CN114740222B - Device and method for measuring uniformity of three-dimensional velocity field between moving blade and static blade grids - Google Patents
Device and method for measuring uniformity of three-dimensional velocity field between moving blade and static blade grids Download PDFInfo
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Abstract
The invention discloses a device and a method for measuring uniformity of a three-dimensional velocity field between a moving blade grid and a stationary blade grid, and belongs to the field of multiphase flow testing. The invention provides a device and a method for measuring the uniformity of a three-dimensional velocity field between a moving blade grid and a static blade grid. The synchronous controller is used for realizing the time sequence control of the enhanced high-speed camera and the pulse laser and realizing the synchronous measurement of the three-dimensional velocity field and the uniformity between the moving and static blade grids. Meanwhile, the invention reconstructs the phosphorescent grid image according to the light intensity characteristic of the laser, and can improve the precision of the speed field to the sub-pixel precision.
Description
Technical Field
The invention belongs to the field of multiphase flow testing, and particularly relates to a device and a method for measuring uniformity of a three-dimensional velocity field between a moving blade grid and a stationary blade grid.
Background
In the field of modern aerospace, high-precision measurement of flow velocity between a moving blade and a stationary blade in an engine and measurement of flow field stability have great significance. However, the space between the moving and static blade grids is small, the speed is high, and the measurement difficulty is caused (the distance between the moving and static blade grids is 8-10 mm, and the rotating speed can reach thousands of turns to tens of thousands of turns). In the machining process, due to manufacturing tolerance, the flow field is unstable, and the uniformity in the period of the flow field needs to be measured with high precision. Conventional measurement methods, such as: pitot tubes and hot air linear velocity meters have large interference on flow fields and slow response, and are difficult to adapt to measurement of high-speed flow fields in small spaces. In recent years, with the development of optical devices and high-speed photography, some optical non-contact speed measurement technologies have been developed rapidly, such as: molecular marker velocimetry (MOV), laser Doppler Velocimetry (LDV), particle Image Velocimetry (PIV), and the like. The laser Doppler velocimetry and the particle image velocimetry need to add tracing particles in a flow field, because the addition of the tracing particles can influence the normal operation of an impeller, and because the inertia of the particles is large, the hysteresis of the particles is large, and meanwhile, the uniformity measurement of the flow field is difficult to realize.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a device and a method for measuring the uniformity of a three-dimensional velocity field between a moving blade grid and a static blade grid.
In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:
a three-dimensional velocity field uniformity measuring device between a moving blade and a stationary blade comprises a pulse laser and an optical path system, wherein the pulse laser is used for emitting laser, the laser enters the optical path system to change an optical path, then is changed into two bundles of sheet-shaped laser through an outlet of the optical path system, and the laser sheets enter a flow field to be measured between the moving blade and the stationary blade to form a staggered laser grid;
the flow field to be detected adopts diacetyl or acetone as a tracer molecule, and the flow field to be detected is in an oxygen-free environment;
a first enhanced high-speed camera and a second enhanced high-speed camera are respectively arranged on two sides of the flow field to be measured, the first enhanced high-speed camera and the second enhanced high-speed camera are respectively connected with a synchronous controller through connecting wires, and the synchronous controller is connected with an image processing system;
the first enhanced high-speed camera and the second enhanced high-speed camera are used for synchronously shooting phosphorescent images generated after tracer molecules are excited.
Further, the optical path system comprises a reflecting mirror, a spectroscope and an air wedge;
when a laser beam is cleaved through air, the laser beam is divided into a plurality of sheet-shaped laser beams, then the laser beam is divided into two laser beams through a spectroscope and a reflector, and the two laser beams enter a flow field to be measured to form a staggered laser grid.
