【作者】 高翔；

【导师】 杨青真；

【作者基本信息】 西北工业大学 ， 航空宇航科学与技术， 2016， 博士

【摘要】 雷达探测和红外探测是目前针对飞行器的主要侦测方式,而发动机的排气系统不仅是飞机后向3μm-5μm波段内的主要辐射源,作为电大腔体也是飞行器后向主要的雷达散射源。因此,如何降低排气系统的红外和雷达信号强度成为隐身飞行器设计研究的重要问题。以此为背景,本文开展了飞行器及其排气系统的红外辐射和电磁散射特性研究。在红外辐射研究方面,发展了红外数值计算方法,并在此基础上研究了气溶胶隐身技术和S弯遮挡技术等红外抑制技术的特点,最后以耦合进/排气系统的飞翼无人机为研究对象,分析了太阳辐射、地面辐射、天空辐射等环境因素对飞翼无人机的红外辐射特性的影响。在电磁散射方面,研究了腔体电磁散射特性计算方法并开展了暗室实验测试验证,最后研究了几何构型设计、介质涂覆等雷达散射截面(RCS,Radar Cross Section)缩减技术。论文的主要研究内容及结果如下:1、在红外辐射计算技术方面:针对红外辐射计算与CFD计算使用网格不一致而带来的计算精度损失的问题,本文提出了基于非结构网格“表面”编号的拓扑方法,避免了将CFD结果数据及网格数据拓展全三维和插值而带来的计算精度损失,此外所提出的网格拓扑方法能够解决包含周期性边界条件的红外辐射问题;对气体辐射的逐线计算方法和Malkmus统计窄谱带模型进行了研究,并在HITEMP数据库基础上采用Malkmus统计窄谱带模型构建了用于3μm-5μm和8μm-14μm气体辐射研究的燃气数据库;针对使用窄谱带模型进行大气衰减作用计算效率较低的问题,将CG近似下的Malkmus模型与HITRAN数据库结合,应用于背景辐射模型的计算,提高了构建背景辐射的计算效率;基于球形粒子光学参数、稀疏粒子系的光学参数以及散射统计概率模型,建立了含粒子介质系的散射模型,并将此模型与反向蒙特卡洛方法相结合,开发了能够计算含粒子介质系红外辐射的方法和计算软件,为气溶胶隐身技术研究提供了有力的工具;通过构建太阳辐射模型、地面辐射模型、天空辐射模型,并以壁面双向反射函数模型模拟飞翼机体表面对太阳辐射的反射,最终实现了处于背景中的飞行器红外辐射数值仿真,为研究目标与环境之间的影响提供了理论与技术支撑。2、在气溶胶红外隐身技术方面:以轴对称排气系统为基础开展了SiO2粒子注入对排气系统的红外抑制效果的研究,获得了粒子注入规律对排气系统的红外辐射强度的影响规律。通过分析粒子的注入流量、注入速度、注入角度、直径以及外流马赫数等参数对粒子注入后的排气系统红外辐射特性的影响,发现了离散颗粒注入流量过大反而会使得排气系统在大角度下的红外辐射增强;在有外流的情况下,粒子注入速度和注入角度对排气系统的红外抑制效果的影响不大;在大探测角下,外流马赫数为0.4时的抑制效率要高于马赫数为0.6和0.8时的抑制效率。3、在几何遮挡红外抑制技术方面:为探索遮挡技术对排气系统红外辐射的影响,对比研究了轴对称排气系统、单S弯排气系统以及双S弯排气系统的红外辐射特性,得出采用双S弯排气系统,能够使红外辐射强度的最大值相比轴对称排气系统减少95%左右,使被锁定距离的最大值降为轴对称排气系统的15%左右;开展了宽高比、第一弯位置、第一弯面积、出口斜切角度以及出口形状等几何参数的变化对双S弯排气系统的气动性能及红外辐射特性影响研究,得到了几何参数变化对双S弯排气系统的气动性能及红外辐射特性的影响规律。4、在背景与目标红外辐射研究方面:采用理论分析与数值模拟相结合的方法,分析研究了“干净构型”及耦合不同进/排气系统的飞翼无人机的气动性能及内外流特性;并对耦合S弯进气道、单S弯或双S弯排气系统的飞翼无人机的红外辐射特性进行了分析研究;结果表明,耦合双S弯排气系统的飞翼无人机具有更低的红外辐射强度;最后,以耦合双S弯进/排气系统的飞翼无人机为对象,开展了无人机蒙皮反射背景辐射的研究,研究表明在3μm-5μm波段内,太阳辐射是飞机蒙皮的主要反射辐射,而在8μm-14μm波段内反射辐射主要来自地面辐射和天空的辐射。5、在电磁散射计算方法与RCS实验测试方面:将迭代物理光学方法与阻抗边界条件相结合,发展了可用于腔体吸波介质涂覆研究的电磁散射计算程序,并将其与红外辐射计算程序进行集成;基于简化的轴对称排气系统模型,对本文的数值方法进行了验证,结果表明,所开发的电磁散射计算程序能够用于研究排气系统这类复杂腔体的电磁散射特性;为消除排气系统的外壁面对RCS测试结果的影响,针对电大尺寸腔体RCS测试的要求,设计研制了分别适用于轴对称排气系统、双S弯排气系统且符合背景噪声要求的两种低散射壳体;采用步进频率测试系统,在暗室中完成了轴对称、双S弯两种排气系统在五个波段下的RCS测试,验证了双S弯结构能够有效地减缩排气系统的RCS。6、在排气系统RCS减缩技术方面:分析对比了简化后的轴对称排气系统、单S弯排气系统以及双S弯排气系统在X波段内的电磁散射特性。研究表明,双S弯结构可使得排气系统的RCS至少减缩74.4%,并进一步分析了宽高比、第一弯面积、第一弯位置等多个几何参数对双S弯排气系统电磁散射特性的影响,探寻了排气系统电磁散射特性随几何参数变化的规律;针对介质涂覆对双S排气系统RCS的影响,开展了双S弯排气系统不同涂覆位置的研究,研究发现介质涂覆能够有效减缩排气系统的RCS,在喷管出口附近壁面涂覆吸波材料具有高的效费比。更多还原

【Abstract】 Radar detection and infrared detection are the main ways to detect aircrafts,while the engine exhaust system,as a typical large cavity,is not only the major radiation source of aircraft in the 3μm-5μm wave band,but also the main scattering source.Therefore,it is an important work on how to reduce the infrared and radar signal intensity of the exhaust system.Under this circumstance,a research was conducted on the infrared(IR)radiation and electromagnetic scattering of an aircraft as well as its exhaust system.In the IR radiation research,a numerical method was developed,and a further research was conducted on the aerosol suppression technique and S shaped nozzle suppression technology.Then based on UAV with inlet and exhaust system,the influence was studied on how solar radiation,earth radiation,and sky radiation affect UVA’s infrared radiation characteristics.In the study of electromagnetic scattering,a calculation method was studied on cavities’ electromagnetic scattering,and then the numerical accuracy was