CN115931361A - Device for measuring three-dimensional speed of jet flow field at tail of aircraft engine - Google Patents
Device for measuring three-dimensional speed of jet flow field at tail of aircraft engine Download PDFInfo
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Abstract
The invention discloses a device for measuring the three-dimensional speed of a tail jet flow field of an aeroengine, which solves the problems of complex test system and low measurement precision faced by tail jet flow performance parameter measurement in ground test of the aeroengine and realizes the three-dimensional measurement of the tail jet flow speed field under high temperature, high speed and strong disturbance. The main technical scheme is as follows: the particle adding device is adopted to actively scatter high-temperature tracer particles into the tail jet flow, the imaging focal length of the high-speed precise imaging system is adjusted through the electric control liquid non-diffraction system, the capture of the geometric form and the characteristics of the particle space in the high-speed tail jet flow is completed, then the particle image flow data is analyzed and processed by utilizing the Lucas-Kanade (LK) optical flow method, and the tail jet flow field speed is calculated by combining the calibration and the solution of the unit pixel length. The three-dimensional velocity measurement method can quickly, efficiently and accurately realize the three-dimensional velocity measurement of the velocity of the tail jet flow field, and has the characteristics of high response speed, high integration level, strong universality and the like.
Description
Technical Field
The invention belongs to the technical field of diagnosis and measurement of air circuit states of aero-engines, and particularly relates to a device for measuring three-dimensional speed of an aero-engine tail jet flow field.
Background
With the increasing competition of air advantages in various aviation industry countries, the problems of reliability, stability and the like of the aircraft engine are highlighted under the angular force of high comprehensive performance such as high pressure ratio, high turbine front temperature, high thrust ratio and the like. According to statistics, the gas circuit fault of the aircraft engine accounts for more than 90% of the aircraft service fault, and is a main cause of safety accidents such as flight delay, military aircraft stop and the like. The tail jet flow is used as a main radiation source of the high-temperature characteristic of the engine, and the relation between the flow field parameters and the running state of the engine becomes the key point of the current research, wherein the distribution of the velocity field of the tail jet flow reflects the combustion process and the combustion efficiency in the engine and comprises the early warning information of the health state of a gas path component. Therefore, the research of the velocity field distribution measuring method has great significance for the analysis of the state of the gas path parameters of the engine, the exploration of energy loss and the fault diagnosis. At present, for measurement of flow field velocity, the traditional methods include an optical method (such as infrared imaging and particle image technology), electrostatic induction and the like, but only single measurement of parameters can be realized, the application range is limited, and meanwhile, due to the fact that asynchronous measurement results cannot be matched, transient characteristics of tail jet flow combustion are difficult to truly reflect. However, the tail jet flow of the engine is highly complex, and is represented by large temperature gradient (core region temperature can reach 1800 ℃), wide pressure range, large flow rate (& gt 1 Ma), complex combustion components and strong turbulence, and the like, and the LDA, LIF and other technologies face severe operating environments during measurement, such as strong noise, self-luminescence, mechanical vibration, electromagnetic interference and the like, which cause the problems of large deviation of the center position of a spectral line, poor spatial resolution, low measurement precision, even measurement failure and the like, and cannot meet the requirement of the full-field accurate measurement of the field speed of the tail jet flow.
Disclosure of Invention
In view of the above, a device for measuring the three-dimensional speed of the tail jet flow field of the aircraft engine is provided, which solves the key technical problems of complex test system, low space-time response resolution capability, large difference of diagnostic model algorithms, low measurement accuracy and the like faced by the measurement of the performance parameters of the tail jet flow in the ground test run of the aircraft engine.
The utility model provides a measuring device of three-dimensional speed in aeroengine tail jet flow field, is applicable to the measurement of the high-temperature high-speed tail jet flow (6) velocity field that the aeroengine tail jet part produced when normally working, includes tracer particle's interpolation subassembly, controller, measurement system device, wherein:
the controller controls the adding component and the measuring system device to synchronously or asynchronously act;
the tracer particle adding assembly is used for conveying tracer particles (7) into a high-temperature high-speed tail jet (6) generated by the time tail jet component.