Furthermore, the air wedge comprises first quartz glass and second quartz glass, one end of the first quartz glass is in contact with one end of the second quartz glass, and a metal wire is arranged between the other ends of the first quartz glass and the second quartz glass;
an air film is formed between the two quartz glasses, and the air film divides a laser beam into a plurality of thin sheets by utilizing the interference of light;
the laser can be completely penetrated on the upper surface of the first quartz glass, one part of the laser is emitted on the lower surface, the other part of the laser is refracted, and the laser is completely emitted on the upper surface of the second quartz glass.
A method for measuring the uniformity of a three-dimensional velocity field between a moving blade grid and a stationary blade grid is carried out based on the device for measuring the uniformity of the three-dimensional velocity field between the moving blade grid and the stationary blade grid, and comprises the following steps:
step one, carrying out a calibration experiment, and calculating the relation between the first enhanced high-speed camera, the second enhanced high-speed camera and the actual space position so as to obtain an image pixel coordinate a
32' and actual space coordinates:
in the formula: (u, v) represents pixel coordinates; (X) w ,Y w ,Z w ) Representing the actual coordinates in space; k is a radical of ij Represents the solution parameter, i =1,2,3,j =1,2,3,4;
step two, in the phosphorescence life of the tracer molecules, two continuous moments t are obtained by utilizing the first enhanced high-speed camera and the second enhanced high-speed camera 1 、t 2 Respectively, as follows:
step three, for t 1 Phosphorescent images obtained by the first enhanced high-speed camera and the second enhanced high-speed camera at the moment
And &>
Matching the grid intersections one by one according to the phosphorescence maximum intensity point to obtain the coordinates of the pixel points of the same grid intersection in the actual space in two different camera-shot pictures, bringing the coordinates of the two pixel points into the actual space, and calculating the coordinates (X) of the actual grid space point w ,Y w ,Z w ) t1 ；
Fourthly, respectively obtaining phosphorescent images of the first enhanced high-speed camera and the second enhanced high-speed camera at two moments
And &>
And &>
Performing cross-correlation calculation to obtain the corresponding relation of grid intersection points in phosphorescent grid pictures captured by the same camera at two different moments; t is calculated by utilizing a cross-correlation algorithm 2 Timing two camera phosphorescent images->
And &>
The coordinates of the pixel points of the middle grid intersection point are substituted to calculate t 2 Coordinates (X) of time grid intersection points in real space w ,Y w ,Z w ) t2 ；
Step five, according to t 1 Time and t 2 Location of time grid intersection in real space (X) w ,Y w ,Z w ) t1 、(X w ,Y w ,Z w ) t2 The relation with time, the three-dimensional velocity field of the flow field is calculated
Further, the second step further comprises:
denoising the phosphorescent image, and enhancing the image contrast;
for a single phosphor grid image, the phosphor beam is fitted with a gaussian function in the direction perpendicular to the grid lines.
Furthermore, the time sequence control of the pulse laser, the first enhanced high-speed camera and the second enhanced high-speed camera is adopted, so that the velocity field of each moving blade passing through the same stationary blade is measured, and the measurement of the uniformity in the period of the flow field is realized by comparing the difference of the velocity fields of different moving blades.
Further, measuring velocity field uniformity specifically operates to:
when the rotating speed of the moving blade is n and the number of the moving blades is k, the time of one rotation of the moving blade is
The time required for the same stator blade to pass 2 adjacent blades is ≥ now>
At the moment, the frequency of the pulse laser is f = nk, and the shooting time ^ of the high-speed camera is greater than or equal to>
The excitation time of the adjacent two times of pulse lasers meets the following conditions:
when in use
When the frequency of the pulsed laser is->
High speed camera shot time
Further, at t 1 At this point, the phosphor grid image is initially distributed midway between the two moving blades.
