CN-121364054-B - Fluorescent microfilament dynamic flow spectrum separation and attached flow quantitative interpretation method

CN121364054BCN 121364054 BCN121364054 BCN 121364054BCN-121364054-B

Abstract

The application discloses a method for separating and quantitatively judging attached flow of a fluorescent microfilament dynamic flow spectrum, which aims to solve the problems of low judging precision and poor result repeatability caused by the fact that the conventional method for displaying the fluorescent microfilament dynamic flow spectrum mainly depends on subjective experience and qualitative observation of operators. The method comprises the following steps of S01, preprocessing a fluorescent microwire image acquired through experiments, S02, calculating position coordinates of the fluorescent microwire image, S03, calculating deflection angles of the fluorescent microwires, generating an angle value set, S04, judging flowing states existing in the fluorescent microwire serial number image, S05, dividing separating and attaching flow boundaries in the fluorescent microwire serial number image, S06, recording and storing the judging flowing states and boundary dividing processes. The application utilizes the physical and mathematical significance of the bimodal coefficient to provide quantitative criteria of the attached flow and the separated flow, and realizes the dynamic tracking of the evolution process by distinguishing the transient flow structure, thereby being beneficial to solving the problem that the unsteady flow field structure is difficult to identify.

Inventors

QI BIN
LI GUOSHUAI
Yang Lejie
LIU GUANGYUAN
PENG XIN
LIU DAWEI
CHEN ZHI
Song Xinshi
WANG ZHENQIANG

Assignees

中国空气动力研究与发展中心高速空气动力研究所

Dates

Publication Date: 20260512
Application Date: 20251223

Claims (8)

1. The method for quantitatively judging the fluorescence microfilament dynamic flow spectrum separation and attached flow is characterized by comprising the following steps of: S01, preprocessing a fluorescent microwire image acquired through experiments, and storing the preprocessed fluorescent microwire image to obtain a fluorescent microwire preprocessed image; S02, partitioning and numbering each fluorescent microwire in the fluorescent microwire pretreatment image, and calculating the position coordinates of each fluorescent microwire to obtain a fluorescent microwire numbering image; S03, calculating the deflection angle of each fluorescent microfilament according to the position coordinate and the number of each fluorescent microfilament in the fluorescent microfilament numbering image, and generating an angle value set, wherein the angle value set comprises the number, the position coordinate and the specific value of the deflection angle of each fluorescent microfilament; s04, judging the flow state existing in the fluorescent microfilament numbered image based on the angle value set, wherein the flow state comprises an attached flow, a separated flow and a mixed flow, and the mixed flow means that the attached flow and the separated flow exist at the same time; S05, dividing the boundary between the separation and attachment flows in the fluorescent microfilament numbered image according to the angular polar coordinate distribution diagram and the size of the double-peak coefficient; s06, recording and storing the judgment flow state and the boundary dividing process.
2. The method according to claim 1, wherein in the step S01, the gray-scale, binarization and noise reduction treatment are sequentially performed on the fluorescent microwire image obtained by the experiment, and the fluorescent microwire preprocessed image is stored.
3. The method according to claim 2, wherein in the step S01, the graying process is performed by obtaining R value, G value, and B value based on RGB three channels of each pixel point in the fluorescent microfilament image obtained by experimental collection, and calculating Gray value Gray of the corresponding pixel point by using formula gray=0.299 r+0.587g+0.114B; The binarization processing is carried out by adopting a local self-adaptive threshold value average method; after the binarization processing is finished, detecting the direction of the fluorescent microfilaments by using the Hessian matrix eigenvector, keeping the gray value change smooth along the direction from the fixed end to the free end of the fluorescent microfilaments, keeping the gray value change sharp in the direction perpendicular to the fluorescent microfilaments, finishing the noise reduction processing, and storing to obtain a fluorescent microfilament pretreatment image.
4. The method according to claim 3, wherein in the step S01, the binarization process is performed by calculating an average value mean (x, y) of all pixels in the neighborhood around each pixel after the completion of the Gray level process, then the local threshold value T (x, y) =mean (x, y) -C of the pixel, and comparing the Gray value Gray (x, y) of the pixel with T (x, y), if Gray (x, y) is not less than T (x, y), then the Gray value Gray (x, y) =255, and if Gray (x, y) < T (x, y), then the Gray value Gray (x, y) =0; Wherein x is the abscissa of the pixel point, y is the ordinate of the pixel point, mean (x, y) is the average value of all pixel gray levels in the neighborhood around a single pixel point, T (x, y) is the local threshold of the pixel point, and C is a constant.
5. The method according to claim 1, wherein in the step S02, the end point coordinates (x 1, y 1) of the fixed end and the end point coordinates (x 2, y 2) of the free end of each fluorescent microfilament are obtained according to the position coordinates of each fluorescent microfilament, the direction vector v of the fluorescent microfilament is calculated by the formula v= (Δx/Δy) = (x 2-x 1)/(y 2-y 1), the angle value is calculated by using the four-quadrant arctan function arctan2 (Δy, Δx), the output range is [ -180 °,180 ° ], and finally the angle value is converted into the range of 0 ° -360 ° by angle normalization.
6. The method according to claim 1, wherein in the step S04, the specific operation of determining the flow state existing in the fluorescent microwire numbering image is as follows: Drawing an angle polar coordinate histogram corresponding to each fluorescent microfilament according to the deflection angle of the fluorescent microfilament, calculating the double peak coefficient of the angle polar coordinate histogram according to a standard double peak coefficient formula to identify the mixed flow state of the separation and attachment flow, wherein b is the standard double peak coefficient, n is the sample capacity, g is the sample skewness, k is the sample kurtosis, Is the sample mean value; the calculation formula of the standard bimodal coefficient b is: ; The calculation formula of the sample skewness g is as follows: ; The calculation formula of the sample kurtosis k is: ; Sample mean The calculation formula of (2) is as follows: 。
7. The method according to claim 1, wherein in the step S05, the position range of the mixed flow state is determined according to the size of the bimodal coefficient of the angular polar coordinate histogram of each fluorescent microfilament, and further the position range of the transition of the attached flow to the separated flow is confirmed, and finally the boundary of the two flow states is determined.
8. The method according to claim 1, wherein in the step S06, the judgment of the flow state and the boundary dividing process are recorded and stored, wherein the polar coordinate histogram of the deflection angle and the flow state of each fluorescent microfilament are stored.

