workload is large and the error is large; therefore, the invention provides a method for rapidly identifying the attack angle of the airfoil profile.
Disclosure of Invention
In order to solve the problems of large workload and inaccurate precision of identifying the angle of attack of the airfoil profile in the prior art, the invention discloses a method for quickly identifying the angle of attack of the airfoil profile, which aims to solve the technical problems that: the workload of identifying the airfoil attack angle is reduced, and the accuracy of identifying the airfoil attack angle is improved.
The purpose of the invention is realized by the following technical scheme.
The invention discloses a method for quickly identifying an attack angle suitable for an airfoil profile, which comprises the following steps of: acquiring a flow field picture through a high-speed camera, performing gray level binarization processing on the flow field picture to acquire a gray level picture, establishing a coordinate system for the gray level picture, and establishing a data matrix for coordinates and gray levels of all pixel points in the gray level picture; identifying leading edge pixel points and trailing edge pixel points in the gray-scale picture according to wing type leading edge and trailing edge judgment criteria, and enabling the leading edge pixel points and the trailing edge pixel pointsAre respectively denoted as A (x)1,y1)、B(x2,y2) (ii) a And calculating an airfoil attack angle according to the coordinates of the leading edge pixel points and the trailing edge pixel points, wherein the airfoil attack angle is recorded as alpha.
The invention discloses a method for quickly identifying an attack angle suitable for an airfoil profile, which further comprises the following steps: the airfoil angle of attack parameter identified by the steps refers to flow analysis and structural design in the field of water dynamics.
According to the airfoil attack angle parameters identified in the steps, the variation range of the airfoil attack angle can be obtained, the corresponding airfoil flow field structure under each attack angle is further observed, whether the dynamic characteristics of the airfoil meet the technical requirements or not is analyzed, and the optimization design of the engineering structure can be guided. In addition, the obtained airfoil angle of attack parameter can provide powerful support for the application in the aspects of health monitoring, structural fault diagnosis, structural vibration control and the like under dynamic change, and has wide application prospect and benefit.
Preferably, in order to improve the contrast of the gray value, the background color is preset to be a color with a small corresponding gray value, and the airfoil color in the flow field picture is preset to be a color with a large corresponding gray value. The gray value difference range with the best contrast effect is as follows, wherein the gray value little finger gray threshold is 140, the gray value big finger gray threshold is 210: 70-200.
Further preferably, the background color of the flow field picture is preset to be dark red, and the corresponding gray value is 130, and the airfoil color in the flow field picture is bright yellow, and corresponds to the gray value 215.
Preferably, the threshold value of the binarization processing of the flow field picture is 150-200.
Preferentially, the determination criterion of the leading edge pixel and the trailing edge pixel is that the gray value of the pixel is 255, the pixel with the minimum X coordinate value is the leading edge pixel, and the pixel with the maximum X coordinate value is the trailing edge pixel.
Further preferably, the wing section judgment criterion is
y＝1E-6x5-0.0001x4+0.0044x3-0.0861x2+0.8206x+0.2172,(x>0)；
y＝6E-8x6-7E-6x5+0.0003x4-0.0074x3+0.0863x2-0.4422x-0.3151,(x<0)。
If the pixel point coordinates (x, y) satisfy the above formula, the boundary is the airfoil.
Preferably, the airfoil angle of attack calculation formula is α ═ β arctan ((y)2-y1)/(x2-x1) And beta is a pixel point correction coefficient.
Further preferably, the value range of the pixel point correction coefficient is 0.95-1.
Has the advantages that:
1. according to the attack angle quick identification method suitable for the wing type, the flow field picture is obtained through the high-speed camera to carry out gray level processing, the pixel points of the leading edge and the pixel points of the trailing edge of the hydrofoil are identified, the quick calculation of the wing type attack angle is further realized, the working efficiency can be obviously improved, and the attack angle measurement precision is high.
2. The invention discloses a method for quickly identifying an attack angle suitable for an airfoil shape. The gray value difference range with the best contrast effect is 70-200, wherein the gray value small-index gray threshold is 140, the gray value large-index gray threshold is 210; the gray contrast effect can be remarkably improved.
3. The invention discloses a method for quickly identifying an attack angle of an airfoil profile, which provides an airfoil profile judgment formula through experimental induction and theoretical processing, further judges the airfoil profile on the basis of judging a front edge and a tail edge, and improves the judgment efficiency.
4. The invention discloses a method for quickly identifying an attack angle of an airfoil, which provides a quick calculation and correction formula of the attack angle through experimental induction and theoretical processing, and improves the identification precision.
