Method and system for simulating aerodynamic optical image quality of supersonic conformal optical system

Abstract

The application relates to a supersonic conformal optical system aerodynamic optical image quality simulation method and system. A fluid calculation domain is created according to a three-dimensional geometric model of a waverider; flow field parameters in the fluid calculation domain are solved to obtain a corresponding temperature field distribution; structural displacement of the waverider and window deformation of an optical window are obtained based on the temperature field distribution; a refractive index field of an outer flow field area is obtained according to the temperature field distribution, and a refractive index field of the optical window area is obtained according to the temperature field distribution, the structural displacement and the window deformation; optical tracing is carried out based on the refractive index fields to obtain a simulation image. The supersonic aerodynamic optical image quality is simulated quickly, and the evaluation efficiency is greatly improved under the premise of ensuring the accuracy. The application can be widely applied to the technical field of supersonic aircraft and the technical field of aerodynamic optics.

Description

Technical Field

[0001] This invention relates to the fields of supersonic aircraft technology and aero-optics technology, and more specifically, to a method and system for simulating and rapidly evaluating the aero-optical image quality of conformal optical systems under supersonic conditions. Background Technology

[0002] During high-speed flight, the optical windows of supersonic vehicles face extremely harsh aerodynamic and thermal environments. On the one hand, the external flow field of the vehicle forms shock waves and boundary layers due to intense compression and viscous friction, resulting in extremely uneven flow field density and temperature distribution. On the other hand, the optical windows generate significant temperature gradients due to aerodynamic heating, triggering thermo-optical effects and structural deformation.

[0003] The combined effect of these factors causes light to be deflected and distorted as it passes through the window, ultimately leading to degradation phenomena in the imaging system such as image shift, blurring, and decreased contrast.

[0004] Currently, simulation methods for aero-optical effects are mainly divided into two categories: one is a coupled method based on computational fluid dynamics and optical tracing, which obtains a high-precision flow field by solving the Navier-Stokes equations and then performs ray tracing; the other is a simplified method based on engineering approximations. The former has high accuracy but is extremely expensive to compute, making it difficult to meet the needs of rapid iterative evaluation; the latter, although computationally fast, often ignores the multi-physics coupling effects of heat, structure, and light, such as the influence of window deformation on the light incident interface and the dynamic correction of the refractive index by thermo-optical effects, resulting in a large deviation between the evaluation results and the actual situation.

[0005] Therefore, existing aero-optical image quality simulation methods have the following main drawbacks: First, it is difficult to balance computational efficiency and accuracy. High-precision coupling methods have high computational costs and require several hours or even days for a single simulation, while traditional engineering approximation methods, although fast, ignore key physical coupling mechanisms and lack accuracy. Secondly, there is a lack of complete modeling of the thermal-mechanical-optical coupling of the window. Existing methods usually treat the window as an ideal geometry, without considering the influence of structural deformation caused by aerodynamic heating on the normal direction of the light incident interface, nor do they consider the correction of the dynamic distribution of the window refractive index by the thermo-optical effect. Third, the image quality evaluation index is singular. Most methods only calculate wave aberration or point spread function, failing to form an end-to-end quantitative evaluation capability from physical field to image degradation, and making it difficult to intuitively reflect the degree of influence of aero-optical effects on actual imaging. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention aims to provide a method for simulating the aero-optical image quality of a supersonic conformal optical system.

[0007] The present invention provides a method for simulating the aerodynamic optical image quality of a supersonic conformal optical system, wherein the supersonic conformal optical system includes a waverider and a conformal optical window, and the steps include: Obtain a three-dimensional geometric model of the waverider and its conformal optical window, and create a fluid computational domain centered on the waverider; The flow field parameters in the computational domain of the fluid are solved at different Mach numbers to obtain the corresponding temperature field distribution; The window deformation of the optical window is obtained based on the temperature field distribution; The refractive index field of the external flow field region is obtained based on the temperature field distribution, and the refractive index field of the optical window region is obtained based on the temperature field distribution and window deformation. Optical tracing is performed based on the refractive index field to obtain a simulated image.

[0008] In a practical application, this invention solves for the flow field parameters in the computational domain of the fluid based on the oblique shock wave relation at different Mach numbers.

[0009] In a practical application, the present invention dynamically corrects the refractive index of the optical window region based on the thermo-optical effect.

[0010] In a practical application, the present invention employs a second-order interpolation method, which determines the interpolation coefficients from the values ​​of neighboring grid nodes in the fluid computational domain, obtains the refractive index and gradient at non-grid nodes, and continuously reconstructs the refractive index field.

