Aircraft imaging flow field steady state and transient state discrimination method

Abstract

The invention discloses an aircraft imaging flow field steady state and transient state discrimination method, and the method carries out the primary processing through a first time, a reverse ray tracing method and a first judgment method, and carries out the secondary processing through a second time and a second judgment method, and is closer to the primary processing in the prior art. Compared with the prior art in which division processing is directly carried out through second time, more data is contained after division, and the processing time is longer, the method has the advantages that the secondary time period can be quickly selected from the long time period, and then the secondary time period is subdivided through secondary processing, so that the obtained steady-state and transient-state conversion time points are more accurate; and the processed data is far smaller than that in the prior art, and the data processing speed is higher.

Description

Technical Field

[0001] The present invention relates to the technical field of flight state determination, and in particular to a method for discriminating between the steady state and transient state of an aircraft imaging flow field. Background Art

[0002] When an aircraft flies at high speed in the atmosphere, real gas effects, shock-induced boundary layer separation and other complex flow fields will occur between the optical dome and the free stream. When light propagates in the flow field, it will be deflected, causing thermal radiation and image transmission interference to the infrared imaging detection system. This phenomenon that the change of the gas medium density causes the optical wavefront to be distorted, thereby having an adverse effect on the imaging performance of the airborne optical system, is called the aerodynamic optical effect; during the ascent and re-entry phases of the aircraft, both experience a transition process from transient to steady state. Exploring the time required for the aircraft to transition from transient to steady state, that is, obtaining the time point when the aircraft transitions to the steady state, is beneficial to accurately cancel the aerodynamic optical effect and avoid the reduction of the performance of the airborne optical system caused by different aerodynamic optical effects in the two flight states;

[0003] However, the existing judgment method separates the aerodynamic optical flow field from the overall light propagation path, and the data required for the judgment is large, time-consuming, and not conducive to quickly giving a judgment result. Summary of the Invention

[0004] In view of the above-mentioned defects or deficiencies in the prior art, it is desirable to provide a method for discriminating between the steady state and transient state of an aircraft imaging flow field.

[0005] A method for discriminating between the steady state and transient state of an aircraft imaging flow field provided by the present invention specifically includes the following steps:

[0006] S100. Simulate the flight scenario of the aircraft to obtain a simulation result;

[0007] S200. Process the simulation result to obtain several gross parameters sorted by flight time. The interval time between each gross parameter is the first time, and each gross parameter includes a head cover temperature cloud map and a flow field density cloud map;

[0008] S300. Process each gross parameter by the reverse ray tracing method to obtain the imaging offset value corresponding to each gross parameter;

[0009] S400. Process each imaging offset value by the first judgment method to obtain a conversion time region, several first transient time periods and several first steady state time periods, where the conversion time region is the time region when the flight state changes from transient to steady state;

[0010] S500. Process the part of the simulation results within the conversion time region to obtain several sub-parameters sorted by flight time. The time interval between adjacent sub-parameters is the second time, and each sub-parameter includes a head cover temperature cloud map.

[0011] S600. Process each of the sub-parameters through a second judgment method to obtain several second steady-state time periods and several second transient time periods.

[0012] According to the technical solution provided by the embodiment of the present application, step S100 specifically includes the following steps:

[0013] S110. Perform proportional three-dimensional modeling on the optical head cover of the aircraft to obtain a simulated head cover.

[0014] S120. Establish a data interaction link with the flight management computer to obtain the flight parameters of the aircraft, where the flight parameters include flight altitude, Mach number, and angle of attack.

[0015] S130. Simulate the flight scenario of the aircraft through simulation software to obtain the simulation results.

[0016] According to the technical solution provided by the embodiment of the present application, the reverse ray tracing method specifically includes the following steps:

[0017] S301. Select the cross-section of the simulated head cover and the aerodynamic optical flow field to establish an X-Y coordinate system, and set the ray tracing initial point, the initial ray incident angle θ 1 , the refractive index N 1 of the gas field inside the head cover, and the step size h.

