高超声速飞行器在大气层内高马赫巡航飞行或再入时，气动加热使得红外光学窗口温度迅速上升，高温气体和红外窗口引起的气动光学效应导致红外导引头识别概率、跟踪精度等性能下降，甚至因探测器响应饱和而失效。为保证红外窗口正常工作并提高其性能，需对其采取制冷措施，常见的冷却方式有内冷、外冷两种。美国于二十世纪八十年代对红外窗口主动冷却开展了深入研究，并已成功应用于高超声速飞行器。我国也于九十年代末对主动冷却内冷方案开展了初步探索，但迄今为止，公开文献尚未见全面、系统的研究报道。

本文对国内外红外窗口冷却技术进行了综合调研，开展了高超声速飞行器红外窗口强度计算和温度影响分析，完成了红外窗口主动冷却内冷方案的数值模拟和实验研究，主要包括以下几方面的内容：

首先，综合考虑红外光学材料的力学性能、物理性能和光学性能，结合大气红外窗口探测波段，选择蓝宝石作为中波红外窗口材料，并应用薄板理论进行了圆形和矩形红外窗口的强度分析，根据结构强度设计准则得到了红外窗口最小厚度与载荷、特征长度的关系。典型情况下，直径60mm的圆形红外窗口最小厚度为3.82mm；边长60mm的正方形红外窗口最小厚度为4.46mm。

其次，应用气动热工程算法分析了高超声速飞行器驻点、头部热流分布，计算获得了典型飞行条件下红外窗口的温度范围，当红外窗口表面热流为100kW/m²时，初始温度为300K的蓝宝石加热40s时温度约为600K。为进一步研究红外窗口温度对探测系统性能的影响，计算分析了蓝宝石窗口中波红外发射率和透过率随温度、厚度的变化规律，开展了窗口热辐射效应的理论计算和实验研究，定量获得了温度、厚度等对蓝宝石红外窗口光学性能的影响。结果表明，蓝宝石窗口温度升高会导致发射率增加、透过率降低。如，5mm厚窗口从293K分别增加到373K和473K时，发射率相应提高了13.7%、32.9%，透过率降低了1.7%、3.2%。当红外窗口温度较高时，自身热辐射显著增强，从而大幅降低了探测系统的有效动态范围。计算结果表明，积分时间为2ms的红外探测器探测目标时，蓝宝石红外窗口的温度最高不宜超过473K。

再者，本文对高超声速飞行器红外窗口内冷方式进行了理论分析，给出了冷却效果的主要影响因素。设计了一款直径63mm、厚度8mm，侧面开有2mm×2mm环形内冷却通道的红外窗口，应用有限元软件研究了冷却剂种类、流速、初始温度以及冷却通道截面形状等因素对红外窗口内冷效率的影响。冷却介质采用流速1m/s、初始温度275K的软化水，冷却通道截面尺寸为2mm×2mm时，当红外窗口表面热流为100kW/m²时，相比无冷却时红外窗口最大降温可达150K，表面热流为25kW/m²时，降温约为70K。

最后，本文还开展红外窗口主动冷却实验研究，分别利用电热风机和电高温加热炉模拟高超声速飞行器气动热流和稳定环境工作温度。采用热流密度为25kW/m²的电热风机长时间加热蓝宝石红外窗口时，通入初始温度290K、流速1m/s的冷却介质水，红外窗口温度下降了约65K。高温加热炉温度为473K和523K时，通入初始温度为290K、流速为1m/s水，红外窗口最高温度分别下降了140K和170K。

本文的研究成果可为高超声速飞行器红外窗口设计提供参考依据。

When the hypersonic vehicle cruises or re-enters at a high Mach speed in the atmosphere, aerodynamic heating causes the temperature of the infrared optical window to rise rapidly. The aerodynamic thermal radiation effect caused by high temperature gas and infrared window may decay the performance of the infrared seeker to recognize the probability and the tracking accuracy or even fail because of the detector saturation. In order to ensure the operation of the infrared window and improve its performance, it is necessary to adopt cooling measures. At present, the common cooling methods of infrared windows mainly include internal cooling and external cooling. In the 1980s, the United States conducted research on active cooling of infrared windows, and achieved certain results successfully applied to hypersonic vehicles. In the late 1990s, China also carried out some preliminary research on the active cooling of internal cooling scheme. But so far, there has been no comprehensive and systematic research report in the public literature.