Compared with the prior art, the invention has the following beneficial effects:
according to the device and the method for measuring the three-dimensional velocity field uniformity between the moving blade and the static blade, the light path system is designed by utilizing light interference, and the staggered laser grids are formed in the flow field to be measured, so that the marking and excitation of tracer molecules are realized. The synchronous controller is used for realizing the time sequence control of the enhanced high-speed camera and the pulse laser and realizing the synchronous measurement of the three-dimensional velocity field and the uniformity between the moving and static blade grids. Meanwhile, the invention reconstructs the phosphorescence grid image according to the light intensity characteristic of the laser, and can improve the speed field precision to the sub-pixel precision.
Furthermore, air wedges are designed according to the wavelength of the laser, the quality of the marking laser can be further improved, the spatial resolution of grids is improved, and a high-quality grid phosphorescence image is formed in a flow field.
Furthermore, according to the rotating speed, the radius and the number of the blades of the moving blade and the static blade cascades, a phosphorescence shooting time sequence is designed, the camera frequency, the pulse laser frequency, the camera exposure time and the like are determined, the measurement of the flow field uniformity can be realized, and the measurement accuracy is improved.
Furthermore, the invention measures the three-dimensional velocity field between the movable and fixed blade grids by using the molecular marker velocity measurement technology, and has no interference to the flow field and high measurement precision.
Drawings
FIG. 1 is a structural diagram of a three-dimensional velocity field measuring device between a moving blade cascade and a stationary blade cascade;
FIG. 2 is a structural view of an optical path system;
FIG. 3 is a block diagram of an air wedge;
FIG. 4 is a phosphorescent grid image.
Wherein: 01-a pulsed laser; 02-laser; 03-a first data transmission line; 04-first enhanced high speed camera; 05-an optical path system; 06-moving blades; 07-a second enhanced high speed camera; 08-a second data transmission line; 09-stationary vanes; 10-a synchronous controller; 11-a third data transmission line; 12-an image processing system; 01-a pulsed laser; 13-a mirror; 14-a beam splitter; 15-air wedge; 16-a first quartz glass; 17-a wire; 18-second quartz glass.
Detailed Description
In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Moreover, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
The invention adopts the molecular marker speed measurement technology to realize the synchronous measurement of the three-dimensional velocity field and the flow field uniformity between the moving and static blade grids. The molecular marker speed measurement technology is a non-invasive and non-contact laser diagnosis technology. The principle is that the laser with specific wavelength is adopted to excite the tracer molecules in the flow field to emit phosphorescence, phosphorescence signals are directly captured after a certain time interval to determine the positions of the tracer molecules, and then the speed is solved according to the displacement-time relation of the tracer molecules. The molecular marker velocity measurement technology can effectively overcome the defects of a laser Doppler velocity measurement method and a particle image velocity measurement method, can be well applied to high-precision measurement of a velocity field between a moving blade and a static blade grid, and can realize uniformity measurement in a flow field period by adopting time sequence control. The invention provides a device and a method for measuring the uniformity of a three-dimensional velocity field between a moving blade grating and a static blade grating based on a molecular marker velocity measurement technology, which can overcome the defects of the conventional test method and realize the synchronous measurement of the uniformity of the three-dimensional velocity field and the velocity field between the moving blade grating and the static blade grating.
The invention is described in further detail below with reference to the accompanying drawings:
referring to fig. 1, fig. 1 is a structural diagram of a three-dimensional velocity field measuring device between a moving blade cascade and a stationary blade cascade, and the high-precision measuring device for the three-dimensional velocity field between the moving blade cascade and the stationary blade cascade is composed of four parts, namely a moving blade cascade structure, an optical path system, an image capturing system and an image processing system. The moving and stationary blade cascade structure is composed of moving blades 06 and stationary blades 09, and the structure can be present in an engine, a gas turbine. The light path system mainly comprises a pulse laser 01, a reflective mirror 13, an air wedge 15 and a spectroscope 14, and is used for constructing a staggered laser grid in a to-be-measured area of the flow field and realizing excitation and marking of tracer molecules in the to-be-measured flow field. The image capturing system mainly comprises a synchronous controller 10, a first enhanced high-speed camera 04 and a second enhanced high-speed camera 07, and can obtain phosphorescent grid images of tracer molecules at two different continuous moments. The image processing system 12 reconstructs a three-dimensional model of the phosphorescent grid according to the phosphorescent grid image of the tracer molecules, and develops a cross-correlation algorithm according to the phosphorescent intensity distribution characteristics to obtain the relationship between grid space positions at different moments, thereby obtaining a three-dimensional velocity field.