[0018] S302. Calculate the refractive index of each point inside the simulated head cover through the first formula, and the first formula is as follows:

[0019] N 2 = N 0 + α * (T - T 0 )

[0020] Where N 2 is the refractive index of the simulated head cover at temperature T, which is obtained from the head cover temperature cloud map in the coarse sub-parameters. N 0 is the refractive index of the simulated head cover at temperature T 0 , and α is the thermo-optic coefficient of the simulated head cover.

[0021] S303. Calculate through the second formula to obtain the refractive index of each point in the aerodynamic optical flow field, and the second formula is as follows:

[0022] N 3 = 1 + K GD * ρ; q = 2, 3,..., m

[0023] Among them, N 3 is the refractive index at the refraction point, K GD is the GD coefficient, ρ is the flow field density at the refraction point, which is obtained from the flow field density cloud map in the coarse-divided parameters;

[0024] S304, calculating by a third formula to obtain a refraction angle after the light is refracted, the third formula is as follows:

[0025] n q *sinθ q =n q+1 *sinθ q+1 ; q=1,2,3,…,m

[0026] Among them, n q is the refractive index of the q-1th refraction point, n q+1 is the refractive index at the qth refraction point, θ q is the incident angle of the light after the q-1th time, θ q+1 is the refraction angle of the light after the qth refraction;

[0027] S305, the light beam follows the initial incident angle θ 1 After being emitted, the light refracts once after each forward step h at the speed of light. The light passes through the internal air field of the hood, the simulated hood, and the aero-optical flow field in sequence. When the light refracts for the qth time and enters the atmospheric free flow from the aero-optical flow field, the coordinates of the qth refraction (x q ,y q ) and the refraction angle θ q+1 ;

[0028] S306, extending the qth refracted light in reverse direction to the Y axis in the XY coordinate system to form an offset point;

[0029] S308, calculating the distance between the offset point and the initial point of the ray tracing, and marking it as the imaging offset value.

[0030] According to the technical solution provided in the embodiment of the present application, the first determination method specifically includes the following steps:

[0031] S401, arranging the imaging offset values ​​in chronological order;

[0032] S402, calculating a first difference between adjacent imaging offset values;

[0033] S403. If the first difference is less than 1% of any one of the two imaging offset values, the time periods corresponding to the adjacent imaging offset values are marked as the first steady-state time periods, and the flight state of the aircraft is in a steady state. Otherwise, the corresponding time periods are marked as the first transient time periods, and the flight state of the aircraft is in a transient state.

[0034] S404. Select, in chronological order, the first transient time period adjacent to a first steady-state time period, and modify the label of this first transient time period to a conversion time region.

[0035] According to the technical solution provided by the embodiment of the present application, the second determination method specifically includes the following steps:

[0036] S601. Mark the front vertex of the simulated nose cone as the end point, and mark the highest surface temperature point of the simulated nose cone as the stagnation point.

[0037] S602. Obtain the end point temperature and the stagnation point temperature corresponding to each of the subdivision parameters, where both the end point temperature and the stagnation point temperature are obtained from the temperature nephogram.

[0038] S603. Calculate the second difference between the end point temperature and the stagnation point temperature in the same set of subdivision parameters.

[0039] S604. If the second difference is less than 1% of any one of the corresponding end point temperature and stagnation point temperature, the corresponding temperature nephogram is a steady-state nephogram. Otherwise, the corresponding temperature nephogram is a transient nephogram.

[0040] S605. The time periods corresponding to the adjacent steady-state nephograms are marked as the second steady-state time periods, and the flight state of the aircraft is in a steady state. Otherwise, the corresponding time periods are marked as the second transient time periods, and the flight state of the aircraft is in a transient state.

[0041] According to the technical solution provided by the embodiment of the present application, there is also a step S111 between step S110 and step S120. The step S111 specifically includes: performing grid division on the aerodynamic optical flow field outside the simulated nose cone.