The measuring system device is used for acquiring image data of the tracer particles (7) in the high-temperature high-speed tail jet flow (6) and determining a velocity field of the high-temperature high-speed tail jet flow (6).
The invention has the technical beneficial effects that:
a certain amount of tracer particles are actively and uniformly scattered into the high-speed tail jet flow field through the tracer particle adding system, then an electric control liquid diffraction-free system is adopted to carry out instantaneous regulation and control on the imaging focal distance of the camera, tracer particle images at different focal distance positions at the same moment are obtained, the controller synthesizes a three-dimensional image through a plurality of particle images, then the movement tracking of the tracer particles in the image is carried out by combining an LK optical flow method, finally the three-dimensional speed of the tail jet flow is measured by combining calibration data, and the testing cost is reduced.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings required to be used in the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present disclosure, and it is obvious for those skilled in the art that other drawings may be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic diagram of a three-stage non-diffractive optical device;
FIG. 2 is a schematic diagram of a concave non-diffractive beam-expanding optic;
wherein:
R 0 、R 1 、R 2 corresponding radii, θ, corresponding to three levels of the first, second and third-level non-diffractive optics, respectively 2 、θ 1 Respectively corresponding to its angle, z 1 、z 3 Corresponding to the area covered by the second and third levels, z 2 The first order focal length of the third order non-diffractive optic 4.
Detailed Description
The embodiments of the present disclosure are described in detail below with reference to the accompanying drawings.
The embodiments of the present disclosure are described below with specific examples, and other advantages and effects of the present disclosure will be readily apparent to those skilled in the art from the disclosure in the specification. It is to be understood that the described embodiments are merely illustrative of some, and not restrictive, of the embodiments of the disclosure. The disclosure may be embodied or carried out in various other specific embodiments, and various modifications and changes may be made in the details within the description without departing from the spirit of the disclosure. It should be noted that the features in the following embodiments and examples may be combined with each other without conflict. All other embodiments, which can be derived by a person skilled in the art from the embodiments disclosed herein without making any creative effort, shall fall within the protection scope of the present disclosure.
It is noted that various aspects of the embodiments are described below within the scope of the appended claims. It should be apparent that the aspects described herein may be embodied in a wide variety of forms and that any specific structure and/or function described herein is merely illustrative. Based on the disclosure, one skilled in the art should appreciate that one aspect described herein may be implemented independently of any other aspects and that two or more of these aspects may be combined in various ways. For example, an apparatus may be implemented and/or a method practiced using any number of the aspects set forth herein. Additionally, such an apparatus may be implemented and/or such a method may be practiced using other structure and/or functionality in addition to one or more of the aspects set forth herein.
The device for measuring the three-dimensional speed of the tail jet flow field of the aircraft engine shown in fig. 1 is suitable for measuring the high-temperature high-speed tail jet flow 6 speed field generated by a tail jet component when the aircraft engine normally works, and comprises an adding component of trace particles, a controller and a measuring system device, wherein:
the controller controls the synchronous or asynchronous action of the adding component and the measuring system device;
and the tracer particle adding component is used for conveying tracer particles 7 into the high-temperature high-speed tail jet flow 6 generated by the time tail jet component.
