CN113237628B - Method for measuring horizontal free flight model attitude of low-speed wind tunnel - Google Patents
Method for measuring horizontal free flight model attitude of low-speed wind tunnel Download PDFInfo
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Abstract
The invention is suitable for the technical field of wind tunnel tests, and provides a method for measuring the attitude of a horizontal free flight model of a low-speed wind tunnel, which comprises the following steps: step S10: placing an aircraft model in a wind tunnel test section, wherein a plurality of cameras are arranged at the tops of two sides of the aircraft model and are positioned outside the wind tunnel test section; step S20: calibrating a plurality of cameras simultaneously; step S30: establishing a world coordinate system and a body axis coordinate system; step S40: setting a plurality of marking points on an aircraft model, and acquiring position information of the marking points in a world coordinate system; step S50: the attitude measurement method provided by the invention can be suitable for the research of the aircrafts of different types in the wind tunnel flying freely horizontally, has good universality and simple operation, can be popularized to other low-speed wind tunnels, and has good engineering application prospect.
Description
Technical Field
The invention relates to the field of wind tunnel tests, in particular to a method for measuring the attitude of a horizontal free flight model of a low-speed wind tunnel.
Background
When a low-speed wind tunnel horizontal free flight test is carried out, the attitude angle (a) of an aircraft model is generally required to be acquired in real timeΨ，θ，φ) Angle of air flow: (α，β) And the related information is used for the feedback of the flight control system or the recording of flight history parameters.
In the prior art, the low-speed wind tunnel model free flight test is generally carried out by a flight attitude reference system arranged in an aircraft modelAcquiring three attitude angles (relative to the wind tunnel shafting) of the aircraft body shaftingΨ，θ，φ) The angle of attack is realized by a vane sensor arranged at the head of the aircraftαSide slip angleβAnd (4) measuring the airflow angle. The defects of the attitude and heading reference system are mainly shown as follows: the difficulty of model design and inertia balancing is increased when the aircraft is arranged in the aircraft; when the aircraft moves violently, the output of the attitude reference system jumps. The adoption of the vane sensor has the following defects: the wind speed below a certain wind speed cannot be used or the measurement error is large; the measuring result of the vane is obviously influenced by the wind speed, the attack angle and the sideslip angle of the aircraft and the mounting position of the vane, so that a large amount of calibration work is required before use; the measurement range is limited, and the device cannot be used for large-attack-angle flight; the size is large, the surface flow field of the aircraft model can be damaged, and the difficulty of system identification and modeling is increased.
Disclosure of Invention
The invention aims to provide a method for measuring the attitude of a horizontal free flight model of a low-speed wind tunnel, which aims to solve the problems in the prior art and comprises the following steps:
step S10: placing an aircraft model in a wind tunnel test section, wherein a plurality of cameras are arranged on two sides of the top of the aircraft model and are positioned outside the wind tunnel test section;
step S20: calibrating a plurality of cameras simultaneously;
step S30: establishing a world coordinate systemo g-x g y g z gAnd body axis coordinate systemo b-x b y b z bWhereino gIs positioned at any point of the lower tunnel wall of the wind tunnel test section,x gthe shaft is parallel to the axis of the wind tunnel test section and points to the incoming flow direction,y gthe shaft is in the plane of the lower tunnel wall of the wind tunnel test section, andy gaxis perpendicular tox gThe axis is directed to the right and,z gthe axis orientation is in accordance with the right hand rule,o bis the center of gravity of the aircraft model,x bthe shaft is directed forward parallel to the fuselage axis,y bthe axis points to the right perpendicular to the plane of reference,z bthe axis orientation conforms to the right hand rule;
step S40: setting a plurality of marking points on an aircraft model, and acquiring position information of the marking points in a world coordinate system;
step S50: and calculating the attitude angle and the airflow angle of the aircraft model according to the position information of the plurality of marking points in the body axis coordinate system.
Further, the camera is an infrared camera.
Further, step S40 includes:
step S401: selecting a plurality of positions on an aircraft model, and respectively setting mark points on the positions;
step S402: the camera emits infrared rays to the mark points;
step S403: the camera receives the reflected light of the mark point;
step S404: the camera collects images of the mark points and stores the images as grey-scale images;
step S405: and acquiring the position of the mark point in the two-dimensional image acquired by the camera according to the information in the gray-scale image.