[0042] According to the technical solution provided by the embodiment of the present application, the G-D coefficient is calculated by the sixth formula, and the sixth formula is as follows:

[0043]

[0044] where λ is the light wavelength, with the unit of um.

[0045] According to the technical solution provided by the embodiment of the present application, in step S305, when the fourth formula is satisfied, the light ray is traced to the free stream of the atmosphere and the light ray stops traveling. The fourth formula is as follows:

[0046] |n q+p -N f |≤δ; p = 1, 2, 3, …, m

[0047] Wherein, n f is the refractive index of the free stream of the atmosphere, n q+p is the refractive index at the (q + p)-th refraction point, and δ is the judgment coefficient.

[0048] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0049] The present invention performs preliminary processing through the first time, the reverse ray tracing method and the first judgment method, and then performs secondary processing through the second time and the second judgment method. It is closer to the preliminary processing than the prior art. Compared with the prior art that directly performs division processing through the second time, the data contained after division is more, and the processing takes longer. The present invention can quickly select a secondary time period in a long time period, and then perform subdivision on the secondary time period through secondary processing, so that the obtained steady-state and transient conversion time points are more accurate, and the processed data is much smaller than that of the prior art, and the data processing speed is faster;

[0050] Furthermore, the reverse ray tracing method of the present invention starts from the inside of the simulated cowling, considering the refraction effect at the optical cowling, which is closer to the actual situation than the prior art. This fluid-structure interaction ray tracing method is beneficial to improving the accuracy of imaging offset and the accuracy of imaging deviation;

[0051] Even further, when the aircraft is in a steady state, since the air resistance and friction at the front end are the most intense, the end point will be the highest temperature point. This result conforms to the objective law. Therefore, by the coincidence of the end point temperature and the stagnation point temperature, it can be judged whether the aircraft is in a steady state. Without calculating multiple formulas in the reverse ray tracing method, directly obtaining the temperature parameters from the corresponding temperature cloud map can accurately and quickly judge the flight state of the aircraft within the corresponding time period. Combined with the preliminary processing, the data processing efficiency is further improved.

[0052] It should be understood that the content described in the summary of the invention is not intended to limit the key or important features of the embodiments of the present invention, nor to limit the scope of the present invention. Other features of the present invention will become easy to understand through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, objects and advantages of the present invention will become more obvious:

[0054] Figure 1 It is a flowchart of the steps of a method for discriminating between the steady state and transient state of an aircraft imaging flow field provided by an embodiment of the present application;

[0055] Figure 2 It is a schematic diagram of the optical path of the reverse ray tracing method provided by an embodiment of the present application;

[0056] Reference numerals in the figure: 1, simulated radome; 2, aerodynamic optical flow field; 3, offset point; 4, initial point of ray tracing. Detailed implementation manners

[0057] The present invention will be further described in detail below with reference to the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related invention, rather than limiting the invention. Additionally, it should be noted that for the convenience of description, only the parts related to the invention are shown in the drawings.

[0058] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and embodiments.

[0059] Please refer to Figure 1 , an embodiment of the present invention provides a method for discriminating between the steady state and transient state of an aircraft imaging flow field, which specifically includes the following steps:

[0060] S100. Simulate the flight scenario of the aircraft to obtain a simulation result;

[0061] In some embodiments, the step S100 specifically includes the following steps:

[0062] S110. Perform an isometric three-dimensional modeling on the optical radome of the aircraft to obtain a simulated radome 1; optionally, SpaceClaim software is used for modeling;

[0063] S111. Perform mesh division on the aerodynamic optical flow field 2 outside the simulated radome 1; optionally, ICEMCFD software is used. The smaller the mesh division, the more accurate the flow field density parameters after simulation;

[0064] S120. Establish a data interaction link with the flight management computer to obtain the flight parameters of the aircraft, where the flight parameters include flight altitude, Mach number, and angle of attack;