5. The method for quickly identifying the attack angle of the airfoil profile, disclosed by the invention, is suitable for measuring the airfoil profile angle in various dynamic boundary streaming without influencing the experimental process by acquiring the flow field picture through the long-distance high-speed camera.
6. The invention discloses a method for quickly identifying an attack angle of an airfoil, which is applicable to the identification of the attack angle parameters of the airfoil in the steps, can obtain the change range of the attack angle of the airfoil, further observe the corresponding flow field structure of the airfoil under each attack angle, analyze whether the dynamic characteristics of the airfoil meet the technical requirements or not, and can guide the optimization design of the engineering structure. In addition, the obtained airfoil angle of attack parameter can provide powerful support for the application in the aspects of health monitoring, structural fault diagnosis, structural vibration control and the like under dynamic change, and has wide application prospect and benefit.
Drawings
FIG. 1 is a flow chart of a method for rapidly identifying an angle of attack for an airfoil according to the present disclosure;
FIG. 2 is a flow chart of the determination and identification of the airfoil leading edge pixel point and the trailing edge pixel point of the fast identification method for the angle of attack of the airfoil, which is disclosed by the invention;
fig. 3 is a schematic view of an airfoil angle of attack calculation suitable for a method for rapidly identifying an angle of attack of an airfoil, which is disclosed by the invention.
Detailed Description
The following describes embodiments of the present invention in detail with reference to the accompanying drawings.
Example 1
As shown in fig. 1, 2, and 3, in the method for rapidly identifying an attack angle applicable to an airfoil profile disclosed in the present embodiment, a flow field picture is obtained by a high-speed camera, a gray level binarization process is performed on the flow field picture to obtain a gray level picture, a coordinate system is established for the gray level picture, and a data matrix is established for coordinates and gray levels of each pixel point in the gray level picture; identifying leading edge pixel points and trailing edge pixel points in the gray-scale picture according to the wing-shaped leading edge and trailing edge judgment criteria, and respectively recording the leading edge pixel points and the trailing edge pixel points as A (x)1,y1)、B(x2,y2) (ii) a And calculating an airfoil attack angle according to the coordinates of the leading edge pixel points and the trailing edge pixel points, and recording the airfoil attack angle as alpha. The background color of the flow field picture is preset to be dark red, the corresponding gray value is 130, and the airfoil profile in the flow field pictureThe color is bright yellow, corresponding to a gray value of 215.
And the threshold value of the binarization processing of the flow field picture is 150-200.
As shown in fig. 2, the determination criterion of the leading edge pixel and the trailing edge pixel is that the gray value of the pixel is 255, the pixel with the minimum X coordinate value is the leading edge pixel, and the pixel with the maximum X coordinate value is the trailing edge pixel.
As shown in FIG. 3, the airfoil determination criteria is
y＝1E-6x5-0.0001x4+0.0044x3-0.0861x2+0.8206x+0.2172,(x>0)；
y＝6E-8x6-7E-6x5+0.0003x4-0.0074x3+0.0863x2-0.4422x-0.3151,(x<0)。
The formula for calculating the angle of attack of the airfoil is alpha ═ beta arctan ((y)2-y1)/(x2-x1) Beta is a pixel point correction coefficient, and the value range of the pixel point correction coefficient is 0.95-1.
As shown in fig. 1, 2, and 3, in the method for quickly identifying an attack angle applicable to an airfoil shape disclosed in the present embodiment, a background of a flow field is first painted with dark red, corresponding to a gray value of 130, and the airfoil shape is painted with bright yellow, corresponding to a gray value of 215, and then a picture of the flow field is obtained by a high-speed camera; carrying out gray level binarization processing on the flow field picture to obtain a gray level picture, wherein the threshold value of the binarization processing of the flow field picture is 160; then establishing a coordinate system XOY for the gray-scale picture, and establishing a data matrix for the coordinates and gray values of all pixel points in the gray-scale picture; because the color of the wing profile is bright yellow, all the wing profiles in the gray level picture are white, namely the gray level value is 255; under the condition of ensuring that the gray value is 255, the pixel point with the minimum X coordinate value is the leading edge pixel point A (X)1,y1) The pixel point with the maximum X coordinate value is the tail edge pixel point B (X)2,y2). Connecting leading and trailing edge pixels A (x)1,y1)、B(x2,y2) Namely the chord length of the wing profile; the attack angle of the airfoil is defined as the included angle between the chord length of the airfoil and the incoming flow direction, and the incoming flow direction is the X direction; therefore, according to the front and rear edge pixel point A (x)1,y1)、B(x2,y2) The coordinate value can calculate the attack angle of the airfoil, and the calculation formula of the airfoil attack angle is alpha-beta-arctan ((y)2-y1)/(x2-x1) Pixel correction coefficient takes on the value of 0.98.
