CN112880567A - Boundary layer thickness measuring method - Google Patents
Boundary layer thickness measuring method Download PDFInfo
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- CN112880567A CN112880567A CN202110025692.5A CN202110025692A CN112880567A CN 112880567 A CN112880567 A CN 112880567A CN 202110025692 A CN202110025692 A CN 202110025692A CN 112880567 A CN112880567 A CN 112880567A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/26—Measuring arrangements characterised by the use of optical techniques for measuring angles or tapers; for testing the alignment of axes
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
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- Y02T90/00—Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation
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Abstract
The invention discloses a boundary layer thickness measuring method which is realized based on a pitot tube displacement measuring device and a double-sided visual ranging system, and comprises the following steps: mounting a pitot tube displacement measuring device at a wind tunnel section to be measured; the pitot tube moving and measuring device comprises a bracket and a pitot tube fixed on the bracket; marking a plurality of marking points on the surface of the pitot tube along the incoming flow direction; moving the pitot tube moving and measuring device; after each movement, measuring a total pressure value and a static pressure value, and measuring the position of each mark point; obtaining the deformation of the pitot tube under the action of aerodynamic force according to the positions of each mark point before and after movement, and correcting the total pressure value and the static pressure value to obtain a corrected total pressure value and a corrected static pressure value; and calculating to obtain the dimensionless speed of the movement; obtaining the dimensionless speed distribution in the boundary layer according to the dimensionless speed of each movement; and selecting the corresponding moving distance when the dimensionless speed is equal to the preset value, and further obtaining the boundary layer thickness of the section to be measured.
Description
Technical Field
The invention relates to the technical field of aeronautics and astronautics industry aerodynamics, in particular to a boundary layer thickness measuring method.
Background
The boundary layer is a thin flow layer with non-negligible viscous force close to the object surface in the fluid circumfluence, and is also called as a flow boundary layer and a boundary layer. This concept was first proposed in 1904 by the founder prandtl who is the current generation of hydrodynamics. In the boundary layer, the fluid tightly attached to the object surface is completely adhered to the object surface, and the flow speed is zero; from the object plane, outward in the normal direction, the fluid velocity rapidly increases to the local free incoming flow velocity. The development, transition and separation of the boundary layer have very important influence on the aerodynamic characteristics of the advanced aircraft and the flow field quality of the large-scale production type wind tunnel.
The thickness of the boundary layer is one of important characteristic parameters of the boundary layer, and the accurate measurement of the thicknesses of the boundary layers at different flow direction positions is a very important research subject in the research field of the boundary layer. At present, the boundary layer thickness is usually measured in a boundary layer pressure measuring rake mode in engineering. The pressure measuring rake generally comprises 10-30 total pressure detecting tubes and 2 static pressure probes, and is used for measuring the total static pressure in the boundary layer, so that the thickness of the boundary layer is measured. However, the number of measuring points in the measuring method is very limited, and the distance between the total pressure detecting tube and the static pressure probe is relatively short, so that flow interference exists to a certain extent, and the measuring error is large.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a boundary layer thickness measuring method.
In order to achieve the purpose, the invention provides a boundary layer thickness measuring method which is realized based on a pitot tube displacement measuring device and a double-sided visual ranging system, and the method comprises the following steps:
mounting a pitot tube displacement measuring device at a wind tunnel section to be measured; the pitot tube moving and measuring device comprises a bracket and a pitot tube fixed on the bracket;
marking a plurality of marking points on the surface of the pitot tube along the incoming flow direction;
moving the pitot tube moving and measuring device;
after each movement, measuring a total pressure value and a static pressure value by adopting a pitot tube, and measuring the position of each mark point by adopting a binocular vision ranging system;
obtaining the deformation of the pitot tube under the action of aerodynamic force according to the positions of each mark point before and after movement, and correcting the total pressure value and the static pressure value to obtain a corrected total pressure value and a corrected static pressure value;
calculating the dimensionless speed of the movement according to the corrected total pressure value and the corrected static pressure value;
obtaining the dimensionless speed distribution in the boundary layer of the section to be measured according to the dimensionless speed of each movement;
and selecting a corresponding moving distance when the dimensionless speed is equal to a preset value from the dimensionless speed distribution in the boundary layer of the section to be measured, and further obtaining the thickness of the boundary layer of the section to be measured.