[0011] In a practical application, the present invention generates a simulated image by convolving an ideal image obtained through optical tracing with a point spread function.

[0012] In a practical application, the present invention also dynamically corrects the incident interface in ray tracing based on the geometric parameters of the deformed window.

[0013] In a practical application, the present invention uses structural similarity index and peak signal-to-noise ratio to evaluate simulated images.

[0014] This invention also provides a supersonic conformal optical system aerodynamic optical image quality simulation system, including... The waverider fluid computational domain creation module obtains a three-dimensional geometric model of the waverider and its conformal optical window, and creates a fluid computational domain centered on the waverider. The flow field parameter calculation module solves the flow field parameters in the fluid computational domain at different Mach numbers and obtains the corresponding temperature field distribution. The structural displacement and window deformation calculation module calculates the window deformation of the optical window based on the temperature field distribution. The refractive index field calculation module obtains the refractive index field of the external flow field region based on the temperature field distribution, and obtains the refractive index field of the optical window region based on the temperature field distribution and window deformation. The simulation image generation module performs optical tracing based on the refractive index field to obtain the simulation image.

[0015] The present invention also provides an electronic device, the electronic device including a processor and a memory storing computer program instructions; the processor executes the computer program instructions to implement the steps of the method of the present invention.

[0016] The present invention also provides a computer-readable storage medium storing computer program instructions, which, when executed by a processor, implement the steps of the method of the present invention.

[0017] This invention enables rapid simulation of supersonic aero-optical image quality, significantly improving evaluation efficiency while maintaining accuracy. It establishes a ray tracing model coupled with thermo-mechanical-optical multiphysics fields, achieving precise tracking of light propagation paths in non-uniform refractive index fields. An end-to-end quantitative evaluation link from flow field to image degradation is constructed, providing standardized image quality metrics such as SSIM and PSNR.

[0018] Through the above-mentioned technical solutions, especially the key innovations such as rapid flow field modeling based on oblique shock wave theory, ray tracing with thermo-mechanical-optical multi-physics coupling, and end-to-end image degradation quantification evaluation, this invention brings significant and beneficial technical effects.

[0019] In terms of flow field modeling, this invention adopts the oblique shock wave theory combined with the θ-β-M relationship to replace the traditional high-precision CFD solution method based on the RANS equation, reducing the flow field solution time from several hours to minutes. Under the premise of ensuring engineering accuracy, it realizes the rapid evaluation of aero-optical image quality, meets the efficiency requirements of the design iteration stage, and effectively solves the contradiction between computational efficiency and accuracy.

[0020] In terms of physical modeling, this invention achieves, for the first time, complete coupling of thermal, mechanical, and optical multiphysics fields. Based on the radial expansion and normal bending deformation of the thermal strain calculation window, the coordinates of the intersection point and the normal direction of the light incident interface are dynamically updated, making the simulation closer to the actual physical process. Simultaneously, the refractive index change at each spatial point within the window is calculated in real time based on the thermo-optical coefficient and temperature field distribution. Simulation results show that as the Mach number increases from 2 to 5, the window temperature increases significantly, the refractive index distribution exhibits a non-uniform gradient, and the window deformation increases accordingly, substantially affecting the light propagation path.

[0021] In ray tracing, this invention employs the fourth-order Runge-Kutta method to solve the ray differential equation, combined with a second-order interpolation method to obtain the refractive index and gradient between grid nodes, effectively avoiding the cumulative error caused by step size selection. The simulation results clearly demonstrate the spatial distribution characteristics of the ray deflection effect in the aberration distribution cloud map, verifying the high accuracy of the tracing algorithm.

[0022] In terms of image quality assessment, this invention provides an end-to-end quantitative assessment capability from the physical field to image degradation. The point spread function is calculated using wavefront aberration, thereby generating a degraded image, and standardized quality indices such as SSIM and PSNR are calculated. Simulation results show that at a fixed Mach number, SSIM gradually decreases from 0.737 at t=3s to 0.494 at t=9s, while PSNR simultaneously decays from 24.6dB to 16.5dB. At a fixed time, for every 1-level increase in Mach number, the image quality degradation increases by over 40%. This quantitative capability provides crucial data support for research on aero-optical effect compensation and suppression techniques, intuitively reflecting the continuous erosion of imaging quality by aerodynamic disturbances. Attached Figure Description

[0023] Figure 1 This is a flowchart of the method of the present invention. Figure 2 This is a flowchart of a simulation method (using Python algorithm) according to an embodiment of the present invention.

[0024] Figure 3 This is a cross-sectional view of the overall mesh in the XZ plane according to an embodiment of the present invention.