The measurement system device is used for acquiring image data of the tracer particles 7 in the high-temperature high-speed tail jet flow 6 and determining a high-temperature high-speed tail jet flow 6 velocity field, and specifically comprises the following steps:
the subassembly that adds of tracer particle includes compressed air source 1, tracer particle blows spray tube 5, tracer particle and adds device 4 and normally closed solenoid valve 3, wherein:
tracer particle blows 5 neighbour tail spouts parts of spray pipe and installs tracer particle and adds device 4, its one end is installed and is equipped with compressed air supply 1, tracer particle blows 5 exhaust direction and sets gradually pressure flowmeter 2 and normally closed solenoid valve 3, normally closed solenoid valve 3 sets up with tracer particle interpolation device 4 is adjacent, the other end carries tracer particle 7 in high-temperature high-speed tail jet 6 under compressed air supply 1's drive, preferably, tracer particle blows spray pipe 5 and is close to 6 export axle centers of tail jet and arrange, tracer particle 7 that compressed air supply 1 provided blows power and satisfies tracer particle 7 and 6 speed synchronization of tail jet.
The measuring system device comprises a photosensitive detector 10 and an electric control liquid diffraction-free system 8, wherein the photosensitive detector 10 and the electric control liquid diffraction-free system 8 are coaxial, and the measuring system device comprises:
an optical lens 9 and an electric control liquid diffraction-free system 8 are sequentially arranged on an imaging light path of the photosensitive detector 10; the rear end of the photosensitive detector 10 is connected with a synchronous trigger 11, the signal interface of the photosensitive detector 10 is a data processing terminal 12, and the optical lens 9 shoots trace particles 7 in tail jet flow 6 at normal incidence to generate image data and transmit the image data to the controller;
the electrically-controlled liquid non-diffraction system 8 is connected with the optical lens 9 and comprises an electrode 16, insulating liquid 14, conducting liquid 15 and a voltage source 17;
the photosensitive detector 10, the optical lens 9, the electric control liquid non-diffraction system 8, the synchronous trigger 11 and the data processing terminal 12 form an electrowetting non-diffraction focal length controllable imaging system.
The optical part of the electrowetting diffraction-free focal length controllable imaging system comprises an electric control liquid diffraction-free system 8, an optical lens 9 and a photosensitive detector 10, and the space position distribution of the tracer particles 7 is observed and imaged. In the process of collecting images, high-temperature radiation interference of the tail jet flow 6 is eliminated by adjusting the exposure value of the optical part, and meanwhile, the photosensitive detector 10 and the programmable control cabinet 13 are controlled by the synchronous trigger 11, so that the starting and stopping time of imaging is ensured to be synchronous with the electric control liquid non-diffraction system 8. And transmitting the acquired image of the tracer particle 7 to a data processing terminal 12 to perform three-dimensional speed online analysis on the tracer particle 7.
And blowing trace particles into the tail jet flow through a trace particle adding system, quickly capturing the space radiation characteristics of the trace particles by adopting an electrowetting non-diffraction focal length controllable imaging system, calibrating the pixel length of the trace particles in an object-image space, analyzing the velocity vector of the trace particles based on an LK optical flow method, and solving the velocity field of the tail jet flow according to the motion response characteristic of the trace particles. The electrowetting diffraction-free focal length controllable imaging system can realize three-dimensional speed measurement of tail jet flow through a single camera, has non-contact, high resolution and quick dynamic response quantitative measurement, greatly simplifies the measurement process and reduces the equipment cost. Meanwhile, the tracer particles are added externally, so that the structure of a spray pipe generating tail jet flow cannot be damaged, and the method is suitable for multi-parameter measurement of a high-speed combustion flow field similar to the tail jet flow.
As a specific implementation manner provided by the present application, the trace particles 7 are particles that are chemically stable and are easily subjected to thermal radiation, so as to ensure that a radiation image acquired by the photosensitive detector 10 is clear, and the photosensitive detector 10 and the electrically controlled liquid non-diffraction system 8 are coaxially arranged, and the normal incidence shoots a tangential plane of the tail jet flow 6, so as to ensure that the velocity field of the tail jet flow 6 is accurately measured.