[0065] S130. Simulate the flight scenario of the aircraft model through simulation software to obtain the simulation results. Fluent software can be used for fluid simulation. Let the simulated nose cap 1 perform simulated flight according to the obtained flight altitude, Mach number, and angle of attack. Fluent software will process the calculation results obtained from the simulation calculation of the gas flow around the aircraft head, and thus convert the calculation results into visual research data with time points. By adopting the Spalart-Allmaras model, it only needs to solve an additional equation, which is simpler and has lower calculation cost compared with two-equation models (such as k-ε or k-ω models). In addition, for boundary layer flow, the Spalart-Allmaras model does not need to use complex wall functions to process the near-wall region, which makes it more convenient to handle complex geometries. At the same time, for separated flow, the Spalart-Allmaras model can usually provide relatively accurate results.

[0066] S200. Process the simulation results to obtain several coarsely divided parameters sorted by flight time. The interval time between each two coarsely divided parameters is the first time. Each coarsely divided parameter includes a nose cap temperature cloud map and a flow field density cloud map.

[0067] Among them, CFD-Post software can be used to process the simulation results, that is, import the visual research data into CFD-Post software. The nose cap temperature cloud map generated by CFD-Post software can not only intuitively display the temperature of each point on the surface of the simulated nose cap 1, but also convert the temperature of each point into data as the basis for subsequent steps. Similarly, the flow field density cloud map can not only display the flow field density outside the simulated nose cap 1, but also convert the density at each location into data as the basis for subsequent steps.

[0068] S300. Obtain the imaging offset values corresponding to each coarsely divided parameter through the reverse ray tracing method.

[0069] In some embodiments, the reverse ray tracing method specifically includes the following steps:

[0070] S301. Select the cross-section of the simulated nose cap 1 and the aerodynamic optical flow field 2 to establish an X-Y coordinate system, and set the ray tracing starting point 4, the initial ray incident angle θ 1 , the refractive index N of the gas field inside the nose cap 1 and the step size h.

[0071] Such as Figure 2As shown, according to the conventional reverse ray tracing technique, a ray is set to pass through the aerodynamic optical flow field 2, the simulated radome 1, and the internal air field of the radome, and finally mapped to the ray tracing initial point 4 according to the initial incident angle of the ray. Therefore, when performing reverse tracing, the end tracing point is first set, that is, the ray tracing initial point 4. Among them, the inside of the radome is basically in a non-moving state, so the refractive index N 1 = 1.

[0072] S302. Calculate the refractive index of each point inside the simulated radome 1 through the first formula. The first formula is as follows:

[0073] N 2 = N 0 + α*(T - T 0 )

[0074] where N 2 is the refractive index of the simulated radome 1 at temperature T, which is obtained from the radome temperature cloud map in the rough division parameters. N 0 is the refractive index of the simulated radome 1 at temperature T 0 , and α is the thermo-optic coefficient of the simulated radome 1;

[0075] The refractive index of a material changes with temperature, and this effect is called the thermo-optic effect. When the ray emitted from the ray tracing initial point travels inside the simulated radome 1, the temperature T of any point can be obtained through the radome temperature cloud map in the rough division parameters. Then, when the basic refractive index n 0 and the basic temperature T 0 are both known, the refractive index n 2 of the simulated radome 1 at this point at temperature T can be calculated, which is convenient for subsequent calculation during ray tracing and refraction.

[0076] S303. Calculate to obtain the refractive index of each point in the aerodynamic optical flow field 2 through the second formula. The second formula is as follows:

[0077] N 3 = 1 + K GD * ρ; q = 2, 3, …, m

[0078] where N 3 is the refractive index at the refraction point, K GD is the G - D coefficient, and ρ is the flow field density at this refraction point, which is obtained from the flow field density cloud map in the rough division parameters; through the above formula calculation, the refractive index of any point inside the aerodynamic optical flow field 2 can be calculated, which is convenient for subsequent calculation during ray tracing and refraction.

