Coaxial rigid rotor model wind tunnel test blade spacing measurement method

Abstract

The invention discloses a coaxial rigid rotor model wind tunnel test blade spacing measurement method, and belongs to the technical field of aviation aerodynamic force wind tunnel tests. The problem that in the prior art, it is difficult to monitor the overlapping azimuth angle of the coaxial rigid rotor helicopter through a traditional blade distance measuring method is solved. The method comprises the following steps: determining a blade waving measurement path, arranging a grating fiber sensor, building a grating fiber measurement system, calculating a data position corresponding to a coincidence phase according to the coincidence phase of upper and lower blades and the number of data acquisition points of one circle of rotation of a rotor, and performing data acquisition and correlation filtering on a low-rotation-speed state and a test state; the initial central wavelength and the central wavelength offset of the grating fiber at the overlapped position of the upper and lower blades are obtained, and deformation reconstruction is performed on the upper and lower rotor blades by adopting a coordinate transformation method of plane points to obtain the distance between the tips of the upper and lower blades in the vertical direction. The method effectively avoids the limitation of measurement of a specific azimuth angle, and can be applied to a coaxial rigid rotor wind tunnel test.

Description

Technical Field

[0001] The invention relates to a method for measuring blade spacing in a coaxial rigid rotor model wind tunnel test, and belongs to the technical field of aviation aerodynamic wind tunnel tests. Background Art

[0002] High speed is one of the main development trends of helicopters. Helicopters of various configurations have been developed. Among them, coaxial rigid rotor helicopters have become one of the key development directions of high-speed helicopters due to their characteristics. The coaxial rigid rotor unloads the rearward blade through lift bias, avoiding the restriction of the forward blade on the high angle of attack stall problem when the flight speed is high, giving full play to its potential and achieving high-speed forward flight. However, the unique flight characteristics of the coaxial rigid rotor lead to its highly complex flow field and significant aerodynamic interference problems.

[0003] Wind tunnel test is an important means to study the aerodynamic characteristics and interference mechanism of coaxial rigid rotors. However, the distance between the upper and lower rotors of a coaxial rigid rotor is relatively close. Under the condition of large lift bias, the upper and lower rotor blades are very likely to collide, which may lead to serious test accidents. In order to ensure the safety of the test, it is necessary to develop real-time monitoring technology for the spacing between the upper and lower rotor blades. At present, the upper and lower blade spacing monitoring mainly adopts the machine vision method, but it can only measure a specific azimuth angle, and cannot monitor all azimuth angles where the upper and lower blades overlap. There are still certain safety hazards.

[0004] In summary, a method for measuring blade spacing in wind tunnel tests of coaxial rigid rotor models is needed. Summary of the invention

[0005] A brief overview of the present invention is provided below in order to provide a basic understanding of certain aspects of the present invention. It should be understood that this overview is not an exhaustive overview of the present invention. It is not intended to identify key or important parts of the present invention, nor is it intended to limit the scope of the present invention. Its purpose is merely to present certain concepts in a simplified form as a prelude to a more detailed description discussed later.

[0006] In view of this, in order to solve the problem that the traditional blade spacing measurement method in the prior art is difficult to monitor the overlapping azimuth angle of a coaxial rigid rotor helicopter, the present invention provides a blade spacing measurement method for a coaxial rigid rotor model wind tunnel test.