The liquid non-diffraction system 8 realizes the non-diffraction light zooming function in an electric control mode, and specifically comprises the following steps: comprises a transparent glass tube (used as a lens barrel), an electrode 16 on the outer wall surface of the glass tube, two incompatible conductive liquid 15 and insulating liquid 14 (dielectric coating is designed to be polyimide or barium titanate) with refractive index difference sealed therein, the conductive liquid 15 and the insulating liquid 14 form an interface type at the transition, and the insulating liquid 14 is, for example, C 12 H 25 Br liquid, the conductive liquid 15 adopts Na2So4 aqueous solution, the possible conductive liquid combined with the aqueous solution may also contain NaCl solution, siloxane, halogenated alkane and the like, and the transparent electrode adopts tin oxide fluorine-doped (FTO) conductive glass. The electrode 16 and the conductive liquid 15 are connected with a voltage source, the interface surface types of the conductive liquid 15 and the insulating liquid 14 are changed according to applied voltage, when the interface surface types are spherical surfaces, the curvature radius of the interface surface types can be correspondingly changed, so that the integral focal length of the imaging system is changed, when voltage is applied to the liquid, charge accumulation is formed at the interface due to a capacitance effect generated by an external electric field, and the focal length of each direction of a light source is adjusted through the change of the curvature radius of the interface surface type, so that a clear image is presented to adjacent particles.
Furthermore, in order to ensure the influence of the surface roughness of the lens barrel on the interface surface type of the liquid lens, the inner wall surface of the lens barrel is processed by ultraprecise turning of diamond with the precision of 0.01 mu m
Secondly, a method for measuring the three-dimensional speed of the jet flow field at the tail of the aeroengine is provided, which is characterized in that the measuring device is adopted, and the method comprises the following steps:
A. the blowing air flow provided by the compressed air source 1 is adjusted to a proper conveying pressure through the pressure flow meter 2, and after the normally closed electromagnetic valve 3 is opened, the trace particles 7 carried in the trace particle adding device 4 are added into the tail jet flow 6 through the blowing nozzle 5. The blowing speed and the adding quantity of the trace particles 7 are respectively controlled by the pressure flowmeter 2 and the trace particle adding device 4; the opening and closing of the normally closed electromagnetic valve 3 are controlled by a programmable control cabinet 13.
B. After the trace particles 7 are blown into the tail jet flow 6, they are heated by the tail jet flow 6 at high temperature to generate soot body radiation, the intensity of which is related to the material of the trace particles 7 and the temperature of the tail jet flow 6. The tracer particles 7 are focused by an electric control liquid diffraction-free system 8 and an optical lens 9 and then imaged on a photosensitive detector 10, and the parameters of a measuring light path are defined as the distance between the optical lens 9 and the section of the tail jet flow 6, namely the object distance u, the distance between the optical lens 9 and the photosensitive detector 10, namely the image distance v, the imaging focal length f of the photosensitive detector 10, the imaging height H of the photosensitive detector 10, the field height H, the aperture diameter d of the optical lens 9, and the mutual relations are as follows:
the radiation noise of the tail jet flow 6 is filtered by adjusting an exposure value through a photosensitive detector 10 and an optical lens 9, and the expression of the exposure value is as follows:
c: in the process of image acquisition, the photosensitive detector 10 and the programmable control cabinet 13 are controlled by the synchronous trigger 11, so that the synchronization between the starting and stopping time of imaging and the electrically-controlled liquid non-diffraction system 8 is ensured, and meanwhile, the electrically-controlled liquid non-diffraction system 8 is in a continuous working state, so that the focusing synchronization of the particle images acquired by the photosensitive detector 10 and the electrically-controlled liquid non-diffraction system 8 is realized. The acquired images of the tracer particles 7 are subjected to analog-to-digital conversion and format conversion in the photosensitive detector 10 and are transmitted to the data processing terminal 12 in real time so as to perform online analysis on the speed of the tracer particles 7;
d: for the acquired trace particle 7 image, because the brightness of the trace particle 7 image is kept unchanged and the speed of the trace particle image changes slowly under ultra-fast exposure, the particle motion vector speed under the space geometric characteristics of the trace particle image is analyzed through an LK optical flow method, and a basic optical flow constraint equation is expressed as follows:
I x u+I y v+I t =03 where lx, ly, and lt are partial derivatives of radiation image gray scale along the x, y direction coordinates and exposure time t, respectively;
u, v score the optical flow vector of the trace particle 7, estimate the optical flow vector using a weighted sum of squares minimization:
A T W 2 AV＝A T W 2 b，5
wherein the content of the first and second substances,
W＝diag(W(X 1 ，L X n ))，/>
p 1 、p 2 、......、p n are the pixel points in the neighborhood W. Solving the equation (5) to obtain an optical flow vector matrix V:
e: based on the formula 1, calibrating the unit length of the pixel by adopting a reflection dot calibration plate, thereby quantitatively obtaining the velocity vector distribution of the tracer particles 7 in the high-speed tail jet flow 6;
f: the electric control liquid non-diffraction system 8 realizes the non-diffraction light zooming function, the interface surface type of the conductive liquid 15 and the insulating liquid 14 is changed mainly according to the applied voltage, when the interface surface type is a spherical surface, the curvature radius of the interface surface type can be correspondingly changed, so that the integral focal length of the imaging system is changed, and therefore when the voltage is applied to the liquid, charge accumulation is formed at the interface due to the capacitance effect generated by an external electric field. The electric control liquid non-diffraction system 8 adopts a double-liquid single zoom lens structure, due to the difference of refractive indexes of double liquids and the action of surface tension, the meniscus points to the conductive liquid 15, and when light parallel to an optical axis reaches the interface of the conductive liquid 15 and the insulating liquid 14, the lens imaging Gaussian formula shows that:
in the formula, n1 is the refractive index of the conductive liquid 15, n2 is the refractive index of the insulating liquid 14, a is the convergence angle formed by the convergence of light, r is the radius of the meniscus, I is the image distance, and h is the distance between the incident parallel light and the optical axis. The incident light is generally considered paraxial and its approximate relationship is:
(a+l)a＝h (8)
based on the equations (7) and (8), when the meniscus is projected by light, it can be obtained according to the matrix optical theory:
since the refractive index of air is 1, the focal length of the bi-liquid lens can be expressed as:
for spherical liquid interfaces, according to the Young-Lippmannn equation and geometric relationships:
in the formula, theta is the initial contact angle epsilon 0 Is the absolute dielectric constant of air, epsilon r Is the relative dielectric constant, gamma, of the dielectric material 12 Is the interfacial tension, and e is the dielectric layer thickness. Thereby, a relation between the lens focal length f and the voltage U is obtained.
J: according to the motion response characteristic of the trace particles 7, the velocity parameter of the high-density characteristic trace particles 7 in the tail jet flow 6 is equivalent to the velocity field distribution of the tail jet flow 6.