[0079] In some embodiments, the second formula is obtained by converting the Lorentz - Lorenz formula. The Lorentz - Lorenz formula is as follows:

[0080]

[0081] Where n is the refractive index of the gas, ρ is the flow field density at the refraction point. When the gas medium is air, the refractive index n≈1, then n 2 +2≈3, n+1≈2, further simplification can obtain the second formula.

[0082] In some embodiments, the GD coefficient is calculated by a sixth formula, and the sixth formula is as follows:

[0083]

[0084] Where, λ is the wavelength of light, in um;

[0085] The GD coefficient is a Gladstone-Dale (GD) constant, which can be used to characterize the relationship between gas density and refractive index. The sixth formula is a commonly used formula for this constant.

[0086] S304, calculating by a third formula to obtain a refraction angle after the light is refracted, the third formula is as follows:

[0087] n q *sinθ q =n q+1 *sinθ q+1 ; q=2,3,…,m

[0088] Among them, n q is the refractive index of the q-1th refraction point, n q+1 is the refractive index at the qth refraction point, θ q is the incident angle of the light after the q-1th time, θ q+1 is the refraction angle of the light after the qth refraction;

[0089] S305, the light beam follows the initial incident angle θ 1 After being emitted, the light refracts once after each forward step h at the speed of light. The light passes through the internal air field of the hood, the simulated hood 1, and the aero-optical flow field 2 in sequence. When the light refracts for the qth time and enters the atmospheric free flow from the aero-optical flow field 2, the coordinates of the qth refraction (x q ,y q ) and the refraction angle θ q+1 ;

[0090] In step S305, the light ray is refracted once after each forward step h. The specific process is as follows:

[0091] When the light travels the first step length h, the light undergoes the first refraction. The coordinates of the first refraction point are (x1 , y 1 ), x 1 = vh * cosθ 1 ; y 1 = vh * sinθ 1 , further according to the position of (x 1 , y 1 ), when in the internal airfield of the nose cone, n 2 = N 1 , when in the simulated nose cone 1, n 2 = N 2 , when in the aerodynamic optical flow field 2, n 2 = N 3 , through the third formula n 1 * sinθ 1 = n 2 * sinθ 2 , obtain the refraction angle θ of this time 2 , as the incident angle θ for the next refraction 2 ;

[0092] When the light travels the second step length h, the light undergoes the second refraction, and the coordinates of the second refraction point are (x 2 , y 2 ), x 2 = vh * (cosθ 1 + cosθ 2 ); y 2 = vh * (sinθ 1 + sinθ 2 ), further according to the position of (x 2 , y 2 ), when in the internal airfield of the nose cone, n 3 = N 1 , when in the simulated nose cone 1, n 3 = N 2 , when in the aerodynamic optical flow field 2, n 3 = N 3 , through the third formula n 2 * sinθ 2 = n 3 * sinθ 3 , obtain the refraction angle θ of this time 3 , as the incident angle θ for the next refraction 3 ;

[0093] When the light travels the q-th step length h, the light undergoes the q-th refraction, and the coordinates of the q-th refraction point are (x q , y q ), x q = vh * (cosθ 1+cosθ 2 +…+cosθ q );y 2 =vh*(sinθ 1 +sinθ 2 +…+sinθ q ), further according to (x q ,y q ) location, when in the internal aura of the hood n q+1 =N 1 , when in the simulated hood 1 n q+1 =N 2 , when in the aero-optical flow field 2 q+1 =N 3 , through the third formula n q *sinθ q =n q+1 *sinθ q+1 , and obtain the refraction angle θ q+1 , as the incident angle θ for the next refraction q+1 ;

[0094] In summary, the entire process of reverse ray tracing is completed, that is, the real light will be at (x q ,y q ) point along the incident angle θ q+1 It enters the aero-optical flow field and falls on the initial point 4 of the ray tracing after q refractions.