[0007] The technical solution is as follows: A method for measuring blade spacing in a coaxial rigid rotor model wind tunnel test comprises the following steps: S1. Arrange grating fiber optic sensors on the blade surfaces of the upper and lower rotors respectively, and determine the blade flapping measurement path; S2. On the blade flapping measurement paths of the upper and lower rotors, grating optical fiber sensors are arranged at equal intervals along the blade span as blade flapping measurement sensors; S3. Install the blades, build the grating fiber measurement system, realize the transmission of rotating optical signals and complete the conversion of optical signals to electrical signals, and realize data and signal acquisition through the external triggering of the azimuth encoder of the data acquisition system; Specifically: the grating fiber measurement system includes a grating fiber sensor, a fiber slip ring rotating ring, a grating fiber demodulator and a data acquisition system connected in sequence; S4. Calculate the blade overlap phase of the upper and lower rotors according to the coaxial rotor blade crossing angle collected by the data acquisition system; S5. Calculate the data points corresponding to the overlap positions of the upper and lower rotor blades according to the overlap phase of the upper and lower rotor blades and the number of data points collected during one rotation of the rotor; S6. Under low speed condition, the grating fiber signal is collected by the grating fiber sensor, and the obtained pre-test data is subjected to correlation filtering; S7. extracting the coincidence phase data points in the pre-test data to obtain the initial center wavelength of the grating fiber at the coincidence position of the upper and lower rotor blades; S8. Under the test state, the grating fiber signal is collected again by the grating fiber sensor, and the obtained test data is correlated and filtered; S9. extract the coincidence phase data points in the test data, obtain the grating fiber center wavelength offset of the blade coincidence position test state of the upper and lower rotors, and reconstruct the blade deformation of the upper and lower rotors respectively by using the coordinate transformation method of the plane point, and then obtain the flapping displacement of the blade tip of the upper and lower rotors; S10. According to the flapping displacement of the blade tips of the upper and lower rotors, the distance between the blade tips of the upper and lower rotor blades in the vertical direction is calculated.

[0008] Furthermore, in S1, firstly, a characteristic profile of the blade is selected, and a number of grating fiber optic sensors are arranged along the chord direction of the blade; secondly, the root of the blade is fixed so that the chord line of the blade is perpendicular to the ground, and a load is applied to the blade tip step to establish a corresponding relationship between the chord position and the strain; finally, according to the corresponding relationship between the chord position and the strain, the chord position when the swing strain is zero is obtained as the blade flapping measurement path.

[0009] Furthermore, in S4, the blade overlap phase of the upper rotor It is expressed as: ; in, is the number of rotor blades, is the coaxial rotor blade crossing angle, The value is 0, 1, 2...7; Lower rotor blade overlap phase It is expressed as: .

[0010] Furthermore, in S5, the data points corresponding to the overlapped positions of the upper rotor blades are It is expressed as: ; in, The number of data points collected for one revolution of the rotor; The data points corresponding to the overlap position of the lower rotor blades It is expressed as: .

[0011] Further, in said S9, according to the working principle of the grating optical fiber sensor, the curvature of the blade deformation at each grating optical fiber sensor is calculated; Curvature It is expressed as: ; in, is the blade thickness, is the effective elastic-optic constant, is the initial center wavelength of the grating fiber at the overlap position of the upper and lower rotor blades, The center wavelength offset of the grating optical fiber in the test state of the blade overlap position of the upper and lower rotors; Linear fit curvature With arc length The relationship between the two is established, and a certain amount of data is interpolated between adjacent discrete curvature values ​​to form n curvature data. ; n curvature data The corresponding arc length The relationship is: ; in, is the slope of the fitting function, is the constant term of the fitting function, =1, 2, 3...n; Using n curvature data And the corresponding arc length information, combined with the coordinate transformation method, establish the Cartesian coordinate system for node coordinate recursion, and then obtain the flapping displacement of the blade tip of the upper and lower rotors in Cartesian coordinates ; Flapping displacement of the rotor blade tip in Cartesian coordinates The calculation process is expressed as: ; ; ; ; ; ; ; ; ; in, for The angle between the tangent vector of a point and the x-axis, Angle The corresponding arc length, for and The radius of curvature of the arc between two points, for The radius of curvature at the point, for The radius of curvature at the point, for Point The horizontal coordinate of the F-frame is for Point The vertical coordinate of the F-frame is for The horizontal coordinate of the point in Cartesian coordinates, for The ordinate of a point in Cartesian coordinates.

[0012] Furthermore, in S10, the distance between the tips of the upper and lower rotor blades in the vertical direction is It is expressed as: ; in, is the distance between the upper and lower rotor blades at rest, is the upper rotor flapping displacement, The flapping displacement of the lower rotor, is the blade pre-taper angle.