The moving and static blade cascade structure can exist in a gas turbine of an engine, quartz glass is adopted to visualize a region to be measured, and meanwhile, in order to avoid the influence of other fluorescence on the phosphorescence of tracer molecules in the shooting process, oxidation blackening treatment should be carried out on the blades. When the tracer molecule is diacetyl or acetone, the gas in the flow field should be free of oxygen. Oxygen causes phosphorescence quenching of the tracer molecules.
Referring to fig. 2, fig. 2 is a structural diagram of an optical path system, in which a laser beam is split into a plurality of laser sheets by an air wedge 15, and then the laser beam is split into two laser beams by a beam splitter 14 and a reflector 13 and forms a staggered laser grid in a flow field to be measured. The method is characterized in that the interference of light is utilized to build a high-quality laser grid, wherein the excited phosphorescence of the tracer molecules is in direct proportion to the laser intensity, and a phosphorescence image reconstruction algorithm is developed according to the laser intensity characteristics, so that the sub-pixel precision of the speed field precision can be improved.
Referring to fig. 3, fig. 3 is a structural view of an air wedge 15, which is mainly composed of two quartz glasses and a metal wire, an air film is formed between the two quartz glasses, and a laser beam is divided into a plurality of thin plates by using light interference. Wherein, the laser of the upper surface of the first quartz glass 16 can be penetrated completely, a part of the lower surface is emitted, and a part is refracted; full emission occurs at the upper surface of the second quartz glass 18.
The laser light interferes on the upper surface and the lower surface of the air film to form laser sheets with alternate light and shade. Because the diameter D of the metal wire is very small, the optical path difference when two phases of dry light meet is about
The conditions for forming the bright and dark stripes are as follows:
thickness difference of air film between two adjacent open stripes
It can be seen that the distance between two adjacent bright lines is l = Δ dsin θ, and the angle of the air film is very small from θ, and is approximately +>
The relationship between the wire diameter D and the clear-grain spacing l between two adjacent wires is ^ or ^>
When the distance between the movable and static blade grids is 10mm, the space of a flow field to be measured is small, and the requirement on the quality of a laser grid is high. Diacetyl is used as tracer, the laser wavelength is 355nm, the L is 20mm, the distance between two bright lines is 1mm, and the diameter of the metal wire is 3.55 multiplied by 10 -6 And m is selected. 6 pieces of bright-line laser are utilized to form a 6 multiplied by 6 laser marking grid in the flow field to be tested, so that the marking and excitation of the flow field to be tested are realized.