verified by a darkroom experiment.Finally,a research was conducted on geometry design,media coating,and other Radar Cross Section(RCS)reduction technologies.The main research contents and results are as follows:(1)In the aspect of the infrared radiation numerical method.A topology method,which is based on the unstructured grids “surface numbering”,was proposed to solve the problem of the data inconsistency and accuracy loss for IR calculation and CFD calculation.The method can avoid transforming the CFD result and calculation mesh to 3D topologically,which could bring the accuracy loss.Besides,the method is also suitable for periodic boundary conditions of infrared radiation.Then a study was carried out on line-by-line calculation method and Malkmus statistical narrow band model,Combing Malkmus statistical narrow band model and HITEMP database,a gas database was built for researching 3μm-5μm and 8μm-14μm gas radiation.Due to low computing efficiency of using narrow-band model to study atmospheric attenuation,a CG approximation Malkmus model was combined with HITRAN database.It reduced the computational time to build background radiation,applying to the background model radiation calculation.For gas transforming into particles medium by using aerosol suppression technology,a particle medium scattering model was built based on the optical parameters of spherical particles,sparse particle and scattering statistical probability model.Combining this model with Reverse Monte Carlo method,a software was developed to calculate the particle medium infrared radiation,which provided a powerful tool to study aerosol suppression methods.Solar radiation model,ground radiation model and sky radiation model was built for considering environment reflectance radiation,then combing those radiation models with Bidirectional Reflectance Distribution Function(BRDF),the wing body surface environment aircraft infrared radiation simulation was finally achieved,which provided support to study the impacts of the target and the environment.(2)In aspect of aerosol inhibition measurements.In order to study the inhibitory effect of SiO2,the axis-symmetry exhaust system with particles was studied.The results show that particle injection can effectively inhibit the IR radiation of the exhaust system and change the constitution of the IR radiation under large detection angle.By analyzing the influences of the particle’s injection flow,injection speed,injection angle,diameter,outflow Mach number and other parameters on the characteristics of the exhaust system IR radiation,another conclusion was found that discrete particles injecting too much into the exhaust system could enhance infrared radiation at large angle.With the existence of outflow,the inhibitory effect of different particle injection speed and angle was not much different.When the outflow Mach number is 0.4,the inhibition efficiency under large detection angle was better than the same case with the outflow Mach number of 0.6 or 0.8.