Numerical Study On The Effect Of External Vibration On Acoustic Vortex Coupling

In solid rocket motors,the problem of unstable combustion has always affected the safety and stability of the engine.The factors affecting the unstable combustion can be roughly divided into three aspects:acoustic unstable combustion,non-acoustic unstable combustion and acoustic vortex coupling.Acoustic vortex coupling is a very important factor in the recent research.There has been a lot of research on the vortex shedding phenomenon of solid rocket engines,but in the previous research,the influence of acoustic vortex coupling under external vibration is currently vacant.There are still relatively few studies on the field of acoustic vortex coupling under vibration,the interaction between structural vibration and pressure oscillation can even lead the engine to explode.Thence in this paper,it will mainly study the direction of the acoustic vortex coupling phenomenon of a solid rocket motor under external vibration.This study is based on ANSYS-FLUENT 15.0 software.By using VKI(Von Karman Institute for Fluid Dynamics)engine,we select the turbulence model of large eddy simulation(LES),and the Coupled algorithm is used of the calculation method.The acoustic vortex coupling of the solid rocket motor combustion chamber is analyzed of different axial vibration frequency,axial vibration amplitude,radial vibration frequency,radial vibration amplitude,and different submerged cavity volume at a single external frequency.In this paper,the effects of pressure oscillation amplitude,vorticity oscillation amplitude and vortex shedding period are analyzed in detail.The results show that:The external vibration has significant influence on the pressure oscillation of solid rocket engine combustion chamber,but the difference of the axial vibration and the radial vibration is that when the axial vibration frequency is close to the first-order acoustic frequency,the pressure amplitude increases sharply;and when the external vibration frequency is farther away from the first-order acoustic frequency,the pressure amplitude decreases.However,the pressure oscillation during radial vibration increases as the external vibration frequency increasesIn addition,analyzing the vorticity filed comprehensively of different frequencies under the axial vibration,we can conclude that the rule of the vortex shedding period.It is influenced by the external axial vibration frequency,the influence of the self-sustaining oscillation in the engine is very little,it can be negligible,and the vortex shedding frequency and the external vibration frequency of the "stable large eddy" are almost the same.However,analyzing the vorticity filed comprehensively of different frequencies under the radial vibration,we can conclude that the rule of the vortex shedding period is different from the axial vibration,the frequency of the radial vibration has little effect on the vortex shedding period.By calculating the cavity volume of four combustion chambers under a single external frequency condition,the pressure amplitude will increase as the cavity of the combustion chamber increases,and the larger the vortex shedding period,the smaller the vortex shedding frequency.Finally,by comparing the pressure amplitude of the axial vibration and the radial vibration under the condition of the same frequency and amplitude,the pressure amplitude of the radial vibration is higher,the Prms/Pmean increased by 42.75%.