Research On Aerodynamic Characteristics Of Optical Window Of High-speed Aircraft Under Jet Cooling

For hypersonic aircraft equipped with infrared imaging and detection systems flying in the atmosphere,the optical window is heated in direct contact with the heat flow of the air,the temperature rises extremely rapidly,and the deformation distribution is uneven,causing flight hazards.Too high temperature will bring a lot of infrared radiation noise.At the same time,due to the thermo-optic effect and the elastic-optic effect,the optical window will make the refractive index field distribution no longer uniform,which will greatly reduce the detection quality of the infrared detection system.Therefore,spray cooling is often used to protect the optical window.Jet cooling can effectively reduce the temperature of the optical window surface,but the influence on the temperature difference distribution of the entire window still needs to be explored.On the other hand,the jet flow makes the outer flow field structure of the fairing more complicated,and complex structures such as mixing layers and shear layers appear,which significantly reduces the quality of the light transmission imaging passing through the flow field.Therefore,it is extremely necessary to explore the comprehensive effect of the cooling jet on the aerodynamic characteristics of the external flow field,the aerodynamic thermal characteristics of the window,and the aerodynamic light transmission characteristics of the window.In this paper,the flow field simulation and thermal simulation of the aircraft at high speed are mainly based on FLUENT and ANSYS software.The flow field characteristics of the aircraft and the aerodynamic thermal characteristics of the optical window under jet cooling conditions are studied.Then,according to the data obtained by the simulation,the light is traced.To calculate the wave aberration of the light after passing through the flow field and the optical window.Finally,taking wave aberration as the evaluation index of optical performance,combined with the aerodynamic characteristics of the aircraft and the thermal characteristics of the optical window,the impact of jet cooling is comprehensively evaluated.The main contents include:(1)Research on the aerodynamic characteristics of the external flow field of highspeed aircraft under the condition of jet cooling.The calculation model of the flow field with concave cavity hood is established with the finite element idea.The effects of flight conditions(flying height,flight Mach number),jet parameters(nozzle velocity,temperature)and surface shape on the aerodynamic characteristics of the aircraft flow field and the cooling effect of the optical window were studied.Preliminary determination of suitable flight conditions and jet parameters will lay a solid foundation for the subsequent thermal response analysis and optical transmission analysis.(2)Research on aerodynamic thermal effect of optical window under the condition of jet cooling.According to the principles of heat transfer and elastic mechanics,the results of the flow field simulation are used as input loads to perform aerodynamic thermal simulation calculations on the optical window under the condition of jet cooling,and the results of the temperature field and thermal deformation field of the optical window are obtained.The results under flow conditions were compared and analyzed to evaluate the cooling effect of the jet flow.(3)Research on joint optical transmission of high-speed aircraft flow field and optical window under the condition of jet cooling.According to the density field obtained by the flow field simulation,and the temperature field and deformation field obtained by the thermal simulation of the side window,the flow field and the refractive index field of the side window are reconstructed using the Gladstone-Dale formula and the thermo-optic effect,and the fourth-order Runge is used The Kuta algorithm performs ray tracing to obtain the wave aberration that reaches the entrance pupil plane.Taking wave aberration as the evaluation criterion of the optical performance of the fairing of high-speed aircraft under the condition of jet cooling,the influence of jet cooling on the optical transmission quality was analyzed.