The enhanced high-speed camera in the image capturing system comprises a high-speed video camera, an image intensifier, a lens, a filter plate and the like, can realize accurate capturing of phosphorescent signals, and needs to be testedFilters of different sizes are selected according to the phosphorescent characteristics of the tracer molecules. The synchronous controller 10 is connected to an image processing system 12 through a third data transmission line 11, the synchronous controller 10 is connected to a first enhanced high-speed camera 04 through a first data transmission line 03, and the synchronous controller 10 is connected to a second enhanced high-speed camera 07 through a second data transmission line 08. Meanwhile, the synchronous controller 10 is used for triggering and controlling the first enhanced high-speed camera 04, the second enhanced high-speed camera 07 and the pulse laser 01, and each frame of image shot by the two cameras is ensured to be synchronous, so that the time sequence control of the pulse laser and the enhanced high-speed camera is realized. Two different time instants t can be obtained continuously during the phosphorescent lifetime of the tracer molecules in the image capture system 1 And t 2 A phosphor grid pattern in the flow field. Wherein the time of continuous shooting is determined by the frequency of the camera
To avoid false information when solving for the velocity field, the maximum displacement of grid nodes in adjacent images should be kept below half the grid spacing ≧>
At this time, the frequency of the camera is->
And because the shooting flow field is a high-speed flow field, the exposure time of each frame of image of the camera is not too long, otherwise, a larger smear is caused, and the solving precision of the speed field is greatly influenced. To ensure the measurement accuracy, the exposure time Δ t should be satisfied->
The image processing part mainly utilizes a tracer molecule phosphorescence image obtained by an image capturing system and combines theoretical analysis and image processing technology to obtain a three-dimensional velocity field between the leaf grids. In the lifetime of diacetyl phosphorescence, a first enhanced high-speed camera 04 and a second enhanced high-speed camera 07 are used for respectively obtaining phosphorescence maps at two continuous momentsThe resulting phosphor grid images are represented as shown in FIG. 4 as:
the method comprises the following steps:
step one, carrying out a calibration experiment, and calculating the position relation between two cameras and an actual space so as to obtain a conversion relation between an image pixel coordinate and an actual space coordinate:
in the formula: (u, v) represents pixel coordinates; (X) w ,Y w ,Z w ) Representing the actual coordinates in space; k is a radical of formula ij Represents the solution parameter, i =1,2,3,j =1,2,3,4);
preprocessing the obtained phosphorescence image, denoising the image by adopting a Gaussian filter and an average filter, removing background noise, uniformly processing the image by utilizing image processing software, enhancing the image contrast and improving the phosphorescence image brightness;
fitting the phosphorescent light beams of the single phosphorescent grid image by adopting a Gaussian function in the direction vertical to the grid lines, so that the spatial resolution of the image is improved, and the image precision is improved to sub-pixels;
step four, for t 1 Phosphorescent images acquired by two cameras at a time
Matching the grid intersection points one by one according to the phosphorescence maximum intensity point to obtain the positions of pixel points of the same grid intersection point in the actual space in two different camera-shot pictures, then bringing the coordinates of the two pixel points into formula 2, and calculating the coordinates (X) of the actual grid space point w ,Y w ,Z w ) t1 ；
Step five, respectively obtaining phosphorescence images of two moments for the camera 1 and the camera 2
And &>
And &>
And performing cross-correlation calculation to obtain the one-to-one correspondence of the grid intersections in the phosphorescent grid pictures captured by the same camera at two different moments. T is calculated by utilizing a cross-correlation algorithm 2 Two camera phosphorescent images at time (< >>
And &>
) Substituting the coordinates of the pixel points of the middle grid intersection point into formula 2, and calculating t 2 Coordinates (X) of time grid intersection points in real space w ,Y w ,Z w ) t2 ；
Step six, according to t 1 Time and t 2 Location of time grid intersection in real space (X) w ,Y w ,Z w ) t1 、(X w ,Y w ,Z w ) t2 The relation with time, thereby obtaining a three-dimensional velocity field of the flow field by calculation
Furthermore, in the actual manufacturing process, the flow field between the moving blade and the static blade grids is not uniform due to the process difference, in order to measure the size of the three-dimensional velocity field between the moving blade and the static blade grids and the non-uniform degree of the flow field, the velocity field of each moving blade passing through the same static blade can be measured by controlling the time sequence of a pulse laser and an enhanced high-speed camera, and the measurement of the uniformity of the flow field in the period can be realized by comparing the difference of the velocity fields between different moving blades. The velocity field inhomogeneity measurement can be described as:
when the rotating speed of the moving blades is n, the number of the moving blades is k, and the time of one rotation of the blades is
The time required for the same stator blade to pass 2 adjacent blades is ≥ h>
At the moment, the frequency of the pulse laser is f = nk, and the shooting time of the high-speed camera is +>
As the phosphorescence service life of the tracer molecules can reach 1ms, in order to ensure that two groups of phosphorescence grid images cannot appear in a flow field to be detected at the same time, the excitation time of two adjacent pulse lasers is satisfied: />
When in use
In order to ensure that two groups of phosphorescent grid images do not appear in a flow field to be measured, the frequency of the pulse laser is
High-speed camera shooting time>
Although the frequency of the pulse laser is reduced, the shooting period of the high-speed camera is increased along with the reduction of the frequency, and the memory of the camera is increased. Meanwhile, in order to ensure the accuracy of measurement, the initial distribution of the phosphor grid image should be arranged at the middle position of the two moving blades at the initial moment.