[0025] Figure 4 This is a schematic diagram of the optical window position of a conformal concave-convex lens optical system using a waverider in an embodiment of the present invention.

[0026] Figure 5 This is a diagram showing the internal structure of a conformal concave-convex lens optical system using a waverider, as described in an embodiment of the present invention.

[0027] Figure 6 Aberration distribution contour maps of a conformal concave-convex lens optical system for waveriders at different Mach numbers and times. Figure 7 For the original, clear images of the aircraft Figure 8 Image degradation caused by aerodynamic light transmission effects at different Mach numbers and times in a conformal concave-convex lens optical system for waveriders. Figure 9 This is a structural diagram of a conformal L-shaped waverider system used in an embodiment of the present invention.

[0028] Figure 10 This is a contour map of aberration distribution at different Mach numbers for a conformal L-type waverider system.

[0029] Figure 11 Image degradation caused by aero-optical transmission effect in the aberration distribution cloud map of a conformal L-type system with different Mach numbers and time for waverider.

[0030] Figure 12This is a graph showing the evolution of the imaging structural similarity of a conformal L-type waverider system over time at full Mach number conditions.

[0031] Figure 13 The curve of peak signal-to-noise ratio as a function of flight time for imaging of the conformal L-type waverider system under full Mach number conditions.

[0032] Figure 14 System structure block diagram of the present invention. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this does not constitute any limitation on the present invention.

[0034] The method flow of this invention is as follows: Figure 1 As shown, the system structure block diagram is as follows: Figure 14 As shown.

[0035] In this embodiment, a conformal optical window on a certain type of waverider helmet is used as the simulation object. The window material is sapphire, and the waverider structure material is iron. The simulation conditions cover Mach numbers from 2 to 5, a flight altitude of 30 km, and an angle of attack of 5°. The simulation method in this embodiment uses a Python algorithm, and its process is as follows: Figure 2 As shown.

[0036] Before the simulation begins, a digital geometric model of the simulation object must first be built or loaded.

[0037] In this embodiment, a three-dimensional geometric model of the waverider and its conformal optical window, such as a STEP format geometric model, is loaded. By traversing the volume and name features of the geometric body, the main structure and the optical window are automatically identified and distinguished, and key geometric parameters such as the center position, normal direction, and size of the window are extracted.

[0038] Subsequently, a fluid computational domain is created centered on the waverider, and a structured mesh is generated, such as... Figure 3 As shown, the grid points are divided into two categories: points on the surface of the waverider (including window region points for optical analysis (refractive index, transmission) and non-window region points for overall thermal analysis (this invention does not involve the processing of non-window region points)); and points inside the fluid domain, providing a geometric carrier for spatial discretization for subsequent multiphysics solutions.

[0039] After completing the geometric modeling, we move on to the rapid flow field modeling and temperature field solution stage.

[0040] For each Mach number condition, this embodiment uses the oblique shock wave theory to solve the flow field parameters independently. Of course, it can also be replaced by a CFD solution method based on the Euler equation or RANS equation, or a method that combines engineering empirical models with CFD, depending on the actual situation and needs.

[0041] The shock angle β is solved numerically using the θ-β-M relationship: Where θ is the airflow deflection angle, M1 is the incoming Mach number, and γ is the specific heat ratio.

[0042] After obtaining the shock wave angle, the pressure p2, density ρ2, and temperature T2 behind the wave are calculated using the oblique shock wave relation: In the formula, p1 is the wavefront pressure, ρ1 is the wavefront density, and T1 is the wavefront temperature.

[0043] After generating the three-dimensional flow field parameter distribution by interpolation along the waverider flow direction and spanwise, the temperature field evolution of the structural region and the window region is calculated by solving the heat diffusion equation: Where α is the thermal diffusivity, determined by the material's thermal conductivity, density, and specific heat capacity. The temperature field in the window region is calculated independently due to the aerodynamic heating input and the material's thermal conductivity. The higher the Mach number, the faster the temperature rises. This temperature field will serve as the input for subsequent thermo-mechanical coupling and thermo-optical effect analysis.

[0044] After obtaining the temperature field distribution, the modeling stage of thermo-mechanical-optical multiphysics coupling is entered.

[0045] First, the window geometry is dynamically updated. The thermal strain of the window is calculated based on the temperature field, and then the structural displacement and window deformation are obtained: in Let be the coefficient of thermal expansion of the material, and ΔT be the temperature change relative to the reference temperature. The window deformation adopts a simplified model of radial expansion plus normal bending. The deformation increases with increasing Mach number. The updated window geometry parameters will be used for dynamic correction of the incident interface in subsequent ray tracing.