Further, the attitude angle includes: yaw angleΨAnd a pitch angleθAngle of rollφSaid yaw angleΨAnd a pitch angleθAngle of rollφRespectively obtained by the following formula:
wherein,R bg a transformation matrix used for transforming the world coordinate system to the body axis coordinate system,
for transforming matricesR bg The value of the second column of the first row,
for transforming matricesR bg The value of the first row and the third column,
transformation matrixR bg The third row and the second column.
Further, the transformation matrixR bg The calculation method comprises the following steps:
connecting any two of the plurality of marking points to form a base line, so that the number of the base lines is more than three;
obtaining a world coordinate system corresponding to the baseline vector of each baseline at different timeso g-x g y g z gAnd body axis coordinate systemo b-x b y b z bCoordinates of the lower part;
from each of said baseline vectors in the world coordinate systemo g-x g y g z gCoordinate system with body axiso b-x b y b z bCoordinate conversion relation between the two, the conversion matrix is obtained by adopting the least square methodR bg 。
Further, the airflow angle includes: angle of attackα、Sideslip angleβSaid angle of attackαAnd angle of sideslipβThe calculation steps are as follows:
step S501: computingtThe virtual center of the time aircraft model is in the world coordinate systemo g-x g y g z gVelocity component (v) of (1) it，v jt，v kt) Wherein v is itIn the world coordinate system for the virtual center of the aircraft modelo g-x g y g z gMiddle edgex gVelocity component of the shaft, v jtIn the world coordinate system for the virtual center of the aircraft modelo g-x g y g z gMiddle edgey gVelocity component of the shaft, v ktIn the world coordinate system for the virtual center of the aircraft modelo g-x g y g z gMiddle edgez gA velocity component of the shaft;
step S502: velocity v of airflow in superimposed wind tunnel test section a Obtaining the world coordinate system of the virtual center of the aircraft modelo g-x g y g z gWith a relative airflow velocity component of (v) it+v a ，v jt，v kt），v it+v a Superimposing the velocity v of the air flow for the virtual center of the aircraft model a In the world coordinate systemo g-x g y g z gMiddle edgex gA velocity component of the shaft;
step S503: calculating the body axis coordinate system of the virtual center of the aircraft modelo b-x b y b z bVelocity component of (1)u b，v b，w b) Whereinu bThe virtual center of the aircraft model is in the body axis coordinate systemo b-x b y b z bMiddle edgex bThe component of the velocity of the shaft is,v ba body axis coordinate system for the virtual center of the aircraft modelo b-x b y b z bMiddle edgey bThe component of the velocity of the shaft is,w ba body axis coordinate system for the virtual center of the aircraft modelo b-x b y b z bMiddle edgez bA velocity component of the shaft;
step S504: according to the body axis coordinate systemo b-x b y b z bVelocity component of (1)u b，v b，w b) CalculatingThe angle of attackαAnd angle of sideslipβ。
Further, the velocity component (v) in step S501 it，v jt，v kt) The calculation method of (2) is as follows:
obtaining a world coordinate system of a virtual center of an aircraft model at the moment to g-x g y g z gThe coordinates ofi t，j t，k t) And the virtual center of the aircraft model at the time of t-delta t is in a world coordinate systemo g-x g y g z gThe coordinates ofi t-Δt，j t-Δt，k t-Δt）；
Calculating the world coordinate system of the virtual center of the aircraft model at the moment to g-x g y g z gSaid velocity component (v) of (a) it，v jt，v kt）：
Wherein t is sampling time, and delta t is sampling interval time;i tin the world coordinate system for the virtual center of the aircraft model at time to g-x g y g z gInx gThe value on the axis of the display is,j tin the world coordinate system for the virtual center of the aircraft model at time to g-x g y g z gIny gThe value on the axis of the display is,k tin the world coordinate system for the virtual center of the aircraft model at time to g-x g y g z gInz gThe value on the axis;i t-Δtthe virtual center of the aircraft model at the time of t-delta t is in a world coordinate systemo g-x g y g z gInx gThe value on the axis of the display is,j t-Δtthe virtual center of the aircraft model at the time of t-delta t is in a world coordinate systemo g-x g y g z gIny gThe value on the axis of the display is,k t-Δtthe virtual center of the aircraft model at the time of t-delta t is in a world coordinate systemo g-x g y g z gInz gThe value on the axis.