[0095] In some embodiments, when the fourth formula is satisfied, the ray is traced to the atmospheric free stream and the ray stops traveling. The fourth formula is as follows:

[0096] |n q+p -N f |≤δ; p=1,2,3,…,m

[0097] Among them, n f is the refractive index of the atmospheric free stream, n q+p is the refractive index at the q+pth refraction point, δ is the determination coefficient; the fourth formula reflects the refractive index at each refraction point of the q+1th, q+2th, ..., q+pth refraction points after the qth refraction of the light and N f The difference is less than δ, which means that the refractive index at the subsequent refraction point is different from the refractive index of the atmospheric free flow n f It is very close, and it can be basically determined that these refraction points are all located in the atmospheric free stream, so the tracking is stopped after the qth refraction.

[0098] S306, extending the qth refracted light in reverse direction to the Y axis in the XY coordinate system to form an offset point 3;

[0099] S308. Calculate the distance between the offset point 3 and the initial ray tracing point 4, and mark it as the imaging offset value.

[0100] As Figure 2 shown, the ray direction formed after the q-th refraction of the ray path can be regarded as the actual incident direction of the ray, that is, the beam travels in a straight line in the free atmosphere flow, enters the aerodynamic optical flow field along the actual incident direction, and is repeatedly refracted through the aerodynamic optical flow field 2, the simulation radome 1, and the internal gas field of the radome, and finally shoots towards the set initial ray tracing point 4. When there is no aerodynamic optical flow field 2, the ray shoots towards the Y-axis along the actual incident direction, and the point where it irradiates on the Y-axis is the offset point 3, and the difference between the two is the above-mentioned imaging offset value.

[0101] S400. Process each of the imaging offset values through the first judgment method to obtain a conversion time region, a number of first transient time periods, and a number of first steady-state time periods, where the conversion time region is the time region when the flight state changes from transient to steady state.

[0102] In some embodiments, the first judgment method specifically includes the following steps:

[0103] S401. Arrange each of the imaging offset values in chronological order.

[0104] S402. Calculate the first difference between adjacent imaging offset values.

[0105] S403. If the first difference is less than 1% of any one of the two corresponding imaging offset values, the time period corresponding to the adjacent imaging offset values is marked as the first steady-state time period, and the flight state of the aircraft is in a steady state. Otherwise, the corresponding time period is marked as the first transient time period, and the flight state of the aircraft is in a transient state.

[0106] S404. Select the first transient time period adjacent to a first steady-state time period in chronological order, and modify the mark of this first transient time period to the conversion time region.

[0107] Since the imaging offset value will change with the change of the aerodynamic optical flow field 2, when the aircraft is in a steady state, its imaging offset value is basically unchanged. Therefore, when the first difference is less than 1% of any one of the two corresponding imaging offset values, it means that the imaging offset value is basically unchanged. Further, it can be judged that when the aircraft is between the two time points represented by these two imaging offset values, its flight state is in a steady state. Within the first transient time period adjacent to a first steady-state time period, it must include the process of the flight state changing from transient to steady state. Therefore, it is separately marked as the conversion time region and awaits subsequent processing.

[0108] S500. Process the part of the simulation results in the conversion time region to obtain several sub-parameters sorted by flight time. The interval time between each sub-parameter is the second time, and each sub-parameter includes a head cover temperature cloud map.

[0109] Among them, the simulation results are visualization research data with time points. The above-mentioned part in the conversion time region refers to the visualization research data whose time points are located in the conversion time region. Its processing method is the same as that of step S200 and will not be elaborated here. In addition, the second time is less than the first time. That is, on the basis of the time points corresponding to the roughly divided parameters, the conversion time region is further subdivided, and the time region of transient to steady state can be understood more accurately.

[0110] S600. Process each sub-parameter through the second judgment method to obtain several second steady-state time periods and several second transient time periods, without the need to use the reverse ray tracing technology anymore, and the processing speed is faster.

[0111] In some embodiments, the second judgment method specifically includes the following steps:

[0112] S601. Mark the front vertex of the simulated head cover 1 as the endpoint, and mark the highest surface temperature point of the simulated head cover 1 as the stagnation point.

