Research On Two-phase Flow Simulation And Profile Optimization Of Solid Rocket Motor Nozzle

As the power unit of solid rocket motor(SRM),nozzle efficiency improvement plays an important role in motor performance.The gas parameters,such as temperature and pressure,vary greatly in nozzle,so the rich flow characteristics and mechanism of complex turbulence and two-phase flow are also worth exploring.And nozzle divergence contour determines inner gas expansion,which affects nozzle performance,therefore it is necessary to carry out the design,analysis and optimization of nozzle contour parameters.In this paper,considering the two-phase flow loss caused by the lag of condensed particles and the expansion loss caused by nozzle contour change,the numerical model is established to analyze the two-phase flow characteristics and study the influence of nozzle divergence contour parameters on its performance under different conditions.Further optimization of nozzle divergence contour parameters is also finished to improve its performance.The main research work includes:Firstly,according to the requirements and principles of nozzle contour design,a two-dimensional axisymmetric submerged SRM nozzle is designed.Its convergent section is an elliptical configuration and the main divergent section is designed by characteristic line method,RAO's method and cubic curve respectively.Then contour distributions are obtained by programming,and the comparison shows that the characteristic contour is slender,its expansion ratio and length don't meet the design requirements of the high-altitude nozzle;RAO contour has large expansion ratio and sufficient gas expansion,suitable for SRM nozzle;Cubic contour is close to RAO contour,its design is simple and easy to adjust parameters.Secondly,the computational grid and simulation model of nozzle pure gas phase and two-phase turbulence flow are established,which are verified by comparison with experiment data.Then the grid scale and turbulent two-phase flow model suitable for flow analysis in this paper are obtained.By flow field analysis and performance comparison of the reference contour nozzle,the characteristics of gas parameters and particle trajectory in two-phase flow field,two-phase hysteresis,and the differences with pure gas flow field are studied.And the influence mechanism of the shock wave structure on gas parameters and nozzle performances is found.Finally,the simulation results of two-dimensional axisymmetric model are compared with that of three-dimensional model,the external field model and the test bench model to verify its reliability.Thirdly,nozzles with different divergence contour parameters are constructed and calculated by the model above.According to the results of flow field analysis and performance calculation,the influence tendencies of different contour parameters(half angle of outlet,initial expansion half angle,length-diameter ratio and expansion ratio)on nozzle performances are explored.The results show that the influence of the initial expansion half angle on nozzle thrust is greater than that of the half angle of outlet.Adjusting them can better the shock wave structure in the divergent section to improve nozzle performance.When the expansion ratio is fixed and the length-diameter ratio is less than 1.2,with the growth of length-diameter ratio,the nozzle thrust gains increase obviously.Increasing the expansion ratio can improve nozzle thrust coefficient but reduce the nozzle efficiency because of two-phase loss growth,and the nozzle thrust is in increasing tendency comprehensively.Then considering the changing of combustion chamber pressure and gas specific heat separately,the effects of nozzle divergence contour parameters on its performance are studied.Later,the influence of contour ablation on the flow field and performances of the nozzle is studied,too.Finally,on the basis of the influence analysis above,the response surface method(RSM)and computational fluid dynamics method(CFD)are combined to construct the divergence contour parameters optimization model under some constraints to improve the nozzle performances.The significance analysis verifies the reliability of this method for the optimization of nozzle contour parameters,and the analysis of optimization results show the influence rules of each parameter on nozzle specific impulse and the interaction among these parameters.After optimizing the nozzle contour,the shock wave structure in the flow field is changed and the nozzle's specific impulse is improved.