Further, in step 503, the virtual center of the aircraft model is in the body axis coordinate systemo b-x b y b z bVelocity component of (1)u b，v b，w b) The calculation formula of (a) is as follows:
（u b，v b，w b）=R bg（v it+v a ，v jt，v kt）。
further, angle of attack in step 504αAnd angle of sideslipβThe calculation formula of (a) is as follows:
α=tan -1（w b /u b），β=sin -1（v b/V）
wherein,Von-body axis coordinate system for virtual center of aircraft modelo b-x b y b z bVelocity component of (1)u b，v b，w b) The velocity vector of (a) is,
。
further, the marker points are seen by at least two of the cameras at the same time.
The beneficial effects of the invention at least have the following aspects:
1. in the prior art, when the attitude of an aircraft model is measured in a wind tunnel, a support frame is usually arranged in a wind tunnel test section, and the aircraft model is fixed on the support frame and can only measure the attitude data of the aircraft model when the aircraft model is static or quasi-static; the attitude measurement method for the low-speed wind tunnel horizontal free flight model can obtain the attitude angle and the airflow angle of the aircraft model in the free flight state.
2. The method adopts the infrared optical motion capture system to obtain the attitude angle of the aircraft model in free flight by a non-contact method, and compared with the prior art, the method replaces the traditional vane sensor and navigation attitude reference system to realize the real-time measurement of the horizontal free flight model attitude of the low-speed wind tunnel, does not damage the surface flow field of the model, does not increase the mass inertia of the model, and reduces the difficulty encountered in the model design process.
3. The infrared optical motion capture system employed in the present invention comprises: the system comprises a camera, mark points, a network switch, a calculation computer, a network cable and the like, wherein the infrared camera can emit infrared rays to irradiate the mark points, the mark points made of reflecting materials enhance the reflecting capacity of infrared rays, so that the mark points in an image collected in the camera are well distinguished from the surrounding environment, the background image is ignored by only processing the image gray information of the mark points, the calculation workload is greatly reduced, the measurement bandwidth of more than 100Hz can be realized, and the system is suitable for the measurement requirement of the horizontal free flight control of the low-speed wind tunnel.
4. The attitude measurement method provided by the invention can be suitable for the research of the horizontal free flight of aircrafts of different models in wind tunnels, has good universality and simple operation of the using method, can be popularized to other low-speed wind tunnels, and has good engineering application prospect.
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In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments of the present invention or in the description of the prior art will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a flow chart of a method for measuring the attitude of a low-speed wind tunnel horizontal free flight model according to the invention;
FIG. 2 is a schematic structural diagram of an apparatus for establishing a world coordinate system and a body axis coordinate system according to the present invention;
FIG. 3 is a schematic diagram of attitude angles in a coordinate system in accordance with the present invention;
FIG. 4 is a state diagram of the aircraft model at various times in the present invention;
FIG. 5 is a schematic view of the air flow angle in a coordinate system of the present invention.
10-camera, 20-aircraft model, 30-wind tunnel test section.
Detailed Description
The following description provides many different embodiments, or examples, for implementing different features of the invention. The particular examples set forth below are illustrative only and are not intended to be limiting.