[0046] At the same time, a complete refractive index field is constructed.

[0047] For the external flow field region, the refractive index variation is mainly determined by the gas density distribution. Since density and temperature are related through the gas law, the density field can be derived from the temperature field distribution. Then, based on the density field, the air refractive index is calculated using the Gladstone-Dale relation (which can be replaced by the Barrell-Sears formula or the Rueger model depending on the operating conditions and actual needs). in This is the Gladstone-Dale constant, which is related to the incident light wavelength; for a working wavelength of 4 μm, it is taken as 2.27 × 10⁻⁶. -4 m 3 / kg.

[0048] For the window region, the refractive index change originates from two aspects: first, the thermo-optical effect caused by the change in material density due to increased temperature; and second, the elasto-optical effect generated by the thermal deformation of the window. Therefore, the dynamic correction of the refractive index by the thermo-optical effect needs to be considered. Where T(x,y,z) is the three-dimensional temperature distribution of the window, x,y,z are the coordinate points of the window, n0(T0) is the refractive index at the reference temperature, dn / dT is the thermo-optic coefficient, and ΔT is the temperature change at the spatial point.

[0049] The above formula generates a three-dimensional refractive index field that varies with time and space, providing input for ray tracing.

[0050] Next, the core ray tracing calculations will be performed.

[0051] Light rays are emitted from the pupil position, each ray corresponding to one pixel in the image. The propagation process of light rays consists of three physical stages: propagation in the external flow field, refraction within the window, and propagation within the window. The propagation trajectory of light rays in a non-uniform refractive index field is described by the differential equation of light rays: Where s is the arc length of the ray path and r is the position vector. The numerical solution of this equation uses the fourth-order Runge-Kutta method (RK4, which can be replaced by the Euler method, the third-order Runge-Kutta method, or the Taylor series expansion method depending on the actual situation and needs), discretizing the ray path into multiple step lengths h. In each iteration of the RK4 method, the step length [s] is... i , s i Calculate the slope at four different positions within [+h], corresponding to four k values. i : Here, f(⋅) is a function describing the rate of change of the ray trajectory.

[0052] k1: Starting slope, at the current position r i Current arc length s i The rate of change of the ray trajectory calculated at that point corresponds to the single-step slope of the Euler method; k2: The slope of the first prediction at the midpoint, used to predict the position r of the midpoint of the step size using k1. i +k1 / 2, the slope calculated at the midpoint; k3: Midpoint second prediction slope. The midpoint position is predicted again using the corrected k2 to calculate a more accurate midpoint slope. k4: Endpoint prediction slope, used to predict the position r of the step-size endpoint. i +k3, the slope calculated at the endpoint.

[0053] During ray tracing, the ray trajectory points cannot fall exactly on the grid nodes, so it is necessary to obtain the refractive index and gradient at non-grid nodes.

[0054] This embodiment employs a second-order interpolation method, determining the interpolation coefficients based on the values ​​of three neighboring grid nodes to achieve continuous reconstruction of the refractive index field. When light propagates to the outer surface of the window, the refraction direction is calculated according to the vector refraction law. Let the unit vector of the incident ray be A, the unit vector of the normal be N, the refractive index on the incident side be n1, and the refractive index on the exit side be n2, then the unit vector T of the refracted ray is calculated by the following formula: Through the above tracing process, the system records the complete path of each ray from incident to exit and accumulates the optical path length: in Let i be the refractive index at the i-th position in the ray tracing. Let be the path length of the light ray between the discrete sampling points in this step. The wavefront aberration of any light ray after passing through the window is the difference between its optical path and the optical path of the principal ray. Based on wave aberration, the pupil function of an optical system can be expressed as the product of amplitude distribution and phase factor. According to Fraunhofer diffraction theory, the point spread function on the image plane is the squared modulus of the Fourier transform of the pupil function.

[0055] Ultimately, the degraded image, which is the simulation result, is generated by convolving the ideal image with a point spread function.

[0056] To quantify the degree of image degradation caused by aero-optical effects, the system calculates the structural similarity index (SSIM) and peak signal-to-noise ratio (PSNR). Of course, other evaluation metrics, such as image offset, modulation transfer function, and edge energy density, can also be added depending on the specific application scenario.

[0057] SSIM evaluates image quality by comparing the similarity of two images in terms of brightness, contrast, and structural features. in The average gray level of the image. , Standard deviation, C1 and C2 are the covariance and stability constants, respectively.

[0058] PSNR characterizes image quality by quantizing the ratio of signal strength to noise interference. in The maximum grayscale value of the image is denoted by , and MSE is the mean squared error. After the simulation is complete, the system outputs the results through the visualization module.

