Reseach On Multiband Radiation Characteristics Of Rocket Engine Exhaust Plume

Radiation of the rocket motor exhaust plume is one of the most important signal of the aircrafts which includes ultraviolet radiation and infrared radiation.In fact,ultraviolet radiation and infrared radiation are the most important.It is of great significance to study the radiation mechanism of the rocket motor exhaust plume and to understand the characteristics of the rocket motor exhaust plume for research on stealth performance of aircraft,ultraviolet warning system,infrared warning system or other detection,identification,tracking system and rocket engine propellant formulation improvement.The purpose of this paper is to establish a multi-wavelength radiation characteristics model of rocket motor exhaust plume.The multi-band characteristics radiation model includes the ultraviolet radiation characteristics and infrared radiation characteristics.Both the ultraviolet radiation and the infrared radiation are considered simultaneously in the process of emission,absorption,and scattering,and both are unified and simultaneously solved.The unified model includes three parts:The first one is exhaust plume flow field model.The second is the radiation characteristic parameter calculation model.The last one is the radiation transmission solution model.The flow field of the exhaust plume belongs to high Reynolds number compressible turbulent flow.For the compressible flow,the energy equation must be solved.For the turbulent flow,the turbulent influence on the flow is taken into consideration.The Realizable k-?model is used to simulate the turbulence in the flow.The exhaust plume emitted through the nozzle contains flammable substances which react with oxygen in the atmosphere to generate secondary combustion.The secondary combustion of the exhaust plume exhaust plume is simulated using a finite-rate chemical reaction model,in which 9components 10 reactions H₂/CO oxidation mechanism and 6 components 7 reactions H₂/O₂oxidation mechanism simulate the chemical reaction processes in different propellant engine plumes.A rigid chemical reaction solver is used to improve the stability of the flow field calculation.Calculation of radiation characteristic parameters includes calculation of ultraviolet radiation characteristic parameters and calculation of infrared radiation characteristic parameters.The characteristics of the UV radiation take into consideration the thermal emission,CO+O chemiluminescence and OH free radical chemiluminescence.Among them,the thermal emission can be calculated using the Planck formula,and the CO+O chemiluminescence can be calculated using an empirical formula.For the OH free radical chemiluminescence,an improved local equilibrium method was established.In this method,not only the excitation reaction but also the collisional deactivation reaction,the predissociative reaction,the radiation deactivation reaction,and the complex reaction were added to make the calculation of the excited OH radicals density more accurate.Finally,the chemiluminescence intensity of the OH radicals was calculated using the HITEMP-2010database.Several commonly used models for the calculation of gas radiation characteristic parameters are introduced in the infrared radiation characteristics parameters,including the line-by-line integration method,the gray gas weighted sum model,the gray gas weighted sum model based on spectral lines,the k distribution model,the full-spectrum k distribution model,etc.The advantages and disadvantages of several methods were analyzed.Finally,in view of the Monte Carlo method for solving the radiative transmission problem in this paper,in order not to increase the computational complexity and reduce the computational cost,considering the calculation accuracy and calculation time comprehensively,and the gray gas weighted sum model based on spectral lines is used to calculate the infrared radiation characteristics parameters of exhaust plume.The radiation transmission problem is solved using the Monte Carlo method.Based on the calculation of the flow field and the calculation of radiation parameters,a multi-band radiation characteristics model based on the Monte-Carlo method for the exhaust plume is established.The calculation results of flow field obtained from the Fluent software is grid preprocessed to fit the computational structure of the Monte Carlo method.Considering the emission,absorption and scattering of photons,the parameters of photon wavelength,photon emission direction,photon emission position,scattering,and transmission are regarded as random processes.Then random functions of these processes are established.The propagation processes and the final destination of each photon are tracked.Finally,the spectra and energy distribution on the imaging plane are statistically calculated to obtain the spectral intensity distribution and radiation intensity spatial distribution of the rocket motor exhaust plume.Comparing the simulation results with the experimental results,the reliability of multi-band radiation characteristics model of rocket engine exhaust plume is verified.This paper also focuses on the infrared radiation characteristics of a certain type of a UAV and its engine plume.A test study on the ground at cruise condition was conducted.Through the test,spectral distribution,long-wave infrared radiation spatial distribution,and medium-wave infrared radiation spatial distribution and shortwave infrared radiance spatial distribution of UAV and its engine at different observation angles was obtained.The test method and test result data provide reference for the research of stealth performance of UAV,and also have important significance for the development of infrared alarm system.UV alarming systems and infrared alarming systems have been developed for many years.The development of infrared alarming,UV alarming,and bicolor alarms constitutes a roadmap for the development of missile warnings over the past decades.Advanced detector arrays and processing technologies have prompted more and more small sensors to be applied on aircrafts.There is a tendency of multi-functional integration such as missile warning,situational awareness and auxiliary navigation.Therefore,the multi-band radiation characteristics model of rocket engine exhaust flume studied in this paper has broad application prospects,and provides theoretical basis and decision-making support for the further improvement of integrated alarm capability.