As shown in fig. 1-2, an embodiment of the present invention provides a method for measuring a horizontal free flight model attitude of a low-speed wind tunnel, which includes the following steps:
step S10: placing an aircraft model 20 in a wind tunnel test section 30, and arranging a plurality of cameras 10 on two sides of the top of the aircraft model and outside the wind tunnel test section;
step S20: calibrating a plurality of cameras simultaneously;
step S30: establishing a world coordinate systemo g-x g y g z gAnd body axis coordinate systemo b-x b y b z bWhereino gIs positioned at any point of the lower tunnel wall of the wind tunnel test section,x gthe shaft is parallel to the axis of the wind tunnel test section and points to the incoming flow direction,y gthe shaft is in the plane of the lower tunnel wall of the wind tunnel test section, andy gaxis perpendicular tox gThe axis is directed to the right and,z gthe axis orientation is in accordance with the right hand rule,o bis the center of gravity of the aircraft model,x bthe shaft is directed forward parallel to the fuselage axis,y bthe axis points to the right perpendicular to the aircraft reference plane,z bthe axis orientation conforms to the right hand rule;
step S40: setting a plurality of marking points on an aircraft model, and acquiring position information of the marking points in a world coordinate system;
step S50: and calculating the attitude angle and the airflow angle of the aircraft model according to the position information of the plurality of marking points in the body axis coordinate system.
The invention adopts an infrared optical motion capture type non-contact measurement system to obtain the position information of a mark point on an aircraft model, the infrared optical motion capture type non-contact measurement system is positioned outside a wind tunnel test section, and the infrared optical motion capture type non-contact measurement system comprises: the system comprises a camera, a cable, a network switch, a resolving computer, a synchronizer and a calibration rod; the camera is connected with the network switch through a cable, the camera transmits the acquired point location information to the network switch, the network switch is electrically connected with the resolving computer through the cable, the network switch transmits the acquired point location information to the resolving computer, and the computer performs operation processing on the point location information; before the test is started, calibrating a plurality of cameras simultaneously, and determining the relative position relation among the cameras.
Establishing a world coordinate system parallel to a wind tunnel test section shaftingo g-x g y g z gDetermining the relative installation position and posture between the camera and the wind tunnel test section, and then adjusting the aircraft model to be parallel to a wind tunnel shafting so that the error range is not more than +/-0.05 degrees.
In the establishment of world coordinate systemo g-x g y g z gThe visual angle of a driver in the aircraft model is adopted,x gthe direction of the axis is the direction of the incoming flow of the wind tunnel air flow velocity viewed by the eyes of the driver, whereiny gThe axial direction is the direction in which the eyes of the driver look to the right; three-dimensional axis coordinate system under constructiono b-x b y b z bWhen the temperature of the water is higher than the set temperature,x bdirection of axisIs parallel to the axis of the fuselage of the aircraft model and points to the direction of the nose of the aircraft model,y bthe direction of the axis is perpendicular to the reference plane of the aircraft model and points to the right, wherein the reference plane of the aircraft model refers to the plane of the aircraft model which makes the left side and the right side symmetrical,y bthe direction of the axis is directed rightward referring to a direction in which the reference plane extends to the right.
Specifically, in step S10, glass windows are distributed at intervals on a tunnel wall on one side of the wind tunnel test section, the cameras are located outside the wind tunnel test section, and a camera is installed at a corresponding position outside each of the glass windows. The number of the cameras may be 4, 6, 8, 10, and the specific number of the cameras may be determined according to the size of the covered field of view, which is not limited herein.
Therefore, the infrared optical motion capture type non-contact measurement system can measure the attitude angle and the airflow angle of the aircraft model in a free flight state in real time, does not damage the flow field on the surface of the aircraft model, replaces a sensor arranged on the aircraft, reduces the extra weight caused by the installation of the sensor on the aircraft model, reduces the difficulty encountered in the design process of the model, and has reference value for further research on the influence of the subsequent attitude angle and airflow angle on the aircraft.
In addition, in the prior art, when the attitude of the aircraft model is measured in the wind tunnel, a support frame is usually arranged in a wind tunnel test section, and the aircraft model is fixed on the support frame and can only measure the attitude data of the aircraft model when the aircraft model is static or quasi-static; the attitude angle and the airflow angle of the aircraft model in the free flight state can be obtained by the attitude measurement method of the low-speed wind tunnel horizontal free flight model.
Further, the camera is an infrared camera.
The camera adopts the camera that has infrared camera lens, infrared camera's camera can send out the infrared light that the wavelength is 850 nm. The light emitted by the infrared camera can be used for distinguishing the target from the surrounding environment, and noise is reduced. In addition, the high-speed camera generally adopted in the prior art cannot obtain required information in real time, can be obtained after post-processing, and cannot be used for controlling feedback of the information, and the camera adopted in the scheme can feed back the acquired information in real time.