(3)In aspect of geometric block suppression technology.In order to find out how geometric block technology influences the IR radiation of exhaust system,the IR radiation of double S exhaust system,single S exhaust system and axisymmetric exhaust system were compared,the results showed that double S exhaust system could reduce the objective of maximum infrared radiation intensity by 95%.The effects of different aspect ratios,different first corner positions,different areas of the first bend,different export miter angles and different outlet shapes influences on the performance and IR radiation characteristics of the double S exhaust system were researched,and the influences laws of the geometric parameter changes on the double S exhaust system was found.(4)In aspect of background and objective infrared radiation research.Combining theoretical analysis with numerical simulation methods,a research was carried out on the aerodynamic performance,the internal and external flow influence of clean flying wing UAV model and flying wing UAV with inlet and exhaust system.A further research was carried out on the flying wing UAV with single S inlet and single S exhaust system,UAV with single S inlet and double S-shaped exhaust system.The results show that flying wing UAV with single S inlet and double S-shaped exhaust system has lower IR signals.Then based on UAV with single S intake and double S exhaust system,a research was conducted in UAV skin reflective background radiation.The results show that solar radiation was the main reflected radiation of aircraft skin within 3μm-5μm wave band,while terrestrial radiation and sky radiation were the main reflected radiation within 8μm-14μm wave band.(5)In aspect of electromagnetic scattering calculation methods research and RCS experiment.The Iterative physical optics(IPO)and impedance boundary condition were combined to develop large cavity dielectric surface coated calculation software,and integrated with infrared radiation calculation software.The calculation methods were certificated on the simplified axis-symmetrical exhaust system model,and the results verify that the IPO calculation software could deal with the exhaust system.In order to minimize the influence of exhaust system wall to RCS results based on large cavity RCS testing requirements,two shells adapting to the weak scattering background noise requirements were built and used in axisymmetric exhaust system test and double S exhaust system test.Using stepped frequency-testing system on axisymmetric exhaust system model and double S exhaust system model under 5 different wave bands in darkroom,it is found out that the double S structure could effectively reduce the RCS of the exhaust system.(6)In aspect of exhaust system RCS dispersion technology.The electromagnetic scattering characteristics of simplified axisymmetric exhaust system,single S exhaust system and double S exhaust system were analyzed in X band,the results show that double S structure reduces the RCS of exhaust system by 74.4%.Geometric parameters of aspect ratios,area of the first bend and first band position influencing electromagnetic scattering characteristics of double S exhaust system were analyzed,and the change laws between geometric parameters and double S exhaust system were obtained.Research on different coating parts of double S exhaust system was also carried out,and the results show that absorbing wave material coating could reduce the RCS of exhaust system,and coating absorbing material on the surface around the outlet of exhaust system has good proportion between the efficiency and cost.更多还原