Research On Integrated Simulation And Optimal Design And Fault Analysis Based On Gap Design For Nozzle

On account of its simplified structure,high reliability and short preparation time for launching,solid rocket motor(SRM)has been widely used in military field.With the development of high energy,large size,high overload and broad adaptability,it leads to higher requirements for design of SRM,especially for nozzle design.Except for performance design,not only its inner flow but also its heat transfer and thermal stress condition are the main aspects for researchers to consider.These are important to keep its high reliability and structural integrity.Focused on gap design and its resulting faults,this thesis studied an integrated coupled analysis method of thermal-structure and its application in gap design of SRM nozzle.An experiment was also conducted.Besides,faults analysis raised by gap design was also included.Listed below are the major contents of the thesis:(1)In accordance with the operating features of SRM,by taking contact heat resistance,energy dissipation during friction and heat radiation between nozzle parts into consideration,an integrated coupled analysis model was founded by considering gap design of nozzle;(2)For nozzle design of one SRM,by adopted directed coupled thermal-structural analysis method,a contact algorithm was also used to describe the nozzle prats’ movements.Thermal-structural analysis of the 9 defined gap match modes were conducted and gap optimal design was carried out based on the flame leak criteria whether there existed a short period that the contact numbers of all the contacts were zero.A structural integrity was check out for the optimal design result.Experiment indicated that the test temperature result agreed well with the simulation results and the relative error was below 20%,which verified the analysis model.Obvious flame leak into the interface between the nozzle insert and the convergent region also agreed well with the simulation results.Effectiveness of the optimal design result and veracity of the analysis model were verified well.(3)To investigate the detail thermo-structural response of different gap sizes,clustering analysis method was adopted.The integrated coupled analysis model,along with clustering analysis,were used together to deeply study the thermo-structural response rules of different gap sizes.The clustering results showed both consistency and otherness of temperature and stress distributions.Meanwhile,optimal design points could reflect the thermos-structrual response rules to some extent and the points were effective.Combination of data mining technology and SRM simulation technology improved design level of SRM and saved experimental costs.Meanwhile,it enhanced acknowledgement of the operating process of SRM nozzle.Lastly,it benefitted for analyzing and prediction of fault diagnosis and failure behaviors.(4)Failure mode caused by gap design was clarified and two destruction modes were defined: stress destruction mode and gap ablation mode.An abnormal ablation was found out on the divergent region during testing experiment of the optimal nozzle.Stress condition and contact number change curve were analyzed and the reason was confirmed that initial gap design was not proper enough that there existed a period that the gap was not closed,which provided an opportunity for the flame to leak into the thermal protection layer.Then,another failure cause analysis was carried out for a graphite nozzle insert to confirm its cause of a throughout crack and a breach during firing test.Stress conditions of the surrounding area were checked out.It is confirmed that the cause was an improper gap design that provided an insufficient space for releasing the expansion stress at the initial period.Local stress concentration was produced and structure damage happened.(5)Based on simulation and firing test phenomenon,a design criteria for non-submerged nozzle was set up that the gap between the nozzle insert and the convergent region shoud be bigger than 0.05 mm and smaller than 0.1mm,the gao between the nozzle insert and the divergent region should be bigger than 0.05 mm and smaller than 0.2mm.Further,a non-submerged nozzle was designed and they were confirmed by related institute.The criteria was demonstrated.This thesis provided a set of efficient and accurate integrated method for nozzle thermal-structural analysis and conducted a fault diagnosis analysis related to gap design.Research enhanced the importance of gap design and brought it up to a relatively important position during SRM nozzle design.