Further, step S40 includes:
step S401: selecting a plurality of positions on an aircraft model, and respectively setting mark points on the positions;
step S402: the camera emits infrared rays to the mark points;
step S403: the camera receives the reflected light of the mark point;
step S404: the camera collects images of the mark points and stores the images as grey-scale images;
step S405: and acquiring the position of the mark point in the two-dimensional image acquired by the camera according to the information in the gray-scale image.
In the above scheme, positions for setting the marking points are selected on the surface of the aircraft model, and the positions of the marking points cannot be located on the same plane when position selection is performed.
The marking points are sheet-type marking points and are adhered to the surface of the aircraft model, so that the surface of the aircraft model cannot be damaged, the aircraft model is convenient to disassemble, the marking points are made of reflecting materials, the reflecting materials have the capacity of enhancing the reflection of infrared rays, and compared with the prior art, the marking points cannot emit rays.
According to the invention, infrared light with the wavelength of 850nm is emitted by an infrared camera and irradiates on a reflective mark point, the mark point and the surrounding environment in an obtained image can be obviously distinguished, the data amount processed by a computer is reduced by only processing the image gray scale information of the mark point and neglecting a background image, the real-time performance is improved, the measurement bandwidth of more than 100Hz can be realized, and the method is suitable for the horizontal free flight control measurement requirement of a low-speed wind tunnel.
It should be noted that the number of the mark points may be 2, 4, 6, or 8, and the specific number may be set according to actual requirements, which is not limited herein.
As shown in fig. 3, further, the attitude angle includes: yaw angleΨAnd a pitch angleθAngle of rollφSaid yaw angleΨAnd a pitch angleθAngle of rollφRespectively obtained by the following formula:
wherein,R bg a transformation matrix used for transforming the world coordinate system to the body axis coordinate system,
for transforming matricesR bg The value of the second column of the first row,
for transforming matricesR bg The value of the first row and the third column,
transformation matrixR bg The third row and the second column.
In the above-described solution, with reference to figure 3,
the angle generated for rotation around the z-axis,θThe angle produced for rotation about the y-axis,
the angle produced for rotation about the x-axis.
Further, the conversion matrix of claimR bg The calculation method comprises the following steps:
as shown in fig. 4, any two of the plurality of marker points are connected to form a baseline, so that the number of the baseline is greater than three;
obtaining world seats corresponding to the baseline vectors of each baseline at different timesMarker systemo g-x g y g z gAnd body axis coordinate systemo b-x b y b z bCoordinates of the lower part;
from each of said baseline vectors in the world coordinate systemo g-x g y g z gCoordinate system with body axiso b-x b y b z bCoordinate conversion relation between the two, the conversion matrix is obtained by adopting the least square methodR bg 。
In the above scheme, the specific implementation process is as follows:
conversion matrix from world coordinate system to body axis systemR bg The following were used:
unfolding to obtain:
wherein
Setting an initial time t0The body axis coordinate system of the aircraft model is parallel to the coordinate axes of the world coordinate system, so that the coordinates of the baseline vector under the body axis coordinate system are not changed along with the change of the attitude of the aircraft model;
then the initial time t0The first baseline vector in the baseline vectors formed by connecting any two marking points on the aircraft model is in the world coordinate systemo g-x g y g z gThe lower coordinate is [ 2 ]x 1，y 1，z 1]Second base line vector in world coordinate systemo g-x g y g z gThe lower coordinate is [ 2 ]x 3，y 3，z 3]The third base line vector is in the world coordinate systemo g-x g y g z gThe lower coordinate is [ 2 ]x 5，y 5，z 5]；