[0013] The beneficial effects of the present invention are as follows: the present invention determines a blade flapping measurement path, arranges grating fiber optic sensors along the flapping measurement path, builds a grating fiber optic measurement system, calculates the overlap phase of the upper and lower blades, calculates the data position corresponding to the overlap phase according to the overlap phase of the upper and lower blades and the number of data collection points for one rotation of the rotor, obtains the initial center wavelength and center wavelength offset of the grating fiber optic at the overlap position of the upper and lower blades after data collection and related filtering in a hovering low-speed state and a test state respectively, reconstructs the deformation of the upper and lower rotor blades respectively by using a coordinate transformation method of a plane point to obtain the flapping displacement of the upper and lower rotor blade tips, and finally obtains the distance between the upper and lower blade tips in the vertical direction according to the spacing between the upper and lower rotor blades in a static state and the rotor pre-cone angle; the present invention realizes quasi-distributed measurement of the flapping of the upper and lower rotor blades through grating fiber optic sensors, and realizes real-time tip distance measurement of all overlap positions of the upper and lower rotors through azimuth triggering technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 This is a flow chart of a method for measuring blade spacing in a coaxial rigid rotor model wind tunnel test; Figure 2 Schematic diagram for the definition of the upper and lower rotor azimuth angles; Figure 3 Schematic diagram for the definition of the upper and lower rotor crossing angles; Figure 4 Schematic diagram of coordinate transformation of plane points; Figure 5 This is a schematic diagram of the rotor tip coordinates. DETAILED DESCRIPTION

[0015] In order to make the technical solutions and advantages of the embodiments of the present invention more clearly understood, the exemplary embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than an exhaustive list of all the embodiments. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0016] refer to Figure 1-Figure 5 The present embodiment is described in detail, a method for measuring blade spacing in a coaxial rigid rotor model wind tunnel test, specifically comprising the following steps: S1. Arrange grating fiber optic sensors on the blade surfaces of the upper and lower rotors respectively, and determine the blade flapping measurement path; S2. On the blade flapping measurement paths of the upper and lower rotors, grating optical fiber sensors are arranged at equal intervals along the blade span as blade flapping measurement sensors; S3. Install the blades, build the grating fiber measurement system, connect the fiber slip ring rotating ring and the grating fiber demodulator to realize the transmission of rotating optical signals and complete the conversion of optical signals to electrical signals, and realize data and signal acquisition through the external trigger of the azimuth encoder of the data acquisition system; Specifically: the grating fiber measurement system includes a grating fiber sensor, a fiber slip ring rotating ring, a grating fiber demodulator and a data acquisition system connected in sequence; S4. Calculate the blade overlap phase of the upper and lower rotors according to the coaxial rotor blade crossing angle collected by the data acquisition system; S5. Calculate the data points corresponding to the overlap positions of the upper and lower rotor blades according to the overlap phase of the upper and lower rotor blades and the number of data points collected during one rotation of the rotor; S6. Check the wind tunnel, coaxial rigid rotor test bench and grating fiber measurement system. After confirming that they are correct, collect the grating fiber signal through the grating fiber sensor at a low speed (30rpm) and perform correlation filtering on the obtained pre-test data; S7. extracting the coincidence phase data points in the pre-test data to obtain the initial center wavelength of the grating fiber at the coincidence position of the upper and lower rotor blades; S8. After the coaxial rigid rotor test bench is started to reach the test speed, the wind tunnel is blown to the test wind speed, and the trim is carried out simultaneously. Under the test state, the grating fiber optic sensor is used to collect the grating fiber optic signal again, and the obtained test data is subjected to correlation filtering. After every 8 laps of data are collected, the azimuth data is averaged to form 1 lap of data; S9. extract the coincidence phase data points in the test data, obtain the grating fiber center wavelength offset of the blade coincidence position test state of the upper and lower rotors, and reconstruct the blade deformation of the upper and lower rotors respectively by using the coordinate transformation method of the plane point, and then obtain the flapping displacement of the blade tip of the upper and lower rotors; S10. Calculate the distance between the tips of the upper and lower rotor blades in the vertical direction according to the flapping displacement of the tips of the upper and lower rotor blades; S11. After completing all test conditions, the wind tunnel is shut down and balancing is carried out simultaneously to ensure that the hub torque is as small as possible. After the wind speed reaches zero, the coaxial rigid rotor test bench is shut down and S10-S11 are repeated during this period, and the spacing between the upper and lower rotor blades is monitored at all times.

