A method and apparatus for testing aerodynamic flow fields

Abstract

This invention relates to an aerodynamic flow field testing method and apparatus, belonging to the field of aerodynamic flow field testing technology. The method involves activating a disturbance source, setting its operating conditions, and transmitting a laser beam through the disturbed aerodynamic flow field to a wavefront sensor to obtain a laser beam pattern. Based on this pattern, a laser wavefront corresponding to the operating conditions is reconstructed. All operating conditions of the disturbance source are changed and iterated. Based on the laser wavefront, the temporal and spatial variation indices of the laser wavefront are calculated and used as the transient and spatiotemporal distribution characteristics of the aerodynamic flow field, respectively, thus completing the aerodynamic flow field test. By acquiring the laser beam pattern and calculating the laser wavefront for various operating conditions of the disturbance source, a more accurate understanding of the aerodynamic flow field variation patterns can be obtained. This helps in analyzing the inherent flow mechanism of aero-optical effects, reduces interference from ambient light, effectively saves the number of trips required to operate the disturbance source, improves testing efficiency, and reduces testing costs.

Description

Technical Field

[0001] This invention belongs to the field of aerodynamic flow field testing technology, and specifically relates to an aerodynamic flow field testing method and apparatus. Background Technology

[0002] Aerodynamic optics is the study of the interaction between light beams and airflow media. With the development and application of high-energy laser technology, airborne lasers, and optical guidance, research on the interaction between light beams and complex flow fields has become more in-depth. The research objects of aerodynamic optics have expanded from low-speed turbulence and subsonic to ultra-hypersonic shear turbulence layers and turbulent boundary layers. The research methods have evolved from statistical methods before the 1980s to current research methods that combine statistical methods with dynamic real-time measurements.

[0003] Whether in laser communication systems, laser energy application systems, or laser illumination systems, beams inevitably propagate through aerodynamic fields. Changes in pressure, temperature, and velocity generated by the flow field alter the density and refractive index distribution along the light propagation path, leading to wavefront phase distortion and aero-optical effects. Schlieren and shading techniques based on refractive index fields generally only provide qualitative observations of these aero-optical effects and do not yield characteristic information about the aerodynamic flow field. Meanwhile, interferometric measurement techniques based on phase changes are expensive and susceptible to environmental interference. Summary of the Invention

[0004] To address the shortcomings of existing technologies and solve the aforementioned problems, an aerodynamic flow field testing method and apparatus are proposed. The laser wavefront obtained from the test is used to analyze the influence of the aerodynamic flow field on the laser transmission channel, thereby realizing aerodynamic flow field testing.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] In a first aspect, the present invention provides an aerodynamic flow field testing method, comprising:

[0007] Turn on the disturbance source to disturb the aerodynamic flow field;

[0008] The operating conditions of the disturbance source are set. The laser is transmitted to the wavefront sensor through the disturbed aerodynamic flow field to obtain the laser spot array. Based on the laser spot array, the laser wavefront corresponding to the operating condition is reconstructed. All operating conditions of the disturbance source are changed and traversed to obtain the laser wavefront corresponding to each operating condition.

[0009] Based on the laser wavefront, the temporal and spatial variation indices of the laser wavefront are calculated. These indices are then used as the transient and spatiotemporal distribution characteristics of the aerodynamic flow field to complete the aerodynamic flow field test.

[0010] The technical solution is further configured such that the disturbance source includes a rotor tower, a helicopter rotor blade, or a wind tunnel, and the operating conditions include rotor speed, rotor collective pitch, spatial position of the wind source, or wind source fan speed.

[0011] The technical solution is further configured such that the laser is emitted by a laser emitting device, and the wavelength, power and aperture of the laser are adjustable.

[0012] The technical solution is further configured such that the laser emitting device and the wavefront sensor are arranged on the same optical axis.

[0013] The technical solution is further configured such that the disturbance source is located on the optical axis of the wavefront sensor.

[0014] The technical solution is further configured such that the disturbance source is located outside the optical axis of the wavefront sensor.