As an improvement of the method, the method further comprises setting the incoming flow speed of the wind tunnel test.
As an improvement of the method, the bracket is vertically arranged on the side wall surface of the section to be measured of the wind tunnel and can freely move up and down, and the pitot tube is fixed on the bracket and is parallel to the incoming flow direction of the wind tunnel.
As an improvement of the above method, a specific way of marking a plurality of mark points on the surface of the pitot tube along the incoming flow direction includes: paint spraying, fluorescent paint spraying, mechanical drilling or standard paper mark sticking are adopted.
As an improvement of the method, the deformation of the pitot tube under the action of the aerodynamic force is obtained according to the position of each mark point before and after the movement, and the total pressure value and the static pressure value are corrected to obtain a corrected total pressure value and a corrected static pressure value; the method specifically comprises the following steps:
obtaining the moving distance of different moving mark points according to the position of each mark point before and after moving, and calculating the deformation of the pitot tube under the action of aerodynamic force according to the moving distance to obtain an included angle alpha between the pitot tube and incoming flow;
from the total pressure value P measured at the ith marking point’ oiAnd static pressure value P’Calculating the total pressure value P of the corrected i-th mark point according to the following formulaoiAnd corrected static pressure value P:
Poi cosα+Psinα=P’ oi
Poi sinα+P cosα=P’。
as a modification of the above method, the dimensionless speed of the movement is calculated from the corrected total pressure value and the corrected static pressure value; the method specifically comprises the following steps:
from the total pressure P of the corrected i-th mark pointoiAnd calculating the ratio of the corrected static pressure value PAccording toThe range is calculated by the following formula to obtain the dimensionless Mach number M of the ith mark point in the boundary layer of the section to be measuredi:
obtaining the dimensionless speed in the boundary layer of the section to be measured according to the following formulaComprises the following steps:
wherein M is the Mach number of incoming flow, ViThe speed corresponding to the i-th mark point, V is the incoming flow speed.
As a modification of the above method, the preset value is 0.99.
Compared with the prior art, the invention has the advantages that:
1. the boundary layer thickness measurement method based on the shift-measurement pitot tube and binocular vision distance measurement can collect more abundant measurement point data, has small flow field interference, and reduces the boundary layer thickness measurement error;
2. the boundary layer thickness measuring method based on the shift-measurement pitot tube and the binocular vision ranging can correct the included angle between the pitot tube and the incoming flow, so that the boundary layer thickness measuring precision is improved.
Drawings
FIG. 1 is a flow chart of the boundary layer thickness measurement method of the present invention.
Detailed Description
The invention provides a boundary layer thickness measuring method based on a shift-measuring pitot tube and binocular vision ranging. And measuring the total pressure value and the static pressure value at different positions by using a single pitot tube, and calculating the dimensionless speed in the boundary layer. Pitot tube position was measured by a mature binocular vision ranging system. A binocular vision ranging system generally arranges mark points of a specific pattern on a measured surface, and two high-resolution cameras are used for shooting a test image; measuring the three-dimensional coordinate value of the mark point by using the principle of binocular stereo vision; and calculating the moving distance or the deformation of the mark points according to the three-dimensional coordinate positions of the characteristic mark points at different moments.
The invention provides a boundary layer thickness measuring method based on a shift-measuring pitot tube and binocular vision ranging, which comprises the following steps:
step 1) processing the surface of a measured object and installing a pitot tube bracket, wherein the bracket can freely move in a direction vertical to the object surface;
step 2) adhering or spraying a plurality of special mark points for binocular vision distance measurement on the surface of the pitot tube along the flow direction;
and 3) under specific inflow parameters, adjusting the position of the pitot tube along the direction vertical to the object plane. At each position, the total static pressure value collected by the pitot tube was recorded. Meanwhile, the displacement of each mark point on the surface of the pitot tube is measured in real time and at high precision by utilizing a mature binocular vision ranging system;
step 4) calculating the deformation of the pitot tube under the action of aerodynamic force according to the displacement difference of different mark points to obtain an included angle between the pitot tube and an incoming flow, so that the total pressure value and the static pressure value measured by the pitot tube are corrected, and the measurement error is further reduced;
step 5) calculating the dimensionless speed distribution in the boundary layer by using the corrected total pressure value and static pressure value;
and 6) defining the boundary of the speed boundary layer when the dimensionless speed is equal to 0.99, and obtaining the thickness of the boundary layer according to the dimensionless speed distribution in the boundary layer.
