Analysis Of Key Heat Transfer Problems In Gun Barrel During Launch Processes

With the higher requirement of weapon performance,the erosion problem of gun barrel is becoming severer and significantly limits its service life.Thermal effect is the dominant factor that affects the erosion and ablation of the gun barrel among all other factors.This dissertation systematically investigates the heat transfer problems during launching process for a large caliber gun.Conduction,convection and radiation heat transfer are all considered and various combined heat transfer models are developed for different working conditions.This dissertation aims to provide theoretical guidelines for the design of the gun barrel in terms of thermal aspect,and contains following contents:a)A heat transfer model for the gun barrel is developed based on classical interior ballistics model.The core flow parameters are calculated from Lagrangian assumption and serve as the third kind of boundary condition for the heat transfer of the gun barrel.The energy equation is discretized and solved by finite difference method.Temperature responses for a single shot and multiple shots are investigated and the effects of material properties and firing rate are considered.During the launch process,the maximum temperature of the bore occurs near the origin the rifle,and reaches 1100K for the cases considered.The temperature of the bore surface decreases when approaching the muzzle.Another important feature is that very large temperature gradient exists near the bore surface.A two-phase interior ballistics model is also used to provide core flow parameters for the heat transfer analysis.This advanced model is solved by MacCormack scheme.This model can model the ignition process of the propellant and can capture the pressure wave in the bore and is more accurate than the classical model.Temperature response of the gun barrel using this model reflects the effect of the ignition process.b)To investigate the thermal control of the gun barrel,heat transfer models for different cooling methods are developed.Firstly,a cross-section heat transfer model is developed using finite element method and considers the effects of chromium plating and mid-wall water cooling on the temperature responses during continuous firings.The effect of structural parameters is also investigated.A two-dimensional conjugate heat transfer model is developed using finite volume method to investigate the influence of outer water cooling method.Results show that chromium plating has the effect of reducing the maximum temperature of the bore surface,while mid-wall cooling method can decrease the increase trend of the maximum temperature.Outer cooling method can take away21%of the total input heat during 30rounds.c)To choose a radiative transfer solver that appropriate for radiation modeling in gun chamber,detailed investigations are performed to determine the accuracies of different solvers in terms of the radiative heat source and radiative heat flux and computational time of various radiative transfer solvers.Differences of P1 method,SP3 method and finite volume method(FVM)in combined conduction and radiation heat transfer problems are investigated and the result of Monte Carlo method is considered as benchmark solution.After this,the performances of P1 method,SP3 method,P3 method,FVM and discrete ordinate method(DOM)are systematically compared for combined natural convection and radiation heat transfer problems.Results of errors and computational time under different parameters are presented.To investigate the combined convection and radiation heat transfer in particle-resolved simulation for the propellant combustion,a hybrid method of lattice Boltzmann method(LBM)and FVM/DOM is developed for regular and complex geometries.d)The high-fidelity non-gray radiation model,SLW method,is investigated,and the contribution of different gray gases in the total radiative heat source and heat flux are determined for several typical cases.A hybrid FVM and P1 method,in which FVM is used to solve the radiative transfer equation(RTE)for some gray gases and P1 for the other gray gases,is proposed and it can decrease the computational time without much loss of accuracies.The SLW is also used to solve a combined conduction and non-gray radiation heat transfer problems,and the effects of many parameters on the temperature and wall heat flux are investigated.e)A radiative heat transfer model in the gun chamber is developed and the SLW method is used to treat the non-gray radiative properties of the high-pressure and high-temperature combustion gases.Finite volume method is used to solve the radiative transfer equation.A particle scale heat transfer model is also developed to investigate the non-gray radiation heat transfer for the ignition process,and the effects of temperature,pressure and void fraction are considered.Mean radiative heat flux of all the particles increases linearly with temperature under low pressure and increases much faster with temperature under higher pressure.f)A two-dimensional heat transfer model considering solar radiation is developed for the gun barrel and solar heating effect is investigated.A more complicated model includes a thermal sleeve is developed to investigate its insulation effect.This model contains conduction,natural convection and radiation.Thermal sleeve can effectively reduce the temperature difference between the upper and lower surfaces of the gun barrel.Without a thermal sleeve,there will be temperature about5-6K for one hour solar heating.The effects of non-gray radiation heat transfer in the air gap is also investigated.The presence of gas radiation will decrease the Nusselt number due to absorption and this difference increases with the increase of the air gap.