As a strategic focus in the military field of various countries worldwide, hypersonic remote sensor technology highlights irreplaceable advantages in performing tasks such as long-range strikes, reconnaissance, monitoring, and rapid response. However, as flight speed increases, the environmental conditions faced by the aircraft become more extreme. Among them, the optical window, a key component of the hypersonic remote sensor, is usually installed on the bottom skin of the aircraft. It serves not only to isolate the external harsh environment but also to ensure that the internal photoelectric load operates in a relatively stable environment. Additionally, it acts as the optical imaging channel that connects the internal photoelectric load with the external environment and is directly involved in imaging, which significantly affects its dynamic imaging performance. More and more scholars are focusing on the impact of multi-physical field coupling on the performance of optical windows. The technical characteristics and application scope of optical windows currently under study are primarily focused on subsonic and supersonic aircraft platforms. However, there is limited public information in recent research on the dynamic imaging performance of optical windows in hypersonic aircraft. Therefore, conducting research on the dynamic imaging performance of hypersonic optical windows, especially through multi-physical field coupling analysis, will help deeply understand the changing dynamics of their performance. This research will provide theoretical support for the design and optimization of optoelectronic payloads and further promote the application of these payloads in hypersonic aircraft.

We propose a multi-physics coupling numerical calculation method that integrates the multidisciplinary fields of flow, heat, structure, and optics to analyze the dynamic imaging performance of optical windows in hypersonic flight environments. This method combines computational fluid dynamics (CFD), finite element analysis (FEA), and optical transmission models to systematically study the influence of thermal effects, aerodynamic pressure, and structural response of optical windows on imaging performance under hypersonic flight conditions. First, the CFD method is used to simulate the flow field of the hypersonic vehicle, the aerodynamic environment of the vehicle surface, and the optical window, obtaining thermal flow and aerodynamic pressure data for the window surface. Then, based on the CFD analysis results, FEA is employed to perform thermal-structural coupling analysis to determine the window surface temperature field. The window deformation caused by the temperature gradient is simulated by combining the thermal expansion characteristics and structural response of the material. Finally, the influence of window surface changes on the light field difference, transmission wave aberration, and imaging performance is analyzed using an optical-mechanical-thermal integration analysis method.

In our study, a multi-physics field coupling numerical calculation method, integrating the multidisciplinary fields of flow, heat, structure, and optics, is proposed to address the complexity of dynamic imaging performance of optical windows in hypersonic environments. First, an aero-thermal-aerodynamic pressure-stress field coupling model is established to obtain the temperature, aerodynamic load distribution, and structural response of the window components under high Mach number flight conditions. Second, an opto-mechanical-thermal integration simulation model of the window components is established to evaluate the transmission wavefront performance (Fig. 10) of the optical window after disturbance. Finally, by combining with the actual optical system model, the law of change is revealed in the dynamic imaging performance of the optical window under hypersonic flight conditions. The results show that, with the increase in flight speed, the temperature of the optical window increases significantly, which leads to a substantial decrease in the optical performance of the optical window assembly (Fig. 11). The modulation transfer function (MTF) decreases by 0.194 (@100 cycle/mm), and the imaging quality of the optical system after focusing (Fig. 12) has an MTF larger than 0.187 (@100 cycle/mm). Through the multi-physics field coupling method proposed in this paper, the performance changes of optical windows under high Mach number flight conditions are predicted more comprehensively and accurately, which breaks through the limitations of single physical field analysis and provides a theoretical basis for the optimization of optical window design.

We study the actual flight environment of the aircraft for the optical window assembly carried by the hypersonic remote sensor, establish an aerodynamic-thermal finite element model for the aircraft, and obtain the aerodynamic heating heat flux density on the window surface in a flight cycle. The optical-mechanical-thermal multi-physics field coupling analysis is conducted on the window component, which reveals that the highest temperature of the window surface reaches about 792 ℃, and the window glass component experiences a non-uniform temperature field distribution. The temperature field is then interpolated into the structural model, and the deformation displacement of the window surface is obtained, causing the flat window glass to transform into a curved surface due to the non-uniform temperature field. Finally, based on optical-mechanical interface technology, the window component is thermally evaluated, and the imaging performance is analyzed. The transmission wave aberration root mean square (RMS) is <0.2903λ (λ=632.8 nm), and the imaging quality MTF of the optical system after focusing is larger than 0.187 (@100 cycle/mm), which meets the performance index requirements of the remote sensor. The multi-physics field coupling method proposed in this paper provides a theoretical basis for the design and optimization of optical windows and lays a foundation for engineering applications in related fields.