Further, establishing a coordinate system by taking the leading edge pixel point A as an origin, and identifying the boundary of the airfoil according to an airfoil judgment criterion, wherein the airfoil judgment criterion is
y＝1E-6x5-0.0001x4+0.0044x3-0.0861x2+0.8206x+0.2172,(x>0)；
y＝6E-8x6-7E-6x5+0.0003x4-0.0074x3+0.0863x2-0.4422x-0.3151,(x<0)。
If the pixel point coordinates meet the formula, the boundary is the wing section.
The airfoil angle of attack parameter identified by the steps can indicate flow analysis and structural design in the field of water dynamics.
According to the airfoil attack angle parameters identified in the steps, the variation range of the airfoil attack angle can be obtained, the corresponding airfoil flow field structure under each attack angle is further observed, whether the dynamic characteristics of the airfoil meet the technical requirements or not is analyzed, and the optimization design of the engineering structure can be guided. In addition, the obtained airfoil angle of attack parameter can provide powerful support for the application in the aspects of health monitoring, structural fault diagnosis, structural vibration control and the like under dynamic change, and has wide application prospect and benefit.
The above detailed description is intended to illustrate the objects, aspects and advantages of the present invention, and it should be understood that the above detailed description is only exemplary of the present invention and is not intended to limit the scope of the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (4)
1. A method for quickly identifying an attack angle suitable for an airfoil is characterized by comprising the following steps: the method comprises the following steps: obtaining flow field pictures by high speed cameraCarrying out gray level binarization processing on the flow field picture to obtain a gray level picture, establishing a coordinate system for the gray level picture, and establishing a data matrix for coordinates and gray levels of all pixel points in the gray level picture; identifying leading edge pixel points and trailing edge pixel points in the gray-scale picture according to wing-shaped leading edge and trailing edge judgment criteria, and respectively recording the leading edge pixel points and the trailing edge pixel points as A (x)1,y1)、B(x2,y2) (ii) a Calculating an airfoil attack angle according to the coordinates of the leading edge pixel points and the trailing edge pixel points, wherein the airfoil attack angle is marked as alpha;
the method also comprises the following steps of carrying out flow analysis and structural design in the hydrodynamic field by applying the airfoil angle of attack parameter identified in the steps;
according to the airfoil attack angle parameters identified in the steps, the variation range of the airfoil attack angle can be obtained, the corresponding airfoil flow field structure under each attack angle is further observed, whether the dynamic characteristics borne by the airfoil meet the technical requirements or not is analyzed, and the optimization design of the engineering structure can be carried out; the obtained airfoil angle of attack parameter can also provide powerful support for the application of health monitoring, structural fault diagnosis and structural vibration control under dynamic change, and has wide application prospect and benefit;
the judgment criterion of the leading edge pixel and the trailing edge pixel is that the gray value of the pixel is 255, the pixel with the minimum X coordinate value is the leading edge pixel, and the pixel with the maximum X coordinate value is the trailing edge pixel;
the wing profile judgment criterion is
y＝1E-6x5-0.0001x4+0.0044x3-0.0861x2+0.8206x+0.2172,(x>0)；
y＝6E-8x6-7E-6x5+0.0003x4-0.0074x3+0.0863x2-0.4422x-0.3151,(x<0)；
If the pixel point coordinates (x, y) meet the formula, the boundary is the wing section boundary;
the airfoil attack angle calculation formula is alpha ═ beta ═ arctan ((y)2-y1)/(x2-x1) β) is a pixel point correction coefficient;
and the value range of the pixel point correction coefficient is 0.95-1.
2. The method for rapidly identifying the angle of attack of the airfoil as claimed in claim 1, wherein: presetting a background color as a color with a small corresponding gray value, and presetting an airfoil color in the flow field picture as a color with a large corresponding gray value; the gray value difference range with the best contrast effect is as follows, wherein the gray value little finger gray threshold is 140, the gray value big finger gray threshold is 210: 70-200.
3. The method for rapidly identifying the angle of attack of the airfoil as claimed in claim 2, wherein: the background color of the flow field picture is preset to be dark red, the corresponding gray value is 130, and the airfoil color in the flow field picture is bright yellow, and corresponds to the gray value 215.
4. The method for rapidly identifying the angle of attack of the airfoil as claimed in claim 2, wherein: and the threshold value of the binarization processing of the flow field picture is 150-200.
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