[0059] The following simulation process of two waverider conformal optical systems further illustrates this point.

[0060] I. Waverider Conformal Concave-Convex Lens Optical System The optical window position of the waverider conformal concave-convex lens optical system structure used in this embodiment is as follows: Figure 4 As shown, the structure of the concave-convex lens system inside the light window is as follows: Figure 4 As shown in the table below, the simulation-related parameters are as follows: Table 1 Waverider Materials Table 2 Optical window parameters Table 3 Optical System Parameters like Figure 6 As shown, under the hyposonic flight condition of Mach number Ma=2, the root mean square (RMS) value of the optical system wave aberration is at an extremely low level overall, with values ​​of 0.018λ, 0.020λ, and 0.021λ at 3s, 6s, and 9s, respectively. The aberration distribution exhibits a typical symmetrical ring-shaped feature of "low at the center and high at the edges," and only shows a slight gradual increase with the extension of flight time. The core reason for this phenomenon is that under the Ma=2 condition, the shock wave intensity in the flow field is weak, the boundary layer thickness outside the optical window is small, the turbulent structure is simple, the airflow compression and heat dissipation effects are limited, and the refractive index distribution of the flow field is well uniform. At the same time, the aerodynamic heating load level is low, and the thermal deformation and thermal lensing effect of the optical window and internal lenses are not significant, only producing small disturbances with the accumulation of time. Therefore, the system aberration is always within a controllable range, which can meet the imaging quality requirements of optical detection in the subsonic / transonic range.

[0061] When the flight Mach number increases to Ma=3, the RMS value of wave aberrations in the optical system exhibits a step increase, reaching 0.049λ, 0.054λ, and 0.057λ at 3s, 6s, and 9s, respectively. The aberration distribution evolves from a symmetrical ring shape to an asymmetrical elliptical shape, with a significant expansion of the high-aberration region at the edges, and the high-aberration region shifts downstream in the flow field. The mechanism is as follows: Under Ma=3 conditions, the shock layer thickness increases significantly, and the flow field outside the window rapidly transitions from laminar to turbulent. The scale and intensity of the turbulent vortex structure increase dramatically, which is transformed into strong pulsations in the flow field refractive index through the Gladstone-Dale relation, becoming the core source of wave aberrations. At the same time, the aerodynamic heating intensity intensifies, and the optical window and internal lenses experience significant thermal deformation, triggering the superposition effect of monochromatic aberrations such as spherical aberration and coma. Furthermore, as the flight time increases, the turbulence in the flow field develops more fully, and the thermal deformation continues to accumulate, ultimately leading to a gradual increase in aberrations, which significantly affects the imaging quality of the system.

[0062] Under hypersonic flight conditions with Mach number Ma=4, the RMS value of the optical system wave aberration is further increased significantly, reaching 0.105λ, 0.118λ, and 0.124λ at 3s, 6s, and 9s, respectively. The aberration distribution exhibits a global non-uniform diffusion characteristic, with a significant increase in aberration in the central region and a large area of ​​continuous band-like distribution of high aberration at the edge. The overall aberration magnitude is close to 1 / 8 of the wavelength, which seriously restricts the imaging resolution. The underlying reason for this phenomenon is that under Ma=4 conditions, the flow field forms a strong shock wave and a complex shear layer structure. The strong convective heat transfer between the high-temperature airflow and the window surface causes the window temperature gradient to increase sharply, resulting in a severe thermal lensing effect. The refractive index of the optical window material is non-uniformly distributed with temperature, which effectively introduces large-scale aberrations. At the same time, the spatial distribution complexity of the flow field density gradient is significantly increased, and multi-directional deflection occurs during beam transmission, causing aberrations to spread from the edge to the center. During long-term flight, the accumulation of thermal stress exacerbates the surface distortion of the optical element, and the multi-field coupling effect further amplifies the aberration disturbance, ultimately manifesting as aberration diffusion across the entire domain and a continuous increase in intensity.

[0063] Under extreme hypersonic flight conditions at Mach number Ma=5, the RMS value of the optical system wave aberration reaches the simulated peak, which is 0.159λ, 0.173λ, and 0.179λ at 3s, 6s, and 9s, respectively. Under this condition, the aerodynamic thermal effect of the flow field reaches its peak, the surface temperature of the window rises sharply, the thermal deformation increases significantly, and the equivalent surface distortion of the optical window is severe, becoming the main source of aberration. At the same time, the density fluctuation intensity and spatial scale of the hypersonic turbulent boundary layer are greatly increased, and the spatial frequency components of the flow field refractive index disturbance are richer, causing complex higher-order aberrations. As the flight time increases, the multi-field coupling effect continues to strengthen, and the thermal deformation of the components and the flow field disturbance form a positive feedback, and the aberration shows an accelerated growth trend. At this time, the system can no longer meet the normal optical detection requirements and needs to be optimized through aerodynamic thermal protection, active flow field control, and aberration compensation algorithms.