[0015] This technical solution is further configured such that the reconstruction of the laser wavefront corresponding to the operating condition based on the laser spot array specifically includes:

[0016] The laser beam pattern is divided into spatial sub-apertures using a microlens array of a wavefront sensor to obtain the intensity distribution information of the sub-aperture beams. The centroid position of the beam is extracted from the intensity distribution information of the sub-aperture beams, and the laser wavefront is reconstructed based on the centroid position.

[0017] This technical solution is further configured such that the time variation index of the laser wavefront includes the peak and trough values, the root mean square value, and the laser beam quality factor.

[0018] The spatial variation indicators of the laser wavefront include the peak and trough values, root mean square value, and the laser beam quality factor as curves over time.

[0019] This technical solution is further configured to calculate the peak and trough values ​​and root mean square value based on the laser wavefront, and obtain the curves of the peak and trough values ​​and root mean square value changing with time, respectively.

[0020] The far-field spot corresponding to the laser wavefront is calculated using the diffraction theorem, and the laser beam quality factor is calculated based on the far-field spot to obtain the curve of the laser beam quality factor changing with time.

[0021] The technical solution is further configured to use Zernike polynomials to decompose the laser wavefront, obtain the Zernike distribution coefficient of the laser wavefront frame by frame, and obtain the phase difference category introduced by the disturbance source under the operating condition.

[0022] This technical solution is further configured to obtain the Zernike distribution coefficient variation curve over time based on the Zernike distribution coefficient of a single-frame laser wavefront, and obtain the power density spectrum of the Zernike distribution coefficient over time using spectral analysis, thereby obtaining the rate of change of the aerodynamic flow field over time.

[0023] This technical solution is further configured to include, before activating the disturbance source, determining the test path of the aerodynamic flow field and acquiring the ambient temperature and humidity.

[0024] Secondly, the present invention also provides an apparatus for implementing an aerodynamic flow field testing method, comprising:

[0025] A laser that emits laser light, the wavelength, power, and aperture of which are adjustable;

[0026] The disturbance source is located inside or to the side of the aerodynamic flow field to be tested;

[0027] The Hartmann sensor is a device in which the laser emitted by the laser is transmitted to the Hartmann sensor through the aerodynamic flow field after being disturbed by the disturbance source. The Hartmann sensor is set on the same optical axis as the laser.

[0028] And a processor, which communicates with the Hartmann sensor.

[0029] The beneficial effects of this invention are:

[0030] 1. To obtain laser spot arrays and calculate laser wavefronts for various operating conditions of disturbance sources, thereby gaining a more accurate understanding of the changes in the aerodynamic flow field, which helps to analyze the inherent flow mechanism of aero-optical effects.

[0031] 2. The laser wavelength is adjustable, thus avoiding the laser wavelength from being close to the dominant wavelength of ambient light in the measurement environment, thereby reducing interference introduced by ambient light. The laser power is adjustable, thus overcoming the energy attenuation caused by absorption, scattering and other effects during laser transmission. The laser aperture is adjustable, so as to ensure that the Hartmann sensor can collect aerodynamic flow field information in a large space.

[0032] 3. By acquiring the laser spot array, the temporal and spatial variation indicators of the laser wavefront can be obtained. The amount of information acquired in a single measurement is large, which effectively saves the number of trips required for the disturbance source and improves the testing efficiency.

[0033] 4. Testing can be completed using lasers, Hartmann sensors, and processors, reducing testing costs and possessing high engineering value and practical significance. Attached Figure Description

[0034] Figure 1 This is a flowchart of the aerodynamic flow field testing method in this invention;

[0035] Figure 2 This is a schematic diagram of the Zernike coefficient decomposition of the laser wavefront in the nth frame of a certain data set;

[0036] Figure 3 This is a graph of the Zernike coefficient-t of the nth term on the laser wavefront under certain data.

[0037] Figure 4 This is a schematic diagram of the Zernike coefficient-t power density spectrum and the cumulative power density spectrum under a certain number of data.

[0038] Figure 5 This is a schematic diagram of the apparatus for implementing the aerodynamic flow field testing method in this invention;

[0039] Figure 6 This is a schematic diagram of another device for implementing aerodynamic flow field testing in this invention.