A process for measuring the uniformity of a speed field between a moving blade grid and a static blade grid comprises the following steps:
1) Selecting the types of tracer molecules according to the characteristics of a flow field to be detected, and determining the wavelength of the excitation laser, the structure of an air wedge and the size of a filter;
2) Determining the frequency and the shooting period of a pulse laser according to the rotating speed and the number of the moving blades;
3) Determining and estimating the flow field velocity V according to the rotating speed of the blade and the diameter of the blade est,max Calculating the camera frequency and the exposure time;
4) Setting parameters of each device, carrying out camera calibration experiment, carrying out speed field measurement experiment between a moving blade and a static blade grid, and simultaneously calculating the speed V of a flow field act ；
5) Comparison V est,max And V act,max Size of (V) if est,max >V act,max And ending the test; if V est,max <V act,max Then need to be according to V act,max The camera frequency and exposure time were recalculated, and the experiment was repeated until the end.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (6)
1. The method for measuring the uniformity of the three-dimensional velocity field between the moving blade and the stationary blade is characterized by being carried out based on a device for measuring the uniformity of the three-dimensional velocity field between the moving blade and the stationary blade, wherein the device for measuring the uniformity of the three-dimensional velocity field between the moving blade and the stationary blade comprises a pulse laser (01) and an optical path system (05), the pulse laser (01) is used for emitting laser (02), the laser (02) enters the optical path system (05) to change an optical path, then is changed into two bundles of sheet-shaped laser through an outlet of the optical path system (05), and the laser sheets enter a flow field to be measured between the moving blade (06) and the stationary blade (09) to form staggered laser grids;
the flow field to be detected adopts diacetyl or acetone as a tracer molecule, and the flow field to be detected is in an oxygen-free environment;
a first enhanced high-speed camera (04) and a second enhanced high-speed camera (07) are respectively arranged on two sides of a flow field to be measured, the first enhanced high-speed camera (04) and the second enhanced high-speed camera (07) are respectively connected with a synchronous controller (10) through connecting wires, and the synchronous controller (10) is connected with an image processing system (12);
the first enhanced high-speed camera (04) and the second enhanced high-speed camera (07) are used for synchronously shooting phosphorescent images generated after tracer molecules are excited, and the method comprises the following steps:
step one, carrying out a calibration experiment, and calculating the position relation between the first enhanced high-speed camera (04), the second enhanced high-speed camera (07) and the actual space so as to obtain a conversion relation between the image pixel coordinate and the actual space coordinate:
in the formula: (u, v) represents pixel coordinates; (X) w ,Y w ,Z w ) Representing the actual coordinates in space; k is a radical of ij Represents the solution parameter, i =1,2,3,j =1,2,3,4;
step two, in the phosphorescence life of the tracer molecules, two continuous time instants t are obtained by utilizing a first enhanced high-speed camera (04) and a second enhanced high-speed camera (07) 1 、t 2 Respectively, as follows:
step three, for t 1 Phosphorescent images obtained by the first enhanced high-speed camera (04) and the second enhanced high-speed camera (07) at the moment
And &>
Carrying out one-to-one matching of grid intersections according to the maximum phosphorescence intensity points to obtain the same grid intersection in the actual space in two different camera shot picturesThe coordinates of the pixel points are then brought into the formula (2), and the coordinates (X) of the actual grid space points are calculated w ,Y w ,Z w ) t1 ；
Fourthly, phosphorescent images at two moments are obtained for the first enhanced high-speed camera (04) and the second enhanced high-speed camera (07) respectively
