Resonance Characteristics Investigation On Solid Rocket Motor Structure And Combustion Chamber Pressure

Large segmented solid rocket engines are prone to unstable combustion during operation.The existence of unstable combustion results in a longer engine development cycle,reduced propulsion performance,and even damage to the structural strength of the engine,which can have serious consequences.Researchers have found that the coupling resonance between the flow field and the sound field of the combustion chamber has a significant effect on the unstable combustion of the engine.If the vortex shedding frequency is coupled to the natural acoustic frequency of the engine,and the vortex coupling is generated,it may induce the pressure oscillation in the combustion chamber to increase.As a result,unstable combustion occurs.Based on research at home and abroad,this paper studies the influence of different structures on the acoustic-vortex coupling resonance,and studies the unstable combustion phenomenon existing in the working process of the engine.Finally,it discusses the measures to suppress the unstable combustion.First,through experimental comparison,the accuracy of the numerical calculation method and the finite element method analysis method was verified,and the pressure oscillation frequency and acoustic mode distribution of the combustion chamber were obtained.Then based on the 1/30 scale model of VKI engine,the effect of different engine structures on the vortex coupling is studied.By changing the height of the baffle,the length of the combustion chamber,the throat diameter of the nozzle,and the airfoil,the changes of pressure amplitude and acoustic mode of the combustion chamber under different structures were obtained.Studies have shown that when the frequency of vortex shedding is equal to the natural frequency of the sound field,an acoustic-vortex coupling resonance phenomenon occurs.Changes in the height of the drug barrier will affect the incoming flow velocity,which will affect the frequency of vortex shedding and the amplitude of pressure oscillations.When the drug barrier is located in the antinode of the speed of sound,small disturbances in the flow field will more easily trigger pressure oscillations;changing the throat diameter will affect pressure oscillation;acousticvortex coupling can occur at different speeds.Finally,numerical calculations are performed at three different working moments of the full-size large-to-diameter rocket engine.The study found that when the pressure oscillation frequency of the combustion chamber is coupled with the natural frequency of the second-order sound,the pressure amplitude increases,and as the engine’s operating time goes by The soundvortex coupling effect of the combustion chamber gradually weakened,and the amplitude of pressure oscillations changed significantly.Based on the research in this paper,the methods of suppressing unstable combustion are summarized,which provides a certain reference for optimizing engine design.