A first baseline vector in a baseline vector formed by any two marking points on the aircraft model at the moment t is in a world coordinate systemo g-x g y g z gThe lower coordinate is [ 2 ]x 2，y 2，z 2]In the axial systemo b-x b y b z bThe lower coordinate is still [ 2 ]x 1，y 1，z 1]Second base line vector in world coordinate systemo g-x g y g z gThe lower coordinate is [ 2 ]x 4，y 4，z 4]In the axial systemo b-x b y b z bThe lower coordinate is still [ 2 ]x 3，y 3，z 3]The third base line vector is in the world coordinate systemo g-x g y g z gThe lower coordinate is [ 2 ]x 6，y 6，z 6]In the axial systemo b-x b y b z bThe lower coordinate is still [ 2 ]x 5，y 5，z 5]Then, there are:
a base line vector consisting of any two marking points is arranged in a world coordinate systemo g-x g y g z gBody-shaft systemo b-x b y b z bThe conversion matrix is obtained by adopting a least square methodR bg 。
Further, as shown in fig. 5, the airflow angle includes: angle of attackα、Sideslip angleβSaid angle of attackαAnd angle of sideslipβThe calculation steps are as follows:
step S501: computingtThe virtual center of the time aircraft model is in the world coordinate systemo g-x g y g z gVelocity component (v) of (1) it，v jt，v kt) Wherein v is itIn the world coordinate system for the virtual center of the aircraft modelo g-x g y g z gMiddle edgex gVelocity component of the shaft, v jtIn the world coordinate system for the virtual center of the aircraft modelo g-x g y g z gMiddle edgey gVelocity component of the shaft, v ktIn the world coordinate system for the virtual center of the aircraft modelo g-x g y g z gMiddle edgez gA velocity component of the shaft;
step S502: velocity v of airflow in superimposed wind tunnel test section a Obtaining the world coordinate system of the virtual center of the aircraft modelo g-x g y g z gWith a relative airflow velocity component of (v) it+v a ，v jt，v kt），v it+v a Superimposing the velocity v of the air flow for the virtual center of the aircraft model a In the world coordinate systemo g-x g y g z gMiddle edgex gA velocity component of the shaft;
step S503: calculating the body axis coordinate system of the virtual center of the aircraft modelo b-x b y b z bVelocity component of (1)u b，v b，w b) Whereinu bThe virtual center of the aircraft model is in the body axis coordinate systemo b-x b y b z bMiddle edgex bThe component of the velocity of the shaft is,v ba body axis coordinate system for the virtual center of the aircraft modelo b-x b y b z bMiddle edgey bThe component of the velocity of the shaft is,w ba body axis coordinate system for the virtual center of the aircraft modelo b-x b y b z bMiddle edgez bA velocity component of the shaft;
step S504: according to the body axis coordinate systemo b-x b y b z bVelocity component of (1)u b，v b，w b) Calculating said angle of attackαAnd angle of sideslipβ。
In the above scheme, the virtual center of the aircraft model may be any point on the aircraft model, and in the embodiment of the present invention, it is preferable to establish the world coordinate systemo g-x g y g z gAnd body axis coordinate systemo b-x b y b z bAnd then, adjusting the virtual center of the aircraft model to coincide with the gravity center of the aircraft model.
Further, the velocity component (v) in step S501 it，v jt，v kt) The calculation method of (2) is as follows:
obtaining a world coordinate system of a virtual center of an aircraft model at the moment to g-x g y g z gIs as followsThe coordinates are (i t，j t，k t) And the virtual center of the aircraft model at the time of t-delta t is in a world coordinate systemo g-x g y g z gThe coordinates ofi t-Δt，j t-Δt，k t-Δt）；
Calculating the world coordinate system of the virtual center of the aircraft model at the moment to g-x g y g z gSaid velocity component (v) of (a) it，v jt，v kt）：
Wherein t is sampling time, and delta t is sampling interval time;i tin the world coordinate system for the virtual center of the aircraft model at time to g-x g y g z gInx gThe value on the axis of the display is,j tin the world coordinate system for the virtual center of the aircraft model at time to g-x g y g z gIny gThe value on the axis of the display is,k tin the world coordinate system for the virtual center of the aircraft model at time to g-x g y g z gInz gThe value on the axis;i t-Δtthe virtual center of the aircraft model at the time of t-delta t is in a world coordinate systemo g-x g y g z gInx gThe value on the axis of the display is,j t-Δtthe virtual center of the aircraft model at the time of t-delta t is in a world coordinate systemo g-x g y g z gIny gThe value on the axis of the display is,k t-Δtthe virtual center of the aircraft model at the time of t-delta t is in a world coordinate systemo g-x g y g z gInz gThe value on the axis.
