Research On Meso-Scale Combustion Model Of NEPE High Performance Propellant

Combustion model is an important basis for combustion simulation and performance study of solid propellant.Up to now,many combustion models of composite solid propel-lants,such as BDP,GDF and PEM,have been proposed.Based on these models,combus-tion performance of composite solid propellants have been extensively studied and a series of valuable results have been achieved.However,many problems related to its combus-tion behavior remain unsolved.Most previous studies of the combustion characteristics of composite solid propellants,such as burning rate and combustion wave structure are from macro-scale.The combustion models above belong to the phenomenological model cat-egory.But in fact,the composite solid propellant has complex three-dimensional hetero-geneous structure in meso-scale,the combustion in meso-level including many complex problems such as gas-solid coupling,simple or detailed chemical reaction mechanism,high temperature gradient and reactive fluid dynamics of complex flame structure.Different from the traditional phenomenological model(BDP,PEM),the meso-scale combustion model of AP/HTPB composite solid propellant developed by CSAR can cal-culate the dynamic combustion process of composite solid propellant under the consider-ation of particles size distribution,spatial distribution and component ratio.The meso-scale combustion model can be used to obtain the gas flame structure,burning rate char-acteristics and gas phase field characteristics,which represents the development direction of the current combustion model of composite solid propellant and has a promising future.At present,the research on meso-scale combustion model of composite solid propel-lant in China has not been reported in public literature,and there may be a certain gap with foreign research results.Reference to the experimental study and the meso-scale combus-tion model of AP/HTPB composite solid propellant developed by CSAR,this paper takes the high energy composite solid propellant NEPE as the research object and establishes its meso-scale combustion model.Some key technical problems in the process of model solving program are solved.Hope to narrow the gap with foreign research on the meso-scale combustion model of composite solid propellant.The research contents of this paper are mainly divided into four parts,as follows:(1)Experimental study on the ignition and combustion of NEPE solid propellantAn experimental system for ignition and combustion of propellant was built to carry out the ignition and combustion experiments of NEPE high-energy composite solid pro-pellant without aluminium particles.Experimental studies were carried out in a high-pressure closed burner with open windows in order to simulate the SRM high pressure conditions.The ignition and combustion process of propellant was photographed by high-speed camera system,and the characteristics of the process and gas flame struc-ture were analyzed in order to deepen the understanding of its combustion process and provide some relevant reference for establishing the meso-combustion model later.The dynamic burning rate measurement experiments based on ultrasonic method and digital image processing method were carried out.(2)Experimental study on aluminium agglomeration on burning surfaceAluminum particles can increase the energy density,specific impulse and combus-tion temperature of propellant,but at the same time,aluminum particles will agglomerate on the combustion surface of propellant,and large size aggregates will lead to the decrease of energy characteristics of propellant.The meso-scale combustion model of NEPE solid propellant established in this paper has not considered the existence of Al particles at present.In order to prepare for the subsequent study of meso-scale combustion with Al particles and aluminum agglomeration model,an experimental study on aluminum ag-glomeration behavior of NEPE high-energy composite solid propellant was carried out.High-speed micro-photography combined with micro-lens technology was used to study the A1 agglomeration behavior of NEPE solid propellant,at atmospheric pressure and high pressure respectively.The dynamic combustion behavior of Al particles at the burning surface and after separation from the burning surface was obtained.The research pro-vides technical support for the subsequent development of agglomeration size measure-ment based on digital image method and the establishment of high precision and wide applicability agglomeration model.(3)Study on random particles packs modelComposite solid propellant is a kind of high filling ratio granular composite ma-terial,the oxidant particles and metal particles are randomly distributed in the matrix,which has complex three-dimensional heterogeneous structure in meso-sacle.The com-bustion performance would be influenced by its heterogeneity.Therefore,the establish-ment of random particles packs model of composite solid propellant is the prerequisite for the simulation of meso-scale combustion model.The random particles packs model of NEPE propellant was established by molecular dynamics method,which the oxidant particles and metal particles in NEPE were simplified as spherical particles and the voids between particles are binders.For different particle types,numbers and size distribution,the random particles packs model of NEPE was established to provide geometric model for subsequent meso-scale combustion model.(4)Study on meso-sclae combustion model of composite solid propellantCombined with experimental research and the related work on the meso-scale com-bustion model of composite solid propellant developed abroad,the meso-scale combus-tion model of NEPE solid propellant without aluminium particles was established,and the program of the model was developed on the platform of OpenFOAM,an open source computational fluid dynamics software.The characteristics of multi-domain,nonlinear strong coupling,dynamic regression of burning surface and multi-component combustion in gas-phase domain in the combustion process of composite solid propellants were fully considered in the meso-scale combustion model of NEPE solid propellant.According to the above characteristics,the relevant algorithms were used in the process of program de-velopment:the zone partitioned method was used to solve the coupling flow field of gas and solid region.Level Set and VOF were combined to realize the dynamic tracking of the burning surface,and the grid topology change method was used to realize the dynamic change of the geometrical topology structure between the gas-solid regions.Based on the developed meso-scale combustion model program,the meso-scale combustion model simulation calculation of NEPE solid propellant was carried out and preliminary simula-tion results were obtained.The research results have high scientific and theoretical significance and engineering application value for the meso-scale construction model establishment and combustion performance prediction of composite solid propellant,and have important reference and guidance role for the formulation design of solid propellant and measures to improve combustion performance.The method of solving the meso-combustion model established in this paper has strong universality and can be extended to the simulation calculation of solid rocket motor,solid-liquid rocket motor and solid fuel ramjet.