[0113] S602. Obtain the endpoint temperature and stagnation point temperature corresponding to each sub-parameter. Among them, both the endpoint temperature and the stagnation point temperature are obtained from the temperature cloud map.

[0114] S603. Calculate the second difference between the endpoint temperature and the stagnation point temperature in the same sub-parameter.

[0115] S604. If the second difference is less than 1% of any one of the corresponding endpoint temperature and stagnation point temperature, the corresponding temperature cloud map is a steady-state cloud map; otherwise, the corresponding temperature cloud map is a transient cloud map.

[0116] S605. Mark the time period corresponding to adjacent steady-state cloud maps as the second steady-state time period, and the flight state of the aircraft is steady state; otherwise, the corresponding time period is marked as the second transient time period, and the flight state of the aircraft is transient state.

[0117] In summary, during the second transient time period and the second transient time period, the flight state of the aircraft is transient; during the second steady-state time period and the second steady-state time period, the flight state of the aircraft is steady state. Finally, the judgment is completed, which is convenient for reducing the negative impact brought by the startup optical effect.

[0118] In the description of this specification, terms such as "connection", "installation", "fixation", etc. shall be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or an indirect connection through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0119] In the description of this specification, the description of terms such as "one embodiment", "some embodiments", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of this application. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or instance. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0120] The above are only the preferred embodiments of this application and are not used to limit this application. For those skilled in the art, this application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the protection scope of this application.

Claims

1. A method for distinguishing steady-state and transient-state flow field of aircraft imaging, characterized in that: The specific steps include: S100, simulating a flight scene of an aircraft to obtain a simulation result; S200, processing the simulation results to obtain a plurality of coarse-divided parameters sorted by flight time, wherein the interval between each coarse-divided parameter is the first time, and each coarse-divided parameter includes a hood temperature cloud map and a flow field density cloud map; S300, processing each of the coarse-divided parameters by a reverse ray tracing method to obtain an imaging offset value corresponding to each of the coarse-divided parameters; S400, processing each of the imaging offset values ​​by a first determination method to obtain a conversion time region, a plurality of first transient time periods, and a plurality of first steady-state time periods, wherein the conversion time region is a time region in which the flight state is converted from a transient state to a steady state; S500, processing the part of the simulation result in the conversion time region, obtaining a plurality of subdivision parameters sorted by flight time, the interval time between each subdivision parameter being a second time, and each subdivision parameter including a hood temperature cloud map; S600: Process each of the subdivided parameters by a second determination method to obtain a plurality of second steady-state time periods and a plurality of second transient time periods.

2. The method for distinguishing steady-state and transient-state flow field of aircraft imaging according to claim 1, characterized in that: The step S100 specifically includes the following steps: S110, performing proportional three-dimensional modeling of the optical hood of the aircraft to obtain a simulated hood (1); S120, establishing a data exchange link with a flight management computer to obtain flight parameters of the aircraft, wherein the flight parameters include flight altitude, Mach number, and angle of attack; S130, simulating the flight scene of the aircraft by using simulation software to obtain the simulation result.