[0064] contrast Figure 7 The original clear image shows that the blurring gradually worsens as the aerodynamic heat load duration increases.

[0065] like Figure 8 As shown, under the hyposonic flight condition of Mach number Ma=2, the overall target imaging quality remains at a high level. The structural similarity (SSIM) at 3s, 6s, and 9s are 0.928, 0.925, and 0.925, respectively, with only a very slight attenuation. The target outline is clear and the details are complete, and the image degradation caused by aerodynamic light transmission effect is extremely low. The core reason for this phenomenon is that under the Ma=2 condition, the flow field shock wave intensity is weak, the boundary layer thickness is small, the flow field refractive index disturbance amplitude is limited, and the wavefront distortion of the beam when transmitted through the window is low, which only produces a slight blurring and contrast attenuation to the imaging. At the same time, the cumulative effect of aerodynamic heating is not significant, and the aberration of the optical system is within a controllable range. Therefore, the target imaging quality is always maintained at a high level, which can meet the accuracy requirements for target detection and identification in the hyposonic range.

[0066] When the flight Mach number increases to Ma=3, the target imaging quality declines significantly. The SSIM at 3s, 6s, and 9s drops to 0.871, 0.863, and 0.857, respectively. The target outline becomes blurred, the detail resolution decreases, and the overall image contrast is reduced. The degradation effect caused by aerodynamic light transmission is significantly enhanced. The mechanism is as follows: Under Ma=3 conditions, the thickness of the shock layer in the flow field increases, turbulence transition intensifies, and the intensity of flow field refractive index pulsation increases significantly. Non-uniform deflection occurs during beam transmission, which effectively introduces aberrations such as coma and astigmatism, resulting in blurring and distortion in target imaging. At the same time, the increased aerodynamic thermal load causes thermal deformation of optical components, further amplifying imaging distortion. As the flight time increases, the flow field turbulence fully develops, and the thermal effect continues to accumulate, ultimately manifesting as a gradual decline in image quality.

[0067] Under hypersonic flight conditions at Mach number Ma=4, the SSIM values ​​at 3s, 6s, and 9s dropped to 0.771, 0.743, and 0.731, respectively. The target outline was severely blurred, and detailed features were almost completely lost, with only the general shape of the target being discernible. Aerodynamic light transmission effects severely limited imaging. The underlying reason for this phenomenon is that under Ma=4 conditions, the strong shock wave and complex shear layer structure cause a drastic non-uniform distribution of the flow field refractive index. When the beam is transmitted through the window, the wavefront distortion is severe, resulting in large-scale aberrations and multi-directional scattering, leading to severe blurring, ghosting, and noise superposition in the target image. At the same time, the thermal lensing effect caused by aerodynamic heating and the thermal deformation of components form multi-field coupling, further deteriorating the image quality. As time progresses, the positive feedback effect of thermal stress and flow field disturbances causes the image degradation to continue to intensify.

[0068] Under hypersonic flight conditions at Mach number Ma=5, the SSIM values ​​at 3s, 6s, and 9s are only 0.626, 0.581, and 0.554, respectively. The target outline is completely blurred, and detailed features are completely lost, allowing only the approximate location of the target to be identified. The aerodynamic light transmission effect has brought the system imaging to near failure. The core factors are: under Ma=5 conditions, the extreme aerodynamic heat and strong turbulence effects are superimposed, and the spatial scale and intensity of the flow field refractive index disturbance reach their peak. Severe wavefront distortion, scattering, and deflection occur during beam transmission, effectively introducing high-order complex aberrations, completely destroying the geometric and grayscale consistency of the target image. At the same time, the thermal deformation of the optical window and the thermal lensing effect reach their extremes, and the multi-physics coupling effect further amplifies the imaging distortion, ultimately leading to severe degradation of the target image, which cannot meet the requirements of normal detection and identification. Compared with the original clear image, it can be seen that the blurring of the image gradually intensifies with the extension of the aerodynamic heat load time, requiring performance improvement through aerodynamic thermal protection, aberration compensation, and image restoration techniques.

