Phenomenology Study On High-speed Target Radiation In Continuous-flow Regime

The primary task of the infrared early warning system is to detect,track,classify and identify(DTCI)potential threat targets in the field of view with high successful alarm rate and low false alarm rate to provide effective pre-protection for the offensive and defensive system.The infrared early warning system focuses on threatening high-speed missiles and aircraft,and the main detectable radiation sources are the rocket exhaust plume and the body of the vehicle.The early warning system is required to identify targets and false alarm sources in a variety of backgrounds considering the complexity of the false alarm source and the emergence of weak-signal feature technology.Thus,this work is facing tremendous challenges.From the perspective of development trends,it is of great significance to study the radiation phenomenon characteristics of targets,including rocket exhaust plumes and hypersonic vehicles,for the detection,classification and identification of early warning system.Especially,some dynamic radiation characteristics of flight events should be pay more attention to during altitude-varying such as stage separation,motor ignition,motor cutoff,etc.In this dissertation,the two types of targets,namely rocket exhaust plumes and typical hypersonic vehicles,are studied,which aims to establish a set of numerical computational models and simulation tools for analyses of radiation phenomenon features of high-speed targets.To understand and know well the changing regularity of radiation phenomenological elements of high-speed targets in terms of time,spectrum,space,motion,direction and energy through the analysis of parameters affecting radiation signatures in steady state and the study of dynamic radiation characteristics related to flight events.And then the temporal-spatial-spectral characteristics of target radiation and the detectability are examined under different detection scenarios.The thesis can be summarized as the following three parts: In the aspect of the theoretical model and computation tool of high-speed target radiation phenomenon research,this thesis takes the rocket exhaust plume and the hypersonic vehicle for research objects.A series of numerical models and corresponding codes are developed,which has the computational capability from the original parameters to optical radiation consisted of reacting flow field module,radiation physical parameter module and radiation transmission module.It is a complete calculation method for simulations of high-speed target optical radiation characteristics in continuous-flow regime.In this thesis,the rocket exhaust plume and hypersonic vehicle flows are computed by using the two-temperature model and the finite-rate chemical reaction model.Since the decoupling between radiation and flow field,the radiation property parameters of high-speed reacting flows are established by the line-by-line(LBL)and the statistical narrow band(SNB)models.The line-of-sight(LOS)method is used to solve the radiative transfer equation.The infrared signature analysis tool(IRSAT)and the signature analysis tool of hypersonic vehicle(SATHV)are programed.Additionally,in order to meet the demand of quick estimation in engineering,a fast-computing infrared signature analysis tool(FIRSAT)for low-altitude exhaust plumes,considering afterburning,entrainment and turbulence,is established based on the “self-similarity” characteristics of a free jet,which can be also used for evaluations of the cutoff temperature of the plume,the size of the inclusion and the contribution of each major component to the radiation in IR signature predictions.For the research on the phenomenological characteristics of high-speed target intrinsic radiation,there are two main contents:(1)the key parameters influencing target radiation under quasi-steady-state conditions,and(2)the time-space-spectrum dynamic characteristics of target optical radiation related to flight events.Firstly,the thesis clarifies the effects of afterburning,scaling motor model,proportioning of propellant and thermal non-equilibrium effect on the radiation signatures of rocket exhaust plumes.Secondly,the ‘opportunity' radiation characteristics of the HTV-2 type vehicle and the X-37 B type vehicle are obtained.The effects of reaction control systems(RCS),change rate of attack of angle on phenomenological elements are examined.Finally,numerical experiments are designed to thoroughly evaluate the unique radiation phenomenological elements related to dynamic flight events,including the operations of motor ignition,motor cutoff,stage separation,altitude-varying flight and the hypersonic vehicle maneuvering.Some valuable phenomena are discovered including the cross relationship between the radiance-altitude curves,the coincidence relationship between the radiance and the chamber pressure trace,the timing relationship between the radiance and the stage-separating altitude,and the relationship between the radiance and the change rate of the angle of attack for a boost gliding vehicle.In the analysis and application of high-speed target radiation phenomenology,the radiation characteristics and the detectability of targets under different detection scenarios are carried out,and the influencing factors of radiation noise are also evaluated.Firstly,the maximum detecting range(MDR)model and the thermal infrared imaging approach are established for space-based and ground-based observation platforms.It is found that the apparent radiant intensity of the rocket exhaust plume along the trajectory has a characteristic altitude between the band pairs from the space-based platform.It reveals that the apparent radiation characteristics and detection range of hypersonic vehicles are strongly dependent on the spectral band,the sensitivity and the observation angle of the detector.A series of radiation effects related to apparent radiation of two types of hypersonic vehicles are found including detection characteristic altitude,radiation enhancement spectral band,blinding zone,and sensitivity enhancement.Secondly,the reliability of three chemical reaction kinetic models and two non-equilibrium temperature index factors for the species formation of thermochemical non-equilibrium hypersonic shock layer in the near-space are assessed and suitable application cases for them are recommended.The calculation model of the non-equilibrium radiation noise of the shock layer is established,and the reliability of the radiation noise prediction in the ultraviolet and infrared bands is verified respectively.Finally,the effect of the size of the optical dome on the time-space-spectrum radiation noise due to the change of trace components at near-ground altitudes is analyzed,and a correlation model of spectral radiation noise,free stream density and velocity is established.