Compared with the traditional boundary layer measurement, the method can collect more abundant measuring point data, has small flow field interference, and can correct the deflection angle between the detection tube and the incoming flow, thereby reducing the boundary layer thickness measurement error.
The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and examples.
Example 1
Embodiment 1 of the invention is a method for measuring the thickness of a boundary layer on the side wall of a certain transonic wind tunnel test section, the thickness of the boundary layer is measured by the method based on a mobile pitot tube and binocular vision ranging, and the specific process is as follows:
step 1) fixing a pitot tube on a bracket on the side wall of the wind tunnel test section, wherein the bracket can freely move in a direction vertical to the side wall surface of the test section.
And a pitot tube bracket is processed and installed at the thickness measuring position of the boundary layer of the side wall of the wind tunnel test section. The carriage is free to move in a direction perpendicular to the side wall surfaces by a motor or other means.
And 2) adhering or spraying a plurality of special mark points for binocular vision distance measurement on the surface of the pitot tube along the flow direction.
3-5 special mark points for binocular vision distance measurement are distributed on the surface of the pitot tube along the flow direction. The marking points can be sprayed by paint, sprayed by fluorescent paint, mechanically drilled or adhered by standard paper marking points. In order to improve the identifiability and the identification precision of the mark points, the shape of the mark points is usually circular.
And 3) carrying out a wind tunnel test of a specific incoming flow Mach number, adjusting the position of the pitot tube along the direction vertical to the side wall of the test section in the test, recording the total pressure value and the static pressure value measured by the pitot tube at each position, and measuring the displacement of each mark point on the surface of the pitot tube in real time and at high precision by using a mature binocular vision distance measuring system.
In the wind tunnel test, the position of the pitot tube is adjusted step by step. At each position, the measured values output from the pitot tube connected total and static pressure sensors were recorded. Meanwhile, the moving distance of each mark point on the surface of the pitot tube is measured in real time and at high precision by utilizing a mature binocular vision ranging system. Because the requirement on the measuring frequency is not high, an industrial camera with low frame frequency and high resolution and low cost can be selected. The displacement measurement precision of the existing mature binocular vision distance measurement system can reach within 0.1 mm.
Step 4) calculating the deformation of the pitot tube under the action of aerodynamic force according to the displacement difference of different mark points to obtain an included angle between the pitot tube and an incoming flow, so that the total pressure value and the static pressure value measured by the pitot tube are corrected, and the measurement error is further reduced;
theoretically, the pitot tube after being installed and fixed should be parallel to the incoming flow. However, in the wind tunnel test process, an included angle exists between the pitot tube and the incoming flow due to the influence of factors such as the installation angle and the aerodynamic force of the pitot tube. And calculating an included angle between the pitot tube and the incoming flow according to the displacement difference of different mark points, and correcting the measured total static pressure. Knowing the measured total pressure value P’ oiAnd static pressure P’Calculating the corrected total pressure value P according to the following formulaoiAnd static pressure value P:
Poi cosα+Psinα=P’ oi
Poi sinα+P cosα=P’
and 5) calculating the dimensionless speed distribution in the boundary layer by using the total static pressure acquired by the pitot tube.
Firstly, a dimensionless Mach number M in a boundary layer of a section to be measured is calculated according to the following formulai:
the above formula is an implicit equation and needs iterative calculation.