[0040] In the attached diagram: 1-Laser, 2-Disturbance source, 3-Hartmann sensor, 4-Processor. Detailed Implementation

[0041] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Based on the embodiments in this application, other similar embodiments obtained by those skilled in the art without creative effort should all fall within the scope of protection of this application. Furthermore, directional terms mentioned in the following embodiments, such as "up," "down," "left," and "right," are only for reference to the directions in the accompanying drawings; therefore, the directional terms used are for illustrative purposes and not for limiting the invention.

[0042] Example 1:

[0043] like Figure 1 As shown, an aerodynamic flow field testing method includes the following steps:

[0044] S100. Turn on the disturbance source to disturb the aerodynamic flow field.

[0045] The disturbance sources include rotor towers, helicopter rotors, or wind tunnels, with different sources corresponding to different operating conditions. Specifically, the operating conditions for rotor towers and helicopter rotors include rotor collective pitch and rotor speed, while the operating conditions for wind tunnels include the spatial location of the wind source and the speed of the wind turbine.

[0046] In addition, for different disturbance sources, it is necessary to record the test scenario (such as rotor tower, helicopter rotor, wind tunnel, etc.), determine the test path of the aerodynamic flow field, and obtain the ambient temperature and humidity, and set up the test experimental device according to the test path.

[0047] S200. Set the operating conditions of the disturbance source. The laser is transmitted to the wavefront sensor through the disturbed aerodynamic flow field to obtain a laser spot array. Based on the laser spot array, reconstruct the laser wavefront corresponding to the operating conditions. Change and traverse all operating conditions of the disturbance source to obtain the laser wavefront corresponding to each operating condition.

[0048] Specifically, the laser is emitted by a laser emitting device, and the wavelength, power, and aperture of the laser are adjustable. The adjustable wavelength avoids the laser wavelength being close to the dominant wavelength of ambient light in the measurement environment, thus reducing interference introduced by ambient light. The laser power is affected by the length of the test path; for longer test paths, a higher laser power should be selected to overcome energy attenuation caused by absorption and scattering effects during laser transmission. The laser aperture is affected by the sub-aperture resolution of the wavefront sensor. To improve the accuracy of the laser wavefront and leverage the detection sensitivity advantage of the light field recording camera in the wavefront sensor, a higher-resolution microlens array is preferable. In this case, the emission aperture needs to be increased to ensure that the wavefront sensor can acquire aerodynamic flow field information over a larger space.

[0049] Preferably, the laser emitting device is arranged on the same optical axis as the wavefront sensor, and the laser wavelength should be selected to correspond to the spectral response curve of the wavefront sensor camera, thereby improving the camera's acquisition response sensitivity.

[0050] Preferably, the reconstructing of the laser wavefront corresponding to the operating condition based on the laser spot array specifically includes:

[0051] The laser beam pattern is spatially sub-apertured using a microlens array of a wavefront sensor to obtain the intensity distribution information of the sub-aperture beams. The centroid position of the beam is extracted from the intensity distribution information of the sub-aperture beams. Combined with the region method or mode method in wavefront reconstruction, the laser wavefront is reconstructed based on the centroid position of the beam. The specific reconstruction process is as follows:

[0052] The laser wavefront W′0 can be represented as:

[0053]

[0054] Where W0(x,y) is the actual original wavefront, W d (x,y) represents the target wavefront that needs to be achieved through correction, and α j Let Z(x,y) be the coefficient of the j-th Zernike polynomial, and let Z(x,y) be the Zernike polynomial in Cartesian coordinates.

[0055] Due to the aperture segmentation effect of the wavefront sensor microlens array, the slope of the centroid of the light spot in the i-th sub-aperture is g. ix g iy It can be represented as:

[0056]

[0057] This leads to the slope wavefront g. ix g iy The relationship between G and the Zernike coefficient is expressed as: G = K·α;

[0058] Where G is the wavefront slope matrix, α is a one-dimensional vector matrix composed of Zernike polynomial coefficients, and K is the laser wavefront matrix. When the number of rows in matrix K is greater than the number of columns, the least squares method can be used to obtain the Zernike coefficient matrix α, i.e., α = K. + G, where K + Given the generalized inverse matrix of K, and after obtaining the Zernike polynomial coefficients, the laser wavefront W′0 can be calculated according to Formula 1.