[0069] II. Conformal L-type system of waverider The waverider conformal L-type optical system structure used in this embodiment is as follows: Figure 9 As shown in the table below, the internal simulation-related parameters are as follows: Table 4 Parameters of the front incident lens group Table 5 Parameters of 45° Plane Mirror Table 6 Parameters of the 45° Rear Imaging Lens Group Figure 10The two-dimensional wavefront aberration distribution at the exit pupil of an L-shaped catadioptric conformal optical system is presented under operating conditions of Ma = 2–5 and t = 9.0 s. The results show that the system can effectively compensate for wavefront distortion caused by hypersonic aero-optical effects: as the Mach number increases from 2 to 5, the RMS value of the wavefront aberration at the exit pupil only slowly increases from 0.002λ to 0.018λ, and the wavefront aberration remains at an extremely low level within λ / 50 under all operating conditions, far less than the aberration threshold of traditional optical systems; the wavefront aberration distribution exhibits a pattern of low aberration at the center and high aberration at the edges, and the distortion morphology only expands gradually with increasing Mach number, without drastic abrupt changes, verifying the excellent suppression capability of the L-shaped catadioptric optical path for aero-optical aberrations. Figure 11 As shown, under Ma=2 conditions, the image quality remained at an extremely high level at the 3s, 6s, and 9s time points, with the SSIM value consistently maintained between 0.973 and 0.981. Visualization results show that the target aircraft's outline is clear and sharp, with excellent detail contrast, and almost unaffected by aero-optical effects. This demonstrates that the optical system possesses superior imaging performance in low-speed / subsonic environments, with minimal image degradation, and that the system's transmittance and aberration correction capabilities are at their optimal levels.

[0070] When the Mach number increases to Ma=3~4, the image quality begins to decline slightly, with the SSIM value slowly dropping from above 0.97 to 0.962~0.969. Visually, the aircraft edges appear slightly blurred, and the contrast is reduced, but the overall structural outline remains clearly discernible, without significant aberration interference. This result verifies the system's adaptability to mesohythmic and hypersonic flow fields, demonstrating its ability to maintain good target recognition capabilities even under conditions of increased aerodynamic disturbance.

[0071] At Mach 5 hypersonic speeds, the SSIM value drops to 0.948–0.952, resulting in significant image blurring and degradation, primarily manifested as edge blurring and detail smoothing. However, the SSIM value remains at a relatively high level above 0.94, indicating that the target aircraft's three-dimensional structural features are intact, without astigmatism or distortion-induced shape distortion. This demonstrates that the system can still effectively detect and identify targets under extreme conditions at Mach 5, exhibiting strong engineering robustness.

[0072] Imaging results from different Mach numbers and time series demonstrate that this catadioptric optical system possesses significant compensation capabilities for hypersonic aero-optical effects. Throughout the entire operating range of Mach 2 to 5, the image quality index SSIM consistently remains above 0.95, exhibiting clear image structure and complete detail. This fully proves that the adopted L-shaped optical path design effectively counteracts the effects of flow field refractive index disturbances and thermal deformation at high Mach numbers, ensuring stable and clear imaging of distant targets in complex flight environments, and fully meeting the engineering application specifications of hypersonic vehicle photoelectric detection systems.

[0073] Figure 12 The evolution curves of the imaging structure similarity (SSIM) of an L-type catadioptric conformal optical system over flight time are presented under Mach numbers ranging from Mach 2 to 8. The results show that the system possesses excellent dynamic compensation capability and long-term robustness against hypersonic aero-optical effects. Throughout the entire flight range, the SSIM generally follows the core physical law that image quality deteriorates with increasing Mach number. At low Mach numbers (Ma=2 and 3), the SSIM remains consistently above 0.96. Specifically, at Ma=2, the SSIM exhibits a slight initial decrease followed by a steady-state recovery, with no significant degradation in image quality. As the Mach number increases to Ma=5–8, aerodynamic heating and flow field disturbances intensify, leading to a gradual decrease in SSIM. A slight decay occurs in the initial flight phase due to transient flow field disturbances and accumulated thermal deformation. After 6 seconds, the flow field enters a fully developed steady state, the window reaches thermal equilibrium, the system's aberration compensation capability is fully utilized, and the SSIM decay rate slows significantly. At Ma=8, the SSIM remains above 0.92 at t=9 seconds. Figure 13 The peak signal-to-noise ratio (PSNR) of an L-shaped catadioptric conformal optical system under Mach numbers from 2 to 8 is presented as a function of flight time. The results show that during hypersonic flight, aerodynamic heating and flow field disturbances exhibit an evolutionary pattern of "transient accumulation → steady-state equilibrium": In the initial stage of flight, rapid aerodynamic heating and a strong transient disturbance in the flow field lead to a sharp increase in window thermal deformation and refractive index gradient, resulting in a continuous increase in imaging aberrations and a decrease in PSNR. As flight time increases, the window and flow field gradually reach thermal equilibrium, and the flow shock structure, boundary layer, and turbulent fluctuations enter a fully developed steady state. Aberration sources tend to stabilize, and the aberration compensation capability of the L-shaped catadioptric conformal optical system is fully utilized, effectively offsetting residual aberrations and ultimately achieving a slow recovery of PSNR. This verifies the system's excellent suppression capability and long-term robustness against hypersonic time-varying aerodynamic optical effects, and validates the excellent suppression effect of the L-shaped catadioptric optical path on hypersonic time-varying aberrations, meeting the engineering application requirements of photoelectric detection systems.