Dimensionless speed in boundary layer of section to be measuredCalculated according to the following formula:
p is boundary layer local static pressure;
Poithe pressure value measured by the pitot tube at the ith marking point;
Mithe Mach number corresponding to the ith mark point;
vi is the speed corresponding to the ith mark point;
v is the incoming flow speed;
m is the incoming flow Mach number.
And 6) defining the boundary of the speed boundary layer when the dimensionless speed is equal to 0.99, and obtaining the thickness of the boundary layer according to the dimensionless speed distribution in the boundary layer.
And 5) calculating the position of the pitot tube when the dimensionless speed is equal to 0.99 according to the dimensionless speed distribution in the boundary layer obtained in the step 5), wherein the distance between the position and the test wall surface of the wind tunnel is the thickness of the local boundary layer.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and are not limited. Although the present invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (7)
1. A boundary layer thickness measuring method is realized based on a pitot tube displacement measuring device and a double-sided visual ranging system, and comprises the following steps:
mounting a pitot tube displacement measuring device at a wind tunnel section to be measured; the pitot tube moving and measuring device comprises a bracket and a pitot tube fixed on the bracket;
marking a plurality of marking points on the surface of the pitot tube along the incoming flow direction;
moving the pitot tube moving and measuring device;
after each movement, measuring a total pressure value and a static pressure value by adopting a pitot tube, and measuring the position of each mark point by adopting a binocular vision ranging system;
obtaining the deformation of the pitot tube under the action of aerodynamic force according to the positions of each mark point before and after movement, and correcting the total pressure value and the static pressure value to obtain a corrected total pressure value and a corrected static pressure value;
calculating the dimensionless speed of the movement according to the corrected total pressure value and the corrected static pressure value;
obtaining the dimensionless speed distribution in the boundary layer of the section to be measured according to the dimensionless speed of each movement;
and selecting a corresponding moving distance when the dimensionless speed is equal to a preset value from the dimensionless speed distribution in the boundary layer of the section to be measured, and further obtaining the thickness of the boundary layer of the section to be measured.
2. The method of claim 1, further comprising setting an incoming flow velocity of a wind tunnel test.
3. The boundary layer thickness measuring method according to claim 1, wherein the bracket is vertically arranged on a side wall surface of the section to be measured of the wind tunnel and can freely move up and down, and the pitot tube is fixed on the bracket and is parallel to the incoming flow direction of the wind tunnel.
4. The method for measuring the thickness of the boundary layer according to claim 1, wherein the specific manner of marking a plurality of marking points on the surface of the pitot tube along the incoming flow direction comprises: paint spraying, fluorescent paint spraying, mechanical drilling or standard paper mark sticking are adopted.
5. The boundary layer thickness measuring method according to claim 1, wherein the deformation of the pitot tube under the action of aerodynamic force is obtained according to the position of each mark point before and after movement, and the total pressure value and the static pressure value are corrected to obtain a corrected total pressure value and a corrected static pressure value; the method specifically comprises the following steps:
obtaining the moving distance of different moving mark points according to the position of each mark point before and after moving, and calculating the deformation of the pitot tube under the action of aerodynamic force according to the moving distance to obtain an included angle alpha between the pitot tube and incoming flow;
from the total pressure value P measured at the ith marking point’ oiAnd static pressure value P’Calculating the total pressure value P of the corrected i-th mark point according to the following formulaoiAnd corrected static pressure value P:
Poicosα+P sinα=P’oi
Poisinα+P cosα=P’。
6. the boundary layer thickness measuring method according to claim 1, wherein the dimensionless speed of the movement is calculated from the corrected total pressure value and the corrected static pressure value; the method specifically comprises the following steps:
from the total pressure P of the corrected i-th mark pointoiAnd calculating the ratio of the corrected static pressure value PAccording toThe range is calculated by the following formula to obtain the dimensionless Mach number M of the ith mark point in the boundary layer of the section to be measuredi:
obtaining the dimensionless speed in the boundary layer of the section to be measured according to the following formulaComprises the following steps:
wherein M is the Mach number of incoming flow, ViThe speed corresponding to the i-th mark point, V is the incoming flow speed.
7. The boundary layer thickness measuring method of claim 1, wherein the preset value is 0.99.
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