In this paper, the infrared window cooling technology at home and abroad is comprehensively researched, and the infrared window intensity calculation and temperature influence analysis of hypersonic vehicle are carried out. The numerical simulation and experimental research of the infrared window internal cooling method are completed, which mainly includes four aspects:

Firstly, according to the characteristics of the atmospheric infrared window, we choose sapphire as the material of medium infrared window, after considering the mechanical properties, physical properties and optical properties of infrared optical materials in many aspects. In this paper, the strength analysis of circular and rectangular infrared windows is carried out by using the thin plate theory. The relationship between the minimum thickness of the infrared window and the load or feature length is obtained according to the structural strength design criteria. Typically, a circular infrared window with a diameter of 60 mm has a minimum thickness of 3.82 mm; a square infrared window with a side length of 60 mm has a minimum thickness of 4.46 mm.

 Secondly, the aerodynamic thermal engineering method is used to analyze the stagnation heat flow and head heat flow distribution of hypersonic vehicles. The temperature range of the infrared window under typical flight conditions is calculated. When the heat flow on the surface of the infrared window is 100 kW/m², the temperature of the sapphire with an initial temperature of 300K is about 600K when heated for 40s. In order to study the influence of infrared window temperature on the performance of the detection system, this paper analyzes the variation of infrared emissivity and transmittance of sapphire window with temperature and thickness, carries out the theoretical calculation and experimental study of window thermal radiation effect, and quantitatively obtains the influence of temperature and thickness on the detection performance of sapphire infrared window. The results show that the increase of sapphire window temperature will lead to an increase in emissivity and a decrease in transmittance. When the temperature of the 5 mm thick window increases from 293 K to 373 K and 473 K, the emissivity increases respectively by 13.7% and 32.9%, the transmittance decreases respectively by 1.7% and 3.2%. When the infrared window temperature is high, its radiation greatly reduces the effective dynamic range of the detection system. Studies have shown that when the integration time of infrared detector is 2ms, the temperature of sapphire infrared window should not exceed 453K.

Furthermore, this paper analyzes the internal cooling method of the infrared window of the hypersonic vehicle and gives the main influencing factors of the cooling effect. An infrared window with a diameter of 63mm and a thickness of 8mm and a 2mm×2mm annular internal cooling channel on the side was designed. The influence caused by the factor which includes coolant type, flow rate, initial temperature, and cross-sectional shape of the cooling channel on the cooling efficiency of the infrared window was studied by using finite element software. When the heat flow on the surface of the infrared window is 100kW/m², the flow rate of the coolant water is 1 m/s, the initial temperature is 275 K, and the cooling channel is 2 mm × 2 mm, the infrared window temperature can be lowered by about 150K compared to no cooling. Similarly, when the heat flux is 25 kW/m², the sapphire infrared window is cooled to about 70K.

Finally, the paper also carried out experimental research on active cooling of infrared window. The electric heat fan is used to simulate the heat flow, and the high temperature heating furnace is used to simulate the stable ambient working temperature. When the electric heating fan stably heats the sapphire infrared window with a heat flow of 25 kW/m², the infrared window cooled by water with an initial temperature of 290K and a flow rate of 1 m/s, the maximum temperature of the infrared window has dropped by at least 65K. The experiment of sapphire infrared window active cooling research is basically consistent with the numerical simulation. When the temperature of the high temperature furnace is 473K and 523K, the infrared window cooled by water with an initial temperature of 290K and a flow rate of 1 m/s, the maximum temperature of the infrared window has dropped respectively by 140K and 170K.

The research results in this paper can provide reference for the design of infrared window for hypersonic vehicles.