And &>
And &>
Performing cross-correlation calculation to obtain the corresponding relation of grid intersection points in phosphorescent grid pictures captured by the same camera at two different moments; t is calculated by utilizing a cross-correlation algorithm 2 Timing two camera phosphorescent images->
And &>
The coordinates of the pixel points of the middle grid intersection point are substituted into the formula (2), and t is calculated 2 Coordinates (X) of time grid intersection points in real space w ,Y w ,Z w ) t2 ；
Step five, according to t 1 Time and t 2 Location of time grid intersection in real space (X) w ,Y w ,Z w ) t1 、(X w ,Y w ,Z w ) t2 The relation with time, the three-dimensional velocity field of the flow field is calculated
By means of time sequence control of the pulse laser (01), the first enhanced high-speed camera (04) and the second enhanced high-speed camera (07), a velocity field of each moving blade (06) passing through the same stationary blade (09) is measured, and the uniformity in the period of the flow field is measured by comparing the difference of the velocity fields of different moving blades (06).
2. The method for measuring the uniformity of the three-dimensional velocity field between the moving blade and the static blade cascades as recited in claim 1, wherein the optical path system (05) comprises a reflector (13), a spectroscope (14) and an air wedge (15);
after passing through an air wedge (15), one laser beam is divided into a plurality of sheet-like laser beams, and then one laser beam is divided into two laser beams through a spectroscope (14) and a reflective mirror (13), and the two laser beams enter a flow field to be measured to form a staggered laser grid.
3. The method for measuring the uniformity of a three-dimensional velocity field between a moving blade cascade and a static blade cascade as claimed in claim 1, wherein the air wedge (15) comprises a first quartz glass (16) and a second quartz glass (18), one end of the first quartz glass (16) is in contact with one end of the second quartz glass (18), and a metal wire (17) is arranged between the other ends of the first quartz glass and the second quartz glass;
an air film is formed between the two quartz glasses, and the air film divides a laser beam into a plurality of thin sheets by utilizing the interference of light;
when laser light is incident, the laser light can fully penetrate through the upper surface of the first quartz glass (16), one part of the laser light is emitted on the lower surface, the other part of the laser light is refracted, and the laser light is fully emitted on the upper surface of the second quartz glass (18).
4. The method for measuring the uniformity of the three-dimensional velocity field between the moving blade and the static blade cascades as recited in claim 1, wherein the second step further comprises the following steps:
denoising the phosphorescent image, and enhancing the image contrast;
for a single phosphor grid image, the phosphor beam is fitted with a Gaussian function in the direction perpendicular to the grid lines.
5. The method for measuring the uniformity of the three-dimensional velocity field between the moving blade and the static blade cascades as recited in claim 4, wherein the operation of measuring the uniformity of the velocity field is specifically as follows:
when the rotating speed of the moving blade (06) is n and the number of the moving blades (06) is k, the time of one rotation of the moving blade (06) is
The time required for the same stator blade (09) to pass through 2 adjacent blades is ^ 5>
At the moment, the frequency of the pulse laser is f = nk, and the shooting time of the high-speed camera is +>
The excitation time of the adjacent two times of pulse lasers meets the following conditions:
when in use
When the frequency of the pulsed laser is->
High-speed camera shooting time->
6. The method of claim 4 wherein the method of measuring the uniformity of the three-dimensional velocity field between the moving and stationary blade cascades is characterized in that t 1 At that moment, the phosphor grid image is initially distributed at a position intermediate the two moving blades.
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