[0017] Furthermore, in S1, firstly, a characteristic profile of the blade is selected, and a number of grating fiber optic sensors are arranged along the chord direction of the blade; secondly, the root of the blade is fixed so that the chord line of the blade is perpendicular to the ground, and a load is applied to the blade tip step to establish a corresponding relationship between the chord position and the strain; finally, according to the corresponding relationship between the chord position and the strain, the chord position when the swing strain is zero is obtained as the blade flapping measurement path.

[0018] Furthermore, in S4, the blade overlap phase of the upper rotor It is expressed as: ; in, is the number of rotor blades, is the coaxial rotor blade crossing angle, The value is 0, 1, 2...7; Lower rotor blade overlap phase It is expressed as: .

[0019] Furthermore, in S5, the data points corresponding to the overlapped positions of the upper rotor blades are It is expressed as: ; in, The number of data points collected for one revolution of the rotor; The data points corresponding to the overlap position of the lower rotor blades It is expressed as: .

[0020] Further, in said S9, according to the working principle of the grating optical fiber sensor, the curvature of the blade deformation at each grating optical fiber sensor is calculated; Curvature It is expressed as: ; in, is the blade thickness, is the effective elastic-optic constant, is the initial center wavelength of the grating fiber at the overlap position of the upper and lower rotor blades, The center wavelength offset of the grating optical fiber in the test state of the blade overlap position of the upper and lower rotors; Linear fit curvature With arc length The relationship between the two is established, and a certain amount of data is interpolated between adjacent discrete curvature values ​​to form n curvature data. ; n curvature data The corresponding arc length It is expressed as: ; in, is the slope of the fitting function, is the constant term of the fitting function, =1, 2, 3...n; Using n curvature data And the corresponding arc length information, combined with the coordinate transformation method, establish the Cartesian coordinate system for node coordinate recursion, and then obtain the flapping displacement of the blade tip of the upper and lower rotors in Cartesian coordinates ; Flapping displacement of the rotor blade tip in Cartesian coordinates The calculation process is expressed as: ; ; ; ; ; ; ; ; ; in, for The angle between the tangent vector of a point and the x-axis, Angle The corresponding arc length, for and The radius of curvature of the arc between two points, for The radius of curvature at the point, for The radius of curvature at the point, for Point The horizontal coordinate of the F-frame is for Point The vertical coordinate of the F-frame is for The horizontal coordinate of the point in Cartesian coordinates, for The ordinate of a point in Cartesian coordinates.

[0021] Furthermore, in S10, the distance between the tips of the upper and lower rotor blades in the vertical direction is It is expressed as: ; in, is the distance between the upper and lower rotor blades at rest, is the upper rotor flapping displacement, The flapping displacement of the lower rotor, is the blade pre-taper angle.

[0022] Although the present invention has been described according to a limited number of embodiments, it will be apparent to those skilled in the art, with the benefit of the above description, that other embodiments may be envisioned within the scope of the invention thus described. In addition, it should be noted that the language used in this specification is selected primarily for readability and teaching purposes, rather than for explaining or defining the subject matter of the present invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the present invention is illustrative, not restrictive, with respect to the scope of the present invention, which is defined by the appended claims.

Claims

1. A method for measuring blade spacing in a coaxial rigid rotor model wind tunnel test, characterized in that: The following steps are involved: S1. Arrange grating fiber optic sensors on the blade surfaces of the upper and lower rotors respectively, and determine the blade flapping measurement path; S2. On the blade flapping measurement paths of the upper and lower rotors, grating optical fiber sensors are arranged at equal intervals along the blade span as blade flapping measurement sensors; S3. Install the blades, build the grating fiber measurement system, realize the transmission of rotating optical signals and complete the conversion of optical signals to electrical signals, and realize data and signal acquisition through the external triggering of the azimuth encoder of the data acquisition system; Specifically: the grating fiber measurement system includes a grating fiber sensor, a fiber slip ring rotating ring, a grating fiber demodulator and a data acquisition system connected in sequence; S4. Calculate the blade overlap phase of the upper and lower rotors according to the coaxial rotor blade crossing angle collected by the data acquisition system; S5. Calculate the data points corresponding to the overlap positions of the upper and lower rotor blades according to the overlap phase of the upper and lower rotor blades and the number of data points collected during one rotation of the rotor; S6. Under low speed condition, the grating fiber signal is collected by the grating fiber sensor, and the obtained pre-test data is subjected to correlation filtering; S7. extracting the coincidence phase data points in the pre-test data to obtain the initial center wavelength of the grating fiber at the coincidence position of the upper and lower rotor blades; S8. Under the test state, the grating fiber signal is collected again by the grating fiber sensor, and the obtained test data is correlated and filtered; S9. extract the coincidence phase data points in the test data, obtain the grating fiber center wavelength offset of the blade coincidence position test state of the upper and lower rotors, and reconstruct the blade deformation of the upper and lower rotors respectively by using the coordinate transformation method of the plane point, and then obtain the flapping displacement of the blade tip of the upper and lower rotors; S10. According to the flapping displacement of the blade tips of the upper and lower rotors, the distance between the blade tips of the upper and lower rotor blades in the vertical direction is calculated.