Description

Fluorescent microfilament dynamic flow spectrum separation and attached flow quantitative interpretation method Technical Field The application relates to the field of aerodynamic flow visualization and identification, in particular to a method for quantitatively judging and reading a dynamic flow spectrum separation and an attached flow of a fluorescent microfilament. Background The fluorescent microfilament dynamic flow spectrum display technology is characterized in that a fluorescent microfilament array is arranged on the surface of an aircraft model, and the movement state of the fluorescent microfilaments under the action of air flow is recorded by utilizing high-speed photography, so that the visual observation of a flow structure is realized. The method is an important means in the field of visualization of the surface flow of the aircraft, and is widely applied due to the advantages of simplicity and convenience in operation, quick response, capability of dynamically displaying transient flow in real time and the like. The flow state disclosed by the dynamic flow spectrum of the fluorescent microfilaments is accurately interpreted, particularly the boundary of a flow separation and attachment area is accurately identified, and the method is very important for determining the safety flight envelope of an aircraft and verifying the accuracy of a Computational Fluid Dynamics (CFD) numerical simulation result, and is a key link for improving the reliability of aerodynamic characteristic analysis. However, the current technique faces the core problem that the interpretation of the detached and attached streams in the fluorescence microwire spectra is largely dependent on subjective experience and qualitative observations by the operator. The subjective judgment-based method has obvious limitations, and is low in interpretation accuracy and poor in result repeatability. The method is characterized in that key information (such as fine separation bubbles, reattachment points and the like) representing the flow state transition is easy to miss, so that details of a flow field are blurred, and boundaries of a separation area and an attachment area are difficult to objectively and quantitatively define. The problems directly weaken the reliability and engineering practical value of the visualization result of the dynamic flow spectrum of the fluorescent microfilaments, are not only unfavorable for the aerodynamic shape optimization design based on flow field details, but also influence the accuracy of the determination of the safe flight envelope. For this reason, a new method is urgently needed to solve the above-mentioned problems. Disclosure of Invention The application aims to provide a method for quantitatively judging the dynamic flow spectrum separation and the attached flow of a fluorescent microfilament, aiming at the problems of low judging precision and poor result repeatability caused by the fact that the current method mainly relies on subjective experience and qualitative observation of operators in the dynamic flow spectrum display method of the fluorescent microfilament. In order to achieve the above purpose, the present application adopts the following technical scheme. A fluorescence microfilament dynamic flow spectrum separation and attached flow quantitative interpretation method comprises the following steps: S01, preprocessing a fluorescent microwire image acquired through experiments, and storing the preprocessed fluorescent microwire image to obtain a fluorescent microwire preprocessed image; S02, partitioning and numbering each fluorescent microwire in the fluorescent microwire pretreatment image, and calculating the position coordinates of each fluorescent microwire to obtain a fluorescent microwire numbering image; S03, calculating the deflection angle of each fluorescent microfilament according to the position coordinate and the number of each fluorescent microfilament in the fluorescent microfilament numbering image, and generating an angle value set, wherein the angle value set comprises the number, the position coordinate and the specific value of the deflection angle of each fluorescent microfilament; s04, judging the flow state existing in the fluorescent microfilament numbered image based on the angle value set, wherein the flow state comprises an attached flow, a separated flow and a mixed flow, and the mixed flow means that the attached flow and the separated flow exist at the same time; S05, dividing the boundary between the separation and attachment flows in the fluorescent microfilament numbered image according to the angular polar coordinate distribution diagram and the size of the double-peak coefficient; s06, recording and storing the judgment flow state and the boundary dividing process. In the step S01, the fluorescent microwire image acquired through experiment is sequentially subjected to graying, binarization and noise reduction treatment, and the fluorescent mi