In order to make the objects, technical solutions and advantages of the present invention more clearly understood, the following further describes the composition and operation principle of the present invention with reference to fig. 1 and 2. However, the present invention is not limited to the following examples. The following is a further detailed description with reference to the accompanying drawings. The invention aims at three-dimensional speed measurement of a jet flow field at the tail of an aeroengine, and mainly comprises the following steps:
A. the tracer particles 7 are stored in the tracer particle adding device 4 in advance, the normally closed electromagnetic valve 3 is opened by using the programmable control cabinet 13, the tracer particles 7 are blown into the tail jet flow 6 under the air flow pressure of the compressed air source 1, and the blowing speed and the adding quantity of the tracer particles 7 are adjusted by the pressure flow meter 2 and the tracer particle adding device 4. B. The optical part of the electrowetting non-diffraction focal length controllable imaging system comprises an electrically-controlled liquid non-diffraction system 8, an optical lens 9 and a photosensitive detector 10, and the spatial position distribution of the tracer particles 7 is observed and imaged. In the process of image acquisition, high-temperature radiation interference of the tail jet flow 6 is eliminated by adjusting the exposure value of the optical part, and meanwhile, the photosensitive detector 10 and the programmable control cabinet 13 are controlled by the synchronous trigger 11, so that the starting and stopping time of imaging is ensured to be synchronous with the electric control liquid non-diffraction system 8. And transmitting the acquired images of the tracer particles 7 to a data processing terminal 12 to perform three-dimensional speed online analysis on the tracer particles 7. C. And analyzing the particle motion vector speed under the space geometric characteristics of the acquired tracer particle 7 image by adopting an LK optical flow method. The basic optical flow constraint equation is expressed as:
I x u+I y v+I i ＝0 (12)
and (3) solving an estimated optical flow vector under the condition of weighted square sum minimization by setting a W (X) weight function in the neighborhood window by using a least square method:
A T W 2 AV＝A T W 2 b (13)
wherein, the first and the second end of the pipe are connected with each other,
W＝diag(W(X 1 ，L X n ))，/>
p 1 、p 2 、...、p n are the pixel points in the neighborhood W. Solving equation (13) to obtain an optical flow vector matrix V:
D. and calibrating the unit length of the pixel by adopting a reflection dot calibration plate, and quantitatively obtaining the three-dimensional velocity vector distribution of the trace particles (7) in the tail jet flow (6).
E. According to the motion response characteristic of the tracer particles (7), the velocity parameter of the tracer particles (7) with high density in the tail jet flow (6) is equivalent to the velocity field distribution of the tail jet flow (6).
The method has the following advantages:
1. the electrowetting diffraction-free focal length controllable imaging system is adopted to observe externally-arranged actively-scattered heated tracer particles in tail jet flow, and the method has the characteristics of non-contact, high resolution, wide dynamic detection and the like.
2. The trace particle image flow acquired by the electrowetting non-diffraction focal length controllable imaging system is resolved based on an LK optical flow method, and the tail jet velocity field can be analyzed in real time and efficiently by means of optimized program compiling and strong data processing terminal computing power, so that the method has good adaptability and high measurement accuracy.
3. The measuring system has the advantages of simple structure, convenient operation, strong universality and strong engineering practical value.
The above description is only for the specific embodiments of the present disclosure, but the scope of the present disclosure is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present disclosure should be covered within the scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be subject to the protection scope of the claims.
Claims (8)
1. The utility model provides a measuring device of aeroengine tail jet flow field three-dimensional speed, is applicable to the measurement of the high-temperature high-speed tail jet flow (6) velocity field that the aeroengine normal operating operation tail jet part produced, its characterized in that, including tracer particle add subassembly, controller, measurement system device, wherein:
the controller controls the adding component and the measuring system device to synchronously or asynchronously act;
the tracer particle adding assembly is used for conveying tracer particles (7) into a high-temperature high-speed tail jet flow (6) generated by the time tail jet component;
the measuring system device is used for acquiring image data of the tracer particles (7) in the high-temperature high-speed tail jet flow (6) and determining a velocity field of the high-temperature high-speed tail jet flow (6).
2. The measuring device according to claim 1, characterized in that the tracer particle adding assembly comprises a compressed air source (1), a tracer particle blowing nozzle (5), a tracer particle adding device (4) and a normally closed solenoid valve (3), wherein:
tracer particle blows spray tube (5) neighbour tail and spouts the part and install tracer particle interpolation device (4), and compressed air supply (1) are installed to its one end, tracer particle blows spray tube (5) exhaust direction and sets gradually pressure flowmeter (2) and normally closed solenoid valve (3), normally closed solenoid valve (3) and tracer particle interpolation device (4) adjacent setting, the other end carry tracer particle (7) in high-speed tail jet stream of high temperature (6) under the drive of compressed air supply (1).
3. The measuring device according to claim 2, wherein the tracer particle blowing nozzle (5) is arranged close to the outlet axis of the tail jet flow (6), and the tracer particle (7) blowing power provided by the compressed air source (1) meets the requirement that the tracer particle (7) and the tail jet flow (6) are synchronous in speed.