2. The method for measuring blade spacing in a coaxial rigid rotor model wind tunnel test according to claim 1, characterized in that: In S1, first, a characteristic profile of the blade is selected, and a number of grating fiber optic sensors are arranged along the chord direction of the blade; secondly, the root of the blade is fixed so that the blade chord line is perpendicular to the ground, and a load is applied to the blade tip step to establish a corresponding relationship between the chord position and the swing strain; finally, based on the corresponding relationship between the chord position and the swing strain, the chord position when the swing strain is zero is obtained as the blade flapping measurement path.

3. The method for measuring blade spacing in a coaxial rigid rotor model wind tunnel test according to claim 2, characterized in that: In S4, the blade overlap phase of the upper rotor It is expressed as: ； in, is the number of rotor blades, is the coaxial rotor blade crossing angle, The value is 0, 1, 2...7; Lower rotor blade overlap phase It is expressed as: 。 4. The method for measuring blade spacing in a coaxial rigid rotor model wind tunnel test according to claim 3 is characterized in that: In S5, the data points corresponding to the overlapped positions of the upper rotor blades It is expressed as: ； in, The number of data points collected for one revolution of the rotor; The data points corresponding to the overlap position of the lower rotor blades It is expressed as: 。 5. The method for measuring blade spacing in a coaxial rigid rotor model wind tunnel test according to claim 4, characterized in that: In the above S9, according to the working principle of the grating optical fiber sensor, the curvature of the blade deformation at each grating optical fiber sensor is calculated; Curvature It is expressed as: ； in, is the blade thickness, is the effective elastic-optic constant, is the initial center wavelength of the grating fiber at the overlap position of the upper and lower rotor blades, The center wavelength offset of the grating optical fiber in the test state of the blade overlap position of the upper and lower rotors; Linear fit curvature With arc length The relationship between the two is established, and a certain amount of data is interpolated between adjacent discrete curvature values ​​to form n curvature data. ; n curvature data The corresponding arc length It is expressed as: ； in, is the slope of the fitting function, is the constant term of the fitting function, =1, 2, 3...n; Using n curvature data And the corresponding arc length information, combined with the coordinate transformation method, establish the Cartesian coordinate system for node coordinate recursion, and then obtain the flapping displacement of the blade tip of the upper and lower rotors in Cartesian coordinates ; Flapping displacement of the rotor blade tip in Cartesian coordinates The calculation process is expressed as: ； ； ； ； ； ； ； ； ； in, for The angle between the tangent vector of a point and the x-axis, Angle The corresponding arc length, for and The radius of curvature of the arc between two points, for The radius of curvature at the point, for The radius of curvature at the point, for Point The horizontal coordinate of the F-frame is for Point The vertical coordinate of the F-frame is for The horizontal coordinate of the point in Cartesian coordinates, for The ordinate of a point in Cartesian coordinates, is n curvature data The corresponding arc length.

6. The method for measuring blade spacing in a coaxial rigid rotor model wind tunnel test according to claim 5, characterized in that: In S10, the distance between the tips of the upper and lower rotor blades in the vertical direction is It is expressed as: ； in, is the distance between the upper and lower rotor blades at rest, is the upper rotor flapping displacement, The flapping displacement of the lower rotor, is the blade pre-taper angle.

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