3. The method for distinguishing steady-state and transient-state flow field of aircraft imaging according to claim 1, characterized in that: The reverse ray tracing method specifically comprises the following steps: S301, select the cross section of the simulated hood (1) and the aerodynamic optical flow field (3) to establish an XY coordinate system, set the ray tracing initial point (4), the initial incident angle of the ray θ1, the refractive index N1 of the air field inside the hood, and the step length h; S302, calculating the refractive index of each point inside the simulated head cover (1) using a first formula, wherein the first formula is as follows: N2=N0+α*(T-T0) Wherein, N2 is the refractive index of the simulated hood (1) when the temperature is T, which is obtained from the hood temperature cloud map in the coarse-divided parameters, N0 is the refractive index of the simulated hood (1) when the temperature is T0, and α is the thermo-optical coefficient of the simulated hood (1); S303, calculating by a second formula to obtain the refractive index of each point in the aero-optical flow field (2), wherein the second formula is as follows: N3=1+K GD *ρ;q=2,3,…,m Where N3 is the refractive index at the refraction point, K GD is the GD coefficient, ρ is the flow field density at the refraction point, which is obtained from the flow field density cloud map in the coarse-divided parameters; S304, calculating by a third formula to obtain a refraction angle after the light is refracted, the third formula is as follows: n q *sinθ q =n q+1 *sinθ q+1 ;q=1,2,3,…,m Among them, n q is the refractive index of the q-1th refraction point, n q+1 is the refractive index at the qth refraction point, θ q is the incident angle of the light after the q-1th time, θ q+1 is the refraction angle of the light after the qth refraction; S305, the light is emitted along the initial incident angle θ1, and the light is refracted once after each forward step h at the speed of light. The light passes through the internal air field of the hood, the simulated hood (1) and the aero-optical flow field (2) in sequence. When the light is refracted for the qth time and enters the atmospheric free flow from the aero-optical flow field (2), the coordinates of the qth refraction (x q ,y q ) and the refraction angle θ q+1 ; S306, extending the qth refracted light in reverse direction to the Y axis in the XY coordinate system to form an offset point (3); S308, calculating the distance between the offset point (3) and the ray tracing initial point (4), and marking it as the imaging offset value.

4. The method for distinguishing steady-state and transient-state flow field of aircraft imaging according to claim 1, characterized in that: The first determination method specifically comprises the following steps: S401, arranging the imaging offset values ​​in chronological order; S402, calculating a first difference between adjacent imaging offset values; S403: If the first difference is less than 1% of any one of the two corresponding imaging offset values, the time period corresponding to the adjacent imaging offset values ​​is marked as a first steady-state time period, and the flight state of the aircraft is steady; if not, the corresponding time period is marked as a first transient time period, and the flight state of the aircraft is transient; S404: Select the first transient time period adjacent to one of the first stable time periods in time sequence, and modify the mark of the first transient time period to a conversion time zone.

5. The method for distinguishing steady-state and transient-state flow field of aircraft imaging according to claim 1, characterized in that: The second determination method specifically comprises the following steps: S601, marking the front vertex of the simulated hood (1) as an endpoint, and marking the point with the highest surface temperature of the simulated hood (1) as a stagnation point; S602, obtaining the endpoint temperature and the stagnation temperature corresponding to each of the subdivided parameters, wherein the endpoint temperature and the stagnation temperature are both obtained from the temperature cloud map; S603, calculating a second difference between the endpoint temperature and the stagnation point temperature in the same subdivided parameter; S604: If the second difference is less than 1% of the corresponding endpoint temperature and the stagnation temperature, the corresponding temperature cloud map is a steady-state cloud map; if not, the corresponding temperature cloud map is a transient cloud map; S605. The time period corresponding to the adjacent steady-state cloud image is marked as a second steady-state time period, and the flight state of the aircraft is steady-state. If not, the corresponding time period is marked as a second transient time period, and the flight state of the aircraft is transient.

6. The method for distinguishing steady-state and transient-state flow field of aircraft imaging according to claim 2, characterized in that: There is also a step S111 between step S110 and step S120, and step S111 specifically comprises: gridding the aerodynamic optical flow field (2) outside the simulated hood (1).

7. The method for distinguishing steady-state and transient-state flow field of aircraft imaging according to claim 3, characterized in that: The GD coefficient is calculated by the sixth formula, which is as follows: Where λ is the wavelength of light, in um.

8. The method for distinguishing steady-state and transient-state flow field of aircraft imaging according to claim 3, characterized in that: In step S305, when the fourth formula is satisfied, the light is traced to the atmospheric free flow and stops traveling. The fourth formula is as follows: |n q+p -N f |≤δ;p=1,2,3,…,m Among them, n f is the refractive index of the atmospheric free stream, n q+p is the refractive index at the q+pth refraction point, and δ is the determination coefficient.

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