[0074] As shown in this embodiment, the present invention constructs a complete and efficient multi-physics coupled aero-optical image quality rapid simulation and evaluation method that balances efficiency and accuracy: a rapid flow field modeling method based on oblique shock wave theory, which uses the θ-β-M relationship to numerically solve the shock wave angle, replacing the traditional time-consuming CFD solution; a window geometry dynamic update method considering thermo-mechanical coupling, which calculates window deformation based on thermal strain and dynamically updates the intersection coordinates and normal direction of the light incident interface; a window refractive index dynamic update method considering thermo-optical effects, which calculates the refractive index change of each spatial point in the window in real time based on the thermo-optical coefficient and temperature field distribution; a high-precision ray tracing method in a non-uniform refractive index field, which uses the fourth-order Runge-Kutta method to solve the ray differential equation and combines second-order interpolation to obtain the refractive index and gradient between grid nodes; and an image degradation quantification evaluation method based on wave aberration, which obtains the optical path difference through ray tracing, calculates the wave aberration distribution, and then generates a degraded image and calculates standardized indicators such as SSIM and PSNR.

[0075] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Those skilled in the art can modify or make equivalent substitutions to the technical solutions of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for simulating the aerodynamic optical image quality of a supersonic conformal optical system, wherein the supersonic conformal optical system includes a waverider and its conformal optical window, the steps of which include: Obtain a three-dimensional geometric model of the waverider and its conformal optical window, and create a fluid computational domain centered on the waverider; The flow field parameters in the computational domain of the fluid are solved at different Mach numbers to obtain the corresponding temperature field distribution; The structural displacement of the waverider and the window deformation of the optical window are obtained based on the temperature field distribution. The refractive index field of the external flow field region is obtained based on the temperature field distribution and structural displacement, and the refractive index field of the optical window region is obtained based on the temperature field distribution and window deformation. Optical tracing is performed based on the refractive index field to obtain a simulated image.

2. The method according to claim 1, characterized in that, The flow field parameters in the computational domain of the fluid are solved based on the oblique shock wave relation at different Mach numbers.

3. The method according to claim 1, characterized in that, The refractive index of the optical window region is dynamically adjusted based on the thermo-optical effect.

4. The method according to claim 1, characterized in that, A second-order interpolation method is used to determine the interpolation coefficients from the values ​​of neighboring grid nodes in the fluid computational domain, obtain the refractive index and gradient at non-grid nodes, and continuously reconstruct the refractive index field.

5. The method according to claim 1, characterized in that, A simulated image is generated by convolving an ideal image obtained through optical tracing with a point spread function.

6. The method according to claim 1, characterized in that, The incident interface in ray tracing is dynamically corrected based on the geometric parameters after the window is deformed.

7. The method according to claim 1, characterized in that, The structural similarity index and peak signal-to-noise ratio are used to evaluate the simulated images.

8. A supersonic conformal optical system aerodynamic optical image quality simulation system, comprising: The waverider fluid computational domain creation module obtains a three-dimensional geometric model of the waverider and its conformal optical window, and creates a fluid computational domain centered on the waverider. The flow field parameter calculation module solves the flow field parameters in the fluid computational domain at different Mach numbers and obtains the corresponding temperature field distribution. The structural displacement and window deformation calculation module calculates the structural displacement of the waverider and the window deformation of the optical window based on the temperature field distribution. The refractive index field calculation module obtains the refractive index field of the external flow field region based on the temperature field distribution and structural displacement, and obtains the refractive index field of the optical window region based on the temperature field distribution and window deformation. The simulation image generation module performs optical tracing based on the refractive index field to obtain the simulation image.

9. An electronic device, characterized in that, The electronic device includes: a processor and a memory storing computer program instructions; the processor, when executing the computer program instructions, implements the steps of the method as described in claims 1-7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer program instructions that, when executed by a processor, implement the steps of the method as described in claims 1-7.

Images