Parametric Analysis On The Performance Of Flexible Variable Structure Nozzle

The ideal single-stage to orbit rocket motor requires high specific impulse,high mass ratio,and high efficiency.The use of altitude compensated nozzles is one of the most effective means of improving motor thrust.Among all the altitude compensated nozzles,the flexible variable structure nozzle is superior to the conventional solid rocket motor nozzle,and can be continuously adjusted and controlled by the nozzle structure in the full airspace altitude range.The flexible variable structure nozzle can fully expand at any altitude,and the motor always works in the optimal state in wide airspace and multi-trajectory.However,the flexible section of the flexible structural nozzle is made of elastic material such as rubber.The supersonic combustion gas flow interacts with the wall of the flexible structure,causes deformation of the nozzle profile,and affects the performance of the nozzle.Therefore,the analysis of the influence of the flexible surface deformation on the performance of the nozzles is of great significance for the design of adaptive adjustment of solid rocket motor.In this study,the influence of the profile variation of the flexible variable structure nozzle on the nozzle performance is studied.Through the parametric analysis of the profile variation and the response analysis of the flow field structure,the influence of the profile deformation on the performance of the flexible variable structure nozzle is achieved.The relationship between the influence of profile scale deformation on the performance of flexible variable structure nozzle and the ability to improve efficiency is obtained.The main research contents are as follows:(1)A two-dimensional flexible variable structure cone nozzle model is established based on the reasonable deformation scale and shape of the flexible section.The influence of flow field structure change and flow loss in the flexible variable structure nozzle are demonstrated by numerical simulations.The deformation dimension of the flexible structure of the nozzle is determined,that is,the deformation shape of the flexible structure of the nozzle is arc-shaped,and the deformation scale is the ratio of the circular chord height to the throat diameter.It is estimated that the deformation scale of the flexible structure profile is less than 0.05,which lays a theoretical foundation for the matching of flexible structural materials.(2)A three-dimensional flexible variable structure cone nozzle model is established to investigate the variation of the flexible structure under bidirectional fluid-solid coupling.The influence of flight altitude,elastic modulus of the flexible material,and flexible section constraint on nozzle performance are analyzed.It is found that the flight altitude has the most significant influence on the nozzle performance.To improve the performance of the flexible variable structure nozzle,elastic material with elastic modulus greater than 107 is suggested.Considering the structural stress distribution,the optimal flexible section constraint method is given,that is,the nozzle extension section adopts a two-stage constraint method.The present parametric study on the flexible variable structure nozzle provides a theoretical basis for the research of deformation of the flexible structure and aerodynamics coupling.It is of significant help to the flexible variable structure nozzle design and the corresponding material selecting in the future work.