Further, in step 503, the virtual center of the aircraft model is in the body axis coordinate systemo b-x b y b z bVelocity component of (1)u b，v b，w b) The calculation formula of (a) is as follows:
（u b，v b，w b）=R bg（v it+v a ，v jt，v kt）。
further, angle of attack in step 504αAnd angle of sideslipβThe calculation formula of (a) is as follows:
α=tan -1（w b /u b），β=sin -1（v b/V）
wherein,Von-body axis coordinate system for virtual center of aircraft modelo b-x b y b z bVelocity component of (1)u b，v b，w b) The velocity vector of (a) is,
。
further, the marker points are seen by at least two of the cameras at the same time.
In the scheme, as long as the same mark point is seen by two cameras at the same time, the position of the mark point in the space at the moment t can be determined according to the camera shooting measurement principle.
The method for measuring the attitude of the low-speed wind tunnel horizontal free flight model provided by the embodiment of the invention can be suitable for the research of aircrafts of different models in horizontal free flight in wind tunnels, has good universality and simple operation, can be popularized to other low-speed wind tunnels, and has good engineering application prospect.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (9)
1. A method for measuring the attitude of a horizontal free flight model of a low-speed wind tunnel is characterized by comprising the following steps:
step S10: placing an aircraft model in a wind tunnel test section, wherein a plurality of cameras are arranged on two sides of the top of the aircraft model and are positioned outside the wind tunnel test section;
step S20: calibrating a plurality of cameras simultaneously;
step S30: establishing a world coordinate systemo g-x g y g z gAnd body axis coordinate systemo b-x b y b z bWhereino gIs positioned at any point of the lower tunnel wall of the wind tunnel test section,x gthe shaft is parallel to the axis of the wind tunnel test section and points to the incoming flow direction,y gthe shaft is in the plane of the lower tunnel wall of the wind tunnel test section, andy gaxis perpendicular tox gThe axis is directed to the right and,z gthe axis orientation is in accordance with the right hand rule,o bis the center of gravity of the aircraft model,x bthe shaft is directed forward parallel to the fuselage axis,y bthe axis points to the right perpendicular to the aircraft reference plane,z bthe axis orientation conforms to the right hand rule;
step S40: setting a plurality of marking points on an aircraft model, and acquiring position information of the marking points in a world coordinate system;
step S50: calculating an attitude angle and an airflow angle of the aircraft model according to the position information of the plurality of marking points in the body axis coordinate system;
the airflow angle includes: angle of attackα、Sideslip angleβSaid angle of attackαAnd angle of sideslipβThe calculation steps are as follows:
step S501: computingtThe virtual center of the time aircraft model is in the world coordinate systemo g-x g y g z gVelocity component (v) of (1) it，v jt，v kt) Wherein v is itIn the world coordinate system for the virtual center of the aircraft modelo g-x g y g z gMiddle edgex gVelocity component of the shaft, v jtIn the world coordinate system for the virtual center of the aircraft modelo g-x g y g z gMiddle edgey gVelocity component of the shaft, v ktIn the world coordinate system for the virtual center of the aircraft modelo g-x g y g z gMiddle edgez gA velocity component of the shaft;
step S502: velocity v of airflow in superimposed wind tunnel test section a Obtaining the world coordinate system of the virtual center of the aircraft modelo g-x g y g z gWith a relative airflow velocity component of (v) it+v a ，v jt，v kt），v it+v a Superimposing the velocity v of the air flow for the virtual center of the aircraft model a In the world coordinate systemo g-x g y g z gMiddle edgex gA velocity component of the shaft;
step S503: calculating the body axis coordinate system of the virtual center of the aircraft modelo b-x b y b z bVelocity component of (1)u b，v b，w b) Whereinu bThe virtual center of the aircraft model is in the body axis coordinate systemo b-x b y b z bMiddle edgex bThe component of the velocity of the shaft is,v ba body axis coordinate system for the virtual center of the aircraft modelo b-x b y b z bMiddle edgey bThe component of the velocity of the shaft is,w ba body axis coordinate system for the virtual center of the aircraft modelo b-x b y b z bMiddle edgez bA velocity component of the shaft;
step S504: according to the body axis coordinate systemo b-x b y b z bVelocity component of (1)u b，v b，w b) Calculating said angle of attackαAnd angle of sideslipβ。