[0059] S300: Based on the laser wavefront, the time and space variation indices of the laser wavefront are calculated. The time and space variation indices of the laser wavefront are used as the transient and spatiotemporal distribution characteristics of the aerodynamic flow field to complete the aerodynamic flow field test.

[0060] Preferably, the temporal variation indicators of the laser wavefront include peak and trough values, root mean square value, and laser beam quality factor; the spatial variation indicators of the laser wavefront include the time variation curves of peak and trough values, root mean square value, and laser beam quality factor, respectively.

[0061] The peak and trough values ​​(PV value) and root mean square value (RMS value) of the laser wavefront are calculated, and the curves of their variation with time t (PV-t curve and RMS-t curve) are obtained respectively.

[0062] The far-field spot corresponding to the laser wavefront is calculated using the diffraction theorem. Based on the far-field spot, the laser beam quality factor β is calculated, and the curve of the laser beam quality factor versus time (β-t curve) is obtained. The laser beam quality factor β is calculated according to its definition. θreal is the far-field divergence angle of the actual beam, and θideal is the far-field divergence angle of the ideal reference beam corresponding to the ideal plane wave.

[0063] Specifically, the transient distribution characteristics of the aerodynamic flow field are analyzed as follows:

[0064] The laser wavefront is decomposed using Zernike polynomials, and the Zernike distribution coefficients of the laser wavefront are obtained frame by frame to obtain the phase difference category introduced by the disturbance source under this operating condition.

[0065] Based on the Zernike distribution coefficient of a single-frame laser wavefront, such as Figure 2As shown, the aberration category can be obtained from the horizontal axis, and the weight of the aberration category can be obtained from the vertical axis. The distribution information of the proportion of primary aberrations (spherical aberration, coma, astigmatism, etc.) in each frame is quantitatively obtained, and then the aberration category introduced by the disturbance source under this operating condition is obtained.

[0066] Specifically, the spatiotemporal distribution characteristics of the aerodynamic flow field are analyzed as follows:

[0067] The Zernike distribution coefficient curve over time (Zernike coefficient-t curve) is obtained based on the Zernike distribution coefficient of a single-frame laser wavefront. The power density spectrum of the Zernike distribution coefficient over time (Zernike coefficient-t power density spectrum) is obtained by using spectral analysis, thus obtaining the rate of change of the aerodynamic flow field over time.

[0068] Based on the Zernike coefficient-t curve, such as Figure 3 As shown, the Zernike coefficient Z of a specified number of terms in a continuously measured laser wavefront is obtained. th By analyzing the degree of oscillation in the line graph, we can initially determine the time-varying characteristics of the aerodynamic flow field introduced by the optical phase difference, and then indirectly estimate the rate of change of the aerodynamic flow field with time under this operating condition.

[0069] Based on the Zernike coefficient-t power density spectrum and the cumulative power percentage curve, the information percentage value is taken to obtain the frequency F corresponding to the intersection point with the Zernike distribution coefficient power density spectrum. Then, the Zernike coefficient Z for a specified number of terms is obtained for that emission. th The frequency of change over time is mainly in the range of 0 to F, while the Zernike coefficient Z is the specified number of terms. th Other frequency components are lower. For example... Figure 4 As shown, the information percentage is 99%. Draw an auxiliary line through the right vertical axis to obtain the horizontal axis frequency F corresponding to the intersection with the Zernike distribution coefficient power density spectral line (F = 2.7 Hz in the figure).

[0070] Example 2:

[0071] like Figure 5 As shown, an apparatus for implementing an aerodynamic flow field testing method includes:

[0072] Laser 1, which emits laser light, the wavelength, power and aperture of which are adjustable;

[0073] Disturbance source 2 is located to the side of the aerodynamic flow field test path;

[0074] The Hartmann sensor 3 is transmitted to the laser emitted by the laser 1 through the aerodynamic flow field test path. The Hartmann sensor 3 and the laser 1 are set on the same optical axis.

[0075] And processor 4, which is connected in communication with Hartmann sensor 3, for processing the laser spot array collected by Hartmann sensor 3.

