Research On Aftereffect Transient Heat Transfer Characteristics Of Tail-Pipe Nozzle

The tail-pipe nozzle is widely used in tactical missiles because of its outstanding stability.During the working process of the tail-pipe nozzle rocket motor,high-temperature gas is produced in the combustion chamber,accelerated in the tail-pipe nozzle,and finally used to propel the missile.When the high-temperature gas flows into the tail-pipe nozzle,alumina deposition and insulation layer ablation occur,which cause the temperature rise of the tail-pipe nozzle.However,due to the heat transfer hysteresis in the tail-pipe nozzle thermal protection structure,the temperature rise of the tail-pipe nozzle outer wall surface occurs at the aftereffect stage.When the temperature of the tail-pipe nozzle outer wall surface exceeds the operating temperature threshold of the thrust vector control system,the high temperature will fail the thermal sensitive electronic equipments of the control system and destroy the rocket motor.In order to ensure the success of the missile combat mission,the temperature of the tail-pipe nozzle outer wall must be strictly confined,and a reasonable thermal protection design must be adopted.Therefore,it is imperative to investigate the aftereffect transient heat transfer characteristics of the tail-pipe nozzle motor.The contents of this thesis consist of three parts:1.A tail-pipe nozzle aftereffect heat transfer computation model is established.According to the physical phenomena of gas-solid two-phase flow,insulation layer ablation,alumina deposition,gas-solid boundary movement,and transient changes in the internal flow field during the working process of the tail-pipe nozzle,the present work establishes a basic computation model for the heat transfer process of the tail-pipe nozzle.This computation model includes convective heat transfer model,insulation layer ablation model,and alumina deposition model.The porous medium model is also employed to solve the gas-solid boundary movement problem caused by insulation layer ablation and alumina deposition so that the boundary movement in the tail-pipe nozzle was numerically realized.2.Conventional nozzle aftereffect heat transfer without insulation lay ablation is simulated and analyzed.The influence of sediment and insulation parameters on the aftereffect heat transfer is analyzed,according to which the tail-pipe nozzle aftereffect heat transfer computation model is modified.The accuracy of the computation model was verified by motor experimental data under different conditions,and the error was found within 15%.At the aftereffect stage,the outer air flows back into the nozzle along the inner wall cooling the deposition.The heat of the sediment and the insulation layer is transferred to both sides of the nozzle inner wall.3.Tail-pipe nozzle aftereffect heat transfer with insulation lay ablation is simulated and analyzed.Parametric analysis of the tail-pipe nozzle aftereffect heat transfer show that,the leading influencial factors of heat transfer are the deposition rate of alumina,the reflux-time,the pyrolysis rate of the thermal insulation,and the thermal conductivity of alumina in the order of importance from the most to least.Insulation layer ablation and alumina deposition change the nozzle inner profile and exacerbate the changes of the internal flow field.At the aftereffect stage,the outer air flows back into the nozzle along the tail-pipe nozzle inner wall,and cools the nozzle.