4. The measuring device according to claim 2, characterized in that the measuring system device comprises a photosensitive detector (10), an electrically controlled liquid non-diffracting system (8), the photosensitive detector (10) and the electrically controlled liquid non-diffracting system (8) being coaxial, wherein:
an optical lens (9) and an electric control liquid non-diffraction system (8) are sequentially arranged on an imaging light path of the photosensitive detector (10); the rear end of the photosensitive detector (10) is connected with a synchronous trigger (11), a signal interface of the photosensitive detector (10) is a data processing terminal (12), and an optical lens (9) shoots trace particles (7) in tail jet flow (6) at normal incidence to generate image data and transmit the image data to a controller;
the electric control liquid non-diffraction system (8) is connected with the optical lens (9) and comprises an electrode (16), insulating liquid (14), conducting liquid (15) and a voltage source (17);
the photosensitive detector (10), the optical lens (9), the electric control liquid diffraction-free system (8), the synchronous trigger (11) and the data processing terminal (12) form an electrowetting diffraction-free focal length controllable imaging system.
5. A measuring device as claimed in claim 4, characterized in that the tracer particles (7) are chemically stable and susceptible to thermal radiation, in order to ensure a sharp radiation image acquired by the photosensitive detector (10).
6. A measuring device according to claim 5, characterized in that the photosensitive detector (10) and the electrically controlled liquid non-diffractive system (8) are arranged coaxially, and the tail jet (6) is photographed at normal incidence in a tangential plane to ensure accurate measurement of the velocity field of the tail jet (6).
7. A method for measuring the three-dimensional speed of an aircraft engine tail jet flow field, which is characterized by using the measuring device as claimed in any one of claims 2 to 6.
8. The measurement method according to claim 7, characterized in that the method comprises:
a: the blowing air flow provided by the compressed air source (1) is regulated to a proper conveying pressure through the pressure flow meter (2), and after the normally closed electromagnetic valve (3) is opened, tracer particles (7) in the tracer particle adding device (4) are carried and added into the tail jet flow (6) through the blowing spray pipe (5); the blowing speed and the adding quantity of the trace particles (7) are respectively controlled by a pressure flowmeter (2) and a trace particle adding device (4);
b: after being blown into the tail jet flow (6), the tracer particles (7) are heated at high temperature by the tail jet flow (6) to generate ash body radiation, the tracer particles (7) are focused by an electric control liquid diffraction-free system (8) and an optical lens (9) and then imaged on a photosensitive detector (10), and the parameters of a measuring light path are defined as: the distance u from an optical lens (9) to the tangent plane of the tail jet flow (6), the distance v from the optical lens (9) to a photosensitive detector (10), the imaging focal length f of the photosensitive detector (10), the imaging height H of the photosensitive detector (10), the field height H, the aperture diameter d of the optical lens (9) and the mutual relationship are as follows:
the radiation noise of the tail jet flow (6) is filtered by adjusting an exposure value through a photosensitive detector (10) and an optical lens (9), and the expression of the exposure value is as follows:
wherein E is the exposure value of the photosensitive detector (10); t is the exposure time of the photosensitive detector (10); i is the light inlet quantity of the optical lens (9) and is determined by the light transmission diameter d and the imaging focal length f;
c: in the process of collecting images, a synchronous trigger (11) is used for controlling a photosensitive detector (10) and a programmable control cabinet (13), so that the starting and stopping time of imaging is ensured to be synchronous with an electric control liquid non-diffraction system (8), and meanwhile, the electric control liquid non-diffraction system (8) is in a continuous working state, so that particle images collected by the photosensitive detector (10) and the electric control liquid non-diffraction system (8) are focused synchronously; the acquired image of the tracer particle (7) is subjected to analog-to-digital conversion and format conversion in the photosensitive detector (10), and is transmitted to the data processing terminal (12) in real time so as to perform online analysis on the speed of the tracer particle (7);