[0076] After laser 1, Hartmann sensor 3, and processor 4 are turned on, wavefront data is recorded and processed to obtain the corresponding wavefront data. Disturbance source 2 is then activated to test the aerodynamic flow field characteristics under different operating conditions, recording data until all operating conditions have been tested. The aerodynamic wavefront data under each operating condition are compared, and the changing patterns are analyzed to complete the aerodynamic flow field characteristic test. This device can accurately collect wavefront data under various operating conditions, thereby obtaining the aerodynamic flow field variation patterns and completing the aerodynamic characteristic test.

[0077] In some other embodiments, such as Figure 6 As shown, disturbance source 2 can also be located inside the aerodynamic flow field test path.

[0078] The present invention has been described in detail above. The above description is only a preferred embodiment of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of this application should still fall within the scope of the present invention.

Claims

1. A method for testing aerodynamic flow fields, characterized in that, include: Turn on the disturbance source to disturb the aerodynamic flow field; The operating conditions of the disturbance source are set. The laser is transmitted to the wavefront sensor through the disturbed aerodynamic flow field to obtain the laser spot array. Based on the laser spot array, the laser wavefront corresponding to the operating condition is reconstructed. All operating conditions of the disturbance source are changed and traversed to obtain the laser wavefront corresponding to each operating condition. Based on the laser wavefront, the temporal and spatial variation indices of the laser wavefront are calculated. These indices are then used as the transient and spatiotemporal distribution characteristics of the aerodynamic flow field to complete the aerodynamic flow field test. The temporal variation indices of the laser wavefront include peak and trough values, root mean square (RMS) values, and laser beam quality factor. The spatial variation indices of the laser wavefront include peak and trough values, RMS values, and laser beam quality factor, each with time-varying curves. Based on the laser wavefront, peak and trough values ​​and RMS values ​​are calculated, and their time-varying curves are obtained. The far-field spot corresponding to the laser wavefront is calculated using the diffraction theorem. Based on the far-field spot, the laser beam quality factor is calculated, and its time-varying curve is obtained. The laser wavefront is decomposed using Zernike polynomials, and the Zernike distribution coefficients of a single frame of the laser wavefront are obtained frame by frame, thus obtaining the phase difference category introduced by the disturbance source under this operating condition. Based on the Zernike distribution coefficients of a single frame of the laser wavefront, the time-varying curve of the Zernike distribution coefficients is obtained. The power density spectrum of the Zernike distribution coefficients with time is obtained using spectral analysis, thus revealing the rate of change of the aerodynamic flow field with time.

2. The aerodynamic flow field testing method according to claim 1, characterized in that, The disturbance source includes a rotor tower, helicopter rotor blades, or a wind tunnel, and the operating conditions include rotor speed, rotor collective pitch, spatial location of the wind source, or wind source fan speed.

3. The aerodynamic flow field testing method according to claim 1 or 2, characterized in that, The laser is emitted by a laser emitting device, and the wavelength, power, and aperture of the laser are adjustable.

4. The aerodynamic flow field testing method according to claim 3, characterized in that, The laser emitting device is set on the same optical axis as the wavefront sensor.

5. The aerodynamic flow field testing method according to claim 1, characterized in that, The reconstruction of the laser wavefront corresponding to the operating condition based on the laser spot array specifically includes: The laser beam pattern is divided into spatial sub-apertures using a microlens array of a wavefront sensor to obtain the intensity distribution information of the sub-aperture beams. The centroid position of the beam is extracted from the intensity distribution information of the sub-aperture beams, and the laser wavefront is reconstructed based on the centroid position.

6. An apparatus for implementing the aerodynamic flow field testing method according to any one of claims 1-5, characterized in that, include: A laser that emits laser light, the wavelength, power, and aperture of which are adjustable; The disturbance source is located inside or to the side of the aerodynamic flow field to be tested; The Hartmann sensor is a device in which the laser emitted by the laser is transmitted to the Hartmann sensor through the aerodynamic flow field after being disturbed by the disturbance source. The Hartmann sensor is set on the same optical axis as the laser. And a processor, which communicates with the Hartmann sensor.

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