2. The attitude measurement method according to claim 1, wherein the camera is an infrared camera.
3. The attitude measurement method according to claim 2, wherein step S40 includes:
step S401: selecting a plurality of positions on an aircraft model, and respectively setting mark points on the positions;
step S402: the camera emits infrared rays to the mark points;
step S403: the camera receives the reflected light of the mark point;
step S404: the camera collects images of the mark points and stores the images as grey-scale images;
step S405: and acquiring the position of the mark point in the two-dimensional image acquired by the camera according to the information in the gray-scale image.
4. The attitude measurement method according to claim 3, wherein the attitude angle includes: yaw angleΨAnd a pitch angleθAngle of rollφSaid yaw angleΨAnd a pitch angleθAngle of rollφRespectively obtained by the following formula:
wherein,R bg a transformation matrix used for transforming the world coordinate system to the body axis coordinate system,
for transforming matricesR bg The value of the second column of the first row,
for transforming matricesR bg The value of the first row and the third column,
transformation matrixR bg The third row and the second column.
5. The attitude measurement method of claim 4, wherein the transformation matrixR bg The calculation method comprises the following steps:
connecting any two of the plurality of marking points to form a base line, so that the number of the base lines is more than three;
obtaining a world coordinate system corresponding to the baseline vector of each baseline at different timeso g-x g y g z gAnd body axis coordinate systemo b-x b y b z bCoordinates of the lower part;
from each of said baseline vectors in the world coordinate systemo g-x g y g z gCoordinate system with body axiso b-x b y b z bCoordinate conversion relation between the two, the conversion matrix is obtained by adopting the least square method
。
6. Attitude measurement according to claim 1Method, characterized in that in step S501 said velocity component (v) is it，v jt，v kt) The calculation method of (2) is as follows:
obtaining a world coordinate system of a virtual center of an aircraft model at the moment to g-x g y g z gThe coordinates ofi t，j t，k t) And the virtual center of the aircraft model at the time of t-delta t is in a world coordinate systemo g-x g y g z gThe coordinates ofi t-Δt，j t-Δt，k t-Δt）；
Calculating the world coordinate system of the virtual center of the aircraft model at the moment to g-x g y g z gSaid velocity component (v) of (a) it，v jt，v kt）：
Wherein t is sampling time, and delta t is sampling interval time;i tin the world coordinate system for the virtual center of the aircraft model at time to g-x g y g z gInx gThe value on the axis of the display is,j tin the world coordinate system for the virtual center of the aircraft model at time to g-x g y g z gIny gThe value on the axis of the display is,k tin the world coordinate system for the virtual center of the aircraft model at time to g-x g y g z gInz gThe value on the axis;i t-Δtthe virtual center of the aircraft model at the time of t-delta t is in a world coordinate systemo g-x g y g z gInx gThe value on the axis of the display is,j t-Δtis t- Δ tWorld coordinate system of virtual center of time aircraft modelo g-x g y g z gIny gThe value on the axis of the display is,k t-Δtthe virtual center of the aircraft model at the time of t-delta t is in a world coordinate systemo g-x g y g z gInz gThe value on the axis.
7. The attitude measurement method of claim 6, wherein the virtual center of the aircraft model is in the body axis coordinate system in step 503o b-x b y b z bVelocity component of (1)u b，v b，w b) The calculation formula of (a) is as follows:
（u b，v b，w b）=R bg（v it+v a ，v jt，v kt）。
8. the attitude measurement method of claim 7, wherein the angle of attack in step 504αAnd angle of sideslipβThe calculation formula of (a) is as follows:
α=tan -1（w b /u b），β=sin -1（v b/V）
wherein,Von-body axis coordinate system for virtual center of aircraft modelo b-x b y b z bVelocity component of (1)u b，v b，w b) The velocity vector of (a) is,
。
9. the attitude measurement method according to claim 3, wherein the marker points are seen by at least two of the cameras at the same time.
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