d: for the collected tracing particle (7) image, because the brightness of the tracing particle (7) image is kept unchanged and the speed of the tracing particle (7) image is changed slowly under ultra-fast exposure, the particle motion vector speed under the space geometric characteristics of the tracing particle (7) image is analyzed through an LK optical flow method, and a basic optical flow constraint equation is expressed as follows:
I x u+I y v+I t ＝0 (3)
in the formula, ix, iy and It are respectively partial derivatives of the radiation image gray level along the coordinate x and y directions and the exposure time t;
u, v are assigned optical flow vectors of the tracer particles (7), the optical flow vectors are estimated using a weighted sum of squares minimization:
in the formula, W (X) is a weight function of each pixel in a neighborhood window, obeys Gaussian distribution, and is solved by using a least square method to obtain:
A T W 2 AV＝A T W 2 b， (5)
wherein the content of the first and second substances,
W＝diag(W(X 1 ，L X n ))，/>
p 1 、p 2 、......、p n are the pixel points in the neighborhood W. Solving the equation (5) to obtain an optical flow vector matrix V: />
E: based on the formula (1), calibrating the unit length of a pixel by adopting a reflection dot calibration board, thereby quantitatively obtaining the velocity vector distribution of the tracer particles (7) in the high-speed tail jet flow (6);
f: the non-diffraction light zooming function of the electric control liquid non-diffraction system (8) is realized, the interface surface type of the conductive liquid (15) and the insulating liquid (14) is changed mainly according to the applied voltage, when the interface surface type is a spherical surface, the curvature radius of the interface surface is correspondingly changed, so that the integral focal length of the imaging system is changed, and therefore when the voltage is applied to the liquid, charge accumulation is formed at the interface due to the capacitance effect generated by an external electric field. The electric control liquid diffraction-free system (8) adopts a double-liquid single zoom lens structure, and due to the difference of refractive indexes of double liquids and the action of surface tension, the meniscus points to the conductive liquid (15), and when light parallel to an optical axis reaches the interface of the conductive liquid (15) and the insulating liquid (14), the light can be known by a Gaussian formula of lens imaging:
wherein n1 is the refractive index of the conductive liquid (15), n2 is the refractive index of the insulating liquid (14), a is the convergence angle formed by the convergence of light rays, r is the radius of a meniscus, I is the image distance, and h is the distance between incident parallel light and the optical axis. The incident light is paraxial light, and the approximate relationship is:
(a+l)a＝h (8)
based on the formula (7) and the formula (8), when the half-plane is projected by light, the following can be obtained according to the matrix optical theory:
since the refractive index of air is 1, the focal length of the two-liquid lens can be expressed as:
for spherical liquid interfaces, according to the Young-Lippmannn equation and geometric relationships:
in the formula, theta is the initial contact angle epsilon 0 Is the absolute dielectric constant of air, epsilon t Is the relative dielectric constant, gamma, of the dielectric material 12 Is the interfacial tension, and e is the dielectric layer thickness. Thereby, a relation between the lens focal length f and the voltage U is obtained.
J: according to the motion response characteristic of the tracer particles (7), the velocity parameter of the high-density characteristic tracer particles (7) in the tail jet flow (6) is equivalent to the velocity field distribution of the tail jet flow (6).
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| CN116718344A (en) * | 2023-08-10 | 2023-09-08 | 中国空气动力研究与发展中心高速空气动力研究所 | Multi-parameter thrust vector jet optical calibration method |
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| CN116718344A (en) * | 2023-08-10 | 2023-09-08 | 中国空气动力研究与发展中心高速空气动力研究所 | Multi-parameter thrust vector jet optical calibration method |
| CN116718344B (en) * | 2023-08-10 | 2023-10-27 | 中国空气动力研究与发展中心高速空气动力研究所 | Multi-